Technical Terms and Definitions

# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


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08/10B local fiber
Networking

8-byte/10-byte local fiber. Fiber channel physical media that supports speeds up to 149.76 Mbps over multimode fiber.

10 BaseF
Networking

10-Mbps baseband Ethernet specification that refers to the 10BaseFB, 10BaseFL, and 10BaseFP standards for Ethernet over fiber-optic cabling.

10 BaseFB
Networking

10-Mbps baseband Ethernet specification using fiber-optic cabling. 10BaseFB is part of the IEEE 10BaseF specification. It is not used to connect user stations, but instead provides a synchronous signaling backbone that allows additional segments and repeaters to be connected to the network. 10BaseFB segments can be up to 2,000 meters long.

10 BaseFP
Networking

10-Mbps fiber-passive baseband Ethernet specification using fiber-optic cabling. 10BaseFP is part of the IEEE 10BaseF specification. It organizes a number of computers into a star topology without the use of repeaters. 10Base FP segments can be up to 500 meters long.

10 Broad36
Networking

10-Mbps broadband Ethernet specification using broadband coaxial cable. 10Broad36, which is part of the IEEE 802.3 specification, has a distance limit of 3,600 meters per segment.

100 BaseFX
Networking

100-Mbps baseband Fast Ethernet specification using two strands of multimode fiber-optic cable per link. To guarantee proper signal timing, a 100BaseFX link exceed 400 meters in length. Based on the IEEE 802.3 standard.

100 BaseT4
Networking

100-Mbps baseband Fast Ethernet specification using four pairs of Category 3, 4, or 5UTP wiring. To guarantee proper signal timing, a 100BaseT4 segment cannot exceed 100 meters in length. Based on the IEEE 802.3 standard.

100 BaseTX
Networking

100-Mbps baseband Fast Ethernet specification using two pairs of either UTP or STP wiring. The first pair of wires is used to receive data, the second is used to transmit. To guarantee proper signal timing a 100BaseTX segment cannot exceed 100 meters in length. Based on the IEEE 802.3 standard.

100 BaseX
Networking

100-Mbps baseband Fast Ethernet specification that refers to the 100BaseFX and 100BaseTX standards for Fast Ethernet over fiber-optic cabling. Based on the IEEE 802.3 standard.

100Base-T
Networking

A networking standard that supports data transfer rates up to 100 Mbps (100 megabits per second). 100BASE-T is based on the older Ethernet standard. Because it is 10 times faster than Ethernet, it is often referred to as Fast Ethernet. Officially, the 100BASE-T standard is IEEE 802.3u. Like Ethernet, 100BASE-T is based on the CSMA/CD LAN access method. There are several different cabling schemes that can be used with 100BASE-T, including: 100BASE-TX: two pairs of high-quality twisted-pair wires 100BASE-T4: four pairs of normal-quality twisted-pair wires 100BASE-FX: fiber optic cables

100VG-AnyLAN
Networking

100-Mbps Fast Ethernet and Token Ring media technology using four pairs of Category 3, 4, or 5 UTP cabling. This high-speed transport technology, developed by Hewlett-Packard, can be made to operate on existing 10BaseT Ethernet networks. Based on the IEEE 802.12 standard.

10Base-2
Networking

One of several adaptations of the Ethernet (IEEE 802.3) standard for Local Area Networks (LANs). The 10Base-2 standard (also called Thinnet) uses 50 ohm coaxial cable (RG-58 A/U) with maximum lengths of 185 meters. This cable is thinner and more flexible than that used for the 10Base-5 standard. The RG-58 A/U cable is both less expensive and easier to place. Cables in the 10Base-2 system connect with BNC connectors. The Network Interface Card (NIC) in a computer requires a T-connector where you can attach two cables to adjacent computers. Any unused connection must have a 50 ohm terminator. The 10Base-2 system operates at 10 Mbps and uses baseband transmission methods.

10Base-T
Networking

This designation is an Institute of Electrical and Electronics Engineers shorthand identifier. The "10" in the media type designation refers to the transmission speed of 10 Mbps. The "BASE" refers to baseband signalling, which means that only Ethernet signals are carried on the medium. The "T" represents twisted-pair; the "F" represents fiber optic cable; and the "2" and "5" refer to the coaxial cable segment length (the 185 meter length has been rounded up to "2" for 200).

10Base5
Networking

The original cabling standard for Ethernet that uses coaxial cables. The name derives from the fact that the maximum data transfer speed is 10 Mbps, it uses baseband transmission, and the maximum length of cables is 500 meters. 10Base5 is also called thick Ethernet, ThickWire, and ThickNet.

10BaseFL
Networking

10-Mbps baseband Ethernet specification using fiber-optic cabling. 10BaseFL is part of the IEEE 10BaseF specification and, while able to interoperate with FOIRL, is designed to replace the FOIRL specification. 10BaseFL segments can be up to 1,000 meters long if used with FOIRL, and up to 2,000 meters if 10BaseFL is used exclusively.

3DES
Software

Triple DES, or 3DES, is an expansion of the DES mode of encryption, except that it uses the DES encrption algorithm 3 times to generate a key up to 112 bites long, instead of only 56 bits long in the case DES. It takes three 64-bit keys, for an overall key length of 192 bits. In Stealth, you simply type in the entire 192-bit (24 character) key rather than entering each of the three keys individually. The Triple DES DLL then breaks the user provided key into three subkeys, padding the keys if necessary so they are each 64 bits long. The procedure for encryption is exactly the same as regular DES, but it is repeated three times. Hence the name Triple DES. The data is encrypted with the first key, decrypted with the second key, and finally encrypted again with the third key.

Consequently, Triple DES runs three times slower than standard DES, but is much more secure if used properly. The procedure for decrypting something is the same as the procedure for encryption, except it is executed in reverse. Like DES, data is encrypted and decrypted in 64-bit chunks. Unfortunately, there are some weak keys that one should be aware of: if all three keys, the first and second keys, or the second and third keys are the same, then the encryption procedure is essentially the same as standard DES. This situation is to be avoided because it is the same as using a really slow version of regular DES.

Note that although the input key for DES is 64 bits long, the actual key used by DES is only 56 bits in length. The least significant (right-most) bit in each byte is a parity bit, and should be set so that there are always an odd number of 1s in every byte. These parity bits are ignored, so only the seven most significant bits of each byte are used, resulting in a key length of 56 bits. This means that the effective key strength for Triple DES is actually 168 bits because each of the three keys contains 8 parity bits that are not used during the encryption process.

4B/5B local fiber
Networking

4-byte/5-byte loc 100 Mbps over multimode fiber. See also TAXI 4B/5B.

A

A&B bit signaling
Concept

Procedure used in T1 transmission facilities in which each of the 24 T1 subchannels devotes one bit of every sixth frame to the carrying of supervisory signaling information. Also called 24th channel signaling.

A-law
Telecommunications

The ITU-T companding standard used in the conversion between analog and digital signals in PCM systems. A-law is used primarily in European telephone networks and is similar to the North American mu-law standard. See also companding and mu-law.

AAL
Lingo

ATM adaptation layer. Service-dependent sublayer of the data link layer. The AAL accepts data from different applications and presents it to the ATM layer in the form of 48-byte ATM payload segments. AALs consist of two sublayers, CS and SAR, AALs differ on the basis of the source-destination timing used, whether they use DBR or VBR, and whether they are used for connection-oriented or connectionless mode data transfer. At present, the four types of AAL recommended by the ITU-T are AAL1, AAL2, AAL3/4, and AAL5.

AAL1
Lingo

ATM adaptation layer 1. One of four AALs recommended by the ITU-T. AAL1 is used for connection-oriented, delay-sensitive services requiring constant bit rates, such as uncompressed video and other isochronous traffic.

AAL2
Lingo

ATM adaptation layer 2. One of four AALs recommended by the ITU-T. AAL2 is used for connection-oriented services that support a variable bit rate, such as some isochronous video and voice traffic.

AAL3/4
Lingo

ATM adaptation layer 3/4. One of four AALs (merger from two initially distinct adaptation layers) recommended by the ITU-T. AAL 3/4 supports both connectionless and connection oriented links, but is primarily used for the transmission of SMDS packets over ATM networks.

AAL5
Lingo

ATM adaptation layer 5. One of four AALs recommended by the ITU-T. AAL5 supports connection-oriented, VBR services, and is used predominantly for the transfer of classic IP over ATM and LANE traffic. AAL5 uses SEAL and is the least complex of the current AAL recommendations. It offers low bandwidth over head and simpler processing requirements in exchange for reduced bandwidth capacity and error-recovery capability.

AARP
Protocol

AppleTalk Address Resolution Protocol. Protocol in the AppleTalk protocol stack that maps a data-link address to a network address.

AARP probe packets
Networking

Packets transmitted by AARP that determine whether a randomly selected node ID is being used by another node in a nonextended AppleTalk network. If the node ID is not being used, the sending node uses that node ID. If the node ID is being used, the sending node chooses a different ID and sends more AARP probe packets.

Abacus

The abacus is a mechanical aid used for counting. Addition, subtraction, division and multiplication can be performed on a standard abacus.

The abacus is typically constructed of various types of hardwoods and comes in varying sizes. The frame of the abacus has a series of vertical rods (at one time perhaps made of bamboo) on which a number of wooden beads are allowed to slide freely. A horizontal beam separates the frame into two sections, known as the upper deck and the lower deck.

Calculations are performed by placing the abacus flat on a table or one's lap and manipulating the beads with the fingers of one hand. Each bead in the upper deck has a value of five; each bead in the lower deck has a value of one.

Beads are considered counted, when moved towards the beam that separates the two decks.

The right-most column is the ones column; the next adjacent to the left is the tens column; the next adjacent to the left is the hundreds column, and so on. After 5 beads are counted in the lower deck, the result is "carried" to the upper deck; after both beads in the upper deck are counted, the result (10) is then carried to the left-most adjacent column. Floating point calculations are performed by designating a space between 2 columns as the decimal-point and all the rows to the right of that space represent fractional portions while all the rows to the left represent whole number digits.

ABM
Lingo

Asynchronous Balanced Mode. An HDLC (and derivative protocol) communication mode supporting peer-oriented, point-to-point communications between two stations, where either station can initiate transmission.

ABR
Lingo

1. available bit rate. QOS class defined by the ATM Forum for ATM networks. ABR is used for connections that do not require timing relationships between source and destination. ABR provides no guarantees in terms of cell loss or delays, providing only best-effort service. Traffic sources adjust their transmission rate in response to information they receive describing the statue of the network and its capability to successfully deliver data. Compare with CBR, UBR, and VBR. 2. area border router. Router located on the border of one or more OSPF areas that connects those areas to the backbone network. ABRs are considered members of both the OSPF backbone and the attached areas. They therefore maintain routing tables describing both the backbone topology and the topology of the other areas.

AC
Lingo

Alternating Current. An electrical power transmission system in which the direction of current flow alternates on a periodic basis.

Accelerator
Hardware

A hardware addition to an existing computing device that increases the computer's processing speed and capabilities.

Access
Networking

Referring to the ability of a computing device to use data or resources beyond its native capabilities.

Access List
Networking

List kept by routers to control access to or from the router for a number of services. For example, the list can prevent packets with a certain IP address from leaving a particular interface on the router.

Access Method
Networking

The type of Media Access Control method that a node uses to gain control of a network.

Accounting Management
Networking

One of five categories of network management defined by ISO for management of OSI networks. Accounting management subsystems are responsible for collecting network data relating to resource usage. See also configuration management, fault management, performance management, and security management.

Accuracy
Networking

Referring to how closely a test instrument's measurements compare to a standard value, usually expressed as a percentage of the value measured.

ACD
Hardware

In telephony, an Automatic Call Distributor (ACD), also known as Automated Call Distribution, is a device or system that distributes incoming calls to a specific group of terminals that agents use. It is often part of a computer telephony integration (CTI) system.

Routing incoming calls is the task of the ACD system. ACD systems are often found in offices that handle large volumes of incoming phone calls from callers who have no need to talk to a specific person but who require assistance from any of multiple persons (e.g., customer service representatives) at the earliest opportunity.

The system consists of hardware for the terminals and switches, phonelines, and software for the routing strategy. The routing strategy is a rule-based set of instructions that tells the ACD how calls are handled inside the system. Typically this is an algorithm that determines the best available employee or employees to respond to a given incoming call. To help make this match, additional data are solicited and reviewed to find out why the customer is calling. Sometimes the caller's caller ID or ANI is used; more often a simple Interactive voice response is used to ascertain the reason for the call.

Originally, the ACD function was internal to the Private Branch Exchange of the company. However, the closed nature of these systems limited their flexibility. A system was then designed to enable common computing devices, such as server PCs, to make routing decisions. For this, generally the PBX would issue information about incoming calls to this external system and receive a direction of the call in response.

ACF
Lingo

Advanced Communications Function. A group of SNA products that provides distributed processing and resource sharing.

ACF/NCP
Lingo

Advanced Communications Function/Network Control Program. The primary SNA NCP. ACF/NCP resides in the communications controller and interfaces with the SNA access method in the host processor to control network communications.

ACID
Lingo

An acronym for a database transaction done correctly over a network. For the transaction to be considered valid it must be : Atomic: The transaction should be done or undone completely; Consistent: A transaction should transform a system from one consitent state to another consistent state; Isolation: Each transaction should happen independently of the other transactions happening simultaneously; Durable: Completed transactions should remain permanent, even during a network or system failure.

ACK
Lingo

(Acknowledgment) In data communications ACK is a character transmitted by the receiver of data to ACKnowledge a signal, information or packet received from the sender. Binary code for ACK is : 00110000. HEX is : 60.

Acknowledgment
Networking

Notification sent from one network device to another to acknowledge that some event (for example, receipt of a message) has occurred. Sometimes abbreviated ACK.

ACR
Lingo

Allows cell rate. Parameter defined by the ATM Forum for ATM traffic management. ACR varies between the MCR and the PCR, and is dynamically controlled using congestion control mechanisms.

ACSE
Lingo

Association control service element. An OSI convention used to establish, maintain or terminate a connection between two applications.

Active Hub
Hardware

Multiported device that amplifies LAN transmission signals.

Active Monitor
Hardware

Device responsible for managing a Token Ring. A network node is selected to be the active monitor if it has the highest MAC address on the ring. The active monitor is responsible for management tasks such as ensuring that tokens are not lost or that frames do not circulate indefinitely.

ActiveX
Software

A loosely defined set of technologies developed by Microsoft. ActiveX is an outgrowth of two other Microsoft technologies called OLE (Object Linking and Embedding) and COM (Component Object Model). As a moniker, ActiveX can be very confusing because it applies to a whole set of COM-based technologies. Most people, however, think only of ActiveX controls, which represent a specific way of implementing ActiveX technologies.

Adapter
Hardware

Hardware that allows a computing device physical access to a network.

Adaptive Routing
Protocol

See dynamic routing.

ADCCP
Protocol

Advanced Data Communications Control Protocol.

Address
Networking

A numerical designation that uniquely refers to a specific communication entity.

Address Mapping
Networking

Technique that allows different protocols to interoperate by translating addresses from one format to another. For example, when routing IP over X.25, the IP addresses must be mapped to the X.25 addresses so that the IP packets can be transmitted by the X.25 network. See also address resolution.

Address Mask
Networking

Bit combination used to describe which portion of an address refers to the network or subnet and which part refers to the host. Sometimes referred to simply as mask. also subnet mask.

Address Resolution
Networking

When two addressing systems refer to the same entity, the process of translating or expressing the address of an entity on one system to the equivalent address of the same entity in the second system. For instance, translating an IP address to its given DNS name.

Address Resolution Protocol
Protocol

See ARP

Address Space
Networking

The range of possible unique addresses allowed by an addressing scheme.

Addressed Call Mode
Networking

Mode that permits control signals and commands to establish and terminate calls in V.25bis.

Adjacency
Networking

Relationship formed between selected neighboring routers and end nodes for the propose of exchanging routing information. Adjacency is based upon the use of a common media segment.

Adjacent Nodes
Networking

1. In SNA, nodes that are connected to a given node with no intervening nodes. 2. In DECnet and OSI, nodes that share a common network segment (in Ethernet, FDDI, or Token Ring networks).

Administrative Distance
Networking

A rate of the trustworthiness of a routing information source. The higher the value, the lower the trustworthiness rating.

Admission Control
Networking

See traffic policing.

ADPCM
Concept

Adaptive differential pulse code modulation. Process by which analog voice samples are encoded into high-quality digital signals.

ADSL
Networking

ADSL (Asymmetric Digital Subscriber Line) is a technology for transmitting digital information at high bandwidth on existing phone lines to homes and businesses. Unlike regular dialup phone service, ADSL provides continously-available, "always on" connection. ADSL is asymmetric in that it uses most of the channel to transmit downstream to the user and only a small part to receive information from the user. ADSL simultaneously accommodates analog (voice) information on the same line. ADSL is generally offered at downstream data rates from 512 Kbps to about 6 Mbps. A form of ADSL, known as Universal ADSL or glite, has been initially approved as a standard by the ITU-TS. ADSL was specifically designed to exploit the one-way nature of most multimedia communication in which large amounts of information flow toward the user and only a small amount of interactive control information is returned. Several experiments with ADSL to real users began in 1996. In 1998, wide-scale installations began in several parts of the U.S. In 2000 and beyond, ADSL and other forms of DSL are expected to become generally available in urban areas. With ADSL (and other forms of DSL), telephone companies are competing with cable companies and their cable modem services.

ADSU
Networking

ATM DSU. Terminal adapter used to access an ATM network via an HSSI-compatible device. See also DSU.

Advertising
Networking

Router process in which routing or service updates are sent at specified intervals so that other routers on the network can maintain lists of usable routes.

AEP
Protocol

AppleTalk Echo Protocol. Used to test connectivity between two AppleTalk nodes. One node sends a packet to another node and receives a duplicate, or echo, of that packet.

AFP
Protocol

AppleTalk Filing Protocol. The Apple proprietary specification for a network file system.

Agent
Networking

1. An active process in a computer that is responsible for a certain type of activity when demanded by an outside entity. 2. In SNMP, the active process in a computing device that is responsible for determining the parameters defined in the MIB (Management Information Base) and reporting them on demand to a Console.

AGP
Hardware

Short for Accelerated Graphics Port, a new interface specification developed by Intel Corporation. AGP is based on PCI, but is designed especially for the throughput demands of 3-D graphics. Rather than using the PCI bus for graphics data, AGP introduces a dedicated point-to-point channel so that the graphics controller can directly access main memory. The AGP channel is 32 bits wide and runs at 66 MHz. This translates into a total bandwidth of 266 MBps, as opposed to the PCI bandwidth of 133 MBps. AGP also supports two optional faster modes, with throughputs of 533 MBps and 1.07 GBps. In addition, AGP allows 3-D textures to be stored in main memory rather than video memory. AGP has a couple important system requirements: The chipset must support AGP. The motherboard must be equipped with an AGP bus slot or must have an integrated AGP graphics system. The operating system must be the OSR 2.1 version of Windows 95, Windows 98 or Windows NT 4.0. And currently, many professional Macintoshes suport AGP. AGP-enabled computers and graphics accelerators hit the market in August, 1997. However, there are several different levels of AGP compliance. The following features are considered optional: Texturing: Also called Direct Memory Execute mode, allows textures to be stored in main memory. Throughput: Various levels of throughput are offered: 1X is 266 MBps, 2X is 533 MBps; and 4X provides 1.07 GBps. Sideband Addressing: Speeds up data transfers by sending command instructions in a separate, parallel channel. Pipelining: Enables the graphics card to send several instructions together instead of sending one at a time.

AIS
Lingo

Alarm indication signal. In a T1 transmission, an all-ones signal transmitted in lieu of the normal signal to maintain transmission continuity and to indicate to the receiving terminal that there is a transmission fault that is located either at, or upstream from, the transmitting terminal.

AIX
Programming

IBM's implementation of Unix.

Alan Turing
People

Alan Turing was an English mathematician and logician who pioneered in the field of computer theory and who contributed important logical analyses of computer processes.

The son of a British member of the Indian Civil Service, Turing studied at Sherborne School and at King's College, Cambridge. Many mathematicians in the first decades of the 20th century had attempted to eliminate all possible error from mathematics by establishing a formal, or purely algorithmic, procedure for establishing truth. The mathematician Kurt Gödel threw up an obstacle to this effort with his incompleteness theorem; Gödel showed that any useful mathematical axiom system is incomplete in the sense that there must exist propositions whose truth can never be determined (undecidable propositions within the system). Turing was motivated by Gödel's work to seek an algorithmic method of determining whether any given propositions were undecidable, with the ultimate goal of eliminating them from mathematics. Instead, he proved in his seminal paper "On Computable Numbers, with an Application to the Entscheidungsproblem [Decision Problem]" (1936) that there cannot exist any such universal method of determination and, hence, that mathematics will always contain undecidable (as opposed to unknown) propositions.

To illustrate this point, Turing posited a simple device that possessed the fundamental properties of a modern computing system: a finite program, a large data-storage capacity, and a step-by-step mode of mathematical operation. This Turing machine, as it was later called, is frequently used as a point of reference in basic discussions of automata theory and was also the theoretical basis for the digital computers that came into being in the 1940s. Turing's work, along with that of Gödel, put to rest the hopes of David Hilbert and his school that all mathematical propositions could be expressed as a set of axioms and derived theorems.

Turing continued his mathematical studies at Princeton University, completing a Ph.D. (1938) under the direction of the American mathematician Alonzo Church. He then returned to England and accepted a renewed fellowship at King's College. During World War II he served with the Government Code and Cypher School, at Bletchley, Buckinghamshire, where he played a significant role in breaking the German "Enigma" codes. In 1945 he joined the staff of the National Physical Laboratory in London to lead the design, construction, and use of a large electronic digital computer that was named the Automatic Computing Engine (ACE). In 1948 he became deputy director of the Computing Laboratory at the University of Manchester, where the Manchester Automatic Digital Machine (MADAM, as it was referred to in the press), the computer with the largest memory capacity in the world at that time, was being built. His efforts in the construction of early computers and the development of early programming techniques were of prime importance. He also championed the theory that computers eventually could be constructed that would be capable of human thought, and he proposed a simple test, now known as the Turing test, to assess this capability. Turing's papers on the subject are widely acknowledged as the foundation of research in artificial intelligence.

Alarm
Networking

Message notifying an operator or administrator of a network problem. See also event and trap.

Algorithm
Concept

A set of rules and decision structures for actions in a specifically defined set of circumstances.

Alias
Lingo

A file whose sole purpose is to represent another file.

Alignment Error
Networking

In IEEE 802.3 networks, an error that occurs when the total number of bits of a received frame is not divisible by eight. Alignment errors are usually caused by frame damage due to collisions.

ALOE
Concept

Archaic. AppleTalk Low Overhead Encapsulation. A vendor-developed alternative to AURP, ALOE provides a mechanism to tunnel AppleTalk protocols inside IP packets, typically in WAN links.

Alphanumeric
Networking

Referring to a group of printable characters that includes the letters of the alphabet in both upper and lower case, the numerals plus a limited group of additional symbols and punctuation marks.

AM
Lingo

Amplitude Modulation. Modulation technique whereby information is conveyed through the amplitude of the carrier signal. Compare with FM and PAM. See also modulation.

Ambient
Concept

Referring to a set of conditions that exist independently of the system of interest.

AMI
Lingo

Alternate mark inversion. Line-code type used on T1 and E1 circuits. In AMI, zeros are represented by 01 during each bit cell, and ones are represented by 11 or 00, alternately, during each bit cell. AMI requires that the sending device maintain ones density. Ones density is not maintained independent of the data stream. Sometimes called binary coded alternate mark inversion. See also ones density.

Amiga
PC's

Amiga is a personal computer designed especially for high-resolution, fast response graphics and multimedia applications. Its microprocessor is based on Motorola's 680x0 line of processors. It was one of the first computers to offer true color. It comes with its own operating system, AmigaOS. Since its first appearance from Commodore Business Machines in 1985, Amiga has become a synonym for fast, high-resolution graphics and best known for its quickly responsive user interface and suitability for playing action games. AmigaOS handles 32-bit instructions and uses preemptive multitasking. Its design favors user input to the extent that it is sometimes described as a realtime operating system (real-time operating system).

Since Amiga was designed as a special-purpose system, AmigaOS, which is written in C and assembler language, is especially compact. All versions of the operating system will run on 512 kilobyte of random access memory. All versions of the Amiga can run at 50 MHz or faster, using an accelerator card. A G4 processor can be used through adding an accelerator card. The Amiga supports plug and play and can be adapted with software to emulate Windows and Mac OS.

The Amiga has the ability to become a video monitor by locking into a video signal from an external source such as a video camera. As a result, Amigas are used by television stations and sports arenas to display video clips on large screens.

Amiga is working on a "Next Generation" system that will use Linux as its basic core. (Earlier plans favored another operating system, QNX.) In September, 1999, Amiga's CEO and President Thomas J. Schmidt, saying that "Amiga was not just about a box," suggested that Amiga might soon be running on other platforms and operating systems.

Amplitude
Concept

In the terminology of wave motion, the height of the wave. Amplitude is usually measured from a reference point of 0. In electrical waves, amplitude is typically expressed in volts.

Analog
Concept

Referring to a system or component that uses a system of measurement, response or storage in which values are expressed a s a magnitude using a continuous scale of measurement.

Analog Transmission
Concept

Signal transmission over wires or through the air in which information is conveyed through variation of some combination of signal amplitude, frequency, and phase.

Anonymous FTP
Protocol

Using FTP without establishing a user ID and password.

ANSI
Organizations

American National Standards Institute. A standards-setting, non-governmental organization founded in 1918, which develops and publishes standards for transmission protocols and high-level languages for "voluntary" use in the United States.

Anti-Virus Software
Software

Software written specifically to combat harmful viruses. Anti-Virus software seeks and removes viruses from your computer. Norton AntiVirus and McAfee VirusScan are two popular Anti-Virus programs.

APaRT
Lingo

Automated packet recognition/translation. Technology that allows a server to be attached to CDDI or FDDI without requiring the reconfiguration of applications or network protocols. APaRT recognizes specific data link layer encapsulation packet types and, when these packet types are transferred from one medium to another, translates them into the native format of the destination device.

API
Lingo

Application Programming Interface. A set of tools and procedures provided by the programmer of an application so that other programmers can control, exchange data with, or extend the functionality of an application.

APNIC
Organizations

APNIC (Asia Pacific Network Information Centre) is one of three Regional Internet Registries currently operating in the world. It provides allocation and registration services which support the operation of the Internet globally. It is a not-for-profit, membership-based organisation whose members include Internet Service Providers, National Internet Registries, and similar organisations. APNIC represents the Asia Pacific region, comprising 62 economies. Its services include IPv4 and IPv6 address delegations and Autonomous Systems number assignments.

APPC
Lingo

Advanced Program-to-Program Communication. IBM SNA system software that allows high-speed communication between programs on different computers in a distributed computing environment. APPC establishes and tears down connections between communicating programs, and consists of two interfaces, a programming interface and a data-exchange interface. The former replies to requests from programs requiring communication; the latter establishes sessions between programs. APPC runs on LU 6.2 devices. See also LU 6.2.

Applet
Programming

A small Java program.

AppleTalk
Networking

An inexpensive local-area network (LAN) architecture built into all Apple Macintosh computers and laser printers. AppleTalk supports Apple's LocalTalk cabling scheme, as well as Ethernet and IBM Token Ring. It can connect Macintosh computers and printers, and even PCs if they are equipped with special AppleTalk hardware and software.

Application
Concept

An independently executable set of algorithms and data structures that perform a specific set of functions.

Application Layer
Networking

Layer 7 of the OSI reference model. This layer provides services to application processes (such as electronic mail, file transfer, and terminal emulation) that are outside of the OSI model. The application layer identifies and establishes the availability of intended communication partners (and the resources required to connect with them), synchronizes cooperating applications, and agreement on procedures for error recovery and control of data integrity. Corresponds roughly with the transaction services layer in the SNA model. See also data link layer, network layer, physical layer, presentation layer, session layer, and transport layer.

APPN
Lingo

Advanced Peer-to-Peer Networking. Enhancement to the original IBM SNA architecture. APPN handles session establishment between peer nodes, dynamic transparent route calculation, and traffic prioritization for APPC traffic. Compare with APPN+. See also APPC.

APPN+
Lingo

Next-generation APPN that replaces the label-swapping routing algorithm with source routing. Also called high-performance routing. See also APPN.

ARA
Lingo

AppleTalk Remote Access. Protocol that provides Macintosh users direct access to information and resources at a remote AppleTalk site.

Architecture
Networking

The sum total of all of the specifications, protocols and implementations that define a particular networking system.

Archive
Networking

A storage of infrequently-used or historical data.

ARIN
Organizations

ARIN is a non-profit organization established for the purpose of administration and registration of Internet Protocol (IP) numbers for the following geographical areas:


ARIN is one of three Regional Internet Registries (RIRs) worldwide which collectively provide IP registration services to all regions around the globe. The others are:

Other registry organizations are separately responsible for registering and maintaining domain names, which are commonly used unique identifiers that are translated into numeric addresses (IP numbers). IP numbers are globally unique, numeric identifiers that computers use to identify hosts and networks connected to the Internet.

ARIN is responsible for maintaining a public trust. Among its responsibilities, ARIN promotes the conservation of IP address space, maintains impartiality while determining the size of address blocks to be allocated or assigned, and supports efforts to keep the global routing tables to a manageable size to ensure routability of information over the Internet. Continued operation of the Internet depends, in part, upon the conservation and efficient use of IP address space.

Among ARIN's tasks are the management of IP numbers, autonomous system numbers (ASNs), and IN-ADDR.ARPA or IP6.INT inverse mapping, as well as database maintenance, verification of reassignment information, and maintaining a routing registry where network operators can submit, maintain, and retrieve router configuration information. Open structures and processes are maintained in all of ARIN's daily operations to ensure that the needs of the Internet community are adequately met.

ARM
Lingo

Asynchronous response mode, HDLC communication mode involving one primary station and at least one secondary station, where either the primary or one of the secondary stations can initiate transmissions. See also primary station and secondary station.

ARP
Protocol

Short for Address Resolution Protocol, a TCP/IP protocol used to convert an IP address into a physical address (called a DLC address), such as an Ethernet address. A host wishing to obtain a physical address broadcasts an ARP request onto the TCP/IP network. The host on the network that has the IP address in the request then replies with its physical hardware address. There is also Reverse ARP (RARP) which can be used by a host to discover its IP address. In this case, the host broadcasts its physical address and a RARP server replies with the host's IP address.

ARPA
Lingo

Advanced Research Projects Agency, Research and development organization that is part of DoD. ARPA is responsible for numerous technological advances in communications and networking. ARPA evolved in DARPA, and then back into ARPA again (in 1994). See also DARPA.

ARPANet
Organizations

The precursor to the Internet, ARPANET was a large wide-area network created by the United States Defense Advanced Research Project Agency (ARPA). Established in 1969, ARPANET served as a testbed for new networking technologies, linking many universities and research centers. The first two nodes that formed the ARPANET were UCLA and the Stanford Research Institute, followed shortly thereafter by the University of Utah.

ASBR
Lingo

Autonomous system boundary router. ABR located between an OSPF autonomous system and a non-OSPF network. ASBRs run both OSPF and another routing protocol, such as RIP, ASBRs must reside on a nonstub OSPF area.

ASCII
Programming

American Standard Code for Information Interchange: This is the global standard for code numbers used by computers to represent all upper and lower-case Latin letters, numbers, and punctuation.

ASIC
Hardware

Pronounced ay-sik, and short for Application Specific Integrated Circuit, a chip designed for a particular application. ASICs are built by connecting existing circuit building blocks in new ways. Since the building blocks already exist in a library, it is much easier to produce a new ASIC than to design a new chip from scratch.

ASP
Software

ASP can mean either Application Service Provider or Active Server Page.

Application Service Provider

An application service provider (ASP) is a company that offers individuals or enterprises access over the Internet to applications and related services that would otherwise have to be located in their own personal or enterprise computers. Sometimes referred to as "apps-on-tap," ASP services are expected to become an important alternative, not only for smaller companies with low budgets for information technology, but also for larger companies as a form of outsourcing and for many services for individuals as well. Early applications include:

Hewlett-Packard, SAP, and Qwest have formed one of the first major alliances for providing ASP services. They plan to make SAP's popular R/3 applications available at "cybercenters" that will serve the applications to other companies. Microsoft is allowing some companies to offer its BackOffice products, including SQL Server, Exchange and Windows NT Server on a rental, pay-as-you-use basis.

Active Server Page

An Active Server Page (ASP) is an HTML page that includes one or more script (small embedded programs) that are processed on a Microsoft Web server before the page is sent to the user. An ASP is somewhat similar to a Server-side include or a common gateway interface (common gateway interface) application in that all involve programs that run on the server, usually tailoring a page for the user. Typically, the script in the Web page at the server uses input received as the result of the user's request for the page to access data from a database and then builds or customizes the page on the fly before sending it to the requestor.

ASP is a feature of the Microsoft Internet Information Server (Internet Information Server), but, since the server-side script is just building a regular HTML page, it can be delivered to almost any browser. You can create an ASP file by including a script written in VBScript or JScript in an HTML file or by using ActiveX Data Objects (ActiveX Data Objects) program statements in the HTML file. You name the HTML file with the ".asp" file suffix. Microsoft recommends the use of the server-side ASP rather than a client-side script, where there is actually a choice, because the server-side script will result in an easily displayable HTML page. Client-side scripts (for example, with JavaScript) may not work as intended on older browsers.

Assembly Language
Software

Assembly langage is a programming language that is once removed from a computer's machine language. Machine languages consist entirely of numbers and are almost impossible for humans to read and write. Assembly languages have the same structure and set of commands as machine languages, but they enable a programmer to use names instead of numbers.

Each type of CPU has its own machine language and assembly language, so an assembly language program written for one type of CPU won't run on another. In the early days of programming, all programs were written in assembly language. Now, most programs are written in a high-level language such as FORTRAN or C. Programmers still use assembly language when speed is essential or when they need to perform an operation that isn't possible in a high-level language.

Asynchronous
Networking

A system of communication in which each discreet delivery of information establishes its own timing impulse rather than having to conform to the timing impulse of previous deliveries.

Asynchronous Transmission
Networking

Term describing digital signals that are transmitted without precise clocking. Such signals generally have different frequencies and phase relationships. Asynchronous transmissions usually encapsulate individual characters in control bits (called start and stop bits) that designate the beginning and end of each character. Compare with Isochronous transmission, plesiochronous transmission, and synchronous transmission.

AT command set
Protocol

Pronounced ay-tee command set, the de facto standard language for controlling modems. The AT command set was developed by Hayes and is recognized by virtually all personal computer modems.

ATDM
Lingo

Asynchronous time-division multiplexing. Method of sending information that resembles normal TDM, except that time slots are allocated as needed rather than preassigned to specific transmitters. Compare with FDM, Statistical multiplexing, and TDM.

ATM
Networking

Short for Asynchronous Transfer Mode, a network technology based on transferring data in cells or packets of a fixed size. The cell used with ATM is relatively small compared to units used with older technologies. The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data hogs the line. Current implementations of ATM support data transfer rates of from 25 to 622 Mbps (megabits per second). This compares to a maximum of 100 Mbps for Ethernet, the current technology used for most LANs. Some people think that ATM holds the answer to the Internet bandwidth problem, but others are skeptical. ATM creates a fixed channel, or route, between two points whenever data transfer begins. This differs from TCP/IP, in which messages are divided into packets and each packet can take a different route from source to destination. This difference makes it easier to track and bill data usage across an ATM network, but it makes it less adaptable to sudden surges in network traffic. When purchasing ATM service, you generally have a choice of four different types of service: Constant Bit Rate (CBR) specifies a fixed bit rate so that data is sent in a steady stream. This is analogous to a leased line. Variable Bit Rate (VBR) provides a specified throughput capacity but data is not sent evenly. This is a popular choice for voice and videoconferencing data. Unspecified Bit Rate (UBR) does not guarantee any throughput levels. This is used for applications, such as file transfer, that can tolerate delays. Available Bit Rate (ABR) provides a guaranteed minimum capacity but allows data to be bursted at higher capacities when the network is free.

ATP
Protocol

AppleTalk Transaction Protocol. Transport-level protocol that allows reliable request-response exchanges between two socket clients.

Attenuation
Telecommunications

The decrease in the power of a signal, light beam, or lightwave either absolutely or as a fraction of a reference value (ie., high-loss: over 100dB/km; medium-loss: 20 to 100 db/km). In other words, attenuation is the loss of volume during transmission.

Attribute
Networking

Configuration data that defines the characteristics of database objects such as the chassis, cards, ports, or virtual circuits of a particular device. Attributes might be preset or user-configurable. On a LightStream 2020 ATM switch, attributes are set using the configuration program or CLI commands.

AUI
Lingo

Attachment unit interface. IEEE 802.3 interface between an MAU and a NIC (network interface card). Also called transceiver cable.

Authentication
Protocol

The process of identifying an individual, usually based on a username and password. In security systems, authentication is distinct from authorization , which is the process of giving individuals access to system objects based on their identity. Authentication merely ensures that the individual is who he or she claims to be, but says nothing about the access rights of the individual.

Authoritative Name Server
Networking

A name server takes one of three roles for a given domain: primary, secondary or non-authoritative.

A Primary Name Server is a server that maintains authoritative records on which machines are in a particular domain; for instance, www.connect.com.au is a machine in the domain connect.com.au. Primary Domain Name Servers store the actual files containing all Internet addressing information and so there are many of them.

Autonomous System
Networking

On the Internet, an autonomous system (AS) is the unit of router policy, either a single network or a group of network that is controlled by a common network administrator (or group of administrators) on behalf of a single administrative entity (such as a university, a business enterprise, or a business division). An autonomous system is also sometimes referred to as a routing domain. An autonomous system is assigned a globally unique number, sometimes called an Autonomous System Number (ASN).

Networks within an autonomous system communicate routing information to each other using an Interior Gateway Protocol (Interior Gateway Protocol). An autonomous system shares routing information with other autonomous systems using the Border Gateway Protocol (Border Gateway Protocol). Previously, the Exterior Gateway Protocol (Exterior Gateway Protocol) was used. In the future, the BGP is expected to be replaced with the OSI Inter-Domain Routing Protocol (IDRP).

Autoreconfiguration
Networking

The process performed by nodes within the failure domain of a Token Ring network. Nodes automatically perform diagnostics in an attempt to reconfigure the network around the failed areas. See also failure domain.

Autoresponder
Lingo

A feature that sends an automated reply to incoming email. For example, when customers send email to your sales@yourdomain.com address, a standard message could be sent back to them.

AWK
Software

An interpreted programming language that is included in most versions of UNIX. The name is derived from the initials of its creators -- Alfred Aho, Peter Weinberger, and Brian Kernighan -- who developed the language in 1977 and 1978. The language is particularly designed for filtering and manipulating textual data. In this respect, it is similar to Perl, though Perl is more powerful.

There are many variants of awk, including gawk, which is the GNU version.

B

B Channel
Telecommunications

Short for Bearer-channel, the main data channel in an ISDN connection. Basic Rate ISDN (BRI) service consists of two 64 Kbps B-channels, and one D-channel for transmitting control information. Primary ISDN service consists of 23 B-channels (in the U.S.) or 30 B-channels (in Europe).

B8ZS
Telecommunications

Binary 8-zero substitution. Line-code type, used on T1 and E1 circuits, in which a special code is substituted whenever 8 consecutive zeros are sent over the link. This code is then interpreted at the remote end of the connection. This technique guarantees ones density independent of the data stream. Sometimes called bipolar 8-zero substitution.

Back End
Networking

Node or software program that provides services to a front end. See also client, front end, and server.

Back End Processor
Hardware

A computer running an application that supplies data to other computers on demand, but has no user interface.

Back-Haul
Telecommunications

In a hierarchical telecommunications network the backhaul portion of the network comprises the intermediate links between the core network, or backbone, of the network and the small subnetworks at the "edge" of the entire hierarchical network. For example, while cell phones communicating with a single cell tower constitute a local subnetwork, the connection between the cell tower and the rest of the world begins with a backhaul link to the core of the telephone company's network (via a point of presence).

Backbone
Networking

Also known as a Backbone Network, a backbone is the part of a communications facility that connects primary nodes. In general, this is a large, in terms of bandwidth, connection that serves multiple users through multiplexing at designated jumping off points. In some ways, this can be compared to the national highway system in how it allows large amounts of vehicles access to most major cities throughout the US.

Background Noise
Telecommunications

Random signals that can be attributed to the unpredictable movement of free electrons in a telephone channel.

Background Task
Programming

A computing task that is executing while another task or application is displaying its user interface.

Backup
Networking

A copy of a set of files made for replacement purposes in case the original set is damaged or lost.

Backward Learning
Concept

Algorithmic process used for routing traffic that surmises information by assuming symmetrical network conditions. For example, if node A receives a packet from node B through intermediate node C, the backward-learning routing algorithm will assume that A can optimally reach B through C.

Balance
Telecommunications

To equalize load or current between parts or elements of a circuit. Balancing a line is to adjust the impedance of circuits and to balance networks to achieve specified gain/loss objectives at junctions fo 2-wire and 4-wire circuits.

Balanced
Telecommunications

The state of impedance on a two-wire line when the impedance to ground as measured from one wire is equal to the impedance to ground as measured from the other wire. A balancing network is a combination of electronic components which stimulate the impedance of a uniform cable or open-wire circuit over a band of frequencies.

Balanced Circuit
Telecommunications

A two-wire telephone circuit in which the two conductors are electronically balanced to each other and to the ground.

Bandwidth
Telecommunications

The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second(bps) or bytes per second. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz). The bandwidth is particularly important for I/O devices. For example, a fast disk drive can be hampered by a bus with a low bandwidth. This is the main reason that new buses, such as AGP, have been developed for the PC.

Bandwidth Reservation
Networking

Process of assigning bandwidth to users and applications served by a network. Involves assigning priority to different flows of traffic based on how critical and delay-sensitive they are. This makes the best use of available bandwidth, and if the network becomes congested, lower-priority traffic can be dropped. Sometimes called bandwidth allocation. See also call priority.

Banner
Lingo

Paid advertisements in the form of graphics (usually rectangular in shape) displayed on a Web page. When viewers click on a banner, they are taken to the advertiser's Web site.

Baseband
Telecommunications

A communication system in which only one signal is carried at any one time.

Baud
Hardware

A unit of measurement for modem speed, synonymous with bits per second (bps). A 56K modem has a speed of 56,000 baud or 56,000 BPS

BBS
Lingo

Bulletin Board System: A computerized meeting system. BBS users can have discussions, make announcements, and upload or download files. There are thousands of BBSs around the world; many of them rely on a direct modem-to-modem connection over a phone line, using a single computer.

Beacon
Networking

Frame from a Token Ring or FDDI device indicating a serious problem with the ring, such as a broken cable. A beacon frame contains the address of the station assumed to be down.

BECN
Telecommunications

Backward explicit congestion notification. Bit set by a Frame Relay network in frames traveling in the opposite direction of frames encountering a congested path. DTE receiving frames with the BECN bit set can request that higher-level protocols take flow control action as appropriate.

BER
Telecommunications

In telecommunication transmission, the bit error rate (BER) is the percentage of bits that have errors relative to the total number of bits received in a transmission, usually expressed as ten to a negative power. For example, a transmission might have a BER of 10 to the minus 6, meaning that, out of 1,000,000 bits transmitted, one bit was in error. The BER is an indication of how often a packet or other data unit has to be retransmitted because of an error. Too high a BER may indicate that a slower data rate would actually improve overall transmission time for a given amount of transmitted data since the BER might be reduced, lowering the number of packets that had to be resent. A BERT (bit error rate test or tester) is a procedure or device that measures the BER for a given transmission.

BERT
Lingo

Bit Error Rate Test. Self-explanatory. A known pattern of bits is transmitted, and erros are counted to determine the BER (Bit Error Rate).

BGP
Protocol

Short for Border Gateway Protocol, an Internet protocol that enables groups of routers (called autonomous systems) to share routing information so that efficient, loop-free routes can be established. BGP is commonly used within and between Internet Service Providers (ISPs). The protocol is defined in RFC 1771.

BGP4
Protocol

BGP Version 4. Version 4 of the predominant interdomain routing protocol used on the Internet. BGP4 supports CIDR and uses route aggregation mechanisms to reduce the size of routing tables.

BIGA
Lingo

Bus Interface Gate Array. Technology that allows the Catalyst 5000 to receive and transmit frames from its packet-switching memory to its MAC local buffer memory without the intervention of the host processor.

Binary
Telecommunications

Where only 2 values or states are possible for a condition, such as "ON" or "OFF", or "one" or "zero." Binary is the property which permits the selection of two distinct possibilities. A binary code makes use of two distinct characters (i.e., "0" and "1," positive and negative pulses). The flow of this information is referred to as a binary stream or binary code.

Binary Switch
Concept

A switch that must exist in one of only two states: on/off, zero/one, etc.

BIND
Protocol

Short for Berkeley Internet Name Domain, a Domain Name Server (DNS). BIND is designed for UNIX systems based on BSD, the version of UNIX developed at the University of California's Berkeley campus.

Binhex
Lingo

BINary HEXadecimal: A method of converting non-text files (non-ASCII) into ASCII. This is needed because Internet email can only handle ASCII.

Biometrics
Lingo

Generally, the study of measurable biological characteristics. In computer security, biometrics refers to authentication techniques that rely on measurable physical characteristics that can be automatically checked. Examples include computer analysis of fingerprints or speech. Though the field is still in its infancy, many people believe that biometrics will play a critical role in future computers, and especially in electronic commerce. Personal computers of the future might include a fingerprint scanner where you could place your index finger. The computer would analyze your fingerprint to determine who you are and, based on your identity, authorize you different levels of access. Access levels could include the ability to use credit card information to make electronic purchases.

Bipolar Signalling
Telecommunications

Bipolar signaling, also called bipolar transmission, is a baseband method of sending binary data over wire or cable. There are two logic states, low and high, represented by the digits 0 and 1 respectively.

The illustration shows a bipolar signal as it might appear on the screen of an oscilloscope. Each horizontal division represents one bit (binary digit). The logic 0 state is -3 volts and logic 1 is +3 volts. This is positive logic. Alternatively, logic 0 might be +3 volts, and logic 1 might be -3 volts; this would be negative logic. Whether positive or negative logic is used, the voltages representing the low and high states are equal and opposite; over time, the average voltage is approximately equal to 0.

A bipolar signal resembles an alternating current (AC) rectangular wave, except that the frequency is not constant. The bandwidth of the signal is inversely proportional to the duration of each data bit. Typical data speeds in baseband are several megabits per second (Mbps); hence the duration of each bit is a fraction of a microsecond.

Bit
Software

Short for binary digit, the smallest unit of information on a machine. The term was first used in 1946 by John Tukey, a leading statistician and adviser to five presidents. A single bit can hold only one of two values: 0 or 1. More meaningful information is obtained by combining consecutive bits into larger units. For example, a byte is composed of 8 consecutive bits.

Bit Clock
Telecommunications

The bits clock is a pusle that synchronizes the entire network or connection. The pulse is a 1-0-1-0-1-0-1-0 stream and is used extensively in SONET networks.

Bit pattern
Networking

A sequence of bits that has a specific purpose or meaning.

Bit rate
Networking

The rate at which bits are transmitted or received during communication, expressed as the number bits in a given amount of time, usually one second.

Bit Stream
Networking

A continuous flow of binary digits (bits), through some form of communications medium_e.g., fiber optics, air (wirless) or twisted-pair, with no break or seperation between the characters.

Bit Stuffing
Networking

The practice of adding bits to a stream of data. Bit stuffing is required by many network and communications protocols for the following reasons: To prevent data being interpreted as control information. For example, many frame-based protocols, such as X.25, signal the beginning and end of a frame with six consecutive 1 bits. Therefore, if the actual data being transmitted has six 1 bits in a row, a zero is inserted after the first 5 so that the dat is not interpreted as a frame delimiter. Of course, on the receiving end, the stuffed bits must be discarded. For protocols that require a fixed-size frame, bits are sometimes inserted to make the frame size equal to this set size. For protocols that required a continuous stream of data, zero bits are sometimes inserted to ensure that the stream is not broken.

Bit Synchronous
Telecommunications

A data transmission technique in which each bit is synchronized against an accurate clock. In asynchronous transmission, this synchronization is held for one character. In synchronous transmissions, this synchronization is held for a block of characters.

Bit-oriented Protocol
Protocol

Class of data link layer communication protocols that can transmit frames regardless of frame content. Compared with byte-oriented protocols, bit-oriented protocols provide full-duplex operation and are more efficient and reliable. Compare with byte-oriented protocol.

Bitmap
Networking

A data structure that uses bits to represent the attributes of an object that is not character-based.

BITNET
Lingo

"Because It's Time" Networking Services. Low-cost, low-speed academic network consisting primarily of IBM mainframes and 9600-bps leased lines. BITNET is now a part of CREN. See also CREN.

Black Box
Lingo

A device that performs a function using mechanisms that are unimportant or impossible to understand.

Black Hole
Networking

Routing term for an area of the internetwork where packets enter, but do not emerge, due to adverse conditions or poor system configuration within a portion of the network.

Blowfish
Software

Blowfish is an encryption algorithm that can be used as a replacement for Data Encryption Standard or (International Data Encryption Algorithm. It is a symmetric (that is, a secret or private key) block cipher that uses a variable-length key, from 32 bits to 448 bits, making it ideal for both domestic and exportable use. Blowfish was designed in 1993 by Bruce Schneier as an alternative to existing encryption algorithms. Designed with 32-bit instruction processors in mind, it is significantly faster than DES. Since its origin, it has been analyzed considerably. Blowfish is unpatented, license-free, and available free for all uses.

Blue screen of death
Lingo

The blue screen of death is a rather terrifying display image containing white text on a blue background that is generated by Windows operating systems when the system has suddenly terminated with an error. The system is locked up and must be restarted. The blue screen may include some hexadecimal values from a core dump that may help determine what caused the crash. The blue screen of death can strike anywhere. At the Comdex trade show, Microsoft Chairman Bill Gates encountered the blue screen during a demonstration of Windows 98. (He had a spare computer standing by.)

BNC
Networking

Bayonet "N" Connector. 1. The locking connector type used in 10Base2 (Thin Ethernet). 2. Any connector similar to the type used by 10Base2 for CATV, and other electronic uses.

BNN
Networking

Boundary network node. In SNA terminology, a subarea node that provides boundary function support for adjacent peripheral nodes. This support includes sequencing, pacing, and address translation.

Board
Lingo

A printed circuit and the substrate on which it lies.

Bob Metcalfe
People

Robert M. "Bob" Metcalfe was born in Brooklyn, New York in 1946 and grew up living on Long Island. By his own admission, at the age of ten he wanted to become an electrical engineer at the Massachusetts Institute of Technology (MIT).

He in fact did enter MIT in 1964 and graduated in 1969 with bachelors degrees in electrical engineering and business management. He did his first net work as captain of the MIT Varsity Tennis Team. In 1970, Metcalfe received a masters degree in applied mathematics from Harvard University, and his Ph.D. in computer science from Harvard in 1973. His doctoral dissertation, written while conducting research on packet switching in the Advanced Research Projects Agency Network (ARPANET) and Aloha computer networks in MIT's project MAC, is now being republished.

In 1972, while working on his Ph.D. at Harvard, Metcalfe began working for Xerox Corporation in their Palo Alto Research Center (PARC). PARC was a breeding ground of genius and innovation, serving as the birth-place of the PC, graphical user interface (GUI), and page-description language (PDL); however, it was not the place where these innovations were developed into successful products.

It was at PARC, in 1973, that Bob Metcalfe and D.R. Boggs invented Ethernet, the local area networking (LAN) technology that turns PCs into communication tools by linking them together. In 1976 Metcalfe and Boggs published a paper titled, "Ethernet: Distributed Packet-Switching for Local Computer Networks." The invention of Ethernet preceded the personal computer, yet it was a breakthrough in computer networking that would eventually tie together 50 million PCs worldwide. In addition to defining the physical media and connections, Ethernet defined how data is transmitted across a local area network (LAN) at 10 megabits per second. Ethernet allows PCs and workstations from different manufacturers to communicate by using agreed-upon standards for sending packets. Of his experiences at PARC, Metcalfe said, "I was given all the equipment I would ever need to do my work. Best of all, I got to work with other geniuses."

In 1976, Metcalfe moved to the Xerox Systems Development Division and managed the microprocessor and communication developments that would eventually lead to the Xerox Star workstation. Star was the first PC to include a bit-map screen, mouse, what-you-see-is-what-you-get(wysiwyg) word processing, Ethernet, and software to include text and graphics in the same document.

While at PARC, Metcalfe began teaching part-time at Stanford University. He taught a course on distributed computing and left in 1983 as a Consulting Associate Professor of Electrical Engineering.

In 1979, Metcalfe left Xerox and founded 3Com Corporation in Santa Clara, California. His purpose in forming 3Com was to promote PC LANs and Ethernet as the standard. Although he was unable to persuade IBM to use Ethernet as a standard, he did bring together Digital Equipment, Intel, and Xerox and made Ethernet the most widely used LAN.

Metcalfe served in many capacities at 3Com - CEO, President, Chairman of the Board, and Division General Manager; however, according to him, his greatest accomplishment came as head of sales and marketing where he increased sales from zero to $1 million per month. Under his guidance, 3Com, which he named for three words - computer, communication, and compatibility - became a Fortune 500 corporation.

In 1990, he retired from 3Com. Outside of the 3Com headquarters in Santa Clara stands a monument to Bob Metcalfe. In 1995, the famous Candlestick Park in San Francisco was renamed 3Com Park. Bob Metcalfe's impact on the world of computers, and most especially on the transformation of the PC from being a data processor to a communication device, had been huge. He had received many awards for his contributions, including the prestigious Grace Murray Hopper Award in 1980 from the Association for Computing Machinery (ACM) and the Alexander Graham Bell Medal in 1988 from the Institute of Electrical and Electronics Engineers (IEEE). However, despite his accomplishments, in 1990, Bob Metcalfe faced a fork in the road. In a 1990 interview with PC Week magazine he said, "It annoys me that 80 percent of journalists are registered Democrats. The journalistic field has a very strange view of itself. What it considers mainstream, I consider left wing. I've thought of becoming a right-wing journalist, just to add some balance."

Beginning in 1991, he spent a year as a visiting fellow at Wolfson College, Oxford University in England. Upon his return, he began his career in journalism by writing for Computerworld, Communications Week, Digital Media, Network Computing, and Technology Review. In 1993 he became Vice-president of Technology for the International Data Group, parent company of InfoWorld Magazine, and began writing "From the Ether," a weekly column on networking, for InfoWorld. It is now syndicated worldwide.

As a journalist, Metcalfe irreverently attacks the computer industry and encourages change. With the popularity of networks and the Internet, one of his observations became known as Metcalfe's Law. It states that a network's value grows proportionately with its number of users. In one of his columns in December 1995, Metcalfe predicted the 1996 collapse of the Internet and said that the information superhighway would become no more than using Federal Express to ship CD-ROMs back and forth.

In 1995, Metcalfe received his first journalism award, the Public Understanding of Science Award, from the San Francisco Exploratorium, and in the same year he was elected to the American Academy of Arts and Sciences. In 1996, he added to his many awards when he received the IEEE Medal of Honor.

In 1996, he also became the chairman of ACM97s, the 50th anniversary conference of the ACM, to examine the next 50 years of computing. Commenting on the conference, Metcalfe said, "ACM97 aims to do more than brainstorm about the future. If we do a good job, we can change the future."

As one of the pioneers in the computer industry and computer networking, Bob Metcalfe is in touch with the people who determine the future direction of communications and information delivery. In 1995, he began gathering industry leaders and the bright, lesser known people in the industry to his house for evenings of serious discussion. While he has had an impact on 50 million people with Ethernet, as a journalist and futurist he continues to be an important force in the world of computers. For the man who just wanted to be an electrical engineer at MIT, and who now serves on the MIT board of trustees, it has already been a tremendous career, with no end in sight.

Bookmark
Lingo

The feature of a Web Browser that lets you save the address (URL) of a web page so you can go back to the page easily at a later time.

Boot
Lingo

A computer's startup operation.

Boot Drive
Lingo

The disk that contains a computers' startup instructions.

Boot PROM
Hardware

Boot programmable read-only memory. Chip mounted on a printed circuit board used to provide executable boot instruction to a computer device.

BOOTP
Protocol

Short for Bootstrap Protocol, an Internet protocol that enables a diskless workstation to discover its own IP address, the IP address of a BOOTP server on the network, and a file to be loaded into memory to boot the machine. This enables the workstation to boot without requiring a hard or floppy disk drive. The protocol is defined by RFC 951.

Border Gateway
Protocol

Router that communicates with routers in other autonomous systems.

Boundary Function
Networking

Capability of SNA subarea nodes to provide protocol support for attached peripheral nodes. Typically found in IBM 3745 devices.

BPDU
Protocol

Bridge protocol data unit. Spanning-Tree Protocol hello packet that is sent out at configurable intervals to exchange information among bridges in the network.

BPS
Telecommunications

Abbreviation of bits per second, the standard measure of data transmission speeds.

BRI
Lingo

Basic Rate Interface. an ISDN service with two bearer channels at 64 KBPS plus a "Data-Link" or control channel at 16 KBPS.

Bridge
Networking

Similar to a hub, a bridge is a product that connects a local area network to another local area network. Like a hub, bridges are "dumb" devices in that they simply connect networks and do no filtering or processing of the packets. The two connected networks do not need to be of the same networking protocols, such as 10Base-T and 100Base-T. Bridges are also used for wide area networking with DSL technologies to bridge DSL to 10Base-T Ethernet.

Bridge Forwarding
Networking

Process that uses entries in a filtering database to determine whether frames with a given MAC destination address can be forwarded to a given port or ports. Described in the IEEE 802.1 standard. See also IEEE 802.1.

Bridge Number
Networking

Number that identifies each bridge in an SRB LAN. Parallel bridges must have different bridge numbers.

Bridge Static Filtering
Networking

Process in which a bridge maintains a filtering database consisting of static entries. Each static entry equates a MAC destination address with a port that can receive frames with this MAC destination address and a set of ports on which the frames can be transmitted. Defined in the IEEE802.1 standard.

Bridging
Telecommunications

The technique whereby additional stations may be served from a 2-point facility by extending the facility from a "bridge" at one of the terminating points of the facility.

Broadband
Telecommunications

Broadband refers to telecommunication that provides multiple channels of data over a single communications medium, typically using some form of frequency or wave division multiplexing. The more common usage is used to denote a communication channel that provides a great than voice-grade communications channel and is therefore capable of handling higher speed data transmissions.

Broadcast
Networking

An information transmission that is intended to be interpreted by all entities capable of receiving it.

Broadcast Address
Networking

Special address reserved for sending a message to all stations. Generally, a broadcast address is a MAC destination address of all ones. Compare with multicast address and unicast address.

Broadcast Domain
Networking

The set of all devices that will receive broadcast frames originating from any device within the set. Broadcast domains are typically bounded by routers because routers do not forward broadcast frames.

Broadcast Search
Networking

Propagation of a search request to all network nodes if the location of a resource is unknown to the requester.

Broadcast Storm
Networking

Undesirable network event in which many broadcasts are sent simultaneously across all network segments. A broadcast storm uses substantial network bandwidth and, typically, causes network time-outs.

brouter
Networking

A brouter (pronounced BRAU-tuhr or sometimes BEE-rau-tuhr) is a network bridge and a router combined in a single product. A bridge is a device that connects one local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or token ring). If a data unit on one LAN is intended for a destination on an interconnected LAN, the bridge forwards the data unit to that LAN; otherwise, it passes it along on the same LAN. A bridge usually offers only one path to a given interconnected LAN. A router connects a network to one or more other networks that are usually part of a wide area network (WAN) and may offer a number of paths out to destinations on those networks. A router therefore needs to have more information than a bridge about the interconnected networks. It consults a routing table for this information. Since a given outgoing data unit or packet from a computer may be intended for an address on the local network, on an interconnected LAN, or the wide area network, it makes sense to have a single unit that examines all data units and forwards them appropriately.

Browser
Software

A browser is an application program that provides a way to look at and interact with all the information on the World Wide Web. The word "browser" seems to have originated prior to the Web as a generic term for user interfaces that let you browse text files online. By the time the first Web browser with a graphical user interface was invented (Mosaic, in 1992), the term seemed to apply to Web content, too. Technically, a Web browser is a client program that uses the Hypertext Transfer Protocol (Hypertext Transfer Protocol) to make requests of Web servers throughout the Internet on behalf of the browser user. A commercial version of the original browser, Mosaic, is in use. Many of the user interface features in Mosaic, however, went into the first widely-used browser, Netscape Navigator. Microsoft followed with its Microsoft Internet Explorer. Today, these two browsers are highly competitive and the only two browsers that the vast majority of Internet users are aware of. Although the online services, such as America Online, Compuserve, and Prodigy, originally had their own browsers, virtually all now offer the Netscape or Microsoft browser. Lynx is a text-only browser for UNIX shell and VMS users. Another recently offered browser is Opera.

BSC
Lingo

Binary synchronous communication. Character-oriented data link layer protocol for half-duplex applications. Often referred to simply as bisync.

BSD
Organizations

Berkeley Software Distribution. UC Berkeley's distribution of the Unix operating system.

Buffer
Telecommunications

A temporary memory storage area for information. In data transmission, a buffer is a temporary storage location for information being sent or received and serves the purpose of flow control.

Bug
Programming

A flaw in a software program.

Bus
Networking

A type of network topology in which nodes are connected along a continuous path that is not a closed circuit. Also refers to a communications channel used by a single computer such as Nubus, SCSI, etc.

Bus Network
Networking

A network in which all nodes are connected to a single wire (the bus) that has two endpoints. Ethernet 10Base-2 and 10Base-5 networks, for example, are bus networks. Other common network types include star networks and ring networks.

Bus Topology
Networking

Linear LAN architecture in which transmissions from network stations propagate the length of the medium and are received by all other stations. Compare with ring topology, star topology, and tree topology.

Bypass Mode
Networking

Operating mode on FDDI and Token Ring networks in which an interface has been removed from the ring.

Bypass Relay
Networking

Allows a particular Token Ring interface to be shut down and thus effectively removed from the ring.

Byte
Software

Abbreviation for binary term, a unit of storage capable of holding a single character. On almost all modern computers, a byte is equal to 8 bits. Large amounts of memory are indicated in terms of kilobytes (1,024 bytes), megabytes (1,048,576 bytes), and gigabytes (1,073,741,824 bytes). A disk that can hold 1.44 megabytes, for example, is capable of storing approximately 1.4 million characters, or about 3,000 pages of information.

C

C
Software

C is a high-level programming language developed by Dennis Ritchie and Brian Kernighan at Bell Labs in the mid 1970s. Although originally designed as a systems programming language, C has proved to be a powerful and flexible language that can be used for a variety of applications, from business programs to engineering. C is a particularly popular language for personal computer programmers because it is relatively small -- it requires less memory than other languages.

The first major program written in C was the UNIX operating system, and for many years C was considered to be inextricably linked with UNIX. Now, however, C is an important language independent of UNIX.

Although it is a high-level language, C is much closer to assembly language than are most other high-level languages. This closeness to the underlying machine language allows C programmers to write very efficient code. The low-level nature of C, however, can make the language difficult to use for some types of applications.

C Bit
Telecommunications

Control Bit. This can pertain to the signaling and control bits used in certain T-carrier systems, for example, M-13 mulitplexing is used to multiplex 28 T-1 signals into a signal T-3 signal through the use of control bits.

C++
Software

C++ is a high-level programming language developed by Bjarne Stroustrup at Bell Labs. C++ adds object-oriented features to its predecessor, C. C++ is one of the most popular programming language for graphical applications, such as those that run in Windows and Macintosh environments.

Cable
Hardware

The transmission media of a network.

Cable Range
Networking

Range of network numbers that is valid for use by nodes on an extended AppleTalk network. The cable range value can be a single network number or a contiguous sequence of several network numbers. Node addresses are assigned based on the cable range value.

Cache
PC's

A group of memory locations set aside for temporary storage of data, especially frequently-used data or data needing high speed retrieval by the CPU.

Call Priority
Networking

Priority assigned to each origination port in circuit-switched systems. This priority defines the order in which calls are reconnected. Call priority also defines which calls can or cannot be placed during a bandwidth reservation.

CAM
Lingo

Content-addressable memory. See associative memory.

CAP
Telecommunications

Competitive Access Provider. This is sometimes known as an AAV, or Alternative Access Provider. CAP's provide an alternative means of establishing a connection between a user organization and an IXC (InterXchange Carrier), completely bypassing the ILEC (Incumbant Local Exchange Carrier). CAP's typically deploy high-capacity SONET fiber optic transmission systems in a ring topology.

Card
Hardware

A circuit board that plugs into a computer's bus to extend the computer's capability.

Carrier
Telecommunications

A carrier (or carrier signal) is a transmitted electromagnetic pulse or wave at a steady base frequency of alternation on which information can be imposed by increasing signal strength, varying the base frequency, varying the wave phase, or other means. This variation is called modulation. With the advent of laser transmission over optical fiber media, a carrier can also be a laser-generated light beam on which information is imposed.

Types of analog modulation of a carrier include amplitude modulation (AM), frequency modulation (FM), and phase modulation. Types of digital modulation include varieties of pulse code modulation (PCM), including pulse amplitude modulation (PAM), pulse duration modulation (PDM), and pulse position modulation (PPM).

Carrier detect (modem lights) is a control signal between a modem and a computer that indicates that the modem detects a "live" carrier that can be used for sending and receiving information.

Carrier System
Telecommunications

A system where several different signals can be combined onto one carrier by changing some feature of the signals transmitting them (modulation) then converting the signals back to their original form (demodulation). Many information channels can be carried by one broadband carrier system.

Case Insensitive
Networking

Referring to a system in which upper case letters are not differentiated from their lower case form.

Case Sensitive
Networking

Referring to a system in which upper case letters are differentiated from their lower case form.

Category 1 Cabling
Networking

One of five grades of UTP cabling described in the EIA/TIA-586 standard. Category 1 cabling is used for telephone communications and is not suitable for transmitting data. Compare with Category 2 cabling, Category 3 cabling, Category 4 cabling, and Category 5 cabling. See also EIA/TIA-586 and UTP.

Category 2 Cabling
Networking

One of five grades of UTP cabling described in the EIA/TIA-586 standard. Category 2 cabling is capable of transmitting data at speeds up to 4 Mbps. Compare with Category 1 cabling, Category 3 cabling, Category 4 cabling, and Category 5 cabling. See also EIA/TIA-586 and UTP.

Category 3 cabling
Networking

One of five grades of UTP cabling described in the EIA/TIA-586 standard. Category 3 cabling is used in 10Base T networks and can transmit data at speeds up to 10 Mbps. Compare with Category 1 cabling, Category 2 cabling, Category 4 cabling, and Category 5 cabling. See also EIA/TIA-586 and UTP.

Category 4 cabling
Networking

One of five grades of UTP cabling described in the EIA/TIA-586 standard. Category 4 cabling is used in Token Ring networks and can transmit data at speeds up to 16 Mbps. Compare with Category 1 cabling, Category 2 cabling, Category 3 cabling, and Category 5 cabling. See also EIA/TIA-586 and UTP.

Category 5 cabling
Networking

One of five grades of UTP cabling described in the EIA/TIA-586 standard. Category 5 cabling is used for running CDDI and can transmit data at speeds up to 100 Mbps Compare with Category 1 cabling, Category 2 cabling, Category 3 cabling, and Category 4 cabling. See also EIA/TIA-586 and UTP.

Catenet
Networking

Network in which hosts are connected to diverse networks, which themselves are connected with routers. The Internet is a prominent example of a catenet.

CATV
Concept

Cable television. Communication system where multiple channels of programming material are transmitted to homes using broadband coaxial cable. Formerly called Community Antenna Television.

CBDS
Lingo

Connectionless Broadband Data Service. European high-speed, packet-switched, datagram-based WAN networking technology. Similar to SMDS.

CBR
Lingo

Constant bit rate. QOS class defined by the ATM Forum for ATM networks. CBR is used for connections that depend on precise clocking to ensure undistorted delivery.

CBT
Lingo

Acronym for computer-based training, a type of education in which the student learns by executing special training programs on a computer. CBT is especially effective for training people to use computer applications because the CBT program can be integrated with the applications so that students can practice using the application as they learn. Historically, CBTs growth has been hampered by the enormous resources required: human resources to create a CBT program. and hardware resources needed to run it. However, the increase in PC computing power, and especially the growing prevalence of computers equipped with CD-ROMs, is making CBT a more viable option for corporations and individuals alike. Many PC applications now come with some modest form of CBT, often called a tutorial. CBT is also called computer-assisted instruction (CAI).

CCITT
Organizations

Abbreviation of Comité Consultatif International Téléphonique et Télégraphique, an organization that sets international communications standards. CCITT, now known as ITU (the parent organization) has defined many important standards for data communications

CCS
Lingo

Common Channel Signaling. Signaling system used in telephone networks that separates signaling information from user data. A specified channel is exclusively designated to carry signaling information for all other channels in the system.

CD
Lingo

Carrier Detect. Signal that indicates whether an interface is active. Also, a signal generated by a modem indicating that a call has been connected.

CDDI
Lingo

Copper Distributed Data Interface. Implementation of FDDI protocols over STP and UTP cabling. CDDI transmits over relatively short distance (about 100 meters), providing data rates of 100Mbps using a dual-ring architecture to provide redundancy. Based on the ANSI Twisted-Pair Physical Medium Dependent (TPPMD) standard.

CDPD
Lingo

Cellular Digital Packet Data. Open standard for two-way wireless data communication over high-frequency cellular telephone channels. Allows data transmissions between a remote cellular link and a NAP. Operates at 19.2 Kbps.

CDVT
Lingo

Cell delay variation tolerance. Parameter defined by the ATM Forum for ATM traffic management. In CBR transmissions, determines the level of jitter that is tolerable for the data samples taken by the PCR.

Cell
Networking

The basic unit for ATM Switching and multiplexing. Cells contain identifiers that specify the data stream to which they belong. Each cell consists of a 5-byte header and 48 bytes of payload. See also cell relay.

Cell Relay
Networking

Network technology based on the use of small, fixed-size packets, or cells. Because cells are fixed-length, they can be processed and switched in hardware at high speeds. Cell relay is the basis for many high-speed network protocols including ATM, IEEE802.6, and SMDS.

Central Office
Telecommunications

Commonly referred to as CO. A Central Office is a building in which subscriber lines are joined to switching equipment for connecting other subscribers to each other. Sometimes a CO may be a wiring center where there might be one or several switching exchanges.

Centrex
Telecommunications

Centrex (central office exchange service) is a service from local telephone companies in the United States in which up-to-date phone facilities at the phone company's central (local) office are offered to business users so that they don't need to purchase their own facilities. The Centrex service effectively partitions part of its own centralized capabilities among its business customers. The customer is spared the expense of having to keep up with fast-moving technology changes (for example, having to continually update their private branch exchange infrastructure) and the phone company has a new set of services to sell. In many cases, Centrex has now replaced the private branch exchange. Effectively, the central office has become a huge branch exchange for all of its local customers. In most cases, Centrex (which is sold by different names in different localities) provides customers with as much if not more control over the services they have than PBX did. In some cases, the phone company places Centrex equipment on the customer premises. Typical Centrex service includes direct inward dialing (Direct Inward Dialing), sharing of the same system among multiple company locations, and self-managed line allocation and cost-accounting monitoring.

Certificate Authority
Organizations

A trusted third-party organization or company that issues digital certificates used to create digital signatures and public-private key pairs. The role of the CA in this process is to guarantee that the individual granted the unique certificate is, in fact, who he or she claims to be. Usually, this means that the CA has an arrangement with a financial institution, such as a credit card company, which provides it with information to confirm an individual's claimed identity. CAs are a critical component in data security and electronic commerce because they guarantee that the two parties exchanging information are really who they claim to be.

CERTnet
Organizations

California Education and Research Federation Network. TCP/IP network, based in Southern California, that connects hundreds of higher-education centers internationally while also providing Internet access to subscribers. CERFnet was founded in 1988 by the San Diego Supercomputer Center and General Automics and is funded by the NSF.

CFA
Telecommunications

Carrier Facility Assignment - This is the location and/or assignment where the Local Exchange Carrier (LEC) will interconnect with the incumbent Telco.

CGA
PC's

Displays for personal computers have steadily improved since the days of the monochrome monitors that were used in word processors and text-based computer systems in the 1970s. In 1981, IBM introduced the Color Graphics Adapter (CGA). This display system was capable of rendering four colors, and had a maximum resolution of 320 pixels horizontally by 200 pixels vertically. While CGA was all right for simple computer games such as solitaire and checkers, it did not offer sufficient image resolution for extended sessions of word processing, desktop publishing, or sophisticated graphics applications.

CGI
Software

Common Gateway Interface; an application that takes input from the client, processes it on the server, and returns the results.

Challenge-Response
Lingo

A common authentication technique whereby an individual is prompted (the challenge) to provide some private information (the response). Most security systems that rely on smart cards are based on challenge-response. A user is given a code (the challenge) which he or she enters into the smart card. The smart card then displays a new code (the response) that the user can present to log in.

Channel
Telecommunications

1) In telecommunications in general, a channel is a separate path through which signals can flow.

2) In the public switched telephone network (public switched telephone network), a channel is one of multiple transmission paths within a single link between network points. For example, the commonly used (in North America) T-carrier system line service provides 24 64 Kbps channels for digital data transmission.

3) In radio and television, a channel is a separate incoming signal or program source that a user can select.

4) In optical fiber transmission using dense wavelength-division multiplexing (dense wavelength division multiplexing), a channel is a separate wavelength of light within a combined, multiplexed light stream.

5) On the World Wide Web, a channel is a preselected Web site that can automatically send updated information for immediate display or viewing on request.

6) In computer and Internet marketing, a channel is a "middleman" between a product creator and the marketplace. Value-added resellers (value-added reseller and retail store chains are examples of channels in this context.

7) Using Internet Relay Chat, a channel is a specific chat group.

8) In IBM mainframe systems, a channel is a high bandwidth connection between a processor and other processors, workstations, printers, and storage devices within a relatively close proximity. It's also called a local connection as opposed to a remote (or telecommunication) connection.

Channel Bank
Telecommunications

A multiplexing device which is used to multiplex or demultiplex several channels on a frequency division, or time division basis.

Channelized E1
Networking

Access link operating at 2.048 Mbps that is subdivided into 30 B-channels and 1 D-channel, Supports DDR, Frame Relay, and X.25. Compare with channelized T1.

Channelized T1
Networking

Access link operating at 1.544 Mbps that is subdivided into 24 channels (23 B-channels and 1D-channel) of 64 Kbps each. The individual channels or groups of channels connect to different destinations. Supports DDR, Frame Relay, and X.25. Also referred to as fractional T1. Compare with channelized E1.

CHAP
Networking

Short for Challenge Handshake Authentication Protocol, a type of authentication in which the authentication agent (typically a network server) sends the client program a key to be used to encrypt the username and password. This enables the username and password to be transmitted in an encrypted form to protect them against eavesdroppers. Contrast with PAP.

Character
Lingo

1. A symbol such as a letter, number or punctuation mark that can be arranged to represent higher units of meaning, such as words and sentences. 2. The group of bits that represents such a symbol.

Charles Babbage
People

Charles Babbage is known to some as the "Father of Computing" for his contributionsto the basic design of the computer through his Analytical machine. His previous Difference Engine was a special purpose device intended for the production of tables.

While he did produce prototypes of portions of the Difference Engine, it was left to Georg and Edvard Schuetz to construct the first working devices to the same design which were successful in limited applications.

Significant Events in His Life: 1791: Born; 1810: Entered Trinity College, Cambridge; 1814: graduated Peterhouse; 1817 received MA from Cambridge; 1820: founded the Analytical Society with Herschel and Peacock; 1823: started work on the Difference Engine through funding from the British Government; 1827: published a table of logarithms from 1 to 108000; 1828: appointed to the Lucasian Chair of Mathematics at Cambridge (never presented a lecture); 1831: founded the British Association for the Advancement of Science; 1832: published "Economy of Manufactures and Machinery"; 1833: began work on the Analytical Engine; 1834: founded the Statistical Society of London; 1864: published Passages from the Life of a Philosopher; 1871: Died.

Chat Script
Networking

String of text that defines the login "conversation" that occurs between two systems. Consist of expect-send pairs that define the string that the local system expects to receive from the remote system and what the local system should send as a reply.

Cheapernet
Lingo

Industry term used to refer to the IEEE 802.3 10Base2 standard or the cable specified in that standard. Compare with Thinnet. See also 10Base2, Ethernet, and IEEE 802.3.

Checksum
Concept

The result of a mathematical operation that uses the binary representation of a group of data as its basis, usually to check the integrity of the data.

Chip
Hardware

A small piece of semiconducting material (usually silicon) on which an integrated circuit is embedded. A typical chip is less than ¼-square inches and can contain millions of electronic components (transistors). Computers consist of many chips placed on electronic boards called printed circuit boards.

There are different types of chips. For example, CPU chips (also called microprocessors) contain an entire processing unit, whereas memory chips contain blank memory.

Chips come in a variety of packages. The three most common are:

In addition to these types of chips, there are also single in-line memory modules (SIMMs), which consist of up to nine chips packaged as a single unit.

Choke Packet
Networking

Packet sent to a transmitter to tell it that congestion exists and that it should reduce its sending rate.

CICNet
Organizations

Regional network that connects academic, reserach, nonprofit, and commercial organizations in the Midwestern United States. Founded in 1988, CICNet was a part of the NSF NET and was funded by the NSF until the NSFNET dissolved in 1995. See also NSFNET.

CIDR
Protocol

Short for Classless Inter-Domain Routing, a new IP addressing scheme that replaces the older system based on classes A, B, and C. With CIDR, a single IP address can be used to designate many unique IP addresses. A CIDR IP address looks like a normal IP address except that it ends with a slash followed by a number, called the IP prefix. For example: 172.200.0.0/16 The IP prefix specifies how many addresses are covered by the CIDR address, with lower numbers covering more addresses. An IP prefix of /12, for example, can be used to address 4,096 former Class C addresses. CIDR addresses reduce the size of routing tables and make more IP addresses available within organizations.

CIR
Networking

Short for committed information rate, a specified amount of guaranteed bandwidth (measured in bits per second) on a Frame Relay service. Typically, when purchasing a Frame Relay service, a company can specify the CIR level they wish. The Frame Relay network vendor guarantees that frames not exceeding this level will be delivered. It's possible that additional traffic may also be delivered, but it's not guaranteed. Some Frame Relay vendors offer inexpensive services with a CIR equal to zero. This essentially means that the network will deliver as many frames as it can, but it doesn't guarantee any bandwidth level.

Circuit
Telecommunications

A telecommunication circuit is any line, conductor, or other conduit by which information is transmitted.

A dedicated circuit, private circuit, or leased line is a line that is dedicated to only one use. Originally, this was analog, and was often used by radio stations as a studio/transmitter link (STL) or remote pickup unit (RPU) for their audio, sometimes as a backup to other means. Later lines were digital, and used for private corporate data networks.

The opposite of a dedicated circuit is a switched circuit, which can be connected to different paths. A POTS or ISDN telephone line is a switched circuit, because it can connect to any other telephone number.

On digital lines, a virtual circuit can be created to serve either purpose, while sharing a single physical circuit.

Circuit Group
Networking

Grouping of associated serial lines that link two bridges. If one of the serial links in a circuit group is in the spanning tree for a network, any of the serial links in the circuit group can be used for load balancing. This load-balancing strategy avoids data ordering problems by assigning each destination address to a particular serial link.

Circuit Noise Level
Telecommunications

The ratio of the circuit noise to a nominal reference point; this ratio is either expressed in decibels (above the reference noise, dbrn) or in adjusted decibels (dba, which reflects a specified adjustment due to external interference).

Circuit Switching
Telecommunications

A switching system that completes a dedicated transmission path from sender to receiver at the time of transmission. The connecting of two or more channels to create a through circuit between two points.

Classic IP Over ATM
Networking

Specification for running IP over ATM in a manner that takes full advantage of the features of ATM. Defined in RFC 1577. Sometimes called CIA.

CLAW
Protocol

Common Link Access for Workstations. Data link layer protocol used by channel-attached RISC System/6000 series systems and by IBM 3172 devices running TCP/IP off-load. CLAW improves efficiency of channel use and allows the CIP to provide the functionality of a 3172 in TCP/IP environments and support direct channel attachment. The output from TCP/IP mainframe processing is a series of IP datagrams that the router can switch without modifications.

CLEC
Hardware

(pronounced see-lek) A Competitive Local Exchange Carrier is a telephone company that competes with an Incumbent Local Exchange Carrier (ILEC) such as a Regional Bell Operating Company (RBOC), GTE, ALLNET, etc. With the passage of the Telecommunications Act of 1996, there has been an explosion in the number of CLECs. The Act allows companies with CLEC status to use ILEC infrastructure in two ways: 1) Access to UNEs Important to CLEC telecommunications networking is the availability of unbundled network elements or UNEs (through a collocation arrangement). UNEs are defined by the Act as any "facility or equipment used in the provision of a telecommunications service," as well as "features, functions, and capabilities that are provided by means of such facility or equipment." For CLECs the most important UNE available to them is the local loop, which connects the ILEC switches to the ILEC's present customers. With the local loop, CLECs will be able to connect their switches with the ILEC's switches, thus giving them access to ILEC customers. 2) Resale Another option open to CLECs is the resale strategy. The Act states that any telecommunications services ILECs offer at retail, must be offered to CLECs at a wholesale discount. This saves the CLEC from having to invest in switches, fiber optic transmission facilities, or collocation arrangements. In any case, a CLEC may decide on one or the other or even both. So, you can see why obtaining CLEC status is very beneficial, especially for ISPs, who may easily get access to the copper loops and other switching elements necessary to provide xDSL services. Recently courts, in response to the growth of cable Internet access, have also required cable companies to follow the same guidelines as ILECs. Applying for CLEC status is a very tedious and complex process that involves a Regulatory Attorney or Consultant, the State Public Utilities Commission, and about 50 other steps. But remember, it will be worth it, and now is a good time, because the courts continually are trying to force ILEC costs to CLECs down and are making access to UNEs easier in the name of fair competition. So, get in before regulators begin to re-regulate the other way.

Client
Software

A program (or software) used to interact with a Server. A Web browser is a specific kind of client.

Client/Server Architecture
Networking

A network architecture in which each computer or process on the network is either a client or a server. Servers are powerful computers or processes dedicated to managing disk drives (file servers), printers (print servers), or network traffic (network servers ). Clients are PCs or workstations on which users run applications. Clients rely on servers for resources, such as files, devices, and even processing power. Another type of network architecture is known as a peer-to-peer architecture because each node has equivalent responsibilities. Both client/server and peer-to-peer architectures are widely used, and each has unique advantages and disadvantages. Client-server architectures are sometimes called two-tier architectures.

CLNP
Protocol

Connectionless Network Protocol. OSI network layer protocol that does not require a circuit to be established before data is transmitted. See also CLNS.

CLNS
Networking

Connectionless Network Service. OSI network layer service that does not require a circuit to be established before data is transmitted. CLNS routes messages to their destinations independently of any other messages. See also CLNP.

Clock
Hardware

1. A component in a computer that provides a timing pulse for other components. 2. The timing pulse of a network transmission.

Clone
Lingo

A computer, software product, or device that functions exactly like another, better-known product. In practice, the term refers to any PC not produced by one of the leading name-brand manufacturers, such as IBM and Compaq.

Cloud
Lingo

In telecommunications, a cloud is the unpredictable part of any network through which data passes between two end points. Possibly the term originated from the clouds used in blackboard drawings or more formal illustrations to describe the nonspecifiable or uninteresting part of a network. Clouds exist because between any two points in a packet-switched network, the physical path on which a packet travels can vary from one packet to the next and, in a circuit-switched network, the specific circuit that is set up can vary from one connection to the next.

CLP
Lingo

Cell loss priority. Field in the ATM cell header that determines the probability of a cell being dropped if the network becomes congested. Cell with CLP = 0 are insured traffic, which is unlikely to be dropped. Cells with CLP = 1 are best-effort traffic, which might be dropped in congested conditions in order to free up resources to handle insured traffic.

Cluster controller
Networking

1. Generally, an intelligent device that provides the connections for a cluster of terminals to be data link. 2. In SNA, a programmable device that controls the input/output operations of attached devices. Typically, an IBM 3174 or 3274 device.

CMI
Lingo

Coded mark inversion. ITU-T line coding technique specified for STS-3c transmissions. Also used in DS-1 systems.

CMIP
Protocol

Common Management Information Protocol.

CMIS
Networking

Common Management Information Services. OSI network management service interface created and standardized by ISO for the monitoring and control of heterogeneous networks. See also CMIP.

CMNS
Networking

Connection-Mode Network Service. Extends local X.25 switching to a variety of media (Ethernet, FDDI, Token Ring).

CMT
Networking

Connection management. FDDI process that handles the transition of the ring through its various states (off, active, connect, and so on), as defined by the ANSI X3T9.5 specification.

CO
Telecommunications

In telephone communication in the United States, a central office (CO) is an office in a locality to which subscriber home and business lines are connected on what is called a local loop. The central office has switching equipment that can switch calls locally or to long-distance carrier phone offices. In other countries, the term public exchange is used.

Coax
Telecommunications

A style of cable that sends the main signal through the single wire that goes through the middle and uses the shielding as the ground signal.

CODEC
Software

  1. In communications engineering, the term codec is used in reference to integrated circuits, or chip that perform data conversion. In this context, the term is an acronym for "coder/decoder." This type of codec combines analog-to-digital conversion and digital-to-analog conversion functions in a single chip. In personal and business computing applications, the most common use for such a device is in a modem.

  2. The term codec is also an acronym that stands for "compression/decompression." A codec is an algorithm, or specialized computer program, that reduces the number of bytes consumed by large files and programs.

    In order to minimize the amount of storage space required for a complicated file, such as a video, compression is used. Compression works by eliminating redundancies in data. Compression can be done for any kind of file, including text, programs, images, audio, video, and virtual reality (VR). Compression can reduce the size of a file by a factor of 100 or more in some cases. For example, a 15-megabyte video might be reduced to 150 kilobytes. The uncompressed file would be far too large to download from the Web in a reasonable length of time, but the compressed file could usually be downloaded in a few seconds. For viewing, a decompression algorithm, which "undoes" the compression, would have to be used.

ColdFusion
Software

A product created by Allaire Corporation of Cambridge, Mass. that includes a server and a development toolset designed to integrate databases and Web pages. With Cold Fusion, a user could enter a zip code on a Web page, and the server would query a database for information on the nearest movie theaters and present the results in HTML form. Cold Fusion Web pages include tags written in Cold Fusion Markup Language (CFML) that simplify integration with databases and avoid the use of more complex languages like C++ to create translating programs. See application server.

Collision
Hardware

In an Ethernet network, a collision is the result of two devices on the same Ethernet network attempting to transmit data at exactly the same time. The network detects the "collision" of the two transmitted packets and discards them both. Collisions are a natural occurrence on Ethernets. Ethernet uses Carrier Sense Multiple Access/ Collision Detect (CSMA/CD) as its method of allowing devices to "take turns" using the signal carrier line. When a device wants to transmit, it checks the signal level of the line to determine whether someone else is already using it. If it is already in use, the device waits and retries, perhaps in a few seconds. If it isn't in use, the device transmits. However, two devices can transmit at the same time in which case a collision occurs and both devices detect it. Each device then waits a random amount of time and retries until successful in getting the transmission sent.

Collision Avoidance
Networking

A Media Access Control (MAC) method in which any node may take control of the network after taking certain steps to insure that the cable is not in use or about to be used by another node.

Collision Detection
Networking

In networks, the process by which a node determines that a collision has occurred. Collisions occur with most networks, so a protocol is required to recover from such events. Ethernet uses CSMA/CD as its collision detection and recovery system.

Collision Domain
Networking

In Ethernet, the network area within which frames that have collided are propagated. Repeaters and hubs propagate collisions; LAN switches, bridges and routers do not. See also collision.

Colo
Lingo

Colocation (sometimes spelled "co-location" or "collocation") is the provision of space for a customer's telecommunications equipment on the service provider's premises. For example, a Web site owner could place the site's own computer server on the premises of the Internet service provider (Internet service provider). Or an ISP could place its network router on the premises of the company offering switching services with other ISPs. The alternative to colocation is to have the equipment and the demarc located at the customer's premises. Colocation is sometimes provided by companies that specialize in Web site hosting.

Commerce Server
Software

Web software that runs some of the main functions of an online storefront such as product display, online ordering, and inventory management. The software works in conjunction with online payment systems to process payments.

Common Carrier
Telecommunications

Licensed, private utility company that supplies communication services to the public at regulated prices.

Communication
Networking

Transmission of information.

Communications Line
Networking

The physical link (such as wire or a telephone circuit) that connects one or more devices to one or more other devices.

Community
Networking

In SNMP, a logical group of managed devices and NMSs in the same administrative domain.

Community String
Networking

Text string that acts as a password and is used to authenticate messages sent between a management station and a router containing a SNMP agent. The community string is sent in every packet between the manager and the agent.

Compiler
Software

A program that translates source code into object code. The compiler derives its name from the way it works, looking at the entire piece of source code and collecting and reorganizing the instructions. Thus, a compiler differs from an interpreter, which analyzes and executes each line of source code in succession, without looking at the entire program. The advantage of interpreters is that they can execute a program immediately. Compilers require some time before an executable program emerges. However, programs produced by compilers run much faster than the same programs executed by an interpreter.

Every high-level programming language (except strictly interpretive languages) comes with a compiler. In effect, the compiler is the language, because it defines which instructions are acceptable.

Because compilers translate source code into object code, which is unique for each type of computer, many compilers are available for the same language. For example, there is a FORTRAN compiler for PCs and another for Apple Macintosh computers. In addition, the compiler industry is quite competitive, so there are actually many compilers for each language on each type of computer. More than a dozen companies develop and sell C compilers for the PC.

Component
Networking

An indivisible unit of functionality, usually embodied in hardware.

Compress
Lingo

Store data in such a way that the file size is reduced.

Configuration
Software

The way a system is set up, or the assortment of components that make up the system. Configuration can refer to either hardware or software, or the combination of both. For instance, a typical configuration for a PC consists of 32MB (megabytes) main memory, a floppy drive, a hard disk, a modem, a CD-ROM drive, a VGA monitor, and the Windows operating system. Many software products require that the computer have a certain minimum configuration. For example, the software might require a graphics display monitor and a video adapter, a particular microprocessor, and a minimum amount of main memory. When you install a new device or program, you sometimes need to configure it, which means to set various switches and jumpers (for hardware) and to define values of parameters (for software). For example, the device or program may need to know what type of video adapter you have and what type of printer is connected to the computer. Thanks to new technologies, such as Plug-and-Play, much of this configuration is performed automatically.

Congestion
Networking

Traffic in excess of network capacity.

Connection
Telecommunications

A path between devices that allows the transmission of speech or data signals. An electrical continuity of circuit between two wires or two units, in a peice piece of apparatus.

Connection-Oriented
Networking

In data networks, a type of computer relationship in which the network equipment constructs a circuit between the two devices for the duration of their relationship. Once the circuit is established, the devices pass information back and forth through the circuit without regard to their physical addresses. The circuit may be physical or virtual.

Connectionless
Networking

Term used to describe data transfer without the existence of a virtual circuit. Compare with connection-oriented. See also virtual circuit.

Connectivity
Networking

A term referring to the ability of a device to trade data and share resources with other devices of a similar and dissimilar type through electronic means including serial and parallel connections, networking and telecommunications.

Connector
Networking

A device that establishes a physical connection between one conductor or circuit and another.

CONP
Protocol

Connection-Oriented Network Protocol, OSI protocol providing connection-oriented operation to upper-layer protocols.

Console
Networking

In SNMP (Simple Network Management Protocol), a software program that has the capability of interacting with an agent, including examining or changing the values of the data objects in the agent's Management Information Base (MIB).

Content
Lingo

The graphics, video, sound and text that makes up a web page is usually referred to as the content.

Contention
Networking

A network access method where all the devices on the network have equal changes of gaining control of the network at any time. Includes Avoidance (CSMA/CA) access methods.

Control Panel
Lingo

All users have access to a Web-based Control Panel that allows you to set mail forwarding options, enable/disable anonymous FTP access, view your statistics, change your password and more. It also allows access to other features, such as an HTML Form Generator, Web-based HTML editor and Perl script checker. Users may also update account contact information at anytime without having to contact customer support.

Convergence
Networking

The speed and ability of a group of internetworking devices running a specific routing protocol to agree on the topology of an internetwork after a change in that topology.

Cookie
Lingo

A cookie is a piece of information sent to a browser by a Web Server. The browser then returns that information to the Web server. This is how some Web pages "remember" your previous visits; for example, an E-Commerce site might use a cookie to remember which items you've placed in your online shopping cart. Cookies can also store user preference information, log-in data, etc.

Core Gateway
Networking

The primary routers in the Internet.

Core Router
Networking

In a packet-switched star topology, a router that is part of the backbone and that serves as the single pipe through which all traffic from peripheral networks must pass on its way to other peripheral networks.

COS
Lingo

1. Class of service. Indication of how an upper-layer protocol requires that a lower-layer protocol treat its messages. In SNA subarea routing, COS definitions are used by subarea nodes to determine the optimal route to establish to given session. A COS definition comprises a virtual route number and a transmission priority field. Also called TOS (type of service). 2. Corporation for Open Systems. Organization that promulgates the use of OSI protocols through conformance testing, certification, and related activities.

COSINE
Concept

Cooperation for Open Systems Interconnection Networking in Europe. European project financed by the European Community (EC) to build a communication network between scientific and industrial entities in Europe. The project ended in 1994.

Cost
Networking

Arbitrary value, typically based on hop count, media bandwidth, or other measures, that is assigned by a network administrator and used to compare various paths through an internetwork environment. Cost values are used by routing protocols to determine the most favorable path to a particular destination: the lower the cost, the better the path. Sometimes called path cost. See also routing metric.

Count to Infinity
Concept

Problem that can occur in routing algorithms that are slow to converge, in which routers continuously increment the hop count to particular networks. Typically, some arbitrary hop-count limit is imposed to prevent this problem.

Courseware
Lingo

Software designed to be used in an educational program.

CPE
Telecommunications

Customer Premise Equipment All telecommunications terminal equipment located on the customer's premises, encompasses everything from black telephones to the most advanced data terminals and PBXs.

CPU
Hardware

Central Processing Unit. The main processor in the computer's configuration that handles processing tasks or directs auxiliary processors (coprocessors) to perform them.

CPU bound
Networking

A computing activity or network interaction whose speed is limited by the speed at which the CPU can perform the necessary computing tasks.

Crash
Networking

An abrupt termination or computing activity caused by an error. In many instances, the computer becomes completely unusable and must be restarted before activity can resume.

CRC
Networking

Cyclic Redundancy Check. A method of insuring data integrity where a calculation is performed using the binary representation of the data itself as the basis of the calculation. The CRC is the numerical result of this calculation and is held separately from the data. The integrity of the data is checked by calculating a new CRC. If the two CRC's match, then there is a high degree of confidence that the data has not changed.

CREN
Organizations

Corporation for Research and Educational Networking. The result of a merger of BITNET and CSNET. CREN is devoted to providing Internet connectivity to its members, which include the alumni, students, faculty, and other affiliates of participating educational and research institutions, via BITNET III. See also BITNET, BITNET III, and CSNET.

Crosstalk
Networking

In electronic signaling, an error condition caused when the signal from one circuit causes a disturbance to the signal of the nearby circuit..

CSLIP
Protocol

Compressed Serial Link Internet Protocol. Extension of SLIP that, when appropriate, allows just header information to be sent across a SLIP connection, reducing overhead and increasing packet throughput on SLIP lines. See also SLIP.

CSMA/CD
Networking

CSMA/CD (Carrier Sense Multiple Access/Collision Detect) is the protocol for carrier transmission access in Ethernet networks. On Ethernet, any device can try to send a frame at any time. Each device senses whether the line is idle and therefore available to be used. If it is, the device begins to transmit its first frame. If another device has tried to send at the same time, a collision is said to occur and the frames are discarded. Each device then waits a random amount of time and retries until successful in getting its transmission sent. CSMA/CD is specified in the IEEE 802.3 standard.

CSNET
Organizations

Computer Science Network. Large internetwork consisting primarily of universities, research institutions, and commercial concerns. CSNET merged with BITNET to form CREN.

CSU
Lingo

Channel service unit. Digital interface device that connects end-user equipment to the local digital telephone loop. Often referred to together with DSU, as CSU/DSU. See also DSU.

CSU/DSU
Telecommunications

A CSU/DSU manages digital transmission, monitors signals for problems, and responds to Central Office commands. It performs many of the functions that modems do, but it does not have to convert digital signals to/from analog, since the end device and the underlying transmission facility are both digital.

Specifically, a CSU/DSU is the device that actually transmits the data across the telephone company line with electrical pulses of +5 and -5 Volts. It also handles framing of the signal with extra bits used to group a series of pulses into a larger structure. Often, this is called ESF, or Extended Super Frame, in the case of T1 lines. The CSU/DSU can perform testing, such as loop-back tests, from either side of the line using the messaging link, and finally, the CSU/DSU either synchronizes its timing to the line or can generate timing on the circuit so that each end can communicate effectively.

CTS
Networking

1. Clear To Send. Circuit in the EIA/TIA-232 specification that is activated when DCE is ready to accept data from DTE. 2. Common transport semantic. Cornerstone of the IBM strategy to reduce the number of protocols on networks. CTS provides a single API for developers of network software and enables applications to run over APPN, OSI, or TCP/IP.

Cut-through Packet Switching
Networking

Packet switching approach that streams data through a switch so that the leading edge of a packet exits the switch at the output port before the packet finishes entering the input port. A device using cut-through packet switching reads, processes, and forwards packets as soon as the destination address is looked up, and the outgoing port determined. Also known as on-the-fly packet switching. Contrast with store and forward packet switching.

CyberCash
Organizations

CyberCash is the name of the company that developed a Web-based payment system. Their CyberCash software enables online payment services for credit cards and Internet check transactions. CyberCash works with all popular browsers.

D

D Channel
Telecommunications

1. Data channel. Full-duplex, 16-kbps (BRI) or 64-kbps (PRI) ISDN channel. Compare to B channel, E channel, and H channel. 2. In SNA, a device that connects a processor and main storage with peripherals.

DAC
Lingo

Dual-attached concentrator. FDDI or CDDI concentrator capable of attaching to both rings of an FDDI or CDDI network. It can also be dual-homed from the master ports of other FDDI or CDDi concentrators.

DACS
Telecommunications

Digital-Access Cross-Connect System. A digital switching device for routing and switching T-1 lines among multiple T-1 ports.

Daemon
Software

A daemon (pronounced DEE-muhn) is a program that runs continuously and exists for the purpose of handling periodic service requests that a computer system expects to receive. The daemon program forwards the requests to other programs (or processes) as appropriate. Each server of pages on the Web has an HTTPD or Hypertext Transfer Protocol daemon that continually waits for requests to come in from Web clients and their users.

Daemon can be confused with demon, which has a different but similar meaning. The New Hacker's Dictionary says that a daemon is a program that runs by itself directly under the operating system whereas a demon is part of a larger application program.

DAL
Lingo

Data Access Language. A data base metalanguage designed by Apple. A superset of SQL.

DARPA
Lingo

Defense Advanced Research Projects Agency. US. government agency that funded research for and experimentation with the Internet. Evolved from ARPA, and then, from 1994, back to ARPA.

DAS
Lingo

Dual attachment station. Device attached to both the primary and the secondary FDDI rings. Dual attachment provides redundancy for the FDDI ring; if the primary ring fails, the station can wrap the primary ring to the secondary ring, isolating the failure and retaining ring integrity. Also known as a Class A station.

DAT
Lingo

Digital Audio Tape. A type of storage media used for the backup of computing data.

Data
Lingo

  1. In computing, data is information that has been translated into a form that is more convenient to move or process. Relative to today's computer and transmission media, data is information converted into binary or digital form.

  2. In computer component interconnection and network communication, data is often distinguished from "control information," "control bits," and similar terms to identify the main content of a transmission unit.

  3. In telecommunications, data sometimes means digital-encoded information to distinguish it from analog-encoded information such as conventional telephone voice calls. In general, "analog" or voice transmission requires a dedicated continual connection for the duration of a related series of transmissions. Data transmission can often be sent with intermittent connections in packet that arrive in piecemeal fashion.

Data Base
Networking

A collection of data that can be selectively retrieved by a type of application knows as a Data Base Management System.

Data Communications
Telecommunications

The transfer of data between two points.

Data Flow Control Layer
Networking

Layer 5 of the SNA architectural model. This layer determines and manages interactions between session partners, particularly data flow. Corresponds to the session layer of the OSI model. See also data link control layer, path control layer, physical control l layer, presentation services layer, transaction services layer, and transmission control layer.

Data Link
Telecommunications

The communications link used for data transmission from source to destination. Furthermore, this can be a cable, or fiber optic transmitter and receiver that transmits digital data between two points.

Data Link Layer
Telecommunications

The Data-Link Layer is the protocol layer in a program that handles the moving of data in and out across a physical link in a network. The Data-Link Layer is layer 2 in the Open Systems Interconnect (OSI) model for a set of telecommunication protocols.

The Data-Link Layer contains two sublayers that are described in the IEEE-802 LAN standards:

The Data-Link Layer assures that an initial connection has been set up, divides output data into data frames, and handles the acknowledgements from a receiver that the data arrived successfully. It also ensures that incoming data has been received successfully by analyzing bit patterns at special places in the frames.

Data Link Protocol
Protocol

The protocol that controls the network signaling and receiving hardware, performing data integrity checks and formatting information according to the rules of the data link.

Data Sink
Hardware

Network equipment that accepts data transmissions.

Data Stream
Networking

All data transmitted through a communications line in a single read or write operation.

Data Transfer
Lingo

In general, any outward-bound traffic from a Web site (with the exception of email) is considered to be data transfer. Each time a Web page, image, MIDI file, etc. is loaded, data transfer is generated. Database This is any collection of data: part numbers, product codes, customer information, etc. It usually refers to data stored on a computer.

Datagram
Networking

Logical grouping of information sent as a network layer unit over a transmission medium without prior establishment of a virtual circuit. IP datagrams are the primary information units in the Internet. The terms frame, message, packet, and segment are also used to describe logical information grouping at various layers of the OSI reference model and in various technology circles.

dB
Lingo

Decibels.

DB Connector
Hardware

Database bus connector. Type of connector used to connect serial and parallel cables to a data bus. DB connector names are of the format DB-x, where x represents the number of (wires) within the connector. Each line is connected to a pin on the connector, but in many cases, not all pins are assigned a function. DB connectors are defined by various EIA/TIA standards.

DCE
Telecommunications

  1. Data communications equipment (EIA expansion).
  2. Data circuit-terminating equipment (ITU-T expansion). Devices and connections of a communications network that comprise the network end of the user-to-network interface. The DCE provides a physical connection to the network, forwards traffic, and provides a clocking signal used to synchronize data transmission between DCE and DTE devices. Modems and interface cards are examples of DCE.

DCV (Digital Crack Value)
Lingo

Gaming that is so good that you forget reality. ex. you wake up and the game control is still in your hand and your game is on pause.

DDM
Lingo

Distributed Data Management. Software in an IBM SNA environment that provides peer-to-peer communication and file sharing. One of three SNA transaction services. See also DIA and SNADS.

DDP
Protocol

Datagram Delivery Protocol. Apple Computer network layer protocol that is responsible for the socket-to-socket delivery of datagrams over an AppleTalk internetwork.

DDR
Lingo

Dial-on-demand routing. Technique whereby a Cisco router can automatically initiate and close a circuit-switched session as transmitting stations demand. The router spoofs keepalives so that end stations treat the session as active. DDR permits routing over ISDN or telephone lines using an external ISDN terminal adapter or modem.

DE
Networking

Discard eligible. See tagged traffic.

De Facto Standard

Standard that exists by nature of its widespread use. Compare with de jure standard. See also standard.

De Jure Standard

Standard that exist because of its approval by an official standards body. Compare with de facto standard. See also standard.

Deadlock
Networking

1. Unresolved contention for the use of a resource. 2. In APPN, when two elements of a process each wait for action by or a response from the other before they resume the process.

Decay
Lingo

A loss in the clarity or readability of an electronic signal caused by the interaction of the signal with its carrier and electrical environment.

Decibel
Networking

A measurement that refers to the ratio of the strength of one signal to another. Decibels are commonly used to express signal loss or the relationship of the signal strength to ambient noise.

DECnet
Networking

Group of communications products (including a protocol suite) developed and supported by Digital Equipment Corporation. DECnet/OSI (also called DECnet Phase V) is the most recent iteration and supports both OSI protocols and proprietary Digital protocols. Phase IV Prime supports inherent MAC addresses that allow DECnet nodes to coexist with systems running other that have MAC address restrictions. See also DNA.

DECnet Routing
Networking

Proprietary routing scheme introduced by Digital Equipment Corporation in DECnet Phase III. In DECnet Phase V, DECnet completed its transition to OSI routing protocols (ES-IS and IS-IS).

Decompress
Protocol

The restoration of a group of compressed files to their original size.

Decryption
Lingo

The reverse application of an encryption algorithm to encrypted data, thereby restoring that data to its original, unencrypted state. See also encryption.

Dedicated LAN
Networking

Network segment allocated to a single device. Used in LAN switched network topologies.

Dedicated Line
Telecommunications

A dedicated line is a telecommunications path between two points that is available 24 hours a day for use by a designated user (individual or company). It is not shared in common among multiple users as dial-up lines are. A dedicated line can be a physical path owned by the user or rented from a telephone company, in which case it is called a leased line. A synonym is nonswitched line (as opposed to a switched or dial-up line).

Default Route
Networking

Routing table entry that is used to direct frames for which a next hop is not explicitly listed in the routing table.

Delay
Networking

The time between the initiation of a transaction by a sender and the first response received by the sender. Also, the time required to move a packet from source to destination over a given path.

Demand Priority
Networking

Media access method used in 100VG-AnyLAN that uses a hub that can handle multiple transmission requests and can process traffic according to priority, making it useful for servicing time-sensitive traffic such as multimedia and video. Demand priority eliminates the overhead of packet collisions, collision recovery, and broadcast traffic typical in Ethernet networks. See also 100VG-AnyLAN.

Demarc
Telecommunications

A demarc, or demarcation point, is the point at which ownership, or responsibility, for a circuit changes between entities. Often a demarc is a patch panel or smartjack which the telephone company manages and from that point toward the customer's equipment (CPE), the customer is responsible for all wiring, power, and equipment.

Demodulation
Networking

Process of returning a modulated signal to its original form. Modems perform demodulation by taking an analog signal and returning it to its original (digital) form. See also modulation.

Demultiplexing
Networking

The separating of multiple input streams that have been multiplexed into a common physical signal back into multiple output streams. See also multiplexing.

Dense Wavelength Division Multiplexing (DWDM)
Telecommunications

Short for Dense Wavelength Division Multiplexing, an optical technology used to increase bandwidth over existing fiber optic backbones.

DWDM works by combining and transmitting multiple signals simultaneously at different wavelengths on the same fiber. In effect, one fiber is transformed into multiple virtual fibers. So, if you were to multiplex eight OC -48 signals into one fiber, you would increase the carrying capacity of that fiber from 2.5 Gb/s to 20 Gb/s. Currently, because of DWDM, single fibers have been able to transmit data at speeds up to 400Gb/s.

A key advantage to DWDM is that it's protocol- and bit-rate-independent. DWDM-based networks can transmit data in IP, ATM, SONET /SDH, and Ethernet, and handle bit rates between 100 Mb/s and 2.5 Gb/s. Therefore, DWDM-based networks can carry different types of traffic at different speeds over an optical channel.

From a QoS standpoint, DWDM-based networks create a lower cost way to quickly respond to customers' bandwidth demands and protocol changes.

DES
Software

Data Encryption Standard (DES) is a widely-used method of data encryption using a private (secret) key that was judged so difficult to break by the U.S. government that it was restricted for exportation to other countries. There are 72,000,000,000,000,000 (72 quadrillion) or more possible encryption keys that can be used. For each given message, the key is chosen at random from among this enormous number of keys. Like other private key cryptographic methods, both the sender and the receiver must know and use the same private key.

DES applies a 56-bit key to each 64-bit block of data. The process can run in several modes and involves 16 rounds or operations. Although this is considered "strong" encryption, many companies use "triple DES", which applies three keys in succession. This is not to say that a DES-encrypted message cannot be broken." Early in 1997, Rivest-Shamir-Adleman (RSA), owners of another encryption approach, offered a $10,000 reward for breaking a DES message. A cooperative effort on the Internet of over 14,000 computer users trying out various keys finally deciphered the message, discovering the key after running through only 18 quadrillion of the 72 quadrillion possible keys! Few messages sent today with DES encryption are likely to be subject to this kind of code-breaking effort.

DES originated at IBM in 1977 and was adopted by the U.S. Department of Defense. It is specified in the American National Standards Institute X3.92 and X3.106 standards and in the Federal FIPS 46 and 81 standards. Concerned that the encryption algorithm could be used by unfriendly governments, the U.S. government has prevented export of the encryption software. However, free versions of the software are widely available on bulletin board services and Web sites. Since there is some concern that the encryption algorithm will remain relatively unbreakable, NIST has indicated DES may not be recertified as a standard and submissions for its replacement are being accepted. The next standard will be known as the Advanced Encryption Standard (AES).

Designated Bridge
Networking

The bridge that incurs the lowest path cost when forwarding a frame from a segment to the route bridge.

Designated Router
Networking

OSPF router that generates LSAs for a multiaccess network and has other special responsibilities in running OSPF. Each multiaccess OSPF network that has at least two attached routers has a designated router that is elected by the OSPF Hello protocol. The designated router enables a reduction in the number of adjacencies required on a multiaccess network, which in turn reduces the amount or routing protocol traffic and the size of the topological database.

Desktop
Networking

In the Macintosh user interface, the background image of the Finder on which the icons for applications, directories and data files are displayed.

Destination Address
Networking

Address of a network device that is receiving data. See also source address.

Deterministic Load Distribution
Networking

Technique for distributing traffic between two bridges across a Distribution circuit group. Guarantees packet ordering between source-destination pairs and always forwards traffic for a source-destination pair on the same segment in a circuit group for a given circuit-group configuration.

Device
Hardware

See node.

Device Driver
Software

Software that acts as an intermediary between a CPU and a peripheral device. The CPU sends a command to the device driver, which translates that command into a command meaningful to the peripheral device.

DHCP
Protocol

Short for Dynamic Host Configuration Protocol, a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device's IP address can even change while it is still connected. DHCP also supports a mix of static and dynamic IP addresses. Dynamic addressing simplifies network administration because the software keeps track of IP addresses rather than requiring an administrator to manage the task. This means that a new computer can be added to a network without the hassle of manually assigning it a unique IP address. Many ISPs use dynamic IP addressing for dial-up users. DHCP client support is built into Windows 95 and NT workstation. NT 4 server includes both client and server support.

DHTML
Protocol

Dynamic HTML is a collective term for a combination of new Hypertext Markup Language (HTML) tags and options, and programming that will let you create Web pages more animated and more responsive to user interaction than previous versions of HTML. Much of dynamic HTML is specified in HTML 4.0. Simple examples of dynamic HTML pages would include (1) having the color of a text heading change when a user passes a mouse over it or (2) allowing a user to "drag and drop" an image to another place on a Web page. Dynamic HTML can allow Web documents to look and act like desktop applications or multimedia productions.

The features that constitute dynamic HTML are included in Netscape Communications' latest Web browser, Navigator 4.0 (part of Netscape's Communicator suite), and by Microsoft's browser, Internet Explorer 4.0. While HTML 4.0 is supported by both Netscape and Microsoft browsers, some additional capabilities are supported by only one of the browsers. The biggest obstacle to the use of dynamic HTML is that, since many users are still using older browsers, a Web site must create two versions of each site and serve the pages appropriate to each user's browser version.

Diagnostic
Lingo

A test or the data from a test which indicates the condition of the state of a computer or network's health.

Dial-up
Telecommunications

Dial-up pertains to a telephone connection in a system of many lines shared by many users. A dial-up connection is established and maintained for a limited time duration. The alternative is a dedicated connection, which is continuously in place. Dial-up lines are sometimes called switched lines and dedicated lines are called nonswitched lines. A dedicated line is often a leased line that is rented from a telephone company.

Differential Encoding
Networking

Digital encoding technique whereby a binary value is denoted by a signal change rather than a particular signal level.

Differential Manchester Encoding
Networking

Digital coding scheme where a mid-bit-time transition is used for clocking, and a transition at the beginning of each bit time denotes a zero. The coding scheme used by IEEE802.5 and Token Ring networks.

Digital
Telecommunications

Digital describes electronic technology that generates, stores, and processes data in terms of two states: positive and non-positive. Positive is expressed or represented by the number 1 and non-positive by the number 0. Thus, data transmitted or stored with digital technology is expressed as a string of 0's and 1's. Each of these state digits is referred to as a binary digit (and a string of bits that a computer can address individually as a group is a byte).

Prior to digital technology, electronic transmission was limited to analog technology, which conveys data as electronic signals of varying frequency or amplitude that are added to carrier waves of a given frequency. Broadcast and phone transmission has conventionally used analog technology.

Digital technology is primarily used with new physical communications media, such as satellite and fiber optic transmission. A modem is used to convert the digital information in your computer to analog signals for your phone line and to convert analog phone signals to digital information for your computer.

Digital Facility
Telecommunications

A switching or transmission facility designed for the handling of digital signals.

Digital Signal
Telecommunications

An information signal which has a limited number of states. Any item of information, whether it is in a data format or not, can be converted to a digital signal, e.g., voice and video, which are usually originated in analog (continuous signal) form, can be converted to digital signals.

Digital Signal Level
Telecommunications

One of several transmission rates in the time-division multiplex hierarchy (i.e., DS1 = 1.544 Mb/s, DS3 = 44.736 Mb/s).

Digital Signature
Software

A digital code that can be attached to an electronically transmitted message that uniquely identifies the sender. Like a written signature, the purpose of a digital signature is to guarantee that the individual sending the message really is who he or she claims to be. Digital signatures are especially important for electronic commerce and are a key component of most authentication schemes. To be effective, digital signatures must be unforgeable. There are a number of different encryption techniques to guarantee this level of security.

Digital Transmission
Telecommunications

The transmission of a digital signal between two or more points. The usual definition applies to the manner in which the transmission carrier is modified to carry the transmitted information. For example, in digital microwave systems, the radio frequency carrier is an analog signal, but its information modulation is derived from the digital signal.

Directed Search
Networking

Search request sent to a specific node known to contain a resource. A directed search is used to determine the continued existence of the resource and to obtain routing information specific to the node. See also broadcast search.

Directory Services
Networking

Services that help network devices locate service providers.

Discovery Architecture
Software

APPN software that enables a machine configured as an APPNEN to automatically fine primary and backup NNs when the machine is brought onto an APPN network.

Discovery Mode
Networking

Method by which an AppleTalk interface acquires information about an attached network from an operational node and then uses this information to configure itself. Also called dynamic configuration.

Distance Vector Routing Algorithm
Concept

Class of routing algorithms that iterate on the number of hops in a route to find a shortest-path spanning tree. Distance vector routing algorithms call for each router to send its entire routing table in each update, but only to its neighbors. Distance vector routing algorithms can be prone to routing loops, but are computationally simpler than link state routing algorithms. Also called Bellman-Ford routing algorithm. See also link state routing algorithm and SPF.

Distortion
Networking

A change in a electronic signal that occurs when different frequency components of the signal decay at different rates. In a signal made up of many frequency components (such as a square wave), the higher frequency components of a signal typically decay faster than the lower frequency components.

Distortion Delay
Networking

Problem with a communication signal resulting from nonuniform transmission speeds of the components of a signal through a transmission medium. Also called group delay.

DLC
Networking

Short for Data Link Control, the second lowest layer in the OSI Reference Model. Every network interface card (NIC) has a DLC address or DLC identifier (DLCI) that uniquely identifies the node on the network. Some network protocols, such as Ethernet and Token-Ring use the DLC addresses exclusively. Other protocols, such as TCP/IP, use a logical address at the Network Layer to identify nodes. Ultimately, however, all network addresses must be translated to DLC addresses. In TCP/IP networks, this translation is performed with the Address Resolution Protocol (ARP). For networks that conform to the IEEE 802 standards (e.g., Ethernet ), the DLC address is usually called the Media Access Control (MAC) address.

DLCI
Networking

Data-link connection identifier. Value that specifies a PVC or SVC in a Frame Relay network. In the basic Frame Relay specification, DLCIs are locally significant (connected devices might use different values to specify the same connection). In the LMI extended specification, DLCIs are globally significant (DLCIs specify individual end devices). See also LMI.

DLL
Lingo

Dynamically Linked Libraries. A component of Microsoft's OLE.

DLSw
Networking

Data-link switching. Interoperability standard, described in RFC 1434, that provides a method for forwarding SNA and NetBIOS traffic over TCP/IP networks using data link layer switching and encapsulation. DLSw uses SSP (Switch-to-Switch Protocol) instead of SRB, eliminating the major limitations of SRB, including hop-count limits, broadcast and unnecessary traffic, timeouts, lack of flow control, and lack of prioritization schemes. See also SRB, and SSP (Switch-to-Switch Protocol).

DMA
Lingo

Direct memory access. The transfer of data from a peripheral device, such as a hard disk drive, into memory without that data passing through the microprocessor. DMA transfers data into memory at high speeds with no processor overhead.

DMAC
Lingo

Destination MAC. The MAC address specified in the Destination Address field of a packet. Compare with SMAC. See also MAC address.

DNA
Lingo

Digital Network Architecture. Network architecture developed by Digital Equipment Corporation. The products that embody DNA (including communications protocols) are collectively referred to as DECnet. See also DECnet.

DNIC
Lingo

Data Network Identification Code. Part of an X.121 address. DNICs are divided into two parts: the first specifying the country in which the addressed PSN is located and the second specifying the PSN itself. See also X.121.

DNS
Networking

(1) Short for Domain Name System (or Service), an Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they're easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 198.105.232.4.

DNSIX
Lingo

Department of Defense Intelligence Information System Network Security for Information Exchange. Collection of security requirements for networking defined by the US. Defense Intelligence Agency.

DoCoMo
Organizations

DoCoMo (meaning "anywhere" in Japanese) is a NTT subsidiary and Japan's biggest mobile service provider, with over 31 million subscribers as of June, 2000. In February, 2000 NTT DoCoMo launched its i-mode service. With over 7 million subscribers, it has overtaken traditional Japanese Internet service providers to become Japan's biggest Internet access platform. DoCoMo's i-mode is the only network in the world that now allows subscribers continuous access to the Internet via mobile telephone. The service lets users send and receive e-mail, exchange photographs, do online shopping and banking, download personalized ringing melodies for their phones, and navigate among more than 7,000 specially formatted Web sites. The current i-mode data transmission speed is just 9.6Kbps, but in spring 2001 NTT DoCoMo will introduce its next-generation mobile system, based on wideband CDMA (W-CDMA), that can support speeds of 384Kbps or faster, making mobile multimedia possible.

DoD
Lingo

Department of Defense. US. government organization that is responsible for national defense. The DoD has frequently funded communication protocol development.

Domain
Lingo

In general, a domain is an area of control or a sphere of knowledge.

1) In computing and telecommunication in general, a domain is a sphere of knowledge identified by a name. Typically, the knowledge is a collection of facts about some program entities or a number of network points or addresses.

2) On the Internet, a domain consists of a set of network addresses. This domain is organized in levels. The top level identifies geographic or purpose commonality (for example, the nation that the domain covers or a category such as "commercial"). The second level identifies a unique place within the top level domain and is, in fact, equivalent to a unique address on the Internet (or Internet Protocol). Lower levels of domain may also be used.

Strictly speaking, in the Internet's domain name system, a domain is a name with which name server records are associated that describe subdomains or hosts. For example, "verio.net" could be a domain with records for "www.verio.net" and "training.verio.net".

3) In Windows NT and Windows 2000, a domain is a set of network resources (applications, printers, and so forth) for a group of users. The user need only to log in to the domain to gain access to the resources, which may be located on a number of different servers in the network.

Domain Name
Networking

A name that identifies one or more IP addresses. For example, the domain name microsoft.com represents about a doze IP addresses. Domain names are used in URLs to identify particular Web pages. For example, in the URL http://www.pcwebopedia.com/index.html, the domain name is pcwebopedia.com.

DOS
Software

The operating system of IBM-compatible personal computers.

Dot Address
Networking

Refers to the common notation for IP addresses in the form where each number n represents, in decimal, 1 byte of the 4-byte IP address. Also called dotted notation or four-part dotted notation.

Dotted Notation
Networking

See dot address.

Doubler
Telecommunications

A device which doubles the distance of certain types of circuits. HDSL (High-bit Digital Subscriber Line) is a repeaterless means of provisioning a T-1 access circuit over a standard UTP local loop. Signal attenuation issues limit the range, however, to 12,000 ft on 24 guage wire, and 9,000 ft on 26 guage wire.

Downlink Station
Networking

See ground station.

Download
Lingo

Transferring a file from a computer on the Internet to your own computer. Things you might download include software, images, email, MIDI files, etc.

Downsizing
Networking

The transfer of computing tasks previously performed by main frame or minicomputers to personal computers.

Downstream Provider
Networking

An ISP that is reselling Verio’s bandwidth. Tier 3 providers that buy connectivity from Verio are downstream providers. Conversely, we are their upstream provider.

Downtime
Networking

1. A temporary interruption in the usability of a computer system. 2. A work stoppage caused by the temporary lack of usability of a computer system.

DQDB
Lingo

Distributed Queue Dual Bus. Data link layer communication protocol, specified in the IEEE802.6 standard, designed for use in MANs. DQDB, which permits multiple systems to interconnect using two unidirectional logical buses, is an open standard that is designed for compatibility with carrier transmission standards and is aligned with emerging standards for BISDN. SIP (SMDS Interface Protocol) is based on DQDB. See also MAN.

DRAM
Hardware

Dynamic random-access memory. RAM that stores information in capacitors that must be periodically refreshed. Delays can occur because DRAMs are inaccessible to the processor when refreshing their contents. However, DRAMs are less complex and have greater capacity than SRAMs. See also SRAM.

Drive
Hardware

A data storage device.

Drop
Networking

Point on a multipoint channel where a connection to a networked device is made.

Drop Cable
Hardware

Drop Cable Generally, a cable that connects a network device (such as a computer) to a physical medium. A type of AUI. See also AUI.

DS-0
Networking

Digital signal level 0. Framing specification used in transmitting digital signals over a single channel at 64-kbps on a T1 facility. Compare with DS-1 and DS-3.

DS-1
Networking

Digital signal level 1. Framing specification used in transmitting digital signals at 1.544-Mbps on a T1 facility (in the United States) or at 2.108-Mbps on an E1 facility (in Europe). Compare with DS-0 and DS-3.

DS-1/DTI
Networking

DS-1 domestic trunk interface. Interface circuit used for DS-1 applications with 24 trunks.

DS-3
Networking

Digital signal level 3. Framing specification used for transmitting digital signals at 44.736-Mbps on a T3 facility. Compare with DS-0 and DS-1. See also E3 and T3.

DSAP
Lingo

Destination service access point. The SAP of the network node designated in the Destination field of a packet. Compare to SSAP. See also SAP (service access point).

DSLAM
Telecommunications

To interconnect multiple DSL users to a high-speed backbone network, the telephone company uses a Digital Subscriber Line Access Multiplexer (DSLAM). Typically, the DSLAM connects to an asynchronous transfer mode (ATM) network that can aggregate data transmission at gigabit data rates. At the other end of each transmission, a DSLAM demultiplexes the signals and forwards them to appropriate individual DSL connections.

DSP
Lingo

Domain specific part. The part of a CLNS address that contains an area identifier, a station identifier, and a selector byte.

DSPU
Lingo

Downstream physical unit. In SNA, a PU that is located downstream from the host.

DSR
Lingo

Data set ready. EIA/TIA-232 interface circuit that is activated when DCE is powered up and ready for use.

DSTP
Protocol

Data Space Transfer Protocol is used to index and categorize data using a XML -based catalogue. Data, no matter how it is stored (e.g. file, type of file, database, or distributed database ), has corresponding XML files, which contain UCK (Universal Correlation Key) tags that act as identification keys. Data is retrieved when a user connects to DSTP servers with a DSTP client and asks for specific information. Data is found and retrieved based on the labels contained in the UCK tags.

DSU
Hardware

Data service unit. Device used in digital transmission that adapts the physical interface on a DTE device to a transmission facility such as T1 or E1. The DSU is also responsible for functions such as signal timing. Often referred to together with CSU, as CSU/DSU. See also CSU.

DSX
Telecommunications

Digital System Cross-connect frame. A manual bay or panel to which T-1 lines and DS1 circuit packs are wired.

DSX-1
Lingo

Cross-connection point for DS-1 signals.

DTE
Hardware

Data Terminal Equipment. The X.25 term for an end node. Device at the user end of a user-network interface that serves as a data source, destination, or both. DTE connects to a data network through a DCE device (for example, a modem) and typically uses clocking signals generated by the DCE. CTE includes devices such as computers, protocol translators, and multiplexers. Compare with DCE.

DTMF
Lingo

Dual tone multifrequency. Use of two simultaneous voice-band tones for dialing (such as touch tone).

DTR
Lingo

Data terminal ready. EIA/TIA 232 circuit that is activated to let the DCE know when the DTE is ready to send and receive data.

DTS
Lingo

Distributed Time Service.

DUAL
Concept

Diffusing Update Algorithm. Convergence algorithm used in Enhanced IGRP that provides loop-free operation at every instant throughout a route computation. Allows routers involved in a topology change to synchronize at the same time, while not involving routers that are unaffected by the change. See also Enhanced IGRP.

Dual Counter-rotation Ring
Networking

Network topology in which two signal paths, whose directions are opposite one another, exist in a token-passing network. FDDI and CDDI are based on this concept.

Dual Homing
Networking

Network topology in which a device is connected to the network by way of two independent access points (points of attachment). One access point is the primary connection, and the other is a standby connection that is activated in the event of a failure of the primary connection.

Dual-homed Station
Hardware

Device attached to multiple FDDI rings to provide redundancy.

Duplex
Telecommunications

In telecommunication, duplex communication means that both ends of the communication can send and receive signal at the same time. full-duplex communication is the same thing. half-duplex is also bidirectional communication but signals can only flow in one direction at a time. Simplex communication means that communication can only flow in one direction and never flow back the other way.

DVMRP
Lingo

Distance Vector Multicast Routing Protocol. Internetwork gateway protocol, largely based on RIP, that implements a typical dense mode IP multicast scheme. DVMRP uses IGMP to exchange routing datagrams with its neighbors. See also IGMP.

DXI
Lingo

Data Exchange Interface. ATM Forum specification, described in RFC 1483, that defines how a network device such as a bridge, router, or hub can effectively act as an FEP to an ATM network by interfacing with a special DSU that performs packet segmentation and reassembly.

Dykstra's Algorithm
Concept

This algorithm was originally developed within the mathematically sphere of knowledge to solve for different puzzles what the shortest path between two points is. The mathematics behind the algorithm can become quite complex so I am only going to summarize in saying that the Dykstra Algorithm is used in OSPF (Open Shortest Path First) during the route determination phase. The algorithm makes some assumptions, including that all paths have a positive cost. It also can handle sevaral paths to the destination and effectively compare them. Of note, when speaking about OSPF, the shortest path is not necessarily the path with the least amount of hops.

More information can be found at many websites on the Internet. One of the better and easier to understand ones is available at theory.stanford.edu. It is an email conversation among several programmers, including some who are just beginning, so the explanations tend to be easier than normal for this topic.

Dynamic Address Resolution
Networking

Use of an address resolution protocol to determine and store address information on demand.

Dynamic Addressing
Networking

A system of addressing in which the computer selects it s own address without the user's intervention.

Dynamic Routing
Networking

Routing that adjusts automatically to network topology or traffic changes. Also called adaptive routing.

E

E Channel
Telecommunications

Echo channel. 64-Kbps ISDN circuit-switching control channel. The E channel was defined in the 1984 ITU-TISDN specification, but was dropped in the 1988 specification. Compare with B channel, D channel, and H channel.

E.164
Telecommunications

ITU-T recommendation for international telecommunication numbering, especially in ISDN, BISDN, and SMDS. An evolution of station telephone numbers.

E1
Networking

Wide-area digital transmission scheme used predominantly in Europe that carries data at a rate of 2.048 Mbps. E1 lines can be leased for private use from common carriers. Compare with T1. See also DS-1.

E3
Telecommunications

Wide-area digital transmission scheme, used predominantly in Europe, that carries data at a rate of 34.368 Mbps. E3 lines can be leased for private use from common carrier. Compare with T3. See also DS-3.

Early Token Release
Networking

Technique used in Token Ring networks that allows a station to release a new token onto the ring immediately after transmitting, instead of waiting for the first frame to return. This feature can increase the total bandwidth on the ring. See also Token Ring.

EARN
Organizations

European Academic Research Network. European network connecting universities and research institutes. EARN merged with RARE to form TERENA. See also RARE and TERENA.

EBCDIC
Lingo

Extended binary code decimal interchange code. Any of a number of coded character sets developed by IBM consisting of 8- bit coded characters. This character code is used by older IBM systems and telex machines. Compare with ASCII.

Echo
Networking

1. In electronic signaling, the reflection of a signal caused by a sudden change in the impedance of the carrier. 2. A network continuity test where packets are sent to a distant node that is obligated to immediately send the packets back.

Echo Channel
Networking

See E channel.

Echo Protocol
Protocol

In the AppleTalk protocol family, a protocol that allows a computer to return test packets. The purpose of Echo Protocol is t test the delivery conditions to a remote node, including reachability, reliability and round trip time.

Echo Test
Networking

A diagnostic test in which packets are sent by one node to another node, which immediately returns them to the original node. The data recorded by the echo test includes the success rate of the return as well as the time needed to complete the round trip.

Echoplex
Networking

Mode in which keyboard characters are echoed on a terminal screen upon return of a signal from the other end of the line indicating that the characters were received correctly.

ECMA
Organizations

European Computer Manufacturers Association. Group ofEuropean computer vendors who have done substantial OSI standardization work.

EDI
Lingo

Electronic Document (or Data) Interchange. The term EDI usually connotes a system where authentication and security methods guarantee the integrity and origin of the information.

EDIFACT
Lingo

Electronic Data Interchange for Administration, Commerce, and Transport. Data exchange standard administered by the United Nations to be a multi-industry EDI standard.

EEPROM
Hardware

Electrically erasable programmable read-only memory. EPROM that can be erased using electrical signals applied to specific pins. See also EPROM.

EGA
PC's

In 1984, IBM introduced the Enhanced Graphics Adapter (EGA) display. It allowed up to 16 different colors and improved the resolution to 640 pixels horizontally by 350 pixels vertically. This improved the appearance of the display and made it possible to read text more easily than with CGA. Nevertheless, EGA did not offer sufficient image resolution for high-level applications such as graphic design and desktop publishing.

EGP
Protocol

Exterior Gateway Protocol. Internet protocol for exchanging routing information between autonomous systems. Documented in RFC 904. Not to be confused with the general term exterior gateway protocol. EGP is an obsolete protocol that has been replaced by BGP. See also BGP.

EIA
Organizations

Electronic Industries Association. Group that specifies electrical transmission standards. The EIA and TIA have developed numerous well-known communications standards, including EIA/TIA-232 and EIA/TIA-449. See also TIA.

EIA-232-D
Telecommunications

(formerly RS-232-D): A serial interface standard for transmission of unbalanced signals between a variety of computer, media, and multimedia peripherals. EIA-232-D transmits at a maximum of 19.2 kbit/s for up to a distance of about 50 feet and uses a 25-pin connector.

EIGRP
Lingo

See Enhanced IGRP.

EISA
Hardware

Extended Industry-Standard Architecture. 32-bit bus interface used in PCs, PC-based servers, and some Unix workstations and servers. See also ISA.

EJB
Programming

Enterprise JavaBeans (EJB) is an architecture for setting up program component, written in the Java programming language, that run in the server parts of a computer network that uses the client/server model. Enterprise JavaBeans is built on the JavaBeans technology for distributing program components (which are called Bean, using the coffee metaphor) to client in a network. Enterprise JavaBeans offers enterprise the advantage of being able to control change at the server rather than having to update each individual computer with a client whenever a new program component is changed or added. EJB components have the advantage of being reusable in multiple applications. To deploy an EJB Bean or component, it must be part of a specific application, which is called a container.

Originated by Sun Microsystems, Enterprise JavaBeans is roughly equivalent to Microsoft's Component Object Model/Distributed Component Object Model architecture, but, like all Java-based architectures, programs can be deployed across all major operating systems, not just Windows. EJB's program components are generally known as servlet (little server programs). The application or container that runs the servlets is sometimes called an application server. A typical use of servlets is to replace Web programs that use the Common Gateway Interface (common gateway interface) and a Practical Extraction and Reporting Language script. Another general use is provide an interface between Web users and a legacy application mainframe application and its database.

In Enterprise JavaBeans, there are two types of beans: session beans and entity beans. An entity bean is described as one that, unlike a session bean, has persistence and can retain its original behavior or state.

ELAN
Networking

Emulated LAN. ATM network in which an Ethernet or Token Ring LAN is emulated using a client-server model. ELANs are composed of an LEC, an LES, a BUS, and an LECS. Multiple ELANs can exist simultaneously on a single ATM network. ELANs are defined by the LANE specification. See also BUS, LANE, LEC, LECS, and LES.

Electromagnetic Interference (EMI)
Networking

Interference in the integrity of a signal caused by radiation. An example is the radiation from a fluorescent light, which emits a broad spectrum of electromagnetic radiation, including radiation that may be harmful to a signal not protected by either shielding or adequate twisting.

Electronic Commerce
Lingo

Conducting business on-line. This includes, for example, buying and selling products with digital cash and via Electronic Data Interchange (EDI).

Electronic Mail
Networking

Widely used network application in which mail messages are transmitted electronically between end users over various types of networks using various network protocols. Often called e-mail.

Electronic Switching System
Telecommunications

A switching system in which control of the switched network resides in computer-like electronic equipment.

EMA
Networking

1. Enterprise Management Architecture. Digital Equipment Corporation network management architecture, based on the OSI network management model.

Email
Protocol

E-mail (electronic mail) is the exchange of computer-stored messages by telecommunication. (Some publications spell it email; we prefer the currently more established spelling of e-mail.) E-mail messages are usually encoded in ASCII text. However, you can also send non-text files, such as graphic images and sound files, as attachments sent in binary streams. E-mail was one of the first uses of the Internet and is still the most popular use. A large percentage of the total traffic over the Internet is e-mail. E-mail can also be exchanged between online service provider users and in networks other than the Internet, both public and private.

E-mail can be distributed to lists of people as well as to individuals. A shared distribution list can be managed by using an e-mail reflector. Some mailing lists allow you to subscribe by sending a request to the mailing list administrator. A mailing list that is administered automatically is called a list server.

E-mail is one of the protocols included with the Transport Control Protocol/Internet Protocol (TCP/IP) suite of protocols. A popular protocol for sending e-mail is Simple Mail Transfer Protocol and a popular protocol for receiving it is POP3. Both Netscape and Microsoft include an e-mail utility with their Web browsers.

Email Server
PC's

A computer used to direct messages to the appropriate place. When you send an email using your client software, it is sent to the server which then processes it and sends it to the appropriate party.

EMIF
Software

ESCON Multiple Image Facility. Mainframe I/O software function that allows one ESCON channel to be shared among multiple logical partitions on the same mainframe. See also ESCON.

EMP
Lingo

Electromagnetic pulse. Caused by lightning and other high-energy phenomena. Capable of coupling enough energy into unshielded conductors to destroy electronic devices. See also Tempest.

Emulation
Networking

A network activity in which a computer acts as if it is another kind of computer or terminal. An example is when a Macintosh user opens a remote terminal session to a VAX, it may run a program that emulates a DEC VT240 terminal.

Emulation Mode
Networking

Function of an NCP that enables it to perform activities equivalent to those performed by a transmission control unit.

EN
Lingo

End node. APPN end system that implements the PU 2.1, provides end-user services, and supports sessions between local and remote CPs. ENs are not capable of routing traffic and rely on an adjacent NN for APPN services. Compare with NN. See also CP.

Encapsulation
Networking

The process of placing one protocol inside of another. Usually implies that the encapsulated protocol was not originally intended by its designers to be carried by the encapsulating protocol.

Encapsulation Bridging
Networking

Carries Ethernet frames from one router to another across disparate media, such as serial and FDDI lines. Contrast with translational bridging.

Encoder
Networking

Device that modifies information into the required transmission format.

Encryption
Software

Encryption is the conversion of data into a form, called a ciphertext, that cannot be easily understood by unauthorized people. Decryption is the process of converting encrypted data back into its original form, so it can be understood.

The use of encryption/decryption is as old as the art of communication. In wartime, a cipher, often incorrectly called a "code," can be employed to keep the enemy from obtaining the contents of transmissions. (Technically, a code is a means of representing a signal without the intent of keeping it secret; examples are Morse code and ASCII.) Simple ciphers include the substitution of letters for numbers, the rotation of letters in the alphabet, and the "scrambling" of voice signals by inverting the sideband frequencies. More complex ciphers work according to sophisticated computer algorithm that rearrange the data bits in digital signals.

In order to easily recover the contents of an encrypted signal, the correct decryption key is required. The key is an algorithm that "undoes" the work of the encryption algorithm. Alternatively, a computer can be used in an attempt to "break" the cipher. The more complex the encryption algorithm, the more difficult it becomes to eavesdrop on the communications without access to the key.

Enhanced IGRP
Protocol

Enhanced Interior Gateway Routing Protocol. Advanced version of IGRP developed by Cisco. Provides superior convergence properties and operating efficiency, and combines the advantages of link state protocols with those of distance vector protocols. Compare with IGRP. See also IGP, OSPF, and RIP.

Eniac

The ENIAC filled an entire room. With its bank of blinking lights and 6,000 manual switches, it looked like something we'd associate with a 1950s science fiction movie. Probably because it's what spawned those movies anyway. ENIAC, the mammoth machine credited with helping to start the computer age, fueled the public's imagination about how science and computers could revolutionize the world. Little did they realize how different that early computer was from the ones that would be built a mere fifty years later.

ENIAC stands for Electronic Numerical Integrator and Computer. John Mauchly and J. Presper Eckert built the machine at the University of Pennsylvania at the behest of the U.S. military. Mauchly had attracted the army's attention when he announced in 1942 that he thought vacuum tubes could be used to speed up the mechanical calculators being used at the time. Speedy calculations was just what the military needed during World War II as they pounded out tables for their weapons arsenal -- tables that could tell a soldier just which settings a particular piece of artillery needed under a particular set of conditions. The calculations involved could take a human days to complete.

By the time ENIAC was completed in November of 1945, the war was over. But ENIAC could do what it was supposed to. Filling up a 30 X 50 foot room, ENIAC was made of 17, 468 vacuum tubes, 70,000 resistors, and 10,000 capacitors -- not to mention all those lights and switches. Most importantly, the metal giant could add 5,000 umbers in a single second. That's not much by today's standards, but it was a thousand times faster than the mechanical calculators everyone had been using.

Unlike your modern desktop, ENIAC couldn't store any programming commands in its memory. It could only do one kind of program at a time, and to change the program meant completely rewiring it. Sometimes it could take a team of scientists two days to reprogram the machine.

Enigma Machine

The Enigma cipher is most well known for it's contributions to World War II on the Germans' side. They developed what came to be known as The Enigma Machine. The machine was based on a system of three rotors that substituted cipher text letters for plain text letters. The rotors would spin in conjunction with each other, thus performing varying substitutions much like the Caeser Shift. When a letter was typed on the keyboard of the machine, it was first sent through the first rotor, which would shift the letter according to its present setting. The new letter would then pass through the second rotor, where it would be replaced by a substitution according to the present setting of the second rotor. This new letter would in turn pass through the third rotor, again being substituted accordingly. Next, this new letter would be bounced off of a reflector, and back through the three rotors in reverse order. The trick that made Enigma so powerful for its time though, was the spinning of the rotors. As the plain text letter passed through the first rotor, the first rotor would rotate one position. The other two rotors would remain stationary until the first rotor had rotated 26 times (the number of letters in the alphabet and therefore, one full rotation). Then the second rotor would rotate one position. After the second rotor had rotated 26 times (26X26 letters, since the first rotor has to rotate 26 times for every time the second rotor rotates), the third rotor would rotate one position. The cycle would continue like this for the entire length of the message. The result was a shifting shift. In other words, an s could be encoded as a b in the first part of the message, and then as an m later in the message. This principle of the shifting rotors allowed for 26 X 26 X 26 = 17576 possible positions of the rotors.

In order for the recipient to decode the message, they would need to know the initial settings of the rotors, and then put the cipher text through the machine to find the plain text. The Germans devised a system by which all of the recipients would set their rotors to predetermined settings according to the date. Each clerk had a book detailing the settings for each day. This presented a major weakness in the system though. Obviously, if anyone could figure out what the settings of the rotors were for a particular day, they would be able to decode that day's messages, assuming they had an Enigma Machine themselves.

The Enigma cipher was eventually broken by Alan Turing and a group of scientists at a later date during the war. The breaking of this code led to the Allies' ability to intercept and decode the Germans' messages, which had wonderous effects on the outcome of the war. Some people speculate that the war might have turned out much differently had the Enigma cipher not been broken.

For more detailed information about the inner workings of the Enigman Machine, go to www.attlabs.att.co.uk/andyc/enigma/about_enigma.html.

There is a web-based version of the Enigma Machine available atEnigma Applet to see how the Enigma Machine worked.

Enterprise network
Networking

A networking system that allows communication and resource sharing among all of a company's business functions and workers. In some circles, this would even include the company's business including its suppliers and distributors.

Entity
Hardware

A hardware (or firmware) device or software process capable of initiating or responding to communication. Entities typically possess a unique address.

Entropy
Concept

1. A measure of the disorder of a system. 2. The thermodynamic tendency of a system to reduce its overall energy state by increasing its disorder. Theoretically, an equilibrium is reached where the energy reduction that can be gained by a further increase in entropy is offset by the energy necessary to contain that increase.

EOT
Lingo

End of Transmission. Generally, a character that signifies the end of a logical group of characters or bits.

EPROM
Hardware

Erasable programmable read-only memory. Nonvolatile memory chips that are programmed after they are manufactured and, if necessary, can be erased by some means and reprogrammed. Compare with EEPROM and PROM.

Equalization
Networking

Technique used to compensate for communications channel distortions.

Error
Telecommunications

A discrepancy between two different states of information which are intended to be identical.

Error checking
Networking

In data transmission, an action where the integrity of data is verified.

Error Control
Networking

Technique for detecting and correcting errors in data transmissions.

Error Rate
Telecommunications

A measure of the ratio of incorrectly received data to the information which are intended to be identical. For example, received versus sent, measured versus true.

Error-correcting Code
Programming

Code having sufficient intelligence and incorporating sufficient signaling information to enable the detection and correction of many errors at the receiver.

Error-detecting Code
Programming

Code that can detect transmission errors through analysis of received data based on the adherence of the data to appropriate structural guidelines.

ES
Lingo

1. End system. Generally, an end-user device on a network. 2. End system. Nonrouting host or node in an OSI network.

ES-IS
Lingo

End System-to Intermediate System. OSI protocol that defines how end systems (hosts) announce themselves to intermediate systems (routers). See also IS-IS.

ESCON
Lingo

Enterprise System Connection. IBM channel architecture that specifies a pair of fiber-optic cables, with either LEDs or lasers as transmitters and a signaling rate of 200 Mbps.

ESCON Channel
Lingo

IBM channel for attaching mainframes to peripherals such as storage devices, backup units, and network interfaces. This channel incorporates fiber channel technology. The ESCON channel replaces the bus and tag channel. Compare with parallel channel. See also bus and tag channel.

ESD
Lingo

Electrostatic discharge. Discharge of stored static electricity that can damage electronic equipment and impair electrical circuitry, resulting in complete or intermittent failures.

ESF
Telecommunications

Extended Superframe Format. A newer T-1 framing standard used in Wide Area Networks (WANs). With this format 24 frames of 192 bits each are grouped together with the 193rd bit providing timing and other functions. In this grouping, the 8,000 bps frame is redefined as follows :

ESnet
Organizations

Energy Sciences Network. Data communications network managed and funded by the U.S. Department of Energy Office of Energy Research (DOE/OER). Interconnects the DOE to educational institutions and other research facilities.

Ethernet
Networking

A local-area network (LAN) protocol developed by Xerox Corporation in cooperation with DEC and Intel in 1976. Ethernet uses a bus or star topology and supports data transfer rates of 10 Mbps. The Ethernet specification served as the basis for the IEEE 802.3 standard, which specifies the physical and lower software layers. Ethernet uses the CSMA/CD access method to handle simultaneous demands. It is one of the most widely implemented LAN standards. A newer version of Ethernet, called 100Base-T (or Fast Ethernet), supports data transfer rates of 100 Mbps. And the newest version, Gigabit Ethernet supports data rates of 1 gigabit (1,000 megabits) per second.

EtherTalk
Networking

1. EtherTalk Link Access Protocol (ELAP), the protocol that places AppleTalk's DDP formatted packets in Ethernet frames. 2. The implementation of AppleTalk using Ethernet as a delivery system. In AppleTalk Phase 1, Ethernet V.2 is used; in Phase 2, 802.3 is used.

ETSI
Organizations

European Telecommunication Standards Institute. Organization created by the European PTTs and the European Community (EC) to propose telecommunications standards for Europe.

EU
Telecommunications

End User. Customers who use (rather than provide) telecommunications services.

EULA
Lingo

Short for End-User License Agreement, the type of license used for most software.

EUnet
Organizations

European Internet. European commercial Internet service provider. EUnet is designed to provide electronic mail, news and other Internet services to European markets.

Event
Networking

Network message indicating operational irregularities in physical elements of a network or a response to the occurrence of a significant task, typically the completion of a request for information. See also alarm and traps.

Excess Rate
Networking

Traffic in excess of the insured rate for a given connection. Specifically, the excess rate equals the maximum rate minus the insured rate. Excess traffic is delivered only if network resources are available and can be discarded during periods of congestion. Compare with insured rate and maximum rate.

EXEC
Software

The interactive command process of the Cisco IOS software.

Expansion
Concept

The process of running a compressed data set through an algorithm that restores the data set to its original size. Compare with companding and compression.

Expedited Delivery
Networking

Option set by a specific protocol layer telling other protocol layers, or the same protocol layer in another device, to handle specific data more rapidly.

Explicit Route
Networking

In SNA, a route from a source subarea to a destination subarea, as specified by a list of subarea nodes and transmission groups that connect the two.

Explorer Frame
Networking

Frame sent out by a networked device in a SRB environment to determine the optimal route to another networked device.

Explorer Packet
Networking

Generated by an end station trying to find its way through a SRB network. Gathers a hop-by-hop description of a path through the network by being marked (updated) by each bridge that it traverses, thereby creating a complete topological map. See also all-routes explorer packet, local explorer packet, and spanning explorer packet.

Extension
Software

A system software addition to the Macintosh OS that extends it functionality.

exterior gateway protocol
Protocol

Any internetwork protocol used to exchange routing information between autonomous systems. Not to be confused with Exterior Gateway Protocol EGP), which is a particular instance of an exterior gateway protocol.

Exterior router
Networking

Router connected to an AURP tunnel, responsible for the encapsulation and deencapsulation of AppleTalk packets in a foreign protocol header (for example, IP). See also AURP and AURP tunnel.

External command
PC's

A MS-DOS command that is not included in command.com. External commands are commonly external either because they require large requirements and/or are not commonly used commands. Many of the external commands are located in the Windowssystem32 or Winntsystem32 directories. If you need to locate the external file in order to delete it, rename it or replace it, you can also find the file through MS-DOS.

Extranet
Networking

An extranet is a private network, built for specific users (e.g., business clients) who don't have access to an intranet.

F

Facilities
Telecommunications

A fancy telco word for "things." It can mean anything and everything. Could be the equipment and services that makes up a telecom system. It could be anywhere you choose to put telecom things.

Facilities Network
Telecommunications

The aggregate of transmission systems, switching systems, and station equipment, it supports a large number of traffic networks.

Facility
Telecommunications

Telecom industry term for a phone or data line.

Failure Domain
Networking

Area in which a failure has occurred in a Token Ring, defined by the information contained in a beacon. When a station detects a serious problem with the network (such as a cable break), it sends a beacon frame that includes the station reporting the failure, its NAUN, and everything in between. Beaconing in turn intitiates a process called autoreconfiguration. See also autoreconfiguration, beacon, and NAUN.

Fan-out Unit
Hardware

Device that allows multiple devices on a network to communicate using a single network attachment.

FAQ
Lingo

Frequently Asked Questions: A compilation of answers to the most common questions on a particular subject.

Fast Ethernet
Networking

A 100 MB network using 4 twisted pairs.

Fast Switching
Networking

Cisco feature whereby a route cache is used to expedite packet switching through a router. Contrast with slow switching.

FAT
PC's

A file allocation table (FAT) is a table that an operating system maintains on a hard disk that provides a map of the cluster (the basic unit of logical storage on a hard disk) that a file has been stored in. When you write a new file to a hard disk, the file is stored in one or more clusters that are not necessarily next to each other; they may be rather widely scattered over the disk. A typical cluster size is 2,048 byte, 4,096 bytes, or 8,192 bytes. The operating system creates a FAT entry for the new file that records where each cluster is located and their sequential order. When you read a file, the operating system reassembles the file from clusters and places it as an entire file where you want to read it. For example, if this is a long Web page, it may very well be stored on more than one cluster on your hard disk.

Until Windows 95 OSR2 (OEM Release 2), DOS and Windows file allocation table entries were 16 bits in length, limiting hard disk size to 128 megabyte, assuming a 2,048 size cluster. Up to 512 megabyte support is possible assuming a cluster size of 8,192 but at the cost of using clusters inefficiently. DOS 5.0 and later versions provide for support of hard disks up to two gigabyte with the 16-bit FAT entry limit by supporting separate FATs for up to four partitions.

Fault Management
Networking

One of five categories of network management defined by ISO for management of OSI networks. Fault management attempts to ensure that network faults are detected and controlled. See also accounting management, configuration management, performance, and security management.

FCC
Organizations

Federal Communications Commission. The United States government agency that regulates electronic communications and the domestic manufacture and importation of communication equipment.

FDDI
Networking

Abbreviation of Fiber Distributed Data Interface, a set of ANSI protocols for sending digital data over fiber optic cable. FDDI networks are token-passing networks, and support data rates of up to 100 Mbps (100 million bits) per second. FDDI networks are typically used as backbones for wide-area networks. An extension to FDDI, called FDDI-2, supports the transmission of voice and video information as well as data. Another variation of FDDI, called FDDI Full Duplex Technology (FFDT) uses the same network infrastructure but can potentially support data rates up to 200 Mbps.

FDDI II
Networking

FDDI II ANSI standard that enhances FDDI. FDDI II provides isochronous transmission for connectionless data circuits and connection-oriented voice and video circuits. Compare with FDDI.

FDL
Telecommunications

Facilities Data Link. An ESF term. ESF extends the superframe from 12 to 24 consecutive and repetitive frames of information. The framing overhead of 8 kbps in previous T-1 versions was used exclusively for purposes of synchronization. ESF takes advantage of newer channel banks and multiplexors which can accomplish this process of synchronization using only 2 kbps of the framing bit of only every fourth frame being used for this purpose. As a result, 6kbps is freed up for other purposes. This allows 2kbps to be used for continuous error checking using a CRC-6 (Cyclic Redundancy Check-6), and 4kbps to be used for FDL which supports the communication of various network information in the form of an in-service monitoring and diagnostics.

FDM
Lingo

Frequency-division multiplexing. Technique whereby information from multiple channels can be allocated bandwidth on a single wire based on frequency. Compare with ATDM, statistical multiplexing, and TDM.

FECN
Telecommunications

Forward explicit congestion notification. Feedback
Telecommunications

The return of part of the power of an output signal to the input side of the device or process.

Female connector
Hardware

Also called "jack". A connector which joins with a male connector by providing recesses into which the male connector inserts its contact points or pins.

FEP
Lingo

Front-end processor. Device or board that provides network interface capabilities for a networked device. In SNA, typically an IBM 3745 device.

Fiber Optics
Telecommunications

A technology in which light is used to transport information from one point to another. More specifically, fiber optics are thin filaments of glass through which light beams are transmitted over long distances carrying enormous amounts of data. A thin silica glass cable (appx 125 micrometers in (diameter) with an outer cladding material around 9 micrometers diameter inner core with a slightly higher index of refraction than the the cladding. Optical fiber is made of glass or plastic, and guides light, whether or not it is used to transmit signals. Optical fiber is an almost ideal transmission medium. It has the following advantages:

Fiber-optic Cable
Hardware

Physical medium capable of conducting modulated light transmission. Compared with other transmission media, fiber-optic cable is more expensive, but is not susceptible to electromagnetic interference and is capable of higher data rates. Sometimes called optical fiber.

Field
Networking

In an information packet, a group of one or more bytes that performs a specific function, such as designating the recipient of the packet, the length of the packet or the type of protocol encoded in the packet.

File system
Networking

Refers to the collection of system software routines that manages and accesses files located on a computer's storage volumes.

File Transfer
Networking

Popular network application that allows files to be moved from one network device to another.

Filter
Software

  1. In computer programming, a filter is a program or section of code that is designed to examine each input or output request for certain qualifying criteria and then process or forward it accordingly. This term was used in UNIX systems and is now used in other operating systems. A filter is "pass-through" code that takes input data, makes some specific decision about it and possible transformation of it, and passes it on to another program in a kind of pipeline. Usually, a filter does no input/output operation on its own. Filters are sometimes used to remove or insert headers or control characters in data.

    In Windows operating systems, using Microsoft's Internet Server Application Programming Interface (Internet Server Application Program Interface), you can write a filter (in the form of a dynamic link library or dynamic link library file) that the operating system gives control each time there is a Hypertext Transport Control (Hypertext Transfer Protocol) request. Such a filter might log certain or all requests or encrypt data or take some other selective action.

  2. In telecommunications, a filter is a device that selectively sorts signals and passes through a desired range of signals while suppressing the others. This kind of filter is used to suppress noise or to separate signals into bandwidth channels.

Finder
Software

A software application included with Macintosh system software that allows users to perform basic file access and management functions using icons and pull-down menus.

Finger
Software

Finger is a program that tells you the name associated with an e-mail address. It may also tell you whether they are currently logon at their system or their most recent logon session and possibly other information, depending on the data that is maintained about users on that computer. Finger originated as part of BSD UNIX.

To finger another Internet user, you need to have the finger program on your computer or you can go to a finger gateway on the Web and enter the e-mail address. The server at the other end must be set up to handle finger requests. A ".plan" file can be created for any user that can be fingered. Commonly, colleges, universities, and large corporations set up a finger facility. Your own Internet access provider may also set up information about you and other subscribers that someone else can "finger."

Firewall
Networking

A firewall is a set of related programs, located at a network gateway server, that protects the resources of a private network from users from other networks. (The term also implies the security policy that is used with the programs.) An enterprise with an intranet that allows its workers access to the wider Internet installs a firewall to prevent outsiders from accessing its own private data resources and for controlling what outside resources its own users have access to. Basically, a firewall, working closely with a router program, filter all network packet to determine whether to forward them toward their destination. A firewall also includes or works with a proxy server that makes network requests on behalf of workstation users. A firewall is often installed in a specially designated computer separate from the rest of the network so that no incoming request can get directly at private network resources. There are a number of firewall screening methods. A simple one is to screen requests to make sure they come from acceptable (previously identified) domain name and Internet Protocol addresses. For mobile users, firewalls allow remote access in to the private network by the use of secure logon procedures and authentication certificates. A number of companies make firewall products. Features include logging and reporting, automatic alarms at given thresholds of attack, and a graphical user interface for controlling the firewall.

FireWire
Hardware

High-speed external data bus intended to replace the SCSI bus in the Macintosh system architecture, as the bus of choice for the connection of storage devices, external video and image I/O, etc.

Firmware
Hardware

Software (programs or data) that has been written onto read-only memory (ROM). Firmware is a combination of software and hardware. ROMs, PROMs and EPROMs that have data or programs recorded on them are firmware.

Flag
Networking

In a packet, a bit (or sometimes a group of bits) that indicates a condition. For example, the ZIP GetNetInfo Reply includes a 1-bit flag that indicates whether the zone name specified either is or is not a valid home zone name for the node that requested the information.

Flag Byte
Networking

In LocalTalk signaling, the bit pattern "01111110", which signals the beginning and ending of a LLAP frame. The Flag Bytes preceding the packets establish the synchronization of the frame similar to the function of an Ethernet preamble.

Flapping
Networking

Routing problem where an advertised route between two nodes alternates (flaps) back and forth between two paths due to a network problem that causes intermittent interface failures.

Flash memory
PC's

Technology developed by Intel and licensed to other semiconductor companies. Flash memory is nonvolatile storage that can be electrically erased and reprogrammed. Allows software images to be stored, booted, and rewritten as necessary.

Flash Update
Networking

Routing update sent synchronously in response to a change in the network topology. Compare with routing update.

Flooding
Networking

Traffic-passing technique used by switches and bridges in which traffic received on an interface is sent out all of the interfaces of that device except the interface on which the information was originally received.

Flow
Networking

Stream of data traveling between two endpoints across a network (for example, from one LAN station to another). Multiple flows can be transmitted on a single circuit.

Flow Control
Networking

Technique for ensuring that a transmitting entity, such as a modem, does not overwhelm a receiving entity with data. When the buffers on the receiving device are full, a message is sent to the sending device to suspend the transmission until the data in the buffers has been processed. In IBM networks, this technique is called pacing.

FM
Lingo

Frequency Modulation. In data transmission, a system of signaling in which the data is encoded by varying the frequency of the signal.

FNC
Organizations

Federal Networking Council. Group responsible for assessing and coordinating U.S. federal agency networking policies and needs.

FOIRL
Lingo

Fiber Optic Inter Repeater Link. An asynchronous fiber optic connection that links two Ethernet repeaters (hubs) with a maximum transmission distance of 2 kilometers when used at 10MBits/sec.

Foobar
Lingo

Foobar is a universal variable understood to represent whatever is being discussed. It's usually used in examples that illustrate concepts and ideas in computer science. For instance, a computer science professor may be discussing different file formats. In this case, he would call the generic-example file foo or foobar, then list the extensions associated with the file formats (e.g. foobar.txt, foobar.gif, foobar.exe, foobar.tar).

When foo or foobar is used, everyone understands that these are just examples, and they don't really exist.

Programmers and administrators also use foo and foobar in a similar context. Files or program s named with foo or foobar are understood not to be permanent and will be changed or deleted at anytime.

Foo, bar, and the compound foobar were commonly used at MIT, Stanford and the Helsinki University of Technology, Finland. Other generic variables are used other places, but only these three are considered universal.

One last note: hackers never use foobar to mean fubar!

Format
PC's

A specification for the arrangement of information. Examples include the format of disk, file or packet.

Forward Channel
Networking

Communications path carrying information from the call initiator to the called party.

Forward Delay Interval
Networking

Amount of time an interface spends listening for topology change information after that interface has been activated for bridging and before forwarding actually begins.

Forwarding
Networking

Process of sending a frame toward its ultimate destination by way of an internetworking device.

Four-part Dotted Notation
Networking

See dot address.

Fourier Transform
Networking

Technique used to evaluate the importance of various frequency cycles in a time series pattern.

FQDN
Networking

A fully qualified domain name consists of a host and domain name, including top-level domain. For example, www.webopedia.com is a fully qualified domain name. www is the host, webopedia is the second-level domain, and.com is the top level domain.

A FQDN always starts with a host name and continues all the way up to the top-level domain name, so www.parc.xerox.com is also a FQDN.

Fractional
Networking

One or more channels of a T-1 service. A complete T-1 carrier contains 24 channels, each of which provides 64 Kbps. Most phone companies, however, also sell fractional T-1 lines, which provide less bandwidth but are also less expensive. Typically, fractional T-1 lines are sold in increments of 56 Kbps (the extra 8 Kbps per channel is used for data management).

FRAD
Lingo

Frame Relay access device. Any network device that provides a connection between a LAN and a Frame Relay WAN.

Fragment
Networking

Piece of a larger packet that has been broken down to smaller units.

Fragmentation
Networking

Process of breaking a packet into smaller units when transmitting over a network medium that cannot support a packet of the original size. See also reassembly.

Frame
Telecommunications

  1. In telecommunications, a frame is data that is transmitted between network points as a unit complete with addressing and necessary protocol control information. A frame is usually transmitted serial binary digit by bit and contains a header field and a trailer field that "frame" the data. (Some control frames contain no data.)

    Here is a simple representation of a frame, based on the frame used in the frame relay access standard:

    -----------Header-------   ----------Trailer---------
    Flag
    (01111110)
    Address field Information (data) field
    (0-4096 bytes)
    Frame check sequence Flag
    (01111110)

    In the figure above, the flag and address fields constitute the header. The frame check sequence and second flag fields constitute the trailer. The information or data in the frame may contain another encapsulated frame that is used in a higher-level or different protocol. In fact, a frame relay frame typically carries data that has been framed by an earlier protocol program.

  2. In Time-Division Multiplexing (TDM), a frame is a complete cycle of events within the time division period.

  3. In film and video recording and playback, a frame is a single image in a sequence of images that are recorded and played back.

  4. In computer video display technology, a frame is the image that is sent to the display image rendering devices. It is continuously updated or refreshed from a frame buffer, a highly accessible part of video RAM (RAM).

Frame Relay
Telecommunications

Frame Relay provides connection-oriented data link layer communication. This means that a defined communication exists between each pair of devices and that these connections are associated with a connection identifier. This service is implemented by using a Frame Relay virtual circuit, which is a logical connection created between two data terminal equipment (DTE) devices across a Frame Relay packet-switched network (PSN). Virtual circuits provide a bi-directional communications path from one DTE device to another and are uniquely identified by a data-link connection identifier (DLCI). A number of virtual circuits can be multiplexed into a single physical circuit for transmission across the network. This capability often can reduce the equipment and network complexity required to connect multiple DTE devices. A virtual circuit can pass through any number of intermediate DCE devices (switches) located within the Frame Relay PSN. Frame Relay virtual circuits fall into two categories: switched virtual circuits (SVCs) and permanent virtual circuits (PVCs).

Frame Relay networks in the U.S. support data transfer rates at T-1 (1.544 Mbps) and T-3 (45 Mbps) speeds. In fact, you can think of Frame Relay as a way of utilizing existing T-1 and T-3 lines owned by a service provider. Most telephone companies now provide Frame Relay service for customers who want connections at 56 Kbps to T-1 speeds. (In Europe, Frame Relay speeds vary from 64 Kbps to 2 Mbps. In the U.S., Frame Relay is quite popular because it is relatively inexpensive. However, it is being replaced in some areas by faster technologies, such as ATM.

Frame Relay Bridging
Networking

Bridging technique, described in RFC 1490, that uses the same spanning-tree algorithm as other bridging functions, but allows packets to be encapsulated for transmission across a Frame Relay network.

Frame Switch
Networking

See LAN switch.

Frames
Programming

In creating a Web site, frames is the use of multiple, independently controllable sections on a Web presentation. This effect is achieved by building each section as a separate HTML file and having one "master" HTML file identify all of the sections. When a user requests a Web page that uses frames, the address requested is actually that of the "master" file that defines the frames; the result of the request is that multiple HTML files are returned, one for each visual section. Links in one frame can request another file that will appear in another (or the same) frame. A typical use of frames is to have one frame containing a selection menu in one frame and another frame that contains the space where the selected (linked to) files will appear.

Frames, originally created by Netscape as an HTML extension and now part of the HTML 4.0, specification are defined with HTML FRAMESET and FRAME tags. Sites that use frames need to create an alternative scheme of pages for requests from browsers that don't support them and possibly for users that prefer a non-frames version.

Framing
Telecommunications

The process of establishing a reference so that time slots or elements within the frame can be indentified.

Free-trade Zone
Networking

Part of an AppleTalk internetwork that is accessible by two other parts of the internetwork that are unable to directly access one another.

Frequency
Networking

1. A measure of the rate of change of a signal. 2. In a periodic signal, the reciprocal of the time necessary to complete one period.

Frequency Division Multiplexing
Telecommunications

FDM (frequency-division multiplexing) is a scheme in which numerous signals are combined for transmission on a single communications line or channel. Each signal is assigned a different frequency (subchannel) within the main channel.

A typical analog Internet connection via a twisted pair telephone line operates at the digital equivalent of 28,800 bits per second. The analog signal, consisting of a frequency-modulated audio tone, requires approximately three kilohertz (3 kHz) of bandwidth for accurate and reliable data transfer. Twisted-pair lines are common in households and small businesses. But major telephone cables, operating between large businesses, government agencies, and municipalities, are capable of much larger bandwidths. Suppose a long-distance cable is available with a bandwidth allotment of three megahertz (3 MHz). This is 3,000 kHz, so in theory, it is possible to place 1,000 signals, each 3 kHz wide, into the long-distance channel. The circuit that does this is known as a multiplexer. It accepts the input from each individual end user, and generates a signal on a different frequency for each of the inputs. This results in a high-bandwidth, complex signal containing data from all the end users. At the other end of the long-distance cable, the individual signals are separated out by means of a circuit called a demultiplexer, and routed to the proper end users. A two-way communications circuit requires a multiplexer/demultiplexer at each end of the long-distance, high-bandwidth cable.

When FDM is used in a communications network, each input signal is sent and received at maximum speed at all times. This is its chief asset. However, if many signals must be sent along a single long-distance line, the necessary bandwidth is large, and careful engineering is required to ensure that the system will perform properly. In some systems, a different scheme, known as Time-Division Multiplexing, is used instead.

Frequency Modulation
Telecommunications

Frequency modulation (FM) is a method of impressing data onto an alternating-current (AC) by varying the instantaneous frequency of the wave. This scheme can be used with analog or digital data.

In analog FM, the frequency of the AC signal wave, also called the carrier, varies in a continuous manner. Thus, there are infinitely many possible carrier frequencies. In narrowband FM, commonly used in two-way wireless communications, the instantaneous carrier frequency varies by up to 5 kilohertz (kHz, where 1 kHz = 1000 hertz) above and below the frequency of the carrier with no modulation. In wideband FM, used in wireless broadcasting, the instantaneous frequency varies by up to several megahertz (MHz, where 1 MHz = 1,000,000 Hz). When the instantaneous input wave has positive polarity, the carrier frequency shifts in one direction; when the instantaneous input wave has negative polarity, the carrier frequency shifts in the opposite direcetion. At every instant in time, the extent of carrier-frequency shift (the deviation) is directly proportional to the extent to which the signal amplitude is positive or negative.

In digital FM, the carrier frequency shifts abruptly, rather than varying continuously. The number of possible carrier frequency states is usually a power of 2. If there are only two possible frequency states, the mode is called frequency-shift keying (FSK). In more complex modes, there can be four, eight, or more different frequency states. Each specific carrier frequency represents a specific digital input data state.

Frequency modulation is similar in practice to phase modulation (phase modulation). When the instantaneous frequency of a carrier is varied, the instantaneous phase changes as well. The converse also holds: When the instantaneous phase is varied, the instantaneous frequency changes. But FM and PM are not exactly equivalent, especially in analog applications. When an FM receiver is used to demodulate a PM signal, or when an FM signal is intercepted by a receiver designed for PM, the audio is distorted. This is because the relationship between frequency and phase variations is not linear; that is, frequency and phase do not vary in direct proportion.

Frequency-Shift Keying
Telecommunications

Frequency-shift keying (FSK) is a method of transmitting digital signals. The two binary states, logic 0 (low) and 1 (high), are each represented by an analog waveform. Logic 0 is represented by a wave at a specific frequency, and logic 1 is represented by a wave at a different frequency. A modem converts the binary data from a computer to FSK for transmission over telephone lines, cables, optical fiber, or wireless media. The modem also converts incoming FSK signals to digital low and high states, which the computer can "understand."

The FSK mode was introduced for use with mechanical teleprinters in the mid-1900s. The standard speed of those machines was 45 baud, equivalent to about 45 bits per second (bits per second). When personal computers became common and networks came into being, this signaling speed was tedious. Transmission of large text documents and programs took hours; image transfer was unknown. During the 1970s, engineers began to develop modems that ran at faster speeds, and the quest for ever-greater bandwidth has continued ever since. Today, a standard telephone modem operates at thousands of bps. Cable and wireless modems work at more than 1,000,000 bps (one megabit per second or 1 Mbps), and optical fiber modems function at many Mbps. But the basic principle of FSK has not changed in more than half a century.

Fresnel Zone
Lingo

(pronounced 'fre-nel' the "s" is silent) The area around the visual line-of-sight that radio waves spread out into after they leave the antenna. This area must be clear or else signal strength will weaken. Fresnel Zone is an area of concern for 2.4 GHz wireless systems. Although 2.4 GHz signals pass rather well through walls, they have a tough time passing through trees. The main difference is the water content in each. Walls are very dry: trees contain high levels of moisture. Radio waves in the 2.4 GHz band absorb into water quite well. This is why microwaves -- which also use the 2.4GHz band -- cook food. Water absorbs the waves, and heat from the energy cooks the food.

Front End
Hardware

Front End Node or software program that requests services of a back end. See also back end, client, and server.

FST
Lingo

Fast Sequenced Transport. Connectionless, sequenced transport protocol that runs on top of the IP protocol. SRB traffic is encapsulated inside of IP datagrams and is passed over an FST connection between two network devices (such as routers). Speeds up data delivery, reduces overhead, and improves the response time of SRB traffic.

FTAM
Lingo

The OSI standard for File Transfer, Access and Management.

FTP
Software

file transfer protocol; a protocol that allows a user on one host to access and transfer files to and fromanother host over a network; FTP is commonly the name of the program the user invokes to execute the protocol.

Full Mesh
Networking

Term describing a network in which devices are organized in a mesh topology, with each network node having either a physical circuit or a virtual circuit connecting it to every other network node. A full mesh provides a great deal of redundancy, but because it can be prohibitively expensive to implement, it is usually reserved for network backbones. See also mesh and partial mesh.

Full-Duplex
Networking

Full-duplex data transmission means that data can be transmitted in both directions on a signal carrier at the same time. For example, on a local area network with a technology that has full-duplex transmission, one workstation can be sending data on the line while another workstation is receiving data. Full-duplex transmission necessarily implies a bidirectional line (one that can move data in both directions).

Fuzzball
PC's

Digital Equipment Corporation LSI-11 computer system running IP gateway software. The NSFnet used these systems as backbone packet switches.

G

Gain
Telecommunications

The ratio between the output signal and the input signal of a device.

Gateway
Networking

A gateway is a network point that acts as an entrance to another network. On the Internet, a node or stopping point can be either a gateway node or a host (end-point) node. Both the computers of Internet users and the computers that serve pages to users are host nodes. The computers that control traffic within your company's network or at your local Internet service provider (ISP) are gateway nodes.

In the network for an enterprise, a computer server acting as a gateway node is often also acting as a proxy server and a firewall server. A gateway is often associated with both a router, which knows where to direct a given packet of data that arrives at the gateway, and a switch, which furnishes the actual path in and out of the gateway for a given packet.

Gateway Host
Lingo

In SNA, a host node that contains a gateway SSCP.

Gateway NCP
Networking

NCP that connects two or more SNA networks and performs address translation to allow cross-network session traffic.

Gateway-to-Gateway Protocol
Protocol

See DDP.

GB
Lingo

Gigabyte

GBps
Lingo

Gigabytes per second.

GDP
Protocol

Gateway Discovery Protocol. Cisco protocol that allows hosts to dynamically detect the arrival of new routers as well as determine when a router goes down. Based on UDP. See also UDP.

geek
People

one whose serious pursuits are in any of these arenae: science, music/art/dance (performance,not spectating) math, gadgetry, literature, and others, to be sure (aka engineer, doctor, professor, maestro). Not to be confused with a nerd or a spazz. Source: The Encycopædia Craigica

Get
Lingo

In SNMP, a command given by the Console to retrieve a single data structure from a MIB.

GHz
Lingo

Gigahertz.

GIF
Lingo

Graphic Interchange Format: A type of image file. GIF files are graphics or pictures, often used on Web pages. Because GIF files contain a maximum of 256 colors, this file format is ideal for simple graphics with minimal shading or color variation. Other types of graphics are better suited for the JPEG file format.

Giga
Lingo

A prefix denoting a billion.

Gigabit
Telecommunications

A gigabit is equal to one billion bits.

Gigabyte
Software

2 to the 30th power (1,073,741,824) bytes. One gigabyte is equal to 1,024 megabytes. Gigabyte is often abbreviated as G or GB.

Gigahertz
PC's

One billion cycles per second.

GNS
Lingo

Get Nearest Server. Request packet sent by a client on an IPX network to locate the nearest active server of a particular type. An IPX network client issues a GNS request to solicit either a direct response from a connected server or a response from a router that tells it where on the internetwork the service can be located. GNS is part of the IPX SAP. See also IPX and SAP (Service Advertisement Protocol).

GNU
Organizations

Self-referentially, short for GNU's not UNIX, a UNIX -compatible software system developed by the Free Software Foundation (FSF). The philosophy behind GNU is to produce software that is non-proprietary. Anyone can download, modify and redistribute GNU software. The only restriction is that they cannot limit further redistribution. The GNU project was started in 1983 by Richard Stallman at the Massachusetts Institute of Technology.

Linux systems rely heavily on GNU software and in the past, GNU systems used the Linux kernel. This close connection has led some people to mistakenly equate GNU with Linux. They are actually quite separate. In fact, the FSF is developing a new kernel called HURD to replace the Linux kernel in GNU systems.

GOSIP
Lingo

Government OSI Profile. US Government procurement standard that specified interoperability standards for computing equipment and software purchased.

Grade
Lingo

Also Level or Category. In the specification of wiring for data networks, a standard designation used to describe the electrical quality of the wiring with regard to its suitability to carry high-speed signals.

Grade of Service
Networking

Measure of telephone service quality based on the probability that a call will encounter a busy signal during the busier hours of the day.

Graphic
Lingo

Any picture or image file within a Web page. Graphics are usually in GIF or JPEG format.

GRE
Lingo

Generic Routing Encapsulation. Tunneling protocol developed by Cisco that can encapsulate a wide variety of protocol packet types inside IP tunnels, creating a virtual point-to-point link to Cisco routers at remote points over an IP internetwork. By connecting multiprotocol subnetworks in a single-protocol backbone environment, IP tunneling using GRE allows network expansion across a single-protocol backbone environment.

Ground
Lingo

An electrical conductor that is neither negatively or positively charged.

Ground Station
Networking

Collection of communications equipment designed to receive signals from (and usually transmit signals to) satellites. Also called a downlink station.

Group 3
Protocol

The universal protocol for sending fax documents across telephone lines. The Group 3 protocol specifies CCITT T.4 data compression and a maximum transmission rate of 9,600 baud. There are two levels of resolution: 203 by 98 and 203 by 196.

Group 4
Protocol

A protocol for sending fax documents over ISDN networks. The Group 400 protocol supports images of up to 400 dpi resolution.

Group Address
Networking

See multicast address.

Guard Band
Networking

Unused frequency band between two communications channels that provides separation of the channels to prevent mutual interference.

GUI
Lingo

Graphical User Interface. This is often used to differentiate between text based interfaces, such as vi, and graphical based programs, such as Microsoft Word. It also can be used to describe operating environments such as X-Windows and BEOS.

H

H Channel
Telecommunications

High-speed channel. Full-duplex ISDN primary rate channel operating at 384 Kbps. Compare with B channel, D channel, and E channel.

Hacker
People

1. An expert computer programmer. 2. A knowledgeable but disruptive computer user.

Half-Duplex
Telecommunications

Half-duplex data transmission means that data can be transmitted in both directions on a signal carrier, but not at the same time. For example, on a local area network using a technology that has half-duplex transmission, one workstation can send data on the line and then immediately receive data on the line from the same direction in which data was just transmitted. Like full-duplex transmission, half-duplex transmission implies a bidirectional line (one that can carry data in both directions).

Handshake
Networking

Sequence of messages exchanged between two or more network devices to ensure transmission synchronization.

Hardware Address
Hardware

An address, fixed at the time of manufacturing, that identifies a network adapter such as an Ethernet card.

HBD3
Lingo

Line code type used on E1 circuits.

HDLC
Lingo

High-level Data Link Control. An ISO standard for encapsulation of data on synchronous links.

HDML
Protocol

Handheld Device Markup Language is used to format content for Web-enabled mobile phones. HDML is phone.com's (formerly known as Unwired Planet) proprietary language, which can only be viewed on mobile phones that use phone.com browsers. HDML came before the WAP standard was created. It uses phone.com's Handheld Device Transport Protocol (HDTP), instead of WAP. Phones access HDML sites the following way: Once the URL is typed into the phone, the phone sends the request to phone.com's UP.Link gateway. The gateway sends a HTTP request to the Web server. The Web servers returns the page via HTTP back to the phone.com UP.Link gateway. The gateway sends the data via HDTP to the wireless carrier's network and down to the phone.

HDSL
Telecommunications

The earliest variation of DSL to be widely used has been HDSL (High bit-rate DSL) which is used for wideband digital transmission within a corporate site and between the telephone company and a customer. The main characteristic of HDSL is that it is symmetrical: an equal amount of bandwidth is available in both directions. For this reason, the maximum data rate is lower than for ADSL. HDSL can carry as much on a single wire of twisted-pair as can be carried on a T1 line in North America or an E1 line in Europe (2,320 Kbps). HDSL can be deployed over standard UTP at distances of up to 12,000 ft on 24 guage wire and up to 9,000 ft on 22 guage wire.

Headend
Networking

The end point of a broadband network. All stations transmittoward the headend; the headend then transmits toward the destination station.

Header
Software

In many disciplines of computer science, a header is a unit of information that precedes a data object. In file management, for example, a header is a region at the beginning of each file where bookkeeping information is kept. The file header may contain the date the file was created, the date it was last updated, and the file's size. The header can be accessed only by the operating system or by specialized programs.

Heap
Hardware

The RAM memory allocated by system software and system extensions to hold frequently used instructions and data not contained in ROM or firmware.

HELLO
Networking

Interior routing protocol used principally by NSF net nodes. HELLO allows particular packet switches to discover minimal delay routes. Not to be confused with the Hello protocol.

Hello Packet
Networking

Multicast packet that is used by routers for neighbor discovery and recovery. Hello packets also indicate that a client is still operating and network-ready.

Hello Protocol
Protocol

Protocol used by OSPF systems for establishing and maintaining neighbor relationships. Not to be confused with HELLO.

Helper Address
Networking

Address configured on an interface to which broadcasts received on that interface will be sent.

HEPnet
Organizations

High-Energy Physics Network. Research network that originated in the United States, but that has spread to most places involved in high-energy physics. Well-known sites include Argonne National Laboratory, Brookhaven National Laboratory, and the Stanford Linear Accelerator Center (SLAC).

Hertz
Telecommunications

Named after the German physicist Heinrich Hertz, Hertz is a unit of frequency (of change in state or cycle in a sound wave, alternating current, or other cyclical waveform) of one cycle per second. It replaces the earlier term of "cycle per second (cps)."

For example, in the United States, common house electrical supply is at 60 hertz (meaning the current changes direction or polarity 120 times, or 60 cycles, a second). (In Europe, line frequency is 50 hertz, or 50 cycles per second.) Broadcast transmission is at much higher frequency rates, usually expressed in kilohertz (KHz) or megahertz (MHz).

In acoustic sound, the range of human hearing is from 0 Hz to roughly 20 KHz (depending on many factors, including age and how loud the drummer in your high school rock band played!). The pitch of Middle C on a piano is 263 Hz. Hertz is also used frequently when describing the individual bands of an audio equalizer. To make that Middle C louder, you could boost other frequencies to around 263 Hz with an equalizer.

Heterogeneous Network
Networking

Network consisting of dissimilar devices that run dissimilar protocols and in many cases support dissimilar functions or applications.

Hexadecimal
Networking

A numerical system with a base of 16 that is useful for expressing digital data. One hexadecimal digit represents for bits.

HFS
Lingo

Hierarchical File System.

Hierarchical Routing
Networking

Routing based on a hierarchical addressing system. For example, IP routing algorithms use IP addresses, which contain network numbers, subnet numbers, and host numbers.

Hint
Networking

In dynamic addressing, an address that a node will test for uniqueness first. The hint is either the last successful address the node used previously (the Macintosh keeps such a hint in PRAM) or a particular address that is specific to a particular model of device (the GatorBox always tries 128 first or LocalTalk networks).

HIPPI
Lingo

High-Performance Parallel Interface. High-performance interface standard defined by ANSI. HIPPI is typically used to connect supercomputers to peripherals and other devices.

Hit
Lingo

A single request from a Web browser for a single item from a Web server. When a browser displays a Web page that contains 2 graphics, 3 hits occur at the server: 1 hit for the HTML page itself, plus a hit for each of the two graphics. See Also: Impressions

Holddown
Networking

State into which a route is placed so that routers will neither advertise the route nor accept advertisements about the route for a specific length of time (the holddown period). Holddown is used to flush bad information about a route from all routers in the network. A route is typically placed in holddown when a link in that route fails.

Homepage
Lingo

The first page of a Web site. Some people choose to have only a homepage, with no supporting pages.

Homologation
Networking

Conformity of a product or specification to international standards, such as ITU-t, CSA, TUV, UL, or VCCI. Enables portability across company and international boundaries.

Hop
Networking

An intermediate connection in a string of connections linking two network devices. On the Internet, for example, most data packets need to go through several routers before they reach their final destination. Each time the packet is forwarded to the next router, a hop occurs. The more hops, the longer it takes for data to go from source to destination. You can see how many hops it takes to get to another Internet host by using the PING or traceroute utilities. Some Internet Service Providers (ISPs) advertise how many hops away from Internet backbone they are. Theoretically, the fewer hops it takes to get your data onto the backbone, the faster your access will be.

Hop Count
Networking

In AppleTalk packets, a 4-bit counter in the DDP header that is incremented each time a packet passes through a router on the way to its destination.

Hop Distance
Networking

A unit of measure used to express the number or routers that a packet must pass through its way to its destination.

Host
Lingo

1.A computer system accessed by a user from a remote location. In the case of two computer systems connected via modem, the "host" is the system containing the data and the "remote" is the computer at which the user is working. 2.A computer that is connected to a TCP/IP network, including the Internet. Each host has a unique IP address. 3.As a verb, "host" means providing the infrastructure for a computer service. A company that hosts a Web server may provide the hardware and software needed to run that server, but does not supply all the content on that server. Ameritech provides hosting services by running and maintaining the server, while allowing customers to maintain their own Web site content.

Host Address
Networking

See host number.

Host Number
Networking

Part of an IP address that designates which node on the subnetwork is being addressed. Also called a host address.

HPCC
Lingo

High Performance Computing and Communications. U.S. government funded program advocating advances in computing, communications, and related fields. The HPCC is designed to ensure US. leadership in these fields through education, research and development, industry collaboration, and implementation of high-performance technology. The five components of the HPCC are ASTA, BRHR, HPCS, IITA, and NREN.

HPCS
Lingo

High Performance Computing Systems. Component of the HPCC program designed to ensure US. technological leadership in high-performance computing through research and development of computing systems and related software. See also HPCC.

HPR
Lingo

High Performance Routing. Second-generation routing algorithm for APPN. HPR provides a connectionless layer with nondisruptive routing of sessions around link failures, and a connection-oriented layer with end-to-end flow control, error control, and sequencing. Compare to ISR. See also APPN.

HSRP
Lingo

Hot Standby Router Protocol. Provides high network availability and transparent network topology changes. HSRP creates a HotStandby router group with a lead router that services all packets sent to the Hot Standby address. The lead router is monitored by other routers in the group, and if it fails, one of the standby routers inherits the lead position and the Hot Standby group address.

HSSI
Lingo

High-Speed Serial Interface. Network standard for high-speed (up to 52 Mbps) serial connections over WAN links.

HTML
Software

hypertext markup language; the language used in the Web to create Web pages with links to other documents, rich text enhancements (bold, italics, etc.), and so on; the source file for what is seen on a Web page is written in HTML

HTTP
Software

hypertext transfer protocol; used in the Web to transfer information from Web servers to Web browsers.

HTTPS
Protocol

HTTPS (Secure Hypertext Transfer Protocol) is a Web protocol developed by Netscape and built into its browser that encrypts and decrypts not only user page requests, but also the pages that are returned by the Web server. HTTPS is really just the use of SSL encryption on the Presentation layer, under its regular HTTP application layering. (HTTPS uses port 443 instead of port 80 in its interactions with TCP on the Transport layer.)

Hub
Networking

In data communications, a hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions. A hub is often called a "dumb" device because it does not do any filtering of layer 2 packets like a switch does. Also, a hub only supports one type of technology, like 10Base-T or 100Base-T, but not both, like a bridge.

Hybrid Network
Networking

Internetwork made up of more than one type of network technology, including LANs and WANs.

Hypertext
Programming

Any text within a document that is linked to another location. The other location could be within the same document, or a different document. Clicking hypertext with your mouse will activate the link. This glossary is made up of hypertext, containing many links.

I

I/O
Hardware

Short for input/output, and pronounced eye-oh. I/O refers to any operation, program, or device whose purpose is to enter data into a computer or to extract data from a computer. One usually uses the term I/O to distinguish noncomputational parts of a program from other parts that are strictly computational, or to distinguish certain devices from other devices. For example, a printer is an I/O device, whereas a CPU is a computational device. All computer applications contain both I/O and computational parts. A word-processing system, for instance, contains I/O components (for entering, displaying, and printing text) as well as non-I/O components (for checking spelling, searching for words, and so on).

I/O Bound
Networking

A computer or network activity whose speed is limited by the time necessary to perform I/O functions.

IAB
Organizations

Internet Architecture Board. Board of internetwork researchers who discuss issues pertinent to Internet architecture. Responsible for appointing a variety of Internet-related groups such as the IANA, IESG, and IRSG. The IAB is appointed by the trustees of the ISOC. See also IANA, IESG, IRSG, and ISOC.

IANA
Organizations

Internet Assigned Numbers Authority. Organization operated under the auspices of the ISOC as a part of the IAB. IANA delegates authority for IP address-space allocation and domain-name assignment to the NIC and other organizations. IANA also maintains a database of assigned protocol identifiers used in the TCP/IP stack, including autonomous system numbers. See also IAB, ISOC, and NIC.

IAS Computer
Hardware

IAS (Institute for Advanced Studies), and IBM 709, was the first general purpose computer. Developed at the Institute for Advanced Studies at Princeton, this system was the first computer designed as a general purpose system with stored instructions. Von Neumann helped design the system, and most computers of the next 30 years or so were referred to as "Von Neumann machines" because they followed the principles he built into this system.

(John) Von Neumann's IAS computer was optimized for scientific calculation. Completed in 1952 at a cost of several hundred thousand dollars, the IAS used 2,300 miniature vacuum tubes. It was built to do the massive calculations needed in meteorology, astronomy, hydrodynamics, and other fields of science, as well as the computation for designing atomic weapons, including the first hydrogen bomb. (Its first problem, for Los Alamos, took sixty days, twenty-four hours a day, to solve!) Numerical computation turned out to be of great value to many fields where the problems were too complex to be answered simply by solving equations. The existence of the computer -- and therefore of the possibility of carrying out lots of calculations quickly -- opened up new fields to mathematical analysis.

iCare
Software

Kenan, Arbor and iCare are often used interchangeably in Verio. Kenan is the company that makes Arbor, the billing software. iCare is the web interface for Arbor.

ICD
Networking

International Code Designator. One of two ATM address formats developed by the ATM forum for use by private networks. Adapted from the subnetwork model of addressing in which the ATM layer is responsible for mapping network layer addresses to ATM addresses. See also DCC.

ICMP
Protocol

Short for Internet Control Message Protocol, an extension to the Internet Protocol (IP) defined by RFC 792. ICMP supports packets containing error, control, and informational messages. The PING command, for example, uses ICMP to test an Internet connection.

Icon
Concept

A pictographic symbol used to represent a computer concept or operation.

IDEA
Software

IDEA, unlike the other block cipher algorithms discussed in this section, is patented by the Swiss firm of Ascom. They have, however, been generous in allowing, with permission, free noncommercial use of their algorithm, with the result that IDEA is best known as the block cipher algorithm used within the popular encryption program PGP.

The IDEA algorithm is interesting in its own right. It includes some steps which, at first, make it appear that it might be a non-invertible hash function instead of a block cipher. Also, it is interesting in that it entirely avoids the use of any lookup tables or S-boxes.
IDEA uses 52 subkeys, each 16 bits long. Two are used during each round proper, and four are used before every round and after the last round. It has eight rounds.

The plaintext block in IDEA is divided into four quarters, each 16 bits long. Three operations are used in IDEA to combine two 16 bit values to produce a 16 bit result, addition, XOR, and multiplication. Addition is normal addition with carries, modulo 65,536. Multiplication, as used in IDEA, requires some explanation.

Multiplication by zero always produces zero, and is not invertible. Multiplication modulo n is also not invertible whenever it is by a number which is not relatively prime to n. The way multiplication is used in IDEA, it is necessary that it be always invertible. This is true of multiplication IDEA style.

The number 65,537, which is 2^16+1, is a prime number. (Incidentally, 2^8+1, or 257, is also prime, and so is 2^4+1, or 17, but 2^32+1 is not prime, so IDEA cannot be trivially scaled up to a 128-bit block size.) Thus, if one forms a multiplication table for the numbers from 1 through 65,536, each row and column will contain every number once only, forming a Latin square, and providing an invertible operation. The numbers that 16 bits normally represent are from 0 to 65,535 (or, perhaps even more commonly, from -32,768 to 32,767). In IDEA, for purposes of multiplication, a 16 bit word containing all zeroes is considered to represent the number 65,536; other numbers are represented in conventional unsigned notation, and multiplication is modulo the prime number 65,537.

IDI
Lingo

Initial domain identifier. In OSI, the portion of the NSAP that specifies the domain.

IDN
Lingo

International Data Number. See X.121.

IDP
Lingo

Initial domain part. The part of a CLNS address that contains an authority and format identifier and a domain identifier.

IDPR
Lingo

Interdomain Policy Routing. Interdomain routing protocol that dynamically exchanges policies between autonomous systems. IDPR encapsulates interautonomous system traffic and routes it according to the policies of each autonomous system along the path. IDPR is currently an IETF proposal. See also policy routing.

IDRP
Protocol

IS-IS Interdomain Routing Protocol. OSI protocol that specifies how routers communicate with routers in different domains.

IDSL
Telecommunications

ISDN Digital Subscriber Line provides DSL technology over existing ISDN lines. Even though the transfer rates for IDSL are about the same as ISDN (144kbps v. 128kbps), and IDSL circuits can only carry data (not voice), the major benefits of switching to IDSL from ISDN are always-on connections, thus eliminating call setup delays; flat rate billing, instead of per minute fees; and transmission of data over the data network, rather than the PSTN. IDSL was developed by Ascend Communications, now part of Lucent Technologies.

IEC
Organizations

International Electrotechnical Commission. Industry group that writes and distributes standards for electrical products and components.

IEEE
Organizations

The Institute or Electrical and Electronic Engineers, a non-profit organization that, among many other activities, endeavors to coordinate, synthesize and promote data networking standards.

IEEE 802.1
Networking

IEEE specification that describes an algorithm that prevents bridging loops by creating a spanning tree. The algorithm was invented by Digital Equipment Corporation. The Digital algorithm and the IEEE 802.1 algorithm are not exactly the same, nor are they compatible. See also spanning tree, spanning-tree algorithm, and Spanning-Tree Protocol.

IEEE 802.12
Networking

IEEE LAN standard that specifies the physical layer and the MAC sublayer of the data link layer. IEEE 802.12 uses the demand priority media-access scheme at 100 Mbps over a variety of physical media. See also 100VG-AnyLAN.

IEEE 802.2
Networking

The committee of the IEEE charged with the responsibility of coordinating standards at the Data Link Layer. The committee also oversees the work of many sub-committees that govern individual Data Link standards such as the 802.3 standard.

IEEE 802.3
Networking

IEEE LAN protocol that specifies an implementation of the physical layer and the MAC sublayer of the data link layer. IEEE 802.3 uses CSMA/CD access at a variety of speeds over a variety of physical media. Extensions to the IEEE 802.3 standard specify implementations for Fast Ethernet. Physical variations of the original IEEE 802.3 specifications include 10Base2, 10Base5, 10BaseF, 10BaseT, and 10Broad36. Physical variations for fast ethernet include 100BaseT, 100BaseT4, and 100BaseX.

IEEE 802.4
Networking

IEEE LAN protocol that specifies an implementation of the physical layer and the MAC sublayer of the data link layer. IEEE 802.4 uses token-passing access over a bus topology and is based on the token bus LAN architecture. See also token bus.

IEEE 802.5
Networking

IEEE LAN protocol that specifies an implementation of the physical layer and MAC sublayer of the data link layer. IEEE 802.5 uses token passing access at 4 or 16 Mbps over STP cabling and is similar to IBM Token Ring. See also Token Ring.

IEEE 802.6
Networking

IEEE MAN specification based on DQDB technology. IEEE 802.6 supports data rates of 1.5 to 155 Mbps. See also DQDB.

IESG
Organizations

Internet Engineering Steering Group. Organization, appointed by the IAB, that manages the operation of the IETF. See also IAB and IETF.

IETF
Organizations

Internet Engineering Task Force. Task force consisting of over 80 working groups responsible for developing Internet standards. The IETF operates under the auspices of ISOC. See also ISOC.

IGMP
Protocol

Internet Group Management Protocol is defined in RFC 1112 as the standard for IP multicasting in the Internet. It's used to establish host memberships in particular multicast groups on a single network. The mechanisms of the protocol allow a host to inform its local router, using Host Membership Reports, that it wants to receive messages addressed to a specific multicast group. All hosts conforming to level 2 of the IP multicasting specification require IGMP.

IGP
Protocol

Interior Gateway Protocol. Internet protocol used to exchange routing information within an autonomous system. Examples of common Internet IGPs include IGRP, OSPF, and RIP. See also IGRP, OSPF, and RIP.

IGRP
Protocol

Interior Gateway Routing Protocol. IGP developed by Cisco to address the problems associated with routing in large, heterogeneous networks. Compare with Enhanced IGRP. See also IGP, OSPF, and RIP.

IITA
Organizations

Information Infrastructure Technology and Applications. Component of the HPCC program intended to ensure U.S. leadership in the development of advanced information technologies. See also HPCC.

ILEC
Telecommunications

Incumbent Local Exchange Carrier; "The" phone company for a given area. Examples are Southwestern Bell, Bell South, Ameritech, Bell Atlantic, Pacific Bell, US West, GTE, etc.

Image Map
Programming

Image Map A graphic used for multiple navigation on a Web page. Image maps contain HTML code that turn specific areas of graphics into links.

IMAP
Protocol

IMAP (Internet Message Access Protocol) is a standard protocol for accessing e-mail from your local server. IMAP (the latest version is IMAP4) is a client/server protocol in which e-mail is received and held for you by your Internet server. You (or your e-mail client) can view just the heading and the sender of the letter and then decide whether to download the mail. You can also create and manipulate folders or mailboxes on the server, delete messages, or search for certain parts or an entire note. IMAP requires continual access to the server during the time that you are working with your mail.

Impedance
Networking

A measure of the opposition to the flow of an alternating signal by its media.

Implementation
Networking

The physical manifestation of a network standard or design.

Impressions
Lingo

Impressions The actual number of people who've seen a specific Web page. Impressions are much more accurate than hits when discerning how much traffic your Web page actually receives. Impressions are sometimes called "page views."

In-band signaling
Networking

Transmission within a frequency range normally used for information transmission. Compare with out-of-band signaling.

Infrared
Networking

1. A portion of electromagnetic spectrum situated between visible light and microwaves. 2. A means of short distance wireless networking that depends on an unobstructed line of sight path.

Initialization
Networking

The entry of a set of process parameters (performed by a human or automatically loaded from a file) that are necessary to begin a software process.

INOC
Organizations

Internet Network Operations Center. BBN group that in the early days of the Internet monitored and controlled the Internet core gateways (routers). INOC no longer exists in this form.

Input/output
Networking

See I/O.

Instance
Concept

In statistical analysis, the single occurrence of a phenomena or event.

Insulator
Hardware

A material that is highly resistant to electrical and/or thermal conduction.

Insured Rate
Networking

The long-term data throughput, in bits or cells per second, that an ATM network commits to support under normal network conditions. The insured rate is 100 percent allocated; the entire amount is deducted from the total trunk bandwidth along the path of the circuit. Compare with excess rate and maximum rate. See also insured burst.

Insured Traffic
Networking

Traffic within the insured rate specified for the PVC. This traffic should not be dropped by the network under normal network conditions. See also CLP and insured rate.

Integrity
Networking

In networking, a desirable condition where the information received is exactly equal to the information sent.

Intelligence
Networking

The ability of a system to use general information to respond appropriately to specific events.

Interarea Routing
Networking

Term used to describe routing between two or more logical areas. Compare with intra-area routing.

Interface
Networking

  1. A user interface, consisting of the set of dials, knobs, operating system commands, graphical display formats, and other devices provided by a computer or a program to allow the user to communicate and use the computer or program. A graphical user interface graphical user interface provides its user a more or less "picture-oriented" way to interact with technology. A GUI is usually a more ergonomic satisfying or user-friendly interface to a computer system.
  2. A programming interface, consisting of the set of statements, functions, options, and other ways of expressing program instructions and data provided by a program or language for a programmer to use.
  3. The physical and logical arrangement supporting the attachment of any device to a connector or to another device.

Interface Device
Telecommunications

A device which meets a standard interface specification on one side and meets some other interface on its other side. The purpose of the device is to allow another device with a nonstandard interface to connect to a standard interface.

Interference
Networking

Unwanted communication channel noise.

Internet
Networking

A global network connecting millions computers. As of 1998, the Internet has more than 100 million users worldwide, and that number is growing rapidly. More than 100 countries are linked into exchanges of data, news and opinions. Unlike online services, which are centrally controlled, the Internet is decentralized by design. Each Internet computer, called a host, is independent. Its operators can choose which Internet services to use and which local services to make available to the global Internet community. Remarkably, this anarchy by design works exceedingly well. There are a variety of ways to access the Internet. Most online services, such as America Online, offer access to some Internet services. It is also possible to gain access through a commercial Internet Service Provider (ISP).

Internet Address
Networking

An address that identifies a communication entity on an internet.

Internet Node Address
Networking

In AppleTalk, the combination of network and node address that uniquely defines an AppleTalk protocol running in a device that is currently active.

Internet Router
Networking

A router that uses the rules of one or more Network Layer protocols to forward packets between networks.

Internet Socket Address
Networking

In AppleTalk, the combination of network, node and socket address that uniquely identifies a software process that is using AppleTalk protocols to communicate.

Internetwork
Networking

Collection of networks interconnected by routers and other devices that functions generally) as a single network. Sometimes called an internet, which is not to be confused with the Internet.

Internetworking
Concept

General term used to refer to the industry that has arisen around the problem of connecting networks together. The term can refer to products, procedures, and technologies.

Internic
Organizations

A collaborative project between AT&T and Network Solutions, Inc. (NSI) supported by the National Science Foundation. The project currently offers the following four services to users of the Internet. InterNIC Directory and Database Services - online white pages directory and directory of publicly accessible databases managed by AT&T. Registration Services - domain name and IP address assignment managed by NSI. Support Services - outreach, education, and information services for the Internet community managed by NSI. Net Scout Services - online publications that summarize recent happenings of interest to Internet users (managed by NSI).

Interoperability
Networking

Ability of computing equipment manufactured by different vendors to communicate with one another successfully over the network.

Interpreter
Software

A program that executes instructions written in a high-level language. There are two ways to run programs written in a high-level language. The most common is to compile the program; the other method is to pass the program through an interpreter.

An interpreter translates high-level instructions into an intermediate form, which it then executes. In contrast, a compiler translates high-level instructions directly into machine language. Compiled programs generally run faster than interpreted programs. The advantage of an interpreter, however, is that it does not need to go through the compilation stage during which machine instructions are generated. This process can be time-consuming if the program is long. The interpreter, on the other hand, can immediately execute high-level programs. For this reason, interpreters are sometimes used during the development of a program, when a programmer wants to add small sections at a time and test them quickly. In addition, interpreters are often used in education because they allow students to program interactively.

Both interpreters and compilers are available for most high-level languages. However, BASIC and LISP are especially designed to be executed by an interpreter. In addition, page description languages, such as PostScript, use an interpreter. Every PostScript printer, for example, has a built-in interpreter that executes PostScript instructions.

Intra-area Routing
Networking

Term used to describe routing within a logical area. Compare with interarea routing.

Intranet
Networking

Intranet A private network inside a company or organization that uses the same kinds of software that you would find on the public Internet, but only for internal use.

Inverse ARP
Protocol

Inverse Address Resolution Protocol. Method of building dynamic routes in a network. Allows an access server to discover the network address of a device associated with a virtual circuit.

IP
Protocol

Abbreviation of Internet Protocol, pronounced as two separate letters. IP specifies the format of packets, also called datagrams, and the addressing scheme. Most networks combine IP with a higher-level protocol called Transport Control Protocol (TCP), which establishes a virtual connection between a destination and a source. IP by itself is something like the postal system. It allows you to address a package and drop it in the system, but there's no direct link between you and the recipient. TCP/IP, on the other hand, establishes a connection between two hosts so that they can send messages back and forth for a period of time. The current version of IP is IPv4. A new version, called IPv6 or IPng, is under development.

IP Multicast
Protocol

Sending out data to distributed servers on the MBone (Multicast Backbone). For large amounts of data, IP Multicast is more efficient than normal Internet transmissions because the server can broadcast a message to many recipients simultaneously. Unlike traditional Internet traffic that requires separate connections for each source-destination pair, IP Multicasting allows many recipients to share the same source. This means that just one set of packets is transmitted for all the destinations.

IP Number (IP Address)
Networking

IP Number (IP Address) The unique 4-part number assigned to each and every computer linked to the Internet (e.g., 206.141.202.111). When you connect to the Internet, your ISP assigns you an IP number for the duration of your connection. DNS converts domain names into IP addresses.

IP switching
Networking

A new type of IP routing developed by Ipsilon Networks, Inc. Unlike conventional routers, IP switching routers use ATM hardware to speed packets through networks. Although the technology is new, it appears to be considerably faster than older router techniques.

IPng
Protocol

Short for Internet Protocol next generation, a new version of the Internet Protocol (IP) currently being reviewed in IETF standards committees. The official name of IPng is IPv6, where the v6 stands for version 6. The current version of IP is version 4, so it is sometimes referred to as IPv4. IPng is designed as an evolutionary upgrade to the Internet Protocol and will, in fact, coexist with the older IPv4 for some time. IPng is designed to allow the Internet to grow steadily, both in terms of the number of hosts connected and the total amount of data traffic transmitted.

IPsec
Protocol

Short for IP Security, a set of protocols being developed by the IETF to support secure exchange of packets at the IP layer. Once it's completed, IPsec is expected to be deployed widely to implement Virtual Private Networks (VPNs). IPsec supports two encryption modes: Transport and Tunnel. Transport mode encrypts only the data portion (payload) of each packet, but leaves the header untouched. The more secure Tunnel mode encrypts both the header and the payload. On the receiving side, an IPSec-compliant device decrypts each packet. For IPsec to work, the sending and receiving devices must share a public key. This is accomplished through a protocol known as Internet Security Association and Key Management Protocol/Oakley (ISAKMP/Oakley), which allows the receiver to obtain a public key and authenticate the sender using digital certificates.

IPX
Protocol

Short for Internetwork Packet Exchange, a networking protocol used by the Novell NetWare operating systems. Like UDP/IP, IPX is a datagram protocol used for connectionless communications. Higher-level protocols, such as SPX and NCP, are used for additional error recovery services. The successor to IPX is the NetWare Link Services Protocol (NLSP).

IPXWAN
Protocol

Protocol that negotiates end-to-end options for new links. When a link comes up, the first IPX packets sent across are IPXWAN packets negotiating the options for the link. When the IPXWAN options have been successfully determined, normal IPX transmission begins. Defined by RFC 1362.

IRC
Lingo

IRC Internet Relay Chat: A method of real time communication, powered by a network of servers.

IRDP
Protocol

ICMP Router Discover Protocol. Enables a host to determine the address of a router that it can use as a default gateway. Similar to ES-IS, but used with IP.

IRN
Networking

Intermediate routing node. In SNA, a subarea node with intermediate routing capability.

IRSG
Organizations

Internet Research Steering Group. Group that is part of the IAB and oversees the activities of the IRTF. See also IAB and IRTF.

IRTF
Organizations

Internet Research Task Force. Community of network experts that consider Internet-related research topics. The IRTF is governed by the IRSG and is considered a subsidiary of the IAB. See also IAB and IRSG.

ISA
Hardware

Industry-Standard Architecture. 16-bit bus used for Intel-based personal computers. See also EISA.

ISDN
Telecommunications

Abbreviation of integrated services digital network, an international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires. ISDN supports data transfer rates of 64 Kbps (64,000 bits per second). Most ISDN lines offered by telephone companies give you two lines at once, called B channels. You can use one line for voice and the other for data, or you can use both lines for data to give you data rates of 128 Kbps, three times the data rate provided by today's fastest modems.

ISP
Lingo

ISP Internet Service Provider: A company that provides access to the Internet. Ameritech.net is an ISP.

ISR
Networking

Intermediate Session Routing. Initial routing algorithm used in APPN. ISR provides node-to-node onnection-oriented routing. Network outages cause sessions to fail because ISR cannot provide nondisruptive rerouting around a failure. ISR has been replaced by HPR. Compare with HPR. See also APPN.

IT
Organizations

Short for Information Technology, and pronounced as separate letters, the broad subject concerned with all aspects of managing and processing information, especially within a large organization or company. Because computers are central to information management, computer departments within companies and universities are often called IT departments. Some companies refer to this department as IS (Information Services) or MIS (Management Information Services).

IT Infrastructure
Concept

In information technology and on the Internet, infrastructure is the physical hardware used to interconnect computers and users. Infrastructure includes the transmission media, including telephone lines, cable television lines, and satellites and antennas, and also the routers, aggregators, repeaters, and other devices that control transmission paths. Infrastructure also includes the software used to send, receive, and manage the signals that are transmitted.

In some usages, infrastructure refers to interconnecting hardware and software and not to computers and other devices that are interconnected. However, to some information technology users, infrastructure is viewed as everything that supports the flow and processing of information.

Infrastructure companies play a significant part in evolving the Internet, both in terms of where the interrconnections are placed and made accessible and in terms of how much information can be carried how quickly.

ITU-T
Organizations

International Telecommunication Union Telecommunication Standardization Sector. International body that develops worldwide standards for telecommunications technologies. The ITU-T carries out the functions of the former CCITT. See also CCITT.

IXC
Organizations

An IXC (interexchange carrier) is a telephone company that provides connections between local exchanges in different geographic areas. IXCs provide interlocal access and transport area service as described in the Telecommunications Act of 1996. They're commonly referred to as simply "long-distance carriers." IXCs include AT&T, MCI, Sprint, and others.

J

J2EE
Programming

The JavaTM 2 Enterprise Edition (J2EE) software specification describes a collection of server-side application programming interfaces (APIs) that provide the functionality for server-side delivery of data and for thin-client software that interacts with users throughout the enterprise. Many Java application vendors have been delivering implementations of the server-side APIs for the last three years, as the individual API specifications have emerged.

The Java technology group at Sun recently (re-)organized many of the Java APIs into three major categories:

Note that all enterprise-related functionality is not located in the J2EE API group; for example, Common Object Request Broker Architecture (CORBA) support, the Java Interface Definition Language (Java IDL), and JDBC are part of the J2SE group.

The J2EE specification includes the following:

An acronym legend follows:

The Java Technology Products & APIs site provides complete coverage of the Java-related technologies, some of which are beyond the scope of this article. The Object Management Group site provides complete coverage, including many tutorials, for IIOP- and ORB-related topics.

Jabber
Networking

1. Error condition in which a network device continually transmits random, meaningless data onto the network. 2. In IEEE 802.3, a data packet whose length exceeds that prescribed in the standard.

Jack
Hardware

The female connector.

Jack Kilby
People

In 1959 electrical engineer Jack S. Kilby invented the monolithic integrated circuit, which is still widely used in electronic systems.

Born in Jefferson City, Missouri, Kilby received a B.S.E.E. degree from the University of Illinois in 1947 and an M.S.E.E. from the University of Wisconsin in 1950.

From 1947 to 1958 he was responsible for the design and development of thick film integrated circuits at the Centralab Division of Globe Union Inc. in Milwaukee. In 1958 he joined Texas Instruments Inc. in Dallas where he was responsible for integrated circuit development and applications. Within a year he had invented the monolithic integrated circuit.

In 1970 Kilby began a leave of absence from the company to work as an individual inventor. Much of his recent work has been directed toward the development of a novel solar energy system.

Jacket
Hardware

The protective outer covering of a computer or network cable.

JANET
Organizations

Joint Academic Network. X.25 WAN connecting university and research institutions in the United Kingdom.

Java
Software

A high-level programming language developed by Sun Microsystems. Java was originally called OAK, and was designed for handheld devices and set-top boxes. Oak was unsuccessful so in 1995 Sun changed the name to Java and modified the language to take advantage of the burgeoning World Wide Web. Java is an object-oriented language similar to C++, but simplified to eliminate language features that cause common programming errors. Java source code files (files with a .java extension) are compiled into a format called bytecode (files with a .class extension), which can then be executed by a Java interpreter. Compiled Java code can run on most computers because Java interpreters and runtime environments, known as Java Virtual Machines (VMs), exist for most operating systems, including UNIX, the Macintosh OS, and Windows. Bytecode can also be converted directly into machine language instructions by a just-in-time compiler (JIT). Java is a general purpose programming language with a number of features that make the language well suited for use on the World Wide Web. Small Java applications are called Java applets and can be downloaded from a Web server and run on your computer by a Java-compatible Web browser, such as Netscape Navigator or Microsoft Internet Explorer.

JavaScript
Software

JavaScript is a scripting language developed by Netscape to enable Web authors to design interactive sites. Although it shares many of the features and structures of the full Java language, it was developed independently. Javascript can interact with HTML source code, enabling Web authors to spice up their sites with dynamic content. JavaScript is endorsed by a number of software companies and is an open language that anyone can use without purchasing a license. It is supported by recent browsers from Netscape and Microsoft, though Internet Explorer supports only a subset, which Microsoft calls Jscript.

Jerry D. Merryman
People

Scientists might come up with great ideas for new technology, but it doesn't make much of a difference unless manufacturers start using the ideas. In the case of the integrated chip, industry was pretty slow on the uptake. The new chip, with its collection of transistors all made from a single crystal, could miniaturize practically anything -- if only someone was interested.

To snag the world's attention, Texas Instruments needed a marketing gimmick. They wanted a flashy product to showcase the IC. A calculator seemed just the thing. In a mere two years, a TI group including Jerry Merryman and James Van Tassel, and led by Jack Kilbydeveloped a calculator small enough to be held in your hand. Just over six inches tall, this portable calculator certainly surpassed the all-transistor calculator released just a year earlier -- that calculator weighed 55 pounds and cost $2,500.

Jerry D. Merryman joined TI in 1963 and remains with the company today; he has worked as an engineer in the design and development of a variety of products and technologies. In addition to his work on the hand-held calculator, Merryman was instrumental in designing and fabricating semiconductor manufacturing equipment. He also made significant contributions to the thermal printing devices that TI used for years in a popular family of data terminal products.

John von Neumann
People

Born in Budapest, Hungary in 1903. After simultaneously earning a doctorate in mathematics from the University of Budapest and a doctorate in chemistry from the University of Zurich, he joined the faculty of the University of Berlin in 1927. He moved to Princeton in 1932 where he became the youngest member of the IAS. During this time, he made important contributions not only to pure and applied mathematics, but also to physics and, in some ways, philosophy (esp. in relation to the quantum paradox). He was also active in the Manhattan Project (the development of the atomic bomb) and was one of President Truman's advisors on the Atomic Energy Commission. His later work on parallel processes and networks has earned him the label of the "father of the modern computer". As Nicholas Kaldor would later write, "He was unquestionably the nearest thing to a genius I have ever encountered."

An astoundingly creative mathematician, John von Neumann has played a rather important role in post-war economic theory through two essential pieces of work: his 1937 paper on a multi-sectoral growth model and his 1944 book (with Oskar Morgenstern) on game theory and uncertainty.

JPEG (or JPG)
Lingo

JPEG (or JPG) Joint Photographic Experts Group: a type of image file, similar to GIF. Whereas the GIF file format is limited to 256 colors or less, JPEG files use millions of colors and can often be compressed to a smaller kilobyte size, making Web pages load faster.

JSP
Programming

Java Server Page (JSP) is a technology for controlling the content or appearance of Web pages through the use of servlets, small programs that are specified in the Web page and run on the Web server, to modify the Web page before it is sent to the user who requested it. Sun Microsystems, the developer of Java, also refers to the JSP technology as the Servlet application program interface (API). JSP is comparable to Microsoft's Active Server Page (ASP) technology. Whereas a Java Server Page calls a Java program that is executed by the Web server, an Active Server Page contains a script that is interpreted by a script interpreter (such as VBScript or JScript) before the page is sent to the user.

Jumper
Hardware

Electrical switch consisting of a number of pins and a connector that can be attached to the pins in a variety of different ways. Different circuits are created by attaching the connector to different pins.

JUNET
Organizations

Japan UNIX Network. Nationwide, noncommercial network in Japan, designed to promote communication between Japanese and other researchers.

K

Karn's Algorithm
Concept

Algorithm that improves round-trip time estimations by helping transport layer protocols distinguish between good and bad round-trip time samples.

Kbps
Telecommunications

Short for kilobits per second, a measure of data transfer speed. Modems, for example, are measured in Kbps. Note that one Kbps is 1,000 bits per second, whereas a KB (kilobyte) is 1,024 bytes. Data transfer rates are measured using the decimal meaning of K whereas data storage is measured using the powers-of-2 meaning of K. Technically, kbps should be spelled with a lowercase k to indicate that it is decimal but almost everyone spells it with a capital K.

KByte
Networking

A unit of measure used to describe an amount of information equal to 1024 (210) bytes.

Keepalive Interval
Networking

Period of time between each keepalive message sent by a network device.

Keepalive Message
Networking

Message sent by one network device to inform another network device that the virtual circuit between the two is still alive.

Kenan
Software

Kenan, Arbor and iCare are often used interchangeably in Verio. Kenan is the company that makes Arbor, the billing software. iCare is the web interface for Arbor.

Kermit
Protocol

A communications protocol and set of associated software utilities developed at Columbia University. Kermit can be used to transfer files or for terminal emulation. It is frequently used with modem connections, although it also supports communications via other transport mechanisms such as TCP/IP. Kermit is noted for its transmission accuracy and slow transmission speeds due to its default settings that optimize for accuracy. However, Kermit can also be tuned to transfer data as quickly as any other data transfer protocol. Kermit is not in the public domain, but Columbia University allows people to use the protocol for free, so almost all communications products support it. However, not all implementations support the full protocol. This has led some people to refer to an advanced version of Kermit as Super Kermit. Actually, there is only one version of the Kermit protocol, which supports all the advanced features usually attributed to Super Kermit, such as sliding windows and long packets. Other file-transfer protocols used by modems include Xmodem and Zmodem.

Kevin Mitnick
People

Mitnick is arguably the world's most well known hacker. His latest imprisonment became an international cause for the hacker community, spear headed by his long time friend, Emmanuel Goldstein.

Mitnick's latest imprisonment wasn't his first, however. He was first arrested when he was 17 for stealing computer manuals. Arrests for other crimes came in 1983 and 1987. In 1988, when he was 25, the FBI arrested him for stealing software from Digital Equipment, a crime which he spent 8 months in prison for.

Fighters for Mitnick's cause run the Official Kevin Mitnick Website, where his life and legal problems are well documented.

Kevin Mitnick has become the focus of several books, including Tsutomu Shimomura's controversial "Takedown: The Pursuit and Capture of America's Most Wanted Computer Outlaw -- By The Man Who Did It."

Kilobit
Telecommunications

One thousand bits. It is usually used to designate 2 to the 10th bits, which is actually 1024 bits. One or more characters or words which are used to identify a record, message or file in an information handling system.

Kilobyte (KB)
Lingo

Kilobyte (KB) A thousand bytes. To be more accurate, one kilobyte actually contains 1024 bytes. Since the prefix "kilo" is associated with 1000, the term kilobyte is used to define 1024 bytes.

Kludge
Lingo

A word used to describe a solution to a problem that lacks elegance or that contains components for a purpose significantly different that their original design purpose.

Konrad Zuse
People

Konrad Zuse is popularly recognized in Germany as the "father of the computer" and his Z1, a programmable automaton built from 1936 to 1938, has been called the "first computer" in the world. Other nations reserve this privilege for one of their own scientists and there has been a long and often acrimonious debate on the issue of the 'true' inventor of the computer. Sometimes the discussion is preempted by specifying in full detail the technological features of a specific machine. The ENIAC, for example, has been called the first large scale general purpose electronic computer in the world. The ENIAC (acronym for Electronic Numerical Integrator and Computer) was built at the Moore School of Electrical Engineering of the University of Pennsylvania from May 1943 to 1945. It solved its first problem in December 1945 and was officially presented in February 1946. Another contender for the title of first computer is the Mark I built by Howard Aiken at Harvard University between 1939 to 1944. The Mark I was an electro mechanical machine, a kind of hybrid between the totally mechanical nature of previous computing devices and the electronics available at the time (Aiken, Hopper 46). The machine built by John Atanasoff (later called the ABC) at Iowa State College from 1938 to 1942 used vacuum tubes, but was restricted to the addition and subtraction of vectors and had an structure inappropriate for universal computation [Burks, Burks 88]. In direct contrast to these three machines, the Z1 was far more flexible and was designed to execute a long and modifiable sequence of instructions contained on a punched tape. Zuse's machines were not purely electronic and were of reduced size. Since the Z1 was completed prior to the Mark I, it has been called the first programmable calculating machine in the world. Of course the old debate will not be closed with this paper, but we want to show here just how advanced the machines built by Zuse were when considered from the viewpoint of modern computer architecture and compared with other early designs of the time.

The university student Konrad Zuse started thinking about computing machines in the 1930s. He realized that he could construct an automaton capable of executing a sequence of arithmetical operations like those needed to compute mathematical tables. Coming from a civil engineering background, he had no formal training in electronics and was not acquainted with the technology used in conventional mechanical calculators. This nominal deficit worked to his advantage, however, because he had to rethink the whole problem of arithmetic computation and thus hit on new and original solutions.

Zuse decided to build his first experimental calculating machine exploiting two main ideas:

  1. The machine would work with binary numbers
  2. The computing and control unit would be separated from the storage
Years before John von Neumann explained the advantages of a computer architecture in which the processor is separated from the memory, Zuse had already arrived at the same conclusions. In 1936 the memory of the planned machine was completed. It was a mechanical device but not of the usual type. Instead of using gears (as done by Babbage in the previous century), Zuse implemented logical and arithmetical operations using sliding metallic rods. The rods could move only in one of two directions (forward or backward) and were therefore appropriate for a binary machine [Zuse 70]. The processor of the Z1 was completed a few months after the storage unit, using the same kind of technology. It worked in concert with the memory but was never very reliable. The main problem was the precise synchronization that was needed in order to avoid applying excessive mechanical stress on the moving parts. It is interesting to point out that in the same year as the memory of the Z1 was completed, Alan Turing wrote his ground-breaking paper on computable numbers in which he formalized the intuitive concept of computability.

The Z1, although unreliable, showed that the architectural design was sound and compelled Zuse to start investigating other kinds of technology. Following the advice of his friend Helmut Schreyer, he considered using vacuum tubes, but gave up the idea in favor of electro mechanical relays which were easier to obtain before and during the war. An "intermediate" simpler model (the Z2) was built using a hybrid approach (a processor built out of relays and a mechanical memory). Immediately afterwards Zuse started building the Z3, a machine consisting purely of relays but with the same logical structure as the Z1. It was ready and operational in 1941 four years before the ENIAC.

L

L2TP
Protocol

Short for Layer Two Tunneling Protocol, an extension to the PPP protocol that enables ISPs to operate Virtual Private Networks (VPNs). L2TP merges the best features of two other tunneling protocols: PPTP from Microsoft and L2F from Cisco Systems. Like PPTP, L2TP requires that the ISP's routers support the protocol.

Label Swapping
Networking

Routing algorithm used by APPN in which each router that a message passes through on its way to its destination independently determines the best path to the next router.

LAN
Concept

LAN Local Area Network: A computer network limited to the immediate area, usually the same building or floor of a building.

LAN Manager
Software

Distributed NOS, developed by Microsoft, that supports a variety of protocols and platforms.

LAN Server
Hardware

A general term used to describe a device that manages and allows the use of more than one kind of resource such as storage or file services, print services, communication services, data base services, etc.

LAN Switch
Hardware

High-speed switch that forwards packets between data-link segments. Most LAN switches forward traffic based on MAC addresses. This variety of LAN switch is sometimes called a frame switch. LAN switches are often categorized according to the method they use to forward traffic: cut-through packet switching or store-and-forward packet switching. Multilayer switches are an intelligent subset of LAN switches. Compare with multilayer switch. See also cut-through packet switching and store and forward packet switching.

LANE
Networking

LAN emulation. Technology that allows an ATM network to function as a LAN backbone. The ATM network must provide multicast and broadcast support, address mapping (MAC-to-ATM), SVC management, and a usable packet format. LANE also defines Ethernet and Token Ring ELANs. See also ELAN.

LAP
Protocol

Link Access Protocol. Any protocol of the Data Link Layer, such as EtherTalk.

LAPB
Lingo

Link Access Procedure, Balanced. Data link layer protocol in the X.25 protocol stack. LAPB is a bit-oriented protocol derived from HDLC. See also HDLC and X.25.

LAPD
Lingo

Link Access Procedure on the D channel. ISDN data link layer protocol for the D channel. LAPD was derived from the LAPB protocol and is designed primarily to satisfy the signaling requirements of ISDN basic access. Defined by ITU-T Recommendations Q.920 and Q.921.

LAPF
Telecommunications

LAPF , or Link Access Procedure to Frame Mode Bearer Services (FR, ISDN), is a modified LAPD standard for Frame Relay. It provides capabilities to establish and release data link connections, transfer acknowledged and unacknowledged data, flow control the transfer of data, and reinitialize the data link connection on detecting an error.

The format of the header is shown in the following illustration.

8 7 6 5 4 3 2 1

Default address field format

(2 octets)

Upper DLCI C/R EA
0
Lower DLCI FECN
(Note)
BECN
(Note)
DE
(Note)
EA
1

EA
Address field extension bit.

C/R
Command Response bit.

FECN
Forward Explicit Congestion Notification.

BECN
Backward Explicit Congestion Notification.

DLCI
Data Link Connection Identifier.

DE
Discard Eligibility indicator.

Larry Wall
People

Larry Wall originally created Perl while a programmer at Unisys. He now works full time guiding the future development of the language as a researcher and developer at O'Reilly & Associates. Larry is known for his idiosyncratic and thought-provoking approach to programming, as well as for his groundbreaking contributions to the culture of free software programming. He is the principal author of the bestselling Programming Perl, known colloquially as "the Camel book."

A snippet from an interview of Larry Wall in the Linux Journal gives this description of why the language is named perl.

"I wanted a short name with positive connotations. (I would never name a language ``Scheme'' or ``Python'', for instance.) I actually looked at every three- and four-letter word in the dictionary and rejected them all. I briefly toyed with the idea of naming it after my wife, Gloria, but that promised to be confusing on the domestic front. Eventually I came up with the name ``pearl'', with the gloss Practical Extraction and Report Language. The 'a' was still in the name when I made that one up. But I heard rumors of some obscure graphics language named 'pearl', so I shortened it to ``perl''. (The ``a'' had already disappeared by the time I gave Perl its alternate gloss, Pathologically Eclectic Rubbish Lister.)

Another interesting tidbit is that the name ``perl'' wasn't capitalized at first. UNIX was still very much a lower-case-only OS at the time. In fact, I think you could call it an anti-upper-case OS. It's a bit like the folks who start posting on the Net and affect not to capitalize anything. Eventually, most of them come back to the point where they realize occasional capitalization is useful for efficient communication. In Perl's case, we realized about the time of Perl 4 that it was useful to distinguish between ``perl'' the program and ``Perl'' the language. If you find a first edition of the Camel Book, you'll see that the title was Programming perl, with a small ``p''. Nowadays, the title is Programming Perl. "

Laser
Networking

Light amplification by simulated emission of radiation. Analog transmission device in which a suitable active material is excited by an external stimulus to produce a narrow beam of coherent light that can be modulated into pulses to carry data. Networks based on laser technology are sometimes run over SONET.

LaserWriter
Hardware

Any of a group of laser printers that uses PostScript as an imaging language and can communicate using AppleTalk protocols.

LATA
Telecommunications

Local Access Transport Areas (200 in the U.S.). A geographic service area defined in the AT&T Modified Final Judgement. The RBOCs (baby Bells) and GTE are restricted to operations within, but not between, LATAs. Long distance service within a LATA is provided by the LEC. Service between LATAs is provided by an IEC. LATAs are represented by a 3-character code.

Latency
Networking

(1) In general, the period of time that one component in a system is spinning its wheels waiting for another component. Latency, therefore, is wasted time. For example, in accessing data on a disk, latency is defined as the time it takes to position the proper sector under the read/write head.

(2) In networking, the amount of time it takes a packet to travel from source to destination. Together, latency and bandwidth define the speed and capacity of a network.

Layer
Concept

A term used to describe a group of communication functions and the protocols implemented to perform them as defined by a network standards organization, most often referring to a group of functions as described by the OSI 7-Layer Model designated by the ISO.

Layer Two Forwarding
Protocol

Often abbreviated as L2F, a tunneling protocol developed by Cisco Systems. L2F is similar to the PPTP protocol developed by Microsoft, enabling organizations to set up virtual private networks (VPNs) that use the Internet backbone to move packets. Recently, Microsoft and Cisco agreed to merge their respective protocols into a single, standard protocol called Layer Two Tunneling Protocol(L2TP).

LDAP
Protocol

Short for Lightweight Directory Access Protocol, a set of protocols for accessing information directories. LDAP is based on the standards contained within the X.500 standard, but is significantly simpler. And unlike X.500, LDAP supports TCP/IP, which is necessary for any type of Internet access. Because it's a simpler version of X.500, LDAP is sometimes called X.500-lite. Although not yet widely implemented, LDAP should eventually make it possible for almost any application running on virtually any computer platform to obtain directory information, such as email addresses and public keys. Because LDAP is an open protocol, applications need not worry about the type of server hosting the directory.

Leaf Internetwork
Networking

In a star topology, an internetwork whose sole access to other internetworks in the star is through a core router.

Learning Bridge
Hardware

Bridge that performs MAC address learning to reduce traffic on the network. Learning bridges manage a database of MAC addresses and the interfaces associated with each address. See also MAC address learning.

Leased Line
Telecommunications

A permanent telephone connection between two points set up by a telecommunications common carrier. Typically, leased lines are used by businesses to connect geographically distant offices. Unlike normal dial-up connections, a leased line is always active. The fee for the connection is a fixed monthly rate. The primary factors affecting the monthly fee are distance between end points and the speed of the circuit. Because the connection doesn't carry anybody else's communications, the carrier can assure a given level of quality. For example, a T-1 channel is a type of leased line that provides a maximum transmission speed of 1.544 Mbps. You can divide the connection into different lines for data and voice communication or use the channel for one high speed data circuit. Dividing the connection is called multiplexing. Increasingly, leased lines are being used by companies, and even individuals, for Internet access because they afford faster data transfer rates and are cost-effective if the Internet is used heavily.

LEC
Lingo

1. LAN Emulation Client. Entity in an end system that performs data forwarding, address resolution, and other control functions for a single ES within a single ELAN. A LEC also provides a standard LAN service interface to any higher-layer entity that interfaces to the LEC. Each LEC is identified by a unique ATM address, and is associated with one or more MAC addresses reachable through that ATM address. See also ELAN and LES.

LECS
Hardware

LAN Emulation Configuration Server. Entity that assigns individual LANE clients to particular ELANs by directing them to the LES that corresponds to the ELAN. There is logically one LECS per administrative domain, and this serves all ELANs within that domain. See also ELAN.

LED
Lingo

Light emitting diode. Semiconductor device that emits light produced by converting electrical energy. Status lights on hardware devices are typically LEDs.

Level 1 Router
Hardware

Device that routes traffic within a single DECnet or OSI area.

Level 2 Router
Hardware

Device that routes traffic between DECnet or OSI areas. All Level 2 routers must form a contiguous network.

Line
Telecommunications

Line has the following definitions:

  1. A pair of wires carrying direct current between a central office and a customer's terminal. A line is the most common type of loop. (also see loop)
  2. In carrier systems, the portion of a transmission system that extends between two terminal locations. The line includes the transmission media and associated line repeaters.
  3. Also used to indicate the side of a piece of central office equipment that connects to or toward the outside plant, the other side of the equipment is called the telco drop side.
  4. A family of equipment or apparatus designed to provide a variety of styles, a range of sizes, or a choice of service features.

Line Code Type
Programming

One of a number of coding schemes used on serial lines to maintain data integrity and reliability. The line code type used is determined by the carrier service provider. See also AMI and HBD3.

Line Conditioning
Networking

Use of equipment on leased voice-grade channels to improve analog characteristics, thereby allowing higher transmission rates.

Line Driver
Hardware

Inexpensive amplifier and signal converter that conditions digital signals to ensure reliable transmissions over extended distances.

Line Noise
Telecommunications

Noise originating in a transmission path.

Line of Sight
Networking

Characteristic of certain transmission systems, such as laser, microwave, and infrared systems, in which no obstructions in a direct path between transmitter and receiver can exist.

Line Speed
Telecommunications

The maximum rate at which signals may be transmitted over a given channel. It is usually measured in baud or bits per second.

Line Turnaround
Networking

Time required to change data transmission direction on a telephone line.

Link
Software

  1. Using hypertext, a link is a selectable connection from one word, picture, or information object to another. In a multimedia environment such as the World Wide Web, such objects can include sound and motion video sequences. The most common form of link is the highlighted word or picture that can be selected by the user (with a mouse or in some other fashion), resulting in the immediate delivery and view of another file. The highlighted object is referred to as an anchor. The anchor reference and the object referred to constitute a hypertext link.

    Although most links do not offer the user a choice of types of link, it would be possible for the user to be provided a choice of link types, such as: a definition of the object, an example of it, a picture of it, a smaller or larger picture of it, and so forth.
  2. In telecommunications, a link is a physical (and, in some usages, a logical) connection between two points.

Link State Routing
Protocol

A routing protocol that takes link loading and bandwidth when selecting between alternate routes. Example: OSPF.

Link State Routing Algorithm
Concept

Routing algorithm in which each router broadcasts or Algorithm multicasts information regarding the cost of reaching each of its neighbors to all nodes in the internetwork. Link state algorithms create a consistent view of the network and are therefore not prone to routing loops, but they achieve this at the cost of relatively greater computational difficulty and more widespread traffic (compared with distance vector routing algorithms). Compare with distance vector routing algorithm. See also Dijkstra's algorithm.

Linus Torvalds
People

Linus Torvald is the creator of the underground and now famous Linux operating system, created initially as a hobby by the young student at the University of Helsinki in Finland. Linus had an interest in Minix, a small UNIX system, and decided to develop a system that exceeded the Minix standards. He began his work in 1991 when he released version 0.02 and worked steadily until 1994 when version 1.0 of the Linux Kernel was released.

This is the only operating system developed by freelance programmers who collaborated from all over the world. Torvald started with UNIX and C classes in the early 1990's.

Linus' contact information is available freely on the web and is:

Snail-mail (work):
     Linus Torvalds
     Transmeta Corp 
     3940 Freedom Circle 
     Santa Clara, CA 95054 
     USA 
Phone (work): 
     +1 (408) 327 9830 x328 
Email: 
     torvalds@transmeta.com

Linux
Software

Linux (often pronounced LIH-nuhks with a short "i") is a UNIX-like operating system that was designed to provide personal computer users a free or very low-cost operating system comparable to traditional and usually more expensive UNIX systems. Linux has a reputation as a very efficient and fast-performing system. Linux's kernel (the central part of the operating system) was developed by Linus Torvalds at the University of Helsinki in Finland. To complete the operating system, Torvalds and other team members made use of system components developed by members of the Free Software Foundation for the GNU project.

Linux is a remarkably complete operating system, including a graphical user interface, X Window System, TCP/IP, the Emacs editor, and other components usually found in a comprehensive UNIX system. Although copyrights are held by various creators of Linux's components, Linux is distributed using the Free Software Foundation copyleft stipulations that mean any copy is in turn freely available to others.

Unlike Windows and other proprietary systems, Linux is publicly open and extendible by contributors. Because it conforms to the Portable Operating System Interface standard user and programming interfaces, developers can write programs that can be ported to other operating systems, including IBM's OS/390 running UNIX. Linux comes in versions for all the major microprocessor platforms including the Intel, , Sparc, and Alpha platforms. Linux is distributed commercially by a number of companies. A magazine, Linux Journal, is published as well as a number of books and pocket references.

Linux is sometimes suggested as a possible publicly-developed alternative to the desktop predominance of Microsoft Windows. Although Linux is popular among users already familiar with UNIX, it remains far behind Windows in numbers of users.

LLC
Lingo

Logical Link Control.

LMI
Lingo

Local Management Interface. Set of enhancements to the basic Frame Relay specification. LMI includes support for a keepalive mechanism, which verifies that data is flowing; a multicast mechanism, which provides the network server with its local DLCI and the multicast DLCI; global addressing, which gives DLCIs global rather than local significance in Frame Relay networks; and a status mechanism, which provides an on-going status report on the 'DLC Is known to the switch. Known as LMT in ANSI terminology.

LOA
Telecommunications

Letter of Agency. A letter that you give to someone whom you allow to represent you and act on your behalf.

Load
Telecommunications

A volume of traffic that equals the sum of the holding times for a number of calls or attempts. Loads are normally expressed in either CCS or ERLANGS. A statement of load is inherently an average of all of the instantaneous loads over a basic time interval such as an hour.

Load Balancing
Networking

Distributing processing and communications activity evenly across a computer network so that no single device is overwhelmed. Load balancing is especially important for networks where it's difficult to predict the number of requests that will be issued to a server. Busy Web sites typically employ two or more Web servers in a load balancing scheme. If one server starts to get swamped, requests are forwarded to another server with more capacity. Load balancing can also refer to the communications channels themselves.

Loading Coil
Telecommunications

A loading coil is an induction device placed on a local loop longer than 18,000 feet that carries analog signals. The device compensates for wire capacitance and boosts the frequencies carrying the voice information. Loading coils cause distortion at the higher frequencies used to carry digital information and so are not used on these local loops.

Local Access Rate
Networking

In a Frame Relay network, the Local Access Rate is simply the rate at which data comes into or out of an interface and is a multiple of either 56Kbps or 64kbps.

Local Bridge
Hardware

Bridge that directly interconnects networks in the same geographic area.

Local Loop
Telecommunications

In telephony, a local loop is the wired connection from a telephone company's central office in a locality to its customers' telephones at homes and businesses. This connection is usually on a pair of copper wires called twisted pair. The system was originally designed for voice transmission only using analog transmission technology on a single voice channel. Today, your computer's modem makes the conversion between analog signals and digital signals. With Integrated Services Digital Network or Digital Subscriber Line, the local loop can carry digital signals directly and at a much higher bandwidth than they do for voice only. Also known as the Circuit and Last Mile.

Local Traffic Filtering
Networking

Process by which a bridge filters out (drops) frames whose source and destination MAC addresses are located on the same interface on the bridge, thus preventing unnecessary traffic from being forwarded across the bridge. Defined in the IEEE 802.1 standard. See also IEEE 802.1.

Local-Area Network
Networking

A computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a wide-area network (WAN).

Most LANs connect workstations and personal computers. Each node (individual computer ) in a LAN has its own CPU with which it executes programs, but it is also able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data. Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions.

There are many different types of LANs Ethernets being the most common for PCs. Most Apple Macintosh networks are based on Apple's AppleTalk network system, which is built into Macintosh computers.

The following characteristics differentiate one LAN from another:

Log File
Networking

A file that contains a list of actions that have occurred on your web server. The statistics of your site are created by referencing the activity log file.

Logical Channel
Networking

Nondedicated, packet-switched communications path between two or more network nodes. Packet switching allows many logical channels to exist simultaneously on a single physical channel.

Login
Networking

A formal procedure where a computing device initiates a sustained connection to another computing device for the purpose of using a resource managed by the computer.

Logout
Networking

A Formal procedure where a computing device severs its connection to another computing device.

Loop
Networking

Route where packets never reach their destination, but simply cycle repeatedly through a constant series of network nodes.

Loopback packet
Networking

A test packet sent by a network adapter with a destination address equal to the adapter's own hardware address. The purpose of this test is typically to establish that the adapter is connected to a network that is functional enough to support a data transmission.

Loopback Test
Telecommunications

A diagnostic test in which the transmitted signal is returned to the sending device after passing through a data communications link or network. This allows a technician to compare the transmitted signal with the return signal and get some sense of what's wrong.

Loss
Networking

The aggregate attenuation of a signal due to interaction with its environment.

LPD
Lingo

Line printer daemon. Protocol used to send print jobs between UNIX systems.

M

M23
Telecommunications

Multiplex 2-to-3. A DS-3 (T-3) signal format that combines seven DS-2s (T-2s) to from a DS-3 (T-3). M23 multiplexor (MUX) combines 7 T-2s into a T-3 at a total signaling rate of 44.736 Mbps, adding more signaling and control bits than the previous technologies of M24 and M12.

MAC
Lingo

Media Access Control. The method whereby a computing device takes control of the transmission media for the purpose of sending an information packet.

Mac address
Networking

Standardized data link layer address that is required for every port or device that connects to a LAN. Other devices in the network use these addresses to locate specific ports in the network and to create and update routing tables and data structures. MAC addresses are 6 bytes long and are controlled by the IEEE. Also known as a hardware address, a MAC-layer address, or a physical address.

MAC address learning
Networking

Service that characterizes a learning bridge, in which the source MAC address of each received packet is stored so that future packets destined for that address can be forwarded only to the bridge interface on which that address is located. Packets destined for unrecognized addresses are forwarded out every bridge interface. This scheme helps minimize traffic on the attached LANs. MAC address learning is defined in the IEEE 802.1 standard.

Machine Language
Software

Machine Language is the lowest-level programming language (except for computers that utilize programmable microcode) Machine languages are the only languages understood by computers. While easily understood by computers, machine languages are almost impossible for humans to use because they consist entirely of numbers. Programmers, therefore, use either a high-level programming language or an assembly language. An assembly language contains the same instructions as a machine language, but the instructions and variables have names instead of being just numbers.

Programs written in high-level languages are translated into assembly language or machine language by a compiler. Assembly language programs are translated into machine language by a program called an assembler.

Every CPU has its own unique machine language. Programs must be rewritten or recompiled, therefore, to run on different types of computers.

MacIP
Protocol

Network layer protocol that encapsulates IP packets in DDS or transmission over AppleTalk. MacIP also provides proxy ARP services.

Magnetic field
Lingo

The area surrounding an electrically charged body in which an electromagnetic force can be detected.

Mail Forwarding
Networking

When you sign up for an Ameritech hosting plan, you'll receive a domain email account (you@yourname.com). You might also have an email address provided by your local ISP. With mail forwarding, all email addressed to you@yourname.com will be sent to your "real" email address. Additional mail forwarding options include the ability to forward different yourname.com email to specific addresses on the Internet. For example, email addressed to webmaster@yourname.com could forward to your "real" email address (provided by your ISP), while sales@yourname.com could forward to a different email address.

Mailing List
Lingo

A group discussion conducted through email messages, specific to a topic or common interest. When a message is sent to a mailing list, each list subscriber receives a copy.

Mainframe
Hardware

An expensive, general purpose computer with the ability to be used by many users simultaneously.

Male connector
Hardware

A connector whose points of electrical contact are exposed.

MAN
Networking

metropolitan-area network. Network that spans a metropolitan area. Generally, a MAN spans a larger geographic area than a LAN, but a smaller geographic area that a WAN.

Managed Object
Networking

In network management, a network device that can be managed by a network management protocol.

MAP
Protocol

Manufacturing Automation Protocol. Network architecture created by General Motors to satisfy the specific needs of the factory floor. MAP specifies a token-passing LAN similar to IEEE 802.4.

MAPI
Networking

Microsoft Application Programming Interface. A programming library for Windows developers that provides messaging services to their applications.

Mask
Networking

See address mask and subnet mask.

MAU
Networking

Media Access Unit. The component of a network adapter that directly attaches to the Transmission media.

Maximum Rate
Networking

Maximum total data throughput allowed on a given virtual circuit, equal to the sum of the insured and uninsured traffic from the traffic source. The uninsured data might be dropped if the network becomes congested. The maximum rate, which cannot exceed the media rate, represents the highest data throughput the virtual circuit will ever deliver, measured in bits or cells per second.

MBONE
Networking

Multicast backbone. The multicast backbone of the Internet. MBone is a virtual multicast network composed of multicast LANs and the point-to-point tunnels that interconnect them.

Mbps
Telecommunications

Short for megabytes per second, a measure of data transfer speed. Mass storage devices are generally measured in MBps.

MCA
Hardware

Micro channel architecture. Bus interface commonly used in PCs and some UNIX workstations and servers.

MCI
Hardware

Multiport Communications Interface. Card on the AGS+ that provides two Ethernet interfaces and up to two synchronous serial interfaces. The MCI processes packets rapidly, without the interframe delays typical of other Ethernet interfaces.

MCR
Lingo

minimum cell rate. Parameter defined by the ATM Forum for ATM traffic management. MCR is defined only for ABR transmissions, and specifies the minimum value for the ACR.

MD5
Software

An algorithm created in 1991 by Professor Ronald Rivest that is used to create digital signatures. It is intended for use with 32 bit machines and is safer than the MD4 algorithm, which has been broken. MD5 is a one-way hash function, meaning that it takes a message and converts it into a fixed string of digits, also called a message digest.

When using a one-way hash function, one can compare a calculated message digest against the message digest that is decrypted with a public key to verify that the message hasn't been tampered with. This comparison is called a "hashcheck."

Media
Networking

The environment in which the transmission signal is carried.

Media Rate
Networking

Maximum traffic throughput for a particular media type.

Megabyte (MB)
Lingo

A million bytes; a thousand kilobytes. To be more accurate, one megabyte actually contains 1,048,576 bytes. Since the prefix "mega" is associated with one million, the term megabyte is used to define 1,048,576 bytes.

Memory
Hardware

In computing, a system where data is stored for direct, highspeed access by a microprocessor.

Memory Allocation
Hardware

The amount of memory, usually RAM, that an process reserves for itself.

Mesh
Networking

Network topology in which devices are organized in a manageable, segmented manner with many, often redundant, interconnections strategically placed between network nodes.

Message
Networking

Application layer (Layer 7) logical grouping of information, often composed of a number of lower-layer logical groupings such as packets. The terms datagram, frame, packet, and segment are also used to describe logical information groupings at various layers of the OSI reference model.

Message Board
Networking

A type of bulletin board where users read and respond to other people's posts.

Message Digest
Software

The representation of text in the form of a single string of digits, created using a formula called a one-way hash function. Encrypting a message digest with a private key creates a digital signature, which is an electronic means of authentication.

Message Switching
Networking

Switching technique involving transmission of messages from node to node through a network. The message is stored at each node until such time as a forwarding path is available.

Message Unit
Networking

Unit of data processed by any network layer.

META tag
Programming

Hidden HTML code that contains information about a Web page, such as who created the page, what the page is about, and which keywords best describe the page's content. Some search engines use this information to list Web pages.

Metalanguage
Programming

A language that represents another language.

Metasignaling
Networking

Process running at the ATM layer that manages signaling types and virtual circuits.

Metcalfe's Law
Concept

"The power of the network increases exponentially by the number of computers connected to it. Therefore, every computer added to the network both uses it as a resource while adding resources in a spiral of increasing value and choice."
     - Bob Metcalfe

Metcalfe's Law is expressed in two general ways:

  1. The number of possible cross-connections in a network grow as the square of the number of computers in the network increases.
  2. The community value of a network grows as the square of the number of its users increase.

MHS
Lingo

1. Message Handling Service. A synonym of X.400 store and forward messaging. 2. Message Handling System. A Novell protocol for mail handling.

MIB
Lingo

Management Information Base. In SNMP, a specification of the data objects and data structures that the Agent is responsible for knowing and reporting to the Console on demand.

MIC
Hardware

Media interface connector. FDDI de facto standard connector.

Micro
Lingo

1. A prefix that denotes a one millionth part of a unit of measure, such as a microsecond or microampere. 2. A prefix that denotes something small. 3. A slang term for any personal computer.

Microcode
Networking

Translation layer between machine instructions and the elementary operations of a computer. Microcode is stored in ROM and allows the addition of new machine instructions without requiring that they be designed into electronic circuits when new instructions are needed.

Microsegmentation
Networking

Division of a network into smaller segments, usually with the intention of increasing aggregate bandwidth to network devices.

Microwave
Networking

1. Any electromagnetic radiation with a wavelength between 1 millimeter and 1 meter. 2. A point-to-point data transmission system employing electromagnetic radiation using a carrier frequency in the microwave region.

Middleware
Software

Software that connects two otherwise separate applications. For example, there are a number of middleware products that link a database system to a Web server. This allows users to request data from the database using forms displayed on a Web browser, and it enables the Web server to return dynamic Web pages based on the user's requests and profile. The term middleware is used to describe separate products that serve as the glue between two applications. It is, therefore, distinct from import and export features that may be built into one of the applications. Middleware is sometimes called plumbing because it connects two sides of an application and passes data between them. Common middleware categories include: TP monitors DCE environments RPC systems Object Request Brokers (ORBs) Database access systems Message Passing

MIDI
Lingo

Musical Instrument Digital Interface: A computerized music file, often used on Web pages.

Midsplit
Hardware

Broadband cable system in which the available frequencies are split into two groups: one for transmission and one for reception.

Milli
Lingo

A prefix denoting a one thousandth part of a unit of measure, such as a millisecond or millimeter.

MILNET
Networking

Military Network. Unclassified portion of the DDN. Operated and maintained by the DISA.

MIME
Protocol

Short for Multipurpose Internet Mail Extensions, a specification for formatting non-ASCII messages so that they can be sent over the Internet. Many e-mail clients now support MIME, which enables them to send and receive graphics, audio, and video files via the Internet mail system. In addition, MIME supports messages in character sets other than ASCII. There are many predefined MIME types, such as GIF graphics files and PostScript files. It is also possible to define your own MIME types. In addition to e-mail applications, Web browsers also support various MIME types. This enables the browser to display or output files that are not in HTML format. MIME was defined in 1992 by the Internet Engineering Task Force (IETF). A new version, called S/MIME, supports encrypted messages.

Mips
Lingo

Millions of instructions per second. Number of instructions executed by a processor per second.

MIS
Lingo

Management Information System. Used to describe the set of computing resources that hold and allow access to the information owned by an organization.

Mode
Lingo

1. One particular method or way of accomplishing a goal. 2. In fiber optic transmission, a particular path between a light source and a receiver. 3. In statistics, the result with the highest frequency within the sample group.

Modem
Hardware

A modem modulates outgoing digital signals from a computer or other digital device to analog signals for a conventional copper twisted pair telephone line and demodulates the incoming analog signal and converts it to a digital signal for the digital device.

In recent years, the 2400 bits per second modem that could carry e-mail has become obsolete. 14.4 Kbps and 28.8 Kbps modems were temporary landing places on the way to the much higher bandwidth devices and carriers of tomorrow. From early 1998, most new personal computers came with 56 Kbps modems. By comparison, using a digital Integrated Services Digital Network adapter instead of a conventional modem, the same telephone wire can now carry up to 128 Kbps. With Digital Subscriber Line (Digital Subscriber Line) systems, now being deployed in a number of communities, bandwidth on twisted-pair can be in the megabit range.

Modulation
Networking

Process by which the characteristics of electrical signals are transformed to represent information. Types of modulation include AM, FM, and PAM.

Moore's Law
Concept

In 1965, Gordon Moore was preparing a speech and made a memorable observation. When he started to graph data about the growth in memory chip performance, he realized there was a striking trend. Each new chip contained roughly twice as much capacity as its predecessor, and each chip was released within 18-24 months of the previous chip. If this trend continued, he reasoned, computing power would rise exponentially over relatively brief periods of time.

Moore's observation, now known as Moore's Law, described a trend that has continued and is still remarkably accurate. It is the basis for many planners' performance forecasts. In 26 years the number of transistors on a chip has increased more than 3,200 times, from 2,300 on the 4004 in 1971 to 7.5 million on the Pentium® II processor.

MOP
Protocol

Maintenance Operation Protocol. Digital Equipment Corporation protocol that provides a way to perform primitive maintenance operations on DECnet systems.

Mosaic
Software

Public-domain WWW browser, developed at the National Center of Supercomputing Applications (NCSA).

MOSPF
Lingo

Multicast OSPF. Intradomain multicast routing protocol used in OSPF networks. Extensions are applied to the base OSPF unicast protocol to support IP multicast routing.

MPLS
Protocol

Multiprotocol Label Switching is an IETF initiative that integrates Layer 2 information about network links (bandwidth, latency, utilization) into Layer 3 (IP) within a particular autonomous system--or ISP --in order to simplify and improve IP -packet exchange. MPLS gives network operators a great deal of flexibility to divert and route traffic around link failures, congestion, and bottlenecks. From a QoS standpoint, ISPs will better be able to manage different kinds of data streams based on priority and service plan. For instance, those who subscribe to a premium service plan, or those who receive a lot of streaming media or high-bandwidth content can see minimal latency and packet loss. When packets enter a MPLS-based network, Label Edge Routers (LERs) give them a label (identifier). These labels not only contain information based on the routing table entry (i.e., destination, bandwidth, delay, and other metrics), but also refer to the IP header field (source IP address), Layer 4 socket number information, and differentiated service. Once this classification is complete and mapped, different packets are assigned to corresponding Labeled Switch Paths (LSPs), where Label Switch Routers (LSRs) place outgoing labels on the packets. With these LSPs, network operators can divert and route traffic based on data-stream type and Internet-access customer.

MPOA
Protocol

Short for Multiprotocol Over ATM, a specification that enables ATM services to be integrated with existing local-area networks (LANs) that use Ethernet, token-ring or TCP/IP protocols. The goal of MPOA is to allow different LANs to send packets to each other via an ATM backbone. Unlike other techniques, such as LAN Emulation (LANE), which operates at level 2 of the OSI Reference Model, MPOA operates at Level 3.

MQI
Lingo

Message Queueing Interface. International standard APO that provides functionality similar to that of the RPC interface. In contrast to RPC, MQI is implemented strictly at the application layer.

MSAU
Lingo

Multistation access unit. Wiring concentrator to which all end stations in a Token Ring network connect. The MSAU provides an interface between these devices and the Token Ring interface.

mSQL
Programming

Mini SQL: A lightweight database engine designed to provide fast access to stored data. See Also: SQL

MTA
Networking

Message Transfer Agent. In x.400, a process that is responsible for storing and forwarding messages.

MTU
Lingo

Maximum Transmission Unit. A specification in a data link protocol that defines the maximum number of bytes that can be carried in any one packet on that link.

Multiaccess Network
Networking

Network that allows multiple devices to connect and communicate simultaneously.

Multicast
Networking

Single packets copied by the network and sent to a specific subset of network addresses. These addresses are specified in the destination address field.

Multicast router
Networking

Router used to send IGMP query messages on their attached local networks. Host members of a multicast group respond to a query by sending IGMP reports noting the multicast groups to which they belong. The multicast router takes responsibility for forwarding multicast datagrams from one multicast group to all other networks that have members in the group.

Multicast Server
Hardware

Establishes a one-to-many connection to each device in a VLAN, thus establishing a broadcast domain for each VLAN segment. The multicast server forwards incoming broadcasts only to the multicast address that maps to the broadcast address.

Multihomed Host
Networking

Host attached to multiple physical network segments in an OSI CLNS network.

Multiplexing
Telecommunications

Multiplexing is sending multiple signal or streams of information on a carrier at the same time in the form of a single, complex signal and then recovering the separate signals at the receiving end. analog signals are commonly multiplexed using frequency-division multiplexing (frequency-division multiplexing), in which the carrier bandwidth is divided into subchannels of different frequency widths, each carrying a signal at the same time in parallel. digital signals are commonly multiplexed using time-division multiplexing (Time-Division Multiplexing), in which the multiple signals are carried over the same channel in alternating time slots. In some optical fiber networks, multiple signals are carried together as separate wavelengths of light in a multiplexed signal using dense wavelength-division multiplexing.

Multiplexor
Telecommunications

A Multiplexor, sometimes known as a MUX, is a device that combines multiple signals into one. Within the telephone system, this usually refers to the ability of the telephone company to multiplex multiple voice lines onto one trunk. The trunk is usally in the form of a T1 or T3 lines, depending on the amount of voice lines that need to be multiplexed.

In fiber networks, a multiplexor is sometimes called a concentrator. It can combine signals either by multiplexing different frequencies of light onto one fiber or by inserting the signals of one fiber channel into the signals of another fiber channel.

Multitasking
Lingo

A descriptive term for a computing device whose operating system can handle several tasks concurrently. In monoprocessors, each active task is given short periods of time to use the CPU in a rotational fashion.

MUX
Telecommunications

MUX (pronounce muks, sometimes spelled "MUX") is an abbreviation for a multiplexor, a device that sends multiple signals on a carrier channel at the same time in the form of a single. Multiplexors, or MUXES, combines the signals, while the receiver is sometimes called a demux (or "DEMUX").

N

N-ISDN
Telecommunications

Narrowband ISDN. Communication standards developed by the ITU-T for baseband networks. Based on 64-kbps B channels and 16- or 64-kbps D channels.

Nagel's Algorithm
Concept

Actually two separate congestion control algorithms that can be used in TCP-based networks. One algorithm reduces the sending window; the other limits small datagrams.

NAK
Lingo

Negative acknowledgment. Response sent from a receiving device to a sending device indicating that the information received contained errors.

Name Caching
Lingo

Method by which remotely discovered host names are stored by a router for use in future packet-forwarding decisions to allow quick access.

Name Server
Networking

Server connected to a network that resolves network names into network addresses.

Name Service
Networking

In AppleTalk, a computing process that has used Name Binding Protocol to register a process so that it may be located using a network resource management like the Chooser.

Nano
Lingo

A prefix that denotes a 1 billionth portion of a unit of measure, as in nanosecond or nanometer.

NAP
Lingo

Network access point. Location for interconnection of internet service providers in the United States for the exchange of packets.

NAS
Organizations

National Account Services. This group is part of Finance and consists of the Collections and Payment Processing departments.

NAT
Protocol

Short for Network Address Translation, an Internet standard that enables a local-area network (LAN) to use one set of IP addresses for internal traffic and a second set of addresses for external traffic. A NAT box located where the LAN meets the Internet makes all necessary IP address translations.

NAT serves three main purposes:

  1. It provides a type of firewall by hiding internal IP addresses.
  2. It also enables a company to use more internal IP addresses. Since they're used internally only, there's no possibility of conflict with IP addresses used by other companies and organizations.
  3. It also allows a company to combine multiple ISDN connections into a single Internet connection.

NAU
Lingo

Network addressable unit. SNA term for an addressable entity. Examples include LUs, PUs, and SSCPs. NAUs generally provide upper-level network services.

NAUN
Lingo

Nearest active upstream neighbor. In Token Ring or IEEE 802.5 networks, the closest upstream network device from any given device that is still active.

NBP
Protocol

Name Binding Protocol. The AppleTalk protocol that associates the name, type and zone of a process with its Internet Socket Address.

NCP
Protocol

Network Control Protocol.

NDIS
Protocol

Short for Network Driver Interface Specification, a Windows device driver interface that enables a single network interface card (NIC) to support multiple network protocols. For example, with NDIS a single NIC can support both TCP/IP and IPX connections. NDIS can also be used by some ISDN adapters. NDIS includes a protocol manager that accepts requests from the network driver (at the transport layer) and passes these requests to the NIC (at the data link layer). So multiple NDIS-conforming network drivers can co-exist. Also, if a computer contains multiple NICs because it is connected to more than one network, NDIS can route traffic to the correct card. NDIS was developed by Microsoft and 3COM. Novell offers a similar device driver for NetWare called Open Data-Link Interface (ODI).

NEARNET
Organizations

Regional network in New England (United States) that links Boston University, Harvard University, and MIT.

Neighboring Routers
Networking

In OSPF, two routers that have interfaces to a common network. On multiaccess networks, neighbors are dynamically discovered by the OSPF Hello protocol.

Nerd
People

one who eschews coolness, as defined by current vogue, due to either disability or disinterest (aka melvin, dork, dweeb). Not to be confused with a geek or a spazz. Source: The Encycopædia Craigica

NET
Lingo

Network entity title. Network addresses, defined by the ISO network architecture, and used in CLNS-based networks.

NetBIOS
Lingo

Network Basic Input/Output System. API used by applications on an IBM LAN to request services from lower-level network processes. These services might include session establishment and termination, and information transfer.

Netiquette
Lingo

Netiquette is etiquette on the Internet. Since the Internet changes rapidly, its netiquette does too, but it's still usually based on the Golden Rule. The need for a sense of netiquette arises mostly when sending or distributing e-mail, posting on Usenet groups, or chatting. To some extent, the practice of netiquette depends on understanding how e-mail, the Usenet, chatting, or other aspects of the Internet actually work or are practiced. So a little preliminary observation can help. Poor netiquette because you're new is one thing, but such practices as spam and flaming are another matter.

NetView
Software

A network and device management system developed by IBM.

NetWare
Software

A trademark of Novell that includes network operating systems and LAN server processes that run on and/or serve many computing platforms, operating systems and protocols.

Network
Networking

Network Any time you connect 2 or more computers together for the purpose of sharing resources, you have a computer network.

Network Adapter
Hardware

A hardware device that translates electronic signals between a computing device's native network hardware and the transmission media. A network adapter may also include memory or additional hardware or firmware to aid or perform the computing device's network operations.

Network Address
Networking

Network layer address referring to a logical, rather than a physical, network device. Also called a protocol address.

Network Administrator
People

A person who is charged with the responsibility of caring for a network and the communication abilities of its users.

Network Analyzer
Software

Hardware or software device offering various network troubleshooting features, including protocol-specific packet decodes, specific preprogrammed troubleshooting tests, packet filtering, and packet transmission.

Network Architecture
Networking

A set of specifications that defines every aspect of a data network's communication system, including but not limited to the types of user interfaces employed, the networking protocols used and the structure and types of network cabling that may be used.

Network Interface
Networking

Boundary between a carrier network and a privately-owned installation

Network Layer
Networking

Layer 3 of the OSI reference model. This layer provides connectivity and path selection between two end systems. The network layer is the layer at which routing occurs. Corresponds roughly with the path control layer of the SNA model.

Network Management
Networking

A set of activities and duties whose goal is to provide high-quality, reliable communication among a group of networked computer users. Typical activities may include resource planning, network design, providing user assistance and training, reconfiguration of the network due to a change in user requirements, assessing user needs and designing appropriate solutions and troubleshooting and remedying network problems as they arise.

Network Node Server
Hardware

SNA NN that provides resource location and route selection services for ENs, LEN nodes, and LUs that are in its domain.

Network Number
Networking

Part of an IP address that specifies the network to which the host belongs.

Network Operating System
Software

A term mostly used in DOS networking systems to refer collectively to the proprietary protocols and network file systems that computers use to exchange data with their LAN Servers.

Network Operator
People

Person who routinely monitors and controls a network, performing tasks such as reviewing and responding to traps, monitoring throughput, configuring new circuits, and resolving problems.

Newbie
Lingo

Someone who is new to the Internet.

Newsgroups
Networking

An Internet message board system, where people meet to discuss a variety of topics. There are thousands of newsgroups on the Internet covering a wide variety of interests.

NFS
PC's

Network File System. A file metalanguage and set of procedure calls to access and manage files that is standard issue on nearly every computer that uses TCP/IP protocols as its standard network protocols. Designed by Sun Microsystems, NFS is now a standard feature of nearly all Unix systems.

NHRP
Protocol

Next Hop Resolution Protocol. Protocol used by routers to dynamically discover the MAC address of other routers and hosts connected to a NBMA network. These systems can then directly communicate without requiring traffic to use an intermediate hop, increasing performance in ATM, Frame Relay, SMDS, and X.25 environments.

Nibble
Lingo

One-half of a byte, which can be represented by a single hexadecimal digit.

NIC
Hardware

1. Network Information Center. The group responsible for the assignment of IP addresses. 2. Network Interface Card. A network adapter on a circuit board that plugs into a computer internal bus architecture. 3. A 16-bit Ethernet chip designed by Texas Instruments.

NID
Telecommunications

Network Interface Device. This term is primarily ised in ISDN terminology. An NID is a device between a telephone protector and the inside wiring to isolate the customer's equipment from the D-Marc.

NIS
Lingo

Network Information System. Protocol developed by Sun Microsystems for the administration of network-wide databases. The service essentially uses two programs: one for finding a NIS server and one for accessing the NIS databases.

NIST
Organizations

National institute of Standards and Technology. Formerly the NBS, this U.S. government organization supports and catalogs a variety of standards.

NIU
Telecommunications

Network Interface Unit. a.k.a.: Smart-Jack. A semi-intelligent device that serves as the logical point of Demarcation between the LEC and the customer's premise equipment (CPE).

NLM
Software

NetWare Loadable Module. Individual program that can be loaded into memory and function as part of the NetWare NOS.

NLSP
Protocol

NetWare Link Services Protocol. Link-state routing protocol bases on IS-IS.

NMS
Lingo

Network management system. System responsible for managing at least part of a network. An NMS is generally a reasonably powerful and well-equipped computer such as an engineering workstation. NMSs communicate with agents to help keep track of network statistics and resources.

NN
Lingo

Network node. SNA intermediate node that provides connectivity, directory services, route selection, intermediate session routing, data transport, and network management services to LEN nodes and ENs. The NN contains a CP that manages the resources of both the NN itself and those of the ENs and LEN nodes in its domain. NNs provide intermediate routing services by implementing the APPN PU 2.1 extensions.

NNI
Lingo

Network-to-Network Interface. ATM Forum standard that defines the interface between two ATM switches that are both located in a private network or are both located in a public network. The interface between a public switch and private one is defined by the UNI standard. Also, the standard interface between two Frame Relay switches meeting the same criteria.

NNTP
Protocol

Short for Network News Transfer Protocol, the protocol used to post, distribute, and retrieve USENET messages. The official specification is RFC 977.

NOC
Organizations

Almost all ISP's and many large companies have a Network Operations Center that monitors their infrastructure and connections across their network. They also are the point of communication about networking issues between ISP's. By conventions, noc@ispname.com is defined as the communications path for this group.

Node
Hardware

A networked computing device that takes a protocol address and can initiate and respond to communication from other networked devices that employ similar protocols.

Noise
Telecommunications

Unwanted electrical signals (or disturbances) introduced into telephone lines by circuit components or natural disturbances which tend to degrade the performance of the line. a.k.a.: Line Noise.

Non-Volatile
Networking

Information that will remain usable by a computer despite loss of power or shutdown.

Northwest Net
Organizations

NSF-funded regional network serving the Northwestern United States, Alaska, Montana, and North Dakota. Northwest Net connects all major universities in the region, as well as many leading industrial concerns.

NOS
Software

Network operating system. Generic term used to refer to what are really distributed file systems.

NREN
Organizations

National Research and Education Network. Component of the HPCC program designed to ensure US. technical leadership in computer communications through research and development efforts in state-of-the-art telecommunications and networking technologies.

NRM
Lingo

normal response mode. HDLC mode for use on links with one primary station and one or more secondary stations. In this mode, secondary stations can transmit only if they first receive a poll from the primary station.

NRZI
Protocol

Non-Return-to-Zero Inverted A method for transmitting and recording data so that it keeps the sending and receiving clocks synchronized. This is especially helpful in situations where bit stuffing is employed -- the practice of adding bits to a data stream so it conforms with communications protocols. These added bits can create a long string of similar bits, which register to the receiver as a single, unchanging voltage. Since clocks adjust on voltage changes, they'll lag behind true time. NRZI ensures that after a 0 bit appears, the voltage will immediately switch to a 1 bit voltage level. These voltage changes allow the sending and receiving clocks to synchronize.

NT-1
Telecommunications

A network termination type. It is an ISDN term. It serves as the physical and electrical termination of the local loop between the LEC and the user premise. In reference - it is much like the smart-jack is on a T-1 line, but for ISDN.

Null Modem
Hardware

Null modem is a communication method to connect two DTEs (computer, terminal, printer etc.) directly using a RS-232 serial cable. The original RS-232 standard only defined the connection of DTEs with DCEs i.e. modems. With a null modem connection the transmit and receive lines are crosslinked. Depending on the purpose, sometimes also one or more handshake lines are crosslinked. Several wiring layouts are in use because the null modem connection is not covered by a standard.

Null modems are commonly used for file transfer between computers, or remote operation. Under the Microsoft Windows operating system, the direct cable connection can be used over a null modem connection. The later versions of MS-DOS were shipped with the InterLnk program. Both pieces of software allow the mapping of a hard disk on one computer as a network drive on the other computer. No Ethernet hardware (such as a network interface card or a modem) is required for this.

The popularity and availability of faster information exchange systems such as Ethernet made the use of null-modem cables less common. Nowadays, such a cable can still be useful to kernel hackers though, since it allows the user to remotely debug a kernel with a minimum of device drivers and code (a serial driver mainly consists of two FIFO buffers and an interrupt service routine). ddb or KGDB can be used to remotely debug BSD systems, for instance. This can also provide a serial console through which the in-kernel debugger can be dropped to in case of kernel panics, in which case the local monitor and keyboard may not be usable anymore (the X11 server reserves those resources if a GUI is used, and dropping to the debugger in the case of a panic won't free them).

NVRAM
Hardware

Non-Volitile Reader Access Memory. RAM memory that does not loose its memory when you shut the power off.

Nyquist's Theorem
Concept

The sampling frequency determines the limit of audio frequencies that can be reproduced digitally. One of the most important rules of sampling is called the Nyquist Theorem, which states that the highest frequency which can be accurately represented is one-half of the sampling rate. So, if we want a full 20 kHz audio bandwidth, we must sample at least twice that fast, i.e. over 40 kHz.

For a practical example of the application of his theorem we can examine the technologies used for digital voice transmission. Voice data for telephony purposes is limited to frequencies less than 4,000 Hz (cycles per second). Because of the requirement for guardbands, the actual frequency that can be utilized over voice grade lines is limited to 3,000 Hz. This limitation has nothing to do with Nyquist's Theorem, but instead is based upon the assumption made by Bell Labs that this frequency rate was good enough to make the voice intelligible (agreed it's not CD quality :).

According to Nyquist, it would take 8,000 samples (2 times 4,000) to capture a 4,000 Hz signal perfectly. That means 8,000 data points must be recorded concerning the amplitude of the analog signal. Now, this does not dictate how precise the information is concerning each sample. But, for the purposes of digital representation (based, of course, on binary arithmetic) one of a 256 range of values can be recorded in each 8 bit sample.

Therefore, if we take a 4K Hz voice grade signal and quantitize it in 256 levels and code each sample using one byte, then it requires 64,000 bits per second to communicate this digitally encoded voice signal in real time (8 bits * 8,000 samples per second = 64K bps) over a circuit.

It is not surprising, therefore, that T-carrier circuits were designed around this requirement, since they are primarily designed to carry voice signals that have been converted from analog to digital signals. The 4K Hz signal is sampled and then transmitted as a time-division multiplexed [TDM] synchronous baseband signal.

For example, look at the DS-1 signal which passes over a T-1 circuit. For DS-1 transmissions, each frame contains 8 bits per channel and there are 24 channels. Also, 1 "framing bit" is required for each of the 24 channel frames.

     24 channels * 8 bits per channel + 1 framing bit = 193 bits per frame. 
     193 bits per frame * 8,000 "Nyquist" samples = 1,544,000 bits per second.
And it just so happens that the T-1 circuit is 1.544 Mbps.--not a coincidence. Each of the 24 channels in a T-1 circuit carries 64Kbps. There are many other places in data communication where Nyquist's theorems can be applied.

O

OC
Telecommunications

Optical Carrier. Series of physical protocols (OC-1, OC-2, OC-3, and so forth), defined for SONET optical signal transmissions. OC signal levels put STS frames onto multimode fiber-optic line at a variety of speeds. The base rate is 51.84 Mbps (OC-1); each signal level thereafter operates at a speed divisible by that number (thus, OC-3 runs at 155.52 Mbps).

OC-1
Telecommunications

Optical Carrier Level 1. 51.84 Mbps. The optical counterpart of STS-1, which is the fundamental signaling rate of 51.84 Mbps on which the SONET (Synchronous Optical Network) hierarchy is based.

OC-192
Telecommunications

Optical Carrier Level 192. SONET channel equal to 9.953 Gbps.

OC-256
Telecommunications

Optical Carrier Level 256. SONET channel equal to 13.27104 Gbps.

OC-3
Telecommunications

Optical Carrier Level 3. A SONET channel equal to three DS-3s, which is equal to 155.52 Mbps.

OC-48
Telecommunications

Optical Carrier Levle 48. SONET channel of 2.488 Gbps. Calculated by multiplying 51.84 Mbps by 48.

OC-768
Telecommunications

Optical Carrier Level 768. SONET transmission rate of 39.812 Gbps. Currently OC-768 is the highest speed level defined for SONET.

Octet
Networking

8 bits. In networking, the term octet is often used (rather than byte) because some machine architectures employ bytes that are not 8 bits long.

ODBC
Protocol

Open DataBase Connectivity. Standard application programming interface for accessing data in both relational and nonrelational database management systems. Using this application programming interface, database applications can access data stored in database management systems on a variety of computers even if each database management system uses a different data storage format and programming interface. ODBC is based on the call level interface specification of the X/Open SQL Access Group and was developed by Digitial Equipment Corporation, Lotus, Microsoft, and Sybase.

ODI
Lingo

Open Data-link Interface. A Novell specification for network interface card device drivers that allows multiple protocol stacks to use the same card simultaneously.

OEM
Lingo

Original Equipment Manufacture. A system of distribution where a company markets equipment purchased from another company under its own label.

Ohm (W)
Concept

A measure of the opposition to the flow of electric current.

Ohm's Law
Concept

Ohm's Law is the mathematical relationship among electric current, resistance, and voltage. The principle is named after the German scientist Georg Simon Ohm.

In direct-current (DC) circuits, Ohm's Law is simple and linear. Suppose a resistance having a value of R ohms carries a current of I amperes. Then the voltage across the resistor is equal to the product IR. There are two corollaries. If a DC power source providing E volts is placed across a resistance of R ohms, then the current through the resistance is equal to E/R amperes. Also, in a DC circuit, if E volts appear across a component that carries I amperes, then the resistance of that component is equal to E/I ohms.

Mathematically, Ohm's Law for DC circuits can be stated as three equations:

E = IR

I = E/R

R = E/I

OLE
Lingo

Object Linking and Embedding. A Microsoft specification for the exchange of data objects between applications.

Ones Density
Telecommunications

A Scheme that allows a CSU/DSU to recover the data clock reliably. The CSU/DSU derives the data clock from the data that passes through it. In order to recover the clock, the CSU/DSU hardware must receive at least one 1 bit value for every 8 bits of data that pass through it. Also called pulse density.

Open
Telecommunications

Means the circuit is not complete. There is no complete path for the current flow. Electrical current cannot flow in the circuit. There could be loose wire, or broken fiber.

Open Source
Software

The concept of open source, as it applies to software, is extremely simple. When software code can be freely distributed and modified by other programmers, the software evolves and improves. This is the guiding idea of a new type of software that has been gaining lots of group, especially since the Internet has gained in popularity in recent years.

More information on open source and some of the software that is available in this system can be found at the www.opensource.org.

Open Wire
Telecommunications

A transmission facility typically consisting of pairs of "bare" conductors supported on insulators which are mounted on poles to form an aerial pole line. Open wire may be used in both communication and power. Most basic of all practical types of transmission media.

OpenDoc
Networking

An open cross-platform, compound document architecture developed by Apple with help and support from Novell and WordPerfect, among others.

OpenView
Software

HP's SNMP console and network management system.

Operating System (OS)
Lingo

This is the software that manages a computer system. Windows 95 is an OS.

OS/2
Software

IBM's operating system for 80x86 based systems.

Oscillate
Networking

A condition where a system changes between two or more configurations on a recurring basis.

Oscilloscope
Hardware

A test device that can capture and display an oscillating electrical signal.

OSF
Organizations

Open Software Foundation.

OSI
Organizations

Open System Interconnection. International standardization program created by ISO and ITU-T to develop standards for data networking that facilitate multivendor equipment interoperability.

OSI 7-Layer Model
Networking

A method of describing the relationships between network protocols by grouping them according to the communication functions the protocols provide. The OSI model defines 7 distinct categories (Layers) that act successively on data as it makes its way between the user and the transmission media.

OSPF
Protocol

Open Shortest Path First is a routing protocol developed for IP networks based on the shortest path first or link-state algorithm.

Routers use link-state algorithms to send routing information to all nodes in an internetwork by calculating the shortest path to each node based on a topography of the Internet constructed by each node. Each router sends that portion of the routing table (keeps track of routes to particular network destinations) that describes the state of its own links, and it also sends the complete routing structure (topography).

The advantage of shortest path first algorithms is that they results in smaller more frequent updates everywhere. They converge quickly, thus preventing such problems as routing loops and Count-to-Infinity (when routers continuously increment the hop count to a particular network). This makes for a stable network.

The disadvantage of shortest path first algorithms is that they require a lot of CPU power and memory. In the end, the advantages out weigh the disadvantages.

OSPF Version 2 is defined in RFC 1583. It is rapidly replacing RIP on the Internet.

Out-of-band signalling
Telecommunications

Transmission using frequencies or channels outside the frequencies or channels normally used for information transfer. Out-of-band signaling is often used for error reporting in situations in which in-band signaling can be affected by whatever problems the network might be experiencing.

Output
Networking

A representation of a system's data that is externally visible.

Overwrite
Lingo

An error condition that occurs when a process stores data in a location that it 1) has not properly allocated for that purpose or 2) has been allocated by another process.

P

Packet
Networking

A packet is the unit of data that is routed between an origin and a destination on the Internet or any other packet-switched network. When any file (e-mail message, HTML file, Graphics Interchange Format file, Uniform Resource Locator request, and so forth) is sent from one place to another on the Internet, the Transmission Control Protocol (TCP) layer of TCP/IP divides the file into "chunks" of an efficient size for routing. Each of these packets is separately numbered and includes the Internet address of the destination. The individual packets for a given file may travel different routes through the Internet. When they have all arrived, they are reassembled into the original file (by the TCP layer at the receiving end).

A packet-switching scheme is an efficient way to handle transmissions on a connectionless network such as the Internet. An alternative scheme, circuit-switched, is used for networks allocated for voice connections. In circuit-switching, lines in the network are shared among many users as with packet-switching, but each connection requires the dedication of a particular path for the duration of the connection.

"Packet" and "datagram" are similar in meaning. A protocol similar to TCP, the User Datagram Protocol(UDP) uses the term datagram.

Pair
Telecommunications

The two wires of a circuit. Those which make up the subscriber's loop from his office to the Central Office (CO).

Paired Cable
Telecommunications

A cable in which all conductors are arranged in twisted pairs. The most common cable used for transmissions.

PAP
Protocol

Short for Password Authentication Protocol, the most basic form of authentication, in which a user's name and password are transmitted over a network and compared to a table of name-password pairs. Typically, the passwords stored in the table are encrypted. The Basic Authentication feature built into the HTTP protocol uses PAP. The main weakness of PAP is that both the username and password are transmitted "in the clear" -- that is, in an unencrypted form. Contrast with CHAP.

Parity Bit
Telecommunications

A binary bit appended to an array of bits to make the sum of all the bits always odd or even.

Parity Checking
PC's

A method of error checking where an extra bit is used to signify the condition of a small group of data bits.

Password
Lingo

A series of characters that enables someone to access a file, computer or program. Your Control Panel is password protected to prevent unauthorized users from changing your information. The password should be a combination of characters that would be difficult to guess.

Patch Panel
Telecommunications

A patch panel is a mounted hardware unit containing an assembly of port locations in a communications or other electronic or electrical system. In a network, a patch panel serves as a sort of static switchboard, using cables to interconnect computers within the area of a local area network (LAN) and to the outside for connection to the Internet or other wide area network (WAN). A patch panel uses a sort of jumper cable called a patch cord to create each interconnection.

Paul Vixie
People

Paul Vixie has been contributing to Internet protocols and UNIX systems as a protocol designer and software architect since 1980. Early in his career, he developed and introduced sends, proxynet, rtty, cron and other lesser-known tools. Today, Paul is considered the primary modern author and technical architect of BINDv8 the Berkley Internet Name Domain Version 8, the open source reference implementation of the Domain Name System (DNS). He formed the Internet Software Consortium (ISC) in 1994, and now acts as Chairman of its Board of Directors. The ISC reflects Paul's commitment to developing and maintaining production quality open source reference implementations of core Internet protocols.

More recently, Paul formed MAPS (Mail Abuse Prevention System), a California nonprofit company established in 1998 with the goal of hosting the RBL (Realtime Blackhole List) and stopping the Internet's email system from being abused by spammers. Vixie is also the Chief Executive Officer of M.I.B.H., Inc., a network engineering company headquartered in Redwood City, CA, which boasts clients such as the Commercial Internet Exchange (CIX) and Altavista Search.

Along with Frederick Avolio, Paul co-wrote "Sendmail: Theory and Practice" (Digital Press, 1995). He has authored or co-authored several RFCs, including a Best Current Practice document on "Classless IN-ADDR.ARPA Delegation" (BCP 20). He is also responsible for overseeing the operation of F.root-servers.net, one of the thirteen Internet root domain name servers.

Payload
Telecommunications

From the prospective of a Network Service Provider, payload is a data feild, block or stream being transported, the part that represents information useful to the user, as opposed to system overhead information.

PCI
Hardware

Acronym for Peripheral Component Interconnect, a local bus standard developed by Intel Corporation. Most modern PCs include a PCI bus in addition to a more general ISA expansion bus. Many analysts, however, believe that PCI will eventually supplant ISA entirely. PCI is also used on newer versions of the Macintosh computer. PCI is a 64-bit bus, though it is usually implemented as a 32-bit bus. It can run at clock speeds of 33 or 66 MHz. At 32 bits and 33 MHz, it yields a throughput rate of 133 MBps. Although it was developed by Intel, PCI is not tied to any particular family of microprocessors.

PDS
Lingo

Processor Direct Slot. One of a large number of computer bus architecture's used in Macintosh computers.

Peek
Lingo

A term used to describe the viewing of network data not ordinarily visible to a user.

Peer
Networking

In networking, a device to which a computer has a network connection that is relatively symmetrical, i.e. where both devices can initiate or respond to a similar set of requests.

Peering
Networking

Peering is the arrangement of traffic exchange between Internet service providers (ISPs). Larger ISPs with their own backbone networks agree to allow traffic from other large ISPs in exchange for traffic on their backbones. They also exchange traffic with smaller ISPs so that they can reach regional end points. Essentially, this is how a number of individual network owners put the Internet together. To do this, network owners and access providers, the ISPs, work out agreements that describe the terms and conditions to which both are subject. Bilateral peering is an agreement between two parties. Multilateral peering is an agreement between more than two parties.

Peering requires the exchange and updating of router information between the peered ISPs, typically using the Border Gateway Protocol (Border Gateway Protocol). Peering parties interconnect at network focal points such as the network access points (network access point) in the United States and at regional switching points. Initially, peering arrangements did not include an exchange of money. More recently, however, some larger ISPs have charged smaller ISPs for peering. Each major ISP generally develops a peering policy that states the terms and conditions under which it will peer with other networks for various types of traffic.

Private peering is peering between parties that are bypassing part of the public backbone network through which most Internet traffic passes. In a regional area, some ISPs exchange local peering arrangements instead of or in addition to peering with a backbone ISP. In some cases, peering charges include transit charges, or the actual line access charge to the larger network. Properly speaking, peering is simply the agreement to interconnect and exchange routing information.

Peripheral
Hardware

1. Any hardware resource used by a computer that is external to a computer's enclosure case that is accessed by serial or parallel connections, or bus architectures such as SCSI, MIDI or VME. 2. Any hardware computing resource that can be accessed by a user.

PERL
Programming

Short for Practical Extraction and Report Language, Perl is a programming language developed by Larry Wall, especially designed for processing text. Because of its strong text processing abilities, Perl has become one of the most popular languages for writing CGI scripts. Perl is an interpretive language, which makes it easy to build and test simple programs.

PGP - Pretty Good Privacy
Protocol

PGP (Pretty Good Privacy) is a popular program used to encryption and decrypt e-mail over the Internet. It can also be used to send an encrypted digital signature that lets the receiver verify the sender's identity and know that the message was not changed en route. Available both as freeware and in a low-cost commercial version, PGP is the most widely used privacy-ensuring program by individuals and is also used by many corporations. Developed by Philip R. Zimmermann in 1991, PGP has become a de facto standard for e-mail security. PGP can also be used to encrypt files being stored so that they are unreadable by other users or intruders.

How It Works

PGP uses a variation of the public key system. In a public key system, each user has a publicly known encryption key and a private key known only to that user. You encrypt a message you send to someone else using their public key. When they receive it, they decrypt it using their private key. Since encrypting an entire message can be time-consuming, PGP uses a faster encryption algorithm to encrypt the message and then uses the public key to encrypt the shorter key that was used to encrypt the entire message. Both the encrypted message and the short key are sent to the receiver who first uses the receiver's private key to decrypt the short key and then uses that key to decrypt the message.

PGP comes in two public key versions - Rivest-Shamir-Adleman and Diffie-Hellman. The RSA version, for which PGP must pay a license fee to RSA, uses the IDEA algorithm to generate a short key for the entire message and RSA to encrypt the short key. The Diffie-Hellman version uses the CAST algorithm for the short key to encrypt the message and the Diffie-Hellman algorithm to encrypt the short key.

For sending digital signatures, PGP uses an efficient algorithm that generates a hashing from the user's name and other signature information. This hash code is then encrypted with the sender's private key. The receiver uses the sender's public key to decrypt the hash code. If it matches the hash code sent as the digital signature for the message, then the receiver is sure that the message has arrived securely from the stated sender. PGP's RSA version uses the MD5 algorithm to generate the hash code. PGP's Diffie-Hellman version uses the SHA-1 algorithm to generate the hash code.

To use PGP, you download or purchase it and install it on your computer system. Typically, it contains a user interface that works with your customary e-mail program. You also need to register the public key that your PGP program gives you with a PGP public-key server so that people you exchange messages with will be able to find your public key. Network Associates maintains an LDAP/HTTP public key server that has 300,000 registered public keys. This server is mirror site at other sites around the world.

Phase
Telecommunications

In electronic signaling, phase is a definition of the position of a point in time (instant) on a waveform cycle. A complete cycle is defined as 360 degrees of phase as shown in the illustation to the right. Phase can also be an expression of relative displacement between or among waves having the same frequency.

Phase Modulation
Telecommunications

Phase modulation (PM) is a form of modulation that represents information as variations in the instantaneous phase of a carrier wave.

Unlike its more popular counterpart, frequency modulation (FM), PM is not very widely used for radio transmissions. This is because it tends to require more complex receiving hardware and there can be ambiguity problems in determining whether, for example, the signal has changed phase by +180° or -180°. PM is used, however, in digital music synthesizers such as the Yamaha DX7, even though these instruments are usually referred to as "FM" synthesizers (both modulation types sound very similar, but PM is usually easier to implement in this area).

Phase-Shift Keying
Telecommunications

Phase-shift keying (PSK) is a method of transmitting and receiving digital signals in which the phase of a transmitted signal is varied to convey information.

There are several schemes that can be used to accomplish PSK. The simplest method uses only two signal phases: 0 degrees and 180 degrees. The digital signal is broken up timewise into individual bits (binary digits). The state of each bit is determined according to the state of the preceding bit. If the phase of the wave does not change, then the signal state stays the same (low or high). If the phase of the wave changes by 180 degrees -- that is, if the phase reverses -- then the signal state changes (from low to high, or from high to low). Because there are two possible wave phases, this form of PSK is sometimes called biphase modulation.

More complex forms of PSK employ four or eight wave phases. This allows binary data to be transmitted at a faster rate per phase change than is possible with biphase modulation. In four-phase modulation, the possible phase angles are 0, +90, -90, and 180 degrees; each phase shift can represent two signal elements. In eight-phase modulation, the possible phase angles are 0, +45, -45, +90, -90, +135, -135, and 180 degrees; each phase shift can represent four signal elements.

Phil Zimmerman
People

Philip R. Zimmermann is the creator of Pretty Good Privacy. For that, he was the target of a three-year criminal investigation, because the government held that US export restrictions for cryptographic software were violated when PGP spread all around the world following its 1991 publication as freeware. Despite the lack of funding, the lack of any paid staff, the lack of a company to stand behind it, and despite government persecution, PGP nonetheless became the most widely used email encryption software in the world. After the government dropped its case in early 1996, Zimmermann founded PGP Inc, which was acquired by Network Associates in December 1997. Zimmermann is now a Senior Fellow at Network Associates, as well as an independent consultant in matters cryptographic.

Physical Address
Networking

A synonym for Hardware Address or MAC - layer address.

Pico
Lingo

A prefix denoting a 1 trillionth portion of a unit of measure, as in picosecond or picofarad.

Pin
Hardware

A type of electrical contact point for a single conductor.

Ping
Networking

Packet Internet Groper

Ping is a basic Internet program that lets you verify that a particular IP address exists and can accept requests. The verb ping means the act of using the ping utility or command. Ping is used diagnostically to ensure that a host computer you are trying to reach is actually operating. If, for example, a user can't ping a host, then the user will be unable to use the File Transfer Protocol (FTP) to send files to that host. Ping can also be used with a host that is operating to see how long it takes to get a response back. Using ping, you can learn the number form of the IP address from the symbolic domain name (see "Tip").

Loosely, ping means "to get the attention of" or "to check for the presence of" another party online. Ping operates by sending a packet to a designated address and waiting for a response. The computer acronym was contrived to match the submariners' term for the sound of a returned sonar pulse.

Ping can also refer to the process of sending a message to all the members of a mailing list requesting an ACK (acknowledgement code). This is done before sending e-mail in order to confirm that all of the addresses are reachable.

Pinouts
Telecommunications

Pin configurations for cabling.

Pixel
Lingo

A unit of measurement for graphics or monitor resolution. A pixel is one dot on a computer screen. Most computer monitors are set to a resolution of 800 x 600, meaning 800 pixels wide by 600 pixels high.

Plain Text
Software

Refers to textual data in ASCII format. Plain text is the most portable format because it is supported by nearly every application on every machine. It is quite limited, however, because it cannot contain any formatting commands.

In cryptography, plain text refers to any message that is not encrypted. Contrast with cipher text.

Plain text is also called clear text.

Plug
Hardware

A synonym for male connector.

Plug-ins
Programming

Software programs that enhance other programs or applications on your computer. There are plug-ins for Internet browsers, graphics programs, and other applications.

Point-of-Presence
Networking

A point-of-presence (POP) is an access point to the Internet. A POP necessarily has a unique Internet Protocol (IP) address. Your Internet service provider (ISP) or online service provider (such as AOL) has a point-of-presence on the Internet and probably more than one. The number of POPs that an ISP or OSP has is sometimes used as a measure of its size or growth rate.

A POP may actually reside in rented space owned by the telecommunications carrier (such as Sprint) to which the ISP is connected. A POP usually includes routers, digital/analog call ggregators, servers, and frequently frame relay or ATM switches.

Point-to-Point
Telecommunications

A private circuit. A connection with only two endpoints.

Poke
Lingo

A term used to refer to the transmission of a packet on a network for test purposes only.

Polarity
Lingo

Term used to describe the orientation of a differential voltage.

Polling
Lingo

A means of Media Access Control where a device may only transmit information when it is given permission to transmit by a controller device.

POP
Networking

Point-of-Presence

A point-of-presence (POP) is the location of an access point to the Internet. A POP necessarily has a unique Internet (Internet Protocol) address. Your independent service provider (Internet service provider) or online service provider (online service provider) has a point-of-presence on the Internet. POPs are sometimes used as one measure of the size and growth of an ISP or OSP.

A POP may actually reside in rented space owned by a telecommunications carrier such as Verio. A POP usually includes router, digital/analog call aggregator, server, and frequently frame relay or asynchronous transfer mode switches.

POP3
Protocol

POP3 (Post Office Protocol 3) is the most recent version of a standard protocol for receiving e-mail. POP3 is a client/server protocol in which e-mail is received and held for you by your Internet server. Periodically, you (or your client e-mail receiver) check your mail-box on the server and download any mail. POP3 is built into the Netmanage suite of Internet products and one of the most popular e-mail products, Eudora. It's also built into the Netscape and Microsoft Internet Explorer browsers.

Port
Software

  1. On computer and telecommunication devices, a port (noun) is generally a specific place for being physically connected to some other device, usually with a socket and plug of some kind. Typically, a personal computer is provided with one or more serial ports and usually one parallel port. The serial port supports sequential, one bit-at-a-time transmission to peripheral devices such as scanners and the parallel port supports multiple-bit-at-a-time transmission to devices such as printers.
  2. In programming, a port (noun) is a "logical connection place" and specifically, using the Internet's protocol, TCP/IP, the way a client program specifies a particular server program on a computer in a network. Higher-level applications that use TCP/IP such as the Web protocol, Hypertext Transfer Protocol, have ports with preassigned numbers. These are known as "well-known ports" that have been assigned by the Internet Assigned Numbers Authority (Internet Assigned Numbers Authority). Other application processes are given port numbers dynamically for each connection. When a service (server program) initially is started, it is said to bind to its designated port number. As any client program wants to use that server, it also must request to bind to the designated port number.

    Port numbers are from 0 to 65536. Ports 0 to 1024 are reserved for use by certain privileged services. For the HTTP service, port 80 is defined as a default and it does not have to be specified in the Uniform Resource Locator (Uniform Resource Locator).
  3. In programming, to port (verb) is to move an application program from an operating system environment in which it was developed to another operating system environment so it can be run there. Porting implies some work, but not nearly as much as redeveloping the program in the new environment. Open standard programming interface (such as those specified in X/Open's 1170 C language specification and Sun Microsystem's Java programming language) minimize or eliminate the work required to port a program.

POSIX
Lingo

Portable Operating Systems Interface. An IEEE standard that specifies requirements for portable UNIX operating systems.

Post Message
Lingo

To send a message to a newsgroup or other type of message board.

PostScript
Programming

An Extensible programming language that is capable of describing and drawing complex images that was developed by Adobe Systems.

POTS
Telecommunications

Plain Old Telephone Service. This refers to a basic dial-up analog line.

Power PC
Hardware

A Motorola-developed RISC chip. Also refers to the successor of the Macintosh powered by this chip.

PowerOpen
Software

Apple's next-generation operating system co-developed with IBM.

PPC
Lingo

1. Process-to-Process Communication. 2. Sometimes used as an acronym for PowerPC.

PPP
Networking

Point-to-Point Protocol

PPP (Point-to-Point Protocol) is a protocol for communication between two computers using a serial interface, typically a personal computer connected by phone line to a server. For example, your Internet server provider may provide you with a PPP connection so that the provider's server can respond to your requests, pass them on to the Internet, and forward your requested Internet responses back to you. PPP uses the Internet protocol (Internet Protocol) (and is designed to handle others). It is sometimes considered a member of the TCP/IP suite of protocols. Relative to the Open Systems Interconnection (OSI) reference model, PPP provides layer 2 (data-link layer) service. Essentially, it packages your computer's TCP/IP packets and forwards them to the server where they can actually be put on the Internet.

PPP is a full-duplex protocol that can be used on various physical media, including twisted pair or fiber optic lines or satellite transmission. It uses a variation of High Speed Data Link Control (High-Level Data Link Control) for packet encapsulation.

PPP is usually preferred over the earlier de facto standard Serial Line Internet Protocol (Serial Line Internet Protocol) because it can handle synchronous as well as asynchronous communication. PPP can share a line with other users and it has error detection that SLIP lacks. Where a choice is possible, PPP is preferred.

PPPoE
Networking

Point-to-Point Protocol over Ethernet

PPPoE (Point-to-Point Protocol over Ethernet) is a specification for connecting multiple computer users on an Ethernet to a remote site through common customer premises equipment (customer premise equipment), which is the telephone company's term for a modem and similar devices. PPPoE can be used to have an office or building-full of users share a common Digital Subscriber Line (Digital Subscriber Line), cable modem, or wireless connection to the Internet. PPPoE combines the Point-to-Point Protocol (Point-to-Point Protocol), commonly used in dialup connections, with the Ethernet protocol, which supports multiple users in a local area network. The PPP protocol information is encapsulated within an Ethernet frame.

PPPoE has the advantage that neither the telephone company nor the Internet service provider (Internet service provider) needs to provide any special support. Unlike dialup connections, DSL and cable modem connections are "always on." Since a number of different users are sharing the same physical connection to the remote service provider, a way is needed to keep track of which user traffic should go to and which user should be billed. PPPoE provides for each user-remote site session to learn each other's network addresses (during an initial exchange called "discovery"). Once a session is established between an individual user and the remote site (for example, an Internet service provider), the session can be monitored for billing purposes. Many apartment houses, hotels, and corporations are now providing shared Internet access over DSL lines using Ethernet and PPPoE.

Premises
Telecommunications

The space occupied by a customer not seperated by a road or public hiway.

PRI
Telecommunications

Primary Rate Interface. An ISDN service over a T1 link that provides 23 data channels "bearer" or "b" Channels" at 64 KBPS and one 16 KBPS control channel (or "D" channel).

Print Spooler
Software

A Software process that accepts a print job from a workstation as if it were a printer and then sends the print job to an actual printer at a later time. There are two styles, a background spooler, where the print spooling process is resident in the same node as the process seeking the print service, and a hardware spooler, where the print spooling process is in a separate node.

Printer Driver
Software

In the Macintosh, a System Extension that is intermediate between the CPU and the printer. It accepts the Macintosh's internal representation of an image and translates it into the control codes and image descriptions necessary for the printer to manufacture an image.

Process
Software

A set of instructions, as in a computer program or application that is currently active, i.e. consuming CPU time and memory resources. While an "application" is a process, that term usually refers to a process that a user can launch from the Finder and directly control, where the use of the term "process" often implies that the process has been launched by the system and is not under direct user control.

Program
Software

A set of instructions that has been coded into a computer language and compiled into a machine language.

Programming Language
Software

A vocabulary and set of grammatical rules for instructing a computer to perform specific tasks. The term programming language usually refers to high-level languages, such as BASIC, C, C++, COBOL, FORTRAN, Ada, and Pascal. Each language has a unique set of keywords (words that it understands) and a special syntax for organizing program instructions.

High-level programming languages, while simple compared to human languages, are more complex than the languages the computer actually understands, called machine languages. Each different type of CPU has its own unique machine language.

Lying between machine languages and high-level languages are languages called assembly languages. Assembly languages are similar to machine languages, but they are much easier to program in because they allow a programmer to substitute names for numbers. Machine languages consist of numbers only.

Lying above high-level languages are languages called fourth-generation languages (usually abbreviated 4GL). 4GLs are far removed from machine languages and represent the class of computer languages closest to human languages.

The question of which language is best is one that consumes a lot of time and energy among computer professionals. Every language has its strengths and weaknesses. For example, FORTRAN is a particularly good language for processing numerical data, but it does not lend itself very well to organizing large programs. Pascal is very good for writing well-structured and readable programs, but it is not as flexible as the C programming language. C++ embodies powerful object-oriented features, but it is complex and difficult to learn. The choice of which language to use depends on the type of computer the program is to run on, what sort of program it is, and the expertise of the programmer.

PROM
Hardware

Programmable Read-Only Memory. Firmware in which a chip has had a program "burned in" to its internal circuitry. The designation "EPROM" indicates that the program is Erasable.

Promiscuous
Networking

A LAN station that receives and processes all of the packets on its network.

Proprietary
Lingo

Meaning that information concerning the methods or implementation of a technology are owned by an individual or a company. "Proprietary" may mean that the information is secret or that the information must be licensed from the owner before it can be used.

Protocol
Protocol

In information technology, a protocol (pronounced PROH-tuh-cahl, from the Greek protocollon, which was a leaf of paper glued to a manuscript volume, describing its contents) is the special set of rules for communicating that the end points in a telecommunication connection use when they send signals back and forth. Protocols exist at several levels in a telecommunication connection. There are hardware telephone protocols. There are protocols between the end points in communicating programs within the same computer or at different locations. Both end points must recognize and observe the protocol. Protocols are often described in an industry or international standard.

Protocol Stack
Networking

A set of network protocol layers that work together. The OSI Reference Model that defines seven protocol layers is often called a stack, as is the set of TCP/IP protocols that define communication over the internet. The term stack also refers to the actual software that processes the protocols. So, for example, programmers sometimes talk about loading a stack, which means to load the software required to use a specific set of protocols. Another common phrase is binding a stack, which refers to linking a set of network protocols to a network interface card (NIC). Every NIC must have at least one stack bound to it. In Windows, the TCP/IP stack is implemented by the Winsock DLL.

Proxy Server
Networking

A server that sits between a client application, such as a Web browser, and a real server. It intercepts all requests to the real server to see if it can fulfill the requests itself. If not, it forwards the request to the real server.

Proxy servers have two main purposes:

  1. Improve Performance: Proxy servers can dramatically improve performance for groups of users. This is because it saves the results of all requests for a certain amount of time. Consider the case where both user X and user Y access the World Wide Web through a proxy server. First user X requests a certain Web page, which we'll call Page 1. Sometime later, user Y requests the same page. Instead of forwarding the request to the Web server where Page 1 resides, which can be a time-consuming operation, the proxy server simply returns the Page 1 that it already fetched for user X. Since the proxy server is often on the same network as the user, this is a much faster operation. Real proxy servers support hundreds or thousands of users. The major online services such as Compuserve and America Online, for example, employ an array of proxy servers.
  2. Filter Requests: Proxy servers can also be used to filter requests. For example, a company might use a proxy server to prevent its employees from accessing a specific set of Web sites.

Pseudocode
Protocol

An outline of a program, written in a form that can easily be converted into real programming statements. For example, the pseudocode for a bubble sort routine might be written:

while not at end of list
compare adjacent elements
if second is greater than first
switch them
get next two elements
if elements were switched
repeat for entire list

Pseudocode cannot be compiled nor executed, and there are no real formatting or syntax rules. It is simply one step - an important one - in producing the final code. The benefit of pseudocode is that it enables the programmer to concentrate on the algorithms without worrying about all the syntactic details of a particular programming language. In fact, you can write pseudocode without even knowing what programming language you will use for the final implementation.

Public-Domain Software
Software

Refers to any program that is not copyrighted. Public-domain software is free and can be used without restrictions. The term public-domain software is often used incorrectly to include freeware, free software that is nevertheless copyrighted.

Publish & Subscribe
Programming

An Apple proprietary method of defining and maintaining a live link between a file and an external piece of data.

PUC
Organizations

Public Utilities Commission; this governmental organization is responsible for setting the tariffs for circuit’s in each local market. This prevents an ILEC from gaining a competitive advantage by forcing them to sell the circuit for the same price whether it is to a end user or a reseller.

PVC
Networking

A PVC (Permanent Virtual Circuit) is a software-defined logical connection in a frame relay network. A feature of frame relay that makes it a highly flexible network technology is that users (companies or clients of network providers) can define logical connections and required bandwidth between end points and let the frame relay network technology worry about how the physical network is used to achieve the defined connections and manage the traffic. The end points and a stated bandwidth called a Committed Information Rate, or CIR, constitute a PVC, which is defined to the frame relay network devices. The bandwidth may not exceed the possible physical bandwidth. Typically, multiple PVCs share the same physical paths at the same time. To manage the variation in bandwidth requirements expressed in the CIRs, the frame relay devices use a technique called statistical multiplexing.

Q

QoS
Lingo

Short for Quality of Service, a networking term that specifies a guaranteed throughput level. One of the biggest advantages of ATM over competing technologies such as Frame Relay and Fast Ethernet, is that it supports QoS levels. This allows ATM providers to guarantee to their customers that end-to-end latency will not exceed a specified level.

Quad
Lingo

A low-grade implementation of twisted pair wire, where four conductors (two pairs) are all twisted together with no independent twisting between the pairs.

Quantum
PC's

The maximum unit of time that a real-time process can occupy the CPU.

Query
Lingo

A general term to describe the formation, usually in a prescribed format, that a computer process would use to retrieve specific information from another process as opposed to a wholesale transfer of data.

QuickTime
Lingo

A multi-media technology developed by Apple.

R

Radio (RF) Frequency
Networking

1. Electromagnetic radiation with a frequency in the range of 10 KHz to 300 GHz. 2. Wireless data communication using such radiation.

RADIUS
Protocol

RADIUS (Remote Authentication Dial-In User Service) is a client/server protocol and software that enables remote access servers to communicate with a central server to authenticate dial-in users and authorize their access to the requested system or service. RADIUS allows a company to maintain user profiles in a central database that all remote servers can share. It provides better security, allowing a company to set up a policy that can be applied at a single administered network point. Having a central service also means that it's easier to track usage for billing and for keeping network statistics. Created by Livingston (now owned by Lucent), RADIUS is a de facto industry standard used by Ascend and other network product companies and is a proposed IETF standard.

RADSL
Telecommunications

RADSL (Rate-Adaptive DSL) is an ADSL technology from Westell in which software is able to determine the rate at which signals can be transmitted on a given customer phone line and adjust the delivery rate accordingly. Westell's FlexCap2 system uses RADSL to deliver from 640 Kbps to 2.2 Mbps downstream and from 272 Kbps to 1.088 Mbps upstream over an existing line.

RAID
PC's

Redundant Array of Independant Disks

RAID (redundant array of independent disks) is a way of storing the same data in different places (thus, redundantly) on multiple hard disk. By placing data on multiple disks, I/O operations can overlap in a balanced way, improving performance. Since multiple disks increases the mean time between failure (MTBF), storing data redundantly also increases fault-tolerance.

A RAID appears to the operating system to be a single logical hard disk. RAID employs the technique of striping, which involves partitioning each drive's storage space into units ranging from a sector (512 bytes) up to several megabytes. The stripes of all the disks are interleaved and addressed in order.

RAM
Hardware

Random Access Memory: This is reusable computer memory, available to all programs on a computer. A computer with 32M of RAM has about 32 million bytes of memory that programs can use. RAM is read/write memory, as opposed to ROM which is read-only memory. RealPlayer A streaming media delivery system for the Internet. Providers of news, entertainment, sports, and business content can create audio and video multimedia content, and deliver it online to audiences worldwide. To create your own RealPlayer files and offer them on your Web site, your hosting service must install special "extensions" for your account. Ameritech offers RealPlayer extensions.

RARP
Protocol

Reverse Address Resolution Protocol. A method for workstations to ask a server for their IP address during bootstrap operations.

RAS
Lingo

Remote access is the ability to get access to a computer or a network from a remote distance. In corporations, people at branch offices, telecommuters, and people who are travelling may need access to the corporation's network. Home users get access to the Internet through remote access to an Internet service provider (Internet service provider). Dial-up connection through desktop, notebook, or handheld computer modem over regular telephone lines is a common method of remote access. Remote access is also possible using a dedicated line between a computer or a remote local area network and the "central" or main corporate local area network. A dedicated line is more expensive and less flexible but offers faster data rates. Integrated Services Digital Network is a common method of remote access from branch offices since it combines dial-up with faster data rates. wireless, cable modem, and Digital Subscriber Line technologies offer other possibilities for remote access. A remote access server is the computer and associated software that is set up to handle users seeking access to network remotely. Sometimes called a communication server, a remote access server usually includes or is associated with a firewall server to ensure security and a router that can forward the remote access request to another part of the corporate network. A remote access server may include or work with a modem pool manager so that a small group of modems can be shared among a large number of intermittently present remote access users. A remote access server may also be used as part of a virtual private network.

RC4
Software

RC4 is a stream cipher designed by Rivest for RSA Data Security (now RSA Security). It is a variable key-size stream cipher with byte-oriented operations. The algorithm is based on the use of a random permutation. Analysis shows that the period of time to crack the cipher is overwhelmingly likely to be greater than 10100 seconds. Eight to sixteen machine operations are required per output byte, and the cipher can be expected to run very quickly in software. Independent analysts have scrutinized the algorithm and it is considered secure.

Reboot
Lingo

A user activity where the user starts a computing device without interrupting its source of electrical power.

Receiver
Networking

The node or process for which a packet or other information is intended.

Redundant
Hardware

Redundant describes computer or network system components, such as fans, hard disk drives, servers, operating systems, switches, and telecommunication links that are installed to back up primary resources in case they fail. A well-known example of a redundant system is the redundant array of independent disks (RAID).

Relay
Telecommunications

An electronically activated switch which connects one set of wires to another

Reliability
Networking

The ability of a system to perform its specified function without failure. The definition of reliability requires a specification of function, variation from function which is unacceptable, time between failures, duration of failures, etc. Many of these definitions can only be expressed in probabilistic terms.

Remote Access
Telecommunications

Remote access is the ability to get access to a computer or a network from a remote distance. In corporations, people at branch offices, telecommuters, and people who are travelling may need access to the corporation's network. Home users get access to the Internet through remote access to an Internet service provider (ISP). Dial-up connection through desktop, notebook, or handheld computer modem over regular telephone lines is a common method of remote access. Remote access is also possible using a dedicated line between a computer or a remote local area network and the "central" or main corporate local area network. A dedicated line is more expensive and less flexible but offers faster data rates. Integrated Services Digital Network (ISDN) is a common method of remote access from branch offices since it combines dial-up with faster data rates. Wireless, cable modem, and Digital Subscriber Line (DSL) technologies offer other possibilities for remote access.

A remote access server is the computer and associated software that is set up to handle users seeking access to network remotely. Sometimes called a communication server, a remote access server usually includes or is associated with a firewall server to ensure security and a router that can forward the remote access request to another part of the corporate network. A remote access server may include or work with a modem pool manager so that a small group of modems can be shared among a large number of intermittently present remote access users.

Repeater
Networking

In telecommunication networks, a repeater is a device that receives a signal on an electromagnetic or optical transmission medium, amplifies the signal, and then retransmits it along the next leg of the medium. Repeaters overcome the attenuation caused by free-space electromagnetic-field divergence or cable loss. A series of repeaters make possible the extension of a signal over a distance. Repeaters are used to interconnect segments in a local area network (). They're also used to amplify and extend wide area network transmission on wire and wireless media.
Because digital signals depend on the presence or absence of voltage, they tend to dissipate more quickly than analog signals and need more frequent repeating. Whereas analog signal amplifiers are spaced at 18,000 meter intervals, digital signal repeaters are typically placed at 2,000 to 6,000 meter intervals.

ResEdit
PC's

A Macintosh utility that allows a user to modify the resource fork of an HFS file.

Reset button
PC's

A small button that, when pushed, will restart a computer.

Resistor
Hardware

A passive electrical device that adds resistance to a circuit.

Resolution (Screen or Monitor)
Hardware

The way things appear on your computer monitor. Resolution is measured in pixels. The lower the resolution, the larger things appear on your screen. Most computer monitors are set at 800 x 600 resolution, meaning 800 pixels wide by 600 pixels high. Some people's monitors are set at 1024 x 768 or higher. Others are set at 640 x 480. When designing a Web site, keep in mind that your Web pages will look different to viewers depending on their monitor resolutions. You can change your own monitor resolution through your computer's Control Panel (for Mac, Windows 95 and Windows 98).

Resource Fork
PC's

In a Macintosh file, the portion of the file that contains such auxiliary information as the menus, the dialog boxes and sounds that a file may require in addition to its data.

Response Time
Networking

The gap between the time when a user initiates an action and the time that the action displays its results.

RF Interference
Networking

Radio Frequency signals that degrade the integrity of a data signal.

RFC
Lingo

Request for Comments

An RFC (Request for Comments) is an Internet formal document or standard that is the result of committee drafting and subsequent review by interested parties. Some RFCs are informational in nature. Of those that are intended to become Internet standards, the final version of the RFC becomes the standard and no further comments or changes are permitted. Change can occur, however, through subsequent RFCs that supercede or elaborate on all or parts of previous RFCs.

Remote Function Call

An RFC (Remote Function Call) is an application program interface to R/3 applications from Systems, Application and Products in Data Processing, the German company that sells a coordinated set of applications and databases to Fortune 1000 companies. SAP customers who wish to write other applications that communicate with R/3 applications and databases can use the RFC interface to do so.

RFS
Networking

Remote File Sharing. The activity of sharing a file among remote computers.

RGB
Software

RGB (red, green, and blue) refers to a system for representing the colors to be used on a computer display. Red, green, and blue can be combined in various proportions to obtain any color in the visible spectrum. Levels of R, G, and B can each range from 0 to 100 percent of full intensity. Each level is represented by the range of decimal numbers from 0 to 255 (256 levels for each color), equivalent to the range of binary numbers from 00000000 to 11111111, or hexadecimal 00 to FF. The total number of available colors is 256 x 256 x 256, or 16,777,216 possible colors.

Ring Network
Networking

A local-area network (LAN) whose topology is a ring. That is, all of the nodes are connected in a closed loop. Messages travel around the ring, with each node reading those messages addressed to it. One of the advantages of ring networks is that they can span larger distances than other types of networks, such as bus networks, because each node regenerates messages as they pass through it.

RIP
Networking

RIP (Routing Information Protocol) is a widely-used protocol for managing router information within a self-contained network such as a corporate local area network () or an interconnected group of such LANs. RIP is classified by the Internet Engineering Task Force (IETF) as one of several internal gateway protocols (Interior Gateway Protocol).

Using RIP, a gateway host (with a router) sends its entire routing table (which lists all the other hosts it knows about) to its closest neighbor host every 30 seconds. The neighbor host in turn will pass the information on to its next neighbor and so on until all hosts within the network have the same knowledge of routing paths, a state known as network convergence. RIP uses a hop count as a way to determine network distance. (Other protocols use more sophisticated algorithms that include timing as well.) Each host with a router in the network uses the routing table information to determine the next host to route a packet to for a specified destination.

RIP is considered an effective solution for small homogeneous networks. For larger, more complicated networks, RIP's transmission of the entire routing table every 30 seconds may put a heavy amount of extra traffic in the network.

RIPE
Organizations

RIPE (Réseaux IP Européens) functions as the IP delegation point for all of Europe within the context of the Internet. It was formed in 1989 and serves a similar function to ARIN within the context of Eurpoe.

The objective of RIPE is to ensure the necessary administrative and technical coordination to allow the operation and expansion of a pan-European IP network.

RJ-45
Networking

Registered Jack 45. This is an 8-pin connector used for data transmissioin over standard telephone wire. This wire can be flat or twisted. Characteristics include: Single line, 2-wire, T/R, PR/PC, programmed data, 8 position, keyed.

RJ-48C
Telecommunications

Registered Jack 48C. An 8-position keyed plug most commonly used for connecting T-1 circuits. RJ-48C is an 8-position plug with 4 wires (2 for transmit, and 2 for receive).

RJ-48S
Networking

One or two lines. Characteristics include: One or two lines. T/R or T/R, T1/R1, LADC or subrate. 8-position, keyed.

RJ-48X
Networking

Single line. Characteristics include: 4-wire, T/R or T1/R1, 1.544 Mbps. 8-position with shorting bar.

Robert Noyce
People

Robert N. Noyce, cofounder of Intel Corporation, was one of the pioneers of semiconductor development.

Born in Iowa, he received a B.A. from Grinnell College (Iowa) in 1949 and a Ph.D. in physical electronics from the Massachusetts Institute of Technology in 1953. He did research at Philco Corporation until 1956, when he joined Shockley Semiconductor Laboratory in Palo Alto, California, to work on transistor technology.

In 1957 Noyce cofounded the Fairchild Semiconductor Corporation in Mountain View, California. He was research director until early 1959 when he became vice president and general manager. As research director of Fairchild Semiconductor, he was responsible for initial development of the firm's silicon mesa and planar transistor product lines. In July 1968 he cofounded Intel Corp. with Gordon E. Moore, who had also been a cofounder of Fairchild Semiconductor and a member of the Shockley laboratory staff. Noyce served as president of Intel until 1975 and chairman of the board from 1975 to 1979.

Noyce held 16 patents for semiconductor devices, methods, and structures. The development of the silicon microchip has been the most important of his accomplishments because the creation of the microprocessor made possible significant reductions in the cost of computing, along with dramatic advances in the miniaturization of electronics and increases in reliability of performance. No single technological development within the data processing/electronics community has been as significant as the chip. Some historians consider the chip to be one of the greatest achievements of twentieth-century technology, making the present pervasiveness of computing possible and affordable in the industrialized world.

Rock's Law
Concept

A very small addendum to Moore's Law is Rock's Law which says that the cost of capital equipment to build semiconductors will double every four years.

ROM
Hardware

Read-Only Memory: This is a computer's unchangeable memory. It's used to store programs that start the computer and run diagnostic functions.

Root Name Server
Networking

On the Internet, the root server system is the way that an authoritative master list of all top-level domain name (such as com, net, org, and individual country codes) is maintained and made available. The system consists of 13 file servers. The central or "A" server is operated by Network Solutions, Inc., the company that currently manages domain name registration, and the master list of top-level domain (TLD) names is kept on the A server. On a daily basis, this list is replicated to 12 other geographically dispersed file servers that are maintained by an assortment of agencies. The Internet routing system uses the nearest root server list to update routing tables.

Round Robin DNS
Lingo

Round robin DNS is a method of managing server congestion by distributing connection loads across multiple servers (containing identical content). Round robin works on a rotating basis in that one server IP address is handed out, then moves to the back of the list; the next server IP address is handed out, then it moves to the end of the list; and so on, depending on the number of servers being used. This works in a looping fashion. Let's say a company has one domain name and three identical home pages residing on three servers with three different IP addresses. When one user accesses the home page it will be sent to the first IP address. The second user who accesses the home page will be sent to the next IP address, and the third user will be sent to the third IP address. In each case, once the IP address is given out, it goes to the end of the list. The fourth user, therefore, will be sent to the first IP address and so forth. Round robin is different than load balancing. Load balancing distributes connection loads across multiple servers, giving preference to those servers with the least amount of congestion. In round robin's case, server distribution remains on a rigid one IP address to one user rotating basis.

Router
Networking

On the Internet, a router is a device or, in some cases, software in a computer, that determines the next network point to which a packet should be forwarded toward its destination. The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to. A router is located at any juncture of networks or gateway, including each Internet POP. A router is often included as part of a network switch.

A router creates or maintains a table of the available routes and their conditions and uses this information along with distance and cost algorithms to determine the best route for a given packet. Typically, a packet may travel through a number of network points with routers before arriving at its destination.

Routing Information Protocol (RIP)
Protocol

A protocol defined by RFC 1058 that specifies how routers exchange routing table information. With RIP, routers periodically exchange entire tables. Because this is inefficient, RIP is gradually being replaced by a newer protocol called Open Shortest Path First (OSPF).

RPC
Networking

Remote Procedure Call. A command given by one computer to a second computer over a network to execute a defined system call, such as in an NFS session.

RS-232C
Hardware

Short for recommended standard-232C, a standard interface approved by the Electronic Industries Association (EIA) for connecting serial devices. In 1987, the EIA released a new version of the standard and changed the name to EIA-232-D. And in 1991, the EIA teamed up with Telecommunications Industry association (TIA) and issued a new version of the standard called EIA/TIA-232-E. Many people, however, still refer to the standard as RS-232C, or just RS-232. Almost all modems conform to the EIA-232 standard and most personal computers have an EIA-232 port for connecting a modem or other device. In addition to modems, many display screens, mice, and serial printers are designed to connect to a EIA-232 port. In EIA-232 parlance, the device that connects to the interface is called a Data Communications Equipment (DCE) and the device to which it connects (e.g., the computer) is called a Data Terminal Equipment (DTE). The EIA-232 standard supports two types of connectors -- a 25-pin D-type connector (DB-25) and a 9-pin D-type connector (DB-9). The type of serial communications used by PCs requires only 9 pins so either type of connector will work equally well. Although EIA-232 is still the most common standard for serial communication, the EIA has recently defined successors to EIA-232 called RS-422 and RS-423. The new standards are backward compatible so that RS-232 devices can connect to an RS-422 port.

RS-422 and RS-423
Hardware

Standard interfaces approved by the Electronic Industries Association (EIA) for connecting serial devices. The RS-422 and RS-423 standards are designed to replace the older RS-232 standard because they support higher data rates and greater immunity to electrical interference. All Apple Macintosh computers contain an RS-422 port that can also be used for RS-232C communication. RS-422 supports multipoint connections whereas RS-423 supports only point-to-point connections.

RS-485
Hardware

An Electronics Industry Association (EIA) standard for multipoint communications. It supports several types of connectors, including DB-9 and DB-37. RS-485 is similar to RS-422 but can support more nodes per line because it uses lower-impedance drivers and receivers.

RSA
Protocol

Rivest-Shamir-Adleman

RSA is an Internet encryption and authentication system that uses an algorithm developed in 1977 by Ron Rivest, Adi Shamir, and Leonard Adleman. The RSA algorithm is the most commonly used encryption and authentication algorithm and is included as part of the Web browser from Netscape and Microsoft. It's also part of Lotus Notes, Intuit's Quicken, and many other products. The encryption system is owned by RSA Security. The company licenses the algorithm technologies and also sells development kits. The technologies are part of existing or proposed Web, Internet, and computing standards.

How the RSA System Works

The mathematical details of the algorithm used in obtaining the public and private keys are available at the RSA Web site. Briefly, the algorithm involves multiplying two large prime numbers (a prime number is a number divisible only by that number and 1) and through additional operations deriving a set of two numbers that constitutes the public key and another set that is the private key. Once the keys have been developed, the original prime numbers are no longer important and can be discarded. Both the public and the private keys are needed for encryption /decryption but only the owner of a private key ever needs to know it. Using the RSA system, the private key never needs to be sent across the Internet.

The private key is used to decrypt text that has been encrypted with the public key. Thus, if I send you a message, I can find out your public key (but not your private key) from a central administrator and encrypt a message to you using your public key. When you receive it, you decrypt it with your private key. In addition to encrypting messages (which ensures privacy), you can authenticate yourself to me (so I know that it is really you who sent the message) by using your private key to encrypt a digital certificate. When I receive it, I can use your public key to decrypt it.

RSVP
Protocol

Short for Resource Reservation Setup Protocol, a new Internet protocol being developed to enable the Internet to support specified Qualities-of-Service (QoS's). Using RSVP, an application will be able to reserve resources along a route from source to destination. RSVP-enabled routers will then schedule and prioritize packets to fulfill the QoS. RSVP is a chief component of a new type of Internet being developed, known broadly as an integrated services Internet. The general idea is to enhance the Internet to support transmission of real-time data.

RTP
Protocol

Short for Real-Time Transport Protocol, an Internet protocol for transmitting real-time data such as audio and video. RTP itself does not guarantee real-time delivery of data, but it does provide mechanisms for the sending and receiving applications to support streaming data. Typically, RTP runs on top of the UDP protocol, although the specification is general enough to support other transport protocols. RTP has received wide industry support. Netscape intends to base its LiveMedia technology on RTP, and Microsoft claims that its NetMeeting product support RTP.

RTSP
Protocol

Short for Real Time Streaming Protocol, a proposed standard for controlling streaming data over the World Wide Web. RTSP grew out of work done by Columbia University, Netscape and RealNetworks and has been submitted to the IETF for standardization. Like H.323, RTSP uses RTP (Real-Time Transport Protocol) to format packets of multimedia content. But whereas H.323 is designed for videoconferencing of moderately-sized groups, RTSP is designed to efficiently broadcast audio-visual data to large groups.

RTT
Lingo

Round Trip Time. the time between the transmission of a packet and the receipt of its acknowledgment or reply.

S

S-HTTP
Protocol

An extension to the HTTP protocol to support sending data securely over the World Wide Web. Not all Web browsers and servers support S-HTTP. Another technology for transmitting secure communications over the World Wide Web -- Secure Sockets Layer (SSL) -- is more prevalent. However, SSL and S-HTTP have very different designs and goals so it is possible to use the two protocols together. Whereas SSL is designed to establish a secure connection between two computers, S-HTTP is designed to send individual messages securely. Both protocols have been submitted to the Internet Engineering Task Force (IETF) for approval as a standard. S-HTTP was developed by Enterprise Integration Technologies (EIT), which was acquired by Verifone, Inc. in 1995.

S/MIME
Protocol

Short for Secure/MIME, a new version of the MIME protocol that supports encryption of messages. S/MIME is based on RSA's public-key encryption technology. It is expected that S/MIME will be widely implemented, which will make it possible for people to send secure e-mail messages to one another, even if they are using different e-mail clients.

SAA
Lingo

Systems Application Architecture. IBM's architecture for communications and application development.

Samba
Software

Samba is a popular freeware program that allows end users to access and use files, printers, and other commonly shared resources on a company's intranet or on the Internet. Samba is often referred to as a Network File System and can be installed on a variety of operating system platform, including: Linux, most common UNIX platforms, OpenVMS, and OS/2.

Samba is based on the common client/server protocol of Server Message Block (Server Message Block Protocol) and Common Internet File System (Common Internet File System). Using client software that also supports SMB/CIFS (for example, most Microsoft Windows products), an end user sends a series of client requests to the Samba server on another computer in order to open that computer's files, access a shared printer, or access other resources. The Samba server on the other computer responds to each client request, either granting or denying access to its shared files and resources.

The Samba SMB/CIFS client is called smbclient.

SAP
Protocol

  1. (Service Advertising Protocol) A NetWare protocol used to identify the services and addresses of servers attached to the network. The responses are used to update a table in the router known as the Server Information Table.
  2. (Secondary Audio Program) An NTSC audio channel used for auxiliary transmission, such as foreign language broadcasting or teletext.
  3. In telco terminology: Service Access Point. The point where service begins for a customer.

Scalability
Networking

The suitability of a system (particularly a network system to operate properly and efficiently when configured on a large scale.

Screen Saver
PC's

A background process that monitors system activity such as mouse clicks and key strokes and takes over the system during prolonged periods of idle activity to cover the screen with a display that will prevent damage to its phosphors either by reducing the intensity of electron flow or by displaying an image that changes often enough to avoid screen "burn-in". Some screen savers also offer a security option by requiring a password before a user can regain control of the system.

Script
Lingo

A list of commands that can run without user interaction. Search Engine A directory of Internet content. If you're looking for specific information on the WWW, a search engine can list Web sites at which you'll likely find that information. Popular search engines include Excite, Snap, Yahoo, and Infoseek.

SCSI
PC's

SCSI (pronounced SKUH-zee and sometimes colloquially known as "scuzzy"), the Small Computer System Interface, is a set of evolving American National Standards Institute standard electronic interfaces that allow personal computers to communicate with peripheral hardware such as disk drives, tape drives, CD-ROM drives, printers, and scanners faster and more flexibly than previous interfaces. Developed at Apple Computer and still used in the Macintosh, the present set of SCSIs are parallel interfaces. SCSI ports are built into most personal computers today and supported by all major operating systems.

In addition to faster data rates, SCSI is more flexible than earlier parallel data transfer interfaces. The latest SCSI standard, Ultra-2 SCSI for a 16-bit bus can transfer data at up to 80 megabyte per second (MBps). SCSI allows up to 7 or 15 devices (depending on the bus width) to be connected to a single SCSI port in daisy-chain fashion. This allows one circuit board or card to accommodate all the peripherals, rather than having a separate card for each device, making it an ideal interface for use with portable and notebook computers. A single host adapter, in the form of a PC Card, can serve as a SCSI interface for a "laptop," freeing up the parallel and serial ports for use with an external modem and printer while allowing other devices to be used in addition.

Although not all devices support all levels of SCSI, the evolving SCSI standards are generally backwards-compatible. That is, if you attach an older device to a newer computer with support for a later standard, the older device will work at the older and slower data rate.

SDH
Protocol

Short for Synchronous Digital Hierarchy, an international standard for synchronous data transmission over fiber optic cables. The North American equivalent of SDH is SONET. SDH defines a standard rate of transmission at 155.52 Mbps, which is referred to as STS-3 at the electrical level and STM-1 for SDH. STM-1 is equivalent to SONET's Optical Carrier (OC) levels -3.

SDLC
Software

There are two definitions for SDLC:

  1. Systems Development Life Cycle

    (SDLC) Any logical process used by a systems analyst to develop an information system, including requirements, validation, training, and user ownership.

    An SDLC should result in a high quality system that meets or exceeds customer expectations, within time and cost estimates, works effectively and efficiently in the current and planned Information Technology infrastructure, and is cheap to maintain and cost-effective to enhance.

  2. Synchronous Data Link Control

    SDLC is a transmission protocol developed by IBM in the 1970s as a replacement for its binary synchronous (BSC) protocol. SDLC is equivalent to layer 2 of the OSI (Open Systems Interconnection) model of network communication. This level of protocol makes sure that data units arrive successfully from one network point to the next and flow at the right pace. SDLC uses the primary station-secondary station model of communication.

    Typically in IBM mainframe networks, the host mainframe is the primary station and workstations and other devices are secondary stations. Each secondary station has its own address. Typically, multiple devices or secondary stations are attached to a common line in what is known as a multipoint or multidrop arrangement. SDLC can also be used for point-to-point communication. SDLC is primarily for remote communication on corporate wide-area networks (wide area network).

    SDLC was a basis for the International Organization for Standardization standard data link protocol, High-Level Data Link Control (High-Level Data Link Control). SDLC essentially became one of several variations of HDLC, the normal response mode (NRM). While SDLC (and normal response mode) are efficient protocols for closed private networks with dedicated lines, other modes of HDLC serve X.25 and frame relay protocols that manage packet on shared-line switched networks like those used by the Internet.

    SDLC became part of IBM's Systems Network Architecture (Systems Network Architecture) and the more comprehensive Systems Application Architecture (Systems Application Architechture) and its more recent Open Blueprint. SDLC is still a commonly encountered and probably the prevalent data link protocol in today's mainframe environment.

    For more information, check out www.sangoma.com/sdlc.htm.

SDSL
Telecommunications

SDSL (Symmetric DSL) is similar to HDSL with a single twisted-pair line, carrying 1.544 Mbps (U.S. and Canada) or 2.048 Mbps (Europe) each direction on a duplex line. It's symmetric because the data rate is the same in both directions.

Secure Server
PC's

A Web server that supports any of the major security protocols, like SSL, that encrypt and decrypt messages to protect them against third party tampering. Making purchases from a secure Web server ensures that a user's payment or personal information can be translated into a secret code that's difficult to crack. Major security protocols include SSL, SHTTP, PCT, and IPSec.

Security
Lingo

Refers to techniques for ensuring that data stored in a computer cannot be read or compromised. Most security measures involve data encryption and passwords. Data encryption is the translation of data into a form that is unintelligible without a deciphering mechanism. A password is a secret word or phrase that gives a user access to a particular program or system.

Security Certificate
Networking

Security Certificate Information used to establish a secure connection by SSL protocol. In order for an SSL connection to be created, both sides must have a valid Security Certificate, issued by the Certificate Authority.

SED
Programming

SED stands for Stream EDitor. Sed is a non-interactive editor, written by the late Lee E. McMahon in 1973 or 1974. A brief history of sed's origins may be found in an early history of the Unix tools, at .

Instead of the user altering a file interactively by moving the cursor on the screen (like with Word Perfect), the user sends a script of editing instructions to sed, plus the name of the file to edit (or the text to be edited may come as output from a pipe). In this sense, sed works like a filter -- deleting, inserting and changing characters, words, and lines of text. Its range of activity goes from small, simple changes to very complex ones.

Sed reads its input from stdin (Unix shorthand for "standard input," i.e., the console) or from files (or both), and sends the results to stdout ("standard output," normally the console or screen). Most people use sed first for its substitution features. Sed is often used as a find-and-replace tool.

Semiconductor
Hardware

A material that is neither a good conductor of electricity (like copper) nor a good insulator (like rubber). The most common semiconductor materials are silicon and germanium. These materials are then doped to create an excess or lack of electrons.

Computer chips, both for CPU and memory, are composed of semiconductor materials. Semiconductors make it possible to miniaturize electronic components, such as transistors. Not only does miniaturization mean that the components take up less space, it also means that they are faster and require less energy.

Serial
Telecommunications

Serial means one event at a time. It is usually contrasted with parallel, meaning more than one event happening at a time. In data transmission, the techniques of time division and space division are used, where time separates the transmission of individual bits of information sent serially and space (on multiple lines or paths) can be used to have multiple bits sent in parallel.

In the context of computer hardware and data transmission, serial connection, operation, and media usually indicate a simpler, slower operation and parallel indicates a faster operation. This indication doesn't always hold since a serial medium (for example, fiber optic cable) can be much faster than a slower medium that carries multiple signals in parallel.

On your PC, the printer is usually attached through a parallel interface and cable so that it will print faster. Your keyboard and mouse are one-way devices that only require a serial interface and line. Inside your computer, much of its circuitry supports bits being moved around in parallel.

Your computer modem uses one of your PC's serial connections or COM ports. Serial communication between your PC and the modem and other serial devices adheres to the RS-232C standard.

Conventional computers and their programs operate in a serial manner, with the computer reading a program and performing its instructions one after the other. However, some of today's computers have multiple processors and can perform instructions in parallel.

Serial Port
Networking

A port on a computing device that is capable of either transmitting or receiving one bit at a time. Examples include the Mac's printer and modem ports.

Serial Transmission
Telecommunications

Sending pulses one after another rather than one at a time.

Server
Hardware

Server A computer or device that manages network resources. The term can refer to a piece of software, or to the machine on which the software is running. A single server machine could be running several different server software packages, thus providing many different services to users on the network.

Server Mirroring
Lingo

Utilizing a backup server that duplicates all the processes and transactions of the primary server. If, for any reason, the primary server fails, the backup server can immediately take its place without any down -time. Server mirroring is an expensive but effective strategy for achieving fault tolerance. It's expensive because each server must be mirrored by an identical server whose only purpose is to be there in the event of a failure. A less expensive technique that is becoming more and more popular is clustering.

Server-Side
Software

Occurring on the server side of a client-server system. For example, on the World Wide Web, CGI scripts are server-side applications because they run on the Web server. In contrast, JavaScript scripts are client-side because they are executed by your browser (the client). Java applets can be either server-side or client-side depending on which computer (the server or the client) executes them.

Session
Networking

An on-going relationship between two computing devices involving the allocation of resources and sustained date flow.

Session Layer
Networking

The layer in the OSI 7-Layer Model that is concerned with managing the resources required for the session between two computers.

Set
Lingo

In SNMP, the command given by the Console that asks the MIB to change the value of a data object in its MIB.

SGI
PC's

Short for Silicon Graphics Incorporated, a company based in Mountain View, California that provides computer hardware and software. SGI was founded by Dr. James Clark in 1982 and had its initial public offering in 1986. It is best known for products used to develop computer graphics such as those used to create special effects and animation in motion pictures. The company has over 10,000 employees world-wide and had sales of $2.9 billion in 1996. SGI formed Silicon Studio in 1994 to serve the interactive digital media market. The company merged with MIPS Computer Systems in 1992, Alias Research and Wavefront Technologies in 1995, and Cray Research in 1996. SGI provides a wide range of hardware and software products that include high-performance workstations and servers to meet the needs of those developing complex computer graphics or manipulating video images. New products include World Wide Web authoring tools and servers.

Shareware
Software

Software distributed on the basis of an honor system. Most shareware is delivered free of charge, but the author usually requests that you pay a small fee if you like the program and use it regularly. By sending the small fee, you become registered with the producer so that you can receive service assistance and updates. You can copy shareware and pass it along to friends and colleagues, but they too are expected to pay a fee if they use the product. Shareware is inexpensive because it is usually produced by a single programmer and is offered directly to customers. Thus, there are practically no packaging or advertising expenses. Note that shareware differs from public-domain software in that shareware is copyrighted. This means that you cannot sell a shareware product as your own.

Shopping Cart
Lingo

A shopping cart is a piece of software that acts as an online store's catalog and ordering process. Typically, a shopping cart is the interface between a company's Web site and its deeper infrastructure, allowing consumers to select merchandise; review what they have selected; make necessary modifications or additions; and purchase the merchandise. Shopping carts can be sold as independent pieces of software so companies can integrate them into their own unique online solution, or they can be offered as a feature from a service that will create and host a company's e-commerce site.

Short
Lingo

The direct connection of two or more conductors of a circuit with each other.

Signal
Telecommunications

  1. In electronics, a signal is an electric current or electromagnetic field used to convey data from one place to another. The simplest form of signal is a direct current (DC) that is switched on and off; this is the principle by which the early telegraph worked. More complex signals consist of an alternating-current (AC) or electromagnetic carrier that contains one or more data streams.

    Data is superimposed on a carrier current or wave by means of a process called modulation. Signal modulation can be done in either of two main ways: analog and digital. In recent years, digital modulation has been getting more common, while analog modulation methods have been used less and less. There are still plenty of analog signals around, however, and they will probably never become totally extinct.

    Except for DC signals such as telegraph and baseband, all signal carriers have a definable frequency or frequencies. Signals also have a property called wavelength, which is inversely proportional to the frequency.

  2. In some information technology contexts, a signal is simply "that which is sent or received," thus including both the carrier (see 1) and the data together.

  3. In telephony, a signal is special data that is used to set up or control communication.

Signal to Noise Ratio
Concept

In an electromagnetic signal, the ratio of the amplitude (strength) of a signal to the amplitude of the ambient radiation and other signal disturbances that are present, usually expressed in decibels (dB).

Signalling
Telecommunications

In telephony, signaling is the exchange of information between involved points in the network that sets up, controls, and terminates each telephone call. In in-band signaling, the signaling is on the same channel as the telephone call. In out-of-band signaling, signaling is on separate channels dedicated for the purpose.

SLA
Lingo

Service Level Agreement. An SLA is a written agreement of what quality of service Verio will provide. Usually downtime, packet loss, and latency are components of an SLA as well as the penalties Verio impose on itself (credits) for falling below the SLA guidelines.

Slewing Rate
Concept

The maximum rate, usually expressed in volts/second, at which an active device such as a transistor or transformer can change its voltage state.

SLIP
Protocol

Short for Serial Line Internet Protocol, a method of connecting to the Internet. Another more common method is PPP (Point-to-Point Protocol). SLIP is an older and simpler protocol, but from a practical perspective, there's not much difference between connecting to the Internet via SLIP or PPP. In general, service providers offer only one protocol although some support both protocols.

SMART
Hardware

Acronym for Self-Monitoring, Analysis and Reporting Technology, an open standard for developing disk drives and software systems that automatically monitor a disk drive's health and report potential problems. Ideally, this should allow you to take proactive actions to prevent impending disk crashes.

Smartjack
Telecommunications

A piece of Telco equipment that terminates the telephone company signal. It can also used to monitor and troubleshoot a T1. It has 5 indicator lights: Power, Receive Loss of Signal (RLOS), Transmit Loss of Signal (TLOS), Loop Back, Alarm.

SMB
Networking

Short for Server Message Block, a message format used by DOS and Windows to share files, directories and devices. NetBIOS is based on the SMB format, and many network products use SMB. These SMB-based networks include Lan Manager, Windows for Workgroups, Windows NT, and Lan Server. There are also a number of products that use SMB to enable file sharing among different operating system platforms. A product called Samba, for example, enables UNIX and Windows machines to share directories and files.

SMDS
Telecommunications

SMDS (Switched Multimegabit Data Service) is a public, packet-switched service aimed at enterprises that need to exchange large amounts of data with other enterprises over the wide-area network on a nonconstant or "bursty" basis. SMDS provides an architecture for this kind of data exchange and a set of services. In general, SMDS extends the performance and efficiencies of a company's local area network (LANs) over a wide area on a switched, as-needed basis. SMDS is connectionless, meaning that there is no need to set up a connection through the network before sending data. This provides bandwidth on demand for the "bursty" data transmission typically found on LANs.

SMDS packets contain up to 7168 bytes of data, which is large enough to accept the most common LAN packets. Each packet includes the source address and the destination address and is sent separately from other packets.

Each enterprise using SMDS is assigned from one to sixteen unique SMDS addresses, depending on needs. An address is a ten digit number that looks like an ordinary telephone number.

SMDS also provides for broadcasting packets to multiple SMDS addresses. Each SMDS company is assigned one or more group addresses that can be used to define destination groups. Group addressing is similar to LAN multicasting. It lets routing protocols, such as TCP/IP, use dynamic address resolution and routing updates.

Since SMDS is a public service, any SMDS customer can exchange data with any other customer. The SMDS Interest Group, an association of service providers, equipment manufacturers, and users, develops technical specifications, promotes awareness of SMDS, stimulates new applications, and ensures worldwide service interoperability, working with its international affiliates. Their home page provides a list of companies providing SMDS services.

SMI
Lingo

Structure of Management Information.

SMIL
Protocol

Short for Synchronized Multimedia Integration Language, a new markup language being developed by the World Wide Web Consortium (W3C) that would enable Web developers to divide multimedia content into separate files and streams (audio, video, text, and images), send them to a user's computer individually, and then have them displayed together as if they were a single multimedia stream. The ability to separate out the static text and images should make the multimedia content much smaller so that it doesn't take as long to travel over the Internet. SMIL is based on the eXtensible Markup Language (XML). Rather than defining the actual formats used to represent multimedia data, it defines the commands that specify whether the various multimedia components should be played together or in sequence.

SMTP
Protocol

Short for Simple Mail Transfer Protocol, a protocol for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP. In addition, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your e-mail application.

SNA
Lingo

Systems Network Architecture. IBM's communications architecture and strategy.

Snailmail
Lingo

The term used to define the method of a letter being physically delivered to a person using the Post Office or some other letter carrier.

SNMP
Protocol

Short for Simple Network Management Protocol, a set of protocols for managing complex networks. The first versions of SNMP were developed in the early 80s. SNMP works by sending messages, called protocol data units (PDUs), to different parts of a network. SNMP-compliant devices, called agents, store data about themselves in Management Information Bases (MIBs) and return this data to the SNMP requesters. SNMP 1 reports only whether a device is functioning properly. The industry has attempted to define a new set of protocols called SNMP 2 that would provide additional information, but the standardization efforts have not been successful. Instead, network managers have turned to a related technology called RMON that provides more detailed information about network usage.

SNMPv2
Protocol

Simple Network Management Protocol Version 2. Offers increased performance, better security, greater portability and greater ability to manage non-network resources.

SOAP
Protocol

Simple Object Access Protocol provides a way for applications to communicate with each other over the Internet, independent of platform. Unlike DCOM's IIOP, SOAP piggybacks a DOM onto HTTP (port 80) in order to penetrate server firewalls, which are usually configured to accept port 80 and port 21 (FTP ) requests. SOAP relies on XML to define the format of the information and then adds the necessary HTTP headers to send it. SOAP was developed by Microsoft, DevelopMentor, and Userland Software and has been proposed to the Internet Engineering Task Force (IETF ) as a standard.

SOCKS
Protocol

A protocol for handling TCP traffic through a proxy server. It can be used with virtually any TCP application, including Web browsers and FTP clients. It provides a simple firewall because it checks incoming and outgoing packets and hides the IP addresses of client applications. There are two main versions of SOCKS -- V4 and V5. V5 adds an authentication mechanism for additional security. There are many freeware implementations of both versions. One of the most common V5 implementations is SOCKS5, developed by NEC. SOCKS was recently accepted as an IETF standard and is documented in RFC 1928, 1929 and 1961.

SOHO
Lingo

Small Office / Home Office. This market segment is positioned between the Enterprise and Consumer markets. Generally less than 50 employees or as few as one.

SONET
Networking

Synchronous Optical Network. A standard for a worldwide digital network using a common transport. SONET can run over copper or fiber.

SONET Ring
Networking

SONET transmission systems are ideally are laid out in a physical ring for purposes of redundancy.

SOP
Lingo

Standard Operating Procedure.

Source
Networking

The node or process transmitting information.

SPAM
Lingo

  1. To mass-mail unrequested identical or nearly-identical email messages, particularly those containing advertising. Especially used when the mail addresses have been culled from network traffic or databases without the consent of the recipients. Synonyms include UCE (Unsolicited Commercial Email), UBE (Unsolicited Bulk Email).
  2. To bombard a newsgroup with multiple copies of a message. This is more specifically called `EMP', Excessive Multi-Posting.
  3. To send many identical or nearly-identical messages separately to a large number of Usenet newsgroups. This is more specifically called 'ECP', Excessive Cross-Posting. This is one sure way to infuriate nearly everyone on the Net.
  4. To cause a newsgroup to be flooded with irrelevant or inappropriate messages.
  5. To crash a program by overrunning a fixed-size buffer with excessively large input data.
  6. Any large, annoying, quantity of output. For instance, someone on IRC who walks away from their screen and comes back to find 200 lines of text might say "Oh no, spam".

     "Go away for a few days, and you will probably have to clear the junk out of your mailbox with a shovel. Sadly, the same is increasingly likely to be true of your virtual mailbox which will, unless you are lucky, be full of spam."
     Economist, Spam, spam, spam, spam, Nov 1, 1997

Span
Telecommunications

Refers to that portion of a high-speed digital system that connects a CO to a CO or a terminal office to a terminal office.

SPARC
PC's

Short for Scalable Processor Architecture, a RISC technology developed by Sun Microsystems. The term SPARC® itself is a trademark of SPARC International, an independent organization that licenses the term to Sun for its use. Sun's workstations based on the SPARC include the SPARCstation, SPARCserver, Ultra1, Ultra2 and SPARCcluster.

Specification
Programming

A document that defines a concept and its allowable implementation forms.

Spider
Lingo

An Internet robot (used by a search engine) that explores the Web at large. Spiders collect Web page addresses based on content found at those pages.

Spike
Lingo

A sudden and transient increase in the voltage from a power supply.

Splice
Telecommunications

The joining of two or more cables together by splicing the conductors pair-to-pair.

SPX
Protocol

Short for Sequenced Packet Exchange, a transport layer protocol (layer 4 of the OSI Model) used in Novell Netware networks. The SPX layer sits on top of the IPX layer (layer 3) and provides connection-oriented services between two nodes on the network. SPX is used primarily by client/server applications. Whereas the IPX protocol is similar to IP, SPX is similar to TCP. Together, therefore, IPX/SPX provides connection services similar to TCP/IP.

SQL
Software

SQL is an abbreviation of structured query language, and pronounced either see-kwell or as separate letters. SQL is a standardized query language for requesting information from a database. The original version called SEQUEL (structured English query language) was designed by an IBM research center in 1974 and 1975. SQL was first introduced as a commercial database system in 1979 by Oracle Corporation.

Historically, SQL has been the favorite query language for database management systems running on minicomputers and mainframes. Increasingly, however, SQL is being supported by PC database systems because it supports distributed databases (databases that are spread out over several computer systems). This enables several users on a local-area network to access the same database simultaneously.

Although there are different dialects of SQL, it is nevertheless the closest thing to a standard query language that currently exists. In 1986, ANSI approved a rudimentary version of SQL as the official standard, but most versions of SQL since then have included many extensions to the ANSI standard. In 1991, ANSI updated the standard. The new standard is known as SAG SQL.

SQL Server
PC's

Generically, any database management system (DBMS) that can respond to queries from client machines formatted in the SQL language. When capitalized, the term generally refers to either of two database management products from Sybase and Microsoft. Both companies offer client-server DBMS products called SQL Server.

Square wave
Concept

An electromagnetic wave that oscillates between two voltage states, theoretically requiring no time to accomplish a state transition.

SS7
Protocol

Signaling System 7 is a telecommunications protocol defined by the International Telecommunication Union (ITU) as a way to offload PSTN data traffic congestion onto a wireless or wireline digital broadband network.

SS7 is characterized by high-speed packet switching and out-of-band signaling using Service Switching (SSPs), Signal Transfer Points (STPs), and Service Control Points (SCPs) (collectively referred to as signaling points, or SS7 nodes). Out-of-band signaling is signaling that does not take place over the same path as the data transfer (or conversation)--a separate digital channel is created (called a signaling link), where messages are exchanged between network elements at 56 or 64 kilobit per second.

SS7 architecture is set up in a way so that any node could exchange signaling with any other SS7-capable node, not just signaling between switches that are directly connected.

The SS7 network and protocol are used for:

SSH
Software

Developed by SSH Communications Security Ltd., Secure Shell is a program to log into another computer over a network, to execute commands in a remote machine, and to move files from one machine to another. It provides strong authentication and secure communications over insecure channels. It is a replacement for rlogin, rsh, rcp, and rdist.

SSH protects a network from attacks such as IP spoofing, IP source routing, and DNS spoofing. An attacker who has managed to take over a network can only force ssh to disconnect. He or she cannot play back the traffic or hijack the connection when encryption is enabled.

When using ssh's slogin (instead of rlogin) the entire login session, including transmission of password, is encrypted; therefore it is almost impossible for an outsider to collect passwords.

SSH is available for Windows, Unix, Macintosh, and OS/2, and it also works with RSA authentication.

SSI
Software

A server-side include is a variable value (for example, a file "Last modified" date) that a server can include in an HTML file before it sends it to the requestor. If you're creating a Web page, you can insert an include statement in the HTML file that looks like this:

Monday, 24-Jul-2000 11:31:36 EDT

and the server will obtain the last-modified date for the file and insert it before the HTML file is sent to requestors.

LAST_MODIFIED is one of several environment variables that an operating system can keep track of and that can be accessible to a server program. The server administrator can make these environment variables usable when the system is set up.

A Web file that contains server-side include statements (such as the "echo" statement above) is usually defined by the administrator to be a file with an "." suffix. You can think of a server-side include as a limited form of common gateway interface application. In fact, the CGI is not used. The server simply searches the server-side include file for CGI environment variables, and inserts the variable information in the places in the file where the "include" statements have been inserted.)

SSL
Software

secure socket layer; an encryption technology for the Web used to provide secure transactions such as the transmission of credit-card numbers for e-commerce.

Standard
Lingo

1. A synonym for specification. 2. A component or way of accomplishing a task that is so frequently and widely used that is seems to be part of a specification.

Standby Monitor
Networking

Device placed in standby mode on a Token Ring network in case an active monitor fails. See also active monitor and ring monitor.

Star Network
Networking

A local-area network (LAN) that uses a star topology in which all nodes are connected to a central computer. The main advantages of a star network is that one malfunctioning node doesn't affect the rest of the network, and it's easy to add and remove nodes. The main disadvantage of star networks is that they require more cabling than other topologies, such as a bus or ring networks. In addition, if the central computer fails, the entire network becomes unusable.

StarLAN
Protocol

CSMA/CD LAN, based on IEEE 802.3, developed by AT&T.

Static Route
Networking

Route that is explicitly configured and entered into the routing table. Static Routes take precedence over routes chosen by dynamic routing protocols.

Statistical Multiplexing
Networking

Technique in which information from multiple logical channels can be transmitted across a single physical channel. Statistical multiplexing dynamically allocates bandwidth only to active input channels, making better use of available bandwidth and allowing more devices to be connected than with other multiplexing techniques. Also referred to as statistical time-division multiplexing or stat mux.

STM-1
Networking

Synchronous Transport Module level 1. One of a number of SDH formats that specifies the frame structure for the 155.52-Mbps lines used to carry ATM cells.

Store And Forward Packet Switching
Networking

Packet-switching technique in which frames are completely processed before being forwarded out the appropriate port. This processing includes calculating the CRC and checking the destination address. In addition, frames must be temporarily stored until network resources are available to forward the message.

STP
Telecommunications

Shielded twisted-pair. Two-pair wiring medium used in a variety of network implementations. STP cabling has a layer of shielded insulation to reduce EMI.

Stub Area
Networking

OSPF area that carries a default route, intra-area routes, and interarea routes, but does not carry external routes. Virtual links cannot be configured across a stub area, and they cannot contain as ASBR.

Stub Network
Networking

Network that has only a single connection to a router.

Subchannel
Telecommunications

In broadband terminology, a frequency-based subdivision creating a separate communications channel.

Subnet
Networking

A subnet (short for "subnetwork") is an identifiably separate part of an organization's network. Typically, a subnet may represent all the machines at one geographic location, in one building, or on the same local area network (LAN). Having an organization's network divided into subnets allows it to be connected to the Internet with a single shared network address. Without subnets, an organization could get multiple connections to the Internet, one for each of its physically separate subnetworks, but this would require an unnecessary use of the limited number of network numbers the Internet has to assign. It would also require that Internet routing tables on gateways outside the organization would need to know about and have to manage routing that could and should be handled within an organization.

The Internet is a collection of networks whose users communicate with each other. Each communication carries the address of the source and destination networks and the particular machine within the network associated with the user or host computer at each end. This address is called the IP address (Internet Protocol address). This 32-bit IP address has two parts: one part identifies the network (with the network number) and the other part identifies the specific machine or host within the network (with the host number). An organization can use some of the bits in the machine or host part of the address to identify a specific subnet. Effectively, the IP address then contains three parts: the network number, the subnet number, and the machine number.

Subnet Address
Networking

Portion of an IP address that is specified as the subnetwork by the subnet mask. See also IP address, subnet mask, and subnetwork.

Subnet Mask
Networking

To facilitate intra-network routing, a single IP network can be divided into many subnets by using some of the most significant bits of the host address portion of the IP address as a subnet ID.

For example, Network 129.5.0.0 has 16 bits assigned as the network ID (specifically 129.5, in dotted decimal, which is 10000001.00000101 in binary) as it is a Class B address (the first number is between 128 and 192).

This leaves the lower 16 bits as the host address.

Using a Subnet Bit Mask of 255.255.255.0 (which in binary is 11111111.11111111.11111111.00000000), specifies that the upper 24 bits (those that are set to a 1) are the network plus subnet address--that is, the 16 bits that we already expected plus the upper 8 bits of the host address. Therefore the network 129.5.0.0 (in this example) would consist of up to 254 subnets (129.5.1.0 through 129.5.254.0) of up to 254 hosts each.

This is useful for subdividing networks, for example, to reduce the number of stations that must receive broadcasts.

Subnetwork
Networking

A subnetwork is a separately identifiable part of a larger network that typically represents a certain limited number of host computers, the hosts in a building or geographic area, or the hosts on an individual local area network. Companies often create subnetworks (sometimes called subnet) when setting up connection to the Internet as a way to manage the limited number of Internet Protocol addresses (IP address) that are available with Internet Protocol version 4.

Subvector
Networking

A data segment of a vector in an SNA message. A subvector consists of a length field, a key that describes the subvector type, and subvector specific data.

Sudo
Software

Sudo (superuser do) is a utility for UNIX-based systems that provides an efficient way to give specific users permission to use specific system commands at the root (most powerful) level of the system. Sudo also logs all commands and arguments. Using sudo, a system administrator can:

SURAnet
Organizations

Southeastern Universities Research Association Network. Network connecting universities and other organizations in the Southeastern United States. SURAnet, originally funded by the NSF and a part of the NSFNET, is now part of BBN Planet.

SVC
Telecommunications

Switched Virtual Circuit

In a network, an SVC (switched virtual circuit) is a temporary virtual circuit that is established and maintained only for the duration of a data transfer session. A permanent virtual circuit (Permanent Virtual Circuit) is a continuously dedicated virtual circuit. A virtual circuit is one that appears to be a discrete, physical circuit available only to the user but that is actually a shared pool of circuit resources used to support multiple users as they require the connections. Switched virtual circuits are part of an X.25 network. Conceptually, they can also be implemented as part of a frame relay network.

SVGA
PC's

Super Video Graphics Array or Ultra Video Graphics Array, almost always abbreviated to Super VGA, Ultra VGA or just SVGA or UVGA is a broad term that covers a wide range of computer display standards.

Originally, it was an extension to the VGA standard first released by IBM in 1987. Unlike VGA—a purely IBM-defined standard—Super VGA was never formally defined. The closest to an "official" definition was in the VBE extensions defined by the Video Electronics Standards Association (VESA), an open consortium set up to promote interoperability and define standards. In this document, there was simply a footnote stating that "The term 'Super VGA' is used in this document for a graphics display controller implementing any superset of the standard IBM VGA display adapter." When used as a resolution specification, in contrast to VGA or XGA for example, the term SVGA normally refers to a resolution of 800 × 600 pixels.

Though Super VGA cards appeared in the same year as VGA (1987), it wasn't until 1989 that a standard for programming Super VGA modes was defined by VESA. In that first version, it defined support for (but did not require) a maximum resolution of 800 × 600 4-bit pixels. Each pixel could therefore be any of 16 different colours. It was quickly extended to 1024 × 768 8-bit pixels, and well beyond that in the following years.

SWIP
Networking

Shared WHOIS Project

According to whois.arin.net, the purpose of a SWIP is as follows:

  1. Updates WHOIS to show which organization is using the assigned IP address space.
  2. Provides a point of contact within the organization to which the IP space is assigned.
  3. Tracks whether a provider has exhausted or is about to exhaust its current CIDR block allocations such that an additional allocation may be justified.

Switch
Networking

A switch is a device that makes decisions on the routing of traffic. Like a hub and a bridge, a switch can connect different network protocols, like 10Base-T and 100Base-T. However, a switch makes decisions based upon the layer 2 packets as they are passed through the device. In the telephone networks, switches are used to connect virtual circuits within the phone network.

A switch may also include the function of the router, a device or program that can determine the route and specifically what adjacent network point the data should be sent to. In general, a switch is a simpler and faster mechanism than a router, which requires knowledge about the network and how to determine the route. Some newer switches also perform the routing functions of layer 3, the Network layer. Layer 3 switches are also sometimes called IP switches.

Switch Room
Telecommunications

That part of a switching center or central office building that houses the actual switching equipment.

Switched 56
Telecommunications

A dial-up communication service available from a telephone service provider that offers a fractional portion of a T1 line built from as many as 24 channels of 56 KBPS each. Also called Fractional T1.

Switching
Telecommunications

The process of interconnecting circuits to form a communication path between pairs of stations out of a population of a much larger number of potential stations. The process may be implemented using a variety of technologies and it includes a number of peripheral functions in addition to the connection function such as call supervision, routing, call recording, etc.

Symmetric Encryption
Software

A type of encryption where the same key is used to encrypt and decrypt the message. This differs from asymmetric (or public-key) encryption, which uses one key to encrypt a message and another to decrypt the message. A common example of this is known as the Caeser 13 key. It simply takes as input a sentence and shifts the letters up by 13 in the alphabet and wraps around when going from Z over to A. To decrypt a message, you can simply use the same 13 letter shift that you did to encrypt the message.

Synchronization
Networking

Establishment of common timing between sender and receiver.

Synchronous Transmission
Telecommunications

A data transmission technique in which the sending and the receiving stations are held in synchronization with each other for the duration of a transmission of a block of data or for the entire transmission. Synchronization is maintained either by high accuracy clocks at both ends of the line or by timing signals included in the transmitted data. The primary alternative to synchronous transmission is asynchronous transmission, which the sending and receiving stations remain in synch only for the duration of a single character.

Syncrhonize
Software

To cause to match exactly.

Syntax
Software

Refers to the spelling and grammar of a programming language. Computers are inflexible machines that understand what you type only if you type it in the exact form that the computer expects. The expected form is called the syntax.

Each program defines its own syntactical rules that control which words the computer understands, which combinations of words are meaningful, and what punctuation is necessary.

System
PC's

Any computer system that can be controlled by a user consisting of a CPU and optional equipment such as display monitors, disk drives, and other peripherals.

System File
PC's

The Macintosh file that contains system software for the Macintosh OS, including patches or replacements to obsolete code contained in ROM.

System Management
Networking

Activities that focus on the care and management of individual computer systems.

System Software
Software

Software in a computing system that provides basic functionality like file management, visual display, and keyboard input and is used by application software to accomplish these functions.

T

T-2
Telecommunications

Four multiplexed T-1 lines offering a communication channel at 6.3 MBPS. Available

T-3
Networking

A connection capable of carrying data at 44,736,000 bits per second. Equivalent to 29 T-1 connections.

T-Carrier
Telecommunications

The T-carrier system, introduced by the Bell System in the U.S. in the 1960s, was the first successful system that supported digitized voice transmission. The original transmission rate (1.544 Mbps) in the T-1 line is in common use today in Internet service provider (Internet service provider) connections to the Internet. Another level, the T-3 line, providing 44.736 Mbps, is also commonly used by Internet service provider. Another commonly installed service is a fractional T-1, which is the rental of some portion of the 24 channels in a T-1 line, with the other channels going unused.

The T-carrier system is entirely digital, using pulse code modulation and Time-Division Multiplexing. The system uses four wires and provides duplex capability (two wires for receiving and two for sending at the same time). The T-1 digital stream consists of 24 64-Kbps channel that are multiplexing. (The standardized 64 Kbps channel is based on the bandwidth required for a voice conversation.) The four wires were originally a pair of twisted pair copper wires, but can now also include coaxial cable, optical fiber, digital microwave, and other media. A number of variations on the number and use of channels are possible.

In the T-1 system, voice signals are sampled 8,000 times a second and each sample is digitized into an 8-bit word. With 24 channels being digitized at the same time, a 192-bit frame (24 channels each with an 8-bit word) is thus being transmitted 8,000 times a second. Each frame is separated from the next by a single bit, making a 193-bit block. The 192 bit frame multiplied by 8,000 and the additional 8,000 framing bits make up the T-1's 1.544 Mbps data rate. The signaling bits are the least significant bits per frame.

T1
Telecommunications

The T1 (or T-1) carrier is the most commonly used digital line in the United States, Canada, and Japan. In these countries, it carries 24 pulse code modulation (pulse code modulation) signals using Time-Division Multiplexing at an overall rate of 1.544 megabit per second. T1 lines use copper wire and span distances within and between major metropolitan areas. A T1 Outstate System has been developed for longer distances between cities.

TAC
Lingo

Terminal Access Controller. Internet host that accepts terminal connections from dial-up lines.

TACACS
Protocol

TACACS (Terminal Access Controller Access Control System) is an older authentication protocol common to UNIX networks that allows a remote access server to forward a user's logon password to an authentication server to determine whether access can be allowed to a given system. TACACS is an encryption protocol and therefore less secure than the later TACACS+ and Remote Authentication Dial-In User Service protocols. A later version of TACACS is XTACACS (Extended TACACS). Both are described in Request for Comments 1492.

In spite of its name, TACACS+ is an entirely new protocol. TACACS+ and RADIUS have generally replaced the earlier protocols in more recently built or updated networks. TACACS+ uses the Transmission Control Protocol (Transmission Control Protocol) and RADIUS uses the User Datagram Protocol (User Datagram Protocol). Some administrators recommend using TACACS+ because TCP is seen as a more reliable protocol. Whereas RADIUS combines authentication and authorization in a user profile, TACACS+ separates the two operations.

Tap
Lingo

An intrusion into a network cable by a connector.

Tariff
Telecommunications

The schedule of rates and regulations pertaining to the services of a communications common carrier. Tariffs are filed with the appropriate regulatory agency.

Task
Lingo

1) Synonym for process. 2) An activity or group of activities necessary to accomplish a goal.

TAXI 4B/5B
Networking

Transparent Asynchronous Transmitter/Receiver Interface 4- byte/5- byte. Encoding scheme used for FDDI LANs, as well as for ATM. Supports speeds of up to 100 Mbps over multimode fiber. TASI is the chipset that generates 4B/5B encoding on multimode fiber.

TCP
Protocol

Abbreviation of Transmission Control Protocol, and pronounced as separate letters. TCP is one of the main protocols in TCP/IP networks. Whereas the IP protocol deals only with packets, TCP enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent. This is extremely useful for applications that require whole, unadulterated packets in order to communicate properly, such as POP3 and SMTP.

TCP/IP
Protocol

Abbreviation for Transmission Control Protocol/Internet Protocol, the suite of communications protocols used to connect hosts on the Internet. TCP/IP uses several protocols, the two main ones being TCP and IP. TCP/IP is built into the UNIX operating system and is used by the Internet, making it the de facto standard for transmitting data over networks. Even network operating systems that have their own protocols, such as Netware, also support TCP/IP.

TCU
Networking

Trunk coupling unit. In Token Ring networks, a physical device that enables a station to connect to the trunk cable.

TDM
Lingo

Time-division multiplexing. Technique in which information from multiple channels can be allocated bandwidth on a single wire based on preassigned time slots. Bandwidth is allocated to each channel regardless of whether the station has data to transmit.

TDR
Hardware

Time domain reflectometer. Device capable of sending signals through a network medium to check cable continuity and other attributes. TDRs are used to find physical layer network problems.

Telco
Lingo

Abbreviation for telephone company.

Telecommunications
Telecommunications

The system of technologies used in telephone communications.

Telephony
Telecommunications

The science and practice of telecommunications.

Telex
Telecommunications

Teletypewriter service allowing subscribers to send messages over the PSTN.

Telnet
Protocol

Telnet is the way you can access someone else's computer, assuming they have given you permission. (Such a computer is frequently called a host computer.) More technically, Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers. The Web or Hypertext Transfer Protocol protocol and the File Transfer Protocol protocol allow you to request specific files from remote computers, but not to actually be logon as a user of that computer. With Telnet, you log on as a regular user with whatever privileges you may have been granted to the specific application and data on that computer.

A Telnet command request looks like this (the computer name is made-up):

telnet the.libraryat.harvard.edu
The result of this request would be an invitation to log on with a userid and a prompt for a password. If accepted, you would be logged on like any user who used this computer every day.

TERENA
Organizations

Trans-European Research and Education Networking Association. Organization that promotes information and telecommunications technologies development in Europe. Formed by the merging of EARN and RARE.

Terminal
Networking

  • In data communications, a terminal is any device that terminates one end (sender or receiver) of a communicated signal. In practice, it is usually applied only to the extended end points in a network, not central or intermediate devices. In this usage, if you can send signals to it, it's a terminal.
  • In telephony, the term Data Terminal Equipment (Data Terminal Equipment) is used to describe the computer end of the DTE-to-DCE (Data Communications Equipment) communication between a computer and a modem.
  • In computers, a terminal (sometimes qualified as a "dumb" terminal) is an end-use device (usually with display monitor and keyboard) with little or no software of its own that relies on a mainframe or another computer (such as a PC server) for its "intelligence." IBM's 3270 Information Display System was a widely-installed system of such terminals in corporations. Many applications designed for the 3270 or other "dumb" terminals are still in use at PCs that emulate or act like a 3270. The VT-100 from Digital Equipment Corporation is another example of a widely-used so-called "dumb" terminal. A variation of this kind of terminal is being revived in the idea of the thin client or network computer.
  • The term is sometimes used to mean any personal computer or user workstation that is hooked up to a network.
  • Terminal Adapter
    Hardware

    Device used to connect ISDN BRI connections to existing interfaces such as EIA/TIA-232. Essentially, an ISDN modem.

    Terminal Emulation
    Networking

    A computing activity in which a computer runs an application and communicates with a host as if it were a terminal such as a DEC VT220.

    Terminal Server
    Networking

    Communications processor that connects asynchronous devices such as terminals, printers, hosts, and modems to any LAN or WAN that uses TCP/IP, X.25, or LAT protocols. Terminal servers provide the internetwork intelligence that is not available in the connected devices.

    Terminator
    Hardware

    Typically, a resistor placed at the end of a bus to prevent the reflection of signals.

    TFTP
    Protocol

    Abbreviation of Trivial File Transfer Protocol, a simple form of the File Transfer Protocol (FTP). TFTP uses the User Datagram Protocol (UDP)and provides no security features. It is often used by servers to boot diskless workstations, X-terminals, and routers.

    TH
    Networking

    Transmission header. SNA header that is appended to the SNA basic information unit (BIU). The TH uses one of a number of available SNA header formats.

    The Open Group
    Organizations

    An international consortium of computer and software manufacturers and users dedicated to advancing multi-vendor technologies. The Open Group was formed in February, 1996 by merging two previously independent groups - the Open Software Foundation (OSF) and X/Open Company Ltd. One of the most important technologies fostered by The Open Group is DCE.

    THEnet
    Organizations

    Texas Higher Education Network. Regional network comprising over 60 academic and research institutions in Texas.

    Thick Ethernet
    Lingo

    Also known as 10Base5.

    Thinnet
    Lingo

    Term used to define a thinner, less expensive version of the cable specified in the IEEE 802.3 10Base2 standard.

    Throughput
    Networking

    Rate of information arriving at, and possibly passing through, a particular point in a network system.

    TIA
    Organizations

    Telecommunications Industry Association. Organization that develops standards relating to telecommunications technologies. Together, the TIA and the EIA have formalized standards, such as EIA/TIA-232, for the electrical characteristics of data transmission.

    TIC
    Hardware

    Token Ring interface coupler. Controller through which an FEP connects to a Token Ring.

    Tier-One Provider
    Networking

    A tier-one internet service provider is an ISP that does not use any other ISP to transfer data across the country. These ISP's typically have private peering arrangements to exchange data directly with other ISP's. These providers typically have multiple connections across the country so that if one connection fails, data can be re-routed along other links.

    Tier-Three Provider
    Networking

    A tier-three service provider generally is a small ISP, possibly having an ISDN, Frame-Relay, or T1 connection to one or more ISP's. These usually only service one metropolitan area.

    Tier-Two Provider
    Networking

    A tier-two provider is generally a regional ISP that uses multiple connections from different ISP's to transmit data across the backbone. Onramp, the first acquisition by Verio, had internal highspeed links between Dallas, Lubbock, Fort-Worth, Austin, and Waco, but used other ISP's to send it's data out to the Internet.

    Tightly Coupled
    Lingo

    A term that describes the relationship between two computing processes whose successful completion and individual performance rates are highly inter-dependent.

    Time-Division Multiplexing
    Telecommunications

    TDM (time-division multiplexing) is a scheme in which numerous signals are combined for transmission on a single communications line or channel. Each signal is broken up into many segments, each having very short duration.

    The circuit that combines signals at the source (transmitting) end of a communications link is known as a multiplexer. It accepts the input from each individual end user, breaks each signal into segments, and assigns the segments to the composite signal in a rotating, repeating sequence. The composite signal thus contains data from all the end users. At the other end of the long-distance cable, the individual signals are separated out by means of a circuit called a demultiplexer, and routed to the proper end users. A two-way communications circuit requires a multiplexer/demultiplexer at each end of the long-distance, high-bandwidth cable.

    If many signals must be sent along a single long-distance line, careful engineering is required to ensure that the system will perform properly. An asset of TDM is its flexibility. The scheme allows for variation in the number of signals being sent along the line, and constantly adjusts the time intervals to make optimum use of the available bandwidth. The Internet is a classic example of a communications network in which the volume of traffic can change drastically from hour to hour. In some systems, a different scheme, known as frequency-division multiplexing (FDM), is preferred.

    Time-Out
    Networking

    Event that occurs when one network device expects to hear from another network device within a specified period of time, but does not. The resulting time-out usually results in a retransmission of information or the dissolving of the session between the two devices.

    TN3270
    Concept

    Terminal Emulation software that allows a terminal to appear to an IBM host as a 3278 Model 2 terminal.

    Token
    Networking

    Frame that contains control information. Possession of the token allows a network device to transmit data onto the network.

    Token bus
    Networking

    LAN architecture using token passing access over a bus topology. This LAN architecture is the basis for the IEEE 802.4 LAN specification.

    Token Passing
    Networking

    A MAC method where stations may only transmit when they are in possession of a special bit sequence (token) passed from station to station.

    Token Ring
    Networking

    A ring topology network that uses token passing for MAC.

    Tool
    Software

    Any device, software program or instrument constructed for the purpose of aiding a human in accomplishing a goal.

    TOP
    Protocol

    Technical Office Protocol.

    Topology
    Networking

    A topology (from Greek topos: place) is a description of any kind of locality in terms of its physical layout. In the context of communication networks, a topology describes pictorially the configuration or arrangement of a (usually conceptual) network, including its nodes and connecting lines. For example, in these pages, whatis describes the topology of bus, ring, and other networks. (Currently, our descriptions are verbal, but pictures are being prepared.)

    Trailer
    Lingo

    The group of bytes that marks the end of a frame and usually contains an error checking mechanism such as a CRC.

    Transceiver
    Hardware

    1. In Ethernet, an electronic device that transforms signals between a node's internal circuitry and the Ethernet signals and also detects collisions. 2. Any device that can simultaneously transmit and receive.

    Transfer Rate
    Networking

    The rate at which data is transferred from one device to another, usually expressed in bit per second or in bytes per second.

    Transient
    Lingo

    A short-lived electrical event.

    Transistor

    A device composed of semiconductor material that amplifies a signal or opens or closes a circuit. Transistors have become the major componet in all digital circuits, including computer microprocessors which now contain millions of microscopic size transistors. Prior to transistors, digital circuits used vacuum tubes, which had many disadvantages. They were larger, used more energy and created more heat.

    Bardeen, Shockley, and Brattain, scientists at the Bell Telephone Laboratories in Murray Hill, New Jersey, were researching the behavior of crystals (germanium) as semi-conductors in an attempt to replace vacuum tubes as mechanical relays in telecommunications. The vacuum tube had been used to amplify music and voic, and it had made long-distance calling practical, but the tubes consumed power, created heat and burned out rapidly requiring high maintenance.

    The teams' research was about to come to a fruitless end when a last attempt to try a purer substance as a contact point was made, and the "point-contact" transistor amplifier was invented. In 1956, the team was rewarded with the Nobel Prize in Physics for the invention of the transistor.

    Bardeen and Brattain, took out a patent for a transistor, Shockley, applied for a patent for the transistor effect and a transistor amplifier. Transistors transformed the world of electronics and had a huge impact on how computers were designed, after their invention, transistors made of semiconductors replaced tubes in the construction of computers.

    Transmission
    Networking

    The activity of sending or conveying information.

    Transmitter
    Telecommunications

    A device which generates the signal to be carried on the transmission media. This usually implies a process of converting the signal from its existing form into a form which is compatible with the media, and also a process of placing that signal on the transmission media at sufficient power to carry it to the intended destination.

    Transport
    Networking

    Any of the functions carried out by protocols in the Network or Transport Layers.

    Transport Protocol
    Protocol

    The Protocol Layer of the OSI 7-Layer Model that is concerned with management of the data flow between source and destination.

    Triple DES
    Software

    Triple DES, or 3DES, is an encryption algorithm based on the popular DES system. 3DES uses the DES algorithm three times in succession to create a key that is up to 112 bits in length, which is significantly more secure than the 56 bit key that DES uses. It takes three 64-bit keys, for an overall key length of 192 bits. In Stealth, you simply type in the entire 192-bit (24 character) key rather than entering each of the three keys individually. The Triple DES DLL then breaks the user provided key into three subkeys, padding the keys if necessary so they are each 64 bits long. The procedure for encryption is exactly the same as regular DES, but it is repeated three times. Hence the name Triple DES. The data is encrypted with the first key, decrypted with the second key, and finally encrypted again with the third key.

    Consequently, Triple DES runs three times slower than standard DES, but is much more secure if used properly. The procedure for decrypting something is the same as the procedure for encryption, except it is executed in reverse. Like DES, data is encrypted and decrypted in 64-bit chunks. Unfortunately, there are some weak keys that one should be aware of: if all three keys, the first and second keys, or the second and third keys are the same, then the encryption procedure is essentially the same as standard DES. This situation is to be avoided because it is the same as using a really slow version of regular DES.

    Note that although the input key for DES is 64 bits long, the actual key used by DES is only 56 bits in length. The least significant (right-most) bit in each byte is a parity bit, and should be set so that there are always an odd number of 1s in every byte. These parity bits are ignored, so only the seven most significant bits of each byte are used, resulting in a key length of 56 bits. This means that the effective key strength for Triple DES is actually 168 bits because each of the three keys contains 8 parity bits that are not used during the encryption process.

    Trojan Horse
    Programming

    A maliciously-created computer program or virus that causes significant damage to a system. Trojan Horses are typically given attractive file names and placed on bulletin board systems. Damage usually occurs when the user launches the Trojan horse on his own system. Named after a successful offensive ploy made by the ancient Greek army at the siege of Troy.

    TrueSpeech
    Software

    Software that compresses speech down to as little as 1/40th its original size. Regular speech files are normally large, causing Web pages to load slowly; TrueSpeech compression allows faster, easier transfer.

    TrueType
    Lingo

    An outline font technology developed as an alternative to Adobe Postscript fonts.

    Truncate
    Networking

    A method of formatting data by removing characters at the end of the data that do not conform to the format desired.

    TTL
    Networking

    TTL (time-to-live) is a value in an Internet Protocol (Internet Protocol) packet that tells a network router whether or not the packet has been in the network too long and should be discarded. For a number of reasons, packets may not get delivered to their destination in a reasonable length of time. For example, a combination of incorrect routing tables could cause a packet to loop endlessly. A solution is to discard the packet after a certain time and send a message to the originator, who can decide whether to resend the packet. The initial TTL value is set, usually by a system default, in an 8-binary digit field of the packet header. The original idea of TTL was that it would specify a certain time span in seconds that, when exhausted, would cause the packet to be discarded. Since each router is required to subtract at least one count from the TTL field, the count is usually used to mean the number of router hop the packet is allowed before it must be discarded. Each router that receives a packet subtracts one from the count in the TTL field. When the count reaches zero, the router detecting it discards the packet and sends an Internet Control Message Protocol (Internet Control Message Protocol) message back to the originating host.

    The default Windows 95/98 TTL value is 32 hops. Some users recommend changing this to 128 if you have difficulty reaching certain sites.

    The Packet Internet or Inter-Network Groper and the traceroute utilities both make use of the TTL value to attempt to reach a given host computer or to trace a route to that host. Traceroute intentionally sends a packet with a low TTL value so that it will be discarded by each successive router in the destination path. The time between sending the packet and receiving back the ICMP message that it was discarded is used to calculate each successive hop travel time.

    Tunneling
    Networking

    A technology that enables one network to send its data via another network's connections. Tunneling works by encapsulating a network protocol within packets carried by the second network. For example, Microsoft's PPTP technology enables organizations to use the Internet to transmit data across a virtual private network (VPN). It does this by embedding its own network protocol within the TCP/IP packets carried by the Internet.

    Tunneling is also called encapsulation.

    Turing Machine
    Hardware

    The Turing machine can be imagined as something like a typewriter, but having the additional quality of being able to read, or scan, other symbols, and to erase them if necessary. Turing settled on the idea of a tape of infinate length, divided into squares, with each square carrying a single symbol. The machine would then move the tape one square at a time, read the symbol, and then either remain at the same state, or move to a new state , depending on what it read. In each case its response would be purely automatic, and determined by the contruction of the machine. The machine would either leave the symbol alone , or erase it and type another, then move the tape by one square and continue. Essentially the Turing machine is simply a device for transforming one string of symbols into another string according to a predetermined set of rules.

    Twisted Pair
    Hardware

    A type of cable that consists of two independently insulated wires twisted around one another. One wire carries the signal while the other wire is grounded and absorbs signal interference. Twisted-pair cable is used by older telephone networks and is the least expensive type of local-area network (LAN) cable. Other types of cables used for LANs include coaxial cables and fiber optic cables.

    U

    UDP
    Protocol

    Short for User Datagram Protocol, a connectionless protocol that, like TCP, runs on top of IP networks. Unlike TCP/IP, UDP/IP provides very few error recovery services, offering instead a direct way to send and receive datagrams over an IP network. It's used primarily for broadcasting messages over a network and for streaming applications such as RealAudio.

    UML
    Software

    Unified Modeling Language

    UML (Unified Modeling Language) is a standard notation for the modeling of real-world objects as a first step in developing an . Its notation is derived from and unifies the notations of three object-oriented design and analysis methodologies: Other ideas also contributed to UML, which was the result of a work effort by Booch, Rumbaugh, Jacobson, and others to combine their ideas, working under the sponsorship of Rational Software. UML has been fostered and now is an accepted standard of the Object Management Group, which is also the home of Common Object Request Broker Architecture, the leading industry standard for distributed object programming. Vendors of computer-aided software engineering products are now supporting UML and it has been endorsed by almost every maker of software development products , including IBM and Microsoft (for its Visual Basic environment).

    Martin Fowler, in his book UML Distilled, observes that, although UML is a notation system so that everyone can communicate about a model, it's developed from methodologies that also describe the processes in developing and using the model. While there is no one accepted process, the contributors to UML all describe somewhat similar approaches and these are usually described along with tutorials about UML itself.

    Among the concepts of modeling that UML specifies how to describe are: class (of objects), object, association, responsibility, activity, interface, use case, package, sequence, collaboration, and state. Fowler's book provides a good introduction to UML. Booch, Rumbaugh, and Jacobson all have or soon will have published the "offficial" set of books on UML.

    Univac

    The UNIVAC I (the name stood for Universal Automatic Computer) was delivered to the Census Bureau in 1951. It weighed some 16,000 pounds, used 5,000 vacuum tubes, and could perform about 1,000 calculations per second. It was the first American commercial computer, as well as the first computer designed for business use. (Business computers like the UNIVAC processed data more slowly than the IAS-type machines, but were designed for fast input and output.) The first few sales were to govenment agencies, the A.C. Nielsen Company, and the Prudential Insurance Company. The first UNIVAC for business applications was installed at the General Electric Appliance Division, to do payroll, in 1954. By 1957 Remington-Rand (which had purchased the Eckert-Mauchly Computer Corporation in 1950) had sold forty-six machines.

    UNIX
    Software

    UNIX is an operating system that originated at Bell Labs in 1969 as an interactive time-sharing system. Ken Thompson and Dennis Ritchie are considered the inventors of UNIX. The name (pronounced YEW-nihks) was a pun based on an earlier system, Multiplexed Information and Computing Se. In 1974, UNIX became the first operating system written in the C language. UNIX has evolved as a kind of large freeware product, with many extensions and new ideas provided in a variety of versions of UNIX by different companies, universities, and individuals. Partly because it was not a proprietary operating system owned by any one of the leading computer companies and partly because it is written in a standard language and embraced many popular ideas, UNIX became the first open or standard operating system that could be improved or enhanced by anyone. A composite of the C language and shell (user command) interfaces from different versions of UNIX were standardized under the auspices of the Institute of Electrical and Electronics Engineers as the Portable Operating System Interface (Portable Operating System Interface). In turn, the POSIX interfaces were specified in the X/Open Programming Guide 4.2 (also known as the "Single UNIX Specification" and "UNIX 95"). Version 2 of the Single UNIX Specification is also known as UNIX 98. The "official" trademarked UNIX is now owned by the The Open Group, an industry standards organization, which certifies and brands UNIX implementations.

    UNIX operating systems are used in widely-sold workstation products from Sun Microsystems, Silicon Graphics, IBM, and a number of other companies. The UNIX environment and the client/server program model were important elements in the development of the Internet and the reshaping of computing as centered in networks rather than in individual computers. Linux, a UNIX derivative available in both "free software" and commercial versions, is increasing in popularity as an alternative to proprietary operating systems.

    Upload
    Lingo

    The activity of transferring a file from a user's computer system to a remote system.

    UPS
    Hardware

    Uninterruptable Power Supply. An electrical supply system that conditions electrical power for a computer system and will allow continued operating in the event of a power failure.

    URL
    Software

    uniform resource locator; an identifier that describes the location of a particular piece of information (e.g.,document) including the protocol used to retrieve that information.

    UseNet
    Organizations

    A worldwide bulletin board system that can be accessed through the Internet or through many online services. The USENET contains more than 14,000 forums, called newsgroups, that cover every imaginable interest group. It is used daily by millions of people around the world.

    User
    People

    A person who uses a computer system to accomplish a non-computing goal, as compared to a programmer or network manager.

    User ID
    Lingo

    This is the account reference name sent to you in the Account Activation Letter. When you need to log on to your site, you will use this item.

    User Interface
    Lingo

    The collection of display symbols and other sensory stimuli made by a computer that present information to a human and the collection of physical action that a human can take to present data to a computer.

    UTP
    Telecommunications

    Unshielded twisting pair wiring.

    UTP Ethernet
    Networking

    1) A synonym for 10BaseT. 2) Any of a number of Ethernet technologies in use before the adoption of the 10BaseT Standard that provided a 10 MBPS network system using CSMA/CD.

    UUCP
    Protocol

    Short for Unix-to-Unix Copy, a Unix utility and protocol that enables one computer to send files to another computer over a direct serial connection or via modems and the telephone system. For most file transfer applications, UUCP has been superseded by other protocols, such as FTP, SMTP and NNTP.

    UUENCODE
    Programming

    UNIX to UNIX Encoding: A method for converting files from Binary to ASCII so that they can be sent across the Internet via email. See Also: MIME

    V

    V.21
    Protocol

    The standard for full-duplex communication at 300 baud in Japan and Europe. In the United States, Bell 103 is used in place of V.21.

    V.22
    Protocol

    The standard for half-duplex communication at 1,200 bps in Japan and Europe. In the United States, the protocol defined by Bell 212A is more common.

    V.22bis
    Protocol

    The worldwide standard for full-duplex modems sending and receiving data across telephone lines at 1,200 or 2,400 bps.

    V.29
    Protocol

    The standard for half-duplex modems sending and receiving data across telephone lines at 1,200, 2,400, 4,800, or 9,600 bps. This is the protocol used by fax modems.

    V.32
    Protocol

    The standard for full-duplex modems sending and receiving data across phone lines at 4,800 or 9,600 bps. V.32 modems automatically adjust their transmission speeds based on the quality of the lines.

    V.32bis
    Protocol

    The V.32 protocol extended to speeds of 7,200, 12,000, and 14,400 bps.

    V.34
    Protocol

    The standard for full-duplex modems sending and receiving data across phone lines at up to 28,800 bps. V.34 modems automatically adjust their transmission speeds based on the quality of the lines.

    V.42
    Protocol

    An error-detection standard for high-speed modems. V.42 can be used with digital telephone networks.

    V.42bis
    Protocol

    A data compression protocol that can enable modems to achieve a data transfer rate of 34,000 bps.

    V.90
    Protocol

    The standard for full-duplex modems sending and receiving data across phone lines at up to 56,600 bps.

    Vacuum Tube

    Back in 1904, British scientist John Ambrose Fleming first showed his device to convert an alternating current signal into direct current. The "Fleming diode" was based on an effect that Thomas Edison had first discovered in 1880, and had not put to useful work at the time. This diode essentially consisted of an incandescent light bulb with an extra electrode inside. When the bulb's filament is heated white-hot, electrons are boiled off its surface and into the vacuum inside the bulb. If the extra electrode (also called an "plate" or "anode") is made more positive than the hot filament, a direct current flows through the vacuum. And since the extra electrode is cold and the filament is hot, this current can only flow from the filament to the electrode, not the other way. So, AC signals can be converted into DC. Fleming's diode was first used as a sensitive detector of the weak signals produced by the new wireless telegraph. Later (and to this day), the diode vacuum tube was used to convert AC into DC in power supplies for electronic equipment.

    Many other inventors tried to improve the Fleming diode, most without success. The only one who succeeded was New York inventor Lee de Forest. In 1907 he patented a bulb with the same contents as the Fleming diode, except for an added electrode. This "grid" was a bent wire between the plate and filament. de Forest discovered that if he applied the signal from the wireless-telegraph antenna to the grid instead of the filament, he could obtain a much more sensitive detector of the signal. In fact, the grid was changing ("modulating") the current flowing from the filament to the plate. This device, the Audion, was the first successful electronic amplifier. It was the genesis of today's huge electronics industry.

    Between 1907 and the 1960s, a staggering array of different tube families was developed, most derived from de Forest's invention. With a very few exceptions, most of the tube types in use today were developed in the 1950s or 1960s. One obvious exception is the 300B triode, which was first introduced by Western Electric in 1935. Svetlana's SV300B version, plus many other brands, continue to be very popular with audiophiles around the world. Various tubes were developed for radio, television, RF power, radar, computers, and specialized applications. The vast majority of these tubes have been replaced by semiconductors, leaving only a few types in regular manufacture and use.

    Van Jacobson
    People

    Van Jacobson, the man widely credited with saving the Internet from an otherwise inevitable congestion collapse in the late 1980s, is chief scientist at networking startup Packet Design, LLC.

    Jacobson began his career in data communications developing control systems for the Department of Energy in the 1970s. He is best known for redesigning the TCP/IP protocol's flow-control algorithms to better handle congestion, preventing the Internet's collapse from traffic congestion in 1988-89. He is also widely recognized for his work on network synchronization effects, scalable multimedia protocols and applications, IP operations tools (e.g., traceroute and pathchar) and high-performance TCP implementations.

    Prior to joining Packet Design as a member of the founding team, Jacobson was chief scientist at Cisco Systems, and before that had been group leader for Lawrence Berkeley Laboratory's Network Research Group.

    Vannevar Bush
    People

    Bush, Vannevar (1890-1974), American scientist, educator, and administrator, born in Everett, Massachusetts, and educated at Tufts College, Harvard University, and Massachusetts Institute of Technology (MIT). During World War I he served with the U.S. Navy as a research engineer. From 1919 to 1971 Bush served in various teaching and administrative positions at MIT and the Carnegie Institution of Washington.

    While at MIT Bush invented the differential analyzer, a device for rapidly and automatically solving complex mathematical problems and a forerunner of the modern computer. Bush is best known for his federal scientific work with the national Defense Research Committee, of which he was chairman; the Office of Scientific Research and Development, which he directed throughout World War II; and the Research and Development Board of the Army and Navy.

    "The first application of hypertext was proposed by Vannevar Bush, US President Roosevelt's science advisor, who was concerned that post-war scientists made best use of the vast amount of research that had gone into the war effort. In his 1945 paper, As We May Think, Bush envisaged the Memex, a device which could create links between related topics in different research papers.

    Vaporware
    Software

    A sarcastic term used to designate software and hardware products that have been announced and advertised but are not yet available.

    VDSL
    Telecommunications

    VDSL (Very high data rate DSL) is a developing technology that promises much higher data rates over relatively short distances (between 51 and 55 Mbps over lines up to 1,000 feet or 300 meters in length). It's envisioned that VDSL may emerge somewhat after ADSL is widely deployed and co-exist with it. The transmission technology (CAP, DMT, or other) and its effectiveness in some environments is not yet determined. A number of standards organizations are working on it.

    VGA
    PC's

    In 1987, IBM introduced the Video Graphics Array (VGA) display system. This has become the accepted minimum standard for PC clones. Many VGA monitors are still in use today. The maximum resolution depends on the number of colors displayed. You can choose between 16 colors at 640 x 480 pixels, or 256 colors at 320 x 200 pixels. All IBM-compatible computers support the VGA standard.

    Vinton Cerf
    People

    Widely known as a "Father of the Internet," Dr. Cerf is the co-designer of the TCP/IP protocol, the computer language that gave birth to the Internet and which is commonly used today. In December 1997, President Clinton presented the U.S. National Medal of Technology to Dr. Cerf and his partner, Robert E. Kahn, for founding and developing the Internet.

    Prior to rejoining MCI in 1994, Dr. Cerf was vice president of the Corporation for National Research Initiatives (CNRI). As vice president of MCI Digital Information Services from 1982-1986, he led the engineering of MCI Mail, the first commercial email service to be connected to the Internet.

    During his tenure from 1976-1982 with the U.S. Department of Defense's Advanced Research Projects Agency (DARPA), Dr. Cerf played a key role leading the development of Internet and Internet-related data packet and security technologies.

    Dr. Cerf served as founding president of the Internet Society from 1992-1995 and is currently serving as its Chairman of the Board. Dr. Cerf is a member of the U.S. Presidential Information Technology Advisory Committee (PITAC) and the Advisory Committee for Telecommunications (ACT) in Ireland. He also sits on the Board of Directors for the Endowment for Excellence in Education, Gallaudet University, Interprophet and Hynomics Corporations. Dr. Cerf is a fellow of the IEEE, ACM, American Association for the Advancement of Science, the American Academy of Arts and Sciences and the National Academy of Engineering.

    Dr. Cerf is a recipient of numerous awards and commendations in connection with his work on the Internet. These include the Marconi Fellowship, the Alexander Graham Bell Award presented by the Alexander Graham Bell Association for the Deaf, the NEC Computer and Communications Prize, the Silver Medal of the International Telecommunications Union, the IEEE Alexander Graham Bell Medal, the IEEE Koji Kobayashi Award, the ACM Software and Systems Award, the ACM SIGCOMM Award, the Computer and Communications Industries Association Industry Legend Award, the Yuri Rubinsky Web Award, the Kilby Award and the Yankee Group/Interop/ Network World Lifetime Achievement Award.

    In December 1994, People Magazine identified Dr. Cerf as one of that year's "25 Most Intriguing People."

    In addition to his work on behalf of MCI and the Internet, Dr. Cerf serves as technical adviser to production for "Gene Roddenberry's Earth: Final Conflict," the number one television show in first-run syndication. He also made a special guest appearance in May 1998. Dr. Cerf also holds an appointment as distinguished visiting scientist at the Jet Propulsion Laboratory where he is working on the design of an interplanetary Internet.

    Dr. Cerf holds a Bachelor of Science degree in Mathematics from Stanford University and Masters of Science and Ph.D. degrees in Computer Science from UCLA. He also holds honorary Doctorate degrees from the Swiss Federal Institute of Technology, Zurich; Lulea University of Technology, Sweden; University of the Balearic Islands, Palma; Capitol College and Gettysburg College.

    Virtual Circuit
    Telecommunications

    A virtual circuit is a circuit or path between points in a network that appears to be a discrete, physical path but is actually a managed pool of circuit resources from which specific circuits are allocated as needed to meet traffic requirements.

    A permanent virtual circuit (Permanent Virtual Circuit) is a virtual circuit that is permanently available to the user just as though it were a dedicated or leased line continuously reserved for that user. A switched virtual circuit (switched virtual circuit) is a virtual circuit in which a connection session is set up for a user only for the duration of a connection. PVCs are an important feature of frame relay networks and SVCs are proposed for later inclusion.

    Virus
    Programming

    Virus A virus is a malicious program whose sole intent is to cause problems on a computer. There are Anti-Virus programs, such as McAfee and Norton Utilities, created to combat viruses.

    Virus Hoax
    Lingo

    Occasionally, rumors are started about viruses that do not exist. These are merely hoaxes.

    Visual Basic
    Software

    A programming language and environment developed by Microsoft. Based on the BASIC language, Visual Basic was one of the first products to provide a graphical programming environment and a paint metaphor for developing user interfaces. Instead of worrying about syntax details, the Visual Basic programmer can add a substantial amount of code simply by dragging and dropping controls, such as buttons and dialog boxes, and then defining their appearance and behavior.

    Although not a true object-oriented programming language in the strictest sense, Visual Basic nevertheless has an object-oriented philosophy. It is sometimes called an event-driven language because each object can react to different events such as a mouse click.

    Since its launch in 1990, the Visual Basic approach has become the norm for programming languages. Now there are visual environments for many programming languages, including C, C++, Pascal, and Java. Visual Basic is sometimes called a Rapid Application Development (RAD) system because it enables programmers to quickly build prototype applications.

    VLAN
    Networking

    A virtual (or logical) LAN is a local area network with a definition that maps workstations on some other basis than geographic location (for example, by department, type of user, or primary application). The virtual LAN controller can change or add workstations and manage loadbalancing and bandwidth allocation more easily than with a physical picture of the LAN. Network management software keeps track of relating the virtual picture of the local area network with the actual physical picture.

    Volano Chat
    Software

    A real-time, live chat interface you can add--quickly and easily--to your Web site. Written in Java, it is compatible with the vast majority of Web browsers and requires no plug-ins.

    W

    WAN
    Lingo

    Wide Area Network. A network that is created between and among devices separated by large distances (typically in excess of 50 miles).

    Warez
    Lingo

    Pronounced wairz or wairss, refers to commercial software that has been pirated and made available to the public via a BBS or the Internet. Typically, the pirate (also called a cracker) has figured out a way to de-activate the copy-protection or registration scheme used by the software. Note that the use and distribution of warez software is illegal. In contrast, shareware and freeware may be freely copied and distributed.

    Web
    Software

    World Wide Web; a hypertext-based, distributed information system created by researchers at CERN in Switzerland, enabling users to create, edit, or browse hypertext documents.

    Web Site
    Lingo

    A Web site is a related collection of World Wide Web files that includes a beginning file called a home page. A company or an individual tells you how to get to their Web site by giving you the address of their home page. From the home page, you can get to all the other pages on their site. For example, the Web site for IBM has the home page address of http://www.ibm.com. (The home page address actually includes a specific file name like index.html but, as in IBM's case, when a standard default name is set up, users don't have to enter the file name.) IBM's home page address leads to thousands of pages. (But a Web site can also be just a few pages.)

    Since site implies a geographic place, a Web site can be confused with a Web server. A server is a computer that holds the files for one or more sites. A very large Web site may be spread over a number of servers in different geographic locations. IBM is a good example; its Web site consists of thousands of files spread out over many servers in world-wide locations. But a more typical example is probably the site you are looking at, whatis.com. We reside on a commercial space provider's server with a number of other sites that have nothing to do with Internet glossaries.

    A synonym and less frequently used term for Web site is "Web presence." That term seems to better express the idea that a site is not tied to specific geographic location, but is "somewhere in cyberspace." However, "Web site" seems to be used much more frequently.

    Webmaster
    People

    The person who creates and maintains a web site.

    Wireless
    Telecommunications

    A System that provides communication without the use of wires.

    Wizard
    Programming

    A utility in a program that outlines a series of sequential tasks to set up a portion of the program. For example, an email program may use a wizard to gather the necessary information to set up an email account.

    WML
    Protocol

    Wireless Markup Language is an XML language used to specify content and user interface for WAP devices; the WAP forum provides a DTD for WML. WML is supported by almost every mobile phone browser around the world. WML pages are requested and served in the same way as HDML pages. For Web servers to serve WML pages, they must contain the text/vnd.wap.wml mime type.

    Workgroup
    Networking

    A group of networked computer users who frequently communicate with each other and share common devices.

    World Wide Web
    Lingo

    A technical definition of the World Wide Web is: all the resources and users on the Internet that are using the Hypertext Transfer Protocol (Hypertext Transfer Protocol).

    A broader definition comes from the organization that Web inventor Tim Berners-Lee helped found, the World Wide Web Consortium (W3C):

    "The World Wide Web is the universe of network-accessible information, an embodiment of human knowledge."

    WWW
    Lingo

    Short for World Wide Web. A system of Internet servers that support specially formatted documents. The documents are formatted in a language called HTML (HyperText Markup Language) that supports links to other documents, as well as graphics, audio, and video files. This means you can jump from one document to another simply by clicking on hot spots. Not all Internet servers are part of the World Wide Web.

    WYSIWYG
    Lingo

    What You See Is What You Get (pronounced "wizzy-wig"): A program that displays a document on your screen exactly as it would appear when printed or published online. The term usually applies to HTML editors, such as Microsoft FrontPage and Macromedia Dreamweaver. These WYSIWYG editors can show you how your Web page will appear online, as you're editing the document.

    X

    X Windows
    Networking

    A way of operating remote systems. The window allows the user to control and application remotely and view the application's output.

    X.25
    Protocol

    The most popular packet-switching protocol for WANs.

    X.400
    Protocol

    The universal protocol for e-mail. X.400 defines the envelope for e-mail messages so all messages conform to a standard format.

    X.500
    Protocol

    An extension to X.400 that defines addressing formats so all e-mail systems can be linked together.

    X.509
    Protocol

    The most widely used standard for defining digital certificates. X.509 is actually an ITU Recommendation, which means that has not yet been officially defined or approved. As a result, companies have implemented the standard in different ways. For example, both Netscape and Microsoft use X.509 certificates to implement SSL in their Web servers and browsers. But an X.509 Certificate generated by Netscape may not be readable by Microsoft products, and vice versa.

    x2
    Protocol

    x2 is a technology from US Robotics (now 3Com) for the downstream transmission of data over ordinary phone lines at 56 Kbps (thousands of bits per second). The 56 Kbps speed is achieved in the downstream direction only (to your home or business). Upstream speed is at the regular maximum speed of 33.6 Kbps. (The actual achieved downstream speed is reported by users to be about 53 Kbps.) x2 provided input to and has been replaced by the V.90 ITU-TS standard. 56 Kbps technologies exploit the fact that most telephone company offices are interconnected with digital lines. Assuming your Internet connection provider has a digital connection to its telephone company office, the downstream traffic from your local Internet access provider can use a new transmission technique on your regular twisted pair phone line that bypasses the usual digital-to-analog conversion. A V.90-equipped modem doesn't need to demodulate the downstream data. Instead, it decodes a stream of multi-bit voltage pulses generated as though the line was equipped for digital information. (Upstream data still requires digital-to-analog modulation.) Unlike Integrated Services Digital Network, the V.90 technology does not require any additional installation or extra charges from your local phone company. On the other hand, the maximum transmission speed of ISDN is twice that of V.90 at 128 Kbps. You also have the flexibility of combining digital and voice transmission on the same line.

    xDSL
    Telecommunications

    Refers collectively to all types of digital subscriber lines, the two main categories being ADSL and SDSL. Two other types of xDSL technologies are High-data-rate DSL (HDSL) and Symmetric DSL (SDSL).

    DSL technologies use sophisticated modulation schemes to pack data onto copper wires. They are sometimes referred to as last-mile technologies because they are used only for connections from a telephone switching station to a home or office, not between switching stations.

    xDSL is similar to ISDN inasmuch as both operate over existing copper telephone lines (POTS) and both require the short runs to a central telephone office (usually less than 20,000 feet). However, xDSL offers much higher speeds - up to 32 Mbps for downstream traffic, and from 32 Kbps to over 1 Mbps for upstream traffic.

    XML
    Protocol

    Short for Extensible Markup Language, a specification developed by the W3C. XML is a pared-down version of SGML, designed especially for Web documents. It allows designers to create their own customized tags, enabling the definition, transmission, validation, and interpretation of data between applications and between organizations. Whether XML eventually supplants HTML as the standard Web formatting specification depends a lot on whether it is supported by future Web browsers. Microsoft Internet Explorer version 5 handles XML, but renders it as CSS, and Mozilla (Netscape) is still in experimenting with XML support.

    Xmodem
    Protocol

    Originally developed in 1977 by Ward Christensen, Xmodem is one of the most popular file-transfer protocols. Although Xmodem is a relatively simple protocol, it is fairly effective at detecting errors. It works by sending blocks of data together with a checksum and then waiting for acknowledgment of the block's receipt. The waiting slows down the rate of data transmission considerably, but it ensures accurate transmission. Xmodem can be implemented either in software or in hardware. Many modems, and almost all communications software packages, support Xmodem. However, it is useful only at relatively slow data transmission speeds (less than 4,800 bps). Enhanced versions of Xmodem that work at higher transmission speeds are known as Ymodem and Zmodem.

    Y

    Ymodem
    Protocol

    An asynchronous communications protocol designed by Chuck Forsberg that extends Xmodem by increasing the transfer block size and by supporting batch file transfers. This enables you to specify a list of files and send them all at one time. With Xmodem, you can send only one file at a time.

    Z

    Zip
    Protocol

    Zone Information Protocol: This is a method of compressing computer data or files into a small size, so they can be transferred quickly over the Internet. There are programs built specifically to zip files, such as WinZip.

    Zmodem
    Protocol

    An asynchronous communications protocol that provides faster data transfer rates and better error detection than Xmodem. In particular, Zmodem supports larger block sizes and enables the transfer to resume where it left off following a communications failure.

    Zone
    Networking

    In an AppleTalk internet, a reference to a logical group of devices and services.

    Zone File
    Networking

    A file that has data describing a part of the domain name space. Zone files hold the information that is needed to resolve domain names to Internet Protocol (IP) numbers.