CID Study Guide

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Introduction to Internetwork Design

This Cramsession Covers Cisco’s CID exam to help you to finish off your process to becoming a CCDP by passing your exam. This Study Guide covers the posted objectives outlined by Cisco and provides links to more information to help in your studies. As outlined by Cisco, there is no way to fully prepare for this exam without first going through the posted objectives and making sure that you are comfortable with what is listed and being able to “design” such technologies from Cisco’s perspective. Make sure you thoroughly go over these objectives and understand them fully while preparing for this exam. The exam covers a very wide range of technologies and that is where the difficulty comes in. Make sure you cover all areas completely as you may only get a few questions from each section. Good Luck.

Network Design Fundamentals

Network Design Fundamentals include having a basic network design methodology. This is outlined as follows – but can change as per which or whose diagram and flowchart you use. They are all generally the same. Here is Cisco’s Original Chart:

Note: You do not need to memorize the numbers; they are listed here to show the order in which they are applied. Memorization of the steps is needed for the CID exam. If step 6 does not work, then go to step 4. The listing below is a more granular breakdown of the methodology.

Methodology and Design Steps

Gather Information	You need to first gather information about the network you are addressing and then analyze the requirements.
Analyze Requirements	Analyze the requirements for the design.
Develop the Internetwork Structure	Before you actually develop the structure, you need the first two steps completed to get an accurate structure development.
Network Performance Estimation	Look at the performance of the network and give a good estimate on how it will work.
Assess Risk and Costs	Every network has cost and risks associated with it; gather them here.
Implement Network	This is where you roll out the network and implement it.
Monitor Network	Now that it exists, you need to monitor it and continue to do so over time. If problems exist, go back and fix things as needed, then re-monitor to see if the issues are resolved.

Design Models

Cisco has many Design Models that you can follow. They are fairly generic and will allow you to guide your design against business and technical needs. A complete listing of design guidance can be found on the Cisco website:

Star	Administration, setup and management is easy but you will have a single point of failure. If this occurs at the center of the star, it may bring down the entire star.
Ring	This model is more costly than the star, but the benefit is that it does not have the single point of failure.
Flat Earth	Very easy to set up but it is not easy to scale to larger networks. This should be used for a very small network where broadcast traffic will not cause a sever impact on the network.
Mesh (Partial)	Added Redundancy, a cleaner solution than the full mesh. You would mesh what needs to be redundant only, making for a scaled down cost. Make sure you know what is redundant and what is not. Because the network is “partially” meshed, you will not have “full” redundancy.
Mesh (Full)	Full redundancy, highly scalable, high cost and more management needed.
3 Tier	Very Scalable. Troubleshooting is easier, and easier to manage. This model is also costly because of the levels of equipment you need to implement.

Make sure you go over these models and know when you would use them in a design.

Cisco’s Hierarchical Model Cisco Documentation: Hierarchical Model This is Cisco’s Hierarchical Model that Cisco wants designers to follow when looking at implementing a network design. It really does help in organizing your thoughts on where to leverage certain products in the Cisco Product line. You need to know the basics of Cisco’s product line for this exam, including knowing the router families, switch families, and WAN switching hardware. Note: For the Exam you will be expected to know how to follow this model to implement a scalable, manageable, high performance campus design. You need to know how to base the design on the hierarchical model. The most comprehensive set of information on this objective can be found on Cisco’s Website Design Guide. Solving Problems with Design Memorize the following model:

Desktop Protocol Design

Know the basics of Implementing, troubleshooting and working with Desktop protocols by Microsoft, Novell and Apple. Microsoft Protocols were designed for flat networks where all the clients and servers are sharing the same media. There are different remedies and methods of encapsulations for handling these problems.

Desktop Protocol Fundamentals

Use the following chart to look at the basics of Desktop Protocols:

NetBIOS	Broadcast-based. Does not have logical addressing functionality and operates primarily at the Session Layer.
NetBEUI	Broadcast-based. Does not have logical addressing functionality and operates at the Transport and Network Layers of the OSI Model. NetBEUI, which must be bridged and cannot be routed, unless encapsulated in another protocol such as NWLINK (NetBIOS over IPX) or NBT (NetBIOS over TCP/IP)
AppleTalk	Versions include Phase 1 (antiquated, does not scale well) and Phase 2 (current version) Phase 2 allows a greater number of hosts per segment (253) and supports Token Ring, Ethernet and FDDI. For more info visit Appletalk on Cisco’s Website about routing and how to route AppleTalk.
IPX/SPX	Stands for Internetwork Packet Exchange, Sequenced Packet Exchange. A routable protocol and has different encapsulations (seen below in the chart) Encapsulations must match to see other machines on the network, or, although it is not recommended, you can run two different encapsulation methods on the same router interface. Use the Ipx route-cache same interface command. The default for Novell 3.X protocol support is Raw Ethernet or ETHERNET_802.3 (Novell-Ether) For Novell 4.X, protocol support is ETHERNET_802.2 (SAP) Raw Ethernet (ETHERNET_802.3) is similar to the IEEE 802.3 frame with no Logical Link Control and FFFF in the DSAP (Destination Service Access Point) and SSAP (Source Service Access Point) Memorize the Frame types chart below for the CID exam. For more info visit IPX/SPX on Cisco’s Website.
TCP/IP	Transmission Control Protocol/Internet Protocol. Is a widely used routable protocol, and its biggest challenge is proper management with addressing, security and broadcast management.

Frame Types

ETHERNET_802.2	Novell4.X	sap	E0E0 in DSAP & SSAP	Standard IEEE frame format includes 802.2 LLC header
ETHERNET_802.3	Novell3.X	novell-ether	FFFF in DSAP & SSAP	Includes IEEE 802.3 length field No IEEE 802.2 LLC header
ETHERNET_SNAP		snap	snap 8137	Extends IEEE 802.2 header by adding SNAP header.
ETHERNET_II		arpa	arpa 8137	Standard Ethernet 2 header

TCP/IP Fundamentals

This is a collection of TCP/IP based addressing fundamentals you will need to be familiar with for the exam:

Private Addressing	The usual address prefixes are 10, 172 and 192. Used for private networks not openly exposed to the Internet (inside a firewall or private network) Full Ranges are: 10.0.0.0 – 10.255.255.255 172.16.0.0 – 172.31.255.255 192.168.0.0 – 192.168.255.255
Public Addressing	Assigned by an ISP and not recommended for private networks. Private to public network communication can be accomplished by NAT through a PIX or other firewall. Options also include VPN (Virtual Private Networks) or extranets secured through PPTP (Point-to-Point Tunneling Protocol) and/or L2TP (Layer 2 Tunneling Protocol)
Hierarchical Addressing	Use address schemes where the different network numbers determine whether a destination is local or remote. Longer subnets masks are used at the access layers. The network prefix gets smaller as you move up the network hierarchy.
Classful Addressing	Subnetting not used and the router (using a routing protocol like RIPv1) will not look at a VLSM. The Router will look at the address as if it was one of the default class A, B, or C addresses. In other words, if you subnet a Class B as so: 152.32.128.X with a Mask of 255.255.255.0, you may think it is a class C address although it is a “B” Subnetting down to the third octet.
VLSM	Variable Length Subnet Masking. Classless addressing allows using, for example, a Class B address with a Class C subnet mask. Usually summarized in this fashion 172.98.98.24/30 (30) or 255.255.255.252. These methods specify the number of bits used to calculate the network portion. This allows effective use of your IP addresses and should only be used with routing protocols that support VLSM, like EIGRP and OSPF.
Secondary Addressing	The assignment of a second IP gateway address for the same interface on a router. This is a convenient way to allow you to switch from one address convention to another simultaneously. This is not recommended and should be used only when you have to.

Basic IP Classes

Class A	1 – 126 (127 Loopback)
Class B	128 – 191
Class C	192 - 223

AppleTalk Basics

Appletalk IOS

Cisco Fundamentals on Appletalk; covers sockets, protocols and how to configure them.

AppleTalk FAQ’s

Cisco Frequently asked questions on Appletalk.

Encapsulation Protocols

PPP	Point-to-Point Protocol. Is an encapsulation standard used over Async Serial, Sync Serial and ISDN. PPP is split into 2 separate protocols: NCP and LCP: NCP: Network Control Protocol. Each NCP is used for configuring the connections of each LAN protocol at the network level (IP, IPX, CDP, etc.) LCP: Link Control Protocol. LCP is a component of PPP and is responsible for authentication, multilink, callback and compression. Note: More info is listed below this chart about PPP.
SLIP	Serial Line Internet Protocol. Only supports TCP/IP. Replaced more and more by PPP. Although this is an older technology, it is still in use today, mostly on older hardware.
HDLC	High-level data link control. Is a bit-oriented synchronous data-link layer 2 protocol. Is a data encapsulation method used on synchronous serial links. Is used for serial lines and this version is proprietary for Cisco. Do not use if connecting to a non-Cisco router or with the AutoInstall feature.
SDLC	Synchronous Data Link Control. SDLC is a bit-oriented, full-duplex serial protocol. Often used in SNA environments.
LAPB	Link Access Procedure (Balanced) Data link layer protocol in the X.25 protocol stack. LAPB is a bit oriented protocol derived from HDLC. Used over unreliable links and X.25. Connection-oriented with ordering and error checking.
STUN	Serial Tunneling. Used to tunnel SNA over WAN links. It supports local ACK used with SDLC on congested WAN links.
PPTP	Point-to-Point Tunneling Protocol. Used to tunnel IP packets securely over the Internet.
GRE	Generic Routing Encapsulation. Used primarily in the backbone. Can be used to tunnel IPX or AppleTalk. Fast switching supported.
NWLINK	Used to encapsulate NetBIOS over IPX. Requires type 20 packets to operate properly. Use the Ipx type-20-propogation command on the interface.
NBT	Used to encapsulate NETBIOS over TCP/IP.
AURP	AppleTalk Update Routing Protocol. Encapsulated in TCP/IP over WAN links. Sends updates only.
IPXWAN	Client and server side software used with PPP to connect servers or clients over a dial-up connection. It is responsible for establishing a routing metric once the connection is made. It is dynamic and requires no configuration.

Multilink PPP

• Allows additional calls or channels to connect to a host for additional bandwidth

• In order to use Multilink with Brand X routers, the routers must comply with RFC1990

• Multilink is configured on the interface

• LCP controls Multilink:

  • Works on Cisco 700 series routers

  • Works on routers running Cisco IOS

  • RFC 1990 allows for vendor compatibility

  • Allows packet fragmentation across channels

  • Sequences packets and performs load calculation on lines or channels

  • 4-Byte field in header allows for proper sequencing

Multilink Multichassis PPP

• Dial-in ISDN channels can be split off to different access servers (a.k.a. stackgroup) or routers

• The access servers (stackgroup) or routers intake the data packets and forward them to a high end MMP process server

• A process server uses SGBP (Stackgroup Bidding Protocol) to do all the packet reassembly

• The advantages are that the stackgroup is very scaleable and less overhead is required from the access servers

Remote Access Design Principals

• Design principals are shaped around the type and numbers of connections that need to be made

• The applications and requirements will depend on the type of users that will be connecting to the network

Users usually fit into these categories:

Mobile Users/Telecommuters	Not connected all the time. Short connections and low bandwidth requirements, usually analog.
Full Time Telecommuters	Usually require faster connections. Longer connect times with higher bandwidth requirements. Use ISDN to run other devices or connections.
Home or Small Office	Requires fast and long connection time. Multi-interface router needed to support LAN and multiple WAN connections.

Access Methods

Remote Gateway	Limited access and limited functionality. It can be used only to get email or access an application.
Remote Node	Most common access method. It is like dialing into a security server, RAS server, modem bank or access server stackgroup. This is the preferred method since it is very flexible and scales well in the Enterprise. Has less overhead and PC appears as if directly connected to the LAN.
Remote Control	A PC dialing in and taking control of another PC on the LAN. User has full function of network services. This requires the most overhead because an extra PC, analog line and modem are required. A good example of this is pcAnywhere.

Routing Protocols

It is important to distinguish between routed and routing protocols

• Routing protocols use metrics; hop counts, ticks, etc. to make a routing decision

• Since routers do not forward broadcasts, routers separate networks into different broadcast domains

• Switches and bridges separate media into separate collision domains

• Routed Protocols are TCP/IP, IPX/SPX and AppleTalk

• For more info on Cisco Routing: Cisco Routing Basics

Protocol List

IGRP	Interior Gateway Routing Protocol. Cisco Proprietary. Distance Vector. Updates every 90 sec. VLSM not supported. Must use IP and Classful IP addresses. Can load balance. For more Information on IGRP: Cisco IGRP Documentation
EIGRP	Enhanced Interior Gateway Routing Protocol. Cisco Proprietary. Hybrid. VLSM Supported. Uses Bandwidth, Delay, Load, Reliability, and MTU for metrics. Supports multi-protocols. Scales well and converges quickly. For More Information on IGRP: Cisco EIGRP Documentation
RIP	Routing Information Protocol. Distance Vector. Does not support VLSM. Updates every 30 sec. Metric is Hop Count. Max Hop count is 15. Chatty and does not scale well. For More Information on RIP: Cisco RIP Documentation
RIPv2	Routing Information Protocol Version 2. Distance Vector. Supports VLSM. Updates every 30 sec. Metric is Hop Count. For More Information on RIPv2: Cisco RIP2 Documentation
OSPF	Open Shortest Path First. Link State. Cost is used as Metric. Uses LSAs to check on links. Backbone is area 0. Supports VLSM and non-contiguous subnets. OSPF recalculates a new table when a route goes down. So, if you have a link flapping, you may want to increase the amount of time to wait; use the spf holdtime command. If not, it could overload the CPU and cause performance issues. OSPF Backbone: Try to stay away from meshing the backbone. Use LAN backbone design and keep everything to one hop. Use as few routers as possible to keep the diameter small. For More Information on OSPF: Cisco OSPF Documentation
BGPv4	Border Gateway Protocol Version 4. Metric is cost. BGP is an Exterior Gateway protocol and is also used to replace EGP (EGP is a particular instance of an exterior gateway protocol and the two should not be confused) BGP performs InterDomain routing in TCP/IP based networks. For More Information on BGP: Cisco BGP Documentation
RTMP	Routing Table Maintenance Protocol. AppleTalk based. Distance Vector. 10 sec update interval. Uses a Hop count as a metric. Very chatty, not recommended for WAN traffic or slow links. For More Information on RTMP: Cisco RTMP Documentation
NLSP	Netware Link Services Protocol. Link State Protocol. Uses cost. Link state for IPX/SPX (Netware) used to fix many of the issues with IPX RIP and SAP. Robust and scales well. Routing information is transmitted only when the topology has changed (IPX RIP Broadcasts every 60 secs) NLSP routers send service updates only when services change (SAP sends every 60 secs) NLSP can support up to 127 hops where RIP supports only 15 hops. For More Information on NLSP: Cisco NLSP Documentation
AURP	AppleTalk Update Based Routing Protocol. Link State. AppleTalk. Tunneled by IP over WAN links. This is Apple’s attempt to create a better WAN-friendly routing protocol than RTMP. RTMP is encapsulated in IP over an AURP Tunnel on WAN links. Reduces WAN traffic because only updates are sent over the wire. Use in an IP only WAN environment. For More Information on AURP: Cisco AURP Documentation

OSPF LSA Information

LSA1	Router Links LSA. Sends information about the routers links.
LSA2	Network Link LSA. Sent by the DR to all routers in the AS. A list of routers in the segment.
LSA3	Summary Link LSA. Sent by ABR’s list of networks available outside the area.
LSA4	Summary Link LSA. Sent by ASBR’s list of networks available outside the area.
LSA5	External Link LSA. Sent by ASBR’s list of external network routes.

Microsoft Design Fundamentals

Workgroups and Domains	Workstations sharing resources are defined as Workgroups when configured to do so (Peer to Peer) The presence of an NT server classifies it as a domain (As long as your server is configured to be a domain) Domains make the administration of resources easier and more secure.
Single Domain Model	Services controlled by one PDC for clients.
Master Domain Model	A collection of domains trusting a single master PDC for centralized administration. Simplifies management of resources.
Multiple Master Domain Model	Resource domains trusting multiple master domain PDCs.
Complete Trust Domain Model	All domains trust all other domains and resources can be administered and shared across these domains.

Campus and Switching Design

Common campus issues are Media, Protocols and Transport. Media issues are caused by high network loads and media contention. Use LAN switching to solve this problem. Another protocol problem is that some do not scale well and are prone to excessive broadcasts. To solve this problem, use routers to segment your network. Transport problems occur when there is not enough bandwidth to support high bandwidth applications. Use ATM, Gigabit Ethernet and/or QOS OIS features to solve these problems. (This is also mentioned in the chart in the beginning of the Cramsession.)

Cut-through	A packet is forwarded once the destination is read. No CRC check.
Store and Forward	The entire packet is processed. Check the CRC, then forwards the packet out the appropriate interface or port.
VLANS	802.1Q is a VLAN standard. VLANS help separate broadcast domains. A router is required for communication between VLANS. Switching separates or creates collision domains.
Distributed Backbone	Each floor or building is isolated by its own router and switch. This setup is more expensive and often requires costly upgrades to scale.
Collapsed Backbone	All floors are wired into a single switch and router. More cost effective, but creates a single point of failure.
BPDU	Bridge Protocol Data Unit. Spanning Tree Protocol hello packet that is sent out at configurable intervals to exchange information among bridges in the network.

Bridging Fundamentals

Transparent	Found in Ethernet Networks. “Transparent” to the Clients on the network. The device (switch) knows where to forward the frame via the MAC table.
Source Route	Found in Token Ring Networks. All forwarding decisions are known in advanced and based on the RIF.
Translational	Translates between Token Ring and Ethernet. Allows both to function in a mixed environment.
Source Route Transparent	Combines both Source Route and Transparent. Needed for Mixed Token Ring and Ethernet networks.
Source Route Translational	Combines both Source Route and Translational. Needed for Mixed Token Ring and Ethernet networks.

Describe the use of Hot Standby Router Protocol (HSRP) in a campus network environment

• HSRP is used in a network environment for Routing Redundancy

• If one router goes down, the other takes over

• This is ideal for Core Router Design where downtime is not an option

Check here for everything you need to know about HSRP and how to configure it: Cisco HSRP

Define Integrated Routing and Bridging (IRB)

• Integrated routing and bridging

• Integrated Services Digital Network (ISDN) User Part

• Upper-layer applications supported by SS7 for connection, set up, and tear down

Asynchronous Transfer Mode (ATM)

ATM (Asynchronous Transfer Mode)

• Like Frame Relay and X.25, it uses PVCs and SVCs to establish connectivity

• Used for high-speed data, video and voice

• It uses cells to transport information in 53 byte cells (48 bytes in the body and 5 bytes in the header)

• ATM uses prefix routing in private networks

ATM Features

• 5 bytes for header, 48 for data

• QOS is effective for managing ATM

• Flexible multiplexing and switching technology

• Low latency thanks to small cells and high speed media

• Supports high performance applications

• Uses SNAP encapsulation to multiplex several protocols

• SVC are disconnected once transmission is complete

• Operates primarily at the Data Link Layer of the OSI model

ATM Components

AAL	ATM Adaptation Layer. Operates at the Data Link Layer, and its primary function is to hide what it is doing to the frames from the higher OSI Layers. Abstraction is right.
ATM Layer	Establishes connections and passes cells through the ATM network.
ATM Physical	Manages the physical transmission of the cells. Does the bit-to-cell conversion.
AAL1	Connection-oriented. Needs time sequencing from source to destination and vice versa.
AAL3/4	Connectionless-oriented; used to transfer SDMS. It loses some payload capacity because of added CRC, MIDs (Message Identifier) and the sequence number. There is a slightly increased delay attributed to the SAR (Sequence Assembly Reassembly) Requires the use of a SDSU for SAR.
AAL5	Connection and connectionless-oriented. Used for data transport. Uses SEAL for SAR.
PNNI	Private Network Node Interface. A hierarchical routing protocol used for ATM routing. It is dynamic and requires little configuration. Scalable, but complex.
IISP	Interim Inter-Switch Signaling Protocol. Is a static routing on ATM network. Uses SVCs when routes go down.
LANE	LAN Emulation. Emulation of a LAN over an ATM network.
LEC	LAN Emulation Clients. Sends its MAC address to the LECS server. It can be a workstation or a router. It is responsible for endpoint functions, address resolution and data forwarding.
LES	LAN Emulation Server. Pseudo-WINS server for ATM. Acts as a register to store the multicast or unicast MAC address information of the LE clients. It accepts LE-ARP requests for destination MAC addresses.
LECS	LAN Emulation Configuration Server. Serves multiple ELANS and maintains a database of all the LEC’s MAC addresses. LECS respond to LEC’s requests by sending the appropriate ELAN information (identifier) Used like DHCP to assign LECs to certain ELANS. This is a one-per-ATM switch.
BUS	Broadcast and Unknown Server. Multicast and broadcast server. Sends traffic to clients of the ELAN it is responsible for.

X.25

• X.25 is a packet-switched Layer 2 protocol that operates at the Data Link Layer of the OSI model *(It also operates at Layer 3)

• This protocol works by encapsulating the Layer 3 protocols

• X.25 was engineered for strong error checking and flow control at Layers 2 and 3

• X.25 uses LAPB and is very reliable

• It also uses sliding windows (much like TCP/IP) for flow control

• Suffers from lower throughput and higher latency than Frame Relay

• X.25 uses SVCs (Switched Virtual Circuits) and PVCs (Permanent Virtual Circuits)

• PVCs are always connected

• X.25 treats connection as a reliable data link; Frame Relay does not

	Transport Layer 4
X.25 Network Layer 3	Network Layer 3
LAPB Datalink Layer 2	Datalink Layer 2
Physical Layer 1	Physical Layer 1

X.25 Components

PAD	Packet Assembler Disassembler. It collects the data transmissions from the terminals and gathers them into a X.25 data stream and vice versa. PAD acts like a multiplexer for the terminals. During configuration of the X.25, you specify whether the interface will act as a DCE or DTE. When configured as a DCE the router behaves as an X.25 switch.
X.121	The addressing standard. Static mappings must be made manually. X.25 does not support ARP. The addressing standard is a 4-digit country code. The following 8 to 11 digits are assigned by the X.25 service provider.
Options for X.25	Windows and packet sizes must match on both sides on the connection. Use the x25 ips command for incoming packet size and x25 ops for outgoing packet size. Window size uses a counter for when to send an acknowledgement (x25 win and x25 wout commands are used) The modulo controls the size of the window. 8 or 128 are used to specify the number of packets. Satellites use X.25 as well. To increase performance, they use modulo 128 which sets the window size higher.

Frame Relay

Frame Relay Components

Frame Relay	Frame Relay requires the use of a CSU/DSU. Like X.25, Frame Relay uses SVCs and PVCs. PVCs are used for frequent and long connection times. SVCs are for sporadic, infrequent traffic. It is a Layer 2 protocol.
LMI	Local Management Interface. There are 3 types: Cisco (Default) ANSI Q.933A The service provider will specify the LMI in use. LMIs control data keep-alives and verify the dataflow. Uses multicast mechanism to provide network server the DCLI. Uses multicast addressing so DLCI has global significance. Verifies the DLCIs in use and status to the local Frame-Relay switch. LMI Autoconfigure: A router with IOS 11.2 and newer does not need to be configured for the LMI. The newer routers will send a signal to the FR switch to determine the LMI in use.
DLCI	Data Link Connection Identifier. Verifies the logical circuits in use and the status from the CPE to the Frame Relay switch.
Encapsulation Types	Two Types are: Cisco (default) IETF If the router is a non-Cisco router, use IETF. This designation can be made per DLCI. Even if all the routers are Cisco, you can communicate with a location with a non-Cisco router. Specify the IETF encapsulation and DLCI. You can use this with the map command. In short, encapsulation can be set to per interface or per destination.
Split Horizon and Routing Updates	Since routing updates should not be sent out from the same interface you receive the update from (as this causes routing loops), the solution to this problem is creating subinterfaces with different DLCIs. Each subinterface has its own DLCI-enabled multipoint connection. Routing updates will now work properly.
Frame Relay Map	This command is used to configure the next hop address on an interface.
Inverse ARP	Takes care of all the mappings for you It builds a Frame-Relay map by querying the Frame-Relay switch during the LMI exchange. It sends an Inverse ARP request for the protocols that are specified on the interface. The downside for the automatic set up is troubleshooting can be a pain.
NBMA Model	Non-Broadcast Multi-Access Model. Mesh between peer routers. Routers are configured as a simulated LAN and are configured as one logical subnet. The downside is processor overhead: each broadcast packet must be processed. Broadcasts are sent out each virtual circuit. Results in performance degradation on the link. To control the amount of bandwidth used on an interface use the frame-relay broadcast-queue command.
Virtual Circuit Routing	Uses Subinterfaces to conquer the split horizon issues. This simulates several point-to-point links.

Voice and Video Basics

VoIP	Voice over IP. The capability to carry normal telephony voice over an IP network while keeping reliability and quality of voice. VoIP enables a router to carry voice traffic over a network (LAN or WAN) In VoIP the DSP does the following: Segments the voice signal into frames. The frames are then are coupled in groups of two. The Groups of two are stored in voice packets. Voice packets are being transported using IP in compliance with ITU-T specification H.323.
VIC	Voice interface card. Connects the system to either the PSTN or to a PBX. Compared with WIC or WAN Interface Card.
VoFR	Voice over Frame Relay. VoFR enables a router to carry voice traffic over Frame Relay. The voice traffic is segmented and encapsulated for transit across Frame Relay using FRF.12 encapsulation.
VoD	Video on demand. System uses video compression to supply video to viewers when requested.
VoATM	Voice over ATM. Voice over ATM enables a router to carry voice traffic over an ATM network. The voice traffic is encapsulated using a special AAL5 encapsulation for multiplexed voice.
VoHDLC	Voice over HDLC. Voice over HDLC enables a router to carry live voice traffic back to back to a second router over a serial line.

Quality of Service Basics

Cisco Documentation

List Quality of Service and its features, which provide better and more predictable network service

What is QoS?

QoS is the capability of a network to provide better service to selected network traffic over various technologies. Primary goals of QoS include:

• Prioritized traffic

• Dedicated bandwidth

• Controlled jitter and latency

• Improved loss characteristics

The features of QoS are going to be highly needed in the future when VoIP and Video over the network really take off because you will need to make this traffic the priority over the network for better performance

Features of QoS

FIFO	First-in, first-out queuing. Basic Store-and-Forward Capability. FIFO queuing stores packets when the network is congested and then forwards the packets in order of arrival when congestion dies off. This is the true picture of “first in - first out”. FIFO is the default queuing algorithm and requires very little (if any) configuration. FIFO queuing does not look at the packet’s priority level, it only sends out the packets in the order they were received.
PQ	Priority queuing. Works on Prioritizing Traffic. Priority queuing can flexibly prioritize according to: Network protocol (IP, IPX, or AT) Incoming interface Packet size Source/destination address Each packet is placed in one of four queues: High Medium Normal Low
CQ	Custom queuing. Works on guaranteeing bandwidth. The traffic is queued in a custom fashion, allowing a specific amount of the queue space to each class of packet. The queues are serviced in a round-robin fashion.
WFQ	Weighted fair queuing. “Cisco's Intelligent Queuing Tool for Today's Networks”. It is a flow based queuing algorithm that does two things at the same time: Interactive traffic is scheduled to the front of the queue to reduce the response time. The algorithm shares the remaining bandwidth fairly among high bandwidth flows. This solution does not starve the bandwidth and makes it so that traffic gets predictable service.

SNA Design

SNA (System Network Architecture) Fundamentals

SNA is a hierarchal network structure. There are several components and possible configurations for configuring an SNA network.

For more information on SNA, check out Cisco's SNA Technology Brief

SNA Terminology

NAUs	Network Addressable Units. All devices that can communicate in an SNA network.
LU	Logical Unit. The software end unit. Software that provides the interaction for the users.
PU	Physical Unit. Controls resources on the node. Loads software and provides the communication with the SSCP.
SSCP	System Services Control Points. Software for the mainframe that is responsible for establishing the lines of communication and controlling resources.
SNA Gateways	Handling direct communication with the mainframe for a dumb terminal or PC would be quite rough without a gateway.
LU Gateway	SDLC uses polling to communicate. Sending polling traffic over the LAN may convince you to establish a gateway. LU gateways are good because the Mainframe has a SSCP session, to the PU session, to the LU gateway. The clients only connect to the LU gateway though NetBIOS, so the Mainframe maintains fewer connections.
PU Gateways	Have a larger amount of overhead and administrative burden. The PCs attached to the PU have to be manually configured on the VTAM.
VTAM	Virtual telecommunications access method. Set of programs that control communication between LUs. VTAM controls data transmission between channel attached devices and performs routing functions.
DLSW DLSW+	Data Link Switching (Plus) Recommended as a scalable solution for traffic over a WAN link. Responsible for multiplexing LLC connections over the WAN link. DLSW+ is Cisco’s enhanced version of DLSW.
STUN	Serial Tunneling.