Chapter 7

Wide Area Network (WAN)

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Outline

Overview WAN Overview Wan Connection Types WAN Cabling Layer 2 Encapsulation Protocols Summary

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WAN Overview

WANs connect remote sites. Connection requirements vary depending on user

requirements, cost, and availability.

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• Provider assigns connection parameters to subscriber

Interfacing BetweenWAN Service Providers

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WAN Connection Types: Layer 1

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Circuit Switching

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Packet Switching

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Modem Transmission

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Introduction to Serial Communication

Transmission system encodes bits into electrical voltage using methods like NRZ-L or AMI

Some of the many serial communications standards include the following:

RS-232-E V.35 High-Speed Serial Interface (HSSI)

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Time-Division Multiplexing

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WAN Encapsulation

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WAN Link Options

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WAN Data-Link Protocols

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Typical WAN Encapsulation Protocols: Layer 2

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Analog Dialup

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ISDN

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ISDN

Router with standard serial interface, connected to a terminal adapter

Router with native ISDN BRI U or S/T interface or PRI

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Leased Line

Leased lines are not only used to provide direct point-to-point connections between Enterprise LANS, they can also be used to connect individual branches to a packet switched network.

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WAN with X.25

X.25 provides a low bit rate, shared-variable capacity that may either be switched or permanent

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Frame Relay

Most Frame Relay connections are based on PVCs rather than SVCs.

It implements no error or flow control. This leads to reduced latency.

Frame Relay provides permanent shared medium bandwidth connectivity that carries both voice and data traffic.

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ATM Asynchronous Transfer Mode (ATM) is a technology

capable of transferring voice, video, and data through private and public networks.

It is built on a cell based architecture rather than on a frame-based architecture.

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DSL

• DSL uses existing twisted-pair telephone lines to transport high-bandwidth data

• DSL service is considered broadband, as it uses multiple frequencies within the same physical medium to transmit data

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ADSL Technology

Splitter

• The local loop connects the splitter to the DSLAM• DSLAM connected to ISP using ATM technology• Voice and data use separate frequency ranges

(voice 0-4Khz, data 20Khx – 1Mhz)

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Cable Modem

Enhanced Cable Modems enable two-way. High speed data transmissions using the same coaxial lines that transmit cable television.

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Modern WAN

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WANs Operate at the Lower Three Levels of the OSI Model

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Comparing WAN Traffic Types

35© 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—5-35

Establishing Serial Point-to-Point Connections

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• Supports only single-protocol environments

HDLC Frame Format

• Uses a proprietary data field to supportmultiprotocol environments

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PPP can carry packets from several protocol suites using NCP.

PPP controls the setup of several link options using LCP.

An Overview of PPP

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PPP Layered Architecture

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PPP and the Data Link Layer

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PPP and the Network Layer

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PPP Operation

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Link Control Protocol Options

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PPP LCP Configuration Options

54© 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—7-54

Completing ISDN CallsISDN BRI and PRI

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What Is ISDN?

• Voice, data, video, and special services

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Standards from the ITU-T

ISDN Standards

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ISDN Access Options

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ISDN 3-Layer Model

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BRI and PRI Call Processing

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ISDN Functions and Reference Points

Functions are devices or hardware.

Reference points are demarcations or interfaces.

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ISDN Functions and Reference Points

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Cisco ISDN BRI Interfaces

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Cisco ISDN PRI Interfaces

67© 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—6-67

Establishing Frame Relay Connections

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Frame Relay Overview

Connections made by virtual circuits Connection-oriented service

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Frame Relay Stack

OSI Reference Model Frame Relay

Physical

Presentation

Session

Transport

Network

Data-Link

Application

EIA/TIA-232, EIA/TIA-449, V.35, X.21, EIA/TIA-530

Frame Relay

IP/IPX/AppleTalk, etc.

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Frame Relay Stack Layered Support

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Local Significance of DLCIs

The data-link connection identifier (DLCI) is stored in the Address field of every frame transmitted.

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Frame Relay Terminology

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Data Link Control Identifier

The 10-bit DLCI associates the frame with its virtual circuit

It is of local significance only - a frame will not generally be delivered with the same DLCI with which it started

Some DLCI’s are reserved

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Local Management Interface (LMI) Three types of LMIs are supported by Cisco

routers: Cisco — The original LMI extensions Ansi — Corresponding to the ANSI standard

T1.617 Annex D q933a — Corresponding to the ITU standard Q933

Annex A

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• Frame Relay default: nonbroadcast multiaccess (NBMA)

Selecting a Frame Relay Topology

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Frame Relay Address Mapping

Use LMI to get locally significant DLCI from the Frame Relay switch.

Use Inverse ARP to map the local DLCI to the remote router network layer address.

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Frame Relay Signaling

Cisco supports three LMI standards: Cisco ANSI T1.617 Annex D ITU-T Q.933 Annex A

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Frame Relay Inverse ARP and LMI Signaling

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Stages of Inverse ARP and LMI Operation

Q&A

Good luck everybody.