Connecting to Remote Networks © 2004 Cisco Systems, Inc. All rights reserved. Understanding WAN Technologies INTRO v2.0—7-1

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-2 Outline Overview What Is a Wide Area Network? Why Are WANs Necessary? How Is a WAN Different from a LAN? WAN Access and the OSI Reference Model WAN Devices The Role of Routers in WANs WAN Data Link Protocols Multiplexing WAN Communication Link Options Summary

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-3 Wide-Area Network

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-4 Need for WANs

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-5 WANs vs. LANs

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-6 WAN Access and the OSI Model

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-7 WAN Devices Routers Terminal servers Modems DSU/CSU WAN networking devices –ATM switches –Frame Relay switches –PSTN/ISDN switches

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-8 Physical Layer: WANs

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-9 WAN—Multiple LANs

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-10 WAN Data-Link Protocols

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-11 Multiplexing Technologies Time-Division Multiplexing (TDM) Frequency-Division Multiplexing (FDM) Statistical Multiplexing

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-12 TDM

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-13 FDM

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-14 Statistical Multiplexing Ch. 1 = 64 kbps PCM packets Ch. 2 = 32 kbps ADPCM packets Ch. 3 = kbps fixed-size packets Ch. N = kbps using variable-size packets

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-15 WAN Link Options

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-16 Summary There are three major characteristics of a WAN: connection of devices that are separated by wide geographical distances; use of the services of carriers, such as telephone companies, cable companies, satellite systems, and network providers; and use of serial connections of various types to access bandwidth over large geographic areas. Many business and home needs require communication among remote users, including communication between users in remote company locations, data sharing among different organizations, access to corporate information by traveling workers, and access to Internet.

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-17 Summary (Cont.) LANs connect computers, peripherals, and other devices in a single building or other small geographic area; WANs transmit data across broad geographic distances. A company, organization or individual must subscribe to an outside WAN service provider to use WAN network services, while LANs are owned typically by the company, organization, or individual that uses them.

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-18 Summary (Cont.) WAN access functions in relation to the OSI reference model, but their function focuses primarily on Layer 1 and Layer 2. The major types of devices used for WAN access environments include routers, communication servers, modems (DSU/CSUs), and other networking devices such as ATM, ISDN, Frame Relay, and PSTN or ISDN switches. Routers have both LAN and WAN interfaces, and while a router is used to segment LANs, it is also used as the WAN connection device.

© 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-19 Summary (Cont.) The data link layer protocols define how data is encapsulated for transmission towards remote sites in a WAN environment, and the mechanisms for transferring the resulting frames. A variety of different technologies, such as ISDN, Frame Relay, or ATM, are used. Multiplexing is a process of sharing different streams of data on a WAN link simultaneously. There are three primary types of multiplexing: TDM, FDM, and statistical multiplexing. Leased lines, circuit-switched connections, and packet- switched connections are three of the different communications link types for a WAN.