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Chapter 11

Chapter 11. Wide Area Networks. O BJECTIVES. Understand X.25 technology and why it is losing popularity. Understand Frame Relay technology and how it was designed to replace X.25. Understand ATM technology and its importance in today’s market. Understand ATM LANs.

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Chapter 11

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  1. Chapter 11 Wide Area Networks

  2. OBJECTIVES Understand X.25 technology and why it is losing popularity. Understand Frame Relay technology and how it was designedto replace X.25. Understand ATM technology and its importance in today’smarket. Understand ATM LANs. Understand point-to-point WAN technologies: T-lines and SONET networks. After reading this chapter, the reader should be able to:

  3. 11.1 POINT-TO-POINT WANs

  4. Figure 11-1 T-1 line

  5. Note: A T-1 line has a data rate of1.544 Mbps

  6. Note: A T-3 line has a data rate of 44.736 Mbps

  7. Technical Focus:Fractional T-Lines Many subscribers may not need the entire capacity of a T- line. To accommodate these customers, telephone companies offer fractional T-line services, which allow several subscribers to share one line by multiplexing their transmissions.

  8. Figure 11-2 SONET

  9. 11.2 SWITCHED WANs

  10. Technical Focus:Tunneling To use an X.25 network, an IP packet uses a technique called tunneling. Because X.25 does not allow IP packets to use their own network layer protocol, the IP packets are encapsulated in the network layer of the X.25 protocol. This can be compared to a car entering a tunnel. To an observer, the car disappears at one side of the tunnel and reappears at the other side. Likewise, an IP packet disappears at the entry point of an X.25 network and reappears at the exit point.

  11. Figure 11-3 Frame Relay network

  12. Figure 11-4 Frame Relay layers

  13. Technical Focus:DLCIs A Frame Relay network uses data link connection identifiers (DLCIs) which act as addresses. Each DLCI defines a channel between two adjacent devices (DTEs or DCEs). A path between a device at one end and another device at the other end is made of several DLCIs as shown in the following figure:

  14. Note: A cell network uses the cell as the basic unit of data exchange. A cell is defined as a small fixed-sized block of information.

  15. Figure 11-5 ATM multiplexing

  16. Figure 11-6 Architecture of an ATM network

  17. Technical Focus:VPIs and VCIs In an ATM network, connection between two end points is accomplished through transmission paths, virtual paths, and virtual circuits as shown in the following figure: The outer cylinder shows a transmission path. The inner cylinders show the virtual path identifiers (VPIs). The lines show virtual circuit identifiers (VCIs).

  18. Figure 11-7 An ATM cell

  19. Figure 11-8 ATM layers

  20. Note: The IP protocol usesthe AAL5 layer.

  21. 11.3 ATM LANs

  22. Figure 11-9 ATM LAN architectures

  23. Connectionless vs. Connection-oriented Physical Address vs. Virtual Connection Identifier Multicasting and Broadcasting Delivery Interoperability Technical Focus:LANE At the surface level, the use of ATM technology in LANs seems plausible. However, on close inspection, we see that many issues need to be resolved, as summarized below: An approach called local area network emulation (LANE) solves the above-mentioned problems and allows stations in a mixed architecture to communicate with each other.

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