McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Chapter 11 Wide Area Networks

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Understand point-to-point WAN technologies: T-lines and SONET networks. 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. After reading this chapter, the reader should be able to: O BJECTIVES Understand ATM LANs.

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. POINT-TO-POINTWANsPOINT-TO-POINTWANs 11.1

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 11-1 T-1 line

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. A T-1 line has a data rate of Mbps Note:

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. A T-3 line has a data rate of Mbps Note:

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. 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.

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 11-2 SONET

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. SWITCHEDWANsSWITCHEDWANs 11.2

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. 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.

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 11-3 Frame Relay network

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 11-4 Frame Relay layers

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. 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:

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. 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. Note:

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 11-5 ATM multiplexing

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 11-6 Architecture of an ATM network

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. 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).

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 11-7 An ATM cell

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 11-8 ATM layers

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. The IP protocol uses the AAL5 layer. Note:

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. ATMLANsATMLANs 11.3

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Figure 11-9 ATM LAN architectures

McGraw-Hill©2003 The McGraw-Hill Companies, Inc. Technical Focus: LANE Connectionless vs. Connection-oriented Physical Address vs. Virtual Connection Identifier Multicasting and Broadcasting Delivery Interoperability 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.