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In this chapter, we show how the virtual-circuit approach can be used in wide-area networks. Two common WAN technologies use virtual-circuit switching. Frame Relay is a relatively high-speed protocol that can provide some services not available in other WAN technologies such as DSL, cable TV, and T lines. ATM, as a high-speed protocol, can be the superhighway of communication when it deploys physical layer carriers such as SONET. | Chapter 18 Virtual-Circuit Networks: Frame Relay and ATM Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18. 18-1 FRAME RELAY Frame Relay is a virtual-circuit wide-area network that was designed in response to demands for a new type of WAN in the late 1980s and early 1990s. Architecture Frame Relay Layers Extended Address FRADs VOFR LMI Topics discussed in this section: 18. Figure 18.1 Frame Relay network 18. VCIs in Frame Relay are called DLCIs. Note 18. Figure 18.2 Frame Relay layers 18. Frame Relay operates only at the physical and data link layers. Note 18. Figure 18.3 Frame Relay frame 18. Frame Relay does not provide flow or error control; they must be provided by the upper-layer protocols. Note 18. Figure 18.4 Three address formats 18. Figure 18.5 FRAD 18. 18-2 ATM Asynchronous Transfer Mode (ATM) is the cell relay protocol designed by the ATM Forum and adopted by the ITU-T. Design Goals Problems Architecture Switching ATM Layers Topics discussed in this section: 18. Figure 18.6 Multiplexing using different frame sizes 18. A cell network uses the cell as the basic unit of data exchange. A cell is defined as a small, fixed-size block of information. Note 18. Figure 18.7 Multiplexing using cells 18. Figure 18.8 ATM multiplexing 18. Figure 18.9 Architecture of an ATM network 18. Figure 18.10 TP, VPs, and VCs 18. Figure 18.11 Example of VPs and VCs 18. Note that a virtual connection is defined by a pair of numbers: the VPI and the VCI. Note 18. Figure 18.12 Connection identifiers 18. Figure 18.13 Virtual connection identifiers in UNIs and NNIs 18. Figure 18.14 An ATM cell 18. Figure 18.15 Routing with a switch 18. Figure 18.16 ATM layers 18. Figure 18.17 ATM layers in endpoint devices and switches 18. Figure 18.18 ATM layer 18. Figure 18.19 ATM headers 18. Figure 18.20 AAL1 18. Figure 18.21 AAL2 18. . | Chapter 18 Virtual-Circuit Networks: Frame Relay and ATM Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18. 18-1 FRAME RELAY Frame Relay is a virtual-circuit wide-area network that was designed in response to demands for a new type of WAN in the late 1980s and early 1990s. Architecture Frame Relay Layers Extended Address FRADs VOFR LMI Topics discussed in this section: 18. Figure 18.1 Frame Relay network 18. VCIs in Frame Relay are called DLCIs. Note 18. Figure 18.2 Frame Relay layers 18. Frame Relay operates only at the physical and data link layers. Note 18. Figure 18.3 Frame Relay frame 18. Frame Relay does not provide flow or error control; they must be provided by the upper-layer protocols. Note 18. Figure 18.4 Three address formats 18. Figure 18.5 FRAD 18. 18-2 ATM Asynchronous Transfer Mode (ATM) is the cell relay protocol designed by the ATM Forum and adopted by the ITU-T. Design .
