西安电子科技大学：《计算机通信与网络》课程教学课件（讲稿）第三部分 数据链路层 第18章 虚电路网络——帧中继和ATM

Data Communications and Networking Forouzan Fourth Edition Chapter 18 虚电路网络： 帧中继和ATM 18.1 Copyright The McGraw-Hill Companies,Inc.Permission required for reproduction or display

18.1 Chapter 18 虚电路网络: 帧中继和ATM Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display

18-1 帧中继 帧中继(Frame Relay)是一种虚电路广域网，设计用 来满足在20世纪80年代末期到90年代早期对新型广 域网的需求 Topics discussed in this section: 体系结构Architecture 帧中继层Frame Relay Layers 扩展地址Extended Address 帧中继组装器/分解器FRAD(Frame Relay assembler//disassemble) 帧中继语音VOFR(Voice Over Frame Relay) 本地管理信息LMI(Local management information) 18.2

18.2 18-1 帧中继 帧中继(Frame Relay)是一种虚电路广域网, 设计用 来满足在20世纪80年代末期到90年代早期对新型广 域网的需求. 体系结构 Architecture 帧中继层 Frame Relay Layers 扩展地址 Extended Address 帧中继组装器/分解器 FRAD (Frame Relay assembler/disassemble) 帧中继语音 VOFR (Voice Over Frame Relay) 本地管理信息 LMI (Local management information) Topics discussed in this section:

Figure18.1帧中继网络 旱旱旱 LAN ≤Router To the rest of Frame Relay network the Internet (WAN) × Router 18.3

18.3 Figure 18.1 帧中继网络

Note 帧中继中的VC称为DLCI. Vc:虚电路标识符(virtual circuit identifier) DLC:数字链路连接标识符(data link connection identifier) 18.4

18.4 帧中继中的VCI称为DLCI. Note VCI: 虚电路标识符 (virtual circuit identifier) DLCI: 数字链路连接标识符 (data link connection identifier)

Figure18.2帧中继层 Simplified core functions of data link layer Data link ANSI standards Physical 18.5

18.5 Figure 18.2 帧中继层

Note 帧中继仅工作在物理层和数据链路层. 18.6

18.6 帧中继仅工作在物理层和数据链路层. Note

Figure18.3帧中继帧 C/R:Command/response BECN:Backward explicit congestion notification EA:Extended address DE:Discard eligibility FECN:Forward explicit congestion notification DLCl:Data link connection identifier Flag Address Information FCS Flag DLCI C/R EA DLCI FECN BECN DE EA 6 bits 1 bit 1 bit 4bits 1 bit 1 bit 1 bit 1 bit 18.7

18.7 Figure 18.3 帧中继帧

Note 帧中继不提供流量和差错控制， 这些必须由上层协议提供. 18.8

18.8 帧中继不提供流量和差错控制, 这些必须由上层协议提供. Note

Figure18.4三种地址格式 DLCI C/R EA=0 DLCI FECN BECN DE EA=1 a.Two-byte address(10-bit DLCI) DLCI C/R EA=0 DLCI C/R EA=0 DLCI FECN BECN DE EA=0 DLCI FECN BECN DE EA=0 DLCI EA=0 DLCI 0 EA=1 DLCI 0 EA=1 b.Three-byte address(16-bit DLCI) c.Four-byte address(23-bit DLCI) 18.9

18.9 Figure 18.4 三种地址格式

Figure 18.5 FRAD X.25 X.25 ATM FRAD Frame FRAD Relay ATM PPP PPP FRAD,Frame Relay Assembler dissembler, 帧中继组装器/分解器 18.10

18.10 Figure 18.5 FRAD FRAD，Frame Relay Assembler / dissembler, 帧中继组装器/分解器