[计算机网络基椽—第五章（局域网）.ppt

Computer Networks, by Cheng Li 第五章 局域网（LAN） 主要内容 IEEE802.3 ETHERNET 网桥-Bridge LAN典型拓扑结构 二、LAN参考模型 LAN标准 三、LAN的数据链路层 LLC的帧结构 2. MAC子层的地址问题 5.2 IEEE 802.3规范 10BASE5 10BASE2 10BASET 10BASEF 多个网段互连 二、IEEE 802.3的体系结构与功能实现 三、IEEE802.3的物理层（与OSI略有不同） 五、交换式802.3LAN 5.3 LAN的扩展（LAN互连）：网桥 网桥对MAC帧的操作 二、网桥的基本原理 网桥的工作过程 三、IEEE802.1D透明网桥 支撑树(spanning tree)的构成 “兜圈子”问题 站表问题 站表问题(2) (1)A发送帧到H (2)B发送帧到A (3)A 移动到 H所在的局域网 (4)A发送帧到E ?各个网桥的站表。 站表问题(3) 站表问题(4) Consider the interconnected LANs showns in Fig.(a). Assume that hosts a and b are on LAN 1, c is on LAN 2, and d is on LAN 8. Initially, hash tables in all bridges are empty and the spanning tree shown in Fig (b) is used. Show how the hash tables of different bridges change after each of the following events happen in sequence, first (a) then (b) and so on. (a) a sends to d. (b) c sends to a. (c) d sends to c. (d) d moves to LAN 6. (e) d sends to a. a) After a sends to d each bridge will have an entry for destination a with appropriate port in its hash table. For example, D’s hash table will now have an entry to forward frames destined to a on LAN 2. b) The second message will be seen by bridges B, D, and A. These bridges will append a new entry in their hash table for frames destined for c. For example bridge D’s hash table will now have another entry to forward frames destined to c on LAN 2. c) The third message will be seen by bridges H, D, A, and B. These bridges will append a new entry in their hash table for frames destined for d. d) No change e) The 4th message will be seen by bridges E, C, B, D, and A. Bridges E and C will append a new entry in their hash table for frames destined for d, while bridges D, B, and A will update their hash table entry for destination d. 5.4 高速LAN 一、 快速以太网 IEEE 802.3U -- 快速以太网 二 Gigabit Ethernet 802.3z Goals Make Ethernet go 10 times faster Remain backward compatible with all existing Ethernet standards Unacknowledged datagram service with both unicast and multicast Use the same