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15章 连接局域网、主干网和虚拟局域网 Connecting LANs, Backbone Networks, and Virtual LANs

Data Communications and Networking Forouzan Fourth Edition Chapter 15 Connecting LANs, Backbone Networks, and Virtual LANs 15.1 Copyright The McGraw-Hill Companies,Inc.Permission required for reproduction or display

15.1 Chapter 15 Connecting LANs, Backbone Networks, and Virtual LANs Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display

15-1 CONNECTING DEVICES In this section,we divide connecting devices into five different categories based on the layer in which they operate in a network. Topics discussed in this section: ●Passive Hubs(无源集线器) ●Active Hubs(有源集线器) Bridges(桥) ●Two-Layer Switches(二层交换) ●Routers(路由器) ●Three-Layer Switches(三层交换) ●Gateways(网关) 15.2

15.2 15-1 CONNECTING DEVICES In this section, we divide connecting devices into five different categories based on the layer in which they operate in a network.  Passive Hubs（无源集线器）  Active Hubs（有源集线器） Bridges（桥）  Two-Layer Switches（二层交换）  Routers（路由器）  Three-Layer Switches（三层交换）  Gateways（网关） Topics discussed in this section:

Figure 15.1 Five categories of connecting devices Application Application Gateway Transport Transport Router or Network three-layer switch Network Bridge Data link or two-layer switch Data link Physical Repeater or hub Physical Passive hub 15.3

15.3 Figure 15.1 Five categories of connecting devices

Note A passive hub is just a connector. 无源集线器只是个连接器，连接来自不同分支 的线路 在星型拓扑中，无源集线器只是一个来自不同 站点的信号冲突点，集线器是冲突点 15.4

15.4 A passive hub is just a connector. Note  无源集线器只是个连接器，连接来自不同分支 的线路  在星型拓扑中，无源集线器只是一个来自不同 站点的信号冲突点，集线器是冲突点

Figure 15.2 A repeater connecting two segments of a LAN Repeater Segment 1 Segment 2 15.5

15.5 Figure 15.2 A repeater connecting two segments of a LAN

Figure 15.3 Function of a repeater Repeater Regenerated Corrupted signal signal a.Right-to-left transmission. Repeater Corrupted Regenerated signal signal b.Left-to-right transmission. 15.6

15.6 Figure 15.3 Function of a repeater

Note A repeater connects segments of a LAN. A repeater forwards every frame; it has no filtering capability. 中继器是仅工作在物理层的设备 中继器能够扩展局域网的物理长度 中继器并不能连接两个局域网，它连接的是同 一局域网的两个分段 中继器转发每一帧，没有过滤能力 15.7

15.7 A repeater connects segments of a LAN. Note  中继器是仅工作在物理层的设备  中继器能够扩展局域网的物理长度  中继器并不能连接两个局域网，它连接的是同 一局域网的两个分段  中继器转发每一帧，没有过滤能力 A repeater forwards every frame; it has no filtering capability

Note A repeater is a regenerator, not an amplifier. 中继器是再生器，不是放大器 15.8

15.8 A repeater is a regenerator, not an amplifier. Note  中继器是再生器，不是放大器

Note A active hub is actually a multipart repeater 常用于星型结构中 是过去常用的连接器 可以如下图那样使用多级连级（级联） 15.9

15.9 A active hub is actually a multipart repeater Note  常用于星型结构中  是过去常用的连接器  可以如下图那样使用多级连级（级联）

Figure 15.4 A hierarchy of hubs ▣ 0000 Hub ▣ 口 Hub Hub 口▣口▣ ▣▣▣口 15.10

15.10 Figure 15.4 A hierarchy of hubs