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