补充：局域网互联.pptVIP

第5讲 局域网互联 网络互联需求 局域网互联需求 局域网覆盖的距离是有限的 局域网能支持的联网的计算机数是有限的 局域网上能传输的通信量是有限的 异种网络互联 分支机构远程访问 网络互联类型 相同类型的局域网互联 不同类型的局域网互联 通过主干网将局域网互联 通过广域网将局域网互联 局域网访问外部计算机系统 网络互联解决方案 OSI/RM的目标就是为各种应用提供一个公共的通信服务，它是独立于联至网上的计算机和操作系统 有四种类型的互联设备：中继器、网桥、路由器、网关，这四种设备的操作属于OSI的不同层次 LAN Devices网络设备 NICs, Repeaters, Hubs 网卡、中继器、集线器 Bridges网桥 Switches交换机 Routers路由器 NIC Specifics NICs provide hosts with access to media by using a MAC address. MAC stands for Media Access Control NICs operate at Layer 2 !! NICs, Repeaters, Hubs To connect two computers, you must... Install a NIC card in each. NICs, Repeaters, Hubs LAYER 1—Transceiver收发器 Transmitter发 and Receiver 收of electronic signals—specialized repeater.中继器 Connects different media technologies Also called a MAU (Media Attachment Unit) NICs, Repeaters, Hubs NICs, Repeaters, Hubs A Dilemma!难题 What’s The Problem? Hubs share bandwidth between all attached devices. 共享带宽 Hubs are stupid, Layer 1 devices. They cannot filter traffic.无法过滤流量 Most LANs use a “broadcast topology,” so every device sees every packet sent down the media.广播方式 Broadcasts广播 Broadcasts Types of Networks Shared media environment 共享介质 Types of Networks Packet switching vs. Circuit switching 分组交换 vs 电路交换 Collisions 冲突 同一时刻多于一台的主机要发送数据时. Collisions occur in broadcast topology: Ethernet LAN technology. Collisions 发生冲突的时候，信号就会彼此干扰，并且会产生一个第三种而且无效的状态 Collisions domain 冲突域 Collision Domains are the area where collisions occur（冲突发生的区域）. Layer 1 devices will not solve collision problems（第一层设备不能解决）. Layer 1 devices simply extend collision domains （第一层设备扩展了冲突域）. Collisions domain: Share access Limits the number of computers Collisions domain: Repeater Propagate传播 collisions Collisions domain: HUB Propagate collisions Collisions domain 冲突域 All of layer 1 interconnections are part of the collision domain. Extending a network with a repeater or a hub, results in a larger collision domain. 4 repeater rule 5.4.3.2.1 Rule规则 5-4-3-2-1 rule 54321规则 5 sections of the network. 4 repeaters o