《计算机网络与因特网》课件第十八章广域网技术知识与路由.pptVIP

Computer Networks and Internets 《计算机网络与因特网》课件 林坤辉 ;PART II Packet Transmission;18.2 Large Networks and Wide Areas大型网络和广域;18.3 Packet Switches 包交换;18.5 Store and Forward存储转发;18.6 Physical Addressing In A WAN 广域网的物理编址;18.7 Next –Hop Forwarding下一站转发;18.8 Source Independence源地址独立性;18.9 Relationship of hierarchical Addresses To Routing层次地址与路由的关系;When the packet reaches the switch to which the destination computer attaches, the switch examines the second part of the address and selects the appropriate computer.;18.10 Routing In A WAN广域网中的路由;18.11 Use of Default Routes缺省路由的使用;Default route or default routing table entry. Only one default entry is allowed. If the forwarding mechanism does not find an explicit entry for a given destination, it uses the default entry.;18.12 Routing Table Computation 路由表计算;18.13 Shortest Path Computation In Graph 图中最短路径计算;18.14 Distributed Route Computation 分布式路由计算;18.15 Distance Vector Routing距离矢量路由;18.16 Link-State Routing (SPF)链接状态路由;18.17 Example WAN Technologies;4.1 广域网结构 虚电路和数据报 虚电路：面向连接，类似电话系统 数据报：无连接，类似电报系统 两者比较 4.2 广域网实例;虚电路方式;数据报方式;两者比较（1）;两者比较（2）;18.17.1 ARPA N E T;4.2.1 PSTN ;18.17.2 X.25;Each X.25 network consists of two or more X.25 packet switches interconnected by leased lines. Computer connected to the packet switches can send and receive packets. X.25 was invented before personal computers became popular. many early X.25 networks were engineered to connect ASCII terminals to remote timesharing computers.;X.25帧层;X.25虚电路;X.25的特点;18.17.3 Frame Relay帧中继; X.25的背景 传输线路：slow，analog，unreliable 计算机：slow，expensive X.25协议复杂，网络保证数据传输的可靠性，而端用户对传输数据的处理相对简单 Intelligent Network/Stupid Terminal;X.25与FR的比较（2）;X.25与FR（2）;FR是轻型化的X.25，与X.25相比 保留了X.25的物理层功能 保留了X.25部分数据链路层功??，并将多路复用功能放在第二层实现 丢弃了X.25第三层;X.25的通信过程;FR的通信过程;优点 FR支持较高速率（T1或T3） FR只包含物理层和数据链路层，比X.25开销小 FR允许支持突发数据，且帧长度可达9000字节 缺点 不提供差错控制功能 对多媒体数据传输的支持不够;X.25与帧中继的比较;4.2.5 SMDS ;作业