Chapter3ComputerNetwork分析.ppt

Computer English Computer English Input and Output Devices Keywords computer networks 计算机网络 distributed system 分布式系统 network n. 网络 Electronic Data Interchange（EDI） 电子数据交换 teleconferencing n. 电信会议 broadcast networks 广播式网络 point-to-point networks 点到点网络 broadcasting n. 广播 multicasting n. 多点播送 Local Area Networks（LAN） 局域网 Metropolitan Area Network（MAN） 城域网 Wide Area Network（WAN） 广域网 Internetwork n. 互联网 Categories of Networks There is no generally accepter taxonomy into which all computer networks fit，but two dimensions stand out as important: transmission technology and scale. We will now examine each of these in turn. Broadly speaking，there are two types of transmission technology: （1）Broadcast networks; （2）Point-to-point networks. 不存在被普遍接受的所有计算机网络都适用的分类法，但是有两个标准很重要：传输技术和规模。下面我们分别进行讨论。 从广义上讲，有两种类型的传输技术： (1)广播式网络 (2)点到点网络 Categories of Networks Broadcast networks have a single communication channel that is shared by all the machines on the network. Short messages，called packets in certain contexts，sent by one machine are receive by all the others. An address field within the packet specifies for whom it is intended. Upon receiving a packer，a machine checks the address field. If the packet is intended for itself，it processes the packet; if the packet is intended for some other machine，it is just ignored. 广播式网络仅有一条通信信道，由网络上的所有机器共享。短消息，即按某种语法组织的分组或包，可以被任何机器发送并被其他所有的机器接收。分组的地址字段指明此分组应被哪台机器接收。一旦收到分组，各机器将检查它的地址字段。如果是发送给它的，则处理该分组，否则将它丢弃。 Categories of Networks Broadcast systems generally also allow the possibility of addressing a packet to all destinations by using a special code in the address field. When a packet with this code is transmitted，it is received and processed by every machine on the network. This mo