论文部分内容阅读
分组交换网X.25是另一类覆盖面很广的通信网络。X.25网用户的通信速率在9.6Kbps到64Kbps之间。用户呼叫目标端口地址建立交换虚电路(SVC)就可以从X.25网的一个入口访问到整个X.25网。用户还可同时呼叫多个端口,建立多条SVC,从而同时与多个地点的局域网络相连。需要指出的是,由于X.25网是在大量使用模拟传输技术,通信线路质量比较差(线路误码率很高)的情况下设计和建造的,为此整个X.25通信网处处都具备纠错能力,可以给用户提供高可靠的通信服务。也正因为如此,X.25网的延迟比电话专线、DDN专线和帧中继都要大。相对而言,X.25技术比较陈旧,速率也较低,对大多数现代计算机网络系统而言不能算是好的选择。当前,一些
Packet Switched Network X.25 is another broad coverage of the communication network. The communication rate of X.25 network users is between 9.6Kbps and 64Kbps. The user calls the target port address to establish the exchange of virtual circuit (SVC) can be from an entrance X.25 network access to the entire X.25 network. Users can also call multiple ports at the same time, creating multiple SVCs to simultaneously connect to multiple local area networks. It should be pointed out that, due to the extensive use of analog transmission technology X.25 network, poor quality of communication lines (line error rate is high) designed and built under the circumstances, for which the entire X.25 communication network are available Error correction capabilities, can provide users with highly reliable communications services. Precisely because of this, X.25 network delay than the telephone line, DDN line and frame relay are larger. Relatively speaking, X.25 technology is relatively old, the rate is also low, for most modern computer network systems can not be considered a good choice. At present, some