本章先讨论广域网基本概念，包括广域网所提供的两种服务——数据报和虚电路。接着要讨论分组转发，即网络交换结点怎样知道应通过哪条路径(path)才能将数据转发到所要通信的目的主机。这就要查找转发表。本章只讨论查找转发表的简单过程，而转发表是如何建立的则在下一章讨论。最后介绍三种广域网，即X.25网、帧中继网和采用ATM技术的广域网。-This chapter will discuss the basic concepts of wide-area network, wide area network, including two types of services provided- Datagram and virtual circuit. Packet forwarding and then to be discussed, namely, network nodes exchange how do I know which path through the (path) data can be transmitted to the host to the purpose of communication. This will be made to find. Discussed in this chapter only to find to express a simple process, and to express is how to set up the discussion in the next chapter. Finally, three types of wide area network, or X.25 networks, frame relay network and the use of ATM wide area network technology.