(112)

(118)

(119)

(116)

(117)

Frame. Relay is simplified form. of(71),similar in principle to(72), in which synchronous, frames of data are routed to different destinations depending on header information. Packets are routed throught one or more Virtual Circuits known as(73). Most Virtual Circuits are(74),which means that the network provider sets up all DLCI connections at subscription time.(75)are also part of the Frame. Relay specification. They privide a link that only lasts only as long as the session.

(114)

(113)

(112)

4台Linux主机通过如图5-2所示的方式互联，则实现PC1与PC4之间互访的步骤为：

1．运行(61)命令关闭计算机，在PC2与PC3上添加第二块网卡(eth1)，重新启动；

2．在PC2与PC3上为第二块网卡分配IP地址，并激活该网络接口，对于PC3，应执行(62)；

3．如果使用routed作为路由器进程，则作为路由器的PC2与PC3仅支持路由协议(63)；如果在PC2与PC3上设置静态路由信息并开启路由功能，对于PC2则应执行(64)；

4．在PC1和PC4上配置各自的默认同关，对于PC1，应执行(65)。

(111)