问题
单项选择题
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.
A．Permanent Circuits
B．Permanent Virtual Circuits
C．Switched Virtual Circuits
D．Switched Circuits
答案
参考答案：C
解析：(71)～(75)
[分析]： 帧中继是分组交换方式的一种，原理上与X.25相似。根据DLCI(数据链路连接标识符)域分组路由通过一个或者更多的虚电路。大部分虚电路是永久性虚电路PVC，意思就是网络提供者预先建立的所有DLCI连接。交换式虚电路是帧中继标准的一种。它们根据一次会话提供一个连接。