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： 帧中继是报文交换的一种简化形式，原则上类似于X.25，每个数据帧通过头信息被路由到不同的日的端。报文通过标有DLCI值的一条或多条虚电包路传输。大部分的虚电路是永久虚电路，这就是说网络提供者在签署的时候就建立了DLCI连接。交换虚电路帧中继规范的一部分，它们提供的链路只是维持在本次会话时间内。