●Frame. Relay is simplified form. of (71) ,similar in principle to (72) ,in which synchron

Question

●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．

(71) A．Datagram Switching

B．Datagram Routing

C．Packet Switching

D．packet Routing

(72) A．X．21

B．X．25

C．X．28

D．X．29

(73) A．DLCIs

B．HDLCs

C．SDLCs

D．DLs

(74) A．Permanent Circuits

B．Permanent Virtual Circuits

C．Switched Virtual Circuits

D．Switching Circuits

(75) A．Permanent Circuits

B．Permanent Virtual Circuits

C．Switched Virtual Circuits

D．Switched Circuits

Answer 1

正确答案：C,B,A,B,C
【解析】帧中继是报文交换的一种简化形式，原理上与X.25类似。其是同步的，每一帧的数据都通过其包头信息路由到不同的目的地。
数据包通过被称之为DLCIs的一条或多条虚电路路由。大部分的虚电路是永久虚电路，也就是网络提供商在签署协议时就已经建立好了所有的DLCI连接。交换虚电路也是帧中继的一种规范，即提供商只在会话期间提供链路。