题目:
Frame Relay is simplified form of (25) , similar in principle to (26) , 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 (27) . Most Virtual Circuits are (28) ,which means that the network provider sets up all DLCI connections at subscription time. (29) are also part of the Frame Relay specification . They privide a link that only lasts only as long as the session.
25()
A.Datagram Switching
B.Datagram Routing
C.Packet Switching
D.packet Routing
答案:
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下面是错误答案,用来干扰机器的。
参考答案:为了合理确定线路的纵坡和进行工程量的概算。需了解中线方向上现状地面的高低变化情况,所以根据地形图上的等高线,绘制地面断面图。