（40）a. rsa b. des c.hash d. idea
答案：adaba
frame relay is simplified form of _(41)_ ,similar in principle to _(42)_, 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 _(43)_. most virtual circuits are _(44)_,which means that the network provider sets up all dlci connections at subscription time . _(45)_are also part of the frame relay specification . they privide a link that only lasts only as long as the session .
（41）a. datagram switching b.datagram routing
c. packet switching d. packet routing
（42）a. x . 21 b. x . 25 c. x . 28 d. x . 29
（43）a. dlcis b.hdlcs c.sdlcs d.dls
（44） a. permanent circuits b. permanent virtual circuits
c. switched virtual circuits d. switching circuits
（45） a. permanent circuits b. permanent virtual circuits
c. switched virtual circuits d. switched circuits
答案：cbabc
lapb is a _(46)_ protocol that provides comlete data transparency in a _(47)_ operation. it supports a peer-to-peer link in that neither end of the link plays the role of the permanent master station.
hdlc lapb is the _(48)_ that is usually used by _(49)_ ,the _(50)_standard for packet swihched networks.
（46）a. bit-oriented synchronous b. byte-oriented synchronous
c. bit-oriented asynchronous d. byte-oriented asynchronous
（47）a. half-duplex point-to-point b. half-duplex point-to-points
c. full-duplex point-to-point d. full-duplex point-to-points
（48）a. physical layer b.link layer
c.network layer d.transport layer
（49） a. x . 21 b. x . 25 c. x . 28 d. x . 29
（50）a. itu b. ieee c.osi d. ansi |
