参考答案：
1．a． 2．b． 3．c． 4．d． 5．a．
6．b． 7．c． 8．d． 9．a． 10．b．
11．c． 12．d． 13．a． 14．d． 15．a
16．d 17．a． 18．b． 19．c． 20．d．
21．a． 22．b． 23．c． 24．d． 25．a．
26．b． 27．c． 28．d． 29．a． 30．b．
31．c． 32．d． 33．a． 34．b． 35．c．
36．d． 37．a． 38．b． 39．c． 40．d．
41．a． 42．b． 43．c． 44．d． 45．a．
flow control is a function that prevents network congestion by ensuring that _(1)_ do not overwhelm_(2)_ with data.
there are three commonly used methods for handling network congestion . _(3)_is used by network devices to temporarily store bursts of excess data in memory until they can be processed. _(4)_ are used by receiving devices to help prevent their buffers from overflowing . _(5)_ is a flow-control scheme in which the source device requires an acknowledgment from the destination after a certain number of packets have been transmitted.
⑴⑵a.transmitting devices b.transmitted devices
c.receiving devices d.received devices
⑶⑷⑸a.buffer b.source-quench messages
c.window d.windowing e.buffering
answer：acebd
the integrated services digital network(isdn) is a set of international standards for access to advanced,all-digital public _(1)_network.
isdn standards have been defined by the _(1)_,a branch of the united nations’ internaational telecommunications union (itu), in the series i and q recommendations.
there are five isdn standard devices.a_(1)_ is any piece of communicating equipment that complies with the isdn standard. _(1)_performs the logical interface functions of switching and local-device control. _(1)_performs the physical interface conversion between the dissimilar customer and network sides of the interface.
⑴a.information b.telecommunications c.global d.local
⑵a.itu-t b.itu-u c. itu-a d. itu-r
⑶⑷⑸a.ta b.te c.nt1 d.nt2 e.et
answer：babcd
sdlc was invented by ibm to replace the older bisynchronous protocol for wide area connections between ibm equipment . a varietion of the _(1)_ protocol called nrm is essentially the same as sdlc.
sdlc is _(2)_ protocol like hdlc , frame relay or x.25.an sdlc network is made up of _(3)_ that controls all communications , and _(4)_ .it is capable of _(5)_ operation, but almost all practical applications aare strictly half duplex.
⑴a.hdlc b.frame relay c.x.25 d.x.21
⑵a.a peer to peer b.a point-to-point
c.not a peer to peer d.a peer to peers
⑶a.a primary station b.one or more primary stations
c.a secondary station d.one or more secondary stations
⑷a.a primary station b.one or more primary stations
c.a secondary station d.one or more secondary stations
⑸a.half duplex b.full duplex
c.half or full duplex d. half and full duplex |
