题目内容
帧中继网的虚电路建立在 (1) ，在用户层面采用的协议是 (2) 。这种网络没有流量控制功能，但增加了拥塞控制功能。如果沿着帧传送方向出现了拥塞，则把帧地址字段中的 (3) 位设置为1，这样接收方就可通过 (4) 协议要求发送方降低数据速率。最适合提供帧中继业务的网络是 (5) 。 2（）
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Directions: Suppose you are Li Ming. During the week-long holiday, you joined a package tour organized by a travel agency to the city of Beijing. But when you got there, you found the services provided [or you rather disappointing. Then you decided to writer a letter to the General Manager to 1) state your purpose of writing, 2) complain about the services, and 3) make some suggestions. You should write about 100 words on ANSWER SHEET 2. Do not sign your own name at the end of the letter. Use "Li Ming" instead. Do not write the address.
Packet-switching wireless networks are preferable (1) when transmissions are (2) bemuse of the way charges are (3) per packet. Circuit-switched networks are preferable for transferring large files or for other lengthy transmissions because customers are (4) for the (5) of time they use the network. 5（）
简答题 简述林德布洛姆在《民主的智力》一书中所指出的渐进方式的优点。
设信道带宽为3000Hz，根据尼奎斯特(Nyquist)定理，理想信道的波特率为 (1) 波特，若采用QPSK调制，其数据速率应为 (2) ，如果该信道信噪比为30dB，则该信道的带宽约为 (3) 。设信道误码率为10-5，帧长为10Kb，差错为单个错，则帧出错的概率为 (4) 。若整个报文被分成5个帧，帧出错的概率为0.1，纠错重发以报文为单位，则整个报文的平均发送次数约为 (5) 次。 4（）
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