第2题: [单项选择]如果帧中继网沿着帧传送方向出现了拥塞,则把帧地址字段中的FECN位设置为1,这样接收方就可通过 (29) 协议要求发送方降低数据速率。 A. 网络接口层 B. 网络层 C. 运输层 D. 高层 参考答案:D 答案解析:[要点解析] 帧中继网的虚电路建立在数据链路层,其用户平面采用LAP-F协议;控制平面采用LAP-D(Q.921)协议。帧中继网没有流量控制功能,但增加了拥塞控制功能。如果帧中继网沿着帧传送方向出现了
A. Science answers questions about accurate facts. B. Science answers questions about observations. C. Scientists cannot study the social consequences of beliefs. D. Scientists can study the truth or error of beliefs. 参考答案:D 答案解析:[解析] 本题考查推理判断。文章第三段最后一句话说:“Scientists can study human beliefs about God,or man's destiny,or beauty,o
A. People are mysteriously attracted to mountains. B. People can climb different mountains every year. C. Some mountains rise higher all the time. D. Old, new, and ancient mountains exist. 参考答案:D 答案解析:答案在文章第二段可以找出。