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问题 单项选择题

奈奎斯特定理描述了有限带宽、无噪声信道的最大数据传输速率与信道带宽的关系，对于二进制数据，若信道带宽B=3000Hz，则最大数据传输速率为

A．300bps

B．3000bps

C．6000bps

D．2400bps

答案

参考答案：C

解析：根据奈奎斯特定理C＝2Blog2L可计算出来，其中B＝3000Hz，信道中只有0和1两种信号，所以L＝2，代入上式即可计算机出信道最大数据传输率C＝6000bps。

单项选择题

Networks can be interconnected by different devices. In the physical layer, networks can be connected by (66) or Hubs, which just move the bits from one network to an identical network. One layer up we find bridges and swiches, which operate at data link layer. They can accept (67) ,examine the MAC address, and forward the frames to a different network while doing minor protocol translation in the process. In the network layer, we have routers that can connect two netwoks. If two networks have (68) network layer, the router may be able to translate between the packet formats. In the transport layer we find transport gateway, which can interface between the two transport connections. Finally, in the application layer, application gateways translate message (69) . As an example, gateways between Internet e-mail and X. 400 e-mail must (70) the e-mail message and change various header fields.

（70）是（）

A.analyze

B.pairs

C.delete

D.create
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社会体育
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