第51題： 以下屬于萬兆以太網物理層標準的是（ ）。
A.IEEE802.3u
B.IEEE802.3a
C.IEEE802.3e
D.IEEE802.3ae
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第52題： IEEE802.11采用了類似于802.3CSMA/CD協議，之所以不采用CSMA/CD協議的原因是（ ）。
A.CSMA/CD協議的效率更高
B.為了解決隱蔽終端問題
C.CSMA/CD協議的開銷更大
D.為了引進其他業(yè)務
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第53題： 無線局域網（WLAN）標準IEEE802.llg規(guī)定的最大數據速率是（ ）。
A.1Mb/s
B.11 Mb/s
C.5 Mb/s
D. 54Mb/s
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第55題： 網絡設計過程包括邏輯網絡設計和物理網絡設計兩個階段，各個階段都要產生相應的文檔，以下選項中，（1）屬于邏輯網絡設計文檔，（2）屬于物理網絡設計文檔。
（1）A.網絡IP地址分配方案
B.設備列表清單
C.集中訪談的信息資料
D.網絡內部的通信流量分布
（2）A.網絡IP地址分配方案
B.設備列表清單
C.集中訪談的信息資料
D.網絡內部的通信流量分布
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第56題： A transport layer protocol usually has several responsibilities .One is to create a process-to-process communication;UDP uses (1)numbers to accomplish this.Another Responsibility is to provide control mechanisms at the  transpt level.UDP does this task at a very minimal level.There is no flow control mechanism and there Is no(2) for received packet. UDP,however ,does provide error control to some extent.If UDP detects an error in the received packet,it will silently drop it.The transport layer also provides a connection mechanism for the processes.The(3)must be able to send streams of data to the transport layer.It is the responsibility of the transport layer at (4)station to make the connection with the receiver.chop the stream into transportable units,number them,and send them one by one.It is the responsibility of th transorort layer at the receiving end to wait until all the different units  belong to th same process have arrived,check and pass those that are(5) free ,and deliver them to the receiving process as a stream.

(1)A. hop   
B. port    
C. route  
D.packet
(2)A. connection   
B. window   
C. acknowledgement  
D.destination
(3)A. jobs   
B. processes   
C. proarams   
D.users
(4)A. sending   
B. routing    
C. switching  
D.receiving
(5)A. call   
B. state    
C. cost  
D.error

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