第52题： IEEE802.11采用了类似于802.3CSMA/CD协议，之所以不采用CSMA/CD协议的原因是（ ）。
A.CSMA/CD协议的效率更高
B.为了解决隐蔽终端问题
C.CSMA/CD协议的开销更大
D.为了引进其他业务
答案解析与讨论：www.cnitpm.com/st/2338218504.html

第53题： 无线局域网（WLAN）标准IEEE802.llg规定的最大数据速率是（ ）。
A.1Mb/s
B.11 Mb/s
C.5 Mb/s
D. 54Mb/s
答案解析与讨论：www.cnitpm.com/st/2338314423.html

第54题： 大型局域网通常组织成分层结构（核心层、汇聚层和接入层），以下关于网络核心层的叙述中，正确的是（ ）。
A.为了保障安全性，应该以分组进行尽可能多的处理
B.将数据分组从一个区域高速地转发到另一个区域
C.由多台二、三层交换机组成
D.提供用户的访问控制
答案解析与讨论：www.cnitpm.com/st/2338422626.html

第56题： 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

答案解析与讨论：www.cnitpm.com/st/233861520.html