问题 单项选择题

IEEE 802.11 MAC层具有多种功能,其中分布式协调功能采用的是______协议,用于支持突发式通信。

A) CSMA/CA
B) CSMA/CB
C) CSMA/CD
D) CSMA/CF

答案

参考答案:A

解析: IEEE 802.11物理层的无线媒体决定了WLAN具有独特的媒体接入控制(MAC) 机制。IEEE 802.11的MAC子层定义了3种访问控制机制:第一种是分布协调功能(DCF),类似于传统的以太网,支持异步数据传输等争用业务,所有要传输数据的用户拥有平等接入网络的机会,它是通过CSMA/CA来实现的;第二种是点协调功能(PCF),基于由接入点AP集中控制的轮询(Poll)方式,主要为对时间敏感的实时业务提供无争用服务;第三种是通过RST/CST来支持信道预约,因此,分布式协调功能采用的是 CSMA/CA协议,答案选A。

完形填空

第二节(共5小题; 每小题2分, 满分10分)阅读下列材料,61— 65题中提到的人们都打算去乡间旅游景点游玩。请将每组人员和他们最合适的地方配对。有一个景点是多余的。

______ 61. Miss Jane and Miss Ann are working for a travelling company. They are focusing on

some points of developing tourism of peculiar style in the countryside. To start new

travelling business in some villages with fine leisure clubs and entertainment

conditions, they need some excellent examples to follow. 

______ 62. Some senior visitors, from America, have just retired. They prefer a holiday in a place

which may remind them of something back home. As believers with religious faith,

they’d like to see some places with the connections between religion and ethics issues.  

______ 63. Mr. John, a scholar from Australia, who devotes himself to literature, is now in Britain on holiday. Having been to some famous attractions, he’s got two days left to see

something more. He is also quite interested in the history of the Great Britain navigation (航海), and the history of early world explorations.

______ 64. A young couple, having just got married, are going on their honey-moon trip. The girl is very interested in the life of the noble families and gardening, while the boy shows more interest in visiting some old houses of famous people. But his love to his bride is enough for him to put her preference first.  

______ 65. Having one free day, a party of students are seeking a particular place to do their research, which will benefit their study of geography. Besides, they prefer to have a

relaxation in nature as well, climbing included. The place should be particular for them.

A.

B.

C.

D.

E.F.

单项选择题 B1型题