问题 单项选择题

IEEE802.11定义了AdHoc无线网络标准。下面关于AdHoc网络的说明中错误的是()。

A.这是一种点对点连接的网络

B.这种网络需要有线网络和接入点的支持

C.以无线网卡连接的终端设备之间可以直接通信

D.这种网络可以是单跳或多跳的

答案

参考答案:B

解析:

IEEE802.11定义了两种无线网络的拓扑结构,一种是基础设施网络(InfrastructureNetworking),另一种是特殊网络(AdHocNetworking)。在基础设施网络中,无线终端通过接入点(Access Point,AP)访问骨干网设备。接入点如同一个网桥,它负责在802.11和802.3MAC协议之间进行转换。

Ad Hoc网络是一种点对点连接,不需要有线网络和接入点的支持,终端设备之间通过无线网卡可以直接通信。这种拓扑结构适合在移动情况下快速部署网络。802.11支持单跳的AdHoc网络,当一个无线终端接入时首先寻找来自AP或其他终端的信标信号,如果找到了信标,则AP或其他终端就宣布新的终端加入了网络;

如果没有检测到信标,该终端就自行宣布存在于网络之中。还有一种多跳的AdHoc网络,无线终端用接力的方法与相距很远的终端进行对等通信。

单项选择题 案例分析题
阅读理解

In the car, I secretly had a look at him through the rearview mirror (后视镜). He looked sad. “What’s the matter, honey?”“I’m nervous. I don’t know if I’ll be able to learn everything in the first grade. What if I can’t pay attention in class?”

My heart melted. I remembered being nervous on the first day of school and I thought I was the only student who felt that way. I was a nervous kid full of self-doubt. Seth behaved much better than I did.

We walked into his school together. He remembered where his new classroom was and recognized his teacher from the ice cream social party they had the day before. He sat down at his desk and chatted with a few of his classmates. He took a few photos of them (with a camera phone because I didn’t allow him to bring the real camera) and then he said in a very serious manner, “Mom, you can go home now. I’ll be OK.” And so he was.

小题1:Seth asked his mother to take him to school probably because _______.

A.he was afraid to be late for class

B.he wanted to share his joy with his mother

C.he felt worried about his school life

D.he was frightened of his new teacher小题2:What did the writer mean by saying “My heart melted” in Paragraph 4?

A.She was very angry with her son.

B.She felt sad because of her son’s words.

C.She was too weak in the mind to face it.

D.She became more understanding of her son.小题3:From the last paragraph we learn that ________.

A.Seth had never seen his new classroom

B.the ice cream social party was to be held soon

C.Seth got along well with his classmates

D.Seth took some photos using a real camera小题4:It can be inferred that in the end Seth felt ______.

A.relaxed

B.frightened

C.serious

D.worried