问题 单项选择题

当千兆以太网发送较短的数据帧时,需要发送大量填充的无用信息(称为载波扩展),从而导致信道利用率较低。为解决该问题,IEEE 802.3z标准采用的方法是______。

A.在原MAC帧中新增一个标识有用信息的“长度”字段
B.将多个小于512B的短帧组合在一起,各个短帧之间设置一个帧间隔标志
C.将数据编码方法由原有的8B/10B修改为64B/66B,以提高编码效率
D.将数据帧的最短长度由原来的64B修改为512B,并采用全双工速率模式

答案

参考答案:B

解析: 依题意,千兆以太网针对该问题的解决措施是:允许各个节点有选择地利用突发模式(BurstMode)来发送帧。其基本思想是:将多个小于512B的短帧组合在一起,拼接成一个大于512B的正常帧发送,在该正常帧内的各个短帧之间,设置一个帧间隔标志(IFG)进行分隔。

单项选择题 B1型题
阅读理解

阅读理解。

     Many people often lose their friends and they don't know how to keep a long friendship.So

how can you keep a long friendship? The following passage explains very well about this matter.

     The first thing you need to do is to become a good listener.In this way,you show your friends

that you are interested in their lives.You want to know more about them and you want to help

them solve their problems.They will cherish the friendship more if they know you care about them.

     The next thing is that you should respect other people's privacy (隐私).People usually don't

like others to know about their private life,so you should show respect toward their privacy.

Sometimes,they need some suggestions from others,but this does not mean that others can know

about their entire life.So respect for privacy is a must for keeping a long friendship.

     The third important thing is that you need to be able to forgive.You must remember that nobody

 is perfect in this world.It is important to forgive others and not to blame them for the mistakes they

have already made.You are not perfect either.Thus you need to apologize to others for the mistakes

you may have made.

     Pay attention to the three things above,and you will be able to have long friendships.

1.This passage is written to tell us________.

A.why a long friendship is important

B.what we can do for our friends

C.how to make friends with others

D.how to keep a long friendship

2.According to the passage,what is the first thing that we need to do?

A.To know more about our friends.

B.To share our happiness and sadness.

C.To be good at listening to our friends.

D.To help our friends solve their problems.

3.From Paragraph 3 we know that________.

A.we should never share our private lives with others

B.some people never care about their privacy

C.it is important to respect other people's privacy

D.some people like sharing their privacy

4.What does the writer suggest you do if your friend makes a mistake?

A.Blame him.      

B.Forgive him.

C.Tell him why it is so.      

D.Leave him immediately.

5.The writer most probably thinks that________.

A.everyone makes mistakes

B.some people are perfect

C.people often make stupid mistakes

D.we shouldn't apologize fpr every mistake