问题 单项选择题

MIB中的信息用TLV形式表示,IP地址192.168.2.3用TLV形式表示时,实际占用的字节数是______。

A.2
B.4
C.6
D.8

答案

参考答案:B

解析: 基本编码规则(BER)将ASN.1表示的抽象类型值编码为字节串,这种字节串的结构为:类型——长度——值,简称TLV。其中,值部分还可以递归地再编码为TLV结构,以具有表达复杂结构的能力。
IP地址192.168.2.3使用ASN.1表示的结果是“40,4,192,168,2,3”,即实际占用6个字节数。其对应的BER编码结果是28 04 C0 A8 02 03。其中,第一个字节“28”的二进制表示是00101000,最左边两位“00”表示通用标签(UNIVERSAL),第3位“1”表示构造类型,剩余比特位“01000”是IP地址(IPAddress)类型的具体标签值;第二个字节“04”指明其后的“值(Value)”部分长度为4个字节;第三个字节“co”的二进制表示是1100 0000,表示十进制数192;第四个字节“A8”的二进制表示是1010 1000,表示十进制数168;第五个字节“02”的二进制表示是00000010,表示十进制数2;第六个字节“03”的二进制表示是0000 0011,表示十进制数3。

单项选择题 A1型题
阅读理解

In real life, the daily struggles between parents and children are around these narrow problems of an extra hour, extra TV show, and so on” said Avi Sadeh, psychology professor at Tel Aviv University. “Too little sleep and more accidents,” he said.

Sadeh and his colleagues found an extra hour of sleep can make a big difference. The children who slept longer, although they woke up more frequently during the night, scored higher on tests, Sadeh reported in the March/April issue of journal Child Development.

“When the children slept longer, their sleep quality was somewhat weak, but in spite of this their performance for study improved because the extra sleep was more significant than the reduction in sleep quality. ” Sadeh said. “Some studies suggested that lack of sleep as a child affects development into adulthood and it’s more likely to develop their attention disorder when they grow older. ”

In earlier studies, Sadeh’s team found that fourth graders slept an average of 8. 2 hours and sixth graders slept an average of 7. 7 hours.

“Previous research has shown children in elementary school need at least nine hours of sleep a night on a regular basis, said Carl Hunt, director of the National Center on Sleep Disorders Research in Bethesda, and high-school-age children need somewhat less, he said, adding the results of insufficient sleep could be serious.

“A tired child is an accident waiting to happen,” Hunt said. “And as kids get older, toys get bigger and the risks higher. ”Hunt also said too little sleep could result in learning and memory problems and long-term effects on school performance.

“This is an important extension of what we already know, ” Hunt said of Sadeh’s research, adding sleep is as important as nutrition(营养) and exercise to good health.

“To put it into reality,” Hunt said, “parents should make sure they know when their children actually are going to sleep and their rooms are conducive to sleeping instead of playing. ”

小题1:What is Child Development?

A A new story                       B A popular book

C. A periodical magazine               D A TV programme

小题2:How many persons are exactly mentioned in the text?

A One          B Two         C Three           D Four

小题3:The underlined phrase “conducive to” (in the last sentence) means ________.

A helping to happen                 B influenced by

C full of                              D acceptable of

小题4:Which of the following statements is NOT true according to the passage?

A.There are some daily struggles between parents and children because of having nothing in common with extra rest time.

B.The children who sleep longer are weak in their study.

C.Lack of sleep as a child has great effect on their development into adulthood.

D.In general, children in elementary school need at least nine hours of sleep a night.