问题 单项选择题

关于因特网中的主机和路由器,以下哪些说法是正确的 Ⅰ.主机通常需要实现TCP协议 Ⅱ.路由器必须实现TCP协议 Ⅲ.主机必须实现IP协议 Ⅳ.路由器必须实现IP协议

A.Ⅰ、Ⅱ和Ⅲ

B.Ⅰ、Ⅱ和Ⅳ

C.Ⅰ、Ⅲ和Ⅳ

D.Ⅱ、Ⅲ和Ⅳ

答案

参考答案:C

解析: TCP协议和IP协议的区别:虽然因特网的管理结构是松散的,但接入因特网的计算机必须遵从一致的约定,即TCP/IP协议。路由器连接两个或多个物理网络,负责将一个网络接收来的IP数据报,经过路由选择,转发到一个合适的网络中。路由器工作在网络层,只和IP协议有关,没有必要实现TCP协议。而主机的程序工作在应用层,为保证数据的可靠传输通常需要实现TCP协议。TCP协议利用IP层提供的不可靠的数据报服务,在将数据从一端发送到另一端时,为应用层提供可靠的数据传输服务。IP协议是实现TCP协议的基础,所以主机必须实现IP协议。

选择题
问答题

American and Japanese researchers are developing a smart car that will help drivers avoid accidents by predicting when they are about to make a dangerous move.

The smart car of the future will be able to tell if drivers are going to turn, change lanes, speed up, slow down or pass another car.

If the driver’s intended action could lead to an accident,the car will activate a warning system or override the move.

(46) " BY shifting the emphasis of car safety away from design of the vehicle itself and looking more toward the driver’s behavior, the developers believe that they can start to build cars that adapt to suit people’s needs , " New Scientist magazine said.

Alex Pentland of the Massachusetts Institute of Technology collaborated on the project with Andrew Liu who works for the Japanese carmaker Nissan.

(47)Tests of their smart car using a driving simulator have shown that it is 95 percent accurate in predicting a driver’s 12 seconds in advance.

(48)The system is based on driving behavior which the researchers say can be divided into chains of sub-actions which include preparatory moves.

It monitors the driver’s behavior patterns to predict the next move.

" To make its predictions, Nissan’s smart car uses a computer and sensors on the steering wheel, accelerator and brake to monitor a person’s driving patterns. (49)A brief training session, in which the driver is asked to perform certain maneuvers, allows the system to calculate the probability of particular actions occurring in two-second time segments, " the magazine said.

Liu has also done work on tracking eye movement to predict driving behavior. (50)He said the smart car could be adapted to monitor eye movement which could give even earlier predictions of when a driver is about to make a wrong move.

(48)The system is based on driving behavior which the researchers say can be divided into chains of sub-actions which include preparatory moves.