问题 问答题 简答题

局域网的主要特点是什么?为什么局域网采用广播通信方式而广域网不采用呢?

答案

参考答案:

局域网LAN是指在较小的地理范围内,将有限的通信设备互联起来的计算机通信网络从功能的角度来看,局域网具有以下几个特点:(1)共享传输信道,在局域网中,多个系统连接到一个共享的通信媒体上。(2)地理范围有限,用户个数有限。通常局域网仅为一个单位服务,只在一个相对独立的局部范围内连网,如一座楼或集中的建筑群内,一般来说,局域网的覆盖范围越位10m~10km内或更大一些。从网络的体系结构和传输检测提醒来看,局域网也有自己的特点:(1)低层协议简单(2)不单独设立网络层,局域网的体系结构仅相当于相当与OSI/RM的最低两层(3)采用两种媒体访问控制技术,由于采用共享广播信道,而信道又可用不同的传输媒体,所以局域网面对的问题是多源,多目的的连连管理,由此引发出多中媒体访问控制技术在局域网中各站通常共享通信媒体,采用广播通信方式是天然合适的,广域网通常采站点间直接构成格状网。

多项选择题
阅读理解

阅读理解。

     Many animals recognize their food because they see it. So do humans. When you see an apple or a piece

of chocolate you know that these are things you can eat. You can also use other senses when you choose

your food. You may like it because it smells good or because it tastes good. You may dislike some types of

food because they do not look, smell or taste very nice. Different animals use different senses to find and

choose their food. A few animals depend on only one of their senses, while most animals use more than one

sense.

     Although there are many different types of food, some animals spend their lives eating only one type. The

giant panda (大熊猫) eats only one particular type of bamboo (竹子). Other animals eat only one type of food

even when given the choice. A kind of white butterfly (蝴蝶) will stay on the leaves of a cabbage, even though

there are plenty of other vegetables in the garden. However, most animals have a more varied diet (多样化饮

食). The bear eats fruits and fish. The fox eats small animals, birds and fruits. The diet of these animals will

be different depending on the season.

     Humans have a very varied diet. We often eat food because we like it and not because it is good for us. In

countries such as France and Britain, people eat foods with too much sugar. This makes them overweight,

which is bad for their health. Eating too much red meat and animal products, such as butter, can also be bad

for the health. Choosing the right food, therefore, has become an area of study in modern life.

1. We can infer from the text that humans and animals _____.

A. depend on one sense in choosing food

B. are not satisfied with their food

C. choose food in similar ways

D. eat entirely different food

2. Certain animals change their choice of food when _____.

A. the season changes

B. the food color changes

C. they move to different places

D. they are attracted by different smells

3. We can learn from the last paragraph that _____.

A. food is chosen for a good reason

B. French and British food is good

C. some people have few choices of food

D. some people care little about healthy diet