问题 单项选择题

下列关于宽带城域网结构的描述中,正确的是

A.用户接入层进行本地的路由、过滤、流量均衡及安全控制等处理

B.核心交换层解决的是“最后一公里”问题

C.边缘汇聚层结构设计的重点是可靠、可扩展性与开放性

D.宽带城域网的网络平台采用层次结构

答案

参考答案:D

解析: 宽带城域网的网络平台采用层次结构,可以分为核心交换层、边缘汇聚层和用户接入层。核心交换层连接多个汇聚层与主干网络,主要承担高速数据交换的功能,设计重点是可靠性、可扩展性与开放性。边缘汇聚层主要承担路由与流量汇聚的功能,根据接入层的用户流量,进行本地路由、过滤、流量均衡、服务质量优先级管理及安全控制等处理。用户接入层主要承担用户接入本地流量控制的功能,解决的是“最后一公里”问题。

阅读理解

Directions: Read the following passage. Complete the diagram by using the information for the passage.

Write NO MORE THAN 3 WORDS for each answer.

     Since it was founded a year ago, the babysitting pool has become increasingly popular in the United States.

More and more mothers have joined it and have benefited from it. What attracts them most is the idea that you

pay your babysitter not in cash, but in paper cards. When you join the babysitting pool, you are given thirty

cards, which are worth 30-minute babysitting time each. For each half an hour while you are gone, th

e babysitter gets paid one card.

     There are rules regulating this service. You should not watch more than three kids at a time including your

own. On big holidays, such as Christmas and Thanksgiving, the babysitter should be paid twice as much,

which means two cards for every half an hour. When you leave the babysitting pool, you should return all the

cards. If you are out of cards, you cannot use money instead. You should have to baby-sit for others to earn

enough cards so that you will have them handy when you yourself need a babysitter.

     Many mothers think highly of this service. It keeps children in constant touch with one another, and makes

life easier for the mothers. Since in most cases, the babysitter is the mother who watches other kids at her

own home, it is still possible for her to do her own things while the kids play with each other. In fact most

mother babysitters find that their own kids are less of a monster and easier to watch when they are around

other playmates. Moreover, since the babysitting pool service does not involve money, it will not be a financial

loss to the family.

     In the past year, the babysitting pool has helped so many mothers with their work that they all think that it

is indeed a good community service worth keeping.

单项选择题