问题 问答题

阅读下列说明,回答问题1至问题3,将解答填入答题纸的对应栏内。【说明】H.323是ITU制定的在局域网上不保证QoS的多媒体通信标准。考查如下H.323标准的系统框图,回答问题1、2和3。

【问题1】在上图的A、B、C、D、E和F等模块中,协议H.263应用于系统框图的(1)模块,协议H.222位于系统框图的(2)模块,协议G728位于系统框图的(3)模块,协议Q.931位于系统框图的(4)模块。

【问题2】H.323视频会议系统适合ISDN等较高速网络,为了适应公用电话网络的低带宽要求,ITU发布了H.324视频会议标准,请说明H.323和H,324标准在协议选择上的主要区别。

【问题3】视频会议系统中呼叫控制的主要目的是什么?

答案

参考答案:

【问题1】(1)A(2)E(3)B(4)D

【问题2】①H.323在视频编解码上选择了H.261和H.263,而H.324仅仅使用了H.263。②

H.323在音频编解码上选择了G711、G723等,而H.324仅仅使用了G723/730。

③H.323在复用上选择了H.222等,而H.324使用了H.223。

【问题3】①管理会议终端。②支持有效的QoS保证。

解析:

本题考查基于H.323协议的多媒体会议系统的基本内容。

多媒体会议系统是多媒体应用设计的一个全新的方向,它是包含未来会议的所有需求并形成视频、音频、图形一体化的解决方案。多媒体会议系统包括视频会议、音频会议、Web会议和即时信息,以及相关信息的即时存储和广播。

国际电信联盟制定的视频会议标准有H.320、H.323、H,324。如表10.1所示。

(1)H.320标准

H.320标准于20世纪90年代初开发,它定义通信的建立、数字电视图像和声音的压缩编码算法,运行在综合业务数字网(ISDN)上。

(2)H.323标准

H.323标准应用于局域网上的桌面电视会议,它是基于带宽无保证信息包交换的多媒体通信系统。H.323描述无QOS保证的LAN多媒体通信终端、设备和服务。其中视频选用H.261和H.263协议,音频选用G711、G722、G728、G.723等协议。复用采用H.222协议,控制采用H.245,呼叫控制采用Q.931协议。

(3)H.324标准在公众交换电话网(PSTN)上的桌面电视会议使用调制解调器,采用H.324标准。

H.324标准是针对极低速率通信网络的多媒体通信标准,所以在视频编解码中,H.324仅仅使用了H,263。在音频编解码中,H.324仅仅使用了G723/730协议。复用采用了H.223协议。

基于网络的多媒体会议系统目前大多趋于采用ITU-T的H.323标准和IETE的SIP标准,以前者使用最为广泛。在视频会议系统中,呼叫控制的主要目的是管理会议终端,支持有效的QoS保证。

阅读理解

阅读理解。

     We are all called upon to make a speech at some point in life, but most of us don't do a very good job.

This article gives some suggestions on how to give an effective speech.

     So, you have to give a speech-and you're terrified. You get nervous, you forget what you want to say,

you stumble over words, you talk too long, and you bore your audience. Later you think, "Thank goodness,

it's over. I'm just no good at public speaking. I hope I never have to do that again."

     Cheer up! It doesn't have to be that bad. Here are some simple steps to take the pain out of speech

making. Ask yourself the purpose of your speech. What is the occasion? Why are you speaking? Then,

gather as many facts as you can on your subject. Spend plenty of time doing your research. Then spend

plenty of time organizing your material so that your speech is clear and easy to follow. Use as many examples

as possible, and use pictures, charts, and graphs if they will help you make your points more clearly. Never

forget your audience. Don't talk over their heads, and don't talk down to them. Treat your audience with

respect. They will appreciate your thoughtfulness.

     Just remember: be prepared. Know your subject, your audience, and the occasion. Be brief. Say what you

have to say and then stop. And be yourself. Let your personality come through so that you make person-to-

person contact with your audience.

     If you follow these simple steps, you'll see that you don't have to be afraid of public speaking. In fact,

you may find the experience so enjoyable that you volunteer to make more speeches! You're not convinced

yet? Give it a try and see what happens.

1. The main idea of this article is _____. [ ]

A. you can improve your speaking ability

B. a poor speaker can never change

C. always make a short speech

D. it is hard to make a speech

2. Paragraph 2 implies (暗示) that _____. [ ]

A. many people are afraid of giving a speech

B. many people are happy to give a speech

C. many people do not prepare for a speech

D. many people talk too long

3. The phrase "talk over their heads" means _____. [ ]

A. speak too loudly

B. look at the ceiling

C. look down upon them

D. use words and ideas that are too difficult

4. All of the following statements are true except that _____. [ ]

A. few people know how to make good speeches

B. a lecturer does not need to organize his speech

C. research is important in preparing a speech

D. there are simple steps you can take to improve your speaking ability

5. The title for this passage may be _____. [ ]

A. Do Not Make a Long Speech

B. How to Give a Good Speech

C. How to Prepare for a Speech

D. Try to Enjoy a Speech

单项选择题