问题 问答题

阅读下列说明,回答问题1至问题3,将解答填入对应栏内。
[说明]
某门户网站提供在线视频点播服务,用户可以通过普通浏览器软件实现实时在线观看视频内容。网站对用户采用会员制管理,只有经过注册的用户在正确登录网站之后才能得到正常服务。

①为了保证用户在线实时观看视频,需要采用什么技术②简要解释其工作特点。③请说明此类应用通常采用的传输层协议以及采用该协议的原因。

答案

参考答案:需要采用流媒体技术。
流媒体的工作特点是可以实现编码的媒体内容边下载边解码边播放,从而可以实现实时在线观看媒体内容,而无需全部下载媒体内容后才能解码播放。
流媒体技术的传输层协议通常采用UDP,主要是因为UDP为无连接的传输协议,可以有效实现允许一定误码率的无延迟的实时性应用,比如实时的视频、音频播放。

解析:网络视频实时传输应用一般采用流媒体技术来实现。所谓流媒体技术就是把连续的音、视频信息经过压缩编码处理后放在服务器上供用户一边下载一边观看、收听,而不需要等整个压缩文件下载到自己的计算机上之后才可以使用的网络传输技术。这样的编码方式中各个段落之间没有关联关系,数据流逐段被处理。
流式视频传输应用需要一定的实时性保障,因此在网络中传输层上实现流式传输通常使用实时性更好的UDP而非TCP。

单项选择题

It was two years ago today that the hunting ban came into force, supposedly ending centuries of tradition. However, the law has been an unmitigated failure—not that either side is shouting about it.
It was a nightmare vision that struck fear and loathing into the hearts of millions. When the hunting ban became law, it was said, 16,000 people would lose their jobs, thousands of hounds would be put down, rotting carcasses would litter the countryside, hedgerows would disappear, riders would face on-the-spot fines, law-abiding people from doctors to barristers would be dragged from their horses and carted off to prison, while dog owners would be prosecuted if their mutt caught a rabbit.
These were just some of the claims as desperate countryside campaigners battled to save their sport in the lead—up to the hunting ban, which Labour rammed into law using the Parliament Act on November 18, 2004.
For many, the fears were real. Others exaggerated as they fought an increasingly aggressive anti-hunting lobby which had rejected acres of independent evidence affirming that hunting is the most humane way of killing foxes. In the battle to "fight prejudice, fight the ban", every emotive argument was deployed.
For its part, the anti-hunting brigade extravagantly claimed that the ban would put an end to the rich parading in red jackets. A senior Labour MP, Peter Bradley, admitted in this newspaper that it was, as many suspected, about "class war". He lost his seat shortly afterwards. But people in red coats did not disappear.
In fact, none of the forecasts came true. What did happen was something nobody had predicted: the spectacular revival and growth of hunting with hounds. In short, the hunting ban has been a failure.
Today, on the second anniversary of the ban’s coming into force on February 18, 2005, new figures show that participation in the sport has never been higher. It is so cheerful that two new packs have been formed, something that has not happened for centuries.
They include the seductively named Private Pack, set up by the financier Roddy Fleming in Gloucestershire. It operates on an invitation—only basis, a sort of hunting private members’ club. This can only mean one thing: like it or not, hunting is cool. Young people are taking it up, enticed by the element of rebellion and the mystique of what actually happens as hunts attempt to keep within the law.

Those who break the hunting ban would ______.

A.lose their jobs

B.bring shame to their fellow people

C.have to kill their horses and dogs

D.face either fines or imprisonment

多项选择题