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  3. We all know the Internet does not run fast enough. What we often do not know is why. When a Web page is slow downloading, we usu

We all know the Internet does not run fast enough. What we often do not know is why. When a Web page is slow downloading, we usu

admin2015-06-23  39
问题     We all know the Internet does not run fast enough. What we often do not know is why. When a Web page is slow downloading, we usually attribute it to the kind of computer we have, the speed of the connection or the time of day. But in fact there are other things that can figure in, and they are often hidden.
    Did you know that there are only 13 "root name servers" in the world, serving all 150 million people using the Internet? A root server is a computer that holds the routing information for the naming system of the Internet. It allows your computer to connect with the host computer of, for example, all the www.apple.com pages. It’s like an electronic directory. Each request for a Web page generates at least two transactions well before any real content is communicated — one from the customer to find the name server, and one from the server to confirm the information to the customer. All that back-and-forth generates huge data traffic, so there is some of your slowdown.
    Significantly, only three of the root name servers are outside the United States — in London, Stockholm and Tokyo. This means that an awful lot of Net access generated outside the United States has to go to one of the servers there to find its way. That makes it slow for users.
    Of course, as with many things about the Internet, the Washington area has a particular advantage. As many as four name servers are here. One is in Hemdon at Network Solutions Inc, and one is College Park at the University of Maryland Computer Science Center. The other two are maintained by the Defense Department’s Network Information Center in Vienna and the Army Resource Lab in Aberdeen, Md. But the military rotates(轮换调防)the servers among undisclosed locations for security purposes.
    The Net is "distance insensitive." In other words, the fact that sites are close to each other does not necessarily mean that traffic will move between them faster than between far-apart sites. Singapore and Phnom Penh, for example, are about 750 miles apart. A data trip from one to the other and back takes 1,100 milliseconds. But from Singapore to Los Angeles, which is many more times distant, the data trip is just 400 milliseconds. This has a lot to do with capacity — the fattest "pipes" of access are to the top-level Internet servers, the backbone computers of the Net, the ones that function like trunk lines, providing long-distance interconnections. If you and the computer host of the page you want to reach are both near a big pipe, signals will travel between you very quickly, even if you are very far away from each other. But even if you are close together the signal will travel slowly if you have a small connecting line.
From the passage, we can infer that______.
选项 A、most Net access has to find their ways from American name servers
B、nowhere has more advanced root name servers than in Washington
C、people in America can get access to the Net faster
D、distance insensitivity is another factor that affects the signal on the Net
答案A
解析 推理题。第三段指出全世界有10个互联网根域名服务器在美国，这就意味着大量的在美国境外进行的网络进入要到美国的服务器上寻找路径。
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