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100 McAfee Internet Security 5.0
Why packets?
Why go through all this trouble, breaking data down into packets? The answer
lies in the origins of TCP/IP. Like the Internet itself, it is a product of the Cold
War. The United States Department of Defense originally developed the
Internet. It was designed to ensure secure communications, even with
multiple communications network failures anticipated in the event of a
nuclear war. TCP/IP solves the problem of network failure by assuming that
a certain amount of noise always exists in the network— noise referring either
to random data errors or more serious system crashes. If you have ever tried
to speak in a noisy room, you know the necessity of repeating yourself—and
that is exactly what TCP/IP is designed to do. Breaking the data down into
packets allows the Internet to seek alternate routes if one route is inaccessible.
If a packet cannot get through or arrives damaged, the receiving computer
simply requests it again until it arrives successfully.
When you send an e-mail message, for example, it is broken into several
packets. Depending on how noisy the network is, each packet may need to be
routed over a separate route in order to find its way to its destination.
Furthermore, network problems may cause some of the packets to be delayed
so they arrive out of order. To compensate, TCP examines each packet as it
arrives to verify that it's OK. Once all the packets are received, TCP puts them
back in their original order. Of course, all of this happens quickly and
automatically, so you will never see the process at work.
The Internet and the Web…what is the difference?
Before the Web, the Internet was mostly command-line driven and
character-based— you had to type in the exact Internet address of the place
you wanted to go at a command line. In 1989, Tim Berners-Lee of the European
Particle Physics Laboratory proposed a new way to share information over the
Internet. The essential feature in Berner-Lee’s vision of the Web is that it links
documents together. When you click a link on a Web page, you are
automatically connected to another Web site. This linking function, combined
with the increasing graphics abilities of home computers, transformed the
Internet into a graphically rich place, complete with video, sound, and
pictures. Through the linking of information together in a graphically
appealing package, the Web made the Internet more attractive to the typical
consumer.
The Internet is a network of linked computers that uses TCP/IP as its
underlying messaging system. The World Wide Web (WWW, or just “Web”
for short) is hosted by the Internet, and is an ever-expanding collection of
documents employing a special coding scheme named Hypertext Markup
Language (HTML).
HTML is a set of commands designed to be interpreted by Web browsers. An
HTML document consists of content (prose, graphics, video, etc.) and a series
of commands that tell a Web browser how to display the content.