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The Internet

Internet: This is a word that I've heard way too often in the last few years. Movies, books, newspapers, magazines, television programs, and practically every other sort of media imaginable has dealt with the Internet recently.


The Internet is the world's largest network of networks . When you want to access the resources offered by the Internet, you don't really connect to the Internet; you connect to a network that is eventually connected to theInternet backbone , a network of extremely fast (and incredibly overloaded!) network components. This is an important point: the Internet is a network of networks  -- not a network of hosts.

A simple network can be constructed using the same protocols and such that the Internet uses without actually connecting it to anything else. Such a basic network is shown in Figure.


A Simple Local Area Network


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I might be allowed to put one of my hosts on one of my employer's networks. We have a number of networks, which are all connected together on a backbone , that is a network of our networks. Our backbone is then connected to other networks, one of which is to an Internet Service Provider (ISP) whose backbone is connected to other networks, one of which is the Internet backbone.

If you have a connection ``to the Internet'' through a local ISP, you are actually connecting your computer to one of their networks, which is connected to another, and so on. To use a service from my host, such as a web server, you would tell your web browser to connect to my host. Underlying services and protocols would send packets (small datagrams) with your query to your ISP's network, and then a network they're connected to, and so on, until it found a path to my employer's backbone, and to the exact network my host is on. My host would then respond appropriately, and the same would happen in reverse: packets would traverse all of the connections until they found their way back to your computer, and you were looking at my web page.

In Figure 4, the network shown in Figure 3 is designated ``LAN 1'' and shown in the bottom-right of the picture. This shows how the hosts on that network are provided connectivity to other hosts on the same LAN, within the same company, outside of the company, but in the same ISP cloud , and then from another ISP somewhere on the Internet.


A Wider View of Internet-connected Networks


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The Internet is made up of a wide variety of hosts, from supercomputers to personal computers, including every imaginable type of hardware and software. How do all of these computers understand each other and work together?

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