1.3: A network of networks

This schematic shows how various pieces of equipment work together to connect you to the Internet. Each unit — router, modem, server — is itself a specialized computer.

Every computer connected to the Internet is part of a smaller network, even the computer in your home. For example, you may use a modem (modulator-demodulator) and dial a local number to connect to an Internet Service Provider (ISP). Early ISPs such as America Online were accessible through plain old telephone service (POTS). Today more and more homes have broadband service, either through a digital subscriber line (DSL) or a cable modem. No matter how you connect with an ISP, you become part of that ISP#&8217;s network.

You also are probably part of a local area network (LAN) that in turn is connected to an ISP or directly to the Internet through a Net Access Point (NAP). At home, if you use a wireless hub, you have established a LAN. You can communicate directly with other computers on the wireless hub. At work, you most certainly are part of a LAN for your company or school. The beauty of the internet is that computers of different make and model, and with differing operation systems, and LANs using various brands of hardware all can talk to each other. That is because they all adhere to the TCP/IP system.

When you connect to your ISP, you become part of its network. The ISP then connects to a larger network through an NAP and becomes part of that network. The Internet is simply a network of networks.

Large communications companies have their own dedicated backbones connecting various regions. In each region, the company has a Point of Presence (POP), a rack full of modems that the ISP's customers connect with.

The amazing thing about the Internet is that it has no overall controlling network. Instead, several high-level networks connect to each other through NAPs.

Protocol of the Internet

Every machine on the Internet has a unique identifying number, called an IP Address. The IP stands for Internet Protocol, the language that computers use to communicate over the Internet.

A protocol is the predefined way that someone who wants to use a service talks with that service. The “someone” could be a person, but more often it is a computer program like a Web browser.