For most users, the Internet starts to work when they log on. They call up the browser program (such as Internet Explorer), and connect via a modem and a telephone line to an Internet Service Provider (ISP). Once the contact has been established, and the identity of the user has been established, the user's computer becomes part of the internet.
"part of" is important. Just as you can access thousands of computers world-wide, they can access your computer. This is a scary thought at first, but there are ways and means, programs and techniques, that can protect you against spying eyes. One of the most effective ways is to use a "firewall" program, which monitors traffic in and out, and will only permit what you authorise.
You now have a connection to your ISPs computer, and through it to the Internet system. But you do not have a direct connection to any other computer. If the link between you and the ISP is out of service, or the ISP computer is down, then you are not connected to the Internet.
Any message leaving your computer (for example, a request to connect to whatsit.com) goes to your ISP, and through your ISP to the world wide Internet system. And data coming back from the outside world can only come to you through your ISP. The ISP is permanently connected to the system through broadband telephone connections called the "backbone". So when you connect to your ISP, you become part of that ISP's network, which in its turn connected to the huge network that spans the world and connects most countries. This is one of the reasons some people think of the internet as a "network of networks".
As a further development of the Internet, service is now becoming available on cable and satellite, using the same infrastructure as pay TV. People with cable or satellite service often have permanent connection to the ISP, and they also enjoy much faster transmission speeds than can be achieved through modems and pairs of copper wire running to the local telephone exchange. Another development is the installation of a second telephone line which the user reserves for internet use. Because of the accounting "package" that many ISPs offer, people can leave their computers permanently connected to the ISP (and, of course, the Internet) through this reserved telephone line.
© James Nelson, 2001.