1.1 What is the Internet?

Although many consider the Internet a recent phenomenon , in reality it has existed and grown since the early 1980s. Above all, the Internet is a communications medium. It has transformed the way information is disseminated or exchanged, is changing the way we do business, access information, and view entertainment today, and holds the promise of becoming as indispensable as the telephone network.

The Internet is a global network of heterogeneous networks enabling computers of all kinds to directly and transparently communicate and share services throughout much of the world. Over 100 million hosts are connected to this network. The Internet is a constantly growing, evolving, and changing network. It is extremely difficult to define the structure of the Internet or explain its characteristics. Some have even referred to it as a living organism that constantly keeps growing at its edges, and as such has a life of it's own. The graph in Figure 1-1 shows the growth of the Internet through 2001 in terms of the number of hosts connected.

Figure 1-1. Host count of nodes attached to the Internet.

What started off as a research network with a few limited hosts has grown into a global-scale commercial network. The Internet has created a class of network operators called Internet service providers (ISPs). Over 6000 ISPs exist around the world today. Some of the bigger ISPs that offer services on a global scale include America Online, with about 30 million subscribers; UUNet, IIJ, NTT/Verio, Cable and Wireless, Earthlink, and Terra.

Fortunately, nobody really owns the Internet. There is no centralized control, and no one can turn it off. Since the Internet is formed by a collection of networks spread across the globe, there is no single company or government that has authority over it. As a result, we have a collection of networks that comprise university and research networks, commercial networks owned and operated by ISPs, networks belonging to governments , and non-government organizations (NGOs) as well.