Chapter 1: Networking Overview

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In this first chapter, fundamental networking concepts are discussed to provide a basis for more advanced discussions in this book. If the reader is already aware of the networking model and types of communication available on the Internet, this chapter may be skipped.

What Is the Internet?

The Internet is quite simply a network of networks. A network can be defined as a collection of computers and specialized devices that support communication between them.

The basic unit of communication on the Internet is the packet. A packet is made up of a payload, which contains the data to be communicated, and a header, which describes the payload and includes information about the sender and intended receiver of the data. To use a simple letter analogy, the packet header is the envelope, which has information describing where the letter originated and where it's going, and the contents of the envelope is the payload-what is being delivered to the recipient.

Packets are originated by hosts, which are those machines that run applications such as Web browsers or e-mail clients. Hosts are also the primary recipients of packets. In addition to hosts, the Internet is also occupied by routers (see Figure 1.1). These specialized devices route packets between networks. For example, a router interconnects a number of independent networks together. When a packet arrives from a network and is destined for another, the router identifies to which particular network the packet should be sent. The router makes these decisions using packet header information; we look more closely at this process in the Introduction to IP Routing section later in this chapter.

Figure 1.1: Fundamental devices on the Internet.

Note 

There are many good historical references of the Internet (which conceptually began in 1962 at MIT); some are even written as RFCs (Request for Comments-the Internet protocols' standardization process). A very interesting reference for the history of the Internet is provided in the References section of this chapter under [Leiner et al].

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