TCP/IP Networking

Although UUCP may be a reasonable choice for low-cost dial-up network links, there are many situations in which its store-and-forward technique proves too inflexible, for example in Local Area Networks (LANs). These are usually made up of a small number of machines located in the same building, or even on the same floor, that are interconnected to provide a homogeneous working environment. Typically, you would want to share files between these hosts, or run distributed applications on different machines.

These tasks require a completely different approach to networking. Instead of forwarding entire files along with a job description, all data is broken up in smaller chunks (packets), which are forwarded immediately to the destination host, where they are reassembled. This type of network is called a packet-switched network. Among other things, this allows to run interactive applications over the network. The cost of this is, of course, a greatly increased complexity in software.

For something concrete to look at as we discuss TCP/IP throughout the following sections, we will consider Groucho Marx University (GMU), situated somewhere in Fredland, as an example. Most departments run their own local area networks, while some share one, and others run several of them. They are all interconnected, and are hooked to the Internet through a single high-speed link.

Suppose your box is connected to a LAN of hosts at the Mathematics Department, and its name is erdos. To access a host at the Physics Department, say quark, you enter the following command:

$ rlogin quark.physics
Welcome to the Physics Department at GMU
(ttyq2) login:

At the prompt, you enter your login name, say andres, and your password. You are then given a shell on quark, to which you can type as if you were sitting at the system's console. After you exit the shell, you are returned to your own machine's prompt. You have just used one of the instantaneous, interactive applications that TCP/IP provides: remote login.