16.1. Introduction

In the previous chapter, we looked at pipes, FIFOs, message queues, semaphores, and shared memory: the classical methods of IPC provided by various UNIX systems. These mechanisms allow processes running on the same computer to communicate with one another. In this chapter, we look at the mechanisms that allow processes running on different computers (connected to a common network) to communicate with one another: network IPC.

In this chapter, we describe the socket network IPC interface, which can be used by processes to communicate with other processes, regardless of where they are running: on the same machine or on different machines. Indeed, this was one of the design goals of the socket interface. The same interfaces can be used for both intermachine communication and intramachine communication. Although the socket interface can be used to communicate using many different network protocols, we will restrict our discussion to the TCP/IP protocol suite in this chapter, since it is the de facto standard for communicating over the Internet.

The socket API as specified by POSIX.1 is based on the 4.4BSD socket interface. Although minor changes have been made over the years, the current socket interface closely resembles the interface when it was originally introduced in 4.2BSD in the early 1980s.

This chapter is only an overview of the socket API. Stevens, Fenner, and Rudoff [2004] discuss the socket interface in detail in the definitive text on network programming in the UNIX System.