Chapter 13. Protocol Handlers

Protocols are the framework for all communication: they indicate to each correspondent how to understand the other side of a conversation. In Linux, communication is understood through a protocol handler at each networking layer. This chapter explains how these handlers are installed, chosen at runtime, and invoked.

To understand the relationship among communication layers and protocols, imagine a possible situation in real life where I have to talk to a stranger. What language should I use? If I'm in Italy I'll begin with Italian, and if I'm in the United States I'll try English. If these don't work, there may be ways to negotiate the use of a different language.

On top of that basic protocol, there are others. When writing a letter, for instance, my relationship with the correspondent determines whether I begin "Dear Madam" or "Hi, gal!" These sorts of choices take place at many layers of real-life communication. Networks have layers too, and the choice of protocols becomes formalized in network code.