Introduction

A protocol is a set of rules which have to be followed in the course of some activity. Originally, the term was used solely of human activities, especially those of a somewhat formal kind, such as the state funeral for King Théoden described in the quotation at the start of this chapter. The chef de protocole for a Head of State sets formal rules for how activities take place according to the niceties of diplomatic practice. But protocols must also be followed in less elevated spheres, such as games of all kinds, the way in which conversations are conducted, and in fact all activities which are governed by custom and convention. If the protocol is not followed, the activity will not be successful.

In this book we shall consider communication protocols, and in particular those which regulate communication between computers. The characteristics of protocols mentioned above are equally evident in this case: A set of formal rules governs the exchange of information, and the communication activity fails if the protocol is not correctly followed.