Overview

Justin S. Morrill, Jr.

Hewlett-Packard Co., Colorado Springs, Colorado

A protocol is an agreed-upon set of rules and procedures that describe how multiple entities interact. A simple example of a protocol in everyday life is the motoring rule specifying that the vehicle to the right at an intersection has the right-of-way, other things being equal. If this traffic protocol is violated, the result might be a serious problem.

When the entities are network devices, protocols are necessary for interaction to happen at all. If two devices follow different protocols, their communication will be no more successful than a conversation between a person speaking French and a person speaking Chinese. As there is more and more essential data traffic over a wide variety of networks, the ability to guarantee protocol interoperability has become increasingly vital. A number of standards have been developed to make that possible.

Among these standards, one has been designed to facilitate complete interoperability across the entire range of network functions: the Open Systems Interconnection (OSI) Reference Model, published by the International Standards Organization (ISO).

In computing and communications, open refers to a nonproprietary standard. An open system is one in which systems from different manufacturers can interact without changing their underlying hardware or software. The OSI model is such a standard and is a useful framework for describing protocols. It is not a protocol itself,...