Terms and Conditions:

John Larmouth wrote:This material is copyright J Larmouth 1994, but permission is hereby given for anyone to make local electronic copies provided no changes are made.

Book Excerpts:

This text aims to provide an intelligent near-beginner (as far as OSI is concerned) with an understanding of Open Systems Interconnection (OSI). Some previous acquaintance with data communications as presented in the many text books on that broad subject would be useful. The book is aimed at the reader who is curious enough to ask: "Why is it that way? What advantages does that approach give? Might there be other or better ways?"

This text is not an exposition of the technical detail of the OSI Standards. Rather it aims to explain why OSI is the shape it is, and to guide the reader in a critical examination of the OSI approach to specifying rules for computer communication (computer protocols). The text should be particularly valuable for those who are newly moving into positions where they are a part of a team developing applications using OSI, either in the International Standards' work or for their own firm. The text would also be useful for those sections of undergraduate and taught masters' courses that are dealing with OSI, either as the main text or as follow-on reading.

The text commences with discussion of the organizations involved in OSI, and with the OSI architecture - the seven-layer model and related concepts, then goes on to consider each of the layers in turn (some in more detail than others), and ends with a single chapter discussing the architecturally interesting features of a (necessarily) limited sample of application layer protocols.

The text does not attempt to give a complete treatment of OSI application layer standards: the choice of subjects to discuss has been made on the basis of whether the application concerned raises interesting or difficult new concepts, or helps to illustrate features discussed earlier in the text. In other words, the selection of applications treated is based on whether a presentation of a particular application is relevant to a general understanding of OSI and how to produce other OSI applications, rather than on whether the application is considered one of the more important in the market-place.

Intended Audience:

Most people reading this text will probably have at least heard of X.25, X.400, X.500, and the 7-layer model. This is not assumed in the main exposition, but examples and illustrations occur from time to time that will be less meaningful without some background knowledge of these areas. Such examples and illustrations can be skipped without much loss.