On Distributed Communications Series

V. History, Alternative Approaches, and Comparisons

Contents
Preface

Summary

This Memorandum describes some of the system design alternatives that delineate the proposed Distributed Adaptive Message Block Network from earlier distributed systems.

The discussion is restricted to systems using identical local switching policies at each switching node, and which do not rely on a single or a small hierarchy of critical routing control centers. A brief history of the development of some sample "distributed networks" is given with emphasis on the development of heuristic routing doctrines able to find "best" surviving paths in a heavily damaged network.

The term "distributed network" is often used as a generic term encompassing different systems. These systems, while appearing superficially identical, have markedly different properties, equipment, and survivability characteristics. Survivability is shown to depend upon the flexibility of switching with the limit of switching flexibility being defined as "perfect switching." These differences of flexibility of switching are often not fully appreciated. One cannot look at a communications network and necessarily predict survivability properties.

Several described example systems are categorized for comparison to aid in evaluating proposed systems and in synthesizing new ones.

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I. Introduction
II. The Distributed Network Concept
III. Early History
IV. Specific Hardware Proposals
V. Conclusions
Appendix A. Summary Charts
Appendix B. The DDD System
List of Publications in the Series