On Distributed Communications Series

I. Introduction to Distributed Communications Networks


The series that this Memorandum introduces describes work on distributed communications. Originally, it was thought that each of the eleven volumes would be able to stand by itself. But, somewhere downstream it became clear that this goal could not be fully met, as each part hinged upon others. Therefore, publication of the individual Memoranda of the series was delayed in order to release the set as a whole.

While the resulting mound of paper forms a frightening pile, it need not all be read in depth, nor will all readers be interested in all the volumes. It is suggested that the present volume be read first especially if the reader is not familiar with its antecedents, B-265 or P-2626. Then the reader should advance directly to the summary overview in Vol. XI. Once in context, it will be easier to selectively examine the other papers of the series in more detail.

Two types of papers will be found. The first set, Vols. I, IV, V, IX, and XI, describes in general terms the underlying system philosophy and what this system approach has to offer. The second set, Vols. II, III, VI, VII, VIII, and X, describes in nuts-and-bolts detail one possible way of implementing the proposed mechanisms. The purpose of this second set is to supply the technical details of the proposed system in sufficient detail, it is hoped, to permit the reader to focus his questions on the potential feasibility of the system in a meaningful manner.

It should be stated at the outset that we are dealing with an extremely complicated system and one that is even more complicated to describe. It would be treacherously easy for the casual reader to dismiss the entire concept as impractically complicated- -especially if he is unfamiliar with the ease with which logical transformations can be performed in a time-shared digital apparatus. The temptation to throw up one's hands and decide that it is all "too complicated," or to say, "It will require a mountain of equipment which we all know is unreliable," should be deferred until the fine print has been read.

In the interim, let us agree on what we mean when we speak of "complexity." It can be defined in several ways; for example, by size, by flexibility, or by number of components. But these are not identical measures. Consider an ancient electro-mechanical computer composed of bays of clacking relays. The logical diagrams are simple--a few conceptually simple boxes perform almost trivial logical functions. But the physical dimensions of the package and the amount of maintenance effort required constitute a frightening aspect of complexity.

Conversely, consider a "shoe-box" of electronic equipment that performs all the functions the larger unit did, plus many new ones, and does them more quickly. It's smaller, more reliable, quieter, and requires less maintenance. But it may actually contain more components and its logical equations may be more difficult to comprehend. Is the shoebox more complex or less complex than its room-size electro-mechanical counterpart?