The first separate appearance

Shannon, Claude E. [Elwood]

Memory Requirements in a Telephone Exchange [Bell Monograph]

New York, N.Y. Bell Telephone Laboratories, Incorporated October 1950. First Separate Edition. 1-7, [1-blank] pages. 10 7/8 x 8 3/8 inches. (275 x 213 mm) Stapled wrappers, printed in grey, light blue, and black. Five holes punched at the spine as issued. A bright, clean copy. Fine. Wraps. [28616]


The Bell System Technical Journal, Vol 29, July 1950, pages 343-349 first published this paper. Since there is no known Bell System Technical Journal offprint for this paper, this Bell Telephone System Technical Publications Monograph (#1758, October 1950) constitutes the first separate edition, the closest a collector can come to a traditional offprint.

"The basic function of an [telephone] exchange is that of setting up a connection between any pair of subscribers. In operation, the exchange must 'remember' in some form which subscribers are connected together until the corresponding calls are completed. This requires a certain amount of internal memory, depending on the number of subscribers, the maximum calling rate, etc." (first paragraph)

The amount of memory a telephone exchange used was critical. If there was too much memory, the cost of new telephone equipment quickly became untenable. If there was too little memory, subscribers might get disconnected or not correctly billed. So Shannon derived a formula for calculating the needed memory (M = 2S log N) and interpreted it using theories from his seminal work “A Mathematical Theory of Communication.” But this theory also provided for the future.

In the 1950s, central office switches (the machines that connected telephone subscribers in cities and large companies) were mechanical or electromechanical. Their electrically connected components (see Strowger or Crossbar switches for more information) allowed for only the most basic call connections.

Shannon's paper helped later engineers size the memory components that would eventually turn into fully electronic switches. Fully electronic telephone switches enabled other significant business features that the telephone companies could charge for - caller id, three-way calling, call forwarding, and eventually revolutionary tools like voicemail. And since electronic memory was a costly component for many years, optimizing this resource was a key profit consideration. While the first fully electronic switch, the #1ESS, wasn't installed until 1965, Shannon's paper provides an early theoretical building block - a piece of the puzzle that helped enable the modern telephone network.

PROVENANCE: The personal files of Claude E. Shannon (unmarked). There were multiple copies of this item in Shannon's files.

REFERENCES:
Sloane and Wyner, "Claude Elwood Shannon Collected Papers," #56
Hook and Norman, "Origins of Cyberspace," #883

COLLECTORS NOTE: The Bell Telephone System Monograph series offered a way to obtain individual articles by Bell scientists regardless of where their work was first published. Many Monographs significantly postdate the original article publication. Because of this, they rarely constitute the coveted (and traditional) article offprint. If the journal of record issued no offprint, the Monograph might be the first separate publication - the closest the collector can come to a traditional offprint. We have done our best to place each Monograph properly in the article’s publishing history and welcome any corrections or additional information, especially regarding issues unknown to us.

Price: $750.00