Electronics in Telephone Switching Systems

SEPTEMBER 1956 Copyright 1956, American Telephone and Telegraph Company NUMBER 5 Electronics in Telephone Switching Systems (Manuscript received March 18, 1956) By A. E. JOEL In recent years a number of f undamentals has been discovered through research which place new tools at the disposal of the circuit and system designers. Examples of this "new art" are concepts such as information theory, dealing with the quantization and transmission of information, and solid state principles from which have developed the transitor and other devices. This paper surveys certain new art principles, techniques and devices as they apply to the design of new telephone switching systems. Over the past forty years a great background and fund of knowledge has developed in the field of telephone switching. Constant improvement in available devices has resulted in increasing the scope of their application. The field has almost reached a point of perfection as an art and is now rapidly entering a more scientific era. The tools of the present day telephone system design engineer are well known and some are illustrated in Figure 1. These are the relay and the various forms of electromechanical switching apparatus. But over the years, while the art employing these tools was developing, the field of electronics has also been developing. Its applications were most needed when dealing with its characteristics of sensitivity rather 991 99G TIIE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMEER 1956 Fig. 1 -- Typical telephone relays and switches.