Electronic telephone exchanges

Abstract

Attention is being given in Britain and other countries to the possibilities of automatic telephone exchanges constructed with electronic switches, in order to determine whether exchanges cheaper and more reliable than the present types using electro-mechanical switches may thereby be produced. The paper discusses some practical forms which electronic exchanges might take, the possibilities and characteristics of such exchanges and-cursorily-the questions of cost and reliability. Multipled, frequency-division and time-division multiplex types of connector switches for speech and line-signal transmission are described, together with typical subscriber's line equipment. General principles of selection systems, with examples of group and free-circuit marking and of a post-setting-up control circuit, are given. Transmission gain and loss, variation of loss, and distortion are features of electronic connector switches not found in existing types using metal-to-metal contacts, but, on the whole, better speech transmission could be given by electronic systems using the connector switches described in the paper, because of the 4-wire switching which would be inherent in most and desirable in all such systems. Estimates of cost show favourable signs, but are as yet indeterminate. Total system costs must take into account line plant, the design of which may be profoundly influenced by electronic exchanges. Reliability has yet to be proved, but here the signs are also favourable.