Line, Trunk, Junctor, and Service Circuits for No. 1 ESS

Centralization of memory and control, long a dominant trend in telephone switching, has come close to t h e ultimate in t h e No. 1 electronic switching system (ESS). Nevertheless, individual circuits are still required on a per-call and even per-line basis to match the widely variable outside world to t h e standardized "inside world" of t h e central processor. 1 These individual circuits, t h e line, junctor, t r u n k and service circuits, provide the subject m a t t e r for this paper. It is obvious t h a t t h e central processor m u s t work at very high speeds if it is to t a k e over all memory and control functions. E v e n though actual signals from customers and other telephone offices come in relatively slowly, t h e central processor m u s t operate rapidly to divide its time among t h e m a n y signals flowing simultaneously over thousands of lines and trunks. W h a t m a y not be so obvious, however, is t h e way in which this centralization affects t h e circuits in contact with lines and t r u n k s during the processing of calls. In No. 1 ESS, these circuits have been reduced to very simple configurations; each circuit performs only a few functions under program control, 2 and different circuits are connected as needed via the switching network. 3 Both flexibility and economy result. 2321