Automatic Toll Switching Systems 



By F. F. SmPLEY 



(Manuscript received May 12, 1952) 



A new automatic toll switching system has been developed by the Bell Tele- 

 phone Laboratories for use at the most important switching centers for 

 implementing the nationwide dialing program. The job of performing the 

 switching functions at such points is the most comprehensive ever performed 

 by any system, requiring a high order of mechanical intelligence. The new 

 switching system uses crossbar switches for the talking coymections and fully 

 exploits the common control principle whereby the equipment used for direct- 

 ing the establishment of connections through the switches is provided in 

 pools common to the office and is used with high efficiency. To perform the 

 complicated translating functions a new device called the card translator 

 has been developed. It iises punched metal cards arid an optical system with 

 phototransistors. Routing changes are made by insertion of previously pre- 

 pared cards in the machine. The switching system was designed with the 

 objective of handling long distance traffic dialed by customers as well as 

 that dialed by operators. 



INTRODUCTION 



This paper deals primarily with the major switching centers required 

 for the nationwide automatic switching plan. These are called Control 

 Switching Points (CSP's) and are supplied with switching equipment 

 endowed with great versatility and a high order of mechanical intelli- 

 gence. Mr. Pilliod's paper^ explains how for purposes of circuit layout 

 and routing, they are assigned different rankings as follows, starting 

 with the lowest ranking: Primary Outlets (PO's), Sectional Centers 

 (SC's), Regional Centers (RC's) and one National Center (NC). Sub- 

 stantially the same equipment is to be provided for all of these centers 

 so that they all will have inherently the same capabilities. They will, 

 however, differ greatly in size. In the United States and Canada, as now 

 envisaged, there will be somewhat under 100 of these CSP's. 



The system which Bell Telephone Laboratories de^'eloped for use at 

 CSP's and which embodies all of the features required at those important 



860 



