THE BELL SYSTEM 



TECHNICAL JOURNAL 



VOL u ME XXXI SEPTEMBER 1952 number 5 



Copyright, 1952, American Telephone and Telegraph Company 



Automatic Switching for Nationwide 

 Telephone Service 



By A. B. CLARK and H. S. OSBORNE 



(Manuscript received May 15, 1952) 



.4 plan for automatic long distance switching, which will ultimately cm- 

 brace the entire area of the United States and extend into Canada and per- 

 haps Mexico, has been formulated and important steps have been taken 

 toward its realization. The plan contemplates that when a telephone cus- 

 tomer places a call with a long distance operator, this operator will be able 

 to establish a connection to any desired telephone simply by playing a 10 

 or 11 digit code into an automatic mechanism. She will receive distinctive 

 signals when the called telephone answers or when the telephone or the toll 

 circuits are busy. She will completely control the establishment of the 

 connection and will have available to her the information necessary for 

 proper billing of the call. The plan also contemplates that telephone cus- 

 tomers will ultimately be able to dial long distance calls themselves, wherever 

 may be the locations of the calling and called telephones. 



INTRODUCTION 



Ever since the invention of the telephone 76 years ago, development 

 work has been pressing forward both in telephone transmission and in 

 switching. These two fields have been closely interrelated in the develop- 

 ment of telephone service on a nationwide basis, and neither could have 

 progressed as it has without corresponding progress in the other. 



The first development of equipment for the mechanical switching of 

 telephone lines was the local dial system to enable one customer to be 



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