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BELL SYSTEM TECHNICAL JOURNAL 



central offices in the United States and eastern Canada. Furthermore, 

 the technical developments in toll circuits have led to great increases 

 in the numbers of circuits along a given route. The extension of the 

 use of carrier telephone has increased the capacity of a 40-wire pole 

 line from 30 circuits to 70 circuits. On the heaviest toll routes, 

 moreover, circuits are now provided by means of toll cable construction, 

 a single cable carrying 200 or 300 circuits. During the past year 



14 



12 



10 



1915 



1920 



1925 



1930 

 (EST.) 



Fig. 3 — Growth in number of toll circuits — -Buffalo to Chicago. 



or two the growth has been so rapid as to stimulate a very large 

 amount of construction of underground toll conduit routes, providing 

 in many cases for several thousands of telephone circuits on a single 

 route. 



General Toll Switching Plan 



The conditions outlined above form the background which has made 

 it both possible and important to adopt a new fundamental arrange- 

 ment for the layout of toll plant and the routing of toll messages. 

 This is called the "General Toll Switching Plan." The purpose of 

 this plan is to provide systematically a basic plant layout designed for 

 the highest practicable standards of service consistent with economy. 



