SWITCHING PLAN FOR TELEPHONE TOLL SERVICE 



433 



including speed, accuracy and directness of routing between any two 

 points in the country and suitable transmission standards. This 

 involves the layout of the plant in such a manner as to limit as much 

 as practicable the number of switches required for providing a con- 

 nection between any two telephones and the establishment of standards 

 of design and construction providing satisfactory transmission over 

 any route thus established. The plan is, therefore, of particular 



50 



40 



30 



20 



10 



1915 



1920 



1925 



1930 

 (EST.) 



Fig. 4 — Growth in number of toll circuits — New York and Chicago 

 to San Francisco, Los Angeles and Seattle. 



value in improving the service conditions of switched toll traffic, 

 that is, traffic requiring the connection of two or more toll circuits. 



The general features of the plan will be understood by reference to 

 Figs. 5 and 6. Figure 5 shows the application of the plan to a limited 

 operating area such, for example, as a State. Within the area are 

 selected a small number of important switching points designated as 

 "primary outlets." Each toll center is connected directly to at least 

 one of these outlets and all primary outlets within the area are directly 

 interconnected. This makes possible the interconnection of any two 

 toll centers within the area with a maximum of two switches and 

 within the part of the area served by one primary outlet, with a 

 maximum of one intermediate switch. 



