SWITCHING PLAN FOR TELEPHONE TOLL SERVICE 



435 



in Fig. 7. The method of routing calls is indicated by Fig. 6. Each 

 primary outlet is connected with at least one regional center and with 

 as many more as practicable. Each regional center is directly con- 

 nected to every other regional center in the country. By this means, 

 any one of the primary outlets, which are the 150 most important 

 switching centers in the country, can be connected to any other 

 primary outlet in the country with a maximum of two switches and 

 within the area served by a regional center with a maximum of one 

 intermediate switch. As an illustration of the concentration of 

 switching which results, New York serves as regional center for the 

 entire northeastern section of the United States and eastern Canada. 



SOLID LINES - FUNDAMENTAL ROUTES OF # REGIONAL CENTER 



GENERAL PLAN Q PRIMARY OUTLET 



DASHED LINES- SUPPLEMENTARY DIRECT • TOLL CENTER 



CIRCUIT GROUPS 



Fig. 6 — General toll switching plan — illustration of interconnection of important 

 switching offices throughout Bell system. 



The extent to which intermediate switching is limited by the 

 application of this plan is indicated by Fig. 8, which shows the maxi- 

 mum number of switches recjuired under the plan between different 

 types of toll centers. It is estimated that the percentage of long 

 haul messages requiring more than one intermediate switch will, 

 by means of this plan, be reduced by more than 50 per cent. 



As an example of the benefit resulting from the adoption of this 

 plan between two remote points, consider a connection which was 

 requested between Pembroke, Ontario and St. Anthony, Idaho. 

 Under the old routing instructions such a call required intermediate 



