be noted, eight regional centers in the United States, and 143 primary 

 outlets including three in the eastern part of Canada. 



While a regional center has direct circuits to all of the primary 

 outlets tributary to it, it also has direct circuits to many other primary 

 outlets. This is illustrated by Fig. 26 showing for the case of the 

 Chicago regional center the direct circuits to a large number of primary 

 outlets throughout the country. In addition, Chicago has, of course, 

 direct circuits to many toll centers which are not primary outlets where 

 the volume of traffic is sufficient to justify such direct circuits. The 

 same is true also of other regional centers and of primary outlets. 



In order that the transmission between any two points in the country 

 over a circuit routed in accordance with the General Toll Switching 

 Plan should be satisfactory, standards were established for each class 

 of toll circuit, that is, for toll circuits between toll centers and primary 

 outlets, between primary outlets and regional centers, etc. These 

 standards provide satisfactory overall transmission for connections 

 between any two points in an operating area, with an economical 

 division of the total transmission loss between the different toll 

 circuits entering into the connection. Generally speaking, these same 

 circuits form parts also of very long connections, switching at primary 

 outlets or regional centers t6 long circuits running to other parts of 

 the country. In order that satisfactory transmission may be given 

 under these conditions, it is necessary that severe requirements be 

 applied to the very long circuits with the result that they must be 

 designed and maintained with great care and coordination throughout 

 their entire length. It is also necessary that transmission gain be 

 inserted at points where circuits are connected together, and therefore 

 that the characteristics of the shorter circuits be such that they do not 

 limit the possibilities of inserting such transmission gains. The 

 application of these various complex requirements for toll circuits, in 

 order that they may form satisfactory links in any connection, short 

 or long, in the nation-wide toll telephone network, is greatly facilitated 

 by the systematic character of the General Toll Switching Plan, and 

 by the recommendations as to minimum performance standards which 

 that plan contains. 



Until recently, the method generally used for inserting transmission 

 gain on through connections of toll circuits was by means of repeaters 

 associated with the cord circuits at the intermediate switching points. 

 About the time that the Toll Switching Plan was established, there 

 was made available an improved method by which the gain of repeaters 

 permanently inserted in the toll line is automatically adjusted at the 

 switching point when the toll circuits are connected together. These 



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