FUNDAMENTAL PLANS FOR TOLL TELEPHONE PLANT 833 



couiiocting points. The telephone offices in each of these places have 

 access through the toll network to practically all of the 50,000,000 tele- 

 phones in the United States and Canada and also to most of the tele- 

 phones in the rest of the world. Currently the Bell Operating Companies 

 are handling toll calls at an a\'erage rate of over 7,000,000 during a 

 business day. The many millions of different connection possibilities 

 which this number of calls involves require a definite and comprehensive 

 switching plan. 



Whenever practicable and economical direct circuits are used to 

 handle toll message traffic between two given points. Much of the traffic 

 in the coinitr^^ is handled this way. However, a substantial volume of 

 business, about 20 per cent, is handled as a matter of economy, by switch- 

 ing toll circuits together. Althougli the volume of traffic between different 

 points may ^'ary o^'er a wide range, it is nevertheless important that 

 adequate service be provided for all possible connections. For example, 

 there are about 110 circuits from Chicago terminating in the toll office 

 serving Minneapolis and St. Paul. These handle about 5500 calls per day. 

 On the other hand, only a few calls a year may be involved between some 

 point in Western Minnesota and a point in Florida. The switching plan 

 described in this paper is devised for the purpose of efficiently and effec- 

 tively establishing connections between any two points regardless of 

 their separation and regardless of whether traffic volume be a few calls 

 per year or many calls per hour. 



ELEMENTS OF THE PROBLEM 



In order to illustrate the problem a specific example may be useful. 

 Fig. 1 is a map of Wisconsin and ]\Iinnesota on which nearly 1200 circles 

 indicate points at which exchange facilities may be connected to the 

 toll network. The extent of the coverage in this area is typical of that 

 found throughout the country. 



The 150 odd larger circles represent existing offices known as "toll 

 centers" - that is, places where operators record toll calls and perform 

 other operations necessary to establish toll connections. These places 

 have switching arrangements of various types depending on how they 

 fit into the switching plan. Some may operate as control switching points 

 in the nationwide plan as described later. 



IMore than 1,000 smaller circles on the map represent "tributaries" - 

 that is, towns where little or no toll operating is done. Toll connections 

 to and from these points are completed at the toll centers which in gen- 

 eral do the toll operating required. 



