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THE BELL SYSTEM TECHNICAL JOURNAL, MARCH, 1954 



abandoned and the loads that would have been offered to such groups 

 were assigned switched routes. A switched route for our purposes is 

 one in which the load between toll centers is carried on two or more inter- 

 toll groups in tandem and may serve simultaneously as a first route for 

 some items of traffic and as an alternate route for other items. 



The cut-and-try process just described resulted finally in the location 

 of all economically sound high usage groups. There remained, then, the 

 problem of determining the number of trunks in each of those groups 

 and in the final groups as well. At this point two rules were estabhshed 

 affecting (1) the order of group load computation and (2) the direction 

 of switched load concentration, respectively. 



The first of these may best be described b}^ considering the conditions 

 illustrated in Fig. G where a portion of the intertoll network with typical 

 homing arrangements and high usage groups is shown. The follo\\'ing as- 

 sumptions regarding alternate routes may be made: 



TCI and TC2 are not switching centers and the load offered to their 

 interconnecting group will be simply terminal traffic between their re- 

 spective toll areas. Since TC1-P02-TC2 has been determined as the 

 most economical alternate route, calls from TCI to TC2 overflowing the 

 high usage group are offered to the TC1-P02 group. Thus a part of the 

 complete offering to TC1-P02 is traffic rerouted from TC1-TC2. It 

 follows then that the TC1-P02 group can not be engineered until the 

 overflow from the TC1-TC2 group has been determined. Similarlj^, the 



P0 2 



TC1(> 



Fig. 6. 



