TRUNK REQUIREMENTS IX ALTERNATE ROUTING NETWORKS 287 



of more than two million items of traffic between toll offices, would need 

 to be devised. 



Over the years since 1945 practical solutions to the problems raised 

 by the conditions have been attained by Bell System engineers and the 

 fruits of their efforts will be put to the test in 1954 during which year 

 the first practical application of "engineered" alternate routing in the 

 intertoll network will be undertaken. 



The remainder of this paper will be devoted to the more important 

 aspects of the traffic engineering techniques used in determining the 

 arrangement and numbers of intertoll trunks required in a multi-alter- 

 nate routing system. 



GENERAL TOLL SWITCHING PLAN 



A brief description of the General Toll Switching Plan* will be ap- 

 propriate here since any discussion of the alternate routing methods 

 necessarily presumes an understanding of the basic pattern for routing 

 traffic. 



The plan under which transmission had been designed and traffic 

 routings determined since 1930 comprehended a maximum connection of 

 5 intertoll trunks in tandem. Early studies of the alternate routing pos- 

 sibilities in toll networks led to the conclusion that a total of 8 intertoll 



o O D D O o 



D 

 O 



RC- REGIONAL CENTER 



PO- PRIMARY OUTLET 



O TC- TOLL CENTER 



Fig. 4 — Illustration of present basic intertoll network showing maximum 

 intertoll trunk linkage. 



links would provide a more economical arrangement of trunks by short- 

 ening some very long final groups that would otherwise be required. 

 Fig. 4 illustrates schematically the arrangement of switching centers in a 

 maximum connection currently in use. 



Fig. 5 shows a schematic of the proposed General Toll Switching Plan 

 in which a connection involving 8 links is possible between TCI and 

 TC2. Such a route would constitute the final route between those TC's 

 and each group in the route would be a low delay final group similar to 



* J. J. Pilliod, Fundamental Plans for Toll Telephone Plant, Communications 

 and Electronics, No. 2, Sept., 1952 and B. S. T. J., 31, Sept., 1952. 



