958 



THE BP:LL system technical journal, JULY 195G 



cause handliug .switched connections manuully was so complicated and 

 expensive that direct trunks were provided wherever they were econom- 

 ical and alternate routes were assigned and used sparingly. The result 

 was that the manual switching plan was characterized by a minimum of 

 switching. 



Under manual operation, operators passed information over every 

 trunk in the connection, as w^ell as over the completed connection, before 

 it was turned over to the customers. If anything was radically wrong with 

 a trunk, the operators recognized it and substituted another trunk. When 

 this was necessary, they could report the defective trunk to the appropri- 

 ate testboard for action. Under these conditions, if trunk losses wandered 

 appreciably from their specified values, the consequences were seldom 

 serious. 



Dial Operation 



With dial operation, not only is the plan more complex (as shown on 

 Fig. 2), with an abundance of alternate routes, but intertoll trunk switch- 

 ing is so fast and reliable that the number of switching points has little 

 effect on speed of service. Thus the dial operating plan can take full ad- 

 vantage of alternate routing and the use of trunks in tandem \\\\\ occur 

 much more freciuently than with manual operation. 



TC = Toll Center PC = Primary Center SC = Sectional Center 



RC = Regional Center 



Fig. 2 — Nationwide dialing plan — dial operation. 



