An Aspect of the Dialing Behavior of Subscribers and Its Effect on the Trunk Plant

T O U R I N G the war it became necessary for the Bell System Companies to lower many service standards. Among these was the standard for the provision of trunks for handling subscriber-dialed calls. In the interest of economy the number of trunks for a given volume of traffic was lowered. It is evident that for any given case there is a lower limit to the number of trunks that should be provided for handling subscriber-dialed calls. Below this limit congestion of calls gets beyond control. The control of congestion is important. In the case of operator-handled calls it is possible to control congestion by filing tickets and placing calls in an orderly fashion. In the case of subscriber-dialed calls the subscriber may with impunity make many, indeed very many, successive dialing attempts to complete a call that is blocked due to a shortage of trunks. If, in a particular office enough subscribers do this simultaneously, a sender shortage may develop with its resulting reaction on the whole office, From the foregoing it is evident that the standard of service for providing trunks in trunk groups handling subscriber-dialed calls is of importance. During the war years, the New York Telephone Company undertook a study to determine the limits below which it would be undesirable to degrade the service. This study was designed to test the reasonableness of the reduction in the inter-office trunk standard from the pre-war basis of providing enough trunks to delay only one out of a hundred calls in the busy hour to a wartime basis of providing enough trunks to delay two calls in every hundred during the busy hour.