Dialing Habits of Telephone Customers 



BY CHARLES CLOS AND ROGER I. WILKINSON 



(Manuscript received October 3, 1951) 



This paper considers the behavior of customers waiting to dial calls, when 

 dial tone is delayed. Tests were made in a panel dial central office, from 

 which were determined: relationship between load carried by a group of 

 line finders and the resultant dial tone delay; measures, by classes of ser- 

 vice, of the fyiagnitude of the generalized trunking formida's "j" factor 

 describing the degree to which customers wait ivhen dial tone is delayed; 

 comparisons of observed and theoretical distributions of the number of 

 simultaneous calls on line finder groups; and statistical accounts of the 

 actions of customers when dial tone is delayed. 



Following World War II the conversion of great quantities of manual 

 telephone equipment to dial, and the addition of large numbers of new 

 telephones, mostly dial, in the Bell System has directed increasing atten- 

 tion to those service problems peculiar to automatic operation. These 

 problems concern chiefly the provision of adequate amounts of equip- 

 ment to give satisfactory service at all times. One of the important 

 factors affecting the amount of equipment needed is the action of the 

 customers themselves when their calls are momentarily blocked due to 

 these equipment shortages. The actions of subscribers whose calls are 

 blocked due to a shortage of trunk ecjuipment have been reported pre- 

 viously.^ This paper considers the behavior of subscribers, waiting to 

 dial calls, when dial tone is delayed. 



During 1949, Bell Telephone Laboratories conducted a series of tests 

 at the New York Telephone Company's Sterling-3 panel dial central 

 office in Brooklyn, X. Y., with the object of increasing the knowledge 

 available regarding subscribers' actions and their effects when dial tone 

 is delayed. 



The following principal results were obtained from the Sterling-3 tests: 



1. The relationship between the load carried by a group of line finders 

 and the resultant dial tone delay. 



2. Measures, by classes of service, of the magnitude of the general- 



1 Charles CIos, "An Aspect of the Dialing Behavior of Subscribers and Its 

 Effect on the Trunk Plant," Bell System Tech. J., 27, July 1948. 



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