38 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



3 4 5 6 7 8 9 10 11 12 



TIME, t, IN SECONDS FROM START OF DIAL TONE TEST 



Fig. 3 — Results of dial tone tests. 



2. A delay formula* for determining the proportion of those test 

 calls encountering congestion which will have a delay in obtaining dial 

 tone of at least time t. 



Some of the theoretical aspects of these formulae are considered in 

 the two sections that follow. 



GENERALIZED TRUNKING FORMULA 



The generalized trunking formula combines in one expression the 

 various assumptions underlying the Erlang B, Poisson, and Erlang C 



* A development by John Riordan paralleling that of Conny Palm's. 



