THEORIES FOR TOLL TRAFFIC ENGINEERING IN THE U. S. A. 467 



Table II^ — Calculation of Loss in a Simple Graded Multiple 

 g = 2, Xi = X2 = S, ai = a2 = a = 1 to 5, C = 1 to 3 



for this example are shown in the lower section of Table III. As before, 

 of course, the "lost" calls are assumed cleared, and do not reappear in 

 the system. 



Example 3: A load of 18 erlangs is offered through four groups of 

 10-point selector switches to twenty- two trunks which have been desig- 

 nated as "high usage" paths in an alternate route plan. Which of the 

 trunk arrangements shown in Fig. 27 is to be preferred, and to what 

 extent? 



Solution: By successive applications of the Equivalent Random 

 method the overflow percentages for each of the three trunk arrange- 

 ments are determined. The results are shown in column 2 of Table IV. 

 The difference in percentage overflow between the three trunk plans is 

 small; however, plan 2 is slightly superior followed by plans 3 and 1 in 



Table III — Calculation of Overflows from a Simple 

 Alternate Route Trunk Arrangement 



Description of load offered to alternate route: A' = 3.25, V = 5.23. 

 ]'"quivalent straight multiple: S = 5.8 trunks, A = 8.00 erlangs (from Fig. 26). 

 Overflow from C = 5 alternate route trunks (enter Figs. 12 and 13 with A = 



8.0 and S + C = 10.8: a' = 0.72, v' = 1.48. 

 Proportion of load to commons which overflows = 0.72/3.25 = 0.22. 

 Proportion of offered load which overflows = 0.72/15.2 = 0.0475. 



