1036 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER, 1953 



While the maintenance problem is at least as complex and difficult as 

 the design problem, it is beyond the scope of this paper. 



SUMMARY 



To summarize the preceding discussion : For the particular conditions 

 in the Bell System, a formula has been set up to give adequate approxi- 

 mations of the lowest practicable loss for practically all intertoll trunks 

 as follows: 

 VNL = VNLF X L + A + B, where: 

 VNL = "Via Net Loss" (db) of the trunk. 

 VNLF = "Via Net Loss Factor;" i.e., a factor which depends on and 

 is appropriate to the type of facilities used in the trunk. 

 L = Length in miles. 

 A = Design allowance for expected variations of circuit loss in 



service (0.4 db). 

 B = Amount to be added if two-wire switching is used; the mag- 

 nitude depends on the passive return loss obtainable on such 

 connections at the two-wire switching office. 

 At each end of the connection a loss of 2 db (/S = 2) is added by ap- 

 propriate means as discussed earlier. 



CONCLUSION 



Let it be emphasized that we have been talking largely of planning 

 for the future in all that has preceded, for the switching plan as outlined 

 is a growing thing and it will be a couple of years before much complex 

 automatic alternate routing is done. And we would be very much sur- 

 prised to escape growing pains and change of ideas as the plan develops. 

 We are confident, however, that the plan is sound economically and 

 transmission-wise; and flexible enough to adapt itself to further de- 

 velopments and experience. 



ACKNOWLEDGMENT 



As in most papers like this it would be prolix to mention all persons 

 who took an active part in the preparation or in the development of the 

 background data. But the author would be remiss if he did not call by 

 name L. L. Bouton, who just prior to his recent retirement from Bell 

 Telephone Laboratories, did much of the basic work on the mathematical 

 concepts involved, on the simplification of these concepts for practical 

 application, and on the re-evaluation of data that was required in 

 these applications. 



