1028 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER, 1953 



The slopes of the Imes can be converted into factors (called "via net 

 factors — VNLF) in terms of db per mile by dividing twice the 

 slope by the velocity of propagation in miles per millisecond. The product 

 of VNLF and circuit length in miles plus 0.4 gives VNL. As an example, 

 for K carrier circuits with a velocity of propagation of 105,000 miles 

 per second, the via net loss factor for *S = 2 would be (2 X 0.10) 

 -^ 105 = 0.0019. 



18 



17 



iS 16 



< 



o 



u. 15 

 O 



g 14 



10 



100 



20 30 40 50 60 70 80 

 ROUND-TRIP DELAY IN MILLISECONDS 



Fig. 3 — Approximate relationships between round-trip delay and permissible 

 working one-way loss for an intertoU trunk from echo standpoint for four-wire 

 circuits and four-wire switching. 



