Echo Performance of Toll Telephone Connections in the United States
F. P. Duffy, G. K. McNees, Ingemar Nåsell, T. W. Thatcher · Bell System Technical Journal · 1975
A field survey to characterize echo performance of toll telephone connections was conducted in 1972. Information on echo path loss and echo path delay for talker echoes was obtained from a sample of nearly 1700 connections in the continental United States. This paper discusses the survey data acquisition techniques, the sample design, and the statistical results. A major result of the survey was the determination that echo path delay is significantly less than previously estimated. For the longest connections (2700 miles or 4345 km), the median round-trip echo delay is 45 ms, 11 ms less than previously calculated from the sum of connection segments.