Echo Performance of Toll Telephone Connections in the United States

Abstract

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.

A Twelve-Channel Digital Echo Canceler

“…On shorter circuits (under about 2000 miles) it can be satisfactorily controlled by the insertion of loss, but longer terrestrial circuits generally require the installation of echo suppressors [3] , [4] . For satellite circuits with their extremely long echopath delays (about 1/2 s) it appears that echo suppressors are no longer even satisfactory and that echo cancelers [ 5 ] must be used.…”