To characterize the transmission performance of the Bell System switched telecommunications network, Bell Telephone Laboratories conducted a survey of toll connections during 1969 and 1970. Connections were established between Bell System end offices chosen by statistical sampling techniques. Both analog and data transmission tests were performed. A summary of analog transmission performance is presented in this paper. It contains estimates for noise, loss, attenuation distortion, envelope delay distortion, peak‐to‐average ratio, frequency offset, level tracking, nonlinear distortion, and phase jitter for toll calls within the Bell System. Accompanying papers discuss data transmission error performance at various speeds between 150 and 4800 bits per second.

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.