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.
Analog-to-digital conversion is required to terminate voice fre quency loops and analog facilities in a digital central office. We demonstrate the appropriateness of the ě a 255 quantization law for application in a local digital office. We show that the transmission performance for parameters determined by the choice of quantization law can all theoretically meet reasonable objectives with the ě at 255 law. However, the crosstalk coupling loss required of analog plant preceding the digital switch may need to be improved to retain an acceptably low probability of intelligible crosstalk. This improvement in analog crosstalk loss may be obviated by more stringent control of the quantizer bias, by maintaining a minimum noise on the disturbed channels, or by a combination of both of these.
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