1969-70 Connection Survey: Low-Speed Data Transmission Performance on the Switched Telecommunications Network

Reasons for Measuring Low-Speed Data Performance Measurements of the accuracy of low-speed data transmission over the Bell System switched network have been included in the 1969-70 Toll Connection Survey; the results arc presented in this article. There is widespread use of teletypewriters, computer ports, and other terminal devices that communicate by means of data organized in characters comprised of several bits, using start-stop transmission, at rates up to 300 bits per second (b/s). About 80,000 terminals of this type were being used for Data-Phone® service at the end of 1970. This article presents the quantity and distribution of the character errors and lost characters observed during the low-speed data tests. These results are expccted to meet a need for characterization of the switched telecommunications network for start-stop transmission of 1385 1.1 1386 THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1971 low-speed data. Further analysis of the data is planned to pinpoint causes of errors for which remedial measures would be profitable, to suggest possible improvements in design of transmission equipment, and to indicate possible usefulness of error control systems. The measurements were planned with the objective of characterizing low-speed data transmission performance as viewed by users. The error statistics are reported for channels extending from a transmitting data set, into which an error-free data signal is sent, to the point at the receiving end at which the characters are used or displayed.