Effectiveness of Error Control in Data Communication over the Switched Telephone Network

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Abstract
This article describes the results of a data communication experiment designed to investigate the effectiveness of error detection and retransmission in providing high-accuracy data transmission over the switched telephone network. Data were encoded into a Bose-Chaudhuri (31,21) error-detecting code and transmitted at 2000 bits per second by a DATA-PHONE data set 201A over a variety of dialed long-distance connections. Transmitted and received data were compared to obtain error data which were analyzed to obtain an estimate of the error performance of the data set and the effectiveness of the code. The results of this analysis are presented. During the test approximately 6.36 × 10 7 31-bit code words or 1.97 × 10 9 bits were transmitted. Of these, 63,002 bits appearing in 29,731 different code words were received incorrectly. Thus, the over-all bit error rate was 3.19 × 10 −5 and the word error rate 4.67 × 10 −4 . The decoder was successful in detecting all but two of the erroneous code words, resulting in an average undetected word error rate of 3.14 × 10 −8 or an average of 9.85 × 10 8 bits between undetected word errors. These results demonstrated that very low undetected error rates can be obtained in practice using an error detection and retransmission system of modest complexity.

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