B.S.T.J. Briefs: Performance of a Forward-Acting Error-Control Systemon the Switched Telephone Network

Performance of a Forward-Acting Error-Control System on the Switched Telephone N e t w o r k By E. J. WELDON, Jr. (Manuscript received March 7, 1966) This brief contains a summary of data taken in the course of a recent error-control experiment. In this experiment data were transmitted over switched voiceband telephone lines at 2000 bits per second using Data-Phone* data set 201A. With the transmitting terminal located at the Holmdel, New Jersey laboratory, connections via the switched network were established to various cities (Baltimore, Cleveland, Dallas, Denver, Louisville, and St. Louis). There a return connection, again via the switched network, was established to the receiving terminal which was also located at Holmdel. Nearly all calls were made during the business day. Errors were corrected by means of a forward-acting cyclic code which was formed by interleaving the (15,9) code generated by x6 + x5 + x4 + 1 to degree i. As a result, (9/15)-2000 = 1200 information bits per second were transmitted. In the first half of the experiment, i was set to 73; in the second half, 200. Since the (15,9) code corrects all bursts of length three or less, the interleaved code can correct all bursts of length 3t or less. Thus, the codes are optimal burst-correctors in the sense that the equality holds in the Reiger bound,1 i.e., , n -- k where b is the guarant eed burst-correcting ability of the code, n is the code length, and k is the number of information symbols in the code. In each case, the i subwords were decoded independently using the Peterson algorithm.2 Decoding in this manner, rather than using the Peterson algorithm to decode the cyclic code of length bi directly, enables the code to correct many error patterns which would otherwise be uncorrectable.