On the Use and Performance of Error-Voiding and Error-Marking Codes

In contrast to payroll or inventory data, which must reach the recipient in its entirety, there is another class of data that includes radar-tracking 1273 1274 T H E B E L L SYSTEM T E C H N I C A L J O U R N A L , OCTOBER 1966 data, remote-sensory data or control data, etc., for which the requirement of completeness is not so stringent. The distinction between these two classes of data is fundamental in the classification of customer requirements in data transmission and the selection of appropriate errorcontrol methods. If the complete data message is required at the receiving station then error control must either be carried out by error detection and retransmission or by forward-acting error correction. Of these two methods the former is the more economical to achieve low error rates. However, if completeness of the transmitted message is not essential and receipt of say 99.9 percent would be satisfactory, then very inexpensive error-voiding techniques may be employed to achieve the desired low error rates. With these techniques an error-detecting code is used to detect and then void (or mark) all detectable errors. If lower void rates are desired some error correction may be introduced and the remaining error-detection capability of the code used to void or mark errors. In order to evaluate these error-voiding methods, the error rates for such codes are estimated in this paper using the error statistics of the Alexander-Gryb-Nast study. 1 Data for which completeness is an important requirement would include payrolls, inventories, orders, sales and banking records, etc.