Checking the Accuracy of Data Transmission
Tracy L. Thompson · ITNOW · 1968
It is well recognised that, in transmitting data from local recording stations to a central computer, it is all important to impose a tight checking system that will reveal any corruptions that may have occurred during transmission. The great expansion in the volume of data which are now being transmitted, and the expectation of even greater expansion in the near future, has focused attention on the necessity of improving transmission line quality, which should eventually result in a substantial reduction in the incidence of corruption. However, whatever degree of improvement in quality may be achieved, there must always be the possibility of occasional corruption, so that some precautions must be taken to detect when this has happened and ensure retransmission. The problem is to devise a system which will give adequate protection with a minimum proportion of redundant signals transmitted. With the international standard 8-element codes, one element provides odd parity for each character, and a customary arrangement is to build up a redundant character for each block of data by feeding the bits in each element position of all characters into the corresponding position of a check counter. The parity bit for each character involves a redundant transmission to the extent of 14·3 per cent. to which must be added a percentage for the extra check character for each block. Although this may not seem unreasonable in the circumstances, the question does arise as to whether adequate protection can be ensured without transmitting the parity element for every character.