A multifrequency data set for parallel transmission up to 20 characters per second
Burton R. Saltzberg, R. Sokoler · Transactions of the American Institute of Electrical Engineers Part I Communication and Electronics · 1962
A low-speed data transmission system that permits communication from machine to machine over the telephone network is described. This data set, as part of the general DATA-PHONE service, provides economical data transmission well-suited to data collection of relatively short messages from many transmitters to a single receiver. It transmits alphabetic and numeric characters, asynchronously, using parallel multifrequency signaling techniques. The system has been field tested over a wide variety of telephone facilities with very satisfactory results.