The design of an error-free data transmission system for telephone circuits

Recent experimental results verify that easily implemented codes can detect essentially all errors occurring in digital data sent over toll-grade telephone circuits. A 2-way communications system uses these codes, first to find and then to request a retransmission of any data in error. The feedback logic is detailed herein, and the buffer required to adapt the system to various data sources is discussed. Extrapolated experimental results indicate an average delivery rate in each direction of approximately 7/8 the modem (modulation system) bit rate with a mean time to error of several hundred years. The philosophy which guided the design of this system can be applied to other media, where high noise bursts or low signal levels occur infrequently.