GB1164531A - System for a Secure Transmission of Data with Checking at the Transmitting End - Google Patents

Abstract

1,164,531. Digital transmission systems. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. 11 Jan., 1967 [12 Jan., 1966], No. 1459/67. Heading H4P. In a binary transmission system in which errors are corrected by repetition and in which all signals received are returned to the transmitter for comparison with the transmitted signals, stores 141-144 are connected successively to store the transmitted signals, the stores being read out, for the comparison, successively under control of clock pulses derived from the returned signals. Start-stop signals from source 11 are stripped of Start and Stop bits at 121 and pass to the transmitter output 31, via unit 122 which adds Start and Stop bits, and to shift register stores 141-144. Successive signals pass to successive stores by way of switch 13. Clock 171, controlled by the Start bits, steps switch 13 and also cyclic switch 172 which passes clock pulses to the selected store. Return signals at 32 are stripped of Start and Stop bits at 163 and compared at 16 with the corresponding signals from stores 141-144. Clock 181 is controlled by the return signals and provides clock pulses via cyclic switch 182 to read out the stores non-destructively. Switch 182 is also controlled by the return signals. If an error is detected source 11 is stopped, the comparator is inhibited, and subsequent return signals step back switch 13 once for each signal so that, at the end of the return signal sequence, the switch is connected to the store containing the first character to be repeated. The signals stored are now repeated, preceded by a tag signal: the stores are read out non-destructively and pass signals via switch 13 to unit 122. When the tag signal is returned source 11 and the comparator are started again. The receiver includes a delay to ensure that the loop transit time is at least one signal length in duration. The receiver also includes a plurality of stores which are cleared on reception of the tag signal so that signals which are to be repeated do not pass to the receiver output.