GB888983A - An arrangement for transmission of information without errors - Google Patents

Abstract

888,983. Type printing telegraphy. STANDARD TELEPHONES & CABLES Ltd. Oct. 21, 1960 [Oct. 22, 1959], No. 36214/60. Class 40(3). In a telegraphy system in which a transmitter transmits characters in a code permitting error detection at a receiver, the characters are stored in groups at both the transmitter and receiver and the ordinal number of any incorrectly received character is recorded in an error store. After the transmission of each group of characters the receiver causes the transmitter to re-transmit at least the characters in which an error was detected, these characters, if correctly received, replacing the original incorrect characters. In a first embodiment, Fig. 1, a complete group of characters is re-transmitted when an error is detected. At the transmitter, signals from a teleprinter 11 are recorded in a store 12 from which the code signals are read out by a scanner 13 and passed to a transmitter 14, whence they pass via a switching unit 15 and are transmitted. At the receiver, the signals pass through a switching unit 55 to a receiver 54 which feeds an error detector 56 and a store 52. If an error is detected the position number N of the incorrect character in the group is recorded in an error store 57. When a complete group has been received, indicated by the reception of a special signal, units 15, 55 are switched. Unit 61 then detects the presence of a signal in the error store 57 and a return transmitter 59 transmits a rerun request to the transmitter, whereupon units 15, 55 are returned to their original state and the complete group is retransmitted. When the retransmitted signals are received only those characters which were previously incorrectly received are passed to the store 52, where they replace the incorrect characters. This procedure is repeated until the complete group of characters is correct, whereupon the stored characters are passed from the store 52 to the printer 51 under the control of a scanner 53. In a second embodiment, Fig. 2 (not shown), only the characters in which an error has been detected are retransmitted. The circuitry is substantially similar to that of Fig. 1 but includes a scanner at the receiver for scanning the error store to cause the return transmitter to request repetition of particular characters, and a scanner at the transmitter for extracting those characters from the store for retransmission. Two stores may be provided at the receiver so that, alternately, one is receiving characters while the other is connected to the printer for printing the information stored in it.