Patent GB-849423-A (GB)
Title: Improvements in or relating to synchronising arrangements for ciphered start-stop telegraph apparatus
Inventor: CHITTLEBURGH WILLIAM FRANCIS S
IPC: H04L9/12
Filed: 1958-05-21
Abstract: 849,423. Secret printing - telegraph systems. STANDARD TELEPHONES & CABLES Ltd. May 15, 1959 [May 21, 1958], No. 16273/58. Class 40 (3). A ciphering telegram system using a startstop combination code and comprising ciphering and deciphering arrangements at the transmitter and receiver respectively constituted by a tape bearing random signals in the combination code which, at the transmitting and receiving stations, are combined with the plain text and cipher signals respectively includes an arrangement for continuously counting the number of times the cipher tape at the transmitter is stepped forward, means for stepping forward the cipher tape a predetermined number of steps and an arrangement for transmitting to. the receiver start-stop check signals representing the number of stepping operations which have occurred at the transmitter, whilst devices at the receiving station count the number of times the cipher record has been stepped forward and operate to step forward the tape until the total number of stepping operations at the receiver is equal to that which has been indicated at the transmitter, the stepping device at the receiver being operative solely if the number of stepping operations registered at the receiver is less than the number of stepping operations at the transmitter when the cipher tape thereat has been stepped forward the predetermined number of times. Transmitter arrangement. Fig. 1. The signals from a teleprinter transmitter I are passed to a ciphering arrangement 2 represented by a contact 6 for a stepping magnet 5 for the cipher tape and contacts 3 for passing the ciphered signals to the output terminal 4. The energizing pulses generated by the closure of stepping contact 6 for the magnet 5 are counted by a storage device 10 comprising a number of binary stages, preferably equal to a multiple of the number of information (or significant) units, e.g. five in the code being used. Before commencing or resuming transmission the actuation of a key 12 brings into operation a generator 11 producing pulses at intervals of 20 m.secs. and operating relay 8 to provide stepping pulses for the magnet 5, these pulses being also utilized to step the binary counter 10. After a predetermined number of pulses, e.g. 32, a counter 14 operates: relay 13 so that the pulses from the generator 11  are passed to a prefix signal generator 16 operative to transmit a number, e.g. five, of prearranged characters to the relay 21 and the outgoing terminal 4. At the end of the prefix signal, a pulse over conductor 22 renders the distributer 17 operative in conjunction with pulses from the generator 11 to operate a number transmitter 20 to transmit to the line start-stop signals corresponding to the setting of the counter device 10. After the transmitter 20 has completed its operation, a pulse over conductor 221 stops the generator 11 and restores the elements 13 and 16 to normal. Receiving arrangements. Fig. 2. The incoming signals are passed via a regenerative repeater 24, preferably as described in Specification 808,189, in which the stop element, if lost, is automatically inserted but it is not inserted in consequence of its absence in the case of the long spacing signal, to a deciphering arrangement 2 and to a teleprinter receiver 27. Each received signal closes a contact 6 to operate magnet 5 to step the cipher tape, and each operating pulse is applied over connection 9 to a binary storage device 10. At the end of a transmission the numbers registered on the binary devices 10 at the transmitter and receiver stations will be identical. At the beginning of transmission after the prefix signal and number signal have been sent, the number registered on the storage device 10 at the receiver will normally be less than that set up on the number receiver 33 after the reception of the prefix signal. The received signals operate the repeater 24 to apply pulses over line 29 to the distributer 31 and when the predetermined prefix signals have been received, an output signal at 44 allows the number receiver 33 to be operated to provide selective outputs 35 corresponding to the number transmitted to the receiver. Normally this number will be greater than that registered on the receiver storage device 10, and a comparator 34 provides a pulse setting into operation a generator 37 which produces a pulse operating the relay 8 so that the stepping magnet 5 is energized to step the cipher tape, and at the same time a pulse is applied to step the binary storage device 10. Subsequently the generator 37 produces a further pulse over conductor 45 to effect a fresh comparison, and if inequality is still detected, a further pulse is passed by the generator 37 to step the cipher tape and the binary store 10. The characters forming the prefix signal and the 5-unit code combinations derived from the setting of the number transmitter 20 will effect the stepping of the cipher tape and the corresponding stepping of the storage device 10 at the receiving station, but they do not influence the storage device 10 at the transmitting station. When equality has been detected by the comparator 34 a pulse over conductor 46 stops the pulse generator 37 and restores the prefix signal receiver to its normal or rest condition. If through interference or other causes the cipher tape had been stepped during the interval between transmissions so that the number registered on the storage device was greater than that transmitted by the device 20 of the sending station and registered on the number receiver 33, the comparator 34 passes a signal over line 41 to an alarm device 40 which calls for action by operators at the transmitting and receiving stations to restore synchronism. In the case in which the transmitter storage device 10 is nearly filled, i.e. almost reached its maximum count, the application of the additional steps could complete its full cycle and effectively set up a small number, which at the receiving end would be smaller than the number set up on its storage device 10 so that the alarm device 40 would be erroneously operated. To deal with such cases the storage device 10 at the transmitter has an additional or final stage e.g. a 10th stage, and the first nine stages are utilized to count up to 512, the 10th stage having its condition changed from 0 to 1 or 1 to 0 on the completion of each cycle. The condition of this stage, also transmitted to the receiver and the 10th stage of the storage device 10 at the receiver being different from that of 10 at the transmitter and registered on receiver 33 causes the receiving arrangement to step automatically through the final stage of its complete cycle until the 10th stages of devices 10, 33 are identical and then to continue stepping until equality with the transmitted number is detected. In case the receiver has, through interference, advanced through a large number of steps, but the number registered on the device 10 is less than that on the number receiver 33, stepping will take place until the 10th stages of devices 10, 33 at the receiver are identical, and a counter 42 operates an alarm device 43 after a predetermined number, for example, 64, of steps of the cipher tape. If the long spacing signal is detected by the repeater 24 a potential on conductor 30 operates a relay 28 so that the cipher tape and the device 10 are not stepped. Specification 843,563 also is referred to.