Patent GB-854718-A (GB)
Title: Improvements in or relating to multichannel communication systems
IPC: H04J3/17
Filed: 1959-02-23
Abstract: 854,718. Multi-channel transmission systems. WESTERN ELECTRIC CO. Inc. Feb. 23, 1959 [April 22, 1958], No.6104/59. Class 40 (4). In a system comprising a plurality of channels connecting geographically-separated points, and in which a switching operation may be required to be effected on these channels simultaneously at both ends, a switching signal is sent from one end to the other which thereupon reverts a verification signal to the originating end, and after a delay corresponding to the time the verification takes to travel to the originating end, effects the switching operation at the receiving end; the switching at the originating end being effected on receipt of the verification signal. The invention is used to switch out TAS1 equipment in the event of its going faulty. As shown, cables 10, 10<SP>1</SP> carrying 36 frequency-multiplexed channels are utilized under normal conditions to carry conversations from 72 transmitting and receiving lines through the use of the TAS 1 transmit and receive equipment 13, 14 in which subscribers, not speaking, may be disconnected from the channel they were using and re-allocated a fresh channel when they recommence speaking. In the event of the near end TASI equipment breaking down, equipment according to the invention connects the first 36 lines through to the 36 channels on a permanent basis and disconnects the remaining 36 lines. Thus when a fault occurs in the TAS1 1 equipment a signal on lead 150 sets the bistable circuit 104 to its "1" condition, the output being fed via AND gate 108 to a timer and repeater circuit 102 which emits 10 ms. pulses at 100 ms. intervals to AND gate 107 which also receives an enabling output from circuit 104 via OR gate 106. The output of gate 108 also operates relay 110 which changes over the connection of the signalling channel (normally used for sending the TAS1 idle speaker disconnect signals) to connect it to the signalling transmitter 117. The latter, enabled by gate 107, sends 10 ms. bursts of switch-out signals, e.g. of the multi-frequency coded type. This signal is decoded in the distant receiver 126 to set the bistable circuit 128 to its " 1 " state. The output from the latter operates the timing circuit 102 via gates 130, 108 and enables gate 107 to cause reversion of the switch-out signal as a verification signal, as described above. The output from circuit 128 is also applied via a delay device 132 to lead 136 which switches out the TASI equipment and permanently connects up the first 36 lines to the 36 channels. The last 36 lines are supplied with a recorded explanatory message. The relays (electronic or otherwise) effecting the change-over are self-locking. The delay of the device 132 is made equal to the signal transmission time for the verification signal which effects change-over at the near end immediately it is received. Thus, at the near end the verification signal sets bi-stable circuit 128 whose output passes gate 131 (since 104 is set) and so by-passes the delay device 132 and is applied to lead 136 to effect switch-over immediately. The signal is also applied via gate 138 to disable the timer circuit 102, and stop the sending of the switch-out signals. Switch-out may be effected manually if desired by setting the bi-stable circuit 104. Switch-in can only be done manually and is effected by operation of bi-stable circuit 104<SP>1</SP>. This operates in a similar manner to circuit 104 to enable gate 107<SP>1</SP> to send a characteristic signal to the far end. There it operates bistable circuit 1281 which initiates the reversion of a similar verification signal, as described above for switch-out and effects switch-in after a delay by energizing lead 137 which unlocks the switch-out relays. Receipt of the verification signal at the near end effects switch-in immediately by the same method. When a switch-in or switch-out signal is sent the output of gate 108 brings up the slow-to-operate relay 139 after 0.5 sec., and this disables the timer and repeater. In the case of the originating station of a switch-out signal, if the verification signal is not received in this period gate 144 is enabled to bring up an alarm and also to effect switch-out at the originating station. In the case of a switch-in operation a lamp 147 is lit when the verification signal is received. Individual switches 23, 27 may be provided for permanently allocating one channel to one line.