Patent GB-592333-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1945-05-19
Abstract: 592,333. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., and BEALE, C. E. May 19, 1945, No. 12678. [Class 40 (iv)] In a system for setting up long distance calls over at least one voicefrequency junction, the general arrangement of which is similar to that described in Specification 584,677, the simulation or mutilation of setting impulses by speech currents is prevented by ensuring that the equipment which responds to setting impulses is in a responsive condition only when. the setting operation is taking place. Subscriber dialling is permitted and the outgoing relay set includes a mechanical impulse regenerator which transmits a 250 ms. compound signal of X and Y frequencies to condition the receiving equipment, prior to X frequency numerical impulses, after which it transmits a 100 ms. Y frequency pulse to restore the receiving equipment to an unresponsive condition. All the facilities provided by the system of Specification 584,677 are included, and the signals employed are the same with the exception of those mentioned above. Outgoing relay set, Figs. 1-8. On the seizure of the junction from a selector level for a call which has not already made use of a V.F. trunk line, the incoming loop energizes relay A which brings up B, holding relay BZ, BB, CC which cuts out a loss pad, and CZ, while SP and SX energize momentarily under control of CS to send out a seizing signal of X frequency for 80 ms. During dialling A responds to loop impulses and repeats them to the magnet RM of a regenerator, which is of the type described in Specification 458,095, while relay C is operated, energizes SC, and disconnects the speaking leads. At the end of the impulse train C releases and brings up BY which prepares the transmit circuit of the regenerator, disconnects SC, and operates SP, SY and SX to send a compound conditioning pulse. Relay SC releases after its slow period, and brings up TY, holding SP and releasing SX and SY to terminate the pulse. The regenerator then re-transmits the stored digits as pulses of X frequency of 70 ms. duration, after which BY falls away followed by TY, during the slow release period of which SP and SY are again momentarily energized to transmit a Y frequency pulse to render the impulse responding equipment again insensitive to X frequency currents. If a prolonged pause is made during dialling such that the regenerator discharges all stored digits, BY will fall away and the reconditioning Y frequency pulse will be transmitted, while the re-operation of BY when dialling is resumed will cause a fresh conditioning pulse to be transmitted. On the reply of the called party a reply signal similar to that in Specification 584,677 is sent back and produces a similar result ; acknowledgement being sent under the control of switch TT, relays SP, SX and SY being operated in positions 2, 3 and 4 of the switch, and SP and SY in position 6, the signal being repeated if necessary. Assuming that the calling party clears first, the relapse of A, B, BB and MA brings up SR, which starts the switch TT to send the clear forward signal, and when the called party hangs up the release signal is received during the interval when TT is beyond position 5. Relay RY is maintained sufficiently long to release the holding relay BZ, whereupon the equipment restores to normal, the busy guard being maintained by CZ. On the other hand, if the called party clears first, RC and RY respond to the clear back signal and energize FA, FB and FC, while MA falls back lighting the supervisory lamp. At the end of the signal FA, FB and FC are disconnected, but before FC falls away FA and FB are reoperated by the next signal and maintain FC. When the calling party clears, the clear forward signal is sent during the intervals of the clear back. The called party may recall a clearing operator by flashing, as in Specification 584,677. A calling operator may send a special signal for trunk offering, forward transfer or re-ringing by unbalancing the line. Differential relay DF responds, followed by TO which starts the switch TT to send the ring forward signal, which is repeated until it is acknowledged, whereupon RY responds to release TO and stop TT in its next home position. In the case of re-ringing after the called party has hung up, however, i.e. with MB and FC operated and clear back being received, operation of DF brings up RK, and when RY responds to the next clear back signal RF operates, starting TT to send the ring forward signal, as before, which is repeated until acknowledged by the lengthening of the interval in the clear back signal, which effects the release of FC and RF, whereupon TT homes and the forward signal is terminated. If the relay set is taken into use over the conductors ATT for the extension of a call which has come in over a V.F. trunk, TR energizes over the incoming loop, brings up CS, SC and BZ and causes the seizing signal to be sent. Operation of CZ terminates this and energizes TS, TSR to switch through and cut out the loss pad and BY to send the compound conditioning pulse, after which BY falls away, but no circuit is made for sending the Y frequency terminating pulse, which is in fact sent from the regenerator on which the digits were originally stored. Relays A, DF, RX, MB and SR are disabled and incoming V.F. pulses pass straight through the relay set which responds only to the long release signal. If the trunk associated with the outgoing relay set is open circuited the reception of a release signal is impossible, so release is effected, independently of the release signal, by a thermostat relay TH connected up in parallel with SR which initiates the clear forward signal. Relay TH energizes after about 10 seconds and brings up RY which remains up long enough to effect the release of BZ. Incoming relay set, Figs. 10-15. In response to the X frequency seizure pulse AX connects up ABZ, ACC, ASS, ARAA and AGP, AI energizes over the forward loop, and ANN pulls up at the end of the signal. On receipt of the conditioning signal AXY operates, releases ACC, and brings up ASG, which inserts a loss pad in the line, AST, and, at the end of the signal, ASI. Numerical impulses are repeated by AA over the loop, while AH controls AC, ACA and ACAR to maintain the impulsing conditions. At the end of the impulsing the reception of the Y frequency pulse by AX results in the release of AST, ASI and ASG, AA and AH being disconnected to render the set unresponsive to X frequency pulses. The response of AD to reversed battery when the called party replies connects up ADD and APX, the latter relay bringing up ASG and starting the switch ATT to send the reply signal which is repeated until acknowledged, whereupon, when ATT is beyond position 5, operation of AXY releases ACC and brings up ARC and ARY, so that ARAA falls away. On the release of ARY at the end of the signal, ARC relapses bringing up ACC and releasing APX, so that ATT homes to terminate the supervisory signal. The transmission of the clear back signal when the called party hangs up, recall of the operator by the called party, and release when the calling party also hangs up are as described in 584,677. Further, if the calling party clears first AHR connects up APZ at once to effect release independently of the called party. The ring forward signal may be used in the face of busy tone to break in on a busy line in which case AACK operates, starts the switch ATT to send the acknowledgement signal, and with terminals 24 and 25 strapped feeds earth forward to produce the cut in facility. If the ring forward is sent for re-ringing APY and APYR are already up and ATT is beyond position 5 so that ALI, ALIR are connected up to produce the lengthening of the interval in the clear back signal as in 584,677, APY releasing on the reply of the called party to terminate the clear back signal. Seizure of a short circuited trunk effects the release of ASS to open the forward loop, and ensure response to the clearing signal. If the group selector switches through to an outgoing relay set over conductors ATT (Fig. 1), AD responds to the momentary reversal of current over TR after AC, ACA have relapsed, and brings up ATS which makes the relay set responsive only to the release signal which causes ABZ to fall away, while ANN holds up to maintain the loop until the release signal terminates.