Patent GB-584677-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q1/446
Filed: 1944-05-05
Abstract: 584,677. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., BEALE, C. E., and HOPLEY, H. E. May 5, 1944, No. 8492. [Class 40 (iv)] In a system in which an operator sets up longdistance calls over at least one voice-frequency junction provided at each end with converting equipment, the supervisory signals consist of a constant-length prefix of combined frequencies followed by a characteristic suffix, the signal being repeated until an acknowledgement signal is received in the interval betweer repetitions. The clear-back signa when the called party hangs up lights the supervisory lamp, but if he takes down his receiver again ir order to recall the operator, the interval between repetitions is lengthened with the effect of flash ing the lamp. A ring-forward signa applied by the operator in order to re-ring the called party is acknow ledged by a lengthening of one interval of the clear-back signa which continues until the party replies. The ring-forward signa may be employed to control initia ringing and also to effect trunk offering or forward transfer when the wanted party is busy. The interval between signal repetition is different for the two direction to avoid possible masking of signals in opposite directions. Outgoing relay set, Figs. 2-7 The seizure of the junction by an operator results in the operation of sleeve relays M, MM, holding relay BZ, relay CC which cuts out a loss pad and relay CZ, while relay SX, SP energize momentarily under the control of CS to send a seizing signal of X frequency for 80 ms during which time the stopper valve SV is disabled to prevent backward transmission. During dialling, relay A responds to loop impulses and repeats them over the junction a impulses of X frequency, and afte the dialling key is restored, relay LR energizes over the sleeve switches through and again disable the valve SV. The reply signal consists of a prefix of frequencies X, Y for 250 ms. followed after 35 ms. by X frequency for 80 ms., the signal being repeated after 600 ms. Relay XY responds to the prefix, disconnects CC and energizes RC which holds during the space, so that RX responds to the X frequency and connects up ACK, MA, MB, the supervisory lamp being dimmed. Relay ACK starts the switch TS to send an acknowledgment signal comprising the compound prefix followed by Y frequency which cuts off the reply signal, relays SC, SY being operative in succession as TS goes to its next home position. If this signal fails to get through, the repetition of the reply signal reoperates ACK and causes its repetition. Assuming that the operator clears first, the relapse of M, MM brings up SR which starts the switch TS to send the clear-forward signal comprising the compound prefix followed by Y frequency, the signal being repeated after 700 ms. if the conditions remain the same when TS reaches its next home position. If the signal is effective, however, the release signal is received during the interval when TS is beyond position 5. This is the same as the clearing signal except that the Y frequency is prolonged for 600 ms. and therefore the operation of RY after that of RC releases holding relay BZ, whereupon the equipment restores to normal, the busy guard being maintained meanwhile by CZ. Assuming on the other hand that the called party clears first, RC, RY respond to the clear-back signal which is the same as the clear-forward signal and energize FA, FB (since M, MM are up), and MA falls back, lighting the supervisory lamp. At the end of the signal, FA relapses and energizes FC which reconnects FA and holds dependent on FB, until the signal is repeated after 600 ms. when a fresh circuit is made for FB, all these relays being slow-to-release. When the operator takes down, the clear-forward signal is sent during the intervals of the clear-back signal, since TS cannot move until RC is back, the latter signal then being replaced by the release signal. If the called party removes his receiver again in order to recall the operator, the interval between repetitions of the clear-back signal is increased sufficiently to release FC, which re-operates MA and produces flashing of the supervisory lamp. The ring-forward signal consisting of the compound prefix followed by X frequency is used for controlling initial ringing when necessary and for re-ringing when the called party has cleared. Assuming that it is used for the latter purpose, relay RR responds to the actuation of the ringing key and operates RK, since FC is up, and the next repetition of the clear-back signal energizes RF; which, when RC falls back, starts the switch TS to send the ring-forward signal. This is repeated until it is acknowledged by a lengthening of the interval between repetitions of the clear-back signal which effects the release of FC, RF. Relay TZ ensures that no further signal is sent even if the ringing key remains actuated. Relay MA re-operates and dims the supervisory lamp when the clear-back signal is stopped by the reply of the called party. In the case of initial ringing, MB is back as no reply signal has been received, and RR operates TO which causes the ring-forward signal to be sent at once and releases in response to an unrepeated acknowledgement signal of the compound prefix followed by Y frequency. The same signal may be used for trunk offering or for forward transfer when the called party is busy. When the outgoing relay set is seized from a group selector on a tandem call, relay TR energizes over the incoming loop, connects up TSR, BZ and causes the seizing signal to be sent. Relay TSR in conjunction with LR switches through, and no further signals can be transmitted since all the relays controlling the switch TS are made ineffective. Moreover, the relay set cannot respond effectively to any signals except the release signal of which the Y frequency suffix is long enough to release BZ. Incoming relay set, Figs. 9-12. The X frequency seizing signal energizes relays ABZ, ACC, AGP, ASS, ARAA and at the end of the signal ANN pulls up and completes the forward loop in which AI operates. Numerical impulses are repeated by AA over the loop and by AH to dialling relay AC which controls ACA, ACAR, ASG, the last relay inserting a loss pad. Moreover, the first impulse of each train operates AG quickly by discharge of a condenser AQB in order to split the line. If any selector switches through to a short-circuit, the opening of the forward loop by ASS ensures response to the clearing signal. The response of relays AD, ADD when the called party replies connects up APX, ASG and the switch ATS is started to send the reply signal comprising the compound prefix followed by X frequency which is repeated until an acknowledgment signal having a Y frequency suffix is received. This arrives when ATS is beyond position 5 and results in the release of APX, ARAA. The release of AD, ADD when the called party hangs up therefore connects up APY and the switch ATS sends the repeated clear-back signal having a Y frequency suffix. If, however, the called party removes his receiver again, the re-operation of AD, ADD connects up ALI, ALIR which release APY when ATS reaches its next home position, whereupon ALI, ALIR relapse in turn and reconnect APY to restart the signal. The interval between repetitions is thus increased and the supervisory lamp is flashed as described above until the called party keeps his receiver off the hook. When the operator clears in response to the clear-back signal, the clearforward signal received with ATS beyond position 5 operates ARY which releases APY and connects up AHR. Relay APZ energizes in the home position of ATS, disconnects holding relay ABZ to initiate release and restarts the switch to send back the release signal in which the Y frequency suffix is lengthened to 600 ms. If the operator clears first, AHR connects up APZ at once. The ring-forward signal which has an X frequency suffix results in the operation of AACK which; if no clear-back signal is being sent, starts the switch ATS to send the usual acknowledgment signal. If initial ringing is controlled by the operator, terminals 31, 32 are strapped and AACK feeds earth forward to unbalance a differential relay. The same signal may be sent in the face of busy tone to break in on a busy line or, alternatively, if terminals 31, 33 are strapped, to transfer the call to a manual board by the operation of AFT. In the latter case, supervisory signals are controlled jointly by the speaking key at the manual board and by the called party, a clear-back signal while he is rung being replaced by a reply signal when he answers. If the ring forward is sent for re-ringing instead of initial ringing, it takes effect when APY is up and ATS is beyond position 5, since the clear-back signal is being transmitted, and therefore connects up ALI, ALIR which, as described above, cause a lengthening of the interval before the clearback signal is repeated. Upon the reply of the called party, the clear-back signal is terminated by the release of APY. If the group selector switches through to an outgoing relay set, relay AD responds to a momentary reversal owing to the connections of relay TR, Fig. 2, after AC has relapsed and connects up ATSR which makes the relay set unresponsive to all signals except the release signal of which the Y frequency suffix is long enough to release ABZ. Relays ANN, ASS remain held as long as the release signal lasts to allow it to pass back to the originating exchange. The feature of through V.F. signalling in tandem calls forms the subject of Specification 584,725.