Patent GB-499821-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1937-07-27
Abstract: 499,821. Semi automatic exchange systems. SIEMENS BROS. & CO., Ltd., HUMPHRIES, H. E., and HENSLER, 13. A. July 27, 1937, No. 20724. [Class 40 (iv)] In an inter-exchange system employing alternating current of voice frequency for control and supervision, different conditions exist in the terminal circuits at either end of a junction before the called party replies and after he clears, and a recall signal from the originating exchange at any stage of the connection restores the terminal circuits to the condition which existed before reply, so that the same sequence of supervisory signals may be exchanged over the junction as when the call was initiated. In the system described, the receipt of a supervisory signal at a tandem exchange temporarily severs the connection thereat, but in the case of a recall signal, no severing takes place and the signal reaches the final exchange provided no supervisorysignal is being transmitted. A frequency X is used for calling, impulsing and recalling, the calling signal comprising a short pulse and the recall signal a long pulse. A second frequency Y is used for supervision and for controlling release, the reply and clearing signals comprising short pulses and the releasing signal two long pulses. Description is given of calls between a central trunk exchange, (Figs. 1, 2) and outlying exchanges of various types. Incoming call at the trunk exchange, (Figs. 1, 2) completed over local switches. The signal receiver VF includes relays X, Y (not shown) responsive to the two signalling frequencies. A calling pulse of X frequency connects up relays B, BA, BR and advances the marking switch M one step. The latter is then set by numerical impulses of X frequency, the digit being 2 in this case, and the routing switch hunts for an idle outlet in the usual manner. Test relay T connects up S which locks and switches through. Relays AX, AY operate when dialling relay C falls back to extend the junction, which is normally terminated by an impedance YN. Subsequent digits are repeated by relay A, and relay D responds to the reply of the called party, and holds A, AX, AY against the occurrence of X frequency in speech. Relay CT energizes over earth pulse wire TS, transferring the junction to a terminating impedance YS and connecting itself and TN to earth pulse wire AM, and the latter relay sends back pulses of Y frequency. This signal is acknowledged by a single Y pulse, which connects up slow-release relay FL, cutting off the reply signal, and a pair of slow-operating relays Z, ZR, the latter disconnecting FL. Relay AR energizes and locks, and B is held by FL until ZR falls back at the end of the pulse. On the relapse of D when the called party hangs up, relays CT, TN again operate to send a clearing signal of Y puises. A long Y pulse to effect release operates FL, Z, ZR, but in this case FL relapses before the end of the pulse and therefore B falls back, followed by BR, A, AX, AY, and the local switches are released. Relay BA is disconnected by ZR at the end of the pulse and releases S, allowing the marking and routing switches to restore. Relay LR pulls up, releasing AR, and CT, TN operate to transmit Y frequency to busy the junction until the switches are normal. If the routing switch fails to find an idle outlet to the local switches, it hunts over the outlets leading to through positions. If these are all engaged, busy tone is sent in the last position of the switch. Incoming call extended to through or suspense position. The routing switch is set as before, the digit being 1 or 3 respectively. When the call is answered, battery on wire S operates SA, which holds A, AX, AY and connects up SB to change the connections of D, TF. Relay T is held over wire P. The call is set up by the operator, and upon reply D energizes to battery on the + wire and sends back the reply signal, after which AR is operated by the acknowledgment signal. The clearing signal is sent when D falls back, but is suppressed by AS should the speaking key be thrown at this time. The release signal is effective as before, except that S and BA are now held by SB until the operator clears. When this occurs, T falls back and short circuits S, which disconnects SA, SB, HA and allows the switches to restore. If the release signal is received before reply, the supervisory lamp. is lighted by the relapse of BR. The operator at the through position may transfer the call to the suspense position by applying low resistance battery to the + wire to operate TF, which brings about the advance of the switch M to position 4 to reset the routing switch. If this operation occurs after the called party has replied, relay AT prevents the transmission of the clearing signal. A recall signal comprising a long pulse of X frequency operates relay RC which releases AR by short-circuiting and flashes the supervisory lamp over wire S until it is disconnected by AS when the speaking key is thrown. Outgoing call from the trunk exchange. When the junction is seized by the trunk selector, GS energizes in the test circuit. Relay HB prepares backward signalling circuits and LR connects up CT, TN to send a calling signal of X frequency, which is cut off when SP pulls up. Relays SA, SB, BA, AX, AY energize to complete the connection to the junction. The operator sets up the connection by means of a key-sender or communicates with the distant operator. The reply signal consisting of Y frequency pulses operates Z, ZR in turn, and these relays respectively connect up CT to sever the junction and apply battery to the + wire to operate D in the incoming trunk circuit to repeat the signal. At the end of a pnlse, AT energizes followed by AR which maintains battery on the + wire, extinguishes the supervisory lamp and connects up TN, and on the relapse of Z, ZR, an acknowledgment pulse is sent by the release of AT. The clearing signal operates Z, ZR, CT as before, but now, since AR is up, FL energizes and holds between pulses, disconnecting D in the incoming trunk circuit to repeat the signal and lighting the supervisory lamp. The release signal from the originating exchange brings about the release of B in the incoming trunk circuit and high resistance battery on the - wire operates CR, which connects CT, TN in series with SP to app]y Y frequency to the junction. The release of GS by the operator's release key closes a slow-stepping circuit for the switch M, which controls CT, TN to send two long Y pulses and finally disconnects these relays and SP, whereupon the circuit is restored to normal. The operation of the recall key connects low resistance battery to the - wire to operate LR, whereupon AR is disconnected and X frequency is applied to the junction. A recall signal from the originating exchange, in addition to its effect in the incoming trunk circuit, passes over the junction to the distant exchange. Call between two outlying exchanges. This is set up over trunk selectors at either side of the operators connecting circuit, both junctions being used in an outgoing capacity. The severance of the junction by CT when a signal is received thereover prevents any effect on the lamp associated with the other junction. Control of junction. 1f the junction is to be used only in an outgoing or in an incoming capacity, key CK is moved upwards or downwards. Key DK serves to put the junction out of use. Relay FW is concerned with the switch-through of 4-wire repeatered junctions, while relays PC, PCA control the insertion of pads, as described in Specification 499,832. Manual outlying exchange with magneto to working, Fig. 3 ; outgoing call. On plugging into the calling jack CJ, sleeve relay SC lights the engaged lamps at other positions and connects up B, F,T. T. Relay F short-circuits the high resistance winding of SC to light lamp ESL, relay B which is slugged by a condenser QA connects up BR, A, and relay T applies X frequency to the trunk until BR pulls up. The operator plugs into the dialling jack DJ, and dialled impulses are repeated by A as X frequency impulses. In response to the reply signal of Y pulses, slow-release relays Z, ZR operate in turn, severing the trunk, disconnecting F and connecting up N, T until ZR restores to send the acknowledgment signal. Lamp ESL is extinguished when ZR falls back. The clearing signal similarly operates Z, ZR, and the latter holds between pulses and relights lamp ESL. When the operator clears, the relapse of SC disconnects B which falls back very slowly and connects up T to send a long Y impulse until B, BR are back. The engaged lamps are maintained alight by Y frequency until release is complete at the distant end. If the operator clears before reply, F being up, the circuit of B is such that Y frequency is sent for 6 seconds to avoid .blocking by NU tone. To recall the trunk exchange, the operator plugs into the dialling jack DJ and throws key RCK to operate F, T and disconnect A, so that X frequency is sent. Incoming call. The calling X frequency signal operates relay XR, which lights the calling and engaged lamps CCL, ESL. When the answering jack AJ is plugged into, J energizes and connects up H, HR, SA, the last relay disconnecting XR. Relays K, T are now controlled over wires TS, AM which are earthed alternately to send the reply signal of Y pulses. The acknowledgment signal operates Z, ZR, brings about the release of J and terminates the reply signal. A magneto clearing signal from the called party operates M, which connects up K, putting T under the control of pulse wire CM to send the clearing signal. A long Y pulse from the trunk exchange when the operator clears brings about the release of H, HR and the operation of N, which connects up T to send Y frequency to busy the junction until the local operator clears, lamp CCL being flashed. Relay M is also connected up by the removal of the plug from jack AJ, with similar results. If the trunk operator clears before the call is answered,