Patent GB-496905-A (GB)
Title: Telephone systems
IPC: H04Q3/00
Filed: 1937-10-22
Abstract: 496,905. Exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Oct. 22, 1937, No. 28866. Convention date, Oct. 29, 1936. [Class 40 (iv)] In long distance working, a toll position capable of extending an incoming toll line to a further toll line or to a switching trunk is provided with a discriminating circuit which in accordance with the character of the incoming and outgoing lines, e.g. voice frequency signalling, ring-down, key impulsing, determines the nature of the supervision and modifies the circuits accordingly. When the incoming line is of voice frequency signalling type, supervisory signals either pass directly between the terminating exchanges or are relayed at the tandem exchange, and only the disconnect signal is effective at the tandem exchange. When a voice frequency signalling line is connected to a composite signalling line, a signal is sent forward to the second tandem exchange to modify the circuits thereat for the direct passage of supervisory signals should the third toll line be of voice frequency signalling type. Call over a toll line with voice frequency signalling between office No. 1 and office No. 2. The line terminates in similar equipment (Figs. 6, 7) at each end, only that at office No. 2 being shown in detail. Forward signals consist of current of 1400 cycles modulated at 15, 25 or 35 cycles, while backward signals consist of current of 1000 cycles similarly modulated. The reception of each signal is acknowledged by a return signal which cuts off the original signal. Plugging into jack 505, Fig. 5, transmits a connect signal of 1400 x 25 cycles over line 513 to a receiving circuit 606, which may be of the kind described in U.S.A. Specification 1,860,446, and which grounds one of wires 607-609 in accordance with the modulation frequency. Relays 610, 619 operate and connect up 703, 714, and a return signal of 1000 x 15 cycles is sent. Relay 714 marks the toll line busy, and by grounding wire 734 extends the line over primary and secondary cross - bar distributers, Fig. 9, to an idle plug circuit, Fig. 10. An attenuation pad 600 is cut out by the relapse of 631, which, however, reoperates if the outgoing line is a local one and replaces the pad. Relay 1006 operates over wire 912, lights lamp CN and connects up 1108 to busy the position circuit, Fig. 11. The relapse of 619 on the cessation of the connect signal connects up start relay 1013 over wires 736, 930, and the operation of 1104 prevents any other start relay from energizing. Relays 1100-1103 and 1127 are operative when the operator's set is plugged into jacks 1163, 1164, and change-over switch 1027 is in the position shown when the incoming line is of the voice frequency type. Start relay 1013 connects up 1001, 1012, the former connecting the operator's set to the incoming line and to plug 1024 and the latter flashing lamp CN. Relay 1130 operates to send back three bursts of challenging tone, which are also heard by the called operator. Extension to a key impulsing trunk, Fig. 21A. The operator inserts plug 1024 in jack 2101, relays 1009, 1010, 2107 energize in the sleeve circuit, and the last relay associates a sender with the trunk 2102. Relays 1004, 1005 energize and the former connects up 1003, which locks in series with 1328 and extends plug 1024 to the discriminator, Figs. 12, 13. Relay 1328 connects battery to the ring of the plug through 1330, which pulls up provided the plug is properly seated and through 1329 disconnects 1202. The latter relay, which is connected up by 1328, starts a timing switch 1207 arranged after an interval to dissociate the discriminator. Relay 1324 extends the ring and tip over wires 1243, 1250 to ground through marginal relay 1325, which is inoperative in this instance, and 1221 operates to transfer these wires to battery through marginal relays 1226, 1331 and 1219, 1220, 1326 respectively, while 1327 again starts timing switch 1207. In the case of a key impulsing trunk, the tip is open while the ring is directly grounded, so that 1226, 1331 energize and connect up 1227, 1332, which make a circuit for 1237 dependent on 1224. Since the incoming line is of voice frequency type, 1232 operates as will be described later, but without effect, since no change in the supervisory circuits is necessary. Relay 1237 prepares the keyset for operation, and when the wanted connection has been set up, cut-off relay 1225 operates, connecting up 1002, which locks under control of 1004, and bringing about the release of 1003, 1328 to dissociate the discriminator. By means of release key 1124, the operator connects up 1011, which locks, disconnects 1013 and prepares a supervisory circuit for 704. Relays 1001, 1012 fall back, completing the talking circuit, extinguishing lamp CN and putting lamp 1057 under control of 1008. Upon reply, 2110 pulls up and disconnects the low resistance winding of sleeve relay 2107, so that marginal relay 1009 operates and releases 1005, which connects up 704 over wires 921, 739. Relay 704 sends back an offhook signal of 1000 x 35 cycles, which increases the resistance of the sleeve circuit at office No. 1, thereby extinguishing lamp 506. Any change in the condition of 704 starts a timing switch 712 and disconnects 707, so that 630 pulls up and extends the signal to the incoming line. The return signal of 1400 x 15 cycles grounds wire 607, which is extended at the proper time by switch 712 to re-operate 707 and release 630. When the called party hangs up, 1005 energizes and disconnects 704 to send an on-hook signal of 1000 x 25 cycles, 705 being up. A flashing signal is sent in the form of alternate on-hook and off-hook signals. A recall signal of 1400 x 25 cycles from office No. 1, like the connect signal, operates 619 which unlocks 1011, and start relay 1013 reconnects line 513 to the operator's position, lamp CN being flashed. A disconnect signal of 1400 x 35 cycles operates 700 and brings about the release of 714, the distributers restore, and a return signal of 1000 x 15 cycles is sent by 703. Relay 1006 falls back and connects up 1008, which lights lamp 1057 and opens the sleeve circuit. When plug 1024 is removed, increased potential across a discharge tube 1063 causes it to break down and make a release circuit for 1008, which is differential. Extension to a busy back circuit, Fig. 21. The operator plugs into jack 2114, whereupon sleeve relay 2116 energizes and connects an interrupter to 2117 to bring in the low resistance winding of 2116 intermittently. Marginal relay 1009 responds and sends back a flashing signal as described above. The discriminator is associated and is at once restored since none of the marginal relays connected up by 1221 operates. The operator dissociates her set by means of key 1124. Extension to another toll line with voice frequency signalling, Figs. 14, 15. On plugging into jack 1401, sleeve relay 1402 energizes, followed by 1403, 1411. An attenuation pad 1437 is cut out by the relapse of 1435. The tip of plug 1024 is now connected to medium resistance ground through relays 1420, 1435, while the ring is connected to high resistance ground through rectifiers 1406 and relays 1414, 1435, with the result that in the discriminator 1219, 1326 energize over the tip and connect up 1210, 1312, which make a circuit for 1200 dependent on 1224. Since the incoming line is of the voice frequency type, 1232 energizes over wires 1147, 1053, 926 in series with 713 (inoperative) and connects up 1228. Relay 1233 now pulls up and applies booster battery to wire 1147 to operate 713, which grounds wire 736 to hold 1011 and thereby lock out the operator. At the same time, booster battery is applied over wires 1253, 1243 to the ring to operate 1414, which disables 1424, 1507 so that backward signals will have no effect at office No. 2. Cut-off relay 1225 pulls up shortly after 1200. Returning to the seizure of the outgoing line, 1411 brings about the operation 1417, 1412, of which the former marks the line busy and adapts the circuit 1425 for receiving 1000 cycle signals, while the latter sends a connect signal of 1400 x 25 cycles, which causes the extension of the line to an idle plug circuit at office No. 3. The signal is cut off by 1513 which energizes as soon as switch 1528, started by 1512 when the line was seized, picks up ground on wire 1455 applied by the return signal of 1000 x 15 cycles. The operator at office No. 3 sets up the call, and offhook and on-hook signals pass directly to office No. 1 and control lamp 506. A recall signal from office No. 1 passes directly to office No. 3. Relay 619, however, responds to this signal and applies booster battery to the tip to operate 1420, but this produces no effect since 1414 is up. A disconnect signal of 1400 x 35 cycles is effective at both offices as described above. Extension to a ring- down toll line, Fig. 16. The operations upon seizure of the line will be described in a later paragraph. Backward signals are relayed through office No. 2 as in the case of a key impulsing trunk. In this case, however, since 713 is up, the operation of 619 in response to a recall signal from office No. 1 applies booster battery to the tip to operate 1620 to re-ring the outgoing line. A ring-back signal from office No. 3 is relayed in a manner will be clear from a later paragraph and lights lamp 506. The operator at office No. 1 comes in by means of key 516. Call over a ring-down toll line between office No. 1 to office No. 2. The line terminates in similar equipment (Fig. 8) at each end, only that at office No. 2 being shown in detail. On plugging into jack 521, 20 cycle ringing current superimposed on 1000 cycle current is transmitted under control of a ringing key. Relay 827 responds, marking the line 524 busy and initiates its extension to an idle plug circuit as in the case of line 513. When the plug circuit, Fig. 10, is serving a ring-down toll line, switch 1027 i