Patent GB-532896-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/58
Filed: 1939-08-15
Abstract: 532,896. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., LONG, D. P., DURKIN, E. W., and PETERS, C. L. Aug. 15, 1939, No. 23560. [Class 40 (iv)] In a system with tandem satellite and subsatellite offices a call received at a tandem satellite from the central office causes a junction to the sub-satellite to be seized, subsequent digits being repeated to the sub-satellite and recorded in discriminating apparatus at the tandem satellite to determine whether the junction shall be held or dropped. In the case of calls originated at a tandem satellite the discriminating apparatus on receiving the local first digit,.which is shared with the sub-satellite, causes the main office junction to be dropped and a junction to the sub-satellite to be seized, one or more subsequent digits being repeated over the latter junction as necessary. Discriminating arrangements for incoming calls are associated with a both-way junction circuit, the same discriminating switch being used on outgoing calls for controlling time and distance metering, a separate wiper being provided for each area and being selected by the initial digit, the position of the wiper after one or two further digits determining the charge rate. The discriminating apparatus for locally originated calls is associated with a finder-group selector link, the apparatus being basically the same at all the offices of the system, and adapted for its particular situation with the aid of jumper connections. It also causes forcible release and single metering of local calls. The discriminator associated with the outgoing end of the junction in calls between a sub-satellite and its tandem satellite also produces single metering and forcible release. The discriminators also act as markers. The invention is described with reference to a network having a numbering scheme as shown in Fig. 1. The apparatus at the exchange is in 50 line units each of which comprises in addition to the line circuits, finder-group selector links, final selectors and both way junction equipment. Up to four units may be used all the group and incoming selectors working on the same multiple. Call-finder, Fig. 6. Line relay SL, Fig. 4, completes a circuit for the first of a group of assigning relays AA-AG and this extends the starting circuit, via a high-speed test relay AT, to the starting circuit of the first link. If this link is idle AT pulls up, locks AA and prevents the operation of AB. Otherwise AB pulls up and the second link is tested and so on. ST in the selected link completes circuits whereby the finder hunts under control of a high-speed test relay HF which on operating removes a short-circuit via a rectifier MRA from the right-hand winding of A which then pulls up energizing B and C. ST then falls and A is held over the loop and its left-hand and middle windings. Permanent loop relay PG in the line circuit operates over the test wire in series with a holding winding of SL to cut off the line winding of the latter and AT falls back. Seizure of junction towards central office. If the apparatus is at a satellite, T14 is jumpered to T8 and, on the operation of ST, junction positions are marked in bank S9. of the group selector and the latter hunts under control of HS. T3 is in this case jumpered to T4 to cause the right-hand winding of A to be short-circuited via rectifier MRB until a junction has been seized. Discrimination at originating office. Switch CS in response to the first digit energizes LC, CT when C falls back, if the call is or may be a local one and then advances automatically to its second starting position 12 in which C is re-operated and provided HS is operated, releases LC. If the circuit is at the central office HS has not been operated, and the group selector is driven to a blank position marked over T17, T18 between the junctions and the final selectors under control of HS. At an ordinary satellite the operation of LC releases the previously seized junction and the group selector is not stepped. Otherwise the operation is similar. At a tandem satellite the central office junction is released and the group selector hunts for an idle junction to the subsatellite, these junctions being marked in bank S9 via terminal T11. At a sub-satellite, since the call may be for the tandem satellite the junction is held over the early terminals in bank CS6 and a circuit is made over T8 and strapped contacts in bank CS1 to prevent the release of HS. In response to the second digit, the switch CS acts as a marker in the central office and ordinary satellite apparatus. In the tandem satellite and sub-satellite the second digit is repeated over the junction and if it indicates a local call LC is re-operated, the junction is dropped and the group selector hunts for a final selector in the group marked by the control switch. When a final selector has been seized, H switches through, A and B fall back and the control switch goes home. Failure of LC to operate after one or two digits as the case may be causes a circuit to be made on CS2, T7 to operate the switching relay H at satellite offices. At the central office, the group selector first hunts for a junction in the group marked by CS in response to the first digit. Final selector, Fig. 7. This is a 25-position 50-line switch connected to serve lines 11 to 10, 21 to 20, 91 to 90, 01 to 00, 75 to 79 and 85 to 89. On the seizure of the switch line relay A, dialling relay C and release relay B are operated. The first digit is repeated to the stepping magnet SM via relay C (ii) and to relays P, Q, which are organized so that an odd digit leaves them both energized to connect up the lower set of wipers of the final selector, an even digit leaving them both de-energized. When C falls at the end of the train the ring trip relay TR is operated. If the first digit is 1, 2, 7 or 8, the selector remains stationary, if 9 it is driven automatically in a circuit over wiper 7 to contact 17 over which C is re-operated, if Q, P being de-energized, it is driven to contacts 18. The first impulse of the second digit, which is repeated to the magnet SM as before, also energizes S. At the end of the digit C and TR fall back in succession to make a fleeting test circuit. If the line is idle H pulls up and releases S. By this means a short burst of continuous ringing current is sent out and then intermittent ringing current via TR (ii). When the called party replies TR switches through and D reverses the line-relay connections. If H fails to operate, busy tone, which is connected up on the operation of S, continues to be sent back. P.B.X. final selector. As shown, the odd tens are used for P.B.X. groups and the terminals of these except the last of each group are earthed in bank 8. If the first line is busy, PX pulls up on the relapse of TR in series with SM which also pulls up. PX re-operates TR whereupon PX and the magnet fall. Interaction continues in this way until H pulls up on an idle line or the last line is reached. Two-way working over junctions, incoming selector. Discrimination at tandem office. The basic circuit shown in Fig. 8 is used for both sets of junctions at the tandem offices but the jumpering between the bank DS2 of a discriminating switch and terminals T3, T4, T5 and T7 is different. It is used also at the other offices with modifications of the jumper connections between terminals T1 .. T11 and banks DS2, DS3. In outgoing calls CO is operated by the impulse relay A when the circuit is seized and cut off the incoming apparatus. Relays B, C also operate and the circuit acts as a repeater, relay CA improving the impulse repeating circuit during each digit, and to control metering as described below. Incoming calls energize AA, HB, B and C. AA repeats the digits to magnet DSM and at the end of each, ground is connected to wiper DS2. At the control office, terminals in bank DS2 corresponding to local first digits are connected to T3 so that L now operates and locks, and since T11 is grounded causes JSM to drive the incoming selector to the position before the local final selectors in which TA is energized over JS9. Operation of L also causes the control switch to be driven to position 13 in readiness for the next digit. In this position of DS, C operates a releasing winding of L which releases TA. The second digit is now received and DS marks the final selector group and operates DC with or without wiper-changing relay WS. The switch JS then hunts in the wanted group under control of TA which in due course energizes H to switch the junction through and is then released. Relays AA, B, DC also are released and the control switch goes home. If the first digit indicates a junction call, earth on wiper DS2 is extended to T5 or T6 to operate DC with or without WS and the switch JS hunts in the junction group marked in banks JS9, JS10, by wiper DS3. In the case of individual satellites the first digit marks a final selector group in all cases. In the case of intermediate satellites the arrangement differs according as the junction is from the central office or from the subsatellite. In both cases, AA, HB, B and C are operated when the junction is seized and JS hunts for the other kind of junction. TA operates to stop the switch but since DC is not yet operated TB is operated instead of H. An impulsing bridge is made at tb1 so that the first digit is repeated over the junction as well as to magnet DSM. In the circuits of the junctions from the sub-satellite, if the first digit is the local one L is operated over DS2 via terminal T3, relays TA, TB are released and S is driven to its next starting position. If the second digit denotes a call local to the sub-satellite the incoming junction is released from the other end. If it denotes a group in the tandem satellite DC is energized over DS2 with or without WS and the switch JS hunts in the group marked in banks JS9 or JS10 by wiper DS3. If the first digit denotes a tandem call, DC