Patent GB-358043-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1930-06-23
Abstract: 358,043. Automatic exchange systems. AUTOMATIC TELEPHONE MANUFACTURING CO., Ltd., Strowger Works. GILLINGS, C., 28. Eldred Road, Mossley Hill, and BELAS, F. T., 24, Stanley Street, all in Liverpool. June 23, 1930, Nos. 19113 and 20588/30. [Class 40 (iv).] In a system wherein overflow traffic is routed through a tandem channel in the event of an alltrunks-busy condition being encountered during the setting up of a connection, a signal is sent back over the trunk conductors to cause the register controller to effect the release of the partially set up connection and the transmission of trains of impulses of different value to set up the call over another route. Figs. 1 to 6 show a system embodying first and second code selectors, a digit switch finder, an A-digit switch and a register controller. Operation of system. A-digit-switch finder. Assuming that a calling subscriber is connected to the first code selector, Figs. 1 and 2, via a non- numerical switch, relay L operates and relays A, B pull up to operate C and initiate the operation of the A-digit finder switch AF which hunts for a free A-digit switch as determined by marking in the bank of wiper 3a. A-digit switch. When a free switch is found, K pulls up to operate relays 1A, 1C and thereby apply dial tone to the calling line and connect relay A over a holding circuit including wipers 2a, 1a and resistance 1YA. Upon reception of the first train of impulses relay L impulses 1A which operates the vertical magnet 1VM. The A-digit switch is arranged to release in the event of the transmission of a single impulse only which may be due to accidental operation of the receiver hook. After the first impulse train 1C releases and completes the circuit of the rotary magnet 1RM and hunting for a free register controller such as that shown in Figs. 5 and 6 takes place. When an idle register controller is found relay H operates over wiper 3b and the rotary magnet circuit is opened and the control leads to wipers 1b .. 3b are switched through. Register controller. Relay 2A now operates and relay 2B prepares the impulse circuit, earths lead 37, and permits operation of BA which earths lead 34 to start the motor driving the pulse springs OPS, SPS for setting the selectors and driving the sender switch wipers 1f . . 4f respectively. Upon reception of the second digit i.e. the first to take effect in the register-controller relay 2A is impulsed to operate the vertical magnet 2VM of .the BC switch comprising wipers 1d .. 6d. Relay 2C is operated in series with 2VM and at the end of the train effects release of the driving magnet UDM to advance the unit switch wipers 1c .. 5c one step. The next impulse train therefore operates rotary magnet 2RM of BC switch to position the wipers 1d .. 6d on contacts corresponding to the digits of the dialled exchange name. Relay 2C again releases and steps switch wipers 1c .. 5c to convey the next train i.e. the first numerical digit to the stepping magnet THDM of the " thousands " switch wipers 1k, 2k. Similarly, the subsequent numerical digits are registered in the hundreds, tens, and units switches, having wipers 1h, 2h, 3h; 1j, 2j, 3j, 1c .. 5c respectively. The units switch serves also as the digit distributer so that the wiring of its sender control bank must be arranged accordingly. As soon as the units switch arrives at the 3rd contact the register controller commences to transmit impulses to route the call to the wanted exchange, since upon the next break of springs SPS, relay IG operates over wipers 2c, 3e to switch the sender switch stepping magnet SDM under the control of springs SPS. When wiper 2f of the sender switch reaches its third contact springs OPS are connected across leads 18, 19 so that after each step of the switch relay A is released to operate the vertical magnet VM of the first code selector. The contacts of the BC switch are cross connected through a distributing frame to the bank contacts of wiper 4f so that the first routed digit is terminated when wiper 4f engages contact marked by wiper 1d to operate relay SZ. SZ short-circuits springs OPS to prevent further impulsing, releases 1G and thereby completes the homing circuit of stepping magnet SDM of the sending switch which moves a few steps to produce an intertrain pause until relay IG is again operated over contact bank. Relay SZ also opens a circuit of magnet CDM to step switch wipers 1e, 2e, 3e, and thereby transfer the marking circuit to wiper 2d of BC switch. The pause must adequately cover the hunting times of the various switches set by the register controller. At the end of the first digit relay C of the first code selector relapses and operates rotary magnet RM and hunting takes place until a free second code selector is found. Relay G interacts with magnet RM when wipers engage busy contacts. When a free second selector is found either HA or HB is operated to switch the connection through to relay 3A. Upon the re-operation of 1G over wiper 1f the second routing digit is transmitted in a manner similar to that previously described, the number of impulses however being determined by the making of contacts of wiper 4f by wiper 2d. The vertical magnet 3VM of the second code selector is thus operated by the impulses after which rotary hunting takes place in search for a disengaged succeeding selector which, when found, causes energization of either 1HA or 1HB to switch through the connection and render the selector responsive to the third train of impulses sent out from the register controller. If less than three digits are necessary to route the call to the required exchange, the contact engaged by wiper 3d of BC switch is cross-connected to terminal DCO so that when wiper 2e marks the contact the driving magnet CDM is operated to move wiper 2e a further step. Assuming the call is successfully routed to the required exchange by a maximum of three routing digits, since the terminal 9 is cross-connected to terminal DCO, the control switch advances its wipers automatically until wiper 2e engages contact connected to wiper 2k of the thousands digit switch. The sender switch then sends out numerical impulses through the medium of wiper 4f and similar operations are repeated for the other digit switches the wipers of which are directly multiplied to the bank contacts of wiper 4/. The arrangement is such that a digit cannot be sent out until the succeeding numerical register switch has moved off normal. After transmission of the units digit, wiper 2e operates cut-off relay CO which effects restoration of relays H, K, BA and in consequence the restoration of the various switches in turn. Metering. If the wanted subscriber is free supervisory relay D is operated and operation of relays DA, DB by pulse cam SP, ZP connects battery to conductor 43 to effect metering. Forced release of A-digit switch in event of delayed dialling. If dialling is not commenced within a predetermined time period relay TP is operated by pulse cam 1SP to prepare 1G, Fig. 4, which operates over cam 1ZP. Relay M is thereby operated to release relays K, A and thereby effect restoration of the A-digit switch. Main and individual supervisory lamps 33, LP are also lit and unobtainable tone is transmitted via condenser QC. Forced release of register controller in event of delay of dialling between digits. If too long a time exists between dialling the digits, relays 1TP, 1M are operated by pulse cams 2SP, 2ZP to operate sender switch which operates relay SZ over im5 to energize relay M over release-conductor 21 and effect release of the A-digit switch and register controller. Re-routing operation of register controller. If in response to the first digit sent out from the register controller the first code selector steps its wipers to a level provided with re-routing facilities, normal post springs NP are operated at this level and if all the outlets at this level are busy the wipers are driven to the eleventh position to operate relay AR. Relay AR operates magnet ZM to restore first code selector to normal and relay BR over wiper 5a to prevent transmission of further impulses and energize relay CR. When the first code selector restores relay BR releases and register controller transmits routing digits for setting up the connection to the tandem-exchange as determined by contacts cr2, cr3, cr4. By the operation of contacts cr5, cr6, cr7, wipers 4d, 5d, 6d determine the code for controlling the switches in the tandem exchange to extend the connection to the wanted exchange after which the numerical digits are transmitted. If the wanted exchange is one which is normally reached through a tandem exchange wipers 1d, 2d are connected to terminal DCO and wiper 3d to terminal TC so that switch skips the positions 1, 2 and in position 3 operates relay CR. Similarly if first code selector finds idle outlet to second code selector, the register controller continues to operate in normal manner to operate the second code selector which if provided with re-routing facilities causes operation of AR, and the circuit changes previously described. In a modified arrangement for effecting release to a separate release lead is not employed. A relay corresponding to AR is operated in the eleventh position of either code selector to energize a marginal relay corresponding to relay BR over the guarding lead extending to the register controller. An arrangement is also described in which the signal sent back to the register controller to cause it to stop transmission is transmitted over the impulsing circuit. In this arrangement the signal consists of a low-frequency current which operates a polarized relay to effect the operation of relays corresponding to AR, BR, CR. System employing main and sub - tandem exchanges. Calls from exchanges in an inner or outer area may be routed via a main tandem exchange when the wanted exchange is distant or via one of the sub-tandem when the desired exchange is loc