Patent GB-311709-A (GB)
Title: Switching arrangement in automatic telephone systems
IPC: H04Q3/00
Filed: 1929-05-13
Abstract: 311,709. Telefonaktiebolaget L. M. Ericsson. May 14, 1928, [Convention date]. Automatic exchange systems.-In the case of an inter-exchange call, the whole designation of the wanted line is recorded at the originating exchange and re-transmitted to the wanted exchange, this operation if necessary being repeated at one or more intermediate exchanges. If all the junctions leading to the wanted exchange over one route are in use, the call is forwarded over an alternative route. A calling subscriber is connected over his line switch SS1 to an idle trunk SL1, and an impulse recorder R1 is taken into use to register the wanted number. The first digit determines the exchange of the wanted subscriber, and if the call is a local one, the line switch SS2 of the wanted subscriber is marked in the recorder and operates to make connection with the trunk SL1. If, on the other hand, the call is for another exchange, a circuit is closed for operating a switch FS1 to seize an idle junction FL1 leading in the required direction, and the whole number registered is transferred over the junction by the impulse sender HR1 to a recorder R2 at the wanted exchange or an intermediate exchange. Local call. Line relav AR1 energizes and connects up magnet ADR1 of the line switch SS1. When an idle trunk SL1 is found, switching relay CR1 energizes in series with relay SAR which connects the trunk to an idle impulse recorder R1 and' relay RI therein energizes over the loop, connecting up sluggish relay RT1, which sends an impulse to magnet DRO to advance the sequence switch SO one step. Dialling tone is transmitted over the lower winding of relay RI, and the impulses corresponding to the hundreds digit are repeated to magnet DR1 of the hundreds register RS1, sluggish relay RT2 being energized during the train and then falling back and sending an impulse to advance the sequence switch SO to position 3. The tens and units digits are stored in a similar manner in the registers RS2, RS3, and the switch SO moves to position 5 in which relay BR energizes, and the appropriate hundreds and tens relays KR, NR operate, closing a marking circuit 17 which extends over relay MR2 in the line switch SS2 of wanted subscriber, and over relay RL1 which connects up relay RR1. Relay MR2 closes a local circuit for line relay AR2, and magnet ADR2 advances the line switch SS2 into engagement with the trunk SL1, which is marked over a circuit 22. Relay RR2 energizes in this circuit and connects up relay SBR, which locks, releases the recorder and completes the feed bridge. Inter-exchange call. The wanted number is registered in the recorder R1 as described above. The setting of the hundreds register RS1 determines that the call is non-local, and when relay RT1 relapses after that digit, relay RR3 energizes, opens the circuit of relay BR and connects up magnet DR7 to step the switch FS1 in search of an idle junction in the required direction, one of the sections of the lowest bank being selectively marked over the hundreds register RS1 and through test relay RL2. 'The junction FL1 terminates in a line switch, which is started by the operation of line relay LR as soon as test relay RL2 pulls up, and a recorder R2 at the distant exchange is taken into use. A control circuit 34 is closed through impulse relay RI1 therein and relay RR4 in the impulse sender HR1, which locks and energizes in turn relays' RR5, RR6. Relay DR5 is of high-resistance and is in series with the magnet DR4 of the counting switch RS4, and relay RR6 when energized opens the control circuit 34 and short-circuits relay RR5 to allow magnet DR4 to operate, so that these relays interact to send impulses to the recorder R2 and to the counting switch RS4 until the latter reaches a position marked by the hundreds register RS1, when relay RR7 pulls up and stops the interaction. Relays RT4, RT5 energize, and magnet DR5 operates to advance the sequence switch RS5 of the sender HR1 to position 2, in which relay RR7 is disconnected. The settings of the tens and units registers are transferred to the recorder R2 in a similar manner, and the sequence switch RS5 then moves to position 4, in which relay SCR energizes in series with relay RR7, extending the talking connection to the junction FL1, and relay SBR energizes, locks in series with relav SCR and releases the recorder. Release is controlled by relay SCR. All direct junctions busy. An individual relay such as FR3 is energized when a junction is taken into use, and if all the junctions leading to a particular exchange are engaged, a chain circuit is closed for relay FR4, which transfers the marking circuit from the hundreds register RS1 to the adjoining section of the bank of the switch FS1, so that the call is routed over an alternative path through an intermediate exchange.