Patent GB-338875-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1929-08-26
Abstract: 338,875. Standard Telephones & Cables, Ltd., Hartley, G. C., and Wright, E. P. G. Aug. 26, 1929. Automatic exchange systems.-In a system in which incoming selectors seized over inter-exchange junctions comprise apparatus such as common - control or bye - path switches, which are common to groups of incoming selectors, in response to an incoming call a free apparatus or a selector associated with a free apparatus is non-numerically connected to the calling junction. Two systems are described; one suitable for areas embodying direct dialling, in which the incoming junction is seized by a free bye-path circuit which receives the dialled impulses whilst a free associated talking link is being found and connected to the calling circuit and the other, for use in register-controller systems, in which the control circuit finds a free link which associates itself to the calling junction a signal being returned when the connection is established io enable the register-controller to transmit the stored digits. In the former case busy tone is returned if dialling is commenced before the calling junction has been connected to a free control unit. Direct-dialling area. Outgoing repeaters, Fig. 3, are associated with each junction and when seized, relay AS operates followed by BS and US, looping the outgoing junction and operating relay L, Fig. 1, at the distant exchange. Relay SA pulls up and connects starting earth to the byepath circuit start lead. Relays D operate in all the free bye-path units (Fig. 4) and the corresponding DM switches begin to hunt. All the incoming junctions are multipled over two levels dmt1 and dmt2 of the bye-path switches which test two junctions simultaneously. When the calling circuit is reached relay T or relay N operates to stop hunting. If the calling junction is found over dmt1, T pulls up and A energizes; if found over dmt2, N operates energizing BJ and A pulls up. Relays B, and BB and KA operate and L and SA release. As the resistance of A is less than L, marginal relay 1S operates in the new loop energizing ES. Relay 1S may be a polarized relay in which case the battery connections to A are the reverse of those to L. The next impulse series is sent by AS (Fig. 3) over the junction to A (Fig. 4) relay CS operating on the first pulse to provide a clean dialling loop. Relay A repeats the impulse train to RM1 which marks a group in which RM2 searches for a free path to the next switching stage. RM1 then searches for a free link which, when found, searches over FM for the calling junction and over SM for the circuit marked by RM2. The bye-path is released from the next switching stage. If dialling had been started before a free bye-path had been connected, relay CS would have energized before ES had pulled up, breaking the loop and returning busy tone from BT. Register controller area.. A repeater, Fig. 3, is not provided, a control circuit, Fig. 2, being used in conjunction with Fig. 1. When a call is made L (Fig. 1) operates over the calling junction energizing SA to connect marking potential to all the free control circuits such as Fig. 2. Relay A (Fig. 2) operates and magnet DM steps switch DM in search of a free link. When an idle circuit is found T operates and the junction finder FM hunts for the calling junction. If the circuit shewn is the first to find the calling junction, K and KA (Fig. 1) operate in series, K allowing B and BB to energize and KA releasing L to remove ground from the start lead freeing the other control circuits. Relay A replaces L across the junction leads and as the battery and earth connections to A are opposite those to L the current flow is reversed over the junction enabling the register controller to transmit the next digit. The group required is marked by RM1, a free circuit is found by RM2 and the switch SM hunts for the marked circuit in the normal manner.