Patent GB-973717-A (GB)
Title: Automatic telecommunication exchange
IPC: H04Q3/42
Filed: 1962-05-04
Abstract: 973,717. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. May 4, 1962 [May 5, 1961], No. 17198/62. Heading H4K. In an automatic exchange in which all originating calls are connected via selection stages to a local junctor (feed-bridge) and a register is then associated with the seized junctor, the latter is released and a new path through said stages to an outgoing junctor is set up if digits indicative of a subscriber in another exchange are recorded in the register. A calling subscriber AB (Fig. 1) is initially connected via a selection chain to a local junctor (this process being fully described in Specification 946,263, and a register LGE is then periodically associated with the junctor via the junctor common control circuit LGJ as is described in Specification 963,329. When digits indicative of a call to a distant exchange have been received in the register, the latter seizes a so-called junctor driver RC which then causes the local junctor to be released (see for instance Specification 963,329), and a new path through the selection stages to an outgoing junctor to be set up. The outgoing junctors (Fig. 6) are scanned periodically via electronic scanners EXA, EXB and the discovery of an outgoing junctor in a seized condition (relay dr operated) causes a register logic circuit LGE to be associated with the junctor whereby transistor tr1 saturates to bring up relay i (the charge on a capacitor cd1 being used to bring about the saturation condition). A " calling " signal which may be of D.C., 50 c./s. A.C. or a voice frequency combination is thus sent over junction CI to the required exchange where a relay r (Fig. 7) of an incoming junctor responds and pulls up relay dr. When this junctor is scanned its relay i is operated to revert a " reply " signal which energizes r (Fig. 6) and hence de thereby notifying the register and the logic circuit that the stored digits should be transmitted. When the calling subscriber has terminated dialling, a junctor driver is associated with the outgoing junctor by the operation of a relay to (common to a small group of such junctors) and a remanent relay c whereby the latter extends " waiting tone " from at to the caller. When all the digits have been registered at the incoming exchange and the availability or otherwise of the called subscriber has been ascertained, an appropriate signal is reverted to the originating exchange. Assuming that the called party is free, a junctor driver is associated with the outgoing junctor via relay to and a remanent relay p and c is released whence ringing tone is returned from ra. At the incoming exchange a junctor driver operates relays to to p to close a ringing circuit and if necessary to revert ringing tone to the caller (via contact p4). A signal indicative of the called party's reply is reverted (relay o operating to release p, Fig. 7) whence c (Fig. 6) is again brought up to cut-off ringing tone and to reverse the polarity on the line wires. Provision is made for both party release. The system is adapted for transit calls by providing each junctor with a remanent relay whereby the incoming and outgoing lines of the junctor can be directly coupled during such a call thereby effectively by-passing the junctor.