Patent GB-1053347-A (GB)
IPC: H04Q3/52
Abstract: 1,053,347. Automatic exchange systems. AUTOMATIC ELECTRIC LABORATORIES Inc. Sept. 23, 1963 [Oct. 16, 1962; Oct. 18, 1962: Nov. 28, 1962], No. 37392/63. Heading H4K. Inlet terminals are selectively connected to outlet terminals through a plurality of switching stages in tandem, each stage comprising a matrix of relays in which at each cross-point there is a unidirectional device in series with a first winding of an associated relay which has a second winding connected in series with a normally-open pair of its own contacts, so that application of a first marking potential to a selected inlet terminal and a second marking potential to a selected outlet terminal causes operation of one cross-point relay in each stage, the first windings of all the operated relays lying in a series path between the selected terminals; the operation of the relays establishes a communication path and also a holding path which passes through the second windings of the relays, their series contacts, and hold conductors in the stages and in inter-stage links, the marking potentials are then removed to open the operating circuits of the relays, and the hold conductors in the inter-stage links are connected to a detecting arrangement which distinguishes the busy links from idle links by means of the potential produced by the holding current in busy links. In the system shown, the lifting of a handset to initiate a call is detected by a line-group marker 200 which identifies the calling line and selects an idle register junctor RJ1 within the register-sender group 600. A path is then temporarily established between the calling line and the selected register junctor via the A, B, C and R matrices and an originating junctor 120, and the calling subscriber receives dial tone. The dialled digits are stored temporarily in a ferrite-core memory 660, coded. and passed to a translator 700 which thereupon obtains switching instructions from a magneticdrum memory 730. These instructions are returned to the register-sender 600 which transmits them via one of the senders 671-680 and the originating junctor 120 to a group selector 300 where they are analysed by a trunk-group marker 400 which controls the further extension of the connection. In the case of a local call, an idle terminating junctor 130 in the relevant time group is located and a path is established to it via the A, B and C matrices of the group selector 300. The connection is extended to the calling line via the E, D, B and A matrices of the line group, and the terminating junctor 130 provides ringing current (of which five different frequencies are available), answer supervision, and talking battery for both parties when the call is answered. The markers and the temporary signalling and control paths are released, the speech connection being held through the junctors and the switching matrices in which each cross-point comprises a reed relay having an operate winding in series with a diode rectifier and a hold winding in series wite a normally-open set of contacts of the relay. The register-sender group 600 and the translator 700 function on a time-division basis. A call to a P.B.X. group of lines causes each idle line of the group to be marked as calling and the marker selects one of them, actual calling lines being meanwhile denied access to the marker. A trunk group 500 provides access from incoming trunks to the register-sender group 600, and a control centre 790 contains equipment for operation analysis and recording.