Patent GB-1285094-A (GB)
Title: A telecommunication exchange system
Inventor: REANEY DONALD
IPC: H04Q3/54
Filed: 1970-05-20
Abstract: 1285094 Automatic exchange systems PLESSEY CO Ltd 19 April 1971 [20 May 1970] 24342/70 Heading H4K A telecommunications system in which privileged subscribers can divert calls to other subscriber stations includes for each privileged subscriber a contact used for all calls to that subscriber and connected such that when in a particular state, calls incoming to that subscriber line are routed to a common transfer unit including a sequentially accessed store, storing at locations allotted to that privileged subscriber his director number and the directory number of the subscriber to whom calls are diverted. General description of system to which the invention is applied.-The system including a switching network including three main and one auxiliary switching stages controlled as in Specification 1,093,637 i.e. a network in which the first and third stages are preselected and extend markings via the control wires to the second stage and a switch in this stage receiving markings from the first and third stages is selected. The network uses reed relay crosspoints. Fig. 1 shows a subscriber line circuit 1, the switching stages 2 to 5, control circuits 9 to 13, an outgoing junctor 6, a local junctor 7 and an incoming junctor 8. The system may be arranged to operate in the assumption that the majority of locally originating calls are outgoing ones. When the subscriber associated with line circuit 1 goes off hook, the line relay produces a pulse on a lead 1b which is a wire of a code point store 14, which generates the directory number of the subscriber in 2 out of 5 code form and transfers it to a call store 15. A register selector 16 selects a register 22 and the calling subscribers directory number is transferred to this register. A register finder 19 connects registers in this state one at a time and giving priority to registers dealing with incoming calls to a call control unit. The call control unit instructs (for the call being described) all free outgoing supervisory relay sets 6 to mark the "C" switch selectors causing access relays 10 to extend test and mark wires to the "B" switching stages as described in the above referred to Specification. Simultaneously the calling subscribers coded number is decoded at 20 into a marking on an identifier lead 1c via a strapping field 21 which converts from directory to equipment numbers and adds class of service information. The marker relay in the line circuit responds operating the "A" switch access relays extending test and marking wires to the "B" switch. A selector 12 selects a B switch receiving markings from both directions. A selector (not shown) selects one of the free out going supervisory relay sets which initiates the switching of the path between it and the subscribers line unit 1. A "K" relay in the subscribers line is operated by the control unit and held by the supervisory relay set. The selected register returns dial tone and initially dialled digits comprising the wanted exchange code are repeated by the selected outgoing supervisory relay set and simultaneously stored in coded form in the register. If the call is for another exchange the register is released and subsequently dialled digits are repeated over the junction. If the call is to the subscribers own exchange the outgoing supervisory set is released and a new path is set up between the caller and a local supervisory set 7. If the called subscriber is busy or unobtainable a tone is returned to the caller and a forced release is effected if he fails to respond. If the called subscriber is free the supervisory set 7 is instructed to operate access relays 10 of the "D" switch in order that the "C" switch selector 13 can select a "D"-"C" trunk associated with the "D" switch to which the supervisory set is connected. The path from this supervisory set to the called subscriber is set up in similar manner. The call control unit and the selected register are released and the call subsequently monitored by the supervisory set. Ringing tone is passed to the calling subscriber and ringing current to the called subscriber. When the called subscriber answers the supervisory set applies periodic positive meter pulses to the "P" wire. At the end of a call if the calling subscriber releases the path is immediately released but if only the called subscriber releases a forced release is effected after a predetermined period and busy tone returned to the caller. Arranging calls to be diverted.-A privileged subscriber can divert calls to another substation by lifting his receiver and after being given access to a register 22 as set out above, dialling a special call transfer code which, when decoded as set out above, enables a relay 25 (Fig. 2) in the line circuit. The relay 25 is maintained in its operative state in which the line 1Ae (referenced 1C in Fig. 1) is disconnected from the line circuit marking relay and connected to the control unit 18 which under these conditions connects the register to a call transfer unit 24. The subscriber dials his own directory number and the marker potential output on line Ale instructs the call control unit to transfer operations to the call transfer unit 24, which stores the dialled directory number in a first storage location. The call transfer unit instructs the clearing of the register and the called subscriber dials the number of a subscriber station to which he wishes calls to be transferred, this number being stored by the call transfer unit in the second storage location associated with that subscriber. Transfer may be restricted to allow transfer only to selected subscribers whose addresses are stored. Diverting calls.-The dialling of the code of a wanted privileged subscriber who is diverting calls from his line causes on decoding his directory number, a marking on lead 1Ae which via the contact of relay 25 in his line circuit is diverted to the call transfer unit which scans the store until a match is found i.e. the stored wanted subscriber directory number is found and the directory number of the subscriber to whom calls are diverted is read from the associated other storage location and used to complete the connection. The privileged subscriber may cancel the diversion by dialling a cancellation code from his own substation. The transfer unit could employ M.O.S.T.'s.