Patent GB-1057421-A (GB)
Title: Electronic switching telephone system
IPC: H04M7/10
Filed: 1964-04-10
Abstract: 1,057,421. Exchange systems. STANDARD TELEPHONES & CABLES Ltd. April 10, 1964 [April 15, 1963], No. 14877/64. Heading H4K. A switching network 21 has line circuits such as 31, 32 on one side and registers and link circuits such as 25, 26 on the other side, trunk circuits having appearances such as 27 and 28 on both sides of the network. All circuits are identified by a time slot in a pulse cycle during which slot the circuit can demand a route across the switching network. The line circuits, links, and registers each have their own pulse cycles. A call is first set up over the network to a register which drops the connection when fully acquainted with call particulars and then connects the call. A call from a trunk is received over the line circuit appearance and is set up to a line circuit by way of its link circuit appearance. Incoming call.-As seen in Figs. 2 and 3 all lines, including trunk lines, are identified in a hundreds, tens and units scanning system using the multiples 41. Both appearances of a trunk line are identified by the same time slot. Calling condition is signalled at terminal 53 to close NOT gate 54 in order to open gate 55 if the trunk circuit is not marked busy from circuit 61. A register 52 scanned over gate 51 is made available by its extension of a mark to terminal Y1 of the network 21. On the occurrence of the trunks time slot gate 59 opens so that AND gate 60 activates circuit 61 to busy the calling trunk circuit and mark its line circuit side appearance X3 in the network 21. A path automatically establishes itself between Y1 and X3 over which dial tone is returned from the register. When fully acquainted with call particulars the register halts the scanning of line circuits and during its own time slot it energizes the line seize bus 66 in coincidence with the marks on the hundreds, tens and units wires 41 appropriate to the wanted line circuit. If this is the line circuit shown in Fig. 2, gates 72, 46 and 74 seize the circuit 62 to put the line circuit busy and mark its terminal X1 in the network 21. Before this the register has marked the wires 41 identifying the calling trunk circuit so that gate 50 in its link side appearance, Fig. 3, opens and over gate 69 sets bi-stable circuit 70 so as to seize the circuit 63 of the link side of the trunk. Circuit 63 restores the busy condition of the trunk circuit and marks the trunks appearance Y4 in the network 21. The required connection is therefore established between X1 and Y4 and the register retires. If the called line circuit is busy the connection is not established within a time measured by the register which connects a busy tone link to its appearance Y5 which connects with the line circuit appearance X3 of the calling trunk. Outgoing call.-Calling condition on gate 81 of line circuit 31, Fig. 2, activates gate 72 and, during the time slot of the subscriber as indicated over gate 46, opens AND gate 74 to seize the line circuit by way of circuit 62 from which the terminal X1 is marked. A waiting register marks a terminal Y1 and returns dial tone over the resulting path X1, Y1. Line scanning is halted when the register is fully acquainted with call particulars and a search is made by the register for a free trunk circuit. Control lens 84 is energized so that the first free trunk circuit scanned over its gate 86 is seized and busied in circuit 63 in its link circuit appearance. Consequently its terminal Y4 is marked and the connection X1, Y4 made joining the calling circuit to its demanded trunk. Operator sets up tandem call.-For calls from ring down offices and the like the operator makes an answer key 91 particular to the calling trunk and makes a dial key 90. A central office trunk circuit 40 is marked over control bus 97 as a result of key operation while energization of a bus 102 causes the trunk circuit to be seized at its line circuit appearance from which a connection materializes to the central office trunk circuit 40.