Patent GB-1037685-A (GB)
Title: High speed electronic switching telephone system
IPC: H04Q3/52
Filed: 1963-12-13
Abstract: 1,037,685. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. Dec. 13, 1963 [Dec. 19, 1962], No. 49441/63. Heading H4K. A telephone exchange includes facilities for setting up preset conference calls by means of a store containing the addresses of all the parties connectable to the conference, which store, on being selected by a subscriber, seizes a plurality of registers, one for each stored address, and causes all the registers to concurrently set-up connections between each of the subscribers whose addresses are stored in the store and a conference link. The system uses a line scanning arrangement, in which the lines are normally scanned at high speed but in the event that a calling line is detected scanning is stopped for a fixed interval of time. If a connection cannot be set up to a register in this interval, scanning restarts and a further opportunity for answering the calling line is not afforded until the next cycle of the scanner. Monostable circuits are used to provide the time interval. Lines, trunks and links are all scanned in the same manner using bi-stable ring counters. A register scanner is started at the end of a link, line of trunk scanning cycle. The switching network comprises a 4-wire PNPN diode selfseeking network of the type described in Specification 978,370. Facilities for setting-up normal conference calls, and calls to frequentlywanted subscribers are provided (see below). Differences of line impedance are compensated, and lightning protection is provided, by a ballast lamp in the phantom of the subscriber's 4-wire line. General. Local call, Figs. 1, 2.-Subscribers' line circuits and outgoing trunk circuits are connected to terminals such as X1 ... X4 of an electronic switching matrix and registers and links are connected to points such as Y1 ... Y4 of the matrix. A free register marks a point such as Y1 and when a calling line circuit is scanned, the scan time for this line is increased to permit a path to fire through to the register, which records the calling line identity as indicated by the time position in the line scan. The register then receives the called line's identity and tests the called line over the busy check bus. If the line is busy and executive cut-in is required, this is effected over the pre-empt bus. The register then marks the link select bus, and when a free link is scanned paths from the link to the calling and called lines are fired over the switching network 22 under control of the register which marks the seize buses. When connection is complete the link marks the call complete bus which frees the register and causes register scanning, which has been inhibited for this operation, to continue. Outgoing trunk call.-If the wanted number is in a different exchange the register marks an appropriate trunk group number lead which causes a counter 41 to select a suitable free trunk whereupon it marks all the rest temporarily busy. When the selected trunk circuit is scanned a path is fired from it to the register which is thus enabled to identify the trunk from the time position. The register then causes paths from the calling subscriber and the identified trunk to be fired to a suitable link circuit as described above. Conference call. Type 1 (normal).-When the calling subscriber sends a special number the register pulses a register conference call bus which causes the first free register conference link 60 (Fig. 1) to be seized and connected to the caller. This link then seizes a conference register 62. This register receives the numbers of the wanted subscribers and sets up the calls from the caller individually to these wanted subscribers as their numbers come in. Conference call. Type 2.-In an emergency a subscriber may make a call which will bring automatically into conference certain predetermined subscribers. When the register receives the appropriate number or signal it seizes a " preset conference link " 69 (Fig. 1) and a store 70 (Fig. 2) which stores the numbers of all the parties required for the call. The number of the link 69 is also written into store 70. The circuit 70 then seizes as many registers as there are numbers stored and feeds the stored numbers into the respective registers which then complete the connections almost simultaneously. Calling frequently wanted subscribers.-A subscriber seizes a register in the usual way. The subscriber also has four wires, energizable by a push-button which applies thereto +, - , or 0 in different combinations to provide abbreviated codes for frequently wanted numbers, and these are connected by a line gate, Fig. 4 (not shown), to four wires 75. When the line scanner scans the calling line the code is gated on to wires 75, decoded to potentials on combinations of verticals of a matrix 76, having horizontals associated by jumpers 80 with the scanned calling subscriber and pulsed at that time. Gates, consisting of plug-in, diode-resistance combinations, are connected at selected cross-points, outputs from these gates being fed to input gates in address store 77 over jumpers 81. These gates feed horizontals associated with the wanted su criber and are cross-connected by diodes to verticals in store 77 indicative of the wanted subscriber and these are connected over leads 84 to the registers to be stored in that register which is connected up to the calling line at the same instant. The call is then set up as before. Subscriber's line circuit. Normal operation.- The subscriber has a four-wire circuit and operation of his hook-switch completes a phantom circuit whereby gate 502 closes. When the line is scanned (terminal 504), and assuming a free register is available (marking on seize terminal 505), gates 510 and 512 (see Scanning arrangements below) open so as to mark points XI, XI<SP>1</SP> whereby a 4-wire path fires through the network to the register. The paths are held by circuits 520, 521. The busy circuit 508 operates to disable the busy lamp and timer 523 and to apply a busy marking to terminal 540. Dialling impulses are repeated by the busy circuit to the network, the hold circuits being maintained by the timer. If the subscriber hangs-up before dialling the timer releases the path. When a register sets up a call from a link to a called free line it applies potential to seize lead 505 and when the called line is scanned (lead 504) gate 510 conducts followed by 512 which applies firing potential to points X1, X1<SP>1</SP> of the network for completion of a four-wire path to the link. Gate 522 enables the ringing signal and ring-back tone gates RS, RBT. When the called subscriber answers the timer 523 switches off to disable 522 and stop the ringing signals. Busy circuit 508 causes extinction of the subscriber's busy lamp. In the case of a call to a busy subscriber the seize potential is ineffective at 509 in the face of the potential applied thereto due to the off-hook signal received from 502. If, however, the subscriber is the calling subscriber, a different voltage seize signal is applied to 509 to override the off-hook signal. Executive cut-in.-A register, as described in Specification 978,370 can recognize the right of a caller to break-in from his class of service or from the existence of ground pulses between each impulse train. To effect a break-in the register on receiving a busy signal over lead 540 in the time position of the called line marks the preempt lead 543 to pulse the hold circuits 520, 521 to release the existing connection. The signal also changes over flip-flop 542. This pulses 522 to cause a short burst of ring signal and ring back to be given to the presently engaged subscribers. This signal also extinguishes the subscriber's preempt light and brings up his busy light. Terminal 551 is marked to signal the registers not to cut in on this line. This facility can also be used for special subscribers who cannot have their calls broken into. For these subscribers lead 543 is pulsed when the call is set up so setting 542 to prevent break in. The hold circuits 520, 521 of the wanted line are pulsed so as to force-release the connection to the other party of the existing call and the wanted party is then connected through the network to the privileged subscriber. Scanning arrangements. Fig. 6.-The line and incoming trunk scanner 26, the link scanner 27 and the outgoing trunk scanner 28 (bi-stable ring counters) are all normally operated at high speed from master clock pulses 23 received over gates 601, 602, 603. When a scanned line requires a connection over the switching matrix potential is received over lead 513 to operate 25 Ásec. flip-flop 615. This provides a slowly rising 25 Ásec. potential from amplifier 631 to gate 512 for firing paths through the network. When 615 restores flip-flop 615 operates for 80 Ásec. to give the switching network time to settle down. During the whole of this 105 Ásec. period gate 601 is inhibited to prevent continuation of line scanning. When a register is ready to transfer a call to a link it energizes terminal 622 which enables 602 to set the link scanner running and also causes 610 to disable the line scan outputs. When an idle link is scanned 621 is energized to operate 35 Ásec. flip-flop 617 to stop the scanning during this period. The link commences to end-mark the network during this period. When 617 restores, 615 is set to further inhibit the scanning and a firing pulse is delivered by 631 to the line circuits marked by the register. After 25 Ásec., 616 operates to inhibit scanning for a further 80 Ásec. as described above. If the scanner encounters a busy link no delay occurs and the scanner steps at high speed. Register scanning normally takes place whenever a line scanner 26, link scanner 27 or outgoing trunk scanner 28 completes its scan, trigger 644 changing over at this time. In the absence of any control signals the scanner is stepped rapidly by means of circuits 646 or 647, 645