Patent GB-196245-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/58
Filed: 1923-01-13
Abstract: 196,245. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Ray, A. J.). April 17, 1922, [Convention date]. Automatic exchange systems; party line systems.-When a call from one exchange to another can be made either over a. direct route or over a route through another exchange, preference is given to the direct route. This is effected by a discriminator which responds to as many digits as are necessary to designate the wanted exchange or sub-exchange, and which, in suitable cases, releases the connection over the long route so far as it has been established by these digits and switches over to the short route, to which subsequent digits are delivered. The invention is specially applicable to systems comprising main exchanges and district offices, some district offices having direct access not only to the main exchanges to which they belong, but also to other district offices or other main exchanges. A portion of a 6-digit network of this kind is shown in Fig. 1, 91, 92, being main exchanges of 10000 lines, 912, 913, district offices of 1000 lines belonging to the main exchange 91, and 9181 a district office of 100 lines also belonging to the exchange 91. The number representing each exchange or district office consists of the digits common to all its subscribers, for example all subscribers on the exchange 92 are numbered 92XXXX, all subscribers on the district office 9181 are numbered 9181XX, and so on. The invention is described in relation to calls originated by the district office 913, which, it will be seen, in addition to trunks to its parent exchange 91 has trunks leading directly to the district offices 912, 9181, and to the near-by main exchange 92. Normally any call originated by a subscriber A, Fig. 4, is extended over non- numerical switches C, C' and a repeater R to a group selector E at the main exchange 91, and thence to its destination.. If, however, the call is destined for the exchange 92 or for either of the district offices 912, 9181 a discriminator SD after responding to the first two, three or four digits releases the connection C<1>, R, E, &c. and operates a non-numerical switch C<6>, C<8> or C<7> to connect the calling line over a direct trunk to the exchange 92, 912. or 9181, where the remaining digits are delivered and complete the connection. If none of the direct trunks are idle, this switchover is prevented and the call is completed over the long route through the exchange 91. If the call is for another subscriber in the district office 913, the discriminator SD after the third digit releases the trunk to the main exchange and extends the call through a switch C' to a local group selector E<5>. If all the trunks to the parent exchange are busy the discriminator still responds to the initial digits to determine whether the call is one that can be completed independently of the parent exchange. If the subscriber A wants a subscriber A<1> on the same two-party line, he sends the single digit O, and the discriminator extends the calling line through a switch C<5> to a ring-back equipment K of special character. In all cases the discriminator after completing its function is at once released for common service. Selection of an idle discriminator and of a trunk line to the parent exchange. When the subscriber A, Fig. 5, lifts down his receiver the tandem non-numerical switches C, C' operate in the usual way to extend the calling line to a repeater R, Fig. 6, associated with the outgoing end of an idle trunk 139, 140 to the parent exchange. A relay 40 energized over the circuit 30 removes ground from a circuit 57 and closes a circuit 55, 442 to energize the starting relay 409, Fig. 9, of the finder F associated with an idle discriminator SD. The finder F operates like a line switch C until it finds the circuit 57 from which ground has been removed, whereupon a. relay 408, being no longer short-circuited, becomes energized and grounds the wires 56, 57, at the same time advancing the distributor D to preselect another idle discriminator in readiness for the next call. The relay 409 relapses and removes ground from the wire 56, but meanwhile a relay 41, Fig. 5, has become energized over this wire and locked itself up, disconnecting relay 40 and grounding the wire 56 at its other end to keep the relay 408 energized. Operation of the discriminator SD, Fig. 9. Dialling tone is supplied to the calling line by a machine T<2>, Fig. 6, through a winding of the line relay 150 of the selector E. The digits dialled by the subscriber are repeated by relay 130, Fig. 6, over the trunk 139, 140 to the parent exchange and also over a circuit 98, 58, 407, 440 to the discriminator SD. This consists of two Strowger switches M, N, each having a wiper (such as 437) which partakes only in the vertical movement of the switch and a wiper (such as 438) which partakes in both vertical and rotary movements. Each digit energizes the sluggish series relay 407 which, at the end of each digit, co-operates with relay 406 to send an impulse to magnet 486, which steps the switch S to its next position. Thus the first and second digits are delivered to the vertical and rotary magnets 449, 448 of the switch N, and the third and fourth digits to corresponding magnets of the switch M. The relapse of relay 407 at the end of each digit grounds the wipers 435 - - 438. Suppose, as a first instance, that the call is for a subscriber in the exchange 92. At the end of the second digit a circuit is closed through wiper 438 and its 92nd terminal to energize relay 402, which closes a circuit 405, 413., 454 to energize relay 560. Fig. 10. This starts the switch C' to hunt till it finds an idle trunk direct to the exchange 92, whereupon relay 561 becomes energized and grounds a circuit 60 to energize relay 42, Fig. 5, which disconnects the calling line from the switch C<1> (thus releasing the trunk to the parent exchange) and connects it over wires 59, 61 to the switch C<6> and thence to the repeater R<6> associated with the trunk to exchange 92, to which the third, fourth, &c. digits are repeated. The relapse of relay 66 disconnects ground from the wire 56 so as to unlock relay 408, Fig. 9, which closes circuits for the release magnets 447, 450, 485 of the switches 11, N, S. To take a second case, suppose the call is for the district office 912. At the end of the second digit a circuit is closed through wiper 438 and its 91st terminal for the right-hand windings of the consequent-pole relays 401, 403, 404, which, however, require current in both windings to become energized. At the end of the third digit a circuit is closed through wiper 435 and its 2nd terminal for the left-hand winding of relay 403, which becomes energized and closes a circuit 405, 414, 456 to energize relay 540, Fig. 10, and the switch C<8> seizes an idle trunk direct to the district office 912. The relay 550 grounds the wire 60 to release the discriminator and the trunk to the parent exchange as in the previous case. Or again, if the call had been for another subscriber in the originating office 913, the relay 404 would have been energized and the switch C<4> set in action. In the case of a call to the district office 9181 a circuit is closed, at the end of the fourth digit, through the wiper 436 and its 81st terminal and the left-hand winding of relay 401, of which the other winding is energized through the wiper 438. In this case the relay 401 sets the switch C<7> in action. If the call is for an exchange which can only be reached through the parent exchange, the discriminator is released in the fifth position of the switch S by the energization of relay 410, which unlocks relay 408. Operation if all direct trunks are busy. If the call is for district office 9181, for example, and all the direct trunks to this office are busy, the multiple chain circuit 525, 526. Fig. 10, will be open so that the switch C<7> will not be set in action and the call will be completed through the parent exchange. Operation if all trunks to the parent exchange are busy. In this case a relay 190, Fig. 6, is energized over a chain circuit 125, 126, 134 and disconnects ground from the test circuits of a number of dummy repeaters R<1>, one of which is seized by the switch C'. Dialling tone is supplied through the lower winding of the line relay 106, which repeats the digits to the discriminator over the circuit 94, 58. If the discriminator is able to complete the call over a direct route the repeater R<1> is released by the energization of relay 42, but if not, the grounding of the circuit 5S, 94 by the wiper 440, Fig. 9, in its fifth position energizes relay 105, Fig. 6, which locks itself up and connects busy tone to the calling line. Reverting party-line calls. To call the subscriber A<1> on his own line, the subscriber A sends the single digit O. At the conclusion of this digit the discriminator closes a circuit through the wiper 437, Fig. 9, and its 10th terminal to energize relay 400, which sets the switch C<5>, Fig. 10, in action to select an idle ring-back equipment K, and the trunk to the parent exchange is released. The line relay 602 energizes relay 603. The subscriber now hangs up his receiver and the relapse of relay 602 energizes relay 601, which locks the relay 603 and connects an interrupter I to a sluggish relay 613. The relay 613 controls a sluggish relay 614, and the relays 613, 614 jointly control a sluggish relay 615. It will be seen that at every operation of the interrupter I the relays 613, 615 are energized alternately. Each time relay 613 is energized ringing current is supplied over the circuit 614, 61, 12 to ring the substation A, and each time the relay 615 is energized ringing current is supplied over the circuit 640, 59, 11 to ring the bell at substation A<1>. When the subscriber A<1> answers the call a relay 616 becomes energized over the line-loop. The relay 616 locks itself up and de-energize