Patent GB-909237-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: BROWELL LESLIE JAMES
IPC: H04Q3/00
Filed: 1960-06-23
Abstract: 909,237. Automatic - exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. May 29, 1961 [June 23, 1960], No. 21982/60. Class 40 (4). A primary line selector of the cross-bar type handling both originating and terminating calls is marked via the line circuit of a wanted subscriber and signals the marker on one wire to effect release of the marker should the line circuit be busy but returns a signal on a second wire so that the marker may condition the selector to terminate a path to the wanted line circuit should this be idle. The selector is part of the exchange described in Specifications 890,235, 890,236 and 890,237, and uses triple group working between ten bridges and twenty six outlets. As shown in Fig. 1, the bridge inlets LK1 to LK10 are multiplied to outlets in groups of three; select magnets 1SM to 9SM determining which group of three outlets is selected and auxiliary select magnets 1AM, 2AM, 3AM, determining which one of the three wires is connected. Adjacent select magnets control a common pivoted select bar so that the adjacent select magnet 9SM and auxiliary select magnet 3AM cannot be energized at the same time. Only two outlets can, therefore, be associated with magnet 9SM which reduces the possible number of outlets to twenty six. Each of the outlets is associated with one of the line circuits which, therefore, fall into three groups according to their dependence on auxiliary magnets 1SM, 2SM, or 3SM. A subscriber's line circuit is shown in Fig. 2 and, additionally to the speech and private wires there are seven control wires to the selector of which SM is marked from terminal M by a marker in pursuit of a subscriber and CO marks the class of service available to the subscriber on outgoing calls, while terminal CT connected to a selected one of sources TCA, TCB, TCC, or TCD, marks the class of service for incoming calls. The selector is shown in Figs. 3, 4, 5 and 6, arranged as in Fig. 7; only one cross-point of the selector being shown from bridge BR1, Fig. 6, connecting the speech and private wires of line circuits SLC1, SLC2, SLC3, Fig. 5, to the bridge inlet which is the link 1LK, Fig. 4, to the secondary selector stage. Only one bridge magnet 1BM, Fig. 6, is shown. The select magnets 1SM to 9SM are shown in Figs. 4 and 6, and the auxiliary select magnets 1AM, 2AM and 3AM are shown in Fig. 3. Originating calls.-A. calling loop operates LR which loops the control wires OC, MA, to the selector and connects wire CO to the negative speech wire to signal the class of service as connected to wire CO by a source OCA, OCB, OCC, OCD, from the selector, see Fig. 5. At the selector the relay G is normally operated and its contacts are shown in the operated state. Supposing the first group subscriber SLC1 is calling, the loop on wires OC, MA, connects call relay OC, Fig. 6, in series with first group select magnet 1AM. Relay OC responds but 1AM does not. A relay OS, Fig. 4, is in parallel with 1AM and responds with OC to disconnect magnet 2AM in case a call is orignated by a second group subscriber and the common select bar of magnets 1AM, 2AM, is balanced. Relay OC signals a start shift circuit SSC on wire AE, Fig. 6, and operates relays OM and M. Failure of OM to operate would cause an alarm to operate to the mark on AE but SSC normally responds to a mark on wire DP to test for secondary trunks with the function of distributing traffic. With OM operated, OC is bridged to permit magnet 1AM to respond. Relays G and OC hold to earth on wire GP from the circuit SSC. Relay M marks wires MO of all free links such as 1LK, Fig. 4, of which the associated bridge magnets are unenergized. Relay MA now responds to connect all first group line circuit wires MA to the selector magnets 1SM to 9SM while OS falls back and has its four windings connected to the odd select magnets 1SM, 3SM, 5SM and 7SM. The relay OS in its present function guards against the balance of two adjacent select magnets acting on the same select bar, should two subscribers of the same group call at the same time, and does this by disconnecting the even magnets should an odd magnet except 9SM be used. The loop on wires OC, MA now operates the magnet 1SM, relay OS operating as just described, and relay MK follows the select magnet. A backward mark from a transmission relay set and register seized for the call now energizes the bridge magnet 1BM over the P wire and the link is marked busy by disconnecting earth. A parallel connection of all bridge magnet contacts earths a lead GB, Fig. 4, so that if the selector is fully occupied this is signalled by removal of earth from GB. The register is now connected to the calling subscriber's line circuit and tests continuity of the negative speech wire, detects class of service over the same path, and tests the positive wire by connecting up relay K in the time circuit which operates with P following to hold K to the P- wire. With P operated, the loop across wires OC, MA is broken and the select magnets 1SM, 1AM, restore with relays OS, M, OM, OC, MA, MK and G. Provided all select magnets are restored G re-operates to condition the selector for further use. The connection is now held from the transmission relay set and the subscriber dials. Had the call come from a subscriber in the second group the magnet 2AM and relay MB would have responded provided no first group call operated OS to gain priority. A third group call would involve magnet 3AM and relay MC provided there is no first or second group call, but with a third group call the magnets 1AM,2AM are disconnected to prevent the other groups interfering once a third group call has got this far. If calls occur simultaneously in all three groups magnet 1SM comes up with OS, which disconnects 2SM, but 3SM operates also. When MA responds, however, MC is disabled and 3SM is released. Similarly, if second and third groups calls coincide, 2AM and 3AM operates, but MB operates to disable MC and release 3AM. The simultaneous occurrence of calls in the same group are given priority according to their position in the contact chain lsm2 to 9sm2 of the selector magnets, Figs. 4 and 6. Call termination.-A wanted line circuit is marked on terminal M from a 500 line marker (not described). The mark is passed to the selector on wire SM and is returned over a contact of relay MAR, MBR or MCR depending on the group of the subscriber, by way of wire AM. If the line circuit is idle the marked wire AM is connected to wire TM, which at the selector signals lead PA to the marker, but if the line circuit is busy the wire AM connects the mark to wire TO to signal the marker on lead PB. A mark on PB releases the marker unless trunk offering is to be made. A mark on PA produces a backward earth from the marker on lead PC to operate relay TC, relay TM following. Relay OC is thereby disconnected so that the selector cannot entertain originating calls from its line circuits. Contacts of TM now connect the wires TM or TO to the appropriate group magnet 1AM, 2AM or 3AM and relays MAR, MBR, MCR, control the connection of the select magnets 1SM to 9SM to the appropriate line circuit group. The relays M and MK operate with the appropriate select magnets and a free link marked by M is seized by the transmission relay set and earth returned on the P-wire to energize the associated bridge magnet from 1BM to 10BM. Energization of a bridge magnet connects the speech path and momentarily pulses a lead RI which fires a cold cathode tube in a route indicator whereby the path may he traced in the event of fault conditions. With the speech path connected the class of service presented by terminal CT in the line circuit is sensed by the register and relay K is operated to the positive wire bringing relays P and LR with it. Ringing current is supplied and all relays and magnets except the bridge magnet release, relay G reoperating when all the select magnets have restored. The selector is now available for further use. As the marker sets up terminations one at a time no interference between groups is to be expected but the selector may be involved with an origination when the marker seeks a termination. In this event the origination in hand is completed and the termination is taken next as is ensured by the disconnection of the operate winding of originating relay OC which remains held over its other winding. When the origination is set up, OC falls back and is then out of service until the selector has handled the termination. Trunk offering.-This is effected in the face of a busy line circuit by causing the marker to ignore the busy connotation of lead PB so that a further bridge on the subscriber's line circuit common is operated and held by a special operator's relay set. The earth holding the further bridge magnet is isolated from the bridge magnet of the existing speech path by a rectifier MR1 so that the intercepting or existing paths may be cleared down independently. The common connection of wires TM and TO by the contacts of relay TM enables a termination to be effected whether the line circuit is idle or busy. Release and alarm circuits.-The transmission relay set releases to disconnect line circuit relay K so that the bridge magnet and relays LR and P follow. If a local call meets busy conditions the transmission relay set releases and K falls back but LR stays up to connect busy tone. A lead PGA is marked with resistance earth to start an appropriate alarm circuit (not described). This alarm circuit is also active if the subscriber fails to dial, as earth ceases to be returned on the P-wire, and is also active if this earth fails or if the line wires are short circuit. If it is wanted to " busy out " the selector the jack TJ1, Fig. 6, is withdrawn and relay G relapses to disconnect the auxiliary magnets and put the selector out of service. Any relapse of relay G connects an alarm lamp LP and an alarm circuit AL which responds if G does not