Patent GB-1251075-A (GB)
IPC: H04Q3/00
Filed: 1968-06-07
Abstract: 1,251,075. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. 29 May, 1969 [7 June, 1968], No. 27276/68. Heading H4K. In a cross-bar system of the self-steering type, two sets of marking leads are provided in the line distributer stage whereby an originating call and a terminating call can be set up simultaneously provided that the calling and called subscribers are not connected to the same switch. Simultaneous calls are dealt with on a priority basis, the order of priority being changed after each call. It should be remembered that the self steering cross-bar system of 890,235 incorporates arrangements for setting- up simultaneous calls in a router stage. The line marker includes separate portions for handling originating and terminating calls as distinct from the system of 909,237. General description (Fig. 1)-A single 500 line, line distributor LD comprises twenty, 26 x 10 B switches linked to eight, 26 x 10 A switches. In the latter 5 inlets OT are for use in originating calls and consequently are connected to transmission bridges TRG each of which has access to a pair of registers REG and also has access to an A switch inlet RSA of a router stage (not shown). The other 5 inlets of the A switches are for terminating calls and so are connected to outlets RSB of B switches in the router stage. The cross-bar switches are arranged for triple group working viz each bridge magnet controls three bridges one only of which is used under the control of an auxiliary select magnet (see 890,235 for example). In each switch the 26th outlet is only used for interception service. It will be apparent that as there are only 8 A switches, each B switch must be connected by two links to two of the A switches and by one link to the remaining 6 A switches. A line marker LMR is associated individually with the line distributer. It includes a sequence circuit SSB for altering the calling priority of the B switches in groups of 5 (the priority within a group remains the same) after each connection is set up and a sequence circuit SSA for similarly altering the priority of the individual A switches. Further details of these sequence circuits can be obtained in Specification 1,077,472. Outgoing call.-Looping of a subscriber's line S (Fig. 2) brings up his line relay LR. A permanent ground alarm and display in the marker is accordingly cut-off by contacts LR3. Relay N comes up from battery and resistor 3 in the switch control circuit DSB1 (Fig. 3) via the marker to lead NB and thence back to earth in the marker via lead LM. An earth is extended over lead CP so as to bring about the operation of an LM relay which corresponds to the outlet level of the calling subscriber, which level is indicated by the continuity over the LM lead due to closure of contacts LR1. Corresponding LM relays for other calling subscribers in this switch (assumed to be the first B switch DSB1) and in other switches are also energized. It is assumed that the sequence switch SSB is marking the lead CSA of the first B switch group with negative potential. Consequently if the marker now removes the negative on the NB lead one and only one N relay in the five switches comprised in the group will remain operated since these relays are arranged in a chain (lead CFA) with DSB1 having the (fixed) highest priority in the chain. The - ve removed from NB is applied to lead MG whereupon relay MO comes up in order to apply marking earth to the originating call marking leads MOL. Each bridge of a B switch has associated therewith one such lead and also has a terminating call marking lead MTL (about which see later), the symbol x 10 near the bridge off-normal contacts 1BM2 indicating the presence of the other nine (not shown) marking inlets of this switch DSB1. In order to prevent a terminating call from interfering, the control relay MT therefor is held-off by contacts MOl. The earth on all marking leads MOL corresponding to free links from switch DSB1 arrives at an inlet of an A switch of which Fig. 4 depicts DSA1. Here the upper MTL and MOL leads are connected to the switch DSB1, the others MTL and MOL leads being connected to other DSB switches. In the case where there are two links between a B and an A switch, the sequence circuit SSA ensures, in an unspecified manner, that only one of the two leads MOL is marked. For the switch shown (and similarly in all other A switches) the earth on MOL brings up OC (Fig. 6)-relay G viz contact G3 is normally operative. Thereupon the A switch terminating call control relay TM is held off by contacts OC2. The marker extends an earth over lead GS to hold G and OC and to bring-up OM. Another terminating call control relay TT (Fig. 4) is held-off by contacts OC7 (leads LA and LB are connected in the marker). With OC and G operative, earth is reverted over lead DS (Fig. 6) to the marker in order to ensure that one and only one LM relay remains operative to denote the highest priority caller in the one B switch whose originating calls are being dealt with (operated N relay). Consequently in the one B switch, a select magnet and an auxiliary magnet e.g. 1SM and 1AM are energized viz for 1SM, contact MO2 of the originating call control relay, contact 1LM1 of the one operative LM relay and contacts CP, MLA of marker control relays (not shown). In addition in all the A switches receiving earth on an MOL lead, the auxiliary and select magnets e.g. 1AM and 1SM, corresponding to the outlet level of the marked MOL lead, are energized in turn. Relay OS (Fig. 5) follows to disable all the unwanted even numbered select magnets once relay MA has come-up with energization of magnet 1AM. (This disablement prevents competition between the two magnets associated with each select bar). Once one AM magnet has operated, the others are held off by the contacts of the operative one of relays MAMCR (top of Fig. 5). Following these operations MK (Fig. 6) comes up to release any unwanted but operated odd-numbered selected magnets. In the interim, relay M (Fig. 4) is brought up to earth on OC provided by the sequence circuit SSA i.e. DSA1 is the first choice A switch for this call. Thereby test earth on leads MA1-MA5 (Fig. 7) is extended from the marker to test relays TA-TE associated with the five inlets I1-I5 of DSA1 leading to the transmission bridges. Simultaneously test potential is extended by contacts M2, M4, M6, M8 to the transmission bridges. Consequently those transmission bridges which are free and which have access to a free register bring up a test relay of TA and TB. (If two transmission bridges have access to a same register only one of these transmission bridges will operate a test relay). Earth (originating over lead GS) is thus sent over OR (Fig. 6) to the marker which responds by dropping M and applying earth to the lead ST. Thus the highest priority test relay i.e. TA holds and the rest drop. Class of service data is sent from the marker via contacts TA5/6/7 to the transmission bridge. The earth on ST also energizes bridge magnet 1BM (Fig. 7) whereby a request for a free register is sent as an earth on the H lead of inlet I1. The same earth is returned to the inlet's P- wire, then over the operated crosspoint to the BA link and thus to energize and hold bridge magnet 1BM in the B switch (Fig. 3). Contacts 1BM2 of this magnet 1BM remove earth from MOL so as to release magnet 1SM and relay OS in the A switch DSA1. G goes down after 1SM. Magnet 1AM de-energizes and the marker is dismissed by removal of earth on DS. MA drops followed by MK, OC, OM and TA. G therefore pulls up again. Earth from the transmission bridge on lead H of inlet I1 holds bridge magnet 1BM. In the line circuit K comes up and holds in series with LR to the earth on the P wire. Contacts K3 provide a busy indication. N is dropped followed by the relevant LM relay whereupon B switch magnets 1SM, 1AM restore. The removal of earth on lead CP completes the dismissal of the marker. MO drops. The seized register reverts dial tone via the transmission bridge whereafter the call is terminated to a local subscriber as detailed below or to an outgoing trunk-in both cases via A and B switches of the router utilizing self steering techniques. Reverting now to the testing for a free transmission bridge, if all these bridges are busy or if none has access to a free register, the marker brings up the M relay in each A switch viz a socalled mass-marking function, whereby test relays in one or more of the A switches should come-up. The switch nearest to DSA1 is chosen over the priority chain formed by ST and STA leads. Thereafter the operation proceeds as detailed above. Terminating call.-The transmission bridge when armed with sufficient information seizes the relevant line marker which then connects earth and - ve battery to leads ME and LE respectively (Fig. 2) in the wanted subscriber's line circuit. If he is free (K3 unoperated), the earth is returned from the marker to lead ML of the switch DSB1 (to which the wanted subscriber is connected) so as to bring up " terminating-call " relay MT. Originating calls from this switch are inhibited by the opening of contacts MT1. Meanwhile - ve on LE is sent to the marker to operate an LT relay corresponding to the outlet level of the wanted subscriber. Thus with a particular LT and MT relay operated, the select and auxiliary magnets e.g. 1SM and 1AM pertinent to the wanted subscriber are energized. Earth is extended over all the terminating call marking leads MTL associated with free bridges of switch DSB1. In each A switch the earth, after traversing the marker via leads LA, LB (Fig. 4), is effective to bring-up relay TT which then holds to earth on MH. (As before, G is normally operative. It should also be remembered, that only one of the leads MTL in Fig. 4 will be carrying an earth marking since the three leads shown emanate from different B switches). Consequent on TT, magnet 1AM is en