Patent GB-917020-A (GB)
Title: Improvements in or relating to automatic systems
Inventor: BROWELL LESLIE JAMES
IPC: H04Q3/00
Filed: 1960-10-28
Abstract: 917,020. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Oct. 24, 1961 [Oct. 28, 1960], No. 37089/60. Class 40 (4). In an exchange in which a plurality of transmission relay sets are available to calling subscribers over line selectors and are terminated in groups on first selectors individual to each group, first choice registers are provided individual to each group and a second choice register is provided in common to a number of groups, there being a connector by means of which any relay set of the number of groups may be connected to its respective first choice register or to the second choice register provided a connector control circuit can nominate a free transmission relay set accessible to the originating trunk together with a free associated register and first selector. The exchange is of the type described in Specification 890,235 in which line circuits are grouped in 20 divisions of 500 lines each. As shown in the block diagram of Fig. 1, each transmission relay set TRS1 to TRS10, served by a first selector 1S, is accessible from one trunk in each of three divisions. The access path to each relay set includes a single marking wire to indicate a call from any division and a separate marking wire for each of the three divisions. By this means the control circuit for the register connector RC, which comprises an allotter AL1, selects the first free transmission relay set and, providing the first selector IS is free, selects the first preferred division should originations occur simultaneously. The register connector RC comprises a cross-bar switch with ten select magnets and a first pair of bridges BR and BR2 whereby a multi-conductor path may be extended from any allotted one of the relay sets TRS1 to TRS10 to the associated first choice register 1REG1 or to the second choice register 2REG1. Three other groups of transmission relay sets TRS11 to TRS20, TRS21 to TRS30, and TRS31 to TRS40, together with associated first choice registers 1REG2, 1REG3 and 1REG4, are similarly accessible from originating trunks and are served by bridges BR3 to BR8 of connector RC, all the evennumbered bridges serving the second choice register 2REG1 in common. Each of the groups controls the connector RC by means of an individual allotter AL1 to AL4. Nomination of transmission relay sets qualifying for selection.-Figs. 2 to 6, which should be arranged as shown in Fig. 7, give the detailed circuits of the transmission relay set TRS1, the connector bridges BR and BR2, andtheallotter AL1. In the quescent state of the transmission relay set TRS1 the relay BA, Fig. 3, is operated and connects the test relay 1MT to the test wire M in the access paths to the relay set from the distribution field TDF, see Fig. 4. The test relay 1MT is connected in a lock-out circuit with the test relays 2MT to 10MT of the other relay sets of the group. When 1MT operates the division identifying leads T1, T2, T3 are extended to discriminating relays GA, GB, GC in allotter AL1, see Fig. 5. If the first selector is free it extends negative resistance battery over a contact g, Fig. 3, to a chain of contacts of the discriminating relays and this enables the first such relay marked over leads T1, T2, T3, in that order, to respond and lock out the other two. The divisions are, therefore, given an order of priority for simultaneous originations. With GA operated, relay RD is energized, Fig. 5, and connects relay 1FC, Fig. 6, which tests for idle battery marking on lead RB of first choice register 1REG1. It may be arranged that a number of transmission relay sets compete for the same first choice register in which circumstances the relay 1FC would be one of a lock-out chain. If the register is idle, 1FC operates and locks up. Should the register be employed, relay RT which operates with RD releases RD slowly to transfer the testing circuit to the second choice register 2REG1. Supposing 1FC responds, the connector RC, Figs. 4 and 5, is seized by operation of relay 1AS, Fig. 6, which forms a lock-out chain with corresponding relays in the allotters AL2 to AL4, and by consequent operation of relays 1RS and H. This connects the select magnets 1SM to 10SM, Fig. 4, to test leads MTA from the relay sets and, since test relay 1MT of the lock-out chain is operated, a path is prepared for magnet 1SM and another path is prepared from test lead MTB for bridge magnet 1BM. A path is made over relay GA to busy the first selector 1S by operating a test relay, not shown. In this condition the relay set and allotter indicate that they qualify for possible selection. Selection of a transmission relay set and first choice register.-Originating trunks available to a subscriber are distributed over trunk sections of the exchange, each of which comprises 160 originating trunks terminated on relay sets such as TRS1. An interrogation of these trunks with the effects described above is carried out from line selector secondary switches where test relays will operate to indicate trunks terminated on relay sets qualifying for selection. A start shift circuit in the line selector switches now indicates the next in cyclic order of trunks to be used and the first qualifying trunk of those so allocated is taken into use. A bridge in the line selector secondary switch operates and connects the private and speech wires back to the primary switch causing earth to be returned on the lead H to the relay set TRS1 supposing that this is the relay set involved. Earth on lead H is passed to leads MTA and MTB to the connector RC where select magnet 1SM operates and completes the path prepared for bridge magnet 1BM which operates and holds over the connector outlet HA to the H lead. A nine conductor path is now extended from the relay set to the register and leads MX, MY are extended from the register to the first selector 1S where according to which one of two possible trunking subsections are to be employed a relay RA or RB responds. Earth on lead IR from the register operates relay MP, Fig. 3, which prepares an " immediate ring " facility from a continuous ringing lead CR and which operates relay J. A contact of J returns the earthed H lead back over the P-wire which effects the extension forward of the speech wires to the relay set. Earth is now extended from the H. wire of the register to hold the originating path. Leads + I and - I of the register are connected with the speech wires and enable class-ofservice to be determined and dial tone to be returned. The control circuits in the primary and secondary line connectors are released and 'return all nominated but unselected relay sets to their quiescent states. With the end of control from the line connectors test relays 1MT1 and GA release in the relay set TRS1 and the allotter, relays RT, 1FC, H, 1AS and 1RS releasing in consequence together with magnet 1SM. The originating connection is now established for dialling and the register may proceed to set up the call. Employment of second choice registers.-As described above, the test made by relay 1FC for a first choice register lasts for as long as relay RD takes to release and, if during this time the register is not marked idle, relay 1FC falls back leaving relay 1SC energized so that a path is prepared for the bridge magnet 2BM giving access over connector RC to the second choice register provided this is marked idle on the lead RB. Relay 1AS now operates in a lock-out chain with relays 2AS, 3AS and 4AS to bar access to the register from allotters AL2, AL3 and AL4. The transmission relay set is thereby nominated for possible selection in the' same way as with a first choice register except that the nomination is subjected to a delay of about 40 ms. and will not mature in competition with an available nomination involving a first choice register as this will have been selected by the line connector stages within the delay period. Register establishes local connection.-Having received the dialled digits the register employs a marker to set up the connection according to the " self-steering principle " described in Specification 890,235 whereby once the switching stages are prepared the register applies earth on lead PO to operate bridge magnet 1BM of first selector 1S which in turn operates a bridge in the next stage and so on up to the called terminal. The register next evaluates the class - of-service to be given the called line by testing the negative wire over lead - O while lead +O makes a test for continuity of the loop over the +ve wire which, if successful, operates the called subscriber's cut-off relay. Relay TC is now operated over the TC lead from the register so that continuous ringing current is supplied to the called line from lead CR to battery RRB. Ringing tone for the calling line is sent direct from the register until earth is removed from lead IR to release MP, whereupon relays B, A and SW respond and BA falls back. Ringing tone source IRT is now connected through as is interrupted ringing current lead IR and the connection is now held independently of the register. Reply.-Lightly adjusted contact f4 of relay F opens to the loop connected by reply and allows F to respond fully, Fig. 3. Relay DT is operated to feed the called line and reverses the calling line polarity. Relays DR and MP follow DT while J releases slowly. Relay MP stays up while J falls back to transmit a 100 ms. hold and metering pulse. Subscriber busy.-Subscribers' line circuits may be conventional or of the " drop-backbusy " type described in Specification 909,237. With conventional line circuits, should the marker find a line busy, preparatory setting up of the called path is not undertaken. Earth is not put on register lead PO and is removed from lead IR so that MP releases. Battery on lead TC operates relay TC followed by relays B and A so that busy tone is connected from BT while the register and connector release. With "drop-back-busy " line ci