Patent GB-1131367-A (GB)
Title: Improvements in or relating to automatic telephone systems
Inventor: HEMMINGS WILLIAM ARCHIBALD CHA
IPC: H04Q3/00
Filed: 1965-11-18
Abstract: 1,131,367. Automatic exchange systems. HER MAJESTY'S POSTMASTER GENERAL, and AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. 31 Oct., 1966 [18 Nov., 1965], No. 48962/65. Heading H4K. A group selector (comprising primary and secondary matrices of cross-point relays, the inlets to the primary stage having individual access circuits and the outlets of the secondary stage being formed into levels each comprising corresponding outlets of the switches comprising the secondary stage) has control equipment which enters service for any one seized access circuit and indicates what links emanate from the primary switch serving the seized access circuit, and has an interrogator which determines what free outlets exist in a numerically indicated level in accordance with the links giving access to the level, and means to nominate one idle outlet for use, the path from access circuit to outlet being set up by first operating a primary switch cross-point and then a secondary switch cross-point. The selector described comprises two switching units SU1, SU2, Fig. 1 (not shown), each unit having four primary switches providing twelve inlets and twenty outlets each and having twenty secondary switches providing four inlets and ten outlets each. The 200 outlets of each switching unit are divided into ten levels of 20 outlets each, or into fewer levels some or all of which comprise 40 outlets. The cross-point relays are preferably reed relays. The levels in each unit are accessible in accordance with a corresponding dialled digit. The outlets may be graded with other units to outgoing trunks. The grading may mix outlets of cross-point selectors and two-motion selectors. Cross-point selectors of the kind described may be worked from or into two-motion selectors. As shown in Figs. 2, 3 and 4 (which show only one access circuit AC, a single cross-point in each stage of the switching unit SU1, and one trunk circuit TC), the common control comprises a call isolating device CI. Relay LR operates in a seized access circuit and contacts LR1 are connected to respective terminals 1X-8X of CI to indicate which of the eight primary switches is involved. Contacts LR2, by selectively bridging one of terminals 1Y-8Y and 1Z-12Z identifies the inlet to CI which responds by operating one and only one relay RA in an array of such relays forming a register connector RC. The lead S from the inlet connects over RC to a register SREG, termed the stage register, to identify the primary switch concerned on leads 1SS-8SS and to seize the register. One of a set of marking leads 1A- 8A is marked from CI with 50 volts negative to interrogate over diodes DIA the set of twenty links available to the access circuit. A busy such link is marked with 10 volts negative. These links are viewed by an interrogatormarker I/TM by way of diodes DIB, the links being grouped in mutually exclusive groups of 4 connected to the test leads 1B-20B which indicate thereby the available links. Interrogator-marker I/TM serves both switching units on the one set of test leads, discrimination being available from the isolator CI on leads 1PS-4PS. Once seized the register SREG returns a proceed-to-send signal to the main register (not shown) which responds by forwarding the required routing digit as one of a number of possible potentials on each leg of the speech wires. The digit is set up in SREG as a mark on leads D1-DO and applied to a variable availability device VA which converts the decimal mark to a mark appropriate to the level grouping employed. If the outlet levels comprise equal groups of 20 the leads D1 to D0 are strapped to corresponding leads AD1 to AD0. If, however, some of the groups have 40 outlets the variable availability device VA operates to inspect a set of 20 of these outlets as first choice outlets and if this set is fully occupied it proceeds to the second set as second choice outlets. The variable availability device VA has an all paths busy relay which normally operates to signal the main register and release the group selector unless the relay is inhibited by notice of an available path on lead FPA from a path selector PS. The particular levels to be interrogated are indicated to the interrogator-marker I/TM over leads 1L(1)- 10L(1) for switching unit SU1 and over leads 1L(2)-10L(2) for SU 2 . The trunk circuits TC are idle if there is no potential on lead C, earth on this lead indicating busy. The interrogatormarker also deems the trunk circuit busy if the C lead has negative battery as can occur if, with mixed switches, the circuit is being tested by an electromagnetic switch in another group selector. The C leads are connected over a matrix of 400 diodes DL, DO, each connection over DL being to one out of ten terminals 1(L1)-10(L1) and each connection over DO being to one out of twenty terminals 1(01)-20(01) for switching unit SU1, a similar set of terminals to I/TM being provided for SU2. To test the outlets in the indicated level, route relays in I/TM place 50 volts negative on a terminal of the set 1 (L1)- 10(L1), for SU1, and all idle trunk circuits in the level of twenty so interrogated show up on the set of twenty terminals 1(01)-20(01), for SU1. Idle links between the primary and secondary switches which give access to available outlets are signalled to the path selector PS which makes a choice from the available routes. The basis of such choice is altered with each successive path by promoting each choice ahead of its preceding choice in pairs. Distribution of traffic over the secondary switches is effected by giving a different starting point in the order of choice for each level. As soon as a choice has been made it is signalled to I/TM over leads 1FB-20FB and a busy mark is put on the C lead of the chosen trunk circuit TC by applying a mark to the appropriate one of leads 1(01)- 20(01), for SU1, which over a diode D0 selects that one of the twenty trunks in the required level. Choice of a route also causes the stage register SREG to signal the main register, which ceases to send the D.C. coded digit on the speech wires, and puts 50 volts positive on lead ILM to operate relay K in the access circuit. With K up LR falls back and 50 volts negative is connected over surge diode D4 to the H-wire. Of the twenty cross-point relays A available to the access circuit that one operates that is marked over leads 1LM-20LM from the path selector PS. The operating path includes a Zener diode in PS the voltage across which over the H-wire operates that one of the ten available B relays that is marked over leads 1TM-10TM from I/TM. The relay HR now oprates in the chosen trunk circuit and busies the C lead forward for the duration of the connection, the existing busy condition from I/TM being removed when the control circuits retire. Although LR is released CI remains seized over RH from SREG until a second digit is received which is taken as confirmation that a proper path has been established. SREG removes 50 volts from ILM, K holds to the H-wire and earth appearing over D2, D3, to a lead FDL precipitates release of the control circuits. The contacts K3 isolate the matrix to permit testing of matrix paths; a diode in this position would also serve. A fault detector and lock-out circuit FDL is available to all the functional control circuits and over leads 1LO-8LO can lock out a primary stage switch in the event of a major fault. The identity of the chosen path is also available to a fault print out device should this be required. Where the group selector is being worked from a preceding stage that does not employ registers for overall control, number sending being by means of loop disconnect pulses, digit conversion equipment is provided in all paths to the access circuits which circuits have an additional relay SR (Fig. 5, not shown). SR operates on seizure to the H-wire and prepares for the operation of LR over the S-wire which does not occur, with its resultant demand on SREG, until a D.C. coded digit is available from the conversion equipment. If the group selector provides a path to a succeeding selector of the loop-controlled type the succeeding selector returns battery feed and earth on the S-wire to release the control equipment of the preceding group selector over which loop disconnect pulses are sent from the conversion equipment. If, however, the group selector provides a path to a selector of the same cross-point type using D.C. coded leg signalling the succeeding selector SR relay connects 12 and 50 volts negative to the speech wires to release the control equipment of the preceding stage.