Patent GB-1374648-A (GB)
Title: Connection unit for linking subscribers to an exchange in a time- division communications switching system
IPC: H04Q11/04
Filed: 1972-06-30
Abstract: 1374648 Automatic exchange systems SOC LANNIONNAISE D'ELECTRONIQUE and COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CIT-ALCATEL 30 June 1972 [30 June 1971] 30845/72 Heading H4K A remote concentrator for linking subscribers over a TDM highway to a TDM central exchange comprises a mini processor which is connectible on a TDM basis over an order wire with a central control of the exchange and a two stage space division switching network for interconnecting subscribers line circuits with a set of junctors of which there is one per time channel on the highway. The network consists in its first stage of groups of switches wherein each group contains a variable number of switches in dependence on traffic requirements and all the switches in a group have corresponding ones of their outlets connected in parallel. The switches may consist of magnetically latched relay, cross-bar or reed relay crosspoints. Components are mounted on printed circuit cards and some integrated circuits are provided. General description.-A concentrator (Fig. 1) has 512 incoming lines B that terminate on line circuits located in block 1. Each circuit has an appearance on a switching network 2 whose 64 outlets terminate on individual junctors in a block 3. The junctors incorporate battery feed and ringing supply and 60 of them are associated, each with a respective one of the channels, on two, 30 channel highways LRO, LR1 via multiplexors 4, 5. Signals such as digit sending using D.C. loop disconnect, ringing, called party reply using battery reversal, and metering are exchanged with central control over order wires LV, LT, the signals occupying time slots associated uniquely with the junctors. Control of the concentrator in respect of line scanning, called party free/busy test, path search and path control is vested in logic unit 6. Logic unit 6.-This comprises a plurality of microprogrammes each consisting of 64, 40 bit words in diode matrix format which are mounted on printed circuit cards for entry into a programme store module. All the usual processing junctions such as add, shift &c. are provided by integrated circuits which are also mounted on circuit cards. Memory is provided for storing line and network status data and for keeping an eye on slow peripheral operation, e.g. by storing a tag in a delay timing circuit such that an interrogation of the peripheral for operation/ inoperation is instituted a preset time after an instruction has been given thereto. Communi. cation within the unit is effected over data buses which consist of a 16 paralel bit address bus and a 16 parallel bit instruction bus that must be used together in order to convey a valid signal. Communication with central control is effected over order wire highways LC for general control data, LU for specific marker data and LS for clock signals. The programming of the unit and some detail of the interconnection of the logic modules is given with reference to Figs. 7-9 (not shown). Junctor, Fig. 6 is formed as one of eight packs on a printed circuit card of which there are eight in a fully equipped concentrator. Each pack includes a polarized line relay (coils RL1, RL2, RL3) having a blade contact ILS for repeating dial pulses over order wire LT to central control. The winding RL3 is short circuited during ringing, i.e. when relay RS is operative, thus ensuring that the line relay is insensitive to the A.C. signal. The windings are formed on a ferrite pot core having an air gap, thus ensuring a high self inductance. The bi-stables shown in the lower part of the Fig. exercises a memory function in respect of:- ringing, PMS which operates driver relay RCS<SP>1</SP> and thus ring relay RS: answering loop detector RD which cuts off ringing after a loop has existed for between 32 and 64 msecs.: battery reversal PM1B: and metering PMTTX. The latter drives an integrated circuit T3 for gating a tone signal from a 12 KHz oscillator, common to all the junctors on a card, on to the speech wires. This permits operation of a subscribers home meter in the event that he is provided with one. The ringing supply comprises a "mains" transformer T3 whose secondaries are connected in series (rather than the usual parallel, thus saving some power that is normally lost due to the low impedance at 50 Hz of the line relay) so as to provide an 80 volt ringing voltage to the speech wires. The memories, apart of course from RD, are controlled by the main exchange central control without buffering by the local logic unit. Trunking.-The network consists of eight groups of AB switches each of which groups can accommodate up to 64 lines (i.e. 512 in all) and which are connected with full availability to sixteen C switches that each have 4 outlets i.e. 64 in all. An AB group may consist of between one and four 16 + 16 switch units in dependence on the traffic load expected but the outlets of all these units are multiplied so that any AB group only has 16 outlets extending towards the C stage. Each unit consists of two stages of 4 x 8 matrices of which there are 4 in the A stage and in 8 the B stage so as to provide full availability. In order to increase the number of lines terminating on a group still further up to say 64, an additional concentration stage of so-called automatic distribution sub-frames may be provided between the line circuits and the switching network (Fig. 5, not shown). The frames may be standard concentrator switches permitting a 60 to 12 concentration but the equivalent switch at the exchange end is not provided since its function is assumed by the logic unit in conjunction with a memory for each frame. In each memory is stored the current allocation of a line to a "trunk" i.e. an inlet to network 2, the memory not being cleared of this information until such time as the trunk is taken into use on a subsequent call. The memory utilizes 6 bits per subscriber address, together possibly with further bits for indicating the line state and a fault condition. A diode matrix type look-up table is used for both-way directory/equipment number translations during the calling and called phases of a connection. Maintenance.-Each logic unit has a visual display of light emitting diodes for providing an instantaneous picture of the condition of the programme store and other key logic modules therein. A unit is programmed for self diagnosis on command by central control. The diagnosis consists in shuffling data around the unit and  observing its progress against a standard. Test commands are conveyed over a 4 parallel bit bus in the unit, this bus having a higher bit rate than the address and instruction buses. Routine testing is effected with the aid of a particular one of the incoming subscriber lines and with four of the junctors having outlets D61-D64 (Fig. 1). Recovery from a fault situation may be instituted locally under manual guidance or remotely by the central control.