Patent GB-1534303-A (GB)
Title: Electronic switching system
IPC: H04Q11/04
Filed: 1976-01-20
Abstract: 1534303 TDM electronic switching systems; concentrators OKI ELECTRIC INDUSTRY CO Ltd and NIPPON TELEGRAPH & TELEPHONE PUBLIC CORP 20 Jan 1976 [3 Feb 1975 19 Feb 1975] 2175/76 Heading H4K A TDM electronic switching system includes a space division switching network acting as a concentrator having a plurality of self latching electronic contacts at each crosspoint said contracts comprising an analogue switch, and an electronic switch control circuit having cyclic read-out-type memories and decoders, the network being connected between subscribers and a TDM central exchange system and is controlled by the control circuit. In an embodiment, Fig. 2(A and B), the space division network SD-ESW is connected between line circuits LC0 to LC31 and subscribers SUB0 to SUB255, i.e. it is used as a line concentrator. Each crosspoint connection e.g. S0-0 is a self latching electronic contact comprising a thyristor or TRIAC switch (Fig. 3 not shown); the contacts are closed by X-Y two dimensional selection and held by speech current through transistors or optocouplers. Each line circuit (Fig. 4 not shown) is capable of supplying speech currents and transmitting signalling tones. G0 to G8 are timedivision gates and LSCN is a line scanner. PHM1 and PHM2 are memories whose outputs, decoded through decoders DEC1, DEC2 respectively, control the X-Y two dimensional selection of the crosspoints of the network SD-ESW. WGT is a writing gate for writing information into the memories PHM I and PHM2. LCC is line concentrator controller for controlling a remote line concentrator and HOW is a howler trunk for applying a bowler tone to a subscriber's handset which is off the hook for an extended period of time. PCM COD/DEC is a PCM converter for further mutiflexing the TDM voice information received on any of the gates G0 to G8. Operation.-The operation of the embodiment will be described with reference to an outgoing call connection; assuming a PCM-24 system is used: Outgoing call connection.-A call generated by a subscriber e.g. SUBO is detected by the scanner LSCN or a central processor unit, not shown. The scanning information and information relating to the subscriber's storing address is transmitted by the central processor and written into an idle channel e.g. CH of the memories PHM1, PHM2 through the writing gate WGT which is controlled by a remote line concentrator through controller LCC or by an intra-office concentrator through the X-terminal of gate WGT. The address of the calling subscriber SUB0 is written in PHM 1 and the information for opening gate G8 is written in PHM2. Every time channel CHx comes up the stored information is read out, decoded by decoder DEC1, DEC2 and used to connect SUB0, through crosspoint S0.8 to line circuit LC8 and to open gate G8 so that the voice information from SUB0 is passed, in TDM mode, to the converter PCM COD/DEC. When the call finishes the information written in channel CHx of memories PHM1, PHM2 is erased by the central processor so that the connection is released. In a modification, Fig. 5, two line concentrators CONC0, CONC1 are used to cater for 512 subscribers. Each concentrator is the same as the one described above with reference to Fig. 2 but the output of the space division switching networks SD-ESW 1 and SD-ESW0 are cross connected, as shown, to increase reliability. In another modification (Figs. 6a, 6b, not shown) an extra row of crosspoints (S0-33 to S255-33) is added together with a single subscriber state detector (CD, Fig. 7, not shown) so that each subscriber is connected to the detector in turn, on a time division basis. The embodiment of Fig. 2 may be further modified to provide a time divisional ring-trip function by the addition of an extra row and an extra column of crosspoints (Fig. 9, not shown) which are connected to the ringing signal (RG) and ringback tone (RB) terminals respectively of a bell ringing circuit (BELL). A speech current supply circuit (Fig. 10, not shown) which has a current source instead of a voltage source may be used in the embodiment of Fig. 2 to obtain a substantially constant speech current. In a modification of the speech current supply circuit (Fig. 11, not shown) a polarity reversal circuit (DIR) is provided. Fig. 12 shows a modification of the emobodiment of Fig. 2 to facilitate intra group switching of a call in the concentrator itself. A first group of gates G0-G31 is connected, via a common time division bus HW to a second group of gates H0-H2 and two memories, Cl, C2, for storing analog signals corresponding to the speech samples of the originating and terminating subscriber are provided. The stored samples are transmitted to the respective subscriber during their relevant time slots. The above described circuits e.g. crosspoint switches, state detectors etc. may be manufactured as IC's on printed circuits.