GB2097224A - Digital concentrator and/or multiplexor - Google Patents

Abstract

In a telephone exchange system, the subscriber lines (TLN1, etc.) are connected in groups of, for example, six to intermediate switching stations (RU) each of which is connected via its own PCM link (Vltg) to an interface (RU-IF) in a central control circuit (CU). Each link is a four-wire line using two two-wire lines, with DC supply thereover from the central control unit to the remote units in phantom. Each remote unit has DC-DC convertor with a "buffer" battery. <IMAGE>

Description

SPECIFICATION Digital concentrator and/or multiplexor This invention relates to peripheral system for connnecting subscriber stations to a telecommunication switching centre, particularly a telephone switching centre, wherein the subscriber stations, particularly such stations which are busy only for a short time, are connected by respective lines to an intermediate switching station associated with those subscriber stations and connected to a switching centre.

In one such system a PCM concentrator forms a peripheral switching system for a switching centre, with concentrating units remote from the switching centre and each asscoiated with a plurality of subscriber stations and connected to the switching centre by at least one PCM link, which preferably consists of a ring line. Each concentrating unit has a control device for setting up a connection from and to the associated subscriber stations, and line circuits associated with those stations. Such line circuits may perform, if desired, analog-to-digital and digital-to-analog conversion, each line circuit being identified by a call number.

Such a system distributes all connecting lines of the system as freely as possible to the concentrating units and can easily change that distribution dependent on changing requirements so that all connecting lines of the concentrator can be utilized. To do this the control device of each such unit effects a time-selective control of a signalling stage, whereby the concentrating unit extracts all call numbers from the bit stream and offers them to all line circuits of the concentrating unit at a time different from the times used for speech channels. Each line circuit is preceded by a comparator, in which the call number identifying that line circuit is stored and these call numbers are compared with each ofered call number.In case of a coincidence of the compared numbers the comparator delivers to the control device of the concentrating unit for the respective line circuit a signal indicating that the line circuit is addressed by the call number offered to it and activates the respective line circuit for the reception of the signal information for it and for the transmission of the signal information delivered by it. When a speech channel has been allocated to a call number, the control device cyclically offers the number to the line circuits at a time corresponding to the channel number, and activates the line circuit identified by that number for reception of incoming speech information. The information from the incoming PCM line is delivered by a bypass gate directly to the outgoing PCM line, except when a line circuit or the signalling stage of the respective concentrating unit has been activated.

Such a system in a concentrator and can be used only as such.

In another system there is an arrangement for connecting a PCM concentrator as a peripheral system to a conventional switching centre operated as a space division system with analog signals, analog-to-digital and digital-to-analog converters being provided between the central station of the PCM concentrator and the space division system. The PCM frame of the concentrator includes PCM speech channels and at least one signal channel. The central station has a control device for converting the dial signals and indicating tones, especially signals representing the last digit, from the signal wires of the space division system to PCM information in the signal channel(s) of the PCM frame and for converting such PCM information from the signal channel(s) of the PCM frame to dial signals indicating tones of the space division system.An analog-to-digital converter and a digital-to-analog converter are permanently associated with each PCM speech channel in the PCM frame. The interfaces used in the concentrator for setting up a connection from the subscriber station to the switching centre are connected, without an interposed subscriber concentration stage, to that selector stage of the space division system in which the first dialled digit is processed, i.e. not processed in the concentrator. The interfaces used in the concentrator to set up a connection from the switching centre to the subscriber station are connected to that selector stage of the space division system in which the last dialled digit not processed in the concentrator is processed.

Such an arrangement can be used only in connection with a conventional switching centre consisting of a space division system and controlled by analog signals, and no concentration is effected.

It is an object of the invention to provide a peripheral system of the kind described first above which can be used as a concentrator and/or multiplexor and can be connected to switching centres consisting of space division or time division multiplex systems and operated by analog and/or digital signals.

According to the invention there is provided a peripheral system for connecting subscriber stations to a telecommunication switching centre, particularly a telephone switching centre, wherein a number of subscriber stations, particularly such stations which are busy only for a short time, are connected by respective lines to an intermediate switching station associated with those subscriber stations and connected to a switching centre, wherein the peripheral system includes a piu- rality of intermediate switching stations at spaced apart locations and each of which serves a plurality of subscriber stations, wherein each intermediate switching station is con nected by at least one and preferably two twowire connecting lines to a central switching device and wherein the system is usable as a multiplexor and/or concentrator and the connection and the exchange of information between the central switching device and the intermediate switching stations are performed in time division multiplex manner.

Such a system has the advantage that it can be used as a multiplexor or concentrator and that both modes of operation can be combined. Another advantage is that the system when used as a multiplexor does not restrict traffic, so that even subscriber stations which are busy for a long time and particularly private branch exchanges can be connected to such a system.

Since in our system the intermediate switching stations are connected to the switching centre or the central switching device by individual lines in a star-shaped pattern, the connecting network is compatible with the layout of existing cable systems since existing local networks are also star-shaped.

The use of individual lines in a star-shaped pattern has the further advantage that the system is reliable because a line defect can only cause a single intermediate switching station to fail, whereas in the system mentioned above a defect and failure of the ring line causes a failure of all connected concentrating units and the subscriber stations associated with them. A defect of a concentrating unit may have the same result.

An embodiment of the invention will now be described with reference to the drawings, in which Figure 1 is a circuit diagram of a peripheral system embodying the invention, Figure 2 shows the circuit of the central switching device, and Figure 3 shows as an example an arrangement in which the power supply in the central switching device has been interrupted and a testing device is connected to the four wire circuit.

In Fig. 1 a central switching device CU is connected by N four-wire connecting lines Vltg to N intermediate switching stations RU.

As shown, each intermediate switching station serves six subscriber stations TLN. One subscriber station TLN has been replaced by a data terminal DE.

The central switching device CU is connected via a central interface subassembly A IF and a multiwire connecting line to a telecommunication centre VmSt. The lines Vltg leading to the intermediate switching stations RU are connected to associated interface subassemblies RU-IF, which include intermediate memories for compensating for differential delays which occur in the various lines due to their different lengths.

A sequence control device SPC controlled by a stored program controls the sequences of operations performed in the central switching device CU. If the switching centre VmSt is so designed that it can perform all or part of the functions of the switching device CU, the latter may be integrated in the telecommunication switching centre entirely or in part.

Fig. 2 shows the circuit of the central switching device CU. Each connecting line has associated with it one interface subassembly RU-IF, one or more central interface subassemblies AIF, a sequence control device SPC controlled by a stored program and all auxiliary subassemblies. The latter are not shown in Fig. 2 because they are not significant for the function of the system according to the invention.

The subassemblies RU-IF, ...., AIF are interconnected by two different buses, namely, a control data bus Sts and a speech bus Sps.

The control data bus Sts connects the sequence control device SPC, which is controlled by a stored program, to the interface subassemblies RU-IF and the central interface subassembly AIF and serves for an exchange of control data. The speech information or data to be exchanged between the interface subassemblies RU-IF and the central interface subassembly AIF are transmitted by the speech bus Sps. It will depend only on the property of the interface subassembly AIF whether the device CU acts as a concentrator or multoplexor. The device CU acts as a multiplexor if the central interface subassembly comprises for each subscriber station TLN a terminal for connection to the switching centre VmSt. In that case the TDM operation provides for a multiple utilization of the connecting lines between the switching device CU and the intermediate switching stations RU.This explains the use of the term "multi plexor".

On the other hand, the device CU acts as a concentrator if the number of terminals in the central interface subassembly and connected to the telecommunication switching centre is less than the number of subscriber stations TLN. In that case, the sequence control device SPC ensures that a desired connection between the switching centre VmSt and a station TLN is set up via a free terminal of the central interface subassembly AIF.

Fig. 3 shows the central switching device CU can be conductively connected to each subscriber station TLN connected to an intermediate switching unit RU. Only the power supply circuit of the central switching device CU is shown in simplified form. The connecting line Ltg1, Ltg2 consists of four-wire circuit and serves to transmit information in TDM manner.

During normal operation the switches K7A, K7B and the switches K8A, K8B are in position N so that the power supply in the switching device CU is connected by a voltage converter SPW to the buffer battery BAT in the intermediate station. For test purposes, for instance, these switches may be set to position P so that the power supply in the device CU is disconnected and, e.g., a test device PG is connected to the four-wire circuit. When the switches K1A ... K6A, KiB ... K6B of the desired subscriber station are closed, the fourwire circuit is conductively connected to that station TLN. As shown this is the case for the station TLN 1.

The switches K1A ... K6A, K1B... K6B are controlled by a control device ST when the same has received the corresponding instructions from the central switching device CU via line Ltg 1.

Claims (8)

1. A peripheral system for connecting subscriber stations to a telecommunication switching centre particularly a telephone switching centre, wherein a number of subscriber stations, particularly such stations which are busy only for a short time, are connected by respective lines to an intermediate switching station associated with those subscriber stations and connected to a switching centre, wherein the peripheral system includes a plurality of intermediate switching staions at spaced apart locations and each of which serves a plurality of subscriber stations, wherein each intermediate switching station is connected by at least one a preferably two two-wire connecting lines to a central switching device and wherein the system is usable as a multiplexor and/or concentrator and the connection and the exchange of information between the central switching device and the intermediate switching stations are performed in time division multiplex manner.

2. A peripheral system according to claim 1, wherein the intermediate switching stations are remotely powered preferably via a fourwire circuit which preferably consists of two two-wire circuits, and wherein each intermediate switching station has a buffer battery which supplies power in case of a short-term failure of the external power supply.

3. A peripheral system according to claim 1 or 2, wherein the lines from the central switching device to each subscriber station connected to an intermediate switching station are conductively connected, so that the subscriber loop can be analogously tested preferably via the four-wire circuit when the power supply has been disconnected.

4. A peripheral system according to claim 1, 2 or 3, wherein the terminals served include data terminals connected to at least one intermediate station, which data terminals digitally co-operate with the intermediate switching station.

5. A peripheral system according to claim 1, 2, 3 or 4, wherein the central switching device has a sequence control device controlled by a stored program, interface subassemblies associated with the intermediate switching stations, and one or more central interface subassemblies for connection to the switching centre.

6. A peripheral system according to claim 5 wherein the interface subassemblies associated with the intermediate switching stations include intermediate memories for buffering the information signals transmitted with different delays to that the writing and reading operations can be performed independently of each other and the sequence in which the information has been written in will be retained.

7. A peripheral system according to claim 1, 2, 3, 4, 5 or 6, wherein a telecommunication switching centre, preferably a pulse code modulation switching centre controlled by a stored program, is provided to perform the functions of the central switching device.

8. A peripheral system for connecting a number of lines to a telecommunication switching centre, substantially as described with reference to the accompanying drawings.