GB2067877A

GB2067877A - Apparatus for Digital Facsimile Transmission

Info

Publication number: GB2067877A
Application number: GB8101650A
Authority: GB
Original assignee: Siemens Corp
Current assignee: Siemens Corp
Priority date: 1980-01-22
Filing date: 1981-01-20
Publication date: 1981-07-30
Also published as: FR2474261B1; JPS56110361A; DE3002188A1; GB2067877B; FR2474261A1

Abstract

In a digital telephone subscriber station T/n of a digital telecommunications network, an analogue (transmitting voice frequency analogue signals) facsimile transmission device Fax is connected via a digital (delta) modem A/W to a multiplexer/demultiplexer Muldex for respectively combining and separating transmitted and received 32 kbit/s subsidiary channels two of which comprise a 64 kbit/s standard channel. One of the two subsidiary channels carries telephone signals and the other carries facsimile transmission signals. One form of the multiplexer/demultiplexer Muldex is described. The digital telephone may be provided with a delta modem A/D. <IMAGE>

Description

SPECIFICATION Apparatus for Digital Facsimile Transmission The invention relates to apparatus for digital facsimile transmission, in particular for transmitting digital signals in a subsidiary channel of a 64 kbit/s standard channel in a further subsidiary channel of which, digital telephone signals are transmitted.

Transmission of this kind, in which telephony and facsimile transmission occurs, for example, in two 32 kbit/s subsidiary channels, which convey respective AM (delta-modulated) signals, of a 64 kbit/s standard channel (see German specification AS 27 29 689), is likely to be found in future service integrated telecommunication networks (ISDN) which permit the transmission and switching of digital signals in respective 64 kbit/s standard channels and which will also comprise appropriate digital telephone equipment and digital facsimile telecopiers in the subscriber stations.

Until such time as a service integrated digital network is introduced and perfected, a large number of the currently available facsimile telecopiers, which transmit voice frequency analogue signals, will be available on the market and will be used within the context of the conventional analogue telecommunications network; the invention illustrates a way in which these analogue telecopiers can be used in a digital network.

According to this invention there is provided apparatus for digital facsimile transmission in a subsidiary channel of a transmission channel comprising a further subsidiary channel in which digital telephone signals can be transmitted, said apparatus comprising a facsimile transmission copier arranged for emitting and receiving voice frequency analogue signals via a digital modulator and demodulator connected to a subsidiary channel multiplexer and demultiplexer arranged to combine and separate the telephone and facsimile signals for transmission and reception respectively.

An embodiment of this invention will now be described, by way of example, with reference to the accompanying drawing in which: Figure 1 is a schematic block diagram of a telephone/facsimile subscriber station embodying this invention; and Figure 2 is a schematic block diagram in greater detail of part of the apparatus shown in Figure 1.

Referring to the drawing, a telephone/facsimile transmission subscriber station Tln of a digital telecommunications network is assumed to be connected via a connection line Al to a digital exchange, not illustrated in the drawing, of the digital telecommunications network.

As can be seen in Figure 1, the subscriber station Tln comprises a digital telephone Fe having a dialling keyboard TT, a display unit Dy, a filter F, an analogue/digital converter A/D, a transmission device C3E which enables transmission and reception via separate respective transmission paths, and clock pulse restoration and synchronisation, and a control device ST whose functions include the exchange of signalling characteristics with the exchange, which latter can be constructed, in particular, to employ microprocessor technology.The subscriber station Tln also includes a facsimile transmission device comprising a telecopier Fax; this will be assumed to consist of an analogue telecopier which can operate in conventional analogue telecommunications networks (for example within the context of the current telefax service), for example a light telecopier HF 1048.

Other subscriber stations within the digital telecommunications network which contains the subscriber station Tln illustrated in the drawing can be designed in a similar manner, although this is not illustrated in the drawing. For data transmission from and to the subscriber stations within the digital telecommunications network, telecommunications standard channels each having a bit rate of 64 kbit/s (for each transmission direction) will be assumed to be available on the connection lines, such as the connection line Al illustrated in the drawing, and on transmission links which have not been illustrated in the drawing, and in exchanges of the digital telecommunications network, the 64 kbit/s standard channel being assumed to comprise two subsidiary telecommunications channels each having a bit rate of 32 kbit/s, one of which is provided for telephony and the other of which is provided for facsimile transmission.

In order that the analogue telecopier Fax which is indicated in the drawing and which emits voice frequency analogue signals via its output a can be used in the digital telecommunications network, at the transmitting end, the telecopier is followed by a digital modulator and, at the receiving end, is preceded by a digital demodulator.The digital modulator and digital demodulator expediently comprise a A modulator-demodulator (A-modem) A/A in which, (in the A-modulator) in dependence upon the sign of the difference between a sample value of the telecopier analogue signal and a predicted value which fundamentally is derived from adding all the previous difference values and which changes in stepped fashion from sample time to sample time, a binary signal element (h M-bit) "0" or "1" is produced and in a feedback arm of the A modulator and at the receiving end (in the A demodulator) in accordance with the A M-bits an integration value in an integrator of a so-called A decoder is reduced or increased (discharge or charge).A-modems of this kind are fundamentally known, for example in the form of the Motorola Codec MC3417, and therefore do not require to be described in detail here.

The A modem A/A is connected via a line link ob to a subsidiary channel multiplexer/demultiplexer Muldex which is assigned to the digital telephone Fe and which groups the telephone digital signals and the remote copy digital signals to form a common bit flow which flows in the outgoing 64 kbit/s standard channel and in the frame of which the telephone signal bits and remote copy signal bits occur at respective predetermined points and which in the opposite transmission direction separates the telephone signal bits and remote copy signal bits contained in the incoming bit flow and allocates them between the telephone Fe and the telecopier Fax.The subsidiary channel multiplexer/demultiplexer Muldex which, as indicated in the drawing, can be under the control of the control device ST and can be formed by cyclically actuated switches; this is illustrated in Figure 2. It is also possible to fulfil the subsidiary channel multiplexer/demultipiexer function by means of a microprocessor (for example of the type INTEL SAB 8080) and a freely addressable ROM (read only memory) in a micro-computer (for example of the type INTEL SBC 80/20), as fundamentally known (from Figure 2 of German specification AS 28 27 040) and thus does not need to be further illustrated here. The microprocessor can be formed by a microprocessor which is in any case contained in the control device ST.

As can be seen from Figure 2 (which like Figure 1 is a single wire illustration), the subsidiary channel multiplexer/demultiplexer Muldex (in respect of each transmission channel) can possess a change-over switch U which is controlled for bit timing via a bit rate line bt under the control of a clock T in the transmission device ijE, and which connects the line link is, between the subsidiary channel multiplexer/deniultiplexer Muldex and the transmittlng/receiving unit S/E of the transmission device UE, alternatively to the line link ib between the subsidiary channel multiplexer/demultiplexer Muldex and the analogue/digital converter A/D (in Figure 1) and the line link ob between the subsidiary channel multiplexer/demultiplexer Muldex and the A moduiator/demodulator A/A (in Figure 1). In this respect Figure 2 indicates that a switch S which can be operated under the control of the control device ST via control line link st or under the control of a synchrnn,ous word receiver SyE in the transmission device UE via a control line sy is interposed into the bit rate line bt.

If, in response to a mixed communications signal which is produced as a result of the actuation of mixed communication key MK on the dialling keyboard TT (in Figure 1) and by means of which a synchronous work transmitter SyS can also be triggered in the transmission device UE (in Figure 1) via the control line link os (in Figure 1), the switch S is supplied with a control signal by the control device ST via the control line st, or if the switch S receives such a control signal via the control line sy in response to a synchronous word received by the synchronous word receiver SyE, the switch S is closed so as to be synchronous in respect of the subsidiary channel and therefore the change-over switch U, which, in the example, in its idle state switches through the telephone channel, is switched back and forth at the bit rate so as to be synchronous in respect of the subsidiary channel.

The circuitry addition explained above making reference to the drawing enables the analogue telecopier Fax of a subscriber station Tin comprising a digital telephone Fe and an analogue telecopier Fax to operate using a second subsidiary channel simultaneously to the digital telephone Fe which operates using a first subsidiary channel of the 64 kbit/s standard channel, so that telephony and facsimile transmission can occur simultaneously between two such subscriber stations in the digital telecommunications network.For high speed facsimile transmission a 32 kbit/s subsidiary channel can for example be provided in which A M-bits, produced by the digital modulator (A/A) in the form of a A modulator, are transmitted by way of digital facsimile signals; in that case for anaiogue/digital conversion the digital telephone Fe will also comprise a A modulator (and demodulator) A/D so that then digital telephone signals can be transmitted, likewise in the form of A M-bits, in the other subsidiary channel, which enables use of a bit rate of for example 32 kbit/s or only 24 kbit/s, of the 64kbit/s standard channel.

The system described above allows not only appropriate digital telecopiers but also existing analogue telecopiers of the telefax service which has already been introduced, to be used in a future service integrated digital network; thus it enables an economy in outlay for the full working life of such analogue telecopiers and at the same time facilitate utilisation of digital network.

The use of a A modulator/demodulator as the modulator/demodulator for the facsimile telecopier is on the one hand relatively low in cost and on the other hand allows relatively high speed telecopying operation.

Also the use of a A modulator/demodulator for the digital telephone enables a smaller bit rate requirement for the telephony in comparison to PCM whilst maintaining at least as good speech quality and allows a correspondingly higher bit rate for the telecopying operation and thus correspondingly lower requirements on the digital modulator which is connected to the analogue telecopier and/or a corresponding acceleration in the teiecopying operation.

Claims

1. Apparatus for digital facsimile transmission in a subsidiary channel of a transmission channel comprising a further subsidiary channel in which digital telephone signals can be transmitted, said apparatus comprising a facsimile transmission copier arranged for emitting and receiving voice frequency analogue signals via a digital modulator and demodulator connected to a subsidiary channel multiplexer and demultipiexer arranged to combine and separate the telephone and facsimile signals for transmission and reception respectively.

2. Apparatus according to claim 1 wherein said modulator and demodulator comprises a delta (A) modem.

3. Apparatus according to claim 2 wherein a digital telephone is provided and includes a delta modem.

4. Apparatus for digital facsimile transmission in a subsidiary channel of a transmission channel comprising a further subsidiary channel in which digital telephone signals can be transmitted, said apparatus being substantially as described herein with reference to the accompanying drawing.

5. A digital telecommunications system comprising interconnected subscriber stations and exchange and including apparatus according to any one of the preceding claims.