CA2197956A1

CA2197956A1 - Method for fax transmission in digital networks

Info

Publication number: CA2197956A1
Application number: CA002197956A
Authority: CA
Inventors: Achim Degenhardt; Michael Alger-Meunier
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1996-02-21
Filing date: 1997-02-19
Publication date: 1997-08-21
Also published as: EP0800323B1; DE19606479C2; DE19606479A1; JPH09298613A; DE59712638D1; KR970064072A; TW359056B; JP4162731B2; CN1171681A; EP0800323A2; EP0800323A3

Abstract

The invention relates to a method for connection of at least three terminals to a line of a digital network, transmitted voice data being compressed if necessary. According to the invention, a check is carried out to determine whether a fax transmission is taking place, and as much transmission capacity as possible is then assigned to the fax transmission, the compression of the voice data being cancelled out.

Description

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Method for fax transmission in diqital networks The invention relates to a method for connection of at least three terminals to a line of a digital network, the transmitted voice data being compressed if necessary.
One widely used digital network is the ISDN
network (Integrated Services Digital Network). The transmission technigue which is used in the ISDN com-prises two voice c~Annels being transmitted on a double copper wire from an ~YchAnge to the subscriber' 8 buil-ding. The two voice chAnnels are also called B-chAnnel 8 and have a transmission capacity of 64 kbit/s each. In addition to the two B_C~Anne18, a control ch~nnel is also transmitted which is also called the D-channel and has a transmission capacity of 16 kbit/s. The two 64 kbit/s B-chAnnels which are available in the ISDN are connected via an appropriate adapter in the eYc~Ange to two ports and, at the subscriber end, to two analogue telepho~e~.
One 64 kbit/s c~nnel and thus, if fast fax units are connected, a best-possible transmission rate as well are available to each of the two subscribers. The network operator has the advantage that no additional wires need be laid.
It is also possible to compress the voice data to 32 kbit/s. Transmission from two analogue subscribers per chAnnel, and thus from a total of four subscribers via one connecting line, is then possible on the ISDN line.
Compression to 16 kbit/s allows eight terminals to be connected. Rnown algorithm~, such as the ADPCM algorithm in accordance with CCITT StAn~rd (Comité Con6ultatif International Telégraphique et Télépho~;gue), for example, are used for compression and decompression, without the voice quality being noticeably reduced.
Howe~er, transmission from $ast fax units and modems suffers in this case, 80 that the full service is no longer available to the subscriber. If fast fax units are used, the compression system does not fully simulate four individual analogue connecting lines. The following - ~1979~6 GR 95 P 1058 D~ - 2 -statements relating to fax signal transmissions apply to the same extent to modem signal transmissions.
The invention is based cn the cbject of providing a method of the type mentioned initially which makes fax transmission possible with a transmission capacity that is as high as possible.
The object is achieved according to the invention in that fax identification is carried, and in that trans-mission capacity is assigned for a fast fax transmission.
Such a method makes it possible to transmit a multiplicity of analogue conversations using a trans-mission capacity which is sufficient for the human voice, of 16, 24 or 32 kbit/s. If a fax signal is identified, then as much transmission capacity as possible is assigned to the fax, in order to achieve transmission that is as fast as possible, in the ideal case at 64 kbit/s. To this end, the fax transmission can be assigned all the free transmission capacity which is not yet occupied by other con~ersations.
The compression and the fax signal identification in conjunction with the assignment of the transmission capacity controlled by it can advantageously be inte-grated in a single electronic module.
The data compression is preferably cancelled out dynamically in this case. In the example of the ISDN
line, 8 bits are transmitted in parallel per ch~nnel, and a transmission capacity of 64 kbit/s is thus achieved. If split between four terminals, there are thus initially 4 bits available to each terminal in the case of data compression. If one of the units is identified as a fax unit, or a signal which is present for transmission is identified as a fax signal, then, for example, one bit can be withdrawn from a voice transmission and the compression there can be increased to 3 bits, and this additional bit can be assigned to the fax signal, 80 that 5 bits are available to it, with a total transmission ~ capacity of 40 kbit/s. In principle, compression can be used which is the same for all conversations. Howe~e~, it may be expedient to compress one voice signal to a greater extent than the other voice signals, in favour of the fax transmission. The fax transmis~ion can also be distributed between both channel~ cf the line. In the example just quoted, with four terminals distributed between two c~Annel~, 1 bit could be withdrawn in each ca~e from the three normal conversations, 80 that a total of 7 bits, and thus 56 kbit/s, are available to the fax unit.
If it is found during the fax transmission that additional transmission capacity has become free as a result of another conversation ~nA; ng, then, in a pre-ferred development of the invention, this capacity which has become free is likewise assigned to the fax trans-mission .
In another embodiment of the invention, it is possible to activate an additional, parallel modem. Such a solution is particularly advantageous in the case of lines which are loaded continuously and heavily. The modem is switched off as long as only voice data are being transmitted. It is switched on only if a faxtransmission is detected, 80 that less energy is consumed overall.
The fax identification is preferably carried out by detection of a 2.1 kHz tone. To this end, a function is implemented directly in the processor of the compres-sion controller, which function comprises a narrowband bAnArA~s filter having a mid-frequency of 2.1 kHz, and having a notch filter which runs in a precisely inverse manner. The tone is detected by comparison of the energy in the 2.1 kHz band with the energy outside the band.
Such identification must be provided for both directions.
In addition to a number of logic gates, it require~ about 1 MIPS (Nillion Instructions Per Second) of computation power per c~Ann~l and direction, that is to ~ay a total of 2 MIPS for separate identification in each direction, since two algorithms are required for this purpose.
However, a first step is preferably used to determine whether a fax signal is present, and a second step is used to determine whether this is an incoming or outgoing ~1~7~
GR 95 P 1058 D~ - 4 -fax signal. The second step can be implemented by chec-king both directions simultaneougly. This achieves a ~aving of about 1 MIPS per ~nn~l, with a correspon~;ng reduction in the power consumption. The algorithm first of all considers the sum of the energies received from both directions. If a tone is identified, that is to say it is found in the first step that a fax signal is actually present, then any desired one, but a specific one, of the two directions is separated from the identi-fication. Depen~;ng on which direction continues to bemeasured in the second step, the tone i8 still identi-fied, or is not. The direction of the fax signal is given directly by this.
The identification of the tone lasts for a relatively long time because of the required identifica-tion reliability. This may last for up to 0.4 8, since the tone must be identified reliably for a certain time duration. After disconnection or suppression of one of the two directions, however, it is possible to deduce the direction of the tone very quickly, since ab~ence of the energy when the tone iB switched off is governed only by the time constant of the filters. The direction identifi-cation thus does not last significantly longer than the identification itself. The fax identification tone is available for at least about 0.5 8, and can be identified reliably within this time.
The invention will be explained further in the following text with reference to an exemplary embodiment which i8 illustrated in the drawing. In detail, in the schematic illustrations:

Fig. 1 shows a block diagram of subscriber con-nections to a digital network, and Fig. 2 shows one possible split of the existing transmission capacities.

Fig. 1 shows four a/b terminal adapters which are designated 1 and by means of which units which are 2197~56 GR 95 P 1058 D~ - 5 -operated in a con~entional analogue manner are connected directly to the ISDN. The terminal adapter in this case carries out the conversion of the analogue sig~als into digital signals, and the control of the protocols in the D-channel. The module, which is designated 2 in the following text, is used to control this system, which is designated PCM-4 (PCM = Pulse Code Modulation). The compressor 3 which carries out the ~oice compression is connected downstream from this system. The fax identifi-cation is integrated in this compressor and can identify,on the one hand, whether a fax signal is present and, on the other hand, likewise identifies the direction in which thi~ fax signal is being transmitted. The identifi-cation is also used to control a modem (not illustrated) which is connected in parallel with the compressor 3. The transmission via the modem which is connected in parallel with the compressor may take place alternatively or in addition to the dynamic data compression. The module 4 represents the interface into the digital network and, in particular, an ISDN-U interface.
Fig. 2 shows schematically the splitting of the signals from four terminals between two channels of an ISDN line. The rhAnnels which are designated 5 and 6 each ha~e a width of 8 bits, which are represented as boxes.
In this case, each channel has a transmisgion capacity of 64 kbit/s. If four terminals El to E4 are connected, 4 bits are assigned to each. The voice data must be com-pressed to 32 kbit/s. If the controller now determines that one of the terminals E1 to E4 is a fax F, then additional transmission capacity is assigned to it, and the voice data of the other terminals are further com-pressed. The assignment of the respectively appropriate bits illustrated in the figure has been chosen arbitrarily and is recorded in each case by the control 3S channel, which is designated the D-channel. In the illus-trated example, the fax signal is thus also split between two channels 5 and 6. Two of the three conversations E1 and E2 have been compressed to 3 bits, and thus 24 kbit/s, and one, E3, has been compressed to 2 bits, 21979Sli GR 95 P 1058 D~ - 6 -and thus 16 kbit/s. The full transmission capacity o$
64 kbit/s is thus available for the fax.

Claims

1. Method for connection of at least three terminals to a line of a digital network, transmitted voice data being compressed if necessary, characterized in that fax identification is carried out, and in that transmission capacity is assigned for a fast fax transmission.

2. Method as claimed in Claim 1, characterized in that the data compression is cancelled out dynamically.

3. Method according to one of Claims 1 or 2, characterized in that the fax transmission is distributed between two channels in the line.

4. Method according to Claim 1, characterized in that an additional parallel modem is activated.

5. Method according to one of the preceding claims, characterized in that the fax identification is carried out by detection of a 2.1 kHz tone.

6. Method according to Claim 5, characterized in that one step is used to determine whether a fax signal is present, and a second step is used to determine whether this is an incoming or outgoing fax.

7. Method according to Claim 6, characterized in that only one defined direction is checked in a second step.