Process for transmitting digitized payload and signalling...

Details Process for transmitting digitized payload and signalling... Process for transmitting digitized payload and signalling...

1997-12-12

2001-10-23

Nguyen, Chau (Department: 2663)

Multiplex communications

Communication techniques for information carried in plural...

Combining or distributing information via time channels

Reexamination Certificate

active

06307870

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of communications technology. More particularly, the present invention relates to a method for transmitting digitized payload and signalling data over a common channel.
BACKGROUND OF THE INVENTION
In telephony, there exists the problem that payload data (for example, acoustic signals such as voice signals) and signalling data, such as information concerning receiver status, digital signals entered via the keypad, ringing signals, etc., must be transmitted over the same channel or the same information transmission medium. Current telephony systems use a pulse code-modulated (PCM) channel, i.e. all data is transmitted digitally. Such a PCM transmission method is described, for example, in the textbook “Traité d'Electricit,” Volume XVIII of “Syst{acute over (e )}mes de Télécommunications” by Pierre-Gérard Fontolliet, published by Ecole Polytechnique Fédéral de Lausanne. Both payload data and signalling data, which may occur simultaneously, must be transmitted using the same single transmission medium.
There are currently two predominant standards for transmitting signalling data over a standard PCM channel: In the European PCM basic system (ITU-T G.732), the signalling data of 30 telephone channels are multiplexed time slots (off-band signalling). This system is known as “Channel Associated Signalling” (CAS). According to the American PCM basic system (ITU-T G.733), signalling data for 24 telephone channels are distributed using the “Bit-Stealing” method over all 24 channels. But both of the above described methods can be used only in multichannel systems. It would be desirable to be able to transmit signalling data and payload data, with relatively low distortion and bandwidth loss, over any single channel.
SUMMARY OF THE INVENTION
The present invention solves the above-described problems, and achieves other advantages, by providing for a method for transmitting digitized payload data and signalling data over one channel with relatively low distortion.
According to an exemplary embodiment of the invention, signalling data is multiplexed with payload data by using suitable coding. For this purpose, signalling bytes can be preceded by at least one header byte. Further, to prevent misinterpretation of a payload data byte corresponding to a header byte, at least one bit of the payload data is inverted for a payload data byte corresponding to the header byte. This results in some distortion which can be minimized by inverting the least significant bit (LSB) of the payload data byte.
The distortion can be further minimized by transmitting multiple header bytes consecutively. In order to ensure that the combination of the multiple header bytes can be distinguished from possible payload data bytes, header bytes are selected which correspond to the maximum value of the payload data and differ only by their sign bit. In the receiver, the payload data byte that was received last is repeated when each header byte is received.
The method according to the present invention makes it possible to transmit signalling data and payload with low distortion over a common channel, and improves the utilization of existing channel capacities.


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International Search Report dated Feb. 11, 2000.
“Systemes de Telecommunications”, Fontoilliet, Traite d'Electricite, pp. 214-224.

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