Telephonic communications – Telephone line or system combined with diverse electrical... – Having transmission of a digital message signal over a...
Reexamination Certificate
1999-04-13
2001-09-18
Woo, Stella (Department: 2643)
Telephonic communications
Telephone line or system combined with diverse electrical...
Having transmission of a digital message signal over a...
C379S377000
Reexamination Certificate
active
06292546
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a device for detecting the busy state or the acquisition of a telephone line on which a modem is connected. It also relates to a modem equipped with such a detection device.
BACKGROUND OF THE INVENTION
A modem is a device for sending and receiving data, generally digital data, travelling via telephone lines.
For sending or receiving data, it is usual to use telephone lines which are used in addition for other uses such as normal telephone communications. This is the case, in particular, for television decoders, such as those using the digital video transmission by satellite standard “DVBS”.
These decoders can be linked automatically, via the modem, to a programme supplier without the user of the telephone line being informed at the moment of the communication.
In general, in order not to disturb the usual use of the telephone line, the modem should be such that it gives priority to the telephone communications, that is to say that, if the line is busy, the modem should not attempt the connection and, if appropriate, it should disconnect itself if the user seeks to use the line.
The modem should thus have available a device for detecting the line acquisition or the busy state of the telephone line.
For this detection, it is known to arrange a detector of the variation in current or voltage on the line linked to the modem. However, the variations in current or voltage caused by a telephone handset acquiring the line are often small and therefore difficult to detect. Moreover, the signal detected has to be applied to the modem via a galvanic separator such as an optical coupler if the telephone line conductors should never be earthed, although such a condition is not necessarily imposed on the modem. Hence, the known detection is complex and expensive.
SUMMARY OF THE INVENTION
The invention remedies these drawbacks.
It is characterized in that the device for detecting the busy state or the acquisition of the telephone line includes a means for comparing the energy received on the input of the modem connected to the said telephone line with a reference derived from the energy sent by the modem onto the telephone line.
In other words, in contrast to the known detection devices which analyse the signal originating from the telephone line, the invention analyses the signal generated within the modem. It results from the observation that, at the output of the modem, the impedance of the telephone line which is connected to it has a noticeable influence on the energy of the LF signal supplied by the modem.
Studies have shown that a difference of three decibels theoretically exists on the LF signal at the input/output of the modem between the case where the line connected is busy and the case where the line is not busy.
Analysis of the LF signal at the input/output of the modem does not necessarily dictate the use of a probe. It can be carried out by a program installed in a processor generally present in the modem or in any associated decoder.
REFERENCES:
patent: 4958371 (1990-09-01), Damoci et al.
patent: 5140631 (1992-08-01), Stahl
patent: 5422939 (1995-06-01), Kramer et al.
patent: 5506891 (1996-04-01), Brown
patent: 6134321 (2000-10-01), Pitsch
patent: WO97/23985 (1997-07-01), None
Copy of the French Search Report citing the above-listed references (AA,AB,AC, AM).
Kolodka Joseph J..
Laks Joseph J.
Thomson Licensing S.A.
Tripoli Joseph S.
Woo Stella
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