Dual tone multi frequency signal detection

Details Dual tone multi frequency signal detection Dual tone multi frequency signal detection

2007-09-18

2007-09-18

Hsu, Alpus H. (Department: 2665)

Multiplex communications

Pathfinding or routing

Combined circuit switching and packet switching

C370S395100, C370S395610, C370S526000, C379S093080, C379S386000

Reexamination Certificate

active

09776620

ABSTRACT:
A signalling tone detector for use in a communications network for the detection of dual frequency multi-tone (DTMF) pairs of signal tones in a time division multiplex (TDM) signal. The detector comprises first and second arrays of adaptive notch filters corresponding to the rows and columns of a subscriber's pushbutton key set. Each said notch filter responds to a respective signal tone by the generation of a corresponding output signal. A logic circuit identifies from a combination of output signals from the adaptive notch filters the presence or absence of a pair of signal tones and, when the presence of a pair of signal tones has been identified, for decodes that pair of tones to corresponding digit information. The detector is used in an arrangement for compressing and packetising TDM traffic for transport over a connectionless network. To prevent distortion, the DTMF tones are decoded to digit information prior to transport over the connectionless network.

REFERENCES:
patent: 5353346 (1994-10-01), Cox et al.
patent: 6075783 (2000-06-01), Voit
patent: 6259691 (2001-07-01), Naudus
patent: 6370244 (2002-04-01), Felder et al.
patent: 6757367 (2004-06-01), Nicol

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