Telephonic communications – Supervisory or control line signaling – Signal receiver
Reexamination Certificate
1998-11-12
2002-08-20
Isen, Forester W. (Department: 2644)
Telephonic communications
Supervisory or control line signaling
Signal receiver
C379S142180, C379S418000
Reexamination Certificate
active
06438224
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to tone detection on full-duplex communication channels, such as telephone lines, and more particularly to methods and apparatus for reducing talk-off and cut-through in the detection of signaling tones, such as DTMF tones.
BACKGROUND OF THE INVENTION
A number of different types of telephonic equipment communicate control information by sending and detecting signaling tones. The Dual-Tone, Multi-Frequency (DTMF) standard is an extensively-used standard for some of these signaling tones. It defines 16 different tone pairs (digits) that are each made up of a low tone and a high tone. The low tone can be a 697 Hz, 770 Hz, 852 Hz, or 941 Hz tone, and the high tone can be a 1209 Hz, 1336 Hz, 1477 Hz, or 1633 Hz tone. A variety of different kinds of circuits exist to detect these tone pairs, including digital filters.
Tone detectors sometimes suffer from “talk-off.” Talk-off occurs when a signal, such as person's voice, is decoded as a tone. This can happen when part of the telephone system is waiting for a signaling tone and sounds in the signal coincidentally include the two tones defined as one of the DTMF tone pairs.
Some tone detectors can also fail to detect tones because of what is known as “cut-through.” DTMF detectors that suffer from cut-through generally detect tones by comparing the magnitude of the energy in the tone frequency ranges with the magnitude of the energy outside of the tone ranges. These detectors may miss signaling tones in the presence of other sounds on the telephone line.
SUMMARY OF THE INVENTION
In one general aspect, the invention features a communication signaling tone detection system that includes an outgoing signaling tone detector responsive to an output from a first station to a communication channel. An incoming signaling tone detector is responsive to an input to the first station from the communication channel. A sensitivity control input of the incoming signaling tone detector is responsive to a detection output of the outgoing signaling tone detector.
In preferred embodiments, the incoming and outgoing signal tone detectors can be DTMF detectors. A CODEC can be operatively connected between an output of the outgoing signaling tone detector, an input of the incoming signaling tone detector, and the communication channel. The communication channel can be connected to an analog public network telephone line. The outgoing signaling tone detector can be less sensitive than the incoming signaling tone detector. The signaling tone detectors can both be implemented as digital filters. The detection output of the outgoing signaling tone detector can be operative to indicate which of a plurality of predetermined signaling tones the detector has received.
In another general aspect, the invention features a method of detecting signaling tones from a communication channel that includes detecting outgoing signaling tones in a communication stream transmitted from a first station over the communication channel to a second station, detecting incoming signaling tones in a communication stream transmitted from the second station over the communication channel to the first station, and altering at least one attribute of the step of detecting incoming signaling tones based on whether signaling tones are detected by the step of detecting outgoing signaling tones.
In preferred embodiments, the steps of detecting can detect DTMF tones as the signaling tones. The step of altering can decrease the sensitivity of the step of detecting when the outgoing signaling tones are detected by the step of detecting spurious signals. The step of altering can temporarily disable the step of detecting. The step of altering can invalidate a result of the step of detecting incoming signaling tones when a same signaling tone is detected by both the step of detecting outgoing signaling tones and the step of detecting incoming signals. The communication stream can be an audio stream. The step of detecting outgoing tones can be less accurate than the step of detecting incoming tones.
In a further general aspect, the invention features a communication signaling tone detection system that includes means for detecting outgoing signaling tones in a communication stream transmitted from a first station over the communication channel to a second station, means for detecting incoming signaling tones in a communication stream transmitted from the second station over the communication channel to the first station, and means for altering at least on attribute of the step of detecting incoming signaling tones based on whether outgoing signaling tones are detected by the means for detecting outgoing signaling tones.
In preferred embodiments, The means for detecting can detect DTMF tones as the signaling tones. The means for altering can include means for decreasing the sensitivity of the step of detecting when the outgoing signaling tones are detected by the means for detecting outgoing signals. The means for altering can include means for temporarily disabling the means for detecting incoming signals. The means for altering can include means for invalidating a result of the means for detecting incoming signals when a same signaling tone is detected by both the means for detecting outgoing signaling tones and the means for detecting incoming signaling tones. The means for detecting outgoing tones can be less accurate than the means for detecting incoming tones.
In another general aspect, the invention features a communication signaling tone detection system that includes a signal characteristic value detector responsive to a communication channel during a measurement period, threshold storage responsive to the signal characteristic value detector, and a threshold detector that is responsive to the threshold storage and to the communication channel during a detection period, and that has a signaling tone reporting output.
In preferred embodiments, the threshold detector can be a DTMF detector. The signal characteristic value detector can be an amplitude detector. The signal characteristic value detector can be a twist detector. The threshold detector can be operative to leave a margin between a threshold value stored by the signal characteristic detector and a detection threshold value. The signal characteristic detector and the threshold detector can be implemented using a digital signal processor.
In a further general aspect, the invention features a communication signaling tone detection system that includes means for measuring a characteristic of a signal while a signaling tone is present on the channel, and for defining a threshold based on the characteristic. The system also includes storage for storing the threshold, and signaling tone detection means responsive to the means for measuring and to the communication channel to detect when a signal on the communication channel exceeds the threshold.
In preferred embodiments, the signal tone detector can be a DTMF detector. The signal characteristic of the signaling tone can be an amplitude of the signaling tone. The signal characteristic of the signaling tone can be a twist value of the signaling tone. The signaling tone detector and the means for measuring and detecting can be implemented using a digital signal processor.
In another general aspect, the invention features a method of detecting signal tones from a communication channel that includes measuring a characteristic of a signal on the communication channel while a first signaling tone is present on the channel, adjusting a detection threshold based on the characteristic measured in the step of measuring, and detecting a second signaling tone according to the adjusted threshold.
In preferred embodiments, the steps of measuring and adjusting can measure and adjust an energy detection threshold. The steps of measuring and adjusting can measure and adjust a twist threshold. The step of measuring can take place while only the signaling tone is present on the communication channel. The method can further include the steps of settin
Harold Jefferey
Isen Forester W.
Mintz Levin Cohn Ferris Glovsky and Popeo P.C.
NMS Communications Corporation
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