Device to block unauthorized modem access over a PBX line
First Claim
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1. A modem detector comprising:
- sampling means for sampling each of a plurality of audio lines, each functioning as a channel for transmission of data;
an average power detector, having an input connected to the sampling means, for detecting the average power on each audio line that is sampled;
means for comparing the detected average power on each sampled audio line with a threshold power level P that would be exceeded if a modem were operating on said line;
means for determining whether said detected average power of a sampled line continuously exceeds said threshold power level P for a period longer than a reference period T, where T is selected to be longer than the time that this threshold power level is likely to be continuously exceeded by normal human speech; and
means for indicating whether such detected average power has continuously exceeded said threshold P for longer than T.
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Abstract
A modem detector that enables detection of whether a modem is coupled to a phone line. When one is detected, various responses can occur, including: hanging up on the modem; checking if the modem linkage is allowable and, if it is not, then hanging up on the modem; and/or logging in the occurrence of an unauthorized modem access. To provide protection against unauthorized modem access, a digital embodiment can be used at the T1 phone line or an analog embodiment can be used after digital telephone data is converted into analog signals.
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Citations
16 Claims
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1. A modem detector comprising:
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sampling means for sampling each of a plurality of audio lines, each functioning as a channel for transmission of data; an average power detector, having an input connected to the sampling means, for detecting the average power on each audio line that is sampled; means for comparing the detected average power on each sampled audio line with a threshold power level P that would be exceeded if a modem were operating on said line; means for determining whether said detected average power of a sampled line continuously exceeds said threshold power level P for a period longer than a reference period T, where T is selected to be longer than the time that this threshold power level is likely to be continuously exceeded by normal human speech; and means for indicating whether such detected average power has continuously exceeded said threshold P for longer than T. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A modem detector that is responsive to digital data, said modem detector comprising:
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sampling means for sampling each of a plurality of audio lines, each functioning as a channel for transmission of data; a digital rectifier responsive to digital data at said sampling means; a digital low-pass filter connected to an output of the digital rectifier; a digital comparator having a first input connected to an output of the digital filter and a second input connected to a digital representation of a reference level P that would be exceeded if a modem were operating on said line; and a timeout counter connected to an output of the digital comparator, said timeout counter having an output on which is provided a modem detect signal indicative of whether this threshold P has been exceeded for longer than a time T that is selected to be longer than the time that this threshold power level is likely to be continuously exceeded by normal human speech.
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16. A modem detector that is resposive to analog data, said modem detector comprising:
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sampling means for sampling each of a plurality of an audio lines, each functioning as a channel for transmission of data; an analog rectifier having an input connected to sampling means and having an output; an analog low pass filter circuit; a comparator connected to the analog rectifier output for comparing a signal on this output against a threshold value P that would be exceeded if a modem were operating on said line; and means for indicating whether this threshold P has been exceeded for longer than a time T that is selected to be longer than the time that this threshold power level is likely to be continuously exceeded by normal human speech.
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Specification