3-way call detection system and method

• US 7,664,243 B2
• Filed: 10/12/2006
• Issued: 02/16/2010
• Est. Priority Date: 11/13/2001
• Status: Active Grant

• Current Assignee: DSI-ITI, Inc.
• Original Assignee: Inmate Telephone, Inc.
• Inventors: Martin, Thomas J.
• Primary Examiner(s): Hong; Harry S
• Application Number:
  US11/546,376
• Publication Number:
  US 20070121828A1
• Time in Patent Office: 1,223 Days
• Field of Search: None
• US Class Current: 379/189
• CPC Class Codes: H04M 1/68 Circuit arrangements for preventing eavesdropping
• CPC Class Codes: H04M 3/2281 Call monitoring, e.g. for law enforcement purposes; Call tracing; Detection or prevention of malicious calls
• CPC Class Codes: H04M 3/305 testing of physical copper line parameters, e.g. capacitance or resistance locating faults in cables G01R31/08
• CPC Class Codes: H04M 3/56 Arrangements for connecting several subscribers to a common circuit, i.e. affording conference facilities video conference systems H04N7/15

Abstract

Disclosed herein is a three-way call detection system and method for detecting the addition of a third party to a pre-existing telephonic connection between a first party and a second party. The system includes a meter for measuring the amplitude of a line voltage of a telephonic connection between two parties, a first filter to remove a frequency band from the line voltage, a white noise generator for generating a low level white noise signal in the removed frequency band, a coupler for combining the white noise signal with the filtered signal, to create an additive line voltage, a second filter that passes only a portion of the additive line voltage including at least a portion of the white noise signal, and a processor for monitoring the passed signal for a shift in amplitude level associated with the addition of a third party to the connection.

Claims

1. A system for detecting addition of a third party to a pre-existing telephonic connection between a first party and a second party, said system comprising:

a meter for measuring an amplitude of a line voltage of the telephonic connection between the first party and the second party, said line voltage having a frequency band F1;

a first filter to remove a frequency band F2 from said line voltage and output a filtered signal, wherein said frequency band F2 is a sufficiently narrow subset of said frequency band F1 that absence of said frequency band F2 from said line voltage is substantially imperceptible to the first party and the second party;

a random noise generator for generating a random noise signal having a frequency band corresponding to said frequency band F2 and an amplitude that is sufficiently less than said amplitude of said line voltage so as to be substantially imperceptible to the first party and the second party when combined with said filtered signal;

a coupler to combine said random noise signal with said filtered signal, thereby outputting an additive line voltage;

a second filter that passes at least a portion of said additive line voltage, including at least a portion of said frequency band F2, said portion being referred to as a band-passed signal; and

a processor for time-domain monitoring of an amplitude of said band-passed signal for a shift associated with addition of the third party to the pre-existing telephonic connection.

2. The system according to claim 1, wherein said frequency band F2 is less than about 300 Hz wide.

3. The system according to claim 1, wherein said amplitude of said random noise signal is at least about 3 dB below said amplitude of said line voltage.

4. The system according to claim 3, wherein said amplitude of said random noise signal is at least about 20 dB below said amplitude of said line voltage.

5. The system according to claim 4, wherein said amplitude of said random noise signal is at least about 40 dB below said amplitude of said line voltage.

6. The system according to claim 1, wherein said band-passed signal is about 1000 Hz wide.

7. The system according to claim 6, wherein said band-passed signal is from about 1000 Hz to about 2000 Hz.

8. The system according to claim 1, wherein said band-passed signal is about 300 Hz wide.

9. The system according to claim 8, wherein said band-passed signal is from about 1000 Hz to about 1300 Hz.

10. The system according to claim 1, wherein said coupler is selected from the group consisting of a voltage adder, a summer, a signal combiner, and a processor preprogrammed with a function that adds two signals for form a combined signal.

11. The system according to claim 1, wherein said amplitude of said line voltage is measured at a location selected from the group consisting of a location of the first party, a telephone switching station, and a telephone central office.

12. The system according to claim 1, wherein at least one of said first filter and said second filter is selected from the group consisting of a notch filter, a band reject filter, a digital signal processor, and a signal-subtracting circuit.

13. The system according to claim 1, wherein said meter is selected from the group consisting of a voltmeter, a multimeter, and a measuring circuit.

14. A method of detecting addition of a third party to a pre-existing telephonic connection between a first party and a second party, said method comprising:

measuring an amplitude of a line voltage of the telephonic connection between the first party and the second party, the measured line voltage having a frequency band F1;

filtering the measured line voltage to remove a frequency band F2 therefrom, thereby creating a filtered signal, wherein the frequency band F2 is a sufficiently narrow subset of the frequency band F1 that absence of the frequency band F2 from the line voltage is substantially imperceptible to the first party and the second party;

generating a random noise signal having a frequency band corresponding to the frequency band F2, wherein an amplitude of the random noise signal is sufficiently less than the amplitude of the line voltage so as to be substantially imperceptible to the first party and the second party when combined with the filtered signal;

combining the random noise signal with the filtered signal to create an additive line voltage;

filtering the additive line voltage to pass at least a portion of the additive line voltage as a band-passed signal, wherein the band-passed signal includes at least some of the frequency band F2; and

monitoring an amplitude of the band-passed signal in the time-domain for a shift associated with addition of the third party to the pre-existing telephonic connection.

15. A method of detecting addition of a third party to a pre-existing telephonic connection between a first party and a second party, said method comprising:

receiving a signal from a telephone handset utilized by one of the first party and the second party, the received signal having a frequency band F1;

filtering the received signal to remove a frequency band F2 therefrom and output a filtered signal, the frequency band F2 being a subset of the frequency band F1;

generating a random noise signal having a frequency band corresponding to the frequency band F2, an amplitude of the random noise signal being sufficiently less than an amplitude of the received signal as to be substantially imperceptible to the first party and the second party when combined with the filtered signal;

combining the random noise signal with the filtered signal to create an additive line signal; and

monitoring a frequency band of the additive line signal for an amplitude shift indicative of addition of the third party, the monitored frequency band including at least a portion of the frequency band F2.