Method and apparatus for detecting a secondary destination of a telephone call based on changes in the telephone signal path

• US 6,141,406 A
• Filed: 05/30/1997
• Issued: 10/31/2000
• Est. Priority Date: 03/27/1997
• Status: Expired due to Term

• Current Assignee: Securus Technologies Incorporated (Securus Special Investments LLC)
• Original Assignee: T-Netix, Inc. (Cognizant Technology Solutions Corp.)
• Inventors: Johnson, John C.
• Primary Examiner(s): Vo, Nguyen
• Assistant Examiner(s): APPIAH, CHARLES NANA
• Application Number:
  US08/866,587
• Time in Patent Office: 1,250 Days
• Field of Search: 379/406, 379/410, 379/411, 379/188, 379/189, 379/377, 379/190, 379/7, 379/167, 379/177, 379/182, 379/202, 370/286, 370/289, 370/290, 370/291
• US Class Current: 379/189
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers
• CPC Class Codes: H04M 1/82 Line monitoring circuits for call progress or status discrimination for detecting caller identity H04M1/573
• CPC Class Codes: H04M 3/002 Applications of echo suppressors or cancellers in telephonic connections in two-way loud-speaking telephone systems H04M9/08, echo suppressors or cancellers per se H04B3/20
• CPC Class Codes: H04M 3/005 Interface circuits for subscriber lines current supply H04M19/00 and subgroups; supervisory, monitoring or testing arrangements H04M3/22 and subgroups; in key telephone systems H04M9/006
• CPC Class Codes: H04M 3/38 Graded-service arrangements, i.e. some subscribers prevented from establishing certain connections queuing arrangements H04Q3/64
• CPC Class Codes: H04M 3/54 Arrangements for diverting calls for one subscriber to another predetermined subscriber based on the calling party profile H04M3/42059; based on location H04M3/42348; based on presence H04M3/42365; to voice mail H04M3/53308
• 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
• CPC Class Codes: H04M 3/568 audio processing specific to telephonic conferencing, e.g. spatial distribution, mixing of participants echo suppression in two-way loud-speaking telephone systems H04M9/02; sound field processing per se H04S7/30
• CPC Class Codes: H04M 3/58 Arrangements for transferring received calls from one subscriber to another; Arrangements affording interim conversations between either the calling or the called party and a third party substation line holding circuits H04M1/80

Abstract

A method and apparatus for detecting whether a remote party has added a secondary telephone destination to a telephone call, for example through the activation of three-way calling service, conference calling or two lining bridging, by identifying an echo characteristic to the telephone connection between the local and the remote telephone and monitoring the echo characteristic to determine whether there is a significant change. The addition of a secondary telephone destination can be verified by continuing to monitor the echo characteristic to determine whether it has returned to its original value.

Claims

1. A method for detecting whether a remote party, using a remote telephone in telecommunication with a local telephone, has added a third party at a secondary telephone destination to said telecommunication comprising:

establishing a telephone connection between the local telephone and the remote telephone;

identifying an echo characteristic to said telephone connection; and

monitoring the echo characteristic for a significant change in the characteristic consistent with the addition of the secondary telephone destination by said remote party.

2. The method of claim 1, wherein said identifying and said monitoring of an echo characteristic is accomplished by ascertaining differences between a signal and an echo of said signal in the time domain.

3. The method of claim 1, wherein said identifying and said monitoring of an echo characteristic is accomplished by ascertaining differences between a signal and an echo of said signal in the frequency domain.

4. The method of claim 3, wherein said monitoring of the echo characteristic is a step selected from the group consisting of identifying differences in the magnitude of the signal and an echo of the signal and identifying differences in the shape of the original signal and an echo of that signal.

5. The method of claim 1, wherein said identifying and said monitoring of an echo characteristic is accomplished by means selected from the group consisting of adaptive filtration with an FIR filter, adaptive filtration with an IIR filter, and adaptive filtration with a lattice filter.

6. The method of claim 1, wherein said identifying of a characteristic echo includes intercepting a signal returned from the remote telephone on the trunk side of the remote central office.

7. The method of claim 1, wherein said identifying of a characteristic echo includes receiving at the local telephone of a signal returned from the remote telephone.

8. The method of claim 1, wherein said identifying of a characteristic echo utilizes signals transmitted from and received by said local telephone.

9. The method of claim 1, wherein the signals transmitted from said local telephone includes a known signal generated for the purpose of identifying and monitoring the echo characteristic.

10. The method of claim 9, wherein the signals generated are selected from the group consisting of a signal with a specific tone and white noise.

11. The method of claim 10, wherein the signals are generated intermittently.

12. The method of claim 10, wherein the signals are generated when the sound being received by the microphone of the local telephone is abated.

13. The method of claim 1, wherein the identifying of a characteristic echo is accomplished by adaptive filtration with an FIR filter.

14. The method of claim 1, wherein the identifying of a characteristic echo is accomplished by summing the squares of the coefficients used by an adaptive FIR filter to minimize the echo.

15. The method of claim 14, wherein said monitoring is accomplished by comparing the sum of the squares output of an adaptive FIR filter to the sum of the squares output of said filter at an earlier time.

16. The method of claim 15, wherein the earlier time is approximately 1 to 3 to seconds earlier.

17. The method of claim 1, further including the step of verifying that a change in the echo characteristic is caused by the addition of a secondary telephone destination by continuing to monitor the echo characteristic after the significant change to determine whether the echo characteristic has returned to its original value.

18. The method of claim 17, wherein the step of verifying comprises continuing to monitor the echo characteristic for a period of approximately 3 seconds to 3 minutes after the significant change to determine whether the echo characteristic has returned to its original value.

19. The method of claim 1, further including the making of a response when it is determined from said monitoring that a significant change in the echo characteristic has occurred consistent with the addition of the secondary telephone destination by said remote party.

20. The method of claim 19, wherein said response is selected from the group consisting of terminating the telephone connection, playing a prerecorded message, generating a tone which may be heard at one or more of the local or remote telephones, muting the microphone of the local telephone, and recording the date and time of the remote party'"'"'s addition of a secondary telephone destination.

21. A method for detecting whether a remote party, using a remote telephone in telecommunication with a local telephone, has added a third party at a secondary telephone destination to said communication:

establishing a telephone connection between the local telephone and the remote telephone;

comparing a transmitted signal and an echo signal with an adaptive FIR filter to generate tap values;

summing the squares of the tap values to identify an echo characteristic to said telephone connection; and

monitoring the echo characteristic for a significant change in the echo characteristic consistent with the addition of the secondary telephone destination by said remote party.

22. The method of claim 21, wherein the monitoring is conducted by comparing a recent value of the echo characteristic to a prior value for such characteristic to determine whether the ratio of the two values falls below a certain predetermined ratio.

23. The method of claim 22, wherein the ratio is in the range of approximately 0.8 to 0.5.

24. The method of claim 22, wherein the ratio is approximately 0.6.

25. The method of claim 21, wherein said comparing of said transmitted signal and said echo signal includes intercepting a signal returned from the remote telephone on the trunk side of the remote central office.

26. The method of claim 21, wherein said comparing of said transmitted signal and said echo signal includes receiving at the local telephone of a signal returned from the remote telephone.

27. The method of claim 21, wherein said comparing of said transmitted signal and said echo signal employs signals transmitted from and received by said local telephone.

28. The method of claim 27, wherein the transmission of signals from said local telephone includes a known signal generated for the purpose of ascertaining and monitoring the echo characteristic.

29. The method of claim 28, wherein the signals generated are selected from the group consisting of a signal with a specific tone and white noise.

30. The method of claim 28, wherein the signals are generated intermittently.

31. The method of claim 30, wherein the signals are generated when the sound being received by the microphone of the local telephone is abated.

32. The method of claim 31, further including the step of verifying that a change in the echo characteristic is caused by the addition of a secondary telephone destination by continuing to monitor the echo characteristic after the significant change to determine whether the echo characteristic returns to its original value.

33. The method of claim 32, wherein the step of verifying comprises continuing to monitor the echo characteristic for a period of approximately 3 seconds to 3 minutes after the significant change in echo characteristic to determine whether the echo characteristic has returned to its original value.

34. The method of claim 21, further including the making of a response when it is determined from said monitoring that a significant change in the echo characteristic has occurred consistent with the addition of the secondary telephone destination by said remote party.

35. The method of claim 34, wherein said response is selected from the group consisting of terminating the telephone connection, playing a prerecorded message, generating a tone which may be heard at one or more of the local or remote telephones, muting the microphone of the local telephone, and recording the date and time of the remote party'"'"'s addition of a secondary telephone destination.

36. The method of claim 32, further including the making of a response when it is determined from said monitoring that a significant change in the echo characteristic has occurred consistent with the addition of the secondary telephone destination by said remote party.

37. The method of claim 36, wherein said response is selected from the group consisting of terminating the telephone connection, playing a prerecorded message, generating a tone which may be heard at one or more of the local or remote telephones, muting the microphone of the local telephone, and recording the date and time of the remote party'"'"'s addition of a secondary telephone destination.

38. The method of claim 37, wherein the monitoring is conducted by comparing a recent value of the echo characteristic to a prior value for such characteristic to determine whether the ratio of the two values falls below a certain predetermined ratio.

39. The method of claim 38, wherein the ratio is in the range of approximately 0.8 to 0.5.

40. The method of claim 38, wherein the ratio is approximately 0.6.

42. The method of claim 38, wherein the signal received by the local telephone includes intercepting a signal returned from the remote telephone on the trunk side of the remote central office.

43. The method of claim 38 wherein the signal received by the local telephone includes receiving at the local telephone of a signal returned from the remote telephone.

41. A method for detecting whether a remote party, using a remote telephone in telecommunication with a local telephone, has added a third party at a secondary telephone destination to said communication:

establishing a telephone connection between the local telephone/equipment and the remote telephone;

inputting the signal transmitted by the local telephone and the signal received by the local telephone into an adaptive FIR filter to generate tap values;

summing the squares of the tap values to identify an echo characteristic to said telephone connection;

monitoring the echo characteristic for a significant change in the echo characteristic resulting from the addition of the secondary telephone destination by said remote party;

verifying that a change in the echo characteristic is caused by the addition of a secondary telephone destination by continuing to monitor the echo characteristic after the significant change to determine whether the echo characteristic has returned to its original value; and

making a response if it is verified from said monitoring that the significant change in the echo characteristic was consistent with the addition of the secondary telephone destination by said remote party.

44. The method of claim 41, wherein the transmission of signals from said local telephone includes a known signal generated for the purpose of ascertaining and monitoring the echo characteristic.

45. The method of claim 44, wherein the signals generated are selected from the group consisting of a signal with a specific tone and white noise.

46. The method of claim 44, wherein the signals are generated intermittently.

47. The method of claim 46, wherein the signals are generated when the sound being received by the microphone of the local telephone is abated.

48. An apparatus for use in determining whether a remote party, using a remote telephone in telecommunication with a local telephone has added a secondary telephone destination to said telecommunication comprising:

first means for determining a characteristic echo associated with the telecommunication between the local telephone equipment and the remote telephone, and

second means for monitoring the echo for significant changes in the echo caused by the addition of a third telephone destination by said remote party.

49. The apparatus of claim 48, in which the first means is selected from the group consisting of an adaptive FIR filter, an adaptive IIR filter, or an adaptive lattice filter.

50. The apparatus of claim 49, in which the FIR, IIR or adaptive lattice filter is emulated by a digital computer.

51. The apparatus of claim 48, in which said second means includes means for comparing a recent value of the echo characteristic with an earlier value of the echo characteristic.

52. The apparatus of claim 51, in which said second means is accomplished by a digital computer.

53. A method for detecting whether a remote party, using a remote telephone in telecommunication with a local telephone, is relaying messages between a third party at a secondary telephone destination to said telecommunication and the party at a local telephone comprising:

establishing a telephone connection between the local telephone and the remote telephone;

identifying an echo characteristic to said telephone connection;

monitoring the echo characteristic for a significant change in the characteristic consistent with the addition of the secondary telephone destination by said remote party;

continuing to monitor the echo after the significant change has occurred to determine whether the echo fluctuates between the characteristic for the telephone connection between the local and remote telephone and the characteristic consistent with the addition of the secondary telephone destination.

54. The method of claim 53, wherein said identifying and said monitoring of an echo characteristic is accomplished by means selected from the group consisting of adaptive filtration with an FIR filter, adaptive filtration with an IIR filter, and adaptive filtration with a lattice filter.

55. The method of claim 54, wherein said identifying of a characteristic echo includes intercepting a signal returned from the remote telephone on the trunk side of the remote central office.

56. The method of claim 54, wherein said identifying of a characteristic echo includes receiving at the local telephone of a signal returned from the remote telephone.

57. The method of claim 54, wherein said identifying of a characteristic echo utilizes signals transmitted from and received by said local telephone.

58. The method of claim 54, wherein the signals transmitted from said local telephone includes a known signal generated for the purpose of identifying and monitoring the echo characteristic, wherein the signals generated are selected from the group consisting of a signal with a specific tone and white noise.

59. The method of claim 58, wherein the signals are generated intermittently.

60. The method of claim 58, wherein the signals are generated when the sound being received by the microphone of the local telephone is abated.

61. The method of claim 54, wherein the identifying of a characteristic echo is accomplished by adaptive filtration with an FIR filter.

62. The method of claim 54, wherein the identifying of a characteristic echo is accomplished by summing the squares of the coefficients used by an adaptive FIR filter to minimize the echo.

63. The method of claim 62, wherein said monitoring is accomplished by comparing the sum of the squares output of an adaptive FIR filter to the sum of the squares output of said filter at an earlier time.

64. The method of claim 63, wherein the earlier time is approximately 1 to 3 to seconds earlier.

65. The method of claim 54, further including the making of a response when it is determined from said monitoring that a significant change in the echo characteristic has occurred consistent with the addition of the secondary telephone destination by said remote party.

66. The method of claim 65, wherein said response is selected from the group consisting of terminating the telephone connection, playing a prerecorded message, generating a tone which may be heard at one or more of the local or remote telephones, muting the microphone of the local telephone, and recording the date and time of the remote party'"'"'s addition of a secondary telephone destination.