Loop status verification system

• US 4,937,851 A
• Filed: 04/28/1989
• Issued: 06/26/1990
• Est. Priority Date: 07/20/1988
• Status: Expired due to Fees

• Current Assignee: Antec Incorporated
• Original Assignee: Keptel, Inc. (CommScope Holding Company, Inc.)
• Inventors: Lynch, Daniel, Hogan, James P.
• Primary Examiner(s): SCHREYER, STAFFORD
• Application Number:
  US07/345,017
• Time in Patent Office: 424 Days
• Field of Search: 379/6, 379/27, 379/32, 379/33
• US Class Current: 379/24
• CPC Class Codes: H04M 11/04 with alarm systems, e.g. fire, police or burglar alarm systems
• CPC Class Codes: H04M 3/30 for subscriber's lines , for the local loop
• CPC Class Codes: H04Q 3/60 for connecting to satellites or concentrators which connect one or more exchange lines with a group of local lines

Abstract

A system is disclosed for verifying the integrity of each one of a number of communication paths, illustratively telephone subscriber loops, that runs between a near end location, illustratively a telephone company central office, and a corresponding remote ("far end") location(s). This system utilizes circuitry, such as a line verification module, that is located at the far end of each path to impart a selected test signal specifically a selected one of a number of sub-audible frequencies, thereto. In one embodiment, the circuitry continously transmits a test signal over the path. The level of the test signal is automatically adjusted such that this signal remains at an approximately constant amplitude regardless of whether that path is in an on-hook or off-hook condition. Central office monitoring circuitry is connected to the near end of every path being verified. For each such path, the monitoring circuitry first "learns" the frequency associated with the test signal appearing over that path, and thereafter detects a cessation or unexpected change in the test signal occurring at the near end thereof that is indicative of a possible loss of path (e.g. loop) integrity and, in turn, provides an appropriate notification specifying that loss.

Claims

1. A system for verifying the integrity of a communication path that connects near end and far end locations comprising:

first means situated at the far end location comprising;

means connected to said communication path for monitoring a characteristic of said path detectable at the far end thereof and indicative of whether the path is in an on-hook or off-hook condition;

means for generating a pre-defined test signal on a substantially continuous basis, wherein said test signal is substantially transparent to communication that will be carried over the path; and

means, responsive to the monitored characteristic and to said test signal generating means and connected to said path, for varying the amplitude of the generated test signal depending upon whether the path is in an on-hook or off-hook condition so as to produce a first signal and for injecting the first signal onto said path, such that the amplitude of the test signal that appears on the path remains essentially constant regardless of the whether the path exists in an on-hook or off-hook condition; and

second means situated at the near end location comprising;

means connected to said path for detecting whether the test signal appears thereon and for providing a control signal corresponding thereto; and

means responsive to said control signal for producing an appropriate notification if the test signal is absent from said path or does not match a prescribed test signal that is expected to appear on the path.

2. The system in claim 1 wherein said pre-defined test signal is a pre-selected sub-audible tone.

3. The system in claim 2 wherein said communication path comprises at least a two wire subscriber loop having separate tip and ring sides and said characteristic monitoring means comprises means for monitoring loop current flowing in said subscriber loop.

4. The system in claim 3 wherein said notification producing means further comprises:

means for storing a value of a pre-defined parameter of said prescribed test signal;

means for measuring a value of the parameter of said test signal that appears on said path; and

means for comparing the measured value of said parameter against the stored value of said parameter so as to determine whether said test signal that appears on said path matches said prescribed test signal.

5. The system in claim 4 wherein said notification producing means further comprises:

means, responsive to said control signal, for successively determining whether said pre-defined test signal appears on said path during each of a pre-determined number of measurement intervals; and

means, responsive to said successively determining means, for producing said notification, after a pre-defined number of measurement intervals has elapsed, if the pre-defined test signal is absent from said path or if the measured value of said parameter does not match the stored value of said parameter.

6. The system in claim 5 further comprising:

a plurality of subscriber loops wherein each of the loops emanates from the near end location and runs to a corresponding one of a plurality of far end locations; and

a separate one of the first means connected to a corresponding one of each of said loops at a far end location thereof; and

wherein said second means further comprises;

means, connected to each of said paths at a near end location thereof, for successively scanning each of said paths on a continual basis during successive measurement intervals and for routing the sub-audible tone appearing on each of the loops to said detecting means.

7. The system in claim 2 wherein the notification producing means further comprises means for accessing from a memory a value of a pre-defined parameter for the prescribed test signal that is to appear over the path and, if no value is currently stored in the memory for said pre-defined parameter, setting the value of said pre-defined parameter for said prescribed test signal to a measured value of the test signal that appears on the path.

8. The system in claim 7 wherein the notification producing means further comprises:

means for selecting one of a plurality of known values for the frequency of the prescribed test signal that is to appear over the path; and

means, responsive to said control signal, for successively determining whether the test signal that appears on the path throughout a pre-defined number of measurement intervals has a frequency value that matches, within a given range, the one selected value and, in response thereto, storing the one selected value in the memory as said pre-defined parameter for said corresponding path.

9. The system in claim 8 wherein said notification producing means further comprises:

means, responsive to said control signal, for successively determining whether the sub-audible tone having a corresponding pre-defined sub-audible frequency appears on the path during each of a pre-determined number of measurement intervals; and

means, responsive to said successively determining means, for producing said notification, after a pre-defined number of measurement intervals has elapsed, if the tone is absent from the path or has a frequency value that does not match a stored frequency value associated with a prescribed test signal that is to appear over the path.

10. The system in claim 9 further comprising:

a plurality of subscriber loops wherein each of the loops emanate from the near end location and run to a corresponding one of a plurality of far end locations; and

a separate one of the first means connected to each one of the loops at a far end location thereof; and

wherein said second means further comprises;

means, connected to each of said loops at a near end location thereof, for successively scanning each of said loops on a continual basis during successive measurement intervals and for routing the sub-audible tone appearing thereon to said detecting means.

11. The system in claim 10 wherein the second means further comprises:

a plurality of separately addressable line test units, wherein each of the line test units verifies a separate pre-defined group of loops; and

a controller for downloading status information regarding each of all currently active loops in a corresponding group of loops into a corresponding one of the line test units and accepting information regarding each of the loops in each group from each of the corresponding line test units and, in response to said accepted information, producing said notification.

12. The system in claim 2 wherein said communication path comprises at least a two wire subscriber loop having separate tip and ring sides and said characteristic monitoring means comprises means for monitoring loop current flowing in said subscriber loop, and said system further comprises:

means for accessing from a memory a value of a pre-defined parameter for the prescribed test signal that is to appear over the path and, if no value is currently stored in the memory for said pre-defined parameter, setting the value of said pre-defined parameter for said prescribed test signal to a measured value of the test signal that appears on the path.

13. The system in claim 12 wherein said notification producing means further comprises:

means for storing a value of a pre-defined parameter of said prescribed test signal;

means for measuring a value of the parameter of said test signal that appears on said path; and

means for comparing the measured value of said parameter against the stored value of said parameter so as to determine whether said test signal that appears on said path matches said prescribed test signal.

14. The system in claim 13 wherein said notification producing means further comprises:

means, responsive to said control signal, for successively determining whether said pre-defined test signal appears on said path during each of a pre-determined number of measurement intervals; and

means, responsive to said successively determining means, for producing said notification, after a pre-defined number of measurement intervals has elapsed, if the pre-defined test signal is absent from said path or if the measured value of said parameter does not match the stored value of said parameter.

15. The system in claim 12 wherein the notification producing means further comprises:

means for selecting one of a plurality of known values for the frequency of the prescribed test signal that is to appear over the path; and

means, responsive to said control signal, for successively determining whether the test signal that appears on the path throughout a pre-defined number of measurement intervals has a frequency value that matches, within a given range, the one selected value and, in response thereto, storing the one selected value in the memory as said pre-defined parameter for the path.

16. The system in claim 15 wherein said notification producing means further comprises:

means, responsive to said control signal, for successively determining whether the sub-audible tone having a corresponding pre-defined sub-audible frequency appears on the path during each of a pre-determined number of measurement intervals; and

means, responsive to said successively determining means, for producing said notification, after a pre-defined number of measurement intervals has elapsed, if the tone is absent from the path or has a frequency value that does not match a stored frequency value associated with a prescribed test signal that is to appear over the path.

17. In a system for verifying the integrity of a two-wire subscriber loop having separate tip and ring sides, a line verification module for connection to said loop at the far end thereof comprising:

means connected to said loop for monitoring a characteristic of said loop detectable at the far end thereof and indicative of whether the loop is in an on-hook or off-hook condition;

means for generating a pre-defined test signal on a substantially continuous basis, wherein said test signal is substantially transparent to communication that will be carried over the loop; and

means, responsive to the monitored characteristic and to said test signal generating means and connected to said loop, for varying the amplitude of the generated test signal depending upon whether the loop is in an on-hook or off-hook condition so as to produce a first signal and for injecting the first signal onto said loop, such that the amplitude of the test signal that appears on the loop remains essentially constant regardless of whether the loop exists in an on-hook or off-hook condition.

18. The line verification module in claim 17 further comprising:

means connected to one side of the subscriber loop for detecting loop current as said characteristic;

means for programmably selecting one of a plurality of pre-defined sub-audible tones as said test signal;

a tone generator, responsive to said programmable selection means, for generating said pre-defined sub-audible tone as said test signal; and

means, responsive to said loop current detecting means and to said test signal, for varying the amplitude of test signal in response to whether said loop is in an on-hook or off-hook condition in order to produce the first signal.

19. A method for verifying the integrity of a communication path that connects near end and far end locations comprising the steps of:

at the far end location;

monitoring a characteristic of a communication path detectable at the far end thereof and indicative of whether the path is in an on-hook or off-hook condition;

generating a pre-defined test signal on a substantially continuous basis, wherein said test signal is substantially transparent to communication that will be carried over the path; and

varying, in response to the monitored characteristic and to said test signal generating step, the amplitude of the generated test signal depending upon whether the path is in an on-hook or off-hook condition so as to produce a first signal and injecting the first signal onto said path, such that the amplitude of the test signal that appears on the path remains essentially constant regardless of the whether the path exists in an on-hook or off-hook condition; and

at the near end location;

detecting whether the test signal appears on said path and providing a control signal corresponding thereto; and

producing, in response to said control signal, an appropriate notification if the test signal is absent from said path or does not match a prescribed test signal that is expected to appear on the path.

20. The method in claim 19 wherein said pre-defined test signal is a pre-selected sub-audible tone.

21. The method in claim 20 wherein said communication path comprises at least a two wire subscriber loop having separate tip and ring sides and said characteristic monitoring step comprises the step of monitoring loop current flowing in said subscriber loop.

22. The method in claim 21 wherein said notification producing step further comprises the steps of:

storing a value of a pre-defined parameter of said prescribed test signal;

measuring a value of the parameter of said test signal that appears on said path; and

comparing the measured value of said parameter against the stored value of said parameter so as to determine whether said test signal that appears on said path matches said prescribed test signal.

23. The method in claim 22 wherein said notification producing step further comprises the steps of:

successively determining, in response to said control signal, whether said pre-defined test signal appears on said path during each of a pre-determined number of measurement intervals; and

producing, in response to said successively determining step, said notification, after a pre-defined number of measurement intervals has elapsed, if the pre-defined test signal is absent from said path or if the measured value of said parameter does not match the stored value of said parameter.

24. The method in claim 20 wherein the notification step further comprises the steps of:

accessing from a memory a value of a pre-defined parameter for the prescribed test signal that is to appear over the path; and

setting, if no value is currently stored in the memory for said pre-defined parameter, the value of said pre-defined parameter for said prescribed test signal to a measured value of the test signal that appears on the path.

25. The method in claim 24 wherein the notification producing step further comprises the steps of:

selecting one of a plurality of known values for the frequency of the prescribed test signal that is to appear over the path;

successively determining, in response to said control signal, whether the test signal that appears on the path throughout a pre-defined number of measurement intervals has a frequency value that matches, within a given range, the one selected value and, in response thereto, storing the one selected value in the memory as said pre-defined parameter for said corresponding path; and

repeating said selecting and successively determining steps using a next successive value from said plurality of known values in the event said selected one value does not exist on the path throughout said pre-defined number of measurement intervals.

26. The method in claim 25 wherein said notification producing step further comprises the steps of:

successively determining, in response to said control signal, whether the sub-audible tone having a corresponding pre-defined sub-audible frequency appears on the path during each of a pre-determined number of measurement intervals; and

producing, in responsive to said successively determining step, said notification, after a pre-defined number of measurement intervals has elapsed, if the tone is absent from the path or has a frequency value that does not match a stored frequency value associated with a prescribed test signal that is to appear over the path.

27. The method in claim 20 wherein said communication path comprises at least a two wire subscriber loop having separate tip and ring sides and said characteristic monitoring step comprises the step of monitoring loop current flowing in said subscriber loop, and said method further comprises the steps of:

accessing from a memory a value of a pre-defined parameter for the prescribed test signal that is to appear over the path; and

setting, if no value is currently stored in the memory for said pre-defined parameter, the value of said pre-defined parameter for said prescribed test signal to a measured value of the test signal that appears on the path.

28. The method in claim 27 wherein said notification producing step further comprises the steps of:

storing a value of a pre-defined parameter of said prescribed test signal;

measuring a value of the parameter of said test signal that appears on said path; and

comparing the measured value of said parameter against the stored value of said parameter so as to determine whether said test signal that appears on said path matches said prescribed test signal.

29. The method in claim 28 wherein said notification producing step further comprises the steps of:

successively determining, in response to said control signal, whether said pre-defined test signal appears on said path during each of a pre-determined number of measurement intervals; and

producing, in response to said successively determining step, said notification, after a pre-defined number of measurement intervals has elapsed, if the pre-defined test signal is absent from said path or if the measured value of said parameter does not match the stored value of said parameter.

30. The method in claim 27 wherein the notification producing step further comprises the steps of:

selecting one of a plurality of known values for the frequency of the prescribed test signal that is to appear over the path;

successively determining, in response to said control signal, whether the test signal that appears on the path throughout a pre-defined number of measurement intervals has a frequency value that matches, within a given range, the one selected value and, in response thereto, storing the one selected value in the memory as said pre-defined parameter for the path; and

repeating said selecting and successively determining steps using a next successive value from said plurality of known values in the event said selected one value does not exist on the path throughout said pre-defined number of measurement intervals.

31. The method in claim 30 wherein said notification producing step further comprises the steps of:

successively determining, in response to said control signal, whether the sub-audible tone having a corresponding pre-defined sub-audible frequency appears on the path during each of a pre-determined number of measurement intervals; and

producing, in response to said successively determining step, said notification, after a pre-defined number of measurement intervals has elapsed, if the tone is absent from the path or has a frequency value that does not match a stored frequency value associated with a prescribed test signal that is to appear over the path.

32. In a system for verifying the integrity of a two-wire subscriber loop having separate tip and ring sides, a method for use in a line verification module for connection to said loop at the far end thereof comprising the steps of:

monitoring a characteristic of said loop detectable at the far end thereof and indicative of whether the loop is in an on-hook or off-hook condition;

generating a pre-defined test signal on a substantially continuous basis, wherein said test signal is substantially transparent to communication that will be carried over the loop; and

varying, in response to the monitored characteristic and to said test signal generating step, the amplitude of the generated test signal depending upon whether the loop is in an on-hook or off-hook condition so as to produce a first signal and for injecting the first signal onto said loop, such that the amplitude of the test signal that appears on the loop remains essentially constant regardless of the whether the loop exists in an on-hook or off-hook condition.

33. The method in claim 32 further comprising the steps of:

detecting loop current flowing in said subscriber loop;

programmably selecting one of a plurality of pre-defined sub-audible tones as said test signal;

in response to said programmable selection step, said pre-defined sub-audible tone as said test signal; and

varying, in responsive to said loop current detecting step and to said test signal, the amplitude of test signal in response to whether said loop is in an on-hook or off-hook condition in order to produce the first signal.