Performance monitoring for loops

Abstract

Loop Performance Monitoring (LPM) for DDS loops is described. Even though DDS loops have Intentional Bipolar Violations (BPVs), a Loop Coding Violations (LCVs) detection strategy based on further processing of BPVs is described. By monitoring LCVs a local loop terminating device can determine Bit Error Rate (BER). A system is described by which an Office Channel Unit (OCU) can process LCV information to determine signal quality of the signal over the incoming local loop. If the signal quality falls below a certain threshold, the OCU can cut the loop off from the DDS circuit and send control codes into the network. A system is also described where a Network Interface Unit (NIU) with the LPM system communicates incoming LCV information to the OCU using low speed signalling over the simplex path between the transmit and receive pairs. The OCU monitors incoming LCVs as well, and thus has the information necessary to determine bi-directional BER performance.

The invention claimed is: 
     
       1. Apparatus for coupling to a communication channel of a local loop circuit in which information is transmitted as a bit stream of alternate mark inversion bipolar pulses comprising: a circuit for detecting the occurrence of an error signal on the communication channel said error signal comprising a bipolar violation in which a communication rule is that a binary one is transmitted as a positive or negative pulse, in opposite polarity to a preceding pulse; and   disabling means for disabling the communication channel by transmitting a predetermined code signal when the frequency of occurrence of certain of such error signals exceeds a predetermined threshold.   
     
     
       2. The apparatus of claim 1 wherein certain of such error signals does not include certain bipolar violations intentionally inserted by a channel user into the bit stream and the predetermined code signal is an abnormal station code signal. 
     
     
       3. The apparatus of claim 1 including enabling means for enabling the communication channel when the frequency of occurrence of error signals drops below the predetermined threshold. 
     
     
       4. In a multipoint circuit having a multipoint junction unit connected to a plurality of branch circuits, each such circuit communicating bit streams of alternate mark inversion bipolar pulses in which as a rule of communication a binary one is transmitted as a positive or negative pulse in opposite polarity to a preceding pulse, and wherein branch circuits alternate between active and idle states such that only one branch circuit is active at a time, an apparatus for coupling to an individual branch circuit comprising: a circuit for detecting the occurrence of streaming errors on the individual branch circuit, said errors being in the form of certain violations of said rule; and   disabling means for disabling the individual branch circuit by transmitting an abnormal station code signal when the level of streaming errors exceeds a predetermined threshold.   
     
     
       5. The apparatus of claim 4 including enabling means for enabling the individual branch circuit when the level of streaming errors drops below the predetermined threshold. 
     
     
       6. Apparatus for coupling to a communication channel of a local loop circuit in which information is transmitted as a stream of digital bits encoded as alternate-mark-inversion bipolar pulses and transmitted on each of two rails of a transmit loop wherein one rail is a positive rail and the other is a negative rail which carries the inverse of the pulses on the other rail and wherein a bipolar violation occurs when a present pulse on one rail has the same polarity as a previous pulse on the same rail, and including a bipolar violation circuit comprising: a first flip-flop circuit responsive to the present pulses from the positive rail and a clock signal to re-time the present positive rail pulses;   a second flip-flop circuit responsive to the present pulses from the negative rail and the clock signal to re-time the present negative rail pulses;   an OR gate having one input coupled to the output of the first flip-flop circuit and another input coupled to the output of the second flip-flop circuit;   a first delay circuit comprising a first multiplexer for storing the present positive rail pulses and a third flip-flop circuit, the first multiplexer having a first input coupled to the output of the first flip-flop circuit, a second input coupled to the output of the OR gate, and a third input coupled to the output of the third flip-flop circuit; the third flip-flop circuit being responsive to the output of the first multiplexer and the clock signal to delay the present positive rail pulses by one pulse interval, such that the outputs of the third flip-flop circuit are the previous positive rail pulses;   a second delay circuit comprising a second multiplexer for storing the present negative rail pulses and a fourth flip-flop circuit, the second multiplexer having a first input coupled to the output of the second flip-flop circuit, a second input coupled to the output of the OR gate, and a third input coupled to the output of the fourth flip-flop circuit; the fourth flip-flop circuit being responsive to the output of the second multiplexer and the clock signal to delay the present negative rail pulses by one pulse interval, such that the outputs of the fourth flip-flop circuit are the previous negative rail pulses;   a first AND gate having one input coupled to the output of the first flip-flop circuit and another input coupled to the output of the first delay circuit, the output of the first AND gate indicating a bipolar violation when pulses from the first flip-flop circuit and the first delay circuit having the same polarity are present; and   a second AND gate having one input coupled to the output of the second flip-flop circuit and another input coupled to the output of the second delay circuit, the output of the second AND gate indicating a bipolar violation when pulses from the second flip-flop circuit and the second delay circuit having the same polarity are present.   
     
     
       7. A loop performance monitor for detecting the occurrence of unintentional bipolar violations in which digital signals are encoded as alternate-mark-inversion bipolar pulses and transmitted on each of two rails of a transmit loop wherein one rail is a positive rail and the other is a negative rail which carries the inverse of the pulses on the other rail and wherein a bipolar violation occurs when a present pulse on one rail has the same polarity as a previous pulse on the same rail, and wherein intentional bipolar violations are indicated by XOV bipolar violation sequences having alternating polarity, said monitor comprising: a first circuit for receiving the present pulses and outputting the present pulses from one rail;   a second circuit for storing the present pulses and outputting the present pulses delayed by one pulse interval, such that the outputs of the second circuit are the previous pulses;   a third circuit for providing an active high output when the previous pulse is a zero level pulse;   a fourth circuit for determining the presence of pulses from the first and second circuit of the same polarity and the presence of an active high output from the third circuit and indicating an XOV sequence upon such occurrence by outputting a present XOV detection pulse;   a fifth circuit for storing the present XOV detection pulses and outputting the present XOV detection pulses delayed by one pulse interval, such that the outputs of the fifth circuit are the previous XOV detection pulses;   a sixth circuit for determining the presence of XOV detection pulses from the fourth and fifth circuit of the same polarity and indicating a non-alternating XOV bipolar violation upon such occurrence.   
     
     
       8. A method of communication in which information is transmitted as a stream of alternate mark inversion bipolar pulses in which as a general rule a binary one is transmitted as a positive or negative pulse in opposite polarity to a preceding pulse comprising the steps of: detecting the occurrence of certain violations of said rule; and   disabling the communication by transmitting a predetermined code signal when the frequency of occurrence of said violations exceeds a predetermined threshold.   
     
     
       9. The method of claim 8 wherein said violations do not include intentionally inserted violations used for signalling the presence of network control information and the predetermined code signal is an abnormal station code signal. 
     
     
       10. The method of claim 8 including the step of enabling the communication channel when the frequency of occurrence of said violations drops below a predetermined threshold. 
     
     
       11. In a multipoint circuit having a multipoint junction unit connected to a plurality of branch circuits, each such circuit communicating bit streams of alternate mark inversion bipolar pulses in which as a rule of communication a binary one is transmitted as a positive or negative pulse in opposite polarity to a preceding pulse, and wherein branch circuits alternate between active and idle states such that only one branch circuit is active at a time, a method of communicating on an individual branch circuit comprising the steps of: detecting the occurrence of streaming errors on the individual branch circuit, said errors being in the form of certain violations of said rule; and   disabling the individual branch circuit by transmitting an abnormal station code signal when the level of streaming errors exceeds a predetermined threshold.   
     
     
       12. The method of claim 11 including the step of enabling the individual branch circuit when the level of streaming errors drops below the predetermined threshold. 
     
     
       13. A method of monitoring loop performance by detecting the occurrence of unintentional bipolar violations in which digital signals are encoded as alternate-mark-inversion bipolar pulses and transmitted on each of two rails of a transmit loop wherein one rail is a positive rail and the other is a negative rail which carries the inverse of the pulses on the other rail and wherein a bipolar violation occurs when a present pulse on one rail has the same polarity as a previous pulse on the same rail, and wherein intentional bipolar violations are indicated by XOV bipolar violation sequences having alternating polarity, comprising the steps of: receiving the present pulses and outputting the present pulses from one rail;   storing the present pulses and outputting the present pulses delayed by one pulse interval, such that the outputs are the previous pulses;   providing an active high output when the previous pulse is a zero level pulse;   determining the presence of present and previous pulses of the same polarity and the presence of an active high output and indicating an XOV sequence upon such occurrence by outputting a present XOV detection pulse;   storing the present XOV detection pulses and outputting the present XOV detection pulses delayed by one pulse interval, such that the outputs are the previous XOV detection pulses;   determining the presence of present and previous XOV detection pulses of the same polarity and indicating a non-alternating XOV bipolar violation upon such occurrence.   
     
     
       14. Apparatus for coupling to a communication channel of a local loop circuit in which the rules of information communication require that information be transmitted as a stream of binary bits in which a binary ONE is represented as a positive or negative pulse in opposite polarity to a preceding pulse and a binary ZERO is represented as an absence of a pulse and wherein, with certain exceptions, a loop code violation occurs when said rules are violated comprising: a logic circuit for detecting the occurrence of loop code violations other than said certain exceptions; and   disabling means for disabling the communication channel by transmitting a predetermined code signal when the frequency of occurrence of detected violations exceeds a predetermined threshold.   
     
     
       15. The apparatus of claim 14 wherein said exceptions comprise certain intentional violations of the rules of communication which are transmitted to convey network control information and said logic circuit also includes a circuit for detecting said certain of such intentional violations. 
     
     
       16. The apparatus of claim 15 wherein an intentional violation comprises intentionally inserting a pulse which has the same polarity as the preceding pulse and wherein said logic circuit includes a circuit for distinguishing between certain of said intentional violations and other loop code violations. 
     
     
       17. A method of communication in which information is transmitted in accordance with rules of communication in which a binary ONE is represented as a positive or negative pulse in opposite polarity to a preceding pulse and a binary ZERO is represented as an absence of a pulse and wherein, with certain exceptions encoded as XOV violations, a loop code violation occurs when said rules are violated comprising the steps of: detecting the occurrence of loop code violations other than those excepted; and   disabling the communication by transmitting a predetermined code signal when the frequency of occurrence of detected loop code violations exceeds a predetermined threshold.   
     
     
       18. Apparatus for coupling to a communication channel of a local loop circuit in which the rules of information communication require that information be transmitted as a stream of binary bits in which a binary ONE is represented as a positive or negative pulse in opposite polarity to a preceding pulse and a binary ZERO is represented as an absence of a pulse and wherein, with certain exceptions encoded as XOV violations, a loop code violation occurs when said rules are violated and wherein network control information may be transmitted in the form of intentional violations of said rules comprising: a first logic circuit for detecting the occurrence of loop code violations other than those excepted; and   a second logic circuit for detecting the occurrence of certain excepted violations of said rules of communication.   
     
     
       19. The apparatus of claim 18 wherein an excepted loop code violation comprises intentionally inserting a pulse which has the same polarity as the preceding pulse. 
     
     
       20. A method of communication in which information is transmitted in accordance with rules of communication in which a binary ONE is represented as a positive or negative pulse in opposite polarity to a preceding pulse and a binary ZERO is represented as an absence of a pulse and wherein, with certain exceptions encoded as XOV violations, a loop code violation occurs when said rules are violated and wherein network control information may be transmitted in the form of XOV violations of said rules comprising the steps of: detecting the occurrence of loop code violations of said rules other than those excepted;   detecting the occurrence of certain XOV violations of said rules; and   disabling the communication by transmitting a predetermined code signal when the frequency of occurrence of detected loop code violations exceeds a predetermined threshold. .Iadd.   
     
     
       21.  Apparatus for coupling to a communication channel of a local loop circuit in which information is transmitted as a bit stream of bipolar pulses comprising: a circuit for detecting the occurrence of an error signal on the communication channel said error signal comprising a bipolar violation in which a communication rule is that a binary one is transmitted as a positive or negative pulse, in opposite polarity to a preceding pulse; and   a monitor circuit for disabling the communication channel when the frequency of occurrence of certain of such error signals exceeds a predetermined threshold..Iaddend..Iadd.   
     
     
       22.  The apparatus of claim 21 wherein certain of such error signals does not include certain bipolar violations intentionally inserted by a channel user into the bit stream..Iaddend..Iadd.23. The apparatus of claim 21 including enabling means for enabling the communication channel when the frequency of occurrence of error signals drops below the predetermined threshold..Iaddend..Iadd.24. In a multipoint circuit having a multipoint junction unit connected to a plurality of branch circuits, each such circuit communicating bit streams of bipolar pulses in which as a rule of communication a binary one is transmitted as a positive or negative pulse in opposite polarity to a preceding pulse, and wherein branch circuits alternate between active and idle states such that only one branch circuit is active at a time, an apparatus for coupling to an individual branch circuit comprising: a circuit for detecting the occurrence of streaming errors on the individual branch circuit, said errors being in the form of certain violations of said rule; and   a monitor circuit for disabling the individual branch circuit when the level of streaming errors exceeds a predetermined   
     
     
        threshold..Iaddend..Iadd.5.  The apparatus of claim 24 including enabling means for enabling the individual branch circuit when the level of streaming errors drops below the predetermined threshold..Iaddend..Iadd.26. A method of communication in which information is transmitted as a stream of bipolar pulses in which as a general rule a binary one is transmitted as a positive or negative pulse in opposite polarity to a preceding pulse comprising the steps of: detecting the occurrence of certain violations of said rule; and   disabling the communication when the frequency of occurrence of said violations exceeds a predetermined threshold..Iaddend..Iadd.27. The method of claim 26 wherein said violations do not include intentionally inserted violations used for signalling the presence of network control information..Iaddend..Iadd.28. The method of claim 26 including the step of enabling the communication channel when the frequency of occurrence of said violations drops below a predetermined threshold..Iaddend..Iadd.29. In a multipoint circuit having a multipoint junction unit connected to a plurality of branch circuits, each such circuit communicating bit streams of bipolar pulses in which as a rule of communication a binary one is transmitted as a positive or negative pulse in opposite polarity to a preceding pulse, and wherein branch circuits alternate between active and idle states such that only one branch circuit is active at a time, a method of communicating on an individual branch circuit comprising the steps of:   detecting the occurrence of streaming errors on the individual branch circuit, said errors being in the form of certain violations of said rule; and   disabling the individual branch circuit when the level of streaming errors exceeds a predetermined threshold..Iaddend..Iadd.30. Apparatus for coupling to a communication channel of a local loop circuit in which the rules of information communication require that information be transmitted as a stream of binary bits in which a binary ONE is represented as a positive or negative pulse in opposite polarity to a preceding pulse and a binary ZERO is represented as an absence of a pulse and wherein, with certain exceptions, a loop code violation occurs when said rules are violated comprising:   a logic circuit for detecting the occurrence of loop code violations other than said certain exceptions; and   a monitor circuit for disabling the communication channel when the frequency of occurrence of detected violations exceeds a predetermined threshold..Iaddend..Iadd.31. The apparatus of claim 30 wherein said exceptions comprise certain intentional violations of the rules of communication which are transmitted to convey network control information and said logic circuit also includes a circuit for detecting said certain   
     
     
        of such intentional violations..Iaddend..Iadd.32.  The apparatus of claim 30 wherein an intentional violation comprises intentionally inserting a pulse which has the same polarity as the preceding pulse and wherein said logic circuit includes a circuit for distinguishing between certain of said intentional violations and other loop code violations..Iaddend..Iadd.33. A method of communication in which information is transmitted in accordance with rules of communication in which a binary ONE is represented as a positive or negative pulse in opposite polarity to a preceding pulse and a binary ZERO is represented as an absence of a pulse and wherein, with certain exceptions encoded as XOV violations, a loop code violation occurs when said rules are violated comprising the steps of: detecting the occurrence of loop code violations other than those excepted; and   disabling the communication when the frequency of occurrence of detected loop code violations exceeds a predetermined threshold..Iaddend.