Performance monitoring for loops

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.

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.

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.

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.