Jitter measurement method and apparatus

Claim 1

Apparatus for measuring the timing jitter of a tributary data stream that has been multiplexed into a higher-rate multiplex stream using pulse stuffing techniques, the multiplex stream including stuffing control bits indicative of the presence or absence of stuffs at predetermined position in said multiplex stream, said apparatus comprising: monitoring means for receiving and monitoring said multiplex stream to detect said stuffing control bits included therein that relates to said tributary, the monitoring means producing both a first signal indicative of the occurrence of a stuff relating to said tributary, and a second signal indicative of the multiplex stream timing; first processing means responsive to said first and second signals to derive therefrom an average-rate signal indicative of the average rate of phase loss of the tributary as compared to a notional reference related to the multiplex stream timing; and second processing means for deriving a jitter signal representative of the timing jitter of said tributary, the second processing means responsive to both said first signal and said average-rate signal to derive therefrom a current value for said jitter signal by updating a preceding value of the jitter signal, this updating involving increasing the jitter signal value by a predetermined amount for each stuff indicated by said first signal while effecting a decrease in jitter signal value at an average rate dependent on the value of said average rate signal.

Claim 16

A method of measuring the timing jitter of a tributary data stream that has been multiplexed into a higher-rate multiplex stream using pulse stuffing techniques, the multiplex stream including stuffing control bits indicative of the presence or absence of stuffs at predetermined positions in said multiplex stream, said method comprising the steps of: monitoring the multiplex stream to detect the stuffing control bits included therein that related to said tributary; utilizing the stuffing control bits to determine both the occurrence of a stuff relating to said tributary and the stuffing ratio of the tributary; and deriving a current value for a jitter signal representative of the tributary timing jitter by updating a preceding value of the jitter signal, this updating involving increasing the jitter signal value for each stuff detected while effecting a decrease in value at an average rate dependent on the value of the stuffing ratio.

Claim 17

A method of measuring the timing jitter of a tributary data stream that has been multiplexed into a higher-rate multiplex stream using pulse stuffing techniques, the multiplex stream including stuffing control bits indicative of the presence or absence of stuffs at predetermined positions in said multiplex stream, said method comprising the steps of: monitoring the multiplex stream to detect the stuffing control bits included therein that related to said tributary; utilizing the stuffing control bits to determine both the occurrence of a stuff relating to said tributary and the stuffing ratio of the tributary; and deriving a current value for a jitter signal representative of the tributary timing jitter by updating a preceding value of the jitter signal, this updating involving increasing the jitter signal value for each stuff detected while effecting a decrease in value at an average rate dependent on the value of the stuffing ratio.