Calculation of clock skew using measured jitter buffer depth
First Claim
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1. A system for calculation of clock skew between two communication ports in a packet network, comprising:
- a transmitting unit comprising a transmitting clock a receiving unit comprising a playout clock, a FIFO playout buffer, and a resampling unit;
a packet data stream between the transmitting unit and the receiving unit;
a packet sample buffer in the resampling unit that receives packet data from the playout buffer and feeds a resampler;
a timing logic module that generates a timing phase signal based on the size change of the playout buffer combined with the packet sample buffer, where the signal tracks the clock frequency offset between the transmitting and playout clocks;
a resampler in the sampling unit that resamples the packet data from the sample packet buffer and uses the timing phase signal to advance or retard the sampling phase of a bank of subfilters within said resampler.
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Abstract
A system and method to measure the clock skew between transmitting and receiving devices operating with independent clock sources over a packet network is described. To provide adaptive playout in an IP telephony device without a sequencing scheme in the packets, the clock skew is measured and recorded. Using a PCM resampler that is implemented with an interpolation filter bank of FIR subfilters, the change in depth of the playout buffer during transmission is analyzed, and this change infers the clock rate associated with the transmission.
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Citations
9 Claims
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1. A system for calculation of clock skew between two communication ports in a packet network, comprising:
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a transmitting unit comprising a transmitting clock a receiving unit comprising a playout clock, a FIFO playout buffer, and a resampling unit;
a packet data stream between the transmitting unit and the receiving unit;
a packet sample buffer in the resampling unit that receives packet data from the playout buffer and feeds a resampler;
a timing logic module that generates a timing phase signal based on the size change of the playout buffer combined with the packet sample buffer, where the signal tracks the clock frequency offset between the transmitting and playout clocks;
a resampler in the sampling unit that resamples the packet data from the sample packet buffer and uses the timing phase signal to advance or retard the sampling phase of a bank of subfilters within said resampler. - View Dependent Claims (2, 3, 4)
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5. A method for calculating clock skew for data transmissions between transmitting and receiving units having independent clocks in a system for voice playout, comprising:
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transmitting data packets from a transmitting unit with an independent clock source;
receiving the data packets into a FIFO buffer;
transmitting data packets from the FIFO buffer to a sample packet buffer in a resampler unit;
generating a timing phase signal to advance or retard sampling based on the change in size of the FIFO buffer combined with the sample packet buffer;
minimizing jitter effect and compensating clock skew by updating the timing phase signal over time;
advancing or retarding samples using a Random Walk Filter to upsample or downsample within an FIR subfilter bank of a resampler. - View Dependent Claims (6, 7, 8, 9)
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Specification