Methods of estimating frequency skew in networks using timestamped packets

A method of estimating and adjusting frequency skew of clocks in a packet processing network, comprising:

• determining a representation of a packet delay variation (PDV) sequence from an initial estimate of frequency skew between master and slave devices in the packet processing network and packets containing timestamps transmitted therebetween, said packets comprising;
• (i) a first plurality of packets transmitted across a packet network in-sync with a master clock within the master device, and (ii) a second plurality of packets transmitted across the packet network in-sync with a slave clock within the slave device;
• determining a statistical characterization of the representation of the PDV sequence from the initial estimate of the frequency skew and the timestamps;
• extracting a statistical mode from the statistical characterization by extracting the statistical mode from an empirical probability distribution function (PDF) of the representation of the PDV sequence, where the statistical mode corresponds to a value at which the PDF has its maximum value;
• generating an updated estimate of the frequency skew by determining a slope between timestamps at indices associated with a plurality of points in the representation of the PDV sequence that are within a range of the statistical mode, said slope specifying a change in master and slave time-of-day (TOD) offsets associated with the timestamps relative to a change in index of the timestamps;
• and
• adjusting, based on the updated estimate of the frequency skew, at least one of the master and slave clocks in the master and slave devices, respectively, to thereby improve synchronization therebetween.

A method of estimating and adjusting frequency skew of clocks in a packet processing network, comprising:

• generating an initial estimate of frequency skew from timestamps transmitted in packets between master and slave devices in the packet processing network, which are separated from each other by a packet network, said packets comprising;
• (i) a first plurality of packets transmitted across the packet network in-sync with a master clock within the master device, and (ii) a second plurality of packets transmitted across the packet network in-sync with a slave clock within the slave device;
• determining a representation of a packet delay variation (PDV) sequence from the initial estimate of the frequency skew and the timestamps;
• determining a statistical characterization of the representation of the PDV sequence from the initial estimate of the frequency skew and the timestamps;
• extracting a statistical mode from the statistical characterization, said extracting comprising extracting the statistical mode from an empirical probability distribution function (PDF) of the representation of the PDV sequence;
• generating an updated estimate of the frequency skew from a set of modal points extracted from the probability density function (PDF) of the representation of the PDV sequence, said modal points aligned to a line having a slope that specifies a change in master and slave time-of-day (TOD) offsets associated with the timestamps relative to a change in index of the timestamps;
• and
• adjusting, based on the updated estimate of the frequency skew, at least one of the master and slave clocks in the master and slave devices, respectively, to thereby improve synchronization therebetween.