  We consider the most general case of source clock frequency recovery (SCFR)
in packet networks, i.e., asynchronous SCFR through aperiodic packet streams,
where there is neither a common reference clock nor any relation between packet
generation intervals and a source clock frequency. We formulate the problem of
asynchronous SCFR with timestamps as a linear case of regression through the
origin (RTO) and propose two schemes, one based on recursive least squares
(RLS) method and the other based on simple heuristics of cumulative ratio of
interarrival and interdeparture times, which provide better estimates of the
source clock frequency with faster convergence than conventional phase-locked
loop (PLL)-based schemes.
