General:
(a). It may be
useful to incorporate a reference to ITU-T G.1050. This is an IP
impairment model that is somewhat oriented toward modeling congestion
over limited bandwidth links, providing a useful tool for experimenting
with and testing PDV measurement techniques. G.1050 is based on a time
series model that was originally developed as a potential PDV
measurement algorithm.
(b) ITU-T
COM12-D98 "Analysis, measurement and modelling of jitter" (2003)
provided some useful background on the sources and measurement of
jitter. This also pointed out some significant characteristics of the
PPDV performance metrics that affect reported values with particular
patterns of delay (e.g. delay ramps, alternate pairs of early late
packets......)
3.4 Service
Level Comparison
IMHO -
percentile based approaches are particularly suitable for SLA
agreements. It is both easy to specify and easy to implement an SLA
measurement of the type "no more than x% of packets shall arrive
later than y milliseconds".
This is a good point when comparing IPDV versus PDV. The percentile in
PDV represents a single simple metric.
This is similar
to (within the scope of?) Y.1540 however reports the percentage of
packets outside some given threshold rather than the threshold that
corresponds to some given percentile.
3.5 Separation
of scheduling/ smoothing PDV from PDV introduced by the network.
Some delay
variation may be introduced by packet scheduling for smoothing purposes
or the queuing of packets within sending systems. Smoothing could
potentially be introduced by shaping devices in the network. If packet
spacing/ size is uniform then this smoothing or shaping would not
necessarily result in PDV however for any system that uses irregular or
bursty packet transmission smoothing/ shaping is likely to result
in PDV that could in some cases significantly exceed the PDV due to
network congestion. From the perspective of network performance
monitoring it is very useful to separate the two components of
smoothing/ shaping PDV (which would result in strong correlation
between delay variation and the bandwidth of the test signal) and PDV
due to other sources (which "should" be weakly correlated or
uncorrelated with the current bandwidth of the test signal).
Regards
Alan
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