Re: [ippm] Comments on draft-morton-ippm-delay-var-as-03.txt

[Al Morton <acmorton at att.com>]

Hi Alan,

I agree with (a) and (b), and wrote a summary of your 2003
contribution
(thanks for the reminder, it was a good one). Perhaps we can post it
on the Packet Performance document sharing site, with your
permission.

I agree with Benoit, the easy SLA formulation is a good point, but
it's one I think will fit better in section 6.5, when we're making
comparisons.

We have a placeholder for the smoothing/queuing separation problem
in
3.5.  I suggest that we see what can be done to solve this
problem
before we introduce it as an evaluation criteria. We've both looked
at this, with no conclusion yet.  IPPM'ers -- For more background
see
http://tools.ietf.org/wg/avt/draft-ietf-avt-rtp-toffset/

Al

At 06:32 AM 8/21/2007, Benoit Claise wrote:
> Alan, 
> > 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.
> We should add that into the draft.
>
> Regards, Benoit.
> > 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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> > ippm at ietf.org 
> >
> > https://www1.ietf.org/mailman/listinfo/ippm
> >  
>
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