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

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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