Re: draft-ietf-bmwg-dcbench-terminology

Hi,
	While we haven't published minutes yet, if you review the audio, you'll note that Al took an action to send his suggested text to the list. Al has fulfilled that action item below - something we greatly appreciate, in advance of the minutes, and in advance of prodding! Thank you Al :)

	Also, on this note, Lucien and Jacob, there was quite a bit of feedback from Scott at the mic on your draft; BMWG minutes and minute takers are excellent, but I strongly suggest you review the audio - it can only help.

Kind regards,
Sarah

> On Nov 3, 2015, at 3:19 PM, MORTON, ALFRED C (AL) <[email protected]> wrote:
> 
> Hi Lucien and Jacob,
> 
> Following the bmwg session yesterday there were several
> reviews and comments expressed.
> 
> I have one section revision to suggest, 
> Al
> (as a participant)
> 
> 
> In the latest draft of Data Center Terminology -01:
> - using the term Jitter, should be delay variation now
> - still citing RFC 3393 almost exclusively, which is too flexible
> - only citing IPDV from RFC 5481, 
> - in the past meeting we agreed on RFC 5481 PDV as primary, IPDV only if you
>  want to understand if traffic has become more bursty in transfer
> - Metric Units section is the place to specify Units of Measure (seconds
>  in this case, not much else)
> 
> I suggest to revise section 3 as follows:
> NEW:
> 
> 3 Delay Variation
> 
> 3.1 Definition
> 
> Delay variation is derived from multiple measurements
> of one-way delay, as described in RFC 3393.
> The mandatory definition of Delay Variation is the PDV form
> from section 4.2 of RFC 5481. When considering a stream of packets,
> the delays of all packets are subtracted from the minimum delay
> over all packets in the stream. This facilitates assessment of 
> the range of delay variation (Max - Min), or a high percentile 
> of PDV (99th percentile, for robustness against outliers).
> 
> If First-bit to Last-bit timestamps are used for Delay measurement, then
> Delay Variation MUST be measured using packets or frames of the 
> same size, since the definition of latency includes the serialization
> time for each packet. Otherwise if using First-bit to First-bit,
> the size restriction does not apply.
> 
> 
> 3.2 Discussion
>   In addition to PDV Range and or a high percentile of PDV,
>   Inter-Packet Delay Variation (IPDV) as defined in section 4.1 of
>   RFC5481 (differences between two consecutive packets) MAY be used
>   for the purpose of determining how packet spacing has changed during
>   transfer, for example to see if packet stream has become closely-spaced
>   or "bursty". However, the Absolute Value of IPDV SHOULD NOT be used, as 
>   this collapses the "busrty" and "dispersed" sides of the IPDV distribution
>   together.
> 
> 3.3 Measurement Units
> 
> The measurement of delay variation is expressed in units of seconds.
> 
> A PDV histogram MAY be provided for the population of packets measured.
> 
> -=-=-=-=-=-=-=-=-=-
> OLD:
> 3 Jitter
> 
> 3.1 Definition
> 
>   The definition of Jitter is covered extensively in RFC 3393. This
>   definition is not meant to replace that definition, but it is meant
>   to provide guidance of use for data center network devices. 
> 
>   The use of Jitter is in according with the variation delay definition
>   from RFC 3393:
> 
>   The second meaning has to do with the variation of a metric (e.g.,
>   delay) with respect to some reference metric (e.g., average delay or
>   minimum delay).  This meaning is frequently used by computer
>   scientists and frequently (but not always) refers to variation in
>   delay.
> 
>   Even with the reference to RFC 3393, there are many definitions of
>   "jitter" possible. The one selected for Data Center Benchmarking is
>   closest to RFC 3393.
> 
> 
> 3.2 Discussion
> 
>   Jitter can be measured in different scenarios:-packet to packet delay
>   variation-delta between min and max packet delay variation for all
>   packets sent.
> 
> 3.3 Measurement Units
> 
>   The jitter MUST be measured when sending packets of the same size.
>   Jitter MUST be measured as packet to packet delay variation and delta
>   between min and max packet delay variation of all packets sent. A
>   histogram MAY be provided as a population of packets measured per
>   latency or latency buckets. Inter-Packet Delay Variation as defined
>   in RFC5481 (differences between two consecutive packets) MAY be used
>   for this purpose.
> 
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