Re: [rmcat] Fw: New Version Notification for draft-hayes-rmcat-sbd-00.txt

[Stefan Holmer <[e-mail]>]

Nice draft! I have a few comments:

You're mentioning that skewness would require all delay measurements to be
stored, and therefore you're computing some different metric which is
related to skew. I wonder if it shouldn't be possible to more accurately
estimate the skew from a histogram instead? That way you at least won't
need to store all delay measurements. Might not be worth the trouble if
your metric works well.

As mentioned by Mirja, it seems a bit error prone to use the max of the OWD
(also, shouldn't it be max_T(OWD)?) when computing the PDV.

Somewhat related to this, I wonder if you have any plans to test this
algorithm on WiFi? I have seen many cases of WiFi with a lot of contention
and/or interference, where the delay gets skewed not because lack of
bandwidth, but because of lower layer retransmissions or because the access
point was busy serving someone else for a moment. I wonder if that can
cause you to incorrectly detect shared bottlenecks, where in reality there
was only a shared WiFi... Now that I think of it, the WiFi effect should
result in positive skewness, while you're looking for negative skewness, so
you may be ok here. :)

It would be good to have the diff() operation defined somewhere. Is it the
diff between successive measurements, or the diff between the flows?

/Stefan


On Fri, Oct 10, 2014 at 5:37 PM, David Hayes <[e-mail]> wrote:

> Dear All,
>
> We have just submitted of our initial shared bottleneck detection
> draft and will value your comments and suggestions.
>
> Regards,
>
> David
>
> Begin forwarded message:
>
> Date: Fri, 10 Oct 2014 08:17:57 -0700
> From: <[e-mail]>
> To: Michael Welzl <[e-mail]>, David Hayes
> <[e-mail]>, Michael Welzl <[e-mail]>, Simone Ferlin
> <[e-mail]>, Simone Ferlin <[e-mail]>, David Hayes
> <[e-mail]> Subject: New Version Notification for
> draft-hayes-rmcat-sbd-00.txt
>
>
>
> A new version of I-D, draft-hayes-rmcat-sbd-00.txt
> has been successfully submitted by David Hayes and posted to the
> IETF repository.
>
> Name:           draft-hayes-rmcat-sbd
> Revision:       00
> Title:          Shared Bottleneck Detection for Coupled
> Congestion Control for RTP Media. Document date:        2014-10-10
> Group:          Individual Submission
> Pages:          12
> URL:
> http://www.ietf.org/internet-drafts/draft-hayes-rmcat-sbd-00.txt
> Status:         https://datatracker.ietf.org/doc/draft-hayes-rmcat-sbd/
> Htmlized:       http://tools.ietf.org/html/draft-hayes-rmcat-sbd-00
>
>
> Abstract:
>    This document describes a mechanism to detect whether end-to-end data
>    flows share a common bottleneck.  It relies on summary statistics
>    that are calculated by a data receiver based on continuous
>    measurements and regularly fed to a grouping algorithm that runs
>    wherever the knowledge is needed.  This mechanism complements the
>    coupled congestion control mechanism in draft-welzl-rmcat-coupled-cc.
>
>
>
>
> Please note that it may take a couple of minutes from the time of
> submission until the htmlized version and diff are available at
> tools.ietf.org.
>
> The IETF Secretariat
>
>
>
> --
>
> -------------------------
> David Hayes
> [e-mail]
> Department of Informatics
> University of Oslo
>
>