Re: [aqm] draft-khademi-alternativebackoff - lightly loaded, high BDP paths

[Naeem Khademi <[e-mail]>]

Hi Simon

Very good point -- I also think this falls into the scope
of draft-ietf-aqm-eval-guidelines aligned with my interpretation of your
words. I believe Section 8.2.2 of
https://tools.ietf.org/html/draft-ietf-aqm-eval-guidelines-08 somewhat
implicitly covers that.

Cheers,
Naeem

On Tue, Oct 13, 2015 at 5:09 AM, Simon Barber <[e-mail]> wrote:

> I was very interested to see this draft discusses a problem with AQMs
>
> AQM schemes like CoDel and PIE use congestion notifications to
>    constrain the queuing delays experienced by packets, rather than in
>    response to impending or actual bottleneck buffer exhaustion.  With
>    current default delay targets, CoDel and PIE both effectively emulate
>    a shallow buffered bottleneck (section II, [ABE2015 <https://tools.ietf.org/html/draft-khademi-alternativebackoff-ecn-01#ref-ABE2015>]).  This
>    interacts acceptably for TCP connections over low BDP paths, or
>    highly multiplexed scenarios (lmany concurrent TCP connections).
>    However, it interacts badly with lightly-multiplexed cases (few
>    concurrent connections) over high BDP paths.  Conventional TCP
>    backoff in such cases leads to gaps in packet transmission and
>    underutilisation of the path.
>
>
> I think it wold be good to add some discussion of this effect to the draft
> on evaluating AQM algorithms. In many access network scenarios the paths
> will be lightly loaded, and sometimes higher BDPs will be experienced. In
> these cases it's good to know that the AQM is not hurting your experience.
>
> Simon
>
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