[Iccrg] Incentives for ECN

[Michael Welzl]

I agree with all of that, with my chair hat on and off.

Cheers,
Michael


On Jul 15, 2011, at 2:27 PM, John Leslie wrote:

> Lachlan Andrew <lachlan.andrew at gmail.com> wrote:
>>
>> There was some discussion on LEDBAT recently about how to motivate
>> users to set the "ECN capable" bit  on LEDBAT flows, which Jana has
>> suggested may be better followed up in ICCRG.
>
>   True...
>
>> My understanding is that it is "essentially" impossible to give an
>> incentive if we follow the letter of RFC3168, which says ECN must be
>> treated "essentially" identically to loss.
>
>   That requirement has proven less than helpful.
>
>> That requirement was written in the days when "TCP friendliness" was
>> seen as essential. These days, there are many proposals that do not
>> aim for TCP friendliness (either being less aggressive like LEDBAT,
>> or more aggressive like CUBIC, HTCP, CTCP, ...).  I think it is time
>> to revisit the requirement that ECN be treated the same as loss.
>
>   I thoroughly agree -- but _how_ do we revisit it?
>
>   As a research question, that's entirely appropriate for ICCRG.
>
>> People may argue that if one flow backs off less because it is
>> receiving ECN instead of loss, then this is "unfair" to the one
>> experiencing loss.  I would argue that "fair" = "no incentive".
>
>   I always argue that "fair" is one grade below "good" ;^)
>
>   But I must agree "fair" and "incentive" are often mutually
> exclusive. :^(
>
>> I would propose that the ICCRG assess any new congestion control
>> algorithm (for "safety", "fairness" or whatever) on the assumption
>> that the flow may receive either ECN or loss while competing flows
>> receive loss.  If this gives acceptable performance, then there is no
>> need to require equal treatment of ECN and loss.
>
>   Interesting...
>
>   I would suggest that the essential feature of ECN is that it  
> delivers
> a congestion signal _sooner_ -- so a CC algorithm which _initially_
> backs off more quickly upon receipt of an ECN mark, but after a few  
> RTTs
> perhaps is more aggresive than vanilla-TCP upon recognizing a loss is
> a concept worth research.
>
>> Of course, any such algorithm is not RFC3168 *compliant*, but it can
>> still be RFC3168 *compatible*.
>
>   :^)
>
> --
> John Leslie <john at jlc.net>
>
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