Re: [ledbat] ECN/AQM

[Lachlan Andrew <[e-mail]>]

Greetings Bob,

Our point of divergence is probably step 1 in your argument.

I was still thinking of LEDBAT as less than best effort.  If it
(permanently) reverts to standard TCP on loss, then it is not longer
less than best effort, since LEDBAT flows will typically be long and
experience at least one loss before most of the transfer is complete.

However, if it only *temporarily* reverts to standard TCP, then step 1
of the argument is misleading.  ECN and loss can differ in how long
they cause the LEDBAT flow to remain aggressive.  If ECN causes it to
remain aggressive longer than loss does, then there is an incentive to
enable ECN (if throughput gives an incentive).  If higher throughput
is not an incentive (that's why we're not using TCP), then smoothness
may be an incentive; ECN could cause a more mild immediate backoff but
revert more quickly to non-TCP behaviour.

You may say that these alternatives are too complex to be worthwhile.
If so, I'd probably agree.  However, I'm arguing that it is *possible*
to give an incentive to use ECN without breaking other design goals.

Cheers,
Lachlan

On 1 July 2011 21:30, Bob Briscoe <[e-mail]> wrote:
> Lachlan,
>
> I'm trying to work out the mental model you have that leads to this
> conclusion. Perhaps you are thinking ECN happens at a shallower point in the
> queue than loss?
>
> I was also thinking the response to ECN could be less - until I thought it
> through a couple of days ago. I posted the logical progression on this list
> which concluded that LEDBAT has to respond the same to ECN and to loss.
>
> See <STEP_BY_STEP_LOGIC> within
> <http://www.ietf.org/mail-archive/web/ledbat/current/msg00479.html>
>
> As you are proposing otherwise, if you say where you disagree with that
> logical progression we might be able to get to the bottom of this?



-- 
Lachlan Andrew  Centre for Advanced Internet Architectures (CAIA)
Swinburne University of Technology, Melbourne, Australia
<http://caia.swin.edu.au/cv/landrew>
Ph [phone]