[Iccrg] Why don't we stop treating ECN and loss similarly?

On 27 oct. 2012, at 11:26, Michael Welzl wrote:

> Hi,
> 
> Here's an idea, inspired by something Bob Briscoe posted to the TSVWG list recently in a discussion of draft-carlberg-tsvwg-ecn-reactions. However, this possibly stupid idea is my own responsibility alone  :-)
> 
> 
> According to RFC 3168, senders must react to ECN just as if packets had been dropped.
> This is to maintain fairness between ECN-compatible and non-compatible flows.
> Because of this requirement, AQMs cannot ECN-mark packets more aggressively than it drops packets from non-ECN-capable flows - else ECN-marked flows would be at a disadvantage.
> 
> We have seen various non-standard congestion control behaviors can co-exist reasonably well with standard TCP in practice. If it was possible to have a milder congestion reaction to ECN-based reaction, it would also be possible to ECN-mark packets earlier, leading to a bigger advantage for everyone using ECN. And none of this is possible when we have the "treat an ECN mark just like loss" rule in place.
> 
> Hence, my question: to incentivize ECN usage and enable better behavior when it's used, shouldn't we remove this rule?
> 

Hi,

(jumping late into this thread)

Likely I am missing something, but I don't see a fundamental difference between, say, having CUBIC compete with non-CUBIC flows and having RFC3168-compliant, ECN-enabled flows compete with "non-standard" ones (non-standard as in, reduce cwnd by less than half).

I don't know if we should *remove* the halve-cwnd-if-ECN-mark rule, but it looks like an interesting experiment to do.

Thanks,

David.

PS: by the way, what does a CUBIC sender do in the face of incoming ECN marks?

> Note that this is not even about a more fine-grain interpretation of ECN feedback - it's more like an intermediate step.
> 
> I'm curious what everyone thinks... am I missing something?
> 
> Cheers,
> Michael
> 
> 
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David ROS
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