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

[Michael Welzl]

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?

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