[Iccrg] ECN feedback discussion

[Scheffenegger, Richard]

Hi,

I just wanted to keep a record of these interesting remarks on the list, for further discussion.

We discussed ECN both in TCPM and ICCRG, and this post is to start the discussion on the working group lists.

During the TCPM session, Matt Mathis made an interesting remark on the microphone. To paraphrase (my understanding), current marking schemes (RED, CoDel, PIE,...) assume that ECN marks get treated like loss by the end systems.  Therefore, they employ a "low density" marking scheme, with marks expected at an (average) rate of around 3% or so at maximum.

Alternative schemes, that start getting deployed at this time, have very simple marking schemes in the network, and give more information to the end systems for processing and reaction there. As a side effect, these newer schemes may run as high as 100% marking for certain periods (longer than a single flows RTT), so they could be classified as "high density" marking scheme.


Later on, Bob noted, that since ECN Nonce is virtually nonexistent (I know only one stack with partial support), why not re-define ECT(1) to be used by high density marking schemes, keeping ECT(0) for low density schemes (as deployed today). For newer stacks, this would allow an even more fine grained reaction to ECN marking levels...

However, ECN security aspects (Nonce) and legacy uses (ECT(1) has the same meaning for existing ECN stacks as ECT(0)) would not be addressed, but then again, current ECN is also virtually not deployed, according to recent studies.

Of course, such a shift in the semantics of ECT(0) vs ECT(1) would also need to have an impact on the future signaling  / feedback scheme used for TCP (DCCP and SCTP would be able to cope already, afaik).

Best regards,

Richard Scheffenegger


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