Re: [trill] WG LC for draft-trill-ecn-support-03 (5/31 to 6:13)

"De Schepper, Koen (Nokia - BE/Antwerp)" <> Fri, 09 June 2017 16:33 UTC

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From: "De Schepper, Koen (Nokia - BE/Antwerp)" <>
To: Susan Hares <>
CC: "" <>, "" <>, "" <>, Bob Briscoe <>
Thread-Topic: [trill] WG LC for draft-trill-ecn-support-03 (5/31 to 6:13)
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Date: Fri, 09 Jun 2017 16:33:29 +0000
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Subject: Re: [trill] WG LC for draft-trill-ecn-support-03 (5/31 to 6:13)
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Hi all,

I reviewed this draft (for the first time) mainly from the point of view of L4S support. I greatly appreciate the forward vision of supporting upcoming ECN functionality, and the flexibility/extensibility of the thrill headers.

Answering question 1: Definitely, L4S ECN marking can drastically improve latency and flow control.

Following comments related to question 2:

I think there is one opportunity not exploited in how L4S ECN is handled: If an ingress node is not supporting ECN, a transit node is allowed to add the Flags word and mark packets with CCE. In case of L4S this case is not covered, and cannot be applied, as NCCE code points are translated by egress nodes as CE or drop if the inner packet is Not-ECT. I think the solution could be to extent the "Arriving TRILL 3-bit codepoint name" table with an extra NCCE name mapping from TRILL-ECN=11 and CCE=0. Table 2 needs to have an extra column with rows (not-ECT, ECT(0), CE, CE). This way an L4S transit node can also insert a Flags word and set NCCE with probability p on top of CCE with p^2. I saw no other combinations that could lead to this arriving situation, and could lead to problems, as current ECN capable transit nodes never mark NCCE.

A typo in section 2: Extesnion should be Extension.


> On 31/05/17 19:48, Susan Hares wrote:
> This begins a  2 week WG LC for draft-ietf-trill-ecn-support which can be
> found at:
> The authors (Donald Eastlake and Bob Biscoe) should indicate whether they
> know of any IPR relating to this draft.
> The TRILL WG should consider the following questions:
> 1) Does this extension of the ECN to TRILL Switches provide for better
> Flow control of IP packets without packet drops?  And is this useful in TRILL
> deployments?
> 2) Do you believe this document is ready for RFC publication?
> Please include the answers to these questions among your comments about
> this draft.
> Sue Hares
> _______________________________________________
> trill mailing list