[tsvwg] draft-white-tsvwg-l4sops-02.txt proposa for additional sections

[Sebastian Moeller <[e-mail]>]

Hi Greg, hi list,

I think that the L4S ops draft could be improved by saying something explicit about the end of the L4S experiment and what differential actions are recommended for participants at that point in time. I made this argument already at the end of https://mailarchive.ietf.org/arch/msg/tsvwg/NXEACkPX1pFriOtqsoifPzoI8Sk/ but I believe that it might have been overlooked there at the end of a long email.

So, here is my proposal to that regard as a new section 6:


6. What L4S-deploying networks should to do at the end of the L4S experiment

This section gives guidance how L4S-deploying networks should respond to any of the two possible outcomes of the IETF-supported L4S experiment.

[COMMENT: I believe that there needs to be a proper definition how the L4S experiment is supposed to be evaluated at the end to decide between success and failure, but the L4S-ops document seems to be the wrong place for that, so I propose to add this to one of the L4S core IDs, preferably to section 6 of https://datatracker.ietf.org/doc/draft-ietf-tsvwg-ecn-l4s-id/ which already contains discussion about what the experiment is supposed to figure out, so adding a section how to evaluate the outcome there seems a natural fit; 
IMHO the deciding factor here could be whether L4S is promoted to proposed standard status after the experiment, if and only if that happens L4S should be considered a success... I base this on the already known problematic side-effects of L4S and the fact that L4S will consume a rather scarce resource in an IP-level code-point the exists in both IPv4 and IPv6, which IMHO should be released ASAP if L4S fails to succeed]

6.1 Successful termination of the L4S experiment

If the L4S experiment is deemed successful, participating networks are encouraged to continue deploying L4S-aware nodes and if possible replace all non-L4S-aware rfc3168 AQM already deployed as far as feasible, or at least restrict rfc3168 AQM to interpret ECT(1) equal to NotECT. Participants are also expected to track the evolution of the L4S standards and adapt their implementations accordingly (e.g. if as part of switching from experimental to standards track, changes in the L4S RFCs become necessary).


6.2 Unsuccesful termination of the L4S experiment

If the L4S experiment is deemed unsuccessful, it might need to be terminated: L4S network nodes should be un-deployed and the ECT(1) codepoint usage should be released/recycled quickly. 
	To achieve the former, participants of the L4S experiment are expected to configure their L4S-aware network nodes such that either the LL-queue of a dual queue AQM gets completely disabled, or that the LL-queue is switched from issuing CE-marks to pure drops; thereby removing L4S-signaling from the network. To achieve the latter, all endpoint hosts need to stop negotiating L4S-congestion signaling. For nodes under control of participating networks that should only require re-configuration of the endpoint hosts. For nodes not under control of participants of the experiment that will be a considerable challenge. To give a strong signal to such out-of-network endpoints drastic measures might be required, like re-marking ECT(1) packets to NotECT or even dropping all ECT(1) packets on network ingress, as these will give clear and strong incentives to endpoints to stop using ECT(1)/L4S-signaling. But to avoid "burning" the ECT(1) codepoint indefinitely, such measures should be restricted to a limited duration (e.g. 24 month) after an unsuccessful termination of the L4S experiment, to allow the ECT(1) codepoint to be recycled for other uses/experiments afterwards.



I am sure that this is not going to be complete and that there will be differing opinions on these sections, but I believe something similar in scope should be added.

Best Regards
	Sebastian