Re: [tsvwg] Review comments on a careful read of the L4S ID

[Sebastian Moeller <[e-mail]>]

Hi Gorry,

see [SM] below for a question.


> On May 6, 2021, at 08:52, Gorry Fairhurst <[e-mail]> wrote:
> 
> 
> Here are some review comments on a careful read of the L4S ID that I hope will help in preparation of a new revision of the draft. More details have been sent to the authors.
> 
> Best wishes,
> 
> Gorry
> [...]
> =================================================================
> 25. Missing drop-only requirement for excluded traffic
>  
> Section 5.4.1.2.  Exclusion of Traffic From L4S Treatment – this text:
>  
>    “The operator MUST NOT alter the end-to-end L4S ECN identifier from
>    L4S to Classic, because its decision to exclude certain traffic from
>    L4S treatment is local-only.”
>  
> ⁃           I think be the word /its/this/ .
> ⁃            Please add a requirement that ECT(1) traffic excluded from L4S treatment MUST be handled as non-ECN traffic (e.g., all congestion signalling is via drops), as Classic AQM treatment and ECN marking produce the wrong results for such traffic.
> =================================================================
[...]

We actually recommend doing exactly that as a measure of last resorts in https://tools.ietf.org/html/draft-white-tsvwg-l4sops-02#page-11
We could:
a) simply accept that divergence
b) add text to the ECN-ID draft to explicitly allow that for extreme situations (or reduce the MUST to a SHOULD, pointing out the cost of doing so)
c) add text to the OPs draft why that violation of the ECN-ID draft is acceptable as a measure of last resort...

Given that this is the final back-stop in the (unlikely) case that the L4S experiment should cause the next congestion collapse I think it made sense to tackle this explicitly, no?


Best Regards
	Sebastian