[tsvwg] A few comments on the L4S Operational Guidance draft

Gorry Fairhurst <gorry@erg.abdn.ac.uk> Tue, 02 March 2021 09:47 UTC

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From: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
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Subject: [tsvwg] A few comments on the L4S Operational Guidance draft
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I've just looked at theL4S Operational Guidance draft as this will be 
presented at the next meeting and I do have a few comments/questions:

(1) There is text that hints that RFC3168 FIFO bottlenecks are rare:
    Since existing studies have hinted that RFC3168 FIFO bottlenecks are
    rare, detections using these techniques may also prove to be rare.
    Therefore, it may be possible for a host to cache a list of end host
    ip addresses where a RFC3168 bottleneck has been detected.

- I suggest “hinted” is not a great choice of words, maybe: suggested 
that FIFO bottlenecks might be rare, or talk about the possibility of 
these bottlenecks?
- This really needs a reference to the suggested evidence? or method to 
- I’m unsure  how such a caching would work, i.e. how the information 
would be aggregated - and how the timeliness could be managed. There 
appears some parallels here with TCB sharing - although different 
mechanism different problem?
- Although perhaps awkward in some stack, the risk seems low: Some short 
explanation of the likely risk in incorrectly classifying a path would 
be helpful.

(2) Text on Disable RFC3168 ECN Marking

    Disabling [RFC3168] ECN marking eliminates the unfairness issue.
    Clearly a downside to this approach is that classic senders will no
    longer get the benefits of Explict Congestion Notification.

- I wonder if this needs to be a lot more clear about what is being 
discussed - is this ECT(0) marking?

(3) Could we cite more the IETF recommendations from RFC 7567?

- I’m wondering whether the recommendations and mitigations can be 
related to RFC 7567, which is the BCP on AQM?

Best wishes,