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Re: [tsvwg] David Black (individual) on safety of L4S for the Internet

Jonathan Morton <chromatix99@gmail.com> Fri, 08 May 2020 23:02 UTC

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From: Jonathan Morton <chromatix99@gmail.com>
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Date: Sat, 09 May 2020 02:02:11 +0300
Cc: "Black, David" <David.Black@dell.com>, "tsvwg@ietf.org" <tsvwg@ietf.org>
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To: Neal Cardwell <ncardwell=40google.com@dmarc.ietf.org>
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Subject: Re: [tsvwg] David Black (individual) on safety of L4S for the Internet
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> On 9 May, 2020, at 1:04 am, Neal Cardwell <ncardwell=40google.com@dmarc.ietf.org> wrote:
> 
> So at least to a first approximation it seems like if an L4S flow is
> bleached by an ISP to Not-ECT, is then treated by the ISP's
> bottlenecks like non-ECN Reno, and then (per the L4S spec) behaves
> like non-ECN Reno, L4S should be safe.

Further to my earlier reply, the fact is that a bug causing loss to be *ignored* for the purpose of congestion control has arisen at least twice in the context of 1/p schemes (both DCTCP and TCP Prague).  So relying on loss as a fallback might not be *entirely* reliable.

And I think Yuchung Cheng has noticed the same aspect of this problem.

 - Jonathan Morton

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