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Re: [tsvwg] [Ecn-sane] per-flow scheduling

Sebastian Moeller <moeller0@gmx.de> Wed, 17 July 2019 21:34 UTC

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From: Sebastian Moeller <moeller0@gmx.de>
In-Reply-To: <350f8dd5-65d4-d2f3-4d65-784c0379f58c@bobbriscoe.net>
Date: Wed, 17 Jul 2019 23:33:17 +0200
Cc: "Holland, Jake" <jholland@akamai.com>, "ecn-sane@lists.bufferbloat.net" <ecn-sane@lists.bufferbloat.net>, tsvwg IETF list <tsvwg@ietf.org>
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References: <350f8dd5-65d4-d2f3-4d65-784c0379f58c@bobbriscoe.net>
To: Bob Briscoe <ietf@bobbriscoe.net>
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Subject: Re: [tsvwg] [Ecn-sane] per-flow scheduling
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Dear Bob, dear IETF team,


> On Jun 19, 2019, at 16:12, Bob Briscoe <ietf@bobbriscoe.net> wrote:
> 
> Jake, all,
> 
> You may not be aware of my long history of concern about how per-flow scheduling within endpoints and networks will limit the Internet in future. I find per-flow scheduling a violation of the e2e principle in such a profound way - the dynamic choice of the spacing between packets - that most people don't even associate it with the e2e principle.

	This does not rhyme well with the L4S stated advantage of allowing packet reordering (due to mandating RACK for all L4S tcp endpoints). Because surely changing the order of packets messes up the "the dynamic choice of the spacing between packets" in a significant way. IMHO it is either L4S is great because it will give intermediate hops more leeway to re-order packets, or "a sender's packet spacing" is sacred, please make up your mind which it is.

> 
> I detected that you were talking about FQ in a way that might have assumed my concern with it was just about implementation complexity. If you (or anyone watching) is not aware of the architectural concerns with per-flow scheduling, I can enumerate them.

	Please do not hesitate to do so after your deserved holiday, and please state a superior alternative.

Best Regards
	Sebastian


> 
> I originally started working on what became L4S to prove that it was possible to separate out reducing queuing delay from throughput scheduling. When Koen and I started working together on this, we discovered we had identical concerns on this.
> 
> 
> 
> Bob
> 
> 
> -- 
> ________________________________________________________________
> Bob Briscoe                               http://bobbriscoe.net/
> 
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