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Re: [tsvwg] Switch testing at 25G with ECN --SCE Draft

"Black, David" <David.Black@dell.com> Sun, 11 August 2019 19:45 UTC

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From: "Black, David" <David.Black@dell.com>
To: Jonathan Morton <chromatix99@gmail.com>, Greg White <g.white@CableLabs.com>
CC: "Scaglione, Giuseppe" <giuseppe.scaglione@hpe.com>, "tsvwg@ietf.org" <tsvwg@ietf.org>
Thread-Topic: [tsvwg] Switch testing at 25G with ECN --SCE Draft
Thread-Index: AQHVTjzVhUHobEZZSO2B4aLiltuEeqbyKfAAgAAHcICAAUMeAIAAGKcAgAAD1wCAAAqVgIAAAdUAgAADKgCAABqKgIACFmaQ
Date: Sun, 11 Aug 2019 11:29:18 +0000
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References: <A8E3F5E9-443D-4F5A-9336-9A0E2E72C278@cablelabs.com> <201908082333.x78NXS0T094756@gndrsh.dnsmgr.net> <AT5PR8401MB07070C672C9F519C05D2D3F599D60@AT5PR8401MB0707.NAMPRD84.PROD.OUTLOOK.COM> <81354E22-777C-4BDB-96E0-0B1F6C1DCCD2@cablelabs.com> <AT5PR8401MB070700703FBF2318808238CF99D60@AT5PR8401MB0707.NAMPRD84.PROD.OUTLOOK.COM> <C9E9A1C7-59CF-4414-82CE-14ABFE74ADB2@gmail.com> <ADCEE0A5-6A32-4106-8557-029C65B2D4C5@cablelabs.com> <AT5PR8401MB07074B665CF7612FAD66E13899D60@AT5PR8401MB0707.NAMPRD84.PROD.OUTLOOK.COM> <6D40C855-EE12-4148-9EE6-E67DE8ADC715@cablelabs.com> <C38E747D-7332-4004-BDED-AACC26115558@gmail.com>
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tsvwg/AU-eiSNbUw83GsI1fY3YVLmff-8>
Subject: Re: [tsvwg] Switch testing at 25G with ECN --SCE Draft
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Posting as an individual, not a WG chair.

> > On 10 Aug, 2019, at 12:54 am, Greg White <g.white@CableLabs.com>
> wrote:
> >
> > Agreed.  I would not expect any different result either, which begs the
> question why does SCE need two different signals (ECT(1) and CE) in a
> datacenter environment?
> 
> Simple: to allow using the same protocol *outside* the datacentre, because
> it coexists cleanly with existing RFC-3168 infrastructure and endpoints.  That
> was always the chief failing of DCTCP.
> 
>  - Jonathan Morton

[David>] That coexistence is also interesting in a datacenter environment, as it stops things from breaking badly if RFC-3168 TCP traffic and DCTCP-SCE traffic are mixed (where DCTCP-SCE receivers are paying attention to both SCE and CE marks).   As for why or how this sort of traffic mixing could happen, the reasons start with "To err is human."

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