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Re: [tsvwg] L4S operational guidance draft

Jonathan Morton <chromatix99@gmail.com> Wed, 18 November 2020 06:55 UTC

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From: Jonathan Morton <chromatix99@gmail.com>
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Date: Wed, 18 Nov 2020 08:55:45 +0200
Cc: "Holland, Jake" <jholland=40akamai.com@dmarc.ietf.org>, Pete Heist <pete@heistp.net>, Wesley Eddy <wes@mti-systems.com>, "tsvwg@ietf.org" <tsvwg@ietf.org>
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References: <b6bc81f5-e1f2-e226-1612-7f1070290bbd@mti-systems.com> <9CC37D46-3783-47DD-A1C8-7106EF437642@akamai.com> <f6ebc50de8d7ee42621a8db673f05d17ed8694c4.camel@heistp.net> <5FAF8D38-369B-4642-AAD2-BD5F7E430542@akamai.com> <HE1PR0701MB28761A98F113177964FC2AF2C2E10@HE1PR0701MB2876.eurprd07.prod.outlook.com>
To: Ingemar Johansson S <ingemar.s.johansson=40ericsson.com@dmarc.ietf.org>
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Subject: Re: [tsvwg] L4S operational guidance draft
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> On 18 Nov, 2020, at 8:44 am, Ingemar Johansson S <ingemar.s.johansson=40ericsson.com@dmarc.ietf.org> wrote:
> 
> I try to understand this input, thanks for raining this BTW. 
> 
> I interpret this as: 
> 1) Flow queue AQMs don't work properly across tunnels, as flow isolation based om 5-tuple does not work
> 2) L4S flows can potentially (or will) get an unfair share as a consequence of #1 above because the bootleneck only implement a RFC3168 ECN marking. 
> 
> Is this understanding correct ?

Essentially yes.

The main assumption is that the AQM is not L4S-aware, ie. treats ECT(1) as meaning the same as ECT(0) as per RFC-3168.  Hence it will apply the same marking rate to all packets in the tunnel, which externally appears to be a single flow and so does not receive the benefit of FQ or AF mechanisms.  If some of those packets belong to L4S AIAD flows while others are conventional AIMD flows, the AIAD flows will respond much less and dominate the AIMD flows.

 - Jonathan Morton

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