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Re: [tsvwg] new tests of L4S RTT fairness and intra-flow latency: defaults ready for testing

Ingemar Johansson S <ingemar.s.johansson@ericsson.com> Wed, 18 November 2020 06:58 UTC

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From: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
To: Jonathan Morton <chromatix99@gmail.com>, Sebastian Moeller <moeller0@gmx.de>
CC: tsvwg IETF list <tsvwg@ietf.org>, Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
Thread-Topic: [tsvwg] new tests of L4S RTT fairness and intra-flow latency: defaults ready for testing
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Date: Wed, 18 Nov 2020 06:58:52 +0000
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Subject: Re: [tsvwg] new tests of L4S RTT fairness and intra-flow latency: defaults ready for testing
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Hi

 

The difference does not look extreme to me. Can't guarantee it but I suspect
that you'll find similar anomalies with e.g. rate based congestion controls.
We had all sorts of interflow fairness issues in the RMCAT work that ended
up in RFCs for NADA and SCReAM and L4S was not on the table then. 

 

Besides this, I don't want to kill this discussion, it is very useful. But.
it delves into congestion control research and perhaps ICCRG is a better
venue for this ? 

 

/Ingemar

 

From: tsvwg <tsvwg-bounces@ietf.org> On Behalf Of Jonathan Morton
Sent: den 18 november 2020 07:45
To: Sebastian Moeller <moeller0@gmx.de>
Cc: tsvwg IETF list <tsvwg@ietf.org>
Subject: Re: [tsvwg] new tests of L4S RTT fairness and intra-flow latency:
defaults ready for testing

 

On 18 Nov, 2020, at 8:21 am, Sebastian Moeller <moeller0@gmx.de
<mailto:moeller0@gmx.de> > wrote:

The changes that Oliver submitted to TCP Prague not only increase the fudge
RTT to 25ms, but they also, as Koen mentioned, increase the time it takes
for Prague to switch to the new fairness mode to 500 RTTs, or 5 seconds at
10ms RTT.
I really wonder how that affects fairness if the shallow queue is used by a
bunch of short flows with 10ms RTT. As far as I can tell the consequences of
this delayed engagement have not been described properly. 

 

Yes, that engagement delay is clearly visible in a time-series plot.  I
think it may even be more than 5 seconds in practice:



 

 - Jonathan Morton

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