Re: [tsvwg] L4S status: #17 Interaction w/ FQ AQMs

Greg White <> Wed, 06 November 2019 16:23 UTC

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From: Greg White <>
To: Sebastian Moeller <>
CC: Pete Heist <>, Wesley Eddy <>, "" <>
Thread-Topic: [tsvwg] L4S status: #17 Interaction w/ FQ AQMs
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Date: Wed, 6 Nov 2019 16:23:18 +0000
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Subject: Re: [tsvwg] L4S status: #17 Interaction w/ FQ AQMs
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Good timing __

We've just wrapped up our findings on Issue 17, and have posted them here (along with some comments on Issue 16 as well): 
(Note, the ns3 repo is not public yet, but will be shortly.   We'll update that page with links within a day or two.)

In summary, we reached the following conclusions:

- the main result of concern was due to a bug in initializing the value of TCP Prague alpha, which has been fixed and demonstrated to resolve the latency impact that was spanning multiple seconds

- the remaining short duration latency spike in the FIFO queue is seen in *all* congestion control variants tested, including BBRv1, NewReno, and Cubic, and is not specific to Prague

- if the CoDel queue is upgraded to perform Immediate AQM on L4S flows, the latency spike can be largely avoided.

We invite a thorough review of the work, but believe that this closes issue #17.

Best Regards,

Greg White, Tom Henderson, Olivier Tilmans

On 11/6/19, 12:59 AM, "Sebastian Moeller" <> wrote:

    Hi Greg,
    > On Sep 11, 2019, at 19:16, Greg White <> wrote:
    > I'm planning on doing testing as well, but it will be more than a day or two to get it done.  Rough timeframe would be 2-3 weeks from now.
    	Since I can not hide my impatience any loger, did anything come out of this yet?
    Best Regards
    > -Greg
    > On 9/11/19, 1:52 AM, "Pete Heist" <> wrote:
    >> On Sep 9, 2019, at 9:01 PM, Wesley Eddy <> wrote:
    >> Since this thread seems to have dwindled, I just wanted to summarize that it looks to me like we have agreement that testing as described is needed.
    >> I updated the issue tracker with a comment saying as much and pointing back to this thread in the archive for reference.
    >> Is anyone planning to perform this testing in a rough timeframe they might want to share?
    >    Hi Wesley, I’ll share results from relevant testing in the next day or two...
    >    Regards,
    >    Pete