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Re: [tcpm] [iccrg] Cwnd growth after fast convergence in CUBIC

"Rosenblum, Wesley" <wesleyr@amazon.com> Fri, 06 November 2020 20:35 UTC

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From: "Rosenblum, Wesley" <wesleyr@amazon.com>
To: Neal Cardwell <ncardwell=40google.com@dmarc.ietf.org>, Lars Eggert <lars@eggert.org>
CC: Vidhi Goel <vidhi_goel@apple.com>, "tcpm@ietf.org" <tcpm@ietf.org>, Martin Thomson <mt@lowentropy.net>, iccrg IRTF list <iccrg@irtf.org>
Thread-Topic: [iccrg] [tcpm] Cwnd growth after fast convergence in CUBIC
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Date: Fri, 06 Nov 2020 20:34:07 +0000
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Subject: Re: [tcpm] [iccrg] Cwnd growth after fast convergence in CUBIC
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Agreed, and this is basically what Vidhi has suggested as well. In my option it is slightly
more clear to introduce cwnd into the calculation of K as Vidhi has done. I suppose it comes 
down to where in a particular implementation one calculates K.

One note: If W_last_max were to be incorporated into K, the special case mentioned in section 
4.8 about exiting hybrid slow start would also need to be updated to mention setting 
W_last_max = W_max = cwnd, as W_last_max  would not have been set in such a case. 

Thanks,
Wesley

On 11/6/20, 6:10 AM, "Neal Cardwell" <ncardwell=40google.com@dmarc.ietf.org> wrote:
>  AFAICT,  changing Eq 2 to the following might fix the RFC and make it
>  match the Linux TCP CUBIC behavior:
>
>         K = cubic_root(W_max - W_last_max*beta_cubic)/C) (Eq. 2)

    best,
    neal

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