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Re: [tcpm] slowstart after idle question

Neal Cardwell <ncardwell@google.com> Thu, 20 April 2017 21:27 UTC

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From: Neal Cardwell <ncardwell@google.com>
Date: Thu, 20 Apr 2017 14:26:44 -0700
Message-ID: <CADVnQyn2p5JczOqZxyTbGvi1FG+2PdXoDe=dfqakoYYwPb_4Sw@mail.gmail.com>
To: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
Cc: "tcpm@ietf.org" <tcpm@ietf.org>, Yuchung Cheng <ycheng@google.com>
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Subject: Re: [tcpm] slowstart after idle question
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Hi Ingemar,

As one data point, YouTube disables tcp_slow_start_after_idle, but
paces when restarting from idle. This is true both in the previous
CUBIC era and also now that BBR is deployed for YouTube TCP traffic.

Yuchung's  presentation from a few years back also has a nice
discussion of some of the related issues:

  https://www.ietf.org/proceedings/88/slides/slides-88-tcpm-9.pdf

neal


On Wed, Apr 19, 2017 at 11:42 PM, Ingemar Johansson S
<ingemar.s.johansson@ericsson.com> wrote:
> Hi
>
>
>
> Possibly a question that would fit better in a Linux net dev forum but
> anyway..
>
>
>
> I have one short question. Is slow start after idle generally disabled
> (net.ipv4.tcp_slow_start_after_idle=0) for instance  for HTTP video
> streaming ?.
>
>
>
> I can imagine that there are some benefits with avoiding the CWND decrease
> in idle periods.
>
> Of course there is a problem that a large amount of data is transmitted when
> new objects are sent to the TCP sockets (shown on page 12 in
> https://www.ietf.org/proceedings/96/slides/slides-96-iccrg-1.pdf ), but
> packet pacing can solve this issue.
>
>
>
>
>
> /Ingemar
>
> ==================================
>
> Ingemar Johansson  M.Sc.
>
> Master Researcher
>
>
>
> Ericsson AB
>
> Wireless Access Networks
>
> Labratoriegränd 11
>
> 971 28, Luleå, Sweden
>
> Phone +46-1071 43042
>
> SMS/MMS +46-73 078 3289
>
> ingemar.s.johansson@ericsson.com
>
> www.ericsson.com
>
>
>
> A mistake is to commit a misunderstanding
>                      Bob Dylan
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