Re: [aqm] TCP ACK Suppression

Clark Gaylord <cgaylord@vt.edu> Wed, 07 October 2015 11:01 UTC

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References: <alpine.DEB.2.02.1510060748480.8750@uplift.swm.pp.se> <D2394BB6.548C5%g.white@cablelabs.com> <0A452E1DADEF254C9A7AC1969B8781284A7D9B66@FR712WXCHMBA13.zeu.alcatel-lucent.com> <5614D4B8.5060403@kit.edu>
Date: Wed, 7 Oct 2015 07:00:58 -0400
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From: Clark Gaylord <cgaylord@vt.edu>
To: "Bless, Roland (TM)" <roland.bless@kit.edu>
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Cc: "LAUTENSCHLAEGER, Wolfram \(Wolfram\)" <wolfram.lautenschlaeger@alcatel-lucent.com>, Greg White <g.white@cablelabs.com>, "aqm@ietf.org" <aqm@ietf.org>
Subject: Re: [aqm] TCP ACK Suppression
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For a good time you should see what satellite modems do! It makes sense
since they need enormous buffers, but it's kinda fun to realize the modern
next to you, even though it's not really operating at layer three, has
chosen to effectively terminate your tcp session, ACKing you, and then
buffers to the other modem, who has its own ACK protocol. Similarly on the
other end. This is why non tcp, like pptp is so bad on satellite.

I'm curious to hear the practical implication of docsis on pptp
performance. If you compare a native tcp to a pptp encapsulated tcp, do you
notice a difference?

--
Clark Gaylord
cgaylord@vt.edu

... thumbed on Android
    auto-correct may have improved this message
    brevity should not be taken to imply curtness  ...
On Oct 7, 2015 4:16 AM, "Bless, Roland (TM)" <roland.bless@kit.edu>; wrote:

> Hi,
>
> Am 07.10.2015 um 09:42 schrieb LAUTENSCHLAEGER, Wolfram (Wolfram):
> > Is this specialized upstream TCP ACK handling, particularly the
> > prioritization a general recommendation in all access technologies?
> > Perhaps it should be, since otherwise up and downstream TCP flows
> interfere
> > in a crazy queue oscillation that is typically misinterpreted by AQMs.
> > Is this topic addressed in some RFC already?
>
> Oh, I hope that this is an exception. Such kind of
> optimizations may cause a lot of trouble since a link
> layer device is interfering with transport layer semantics.
> We all know that exactly these kinds of interference
> eventually end up in problems with end-to-end transparency and
> deployment of new protocol options. At least it interferes with
> the ACK clocking expectation of some congestion control algorithms...
>
> Regards,
>  Roland
>
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