netdev - Re: Linux TCP's Robustness to Multipath Packet Reordering

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Date:	Mon, 20 Jun 2011 13:42:45 +0300 (EEST)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Dominik Kaspar <dokaspar.ietf@...il.com>
cc:	Alexander Zimmermann <alexander.zimmermann@...sys.rwth-aachen.de>,
	Netdev <netdev@...r.kernel.org>,
	Yuchung Cheng <ycheng@...gle.com>,
	Carsten Wolff <carsten@...ffcarsten.de>,
	John Heffner <johnwheffner@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Lennart Schulte <Lennart.Schulte@...sys.rwth-aachen.de>,
	Arnd Hannemann <arnd@...dnet.de>
Subject: Re: Linux TCP's Robustness to Multipath Packet Reordering

On Sun, 19 Jun 2011, Dominik Kaspar wrote:

> Ah... the receiver DSACKs the "original" packet. However, the sender
> already received an ACK for its retransmission and advances SND.UNA.
> When the DSACK finally arrives, it is actually outside of the SND.UNA
> - SND.NXT range, which causes the DSACK to trigger "SACK reneging".
> Did I get that right? :-)

Where did you get this idea of reneging?!? Reneging has nothing to do with 
DSACKs, instead it is only detected if the cumulative ACK stops to such 
boundary where the _next_ segment is SACKed (i.e., some reason the 
receiver "didn't bother" to cumulatively ACK for that too). ...That 
certainly does not happen (ever) for out of window DSACKs.

-- 
 i.
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