netdev - TCP fast retransmit

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Message-ID: <2D9E1426-D432-4D08-BF28-FD2615AAEDBA@mpi-bpc.mpg.de>
Date:	Fri, 25 Nov 2011 14:33:18 +0100
From:	"Esztermann, Ansgar" <Ansgar.Esztermann@...-bpc.mpg.de>
To:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: TCP fast retransmit

[originally posted to lkml]
Hello list,

is there some documentation available on TCP fast retransmit? There seem to be quite a lot of descriptions -- from informal to scholarly papers -- on the various algorithms available to calculate the proper size of the congestion window, but I have been unable so far to find out *when* a fast retransmit is triggered. RFC 2581 states the third dupACK "should" do it, and this seems to be quoted fairly often. However, I can easily produce connections that fail to perform fast retransmit even after 5 dupACKs. Some people mention Linux uses a different (presumable more sophisticated) algorithm to trigger fast retransmits, but no-one seems to elaborate.

Thanks,

A.
-- 
Ansgar Esztermann
DV-Systemadministration
Max-Planck-Institut für biophysikalische Chemie, Abteilung 105
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