From: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Date: Sun, 3 Jul 2011 15:55:03 +0000 (-0600)
Subject: dccp ccid-2: Perform congestion-window validation
X-Git-Tag: v3.1-rc1~316^2~253
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=113ced1f52e5ed2dfedc0771a1b11b536cde8168;p=pandora-kernel.git

dccp ccid-2: Perform congestion-window validation

CCID-2's cwnd increases like TCP during slow-start, which has implications for
 * the local Sequence Window value (should be > cwnd),
 * the Ack Ratio value.
Hence an exponential growth, if it does not reflect the actual network
conditions, can quickly lead to instability.

This patch adds congestion-window validation (RFC2861) to CCID-2:
 * cwnd is constrained if the sender is application limited;
 * cwnd is reduced after a long idle period, as suggested in the '90 paper
   by Van Jacobson, in RFC 2581 (sec. 4.1);
 * cwnd is never reduced below the RFC 3390 initial window.

As marked in the comments, the code is actually almost a direct copy of the
TCP congestion-window-validation algorithms. By continuing this work, it may
in future be possible to use the TCP code (not possible at the moment).

The mechanism can be turned off using a module parameter. Sampling of the
currently-used window (moving-maximum) is however done constantly; this is
used to determine the expected window, which can be exploited to regulate
DCCP's Sequence Window value.

This patch also sets slow-start-after-idle (RFC 4341, 5.1), i.e. it behaves like
TCP when net.ipv4.tcp_slow_start_after_idle = 1.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
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