BicTCP Implementation Bug

[Yee-Ting Li]

Hi,

We have discovered a serious implementation bug in BicTCP on the Linux 
kernels. Note that because BicTCP is ON by default, this affects all 
users of kernel versions 2.6.8 and above.

For further details please see: 
http://www.hamilton.ie/net/bic-fix/Linux%20BicTCP.pdf

and the patch is:

Index: linux-2.6.10/include/net/tcp.h
===================================================================
--- linux-2.6.10.orig/include/net/tcp.h Fri Dec 24 21:34:00 2004
+++ linux-2.6.10/include/net/tcp.h      Thu Feb 17 14:13:14 2005
@@ -1280,8 +1280,7 @@
                if (sysctl_tcp_bic_fast_convergence &&
                    tp->snd_cwnd < tp->bictcp.last_max_cwnd)
                        tp->bictcp.last_max_cwnd
-                               = (tp->snd_cwnd * 
(2*BICTCP_1_OVER_BETA-1))
-                               / (BICTCP_1_OVER_BETA/2);
+                           = tp->snd_cwnd - ( tp->snd_cwnd / 
(BICTCP_1_OVER_BETA*2) );
                else
                        tp->bictcp.last_max_cwnd = tp->snd_cwnd;

-
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