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Re: [lwip-users] How to decrease TCP repeat time

From: Kieran Mansley
Subject: Re: [lwip-users] How to decrease TCP repeat time
Date: Fri, 19 Jun 2009 13:52:27 +0100

On Fri, 2009-06-19 at 08:22 -0400, Éric Lacasse wrote:
> Hi all,
> Each time there is a collision (not treated by the hardware), retry
> TCP time is about 1 second. Do you know how to decrease it (by a
> factor of 10 maybe) ? We have our own Ethernet network (only ARM
> processor running LWIP stack).  Connection to the other device is done
> toward a router.

That's just the way TCP is.  It's quite conservative.  There have been a
number of things done since TCP was first specified to try and help in
cases like this, but the only one that lwIP supports is the fast
retransmission algorithm which should spot a missing packet if there are
a few more that follow and don't get lost.  If the last (or nearly last)
packet in a burst is the one that gets dropped it doesn't help you
though - you still have to wait for the slow retransmission timer to

If you want to be non-standard, you could decrease the slow
retransmission timeout, but you should read up on why it was designed to
be like this and work out if that would be safe for your network - it
all rather depends on the round trip time of the connection.


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