From owner-freebsd-net@FreeBSD.ORG  Mon May 22 13:39:34 2006
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Date: Mon, 22 May 2006 15:39:32 +0200
From: Marcin Jessa <lists@yazzy.org>
To: mag@intron.ac
Message-ID: <20060522153932.1c789788@marcin>
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Cc: freebsd-net@freebsd.org
Subject: Re: How to Quicken TCP Re-transmission?
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On Mon, 22 May 2006 19:51:33 +0800
mag@intron.ac wrote:

> Hi,
>      I want to transmit data between host A and host B. The link
> between these two hosts is really bad: PING reports 30% packet loss
> and about 60 ms return delay. This means if timed out for 1 second,
> the data must have been lost.
>      I keep "net.inet.tcp.rexmit_min" and "net.inet.tcp.rexmit_slop"
> untouched. But TCPDUMP tells me that if some data are lost,
> re-transmission will be done 64 seconds after last transmission!
>      How to quicken TCP re-transmission?
>      How to tune "net.inet.tcp.rexmit_min" and
> "net.inet.tcp.rexmit_slop"?

You can take a look at SCPS - http://www.scps.org/
Their protocol is used on lossy links with big latency and
packet loss (such as satellites) and overcomes shortcomings of TCP.
It works with divert mechanism of FreeBSD and I ported the
tap device part as well to both NetBSD / FreeBSD (experimental).

Cheers,
Marcin.