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Date: Mon, 22 May 2006 14:06:48 +0100
From: Brian Candler <B.Candler@pobox.com>
To: mag@intron.ac
Message-ID: <20060522130648.GB33204@uk.tiscali.com>
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Cc: freebsd-net@freebsd.org
Subject: Re: How to Quicken TCP Re-transmission?
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On Mon, May 22, 2006 at 07:51:33PM +0800, mag@intron.ac wrote:
>     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

How big are the pings? Try

    ping -c100 -s1472 x.x.x.x

to send 1500-byte pings (20 bytes IP header + 8 bytes ICMP header + 1472
bytes padding). This will give you a more realistic indication of packet
loss for TCP transfers than the small pings you get by default.

TCP performs really, really badly on packet loss over 5%. I don't think that
any amount of tweaking will cope with 30% packet loss.

Perhaps a mechanism which sends each packet 3 times would work, but then
tripling the load on your link will increase your packet loss even more,
perhaps leading to total collapse.

Regards,

Brian.