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Date: Wed, 9 Jul 2003 10:56:33 -0700 (PDT)
From: Kevin Stevens <Kevin_Stevens@pursued-with.net>
To: Max Clark <max.clark@media.net>
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Subject: Re: How do I max a 6Mbps link
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On Wed, 9 Jul 2003, Max Clark wrote:

> Hi all,
>
> What configuration changes do I need to make to two freebsd-stable boxes to
> fully max out a 6Mbps/220ms network link? This is for bulk 500+MB file
> transfers.

You need to increase the maximum TCP window size setting (not sure what
sysctl it is) to around 256KB to accommodate the bandwidth/latency
product.  In brief, 6Mb/1500B frames = 500 frames/sec.  Using 250ms for
simplicity, you need a large enough TCP window to handle 1/4 of that (125
frames x 1500 bytes/frame = 183KB, round up to 256KB) to permit continuous
streaming.  Note that TCP windows actually only go to 64KB, you need to
use TCP window scaling as a multiplier to go beyond that.  Both stations
must support it.

You can find more info on this on the web, look for
high-latency/high-bandwidth.

KeS