How do I max a 6Mbps link
Kevin Stevens
Kevin_Stevens at pursued-with.net
Wed Jul 9 10:55:47 PDT 2003
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
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