increasing transmit speeds in WAN setting?

Moses Leslie marmoset at
Thu Oct 19 05:31:48 UTC 2006


We're running 6.1-R, and are having difficulty getting decent speeds as
latency increases.  The server is connected via gbit copper, and is gbit
or better to the internet (depending on the path).

For everything local, we're able to get what you'd expect (300+MBit
without really any tuning).  However, when the latency is 60-80ms (IE
across the US), we're unable to get better than around 300KB/s.

It appears to be possibly related to the tcp.inflight stuff, but disabling
it or messing with some of the related sysctls doesn't appear to help
much.  Downloads often start quickly, but are then throttled back down to
300KB/s within 10 seconds or so.  We've changed the hz (100 to 10000), the
net.inet.tcp.sendspace, kern.ipc.maxsockbuf, and tried different
variations on the inflight tunables, but nothing has made a positive
difference of more than ~20KB/s at best.

If the server is running linux (2.6 kernel with default TCP settings), we
can get much better speeds, 600-1000KB/s easily.  If we were going for
time/distance records, we would try changing around tcp settings on the
client, but we're trying to maximize performance for standard surfers who
wouldn't know how to do that, so we're looking for anything that is server
side only.

We've been searching high and low for any tuning ideas but aren't able to
find anything that's made a difference.  From looking at how the
congestion stuff works in the source, it appears that something like:

might be happening here, but we're kind of stabbing in the dark.

Does anyone have any tuning ideas for 6.1 in a WAN setting?



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