[Gllug] Slow over 2meg Satellite

[andy at mac1systems.com]

Hi,

One of my systems is acting as the main server (NATing and SQUIDing) in
Africa.  Its connected to the UK via a satellite link.

Has anyone experience of using satellite links and how to get a decent
throughput?  It seems its a common problem having reasonably fast pipes
with large delay (700ms in this case).

I've googled for days now and tried various things (mainly those discussed
at http://www.psc.edu/networking/perf_tune.html which most other articles
seem to reference).

I've increaed the buffers, turned on SACK, Timestamps and windows scaling
using the following:

	echo 1 > /proc/sys/net/ipv4/tcp_timestamps
	echo 1 > /proc/sys/net/ipv4/tcp_window_scaling
        echo 1 > /proc/sys/net/ipv4/tcp_sack

       	echo 8388608 > /proc/sys/net/core/wmem_max
       	echo 8388608 > /proc/sys/net/core/rmem_max
       	echo "4096 87380 4194304" > /proc/sys/net/ipv4/tcp_rmem
       	echo "4096 65536 4194304" > /proc/sys/net/ipv4/tcp_wmem

But it doesn't seem to have made any effect.  Running tests from a PC
connected to the server and FTP directly from the server shows throughput
of only about 20k tops (and often a lot less) even though only about 30% of
the pipe is being used.

If I go to the test site mentioned on the psc.edu site

telnet syntest.psc.edu 7960

I get
=======================================================
! Variable        : Val       : Warning (if any)
!=======================================================
SACKEnabled       : 3         :
TimestampsEnabled : 1         :
CurMSS            : 1448      :
WinScaleRcvd      : 0         : WARN - 0 WinScale Received
CurRwinRcvd       : 5840      :
!
! End of SYN options
!
Which shows Windows scaling is not enabled.  But
cat /proc/sys/net/ipv4/tcp_window_scaling
returns 1.

Is there anything else I need to do to get window scaling working?

Thanks

Andy




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