At the moment i´m doing my diploma thesis at Nortel Networks and we´re
testing the performance of TCP over Satellite with both Linux Kernel Version
2.2.16 and 2.4.1.
After long reading which TCP parameters and extensions are significant for
the satellite performance of Linux i did a test today with the following
parameters enabled in the proc-filesystem.
tcp_sack enabled, tcp_window_scaling enabled, tcp_timestamps enabled (i
suppose a value equal to 1 denotes that an option is enabled, right ?)
Furthermore for 2.4.1: tcp_dsack enabled, tcp_fack enabled, tcp_ecn enabled.
The window sizes were set as following:
for 2.2.16: /proc/sys/net/core/rmem-default, rmem_max, wmem_default,
wmem_max all of them : 262140
for 2.4.1: /proc/sys/net/ipv4/tcp_wmem, tcp_rmem all of them: 262140
262140 262140 (min, default, max) (with echo 262140 262140 262140 >
/proc/sys...., i hope this is right) and /proc/sys/net/core/rmem-default,
rmem_max, wmem_default, wmem_max all of them : 262140
Nevertheless when we did ftp-sessions between the 2 Linux-machines we never
achieved a transfer rate of considerably more than 40 kByte over a 2
Mbit-satellite channel !!!
A colleague of mine who did the same transfers with a Windows2000-machine
was able to achieve transfer rates of allmost 150kByte.
So what is wrong with my setup ? Actually with SACK enabled and Window
Scaling enabled and the huge TCP window sizes I´ve specified performance
should be much better. I would have expected about 1...1.5 MBit instead of
300 kBit !
I hope you find a failure of mine and will be able to help me with my
problem.
Thank you very much in advance !
Yours sincerely,
Bernd Sturm
Bernd Sturm
ND Satcom
phone: 0049-7545 / 96-8847
mailto:Bernd.Sturm@xxxxxxxxxxxx
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