FC2 and TCP/IP over satellite

Still looking for help on tuning TCP/IP to get better bandwidth over a
satellite link. Tried tweaking various kernel parameters but didn't seem
to help much. How do I tweak the default TCP/IP packet size? Any other
pointers greatly appreciated.

Philip N. Daly wrote:
> Still looking for help on tuning TCP/IP to get better bandwidth over a
> satellite link. Tried tweaking various kernel parameters but didn't seem
> to help much. How do I tweak the default TCP/IP packet size? Any other
> pointers greatly appreciated.

i don't say what you using as satellite connection (if is biderection or
not) anyway the follow link can help you :

http://www.psc.edu/networking/projects/tcptune/

I use a biderection satellite up 1mbit/s and instead to change something
in /proc/sys/net/ i have preffered change the packet size in my
application.However is problem of your satellite carrier, the only thing
you can do is test test and test using netperf,iperf ...
If you consider that my satellite network admin say me that the best
performance i have if use packet size of 1400 byte, i've tried with
this parameter but i lost too many packet , 1200byte ,instead, is the
better solution for me!!

sorry for my bad english...
peppe

joy wrote:
> Philip N. Daly wrote:
>
>> Still looking for help on tuning TCP/IP to get better bandwidth over a
>> satellite link. Tried tweaking various kernel parameters but didn't seem
>> to help much. How do I tweak the default TCP/IP packet size? Any other
>> pointers greatly appreciated.
>
>
> i don't say what you using as satellite connection (if is biderection or
> not) anyway the follow link can help you :

The link is an EMS-3000 bi-directional, 256 kbps down and 512 kbps up
(inverted from the usual sense). A ethernet cable (twisted) connects the
satellite receiver to a Fedora Core 2 linux box (GHz class, dual CPU).
The IP address is static and the link appears to be very robust (when
compared to our previous ISDN line which was mega-flaky!).

Doing scp on 2 Mb images we're seeing ~128 kbps in each direction so
we're losing 50% of the bandwidth on the way down and 75% on the way up!

P

> > i don't say what you using as satellite connection (if is biderection or
> > not) anyway the follow link can help you :
>
> The link is an EMS-3000 bi-directional, 256 kbps down and 512 kbps up
> (inverted from the usual sense). A ethernet cable (twisted) connects the
> satellite receiver to a Fedora Core 2 linux box (GHz class, dual CPU).
> The IP address is static and the link appears to be very robust (when
> compared to our previous ISDN line which was mega-flaky!).
>
> Doing scp on 2 Mb images we're seeing ~128 kbps in each direction so
> we're losing 50% of the bandwidth on the way down and 75% on the way up!

You may want to talk to your provider. So far, I've never seen a
satellite (or even microwave) that would perform anywhere near what the
salesmen claimed other than in exceptional situations.

That being said, the greatest killer on that sort of connection is the
latency. You probably want to fiddle with the tcp window settings to a
fairly large number to allow more data to be "in-flight" before an
acknowledgement.. Be aware that setting it larger than 64KB takes just a
bit more, but google will help you find the steps if you need them. : )

steve

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Philip N. Daly regaled us with the following:

> Doing scp on 2 Mb images we're seeing ~128 kbps in each direction so
> we're losing 50% of the bandwidth on the way down and 75% on the way up!
>
> P

Consider that you won't really get a sense for the true speed of a satellite
link unless you are transferring files that are *very* large; 2Mb isn't
large enough.

Satellite links have an inherent delay of about 0.6 sec; the length of time
required for signal to travel from earth-to-satellite or
satellite-to-earth. For smallish transfers, that will adversely affect the
measured throughput.

During the transfer of a data collection of 20Mb or better, you will see
transfer speeds ramp up dramatically.

Search the Web for satellite link speed measurement sites; some of those
offer very large data collections you may use to get a truer measure of
your throughput.

- --
Skorpion [skorpion at suespammers dot org]
"Don't attribute to malice that which can be adequately explained by
stupidity."

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Skorpion wrote:
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>
> Philip N. Daly regaled us with the following:
>
>
>>Doing scp on 2 Mb images we're seeing ~128 kbps in each direction so
>>we're losing 50% of the bandwidth on the way down and 75% on the way up!
>>
>>P
>
>
> Consider that you won't really get a sense for the true speed of a satellite
> link unless you are transferring files that are *very* large; 2Mb isn't
> large enough.
>
> Satellite links have an inherent delay of about 0.6 sec; the length of time
> required for signal to travel from earth-to-satellite or
> satellite-to-earth. For smallish transfers, that will adversely affect the
> measured throughput.
>
> During the transfer of a data collection of 20Mb or better, you will see
> transfer speeds ramp up dramatically.

Thanks. I can also create 32Mb data sets so will try with one of them. P.