Problems with Ad-Hoc Mode

Dan Williams dcbw at
Wed Feb 18 10:06:21 EST 2009

On Wed, 2009-02-18 at 09:49 -0500, Dave Kroetsch wrote:
> Hi guys,
> I'm running a Unex 8385 CF module on an ARM processor running kernel 
> 2.6.22 and a backported version of the latest driver from the git.
> We've got a setup where two systems (identically configured) are running 
> an ad-hoc network.  UDP transfers seem to be quite snappy and we're 
> getting ping times of 1-2ms or so.  Next, we start a test as follows:
> 	- start continuous (not flood) pings from machine A to B
> 	- SCP a large file from A to B
> scp transfer rates start at a reasonable rate, about 300kB/s, and drop 
> to like 20kB/s and all of a sudden ping times run up to 500ms-1s.

Can you periodically run iwconfig and see what the rate it reports?  It
could be an issue with TX rate adaptation.  Just a thought.


> We change RTS thres to 32, and set the rate to 6M manually and the world 
> is a better place and ping times stay sub 10ms and the transfer rate 
> stays around 300kB/s.  It seems to be related to a combination of RTS 
> and the connection rate.
> We've also noticed that if we're running our UDP server (just sitting 
> there listening for messages on its own port) while we do this test, the 
> ping rate stays low even after the scp is finished until we kill our UDP 
> server.
> This only seems to occur when we use the libertas wifi.  Other 
> connections work fine.  Any chance this rings any bells for anyone? 
> This is proving to be a very weird problem to debug!
> Thanks,
> 	Dave
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