Problems with Ad-Hoc Mode

Dave Kroetsch dave at
Wed Feb 18 09:49:27 EST 2009

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.

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 

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!


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