Atheros driver and radiotap reliability

[Sam Pierson]

On 8/30/05, Sam Leffler <sam at errno.com> wrote:
> David appears to be talking about how netbsd works.  Understand that
> David does not work on FreeBSD; I'm not even sure he uses it.
...
> tcpdump and ethereal get the same data.  If they display it differently
> given identical data then one is wrong.  If you have an example of where
> things are wrong please present it.
I tried and it looks like everything is being displayed correctly and that
tcpdump and ethereal are displaying the same values.  The only reason
I said they looked different is that in the morning when I examined a
few hundred frames with ethereal, the values were consistently 10dB 
lower than what I had observed through tcpdump.  I'm very glad that
they are displaying the same values now though.

> > *it*, referring to the rssi value above?
> 
> "it" = ds->ds_rxstat.rs_rssi which is the value returned by the hardware.

Alright, it makes much more sense now.  You said earlier that we can use
the RSSI value and correspond each unit to ~.5dBm above the noise
floor.  I didn't see anything being passed through the hardware which
records the noise on that same per packet basis, but I can get ahold
of the average noise floor for the environment.  Will this affect the 
accuracy of the measurements to the point where they will be 
significantly skewed?  

(Thanks for the help, again, it seems like there isn't a lot of information
out there regarding these topics)

-Sam