Monitoring mode gets frames from more than one channel!

Ajeet fromkth+hostap at fastmail.fm
Fri Feb 11 06:54:12 EST 2005


Jouni Malinen wrote:
> On Thu, Feb 10, 2005 at 07:19:52AM -0800, Ajeet Nankani wrote:
> 
> 
>>Even though i am monitoring on particular channel(channel 1), but i also
>>get frames(not all but most) from AP operating on other channel(channel
>>6).
>>Why is like that?
> 
> 
> That's the way IEEE 802.11b works.. Different channels are using
> different center frequencies, but they are overlapping and radios can
> receive frames from other channel, although with limited signal
> strength.
> 


But my APs are on channel 1 and 6, hence does not overlap AFAIK, so if i 
set a PC-card in monitor mode on channel 1 it should not pickup frames 
from channel 6...am i right here? Also there are not any other APs or 
STAs in vicinity operating on any channels.

> 
>>What to do to capture frames "only" on particular channel?
> 
> 
> That would be a bit difficult since you would need to have a receiver on
> all channels in order to find out which one is actually sending the
> frame (e.g., based on the signal strength).
> 


As i already said that i know that there are not any other APs in my 
area so i know which channels are actually sending.

The other use of dedicated monitoring on every channel is to analyze how 
the STA is scanning(active scanning), by receiving probe requests on 
every channel and analyzing the timings of those frames.

Any comments??

-ajeet.



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