Proprietary info sent on air?

Francesco Sigona francesco.sigona at
Thu May 29 11:14:21 EDT 2003

> On Mon, May 26, 2003 at 12:23:02PM +0200, Francesco Sigona wrote:
> > Does anyone of you know if some kind of proprietary info is sent in
frames by a Prism2-based card?
> Prism2 firmware seems to reply to some signal quality related data frame
> (used by at least Lucent client utils). However, this is not related to
> the other part of your question.
> > My question arises by observation of the size of beacon frames, sent by
a card in master mode. By sniffing them via ethereal on a dedicated station,
I can see a size of 59 bytes. But if I check the behaviour of
RxMulticastOctests and the RxMulticastFrames counters in an associated
station, in a session where beacons are the olny frame sent, I can easily
compute the size (RxMulticastOctests / RxMulticastFrames ) and I get always
63 bytes.
> > What is this 4 bytes difference?
> > They are really sent on air, or are computed locally by the receving
> Not knowing your sniffer setup, I need to guess here.. I would assume
> that you used Prism2 card in monitor mode as the sniffer. It removes FCS
> (frame check sequence) from the received frames before passing them to
> the host system. FCS is four octets, so it explains the difference you
> see in the sizes. IEEE 802.11 uses FCS in all frames.

I think you're right.
I've checked the same difference of 4 octets in data frames also.
I didn't think to FCS field.
> -- 
> Jouni Malinen                                            PGP id EFC895FA
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