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Date: Tue, 30 Aug 2005 12:17:01 -0500
From: Sam Pierson <samuel.pierson@gmail.com>
To: Sam Leffler <sam@errno.com>
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References: <d9204e4c050829120713734e3d@mail.gmail.com>
	<4313A2EC.5070300@errno.com>
Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org>
Subject: Re: Atheros driver and radiotap reliability
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On 8/29/05, Sam Leffler <sam@errno.com> wrote:
> Sam Pierson wrote:
> >I had some correspondence with the ethereal developers and David Young
> > and apparently there is a bug in how ethereal handles the radiotap head=
er.
>=20
> News to me; the last time I checked it looked correct.

I'm not sure.  David told me this:
FYI, ethereal's radiotap dissector was broken the last time I checked. :-(
It does not obey the alignment rules for radiotap fields: the radiotap
producer (usually, the kernel) inserts zeroes to ensure natural
alignment of all multi-byte fields.  Ethereal does not account for this.
The tcpdump sources get this right.

> The radiotap header includes the rssi returned by the hardware for rx'd
> frames.
>                          sc->sc_rx_th.wr_antsignal =3D ds->ds_rxstat.rs_r=
ssi;

I get (slightly) different values for the RSSI displayed in ethereal (if it=
's=20
correctly being displayed, still looking) than the SS displayed in dB by=20
tcpdump.  Is the SSI displayed by ethereal the sc->sc_rx_th.wr_antsignal
being passed through? =20
=20
> Nothing is recorded for tx frames.  You can typically treat it as being
> in .5dBm units relative to the current noise floor. =20

*it*, referring to the rssi value above?

Thanks for the help,

Sam