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From: Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
To: Guy Harris <guy-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>,
	Felix Fietkau <nbd-p3rKhJxN3npAfugRpC6u6w@public.gmane.org>
Cc: "radiotap-sUITvd46vNxg9hUCZPvPmw@public.gmane.org"
	<radiotap-sUITvd46vNxg9hUCZPvPmw@public.gmane.org>
Subject: Re: multi-antenna handling
Date: Wed, 25 Jun 2014 09:04:49 +0200
Message-ID: <1403679889.4140.2.camel@jlt4.sipsolutions.net> (raw)
In-Reply-To: <C7AC152F-CCC4-48E7-B752-71655EFD0C58-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>

On Tue, 2014-06-24 at 18:53 -0700, Guy Harris wrote:

> > FWIW, I've now implemented this in Linux (in mac80211), although I start
> > a new radiotap namespace for each antenna, separate from the first one,
> > so you'll see
> > 
> > * any of: TSF, flags, rate, channel, MCS, a-mpdu, VHT, ...
> > (new radiotap namespace)
> > * ant signal: -40 dBm
> > * anntenna: 0
> > (new radiotap namespace)
> > * ant signal: -45 dBm
> > * anntenna: 1
> > ... for however many antennas/chains there are.
> 
> So is the idea that, in the first radiotap-namespace block, there will
> be no per-antenna information such as the antenna signal - the only
> per-antenna information will be in the subsequent namespace blocks?

Exactly. It would have seemed strange to include the per-antenna fields
in general since the other data isn't specific to an antenna. It also
shows nicer in wireshark this way :)

> Context: somebody asked on ask.wireshark.org about a capture from a
> D-Link router running OpenWRT; he claims that the router has 2
> antennas, but the capture has 3 antenna signal strength values, the
> first of which is in the first radiotap namespace:
> 
> 	http://ask.wireshark.org/questions/33994/why-there-are-3-rssi-values-in-the-radiotap-header-for-a-dual-antenna-wireless-card

That's a bit strange - might be a driver quirk. The code I wrote has to
rely on the driver, adding Felix who might know more, I don't know how
ath9k works in this regard.

johannes

  parent reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-20 16:50 Johannes Berg
     [not found] ` <1345481425.4459.46.camel-8upI4CBIZJIJvtFkdXX2HixXY32XiHfO@public.gmane.org>
2013-07-08  8:59   ` Johannes Berg
     [not found]     ` <1373273952.8312.7.camel-8Nb76shvtaUJvtFkdXX2HixXY32XiHfO@public.gmane.org>
2014-06-25  1:53       ` Guy Harris
     [not found]         ` <C7AC152F-CCC4-48E7-B752-71655EFD0C58-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
2014-06-25  7:04           ` Johannes Berg [this message]
     [not found]             ` <1403679889.4140.2.camel-8Nb76shvtaUJvtFkdXX2HixXY32XiHfO@public.gmane.org>
2014-06-25 13:09               ` Matteo Cypriani
     [not found]                 ` <20140625090901.fa121a689f823f3af1db1e3a-yxGd9NVxpOI@public.gmane.org>
2014-06-25 15:11                   ` Johannes Berg
     [not found]                     ` <1403709105.4140.13.camel-8Nb76shvtaUJvtFkdXX2HixXY32XiHfO@public.gmane.org>
2014-06-26  2:07                       ` Guy Harris
     [not found]                         ` <636CB894-79D9-4CC3-B820-833761A9666D-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
2014-06-26  6:20                           ` Johannes Berg
     [not found]                             ` <1403763600.4131.3.camel-8Nb76shvtaUJvtFkdXX2HixXY32XiHfO@public.gmane.org>
2014-06-26  8:24                               ` Felix Fietkau
2018-12-30 21:47                               ` "Overall" and per-chain signal/noise values (was Re: multi-antenna handling) Guy Harris
     [not found]                                 ` <0836AF8F-37B1-4E52-B14C-7D7B31D4C5E8-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
2019-01-15 13:19                                   ` Johannes Berg

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