From: Simon Wunderlich <sw@simonwunderlich.de>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: linux-wireless@vger.kernel.org, Eliad Peller <eliad@wizery.com>,
        mathias.kretschmer@fit.fraunhofer.de
Subject: Re: [PATCH] mac80211: allow scans on radar channels, unless there is CAC or CSA
Date: Thu, 20 Sep 2018 12:27:05 +0200
Message-ID: <2969898.mUHQksrBSp@prime> (sfid-20180920_122711_665008_BF9608CC)
In-Reply-To: <1537435276.3874.14.camel@sipsolutions.net>
References: <20180918141633.10282-1-sw@simonwunderlich.de> <1537435276.3874.14.camel@sipsolutions.net>
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On Thursday, September 20, 2018 11:21:16 AM CEST Johannes Berg wrote:
> On Tue, 2018-09-18 at 16:16 +0200, Simon Wunderlich wrote:
> > Operating on a DFS channel doesn't mean we can't leave it for a short
> > time - actually, some features like off-channel CAC work by leaving the
> > operation channel to check other channels for availability (although
> > off-channel CAC isn't implemented in mac80211). In our case, we want to
> > use mesh while doing background surveys on other channels from time to
> > time.
> 
> Actually ... as far as I can tell it *does* mean that, at least
> currently for FCC.


Mhm. I remember you said that before. But I can't find references for it. I 
checked the FCC 15.407 document [1] but couldn't find anything in favor or 
against that. Same for the measurement procedures [2]. I also couldn't find 
off-channel CAC in FCC, which I used for my argument in ETSI:

In ETSI 301 893 [3] they talk about non-continuous checks for off-channel CAC 
(in 4.2.6.2.3, second paragraph) and continuous period for CAC (4.2.6.2.2.2, 
first paragraph). Continuity is not mentioned for in-service monitoring 
(4.2.6.2.4), but off-channel CAC could only work when continuity is not 
required.

I'd appreciate if you (or someone else) can point me to where it's stated that 
we can't leave the channel for the a short time. I'm assuming that we are back 
fast enough to ensure the required detection probability.

Cheers,
     Simon

[1] https://www.law.cornell.edu/definitions/index.php?
width=840&height=800&iframe=true&def_id=41106ee4d951847389e55571a5e5e8aa&term_occur=1&term_src=Title:
47:Chapter:I:Subchapter:A:Part:15:Subpart:E:15.407
[2] https://apps.fcc.gov/kdb/GetAttachment.html?id=V2DzGgztnfxjTcht59nQ7Q%3D
%3D&desc=905462%20D02%20UNII%20DFS%20Compliance%20Procedures%20New%20Rules
%20v02&tracking_number=27155
[3] https://www.etsi.org/deliver/etsi_en/301800_301899/301893/02.01.01_60/
en_301893v020101p.pdf
> 
> johannes


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