[PATCH 2/2] hostapd: Add DFS CAC and radar detection

Simon Wunderlich simon.wunderlich at s2003.tu-chemnitz.de
Thu Sep 19 07:51:37 EDT 2013


Hey Janusz,

On Tue, Sep 17, 2013 at 08:44:37PM +0200, Janusz Dziedzic wrote:
> On 17 September 2013 18:25, Simon Wunderlich
> <simon.wunderlich at s2003.tu-chemnitz.de> wrote:
> > Hey Janusz,
> >
> > On Mon, Sep 16, 2013 at 07:40:07AM +0200, Janusz Dziedzic wrote:
> >> Add DFS CAC handling, radar detection.
> >> By default after radar detected or
> >> channel became unavailable random channel
> >> will be choose.
> >>
> >> Signed-hostap: Simon Wunderlich <siwu at hrz.tu-chemnitz.de>
> >> Signed-hostap: Janusz Dziedzic <janusz.dziedzic at tieto.com>
> >
> > Thanks a lot for the rewrite - looks good to me and works well here, so
> > feel free to add:
> >
> > Tested-by: Simon Wunderlich <siwu at hrz.tu-chemnitz.de>
> >
> Thanks for review and tests.
> 
> > Also the patch looks good in general. This series is still missing the
> > dfs channel list patch which is in another patch Jouni has still backed
> > up [1] (doesn't apply currently, but it's trivial to fix). Would be good
> > to merge this as well.
> >
> > Just one remark: What do we do if all channels are taken? Your current
> > implementation will then simply close hostapd, but I'm not sure if this
> > is desired behaviour - shouldn't we rather keep it running and wait for one
> > channel to come back (when the Non-occupancy-period is over) and try again?
> >
> I think we should never hit this case. Base of spec I changed getting
> new channel little bit.
> Currently we get random channel from list of:
> -  "standard" 5G channels (!disabled) - defined by regdomain
> -  DFS usable + availabe channels.
> 
> Even all DFS channels will be unavailable we should get still
> "standard" channels list I think.

If we want to use 5 GHz outdoors we may only use outdoor channels. These must be
limited e.g. by using the DFS channel option in the pending patch[1]. Jumping back
to a non-DFS channel is not an option for outdoors, at least in Europe all outdoor
channels require DFS. So it might happen that all channels become unavailable for
some time.

In this case, your current implementation will just stop the hostapd (I've tested
after applying the channel list patch [1]), and while this is one option to handle
it, I feel that's not the best ... :)

> 
> >
> > [1] http://w1.fi/p/dfs/0002-hostapd-Add-config-option-for-DFS-channels.patch

Cheers,
	Simon
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