[RFC 0/6] Using DFS channels in 802.11s mesh mode

Jouni Malinen j at w1.fi
Thu Dec 1 10:51:16 PST 2016

On Mon, Nov 28, 2016 at 04:38:37PM +0100, Benjamin Berg wrote:
> I have been working a bit on allowing channels which require DFS to be used
> for mesh mode. There are still a number of rough edges, but the following
> patches add very limitted DFS support.
> What currently works is that wpa_supplicant will start the CAC when required
> and will use the channel if it is available. In general it will also correctly
> switch the channel if radar is detected (during CAC or operation).

I'm a bit concerned about enabling channels requiring DFS for mesh based
only on the existing radar detection and DFS functionality that has been
certified in AP mode. While radar detection itself would hopefully work
fine, I'd want to get somewhat better understanding on potential
implication this could have or alternatively, use a new driver
capability advertisement for mesh-DFS that would be enabled explicitly
for drivers that have been tested in this combination.

How does the channel switch on radar detection during operation work
between the multiple devices? Will all STAs in the mesh BSS move to the
same channel? Who decides which channel to use? And will all the STAs
stop transmission immediately on radar detection and meet the FCC
requirements for total aggregate TX time after this for any following
frames needed for coordination to the channel change? That limit is
pretty small if it were to be interpreted as a total aggregate over all
STAs in the mesh..

Does something prevent a non-radar-detect-capable STA from joining an
already operating mesh on a DFS channel?

Jouni Malinen                                            PGP id EFC895FA

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