Re: [PATCH 0/7] extend mac80211 mesh DFS and CSA functionality

[Simon Wunderlich <sw@simonwunderlich.de>]

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On Tuesday, May 16, 2017 1:55:46 PM CEST Bastian Bittorf wrote:
> * Simon Wunderlich <sw@simonwunderlich.de> [16.05.2017 12:24]:
> >  * station A detects a Radar, and informs userspace
> >  * userspace of station A will initiate a CSA, kernel will execute it
> >  (action> 
> > frame, beacons)
> > 
> >  * station B picks up the CSA, and executes it as well
> >  * station B also marks the channel as unavailable
> >  * both station A and station B will send an event to userspace once the
> > 
> > channel switch is complete
> 
> ah, I remember the slides from last battlemesh.
> 
> The "problems" in userspace are: we must maintain a global list
> (so each node) which channel is the next best and we must time
> the final channel switch. IMHO the specs are saying, that we must
> switch within 30 secs after detecting the first radar-pattern.
> Also we must mark/show the new channel somehow for new/crashed/upcoming
> nodes. quite hard...

The timing is not a big problem, since the switch does not happen immediately 
but is performed after a "countdown" which is part of the channel switch 
announcement IEs. The specific rules for the countdown depend on the regulatory 
domain, but it's usually something between 1 and 5 seconds where payload traffic 
must not be transmitted (at least for the DFS case).

The bigger problem appears when a node is missing the CSA for whatever reason, 
or is joining the network - worst case, the mesh network can split into clouds 
on different channels. This is where we need the global list, or showing the 
next channel, etc. :)

Cheers,
     Simon

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