  In this paper we consider a Wireless Mesh Network (WMN) integrating SDN
principles. The Wireless Mesh Routers (WMR) are OpenFlow capable switches that
can be controlled by SDN controllers, according to the wmSDN (wireless mesh
SDN) architecture that we have introduced in a previous work. We consider the
issue of controller selection in a scenario with intermittent connectivity. We
assume that over time a single WMN can become split in two or more partitions
and that separate partitions can merge into a larger one. We assume that a set
of SDN controllers can potentially take control of the WMRs. At a given time
only one controller should be the master of a WMR and it should be the most
appropriate one according to some metric. We argue that the state of the art
solutions for "master election" among distributed controllers are not suitable
in a mesh networking environment, as they could easily be affected by
inconsistencies. We envisage a "master selection" approach which is under the
control of each WMR, and guarantees that at a given time only one controller
will be master of a WMR. We designed a specific master selection procedure
which is very simple in terms of the control logic to be executed in the WMR.
We have implemented the proposed solution and deployed it over a network
emulator (CORE) and over the combination of two physical wireless testbeds
(NITOS and wiLab.t).
