C. OpenFlow for Wireless Mesh Networks
OpenFlow could be very useful for wireless mesh network
(WMN) management. Today WMN is often used in community
networks or military applications for re-tasking from time to
time. For example, an Internet provider may re-program a
community mesh network to set up different IPTV services. A
military center may want to re-configure a wireless network to
Fig. 21.
OpenFlow for WMN management.
adapt to different surveillance scenarios. Existing mesh network
nodes are full fledged with all physical to application layer
functionalities. The network manager needs to setup each mesh
node individually since each node may have vendor-specific
programming features or proprietary device management pro-
files. Overall, today it is very difficult to perform rapid re-
tasking or policy changes in the heterogeneous mesh clients
(such as laptops, PDAs, phones, etc.) in a mesh network.
OpenFlow decouples network control and hardware commu-
nications completely, and leave only basic data forwarding
functions in each node, while the entire network can be eas-
ily re-programmed through a standard network OS (such as
NOX) running in a control panel. As long as different vendors’
products support OpenFlow’s flow table managements, a mesh
network can be easily re-tasked through a standard network
control script programming.
To make OpenFlow applicable to WMN, we need to over-
come a few challenges [20], [117]:
• Challenge 1: Fading channel: Unlike Stanford OpenFlow
testbed where fixed wired network is the backbone, WMN
has wireless channels everywhere (issues: radio fading,
hidden terminal problem, wireless broadcast nature, etc.).
• Challenge 2: Dynamic Topology: Due to WMN link
variations and nodes membership dynamics, the network
topology changes at a much higher pace than in wired
network. The OpenFlow needs to build a control plane to
perform autonomous topology discovery and swiftly react
on changes of the WMN topology.
• Challenge 3: In-band or out-band control: OpenFlow often
adopts out-of-band signaling, that is, the channel to NOX
is separate from the actually data forwarding network.
However, in WMN we may not have different RF channels
for separate control. On the other hand, using in-band
control would decrease data network throughout.
Fig. 21 shows the basic principle of using OpenFlow for
WMN control. The WMN has both mesh routers and mesh
clients. A radio channel control strategy is achieved by the
control panel for router-to-router, router-to-client, and client-to-
client communications. The control server in control plane can
perform mobility management, routing strategy, and channel
assignment.
In [20] an OpenFlow-enabled mesh routing scheme is pro-
posed. It has OpenFlow-enabled routers, clients and gateways.
Each node has multiple radio cards for multi-radio commu-
nications. The data path uses local sockets to talk with the
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IEEE COMMUNICATION SURVEYS & TUTORIALS, VOL. 16, NO. 4, FOURTH QUARTER 2014
control plane units. The control path communicates with NOX
via secure channel. Connection to Internet is achieved through
mesh gateways.
In [20] the in-band wireless communications are used be-
tween the controller and the switches. The high-quality chan-
nels are used for controller-to-server communications since
the controller’s commands cannot be lost even there is signal
fading.
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