are exchanged in a global control plane on a dedicated channel or dedicated time
slot [ 4 ].
(b) Route Selection
Route selection is where WMNs are distinguished from the other wireless
multi-hop networks. It is considered the most important component in WMN
routing. Depending on how the route is selected, this will affect how the protocol
and the network as a whole will satisfy the performance requirements and QoS
As the WMN has its own objectives such as satisfying a reasonable level of
QoS and load balancing, many unique routing selection metrics are introduced for
use in WMNs. They are mostly related to link quality, interference (both intra-flow
and inter-flow), reliability, and other criteria that are indicators of the path quality
and suitability for providing satisfactory QoS.
In Table 3.1 , we illustrate the common route selection metrics introduced and
used by the WMN routing protocols available in the literature [ 4 , 53 ].
The most common technique for measuring metric parameters is sending probe
packets. Probe packets can be sent either in a unicast or broadcast mode. Gener-
ating and sending probe packets can be done either actively, passively, or in a
cooperative approach. In ''active'' probing, special probe control packets are
generated and exchanged for this purpose. In ''passive'' probing, data packets can
be utilized for the probing purposes too, so no extra overhead is needed. In
''cooperative'' probing, a node overhears data packets transmitted by its neighbors
to estimate the link quality to each neighbor. Active probing is considered the most
common measurement technique [ 57 ].
(c) Route Representation and Data Forwarding
Some protocols are based on exact route representation and others utilize some
route guidance for data forwarding.
(1) Exact Route
- As the LQSR protocol is a variant of the DSR protocol, it makes use of the
source routing approach.
- The Multipath Mesh (MMESH) protocol [ 58 ] is based also on the source
routing approach as well as allowing the source to have multiple paths for
(2) Route Guidance
- The Extremely Opportunistic Routing (ExOR) protocol [ 59 ] follows the self-
routing approach so does not have an explicit routing path before data
transmission starts. In ExOR data packets are buffered and broadcast in bat-
ches. Among the nodes that receive this batch, only one node will be selected
to forward it and this is what is known as the opportunistic routing.