communicate directly with each other if they are out of radio range [42]. Routing in ad hoc
networks has certain challenges for example; the nodes in the ad hoc network can move
around with any velocity or direction, this implies that the nodes can move out of and into the
range of different nodes. Therefore, the routing protocols in ad hoc network must be able to
be adapted to the dynamic changes in the topology of the wireless network. Some routing
protocols can keep up to date state information about the topology with periodic update
messages. Other routing protocols reduce or remove the state information kept in nodes.
The basic communication mechanism is the transmittal of data between a pair of hosts or
devices, one side sending, the other, receiving. This type of communication mechanism is
called point to point communication. A telephone call is an example of point to point link
between two phones. However, telephone calls are multiplexed into a company trunk; the
individual call is part of point to point session. End to end connection refers to a connection
between two systems or devices. For example, where the packets are transferred between two
routers represents point to point link. Therefore, the Internet connection can be considered of
multi point to point links. The other type of communication mechanisms is the point to
multipoint mechanism. At this kind of communication, one sender is sending the same
information to a set of receivers; these receivers have a common feature(s). For example, a
mainframe and its terminals that perform a specific application. The device that provides the
multipoint connection is usually an intelligent controller that manages the flow of
information from the multiple devices attached to it. One more type of communication
mechanisms is multipoint to multipoint, at this type of communication each device is a
sender and sending the information to all other devices connected. Each of theses devices can
be sender and receiver at the same time.
The routing paths between any pair of hosts can be symmetric or asymmetric. For a pair of
hosts A and B, if the path from A to B (forward direction) is different from the path from B
to A (reverse direction), we say that the pair of paths between A and B exhibit routing
asymmetry [33]. On the other hand if the forward path is the similar to the reverse path, we
say that the pair of paths is symmetric.