Wireless Network Design: Optimization Models and Solution ...

9 Routing in Mobile Ad Hoc Networks 201
to allow communication over multiple “hops” between nodes not directly within
wireless transmission range of one another.
However, this characteristic is not sufficient to ensure network connectivity. Furthermore,
packets must be directed through the network. In other words, a path
has to be determined from the source to its destination. This is so-called routing.
A simple way to perform routing would be to enter static routes by integrating a
fixed routing table in each node according to the topology. Obviously, as nodes in
a multi-hop ad hoc network move about or join/leave the network, and as wireless
transmission conditions such as sources of interference change, this technique is not
practical. Routing must result from a specific algorithm which calculates routes automatically
and dynamically, that is to say from a multi-hop wireless ad hoc network
routing protocol.
Before presenting the standardized routing protocols in Section 9.4, we remind the
reader that multi-hop ad hoc networks have the following characteristics:
• Dynamic topologies. Nodes, which are able to forward packets, can move arbitrarily.
This mobility results in the topology changing randomly and rapidly at
unpredictable times.
• Limited physical security. Attacks, such as denial-of-service or eavesdropping,
are often easier to launch in wireless networks than in wired ones. Ad hoc networks
at least have the advantage of being totally decentralized.
• Omnidirectional radio transmission. Since packets are broadcast to all neighboring
nodes, simultaneous data exchange between nodes close to each other is not
possible.
• Possible unidirectional links. Because of interference, fading, or limited transmission
range of some wireless network interfaces, links can be unidirectional.
• Constraints on bandwidth and energy. These resources are quite limited. The former
due to the intrinsic properties of radio interfaces and the effects of multiple
access, noise, etc.; the latter due to the characteristics of wireless mobile nodes
forming the multi-hop ad hoc network, which often rely on batteries.
Fig. 9.1 Ad hoc network example