Wireless Network Design: Optimization Models and Solution ...

208 Khaldoun Al Agha and Steven Martin
Network) has enabled radio multi-hop communications on an extensive geographic
area. In Figure 9.4, the PRs represent nodes which are connected by radio links. All
PRs can communicate directly by radio (left side of the figure) or by using intermediate
PRs (right side). The later is called multi-hop communications. If, for example,
a communication must pass by three radio links, one speaks of three hops. The PR-
Net is the basis of ad hoc networks. The reader will find a complete description of
packet radio networks in [11].
PR
PR
PR
PR
Radio Link
Fig. 9.4 Examples of PR-network
PR PR
PR
MANET was created in 1995 in order to provide RFC to propose routing protocols
for ad hoc networks. At that time, only Hiperlan1 could provide information
forwarding in an ad hoc environment. However, Hiperlan1 was creating a layer 2
routing which was not compliant with other standards. The objective of MANET is
to adapt IP routing to work in ad hoc networks. We summarize four protocols which
belong to two different concepts: reactive and proactive.
9.4.2 Reactive Protocols
Reactive protocols offer routes for information flows only on demand. It means that
the protocol will react to find a route when a source node needs to send information
to a destination node. During the remaining time, the node is idle or active to participate
in the forwarding process to serve other source nodes. The reactive protocols
do not consume many resources when idle, however to discover a route (since they
don’t have any topology information), they flood requests among the network and
in this case consume a huge amount of the network resources. Examples of reactive
protocols are AODV [16] and DSR [10].
9.4.2.1 AODV (Ad hoc On Demand Distance Vector)
AODV today has many successes and is used in many systems. The Zigbee and the
Wi-Fi mesh networks use an adapted version of AODV. AODV belongs to the class
of distance vector routing protocols. In these protocols, to reach a destination, the
mobile node uses the next hop allowing the smallest distance in number of hops
between it and the destination. AODV is a reactive protocol; hence mobile nodes do
not retain any information for nodes not concerned by the active traffic information
PR
PR