location-based routing protocols. Unlike the other types of networks where posi-
tion and velocity information require adding special components to the nodes,
most vehicles already have these components built-in. In addition, with the
availability of the on-board unit that can have access to navigation software and
road maps, these sources of information can help routing protocols to make better
informed decisions regarding the optimum paths.
All these distinguishing challenges and features should be considered in
designing a routing protocol for VANETs to be as efficient as possible and to meet
the requirements and needs of the vehicular environment; the most important
design considerations are handling the highly dynamic topology and intermittent
connectivity to maintain connectivity among vehicles.
As shown in the discussion in this section, each network paradigm has certain
design considerations that distinguish its routing requirements from the other
paradigms and impose designing a distinctive set of routing protocols to meet such
requirements and performance goals.
3.3 Classification and Directions
In this section, we discuss the popular classifications of the routing protocols for
each network paradigm.
Mobile Ad-Hoc Networks
The most popular classification of routing protocols in MANETs is the classifi-
cation according to how the route is discovered. For discovering a route or path,
the routing protocol can follow the proactive, reactive or hybrid techniques, as
shown in Fig. 3.1 .
Wireless Sensor Networks
As hierarchical and position-based routing schemes are common in WSNs to
enhance scalability and improve energy efficiency, it is preferable to classify
routing protocols according to network structure as illustrated in Fig. 3.2 . The
routing protocols can be classified as position-based or topology-based protocols.
• Topology-Based Routing
Topology-based routing depends on the use of information about the links and
edges connecting the nodes in establishing routes. It can be further classified into
flat and hierarchical routing.
- Flat Routing: In flat networks, all nodes are in the same level and they all play
the same role and collaborate together to perform the sensing task [ 2 ].