Routing protocol DSDV uses proactive “table driven”
routing, while AODV and DSR use reactive “on-demand”
routing. Protocol DSDV periodically updates its routing
tables, even in cases when network topology doesn’t
change. AODV protocol has inefficient route
maintenance, because it has to initiate a route discovery
process every time network topology changes. Both
protocols, AODV and DSR, use route discovery process,
but with different routing mechanisms. In particular,
AODV uses routing tables, one route per destination, and
destination sequence numbers as a mechanism for
determining freshness of routes and route loops
prevention. On the other hand, DSR uses source routing
and route caching, and doesn’t depend on any periodic or
time-based operations.
Generally, we can conclude that in low mobility and
low load scenarios, all three protocols react in a similar
way, while with mobility or load increasing DSR
outperforms AODV and DSDV routing protocols. Poor
performances of DSR routing protocol, when mobility or
load are increased, are the consequence of aggressive use
of caching and lack of any mechanism to expire stale
routes or determine the freshness of routes when multiple
choices are available.
However, there are many other challenges to be faced in
routing protocols design. A central challenge is the
development of the dynamic routing protocol that can
efficiently find routes between two communication nodes.
Also, in order to analyze and improve existing or new
MANET routing protocols, it is desirable to examine other
metrics like power consumption, fault tolerance, number
of hops, jitter, etc. in various mobility and traffic models.