route cache to verify the availability of a route and initiate a route request if
such route to the destination is not available in its route cache [ 50 ].
A route discovery consists of two processes; these are route
request and route reply. A route request (RREQ) message is broadcast over
the network to find all possible routes to destination. A route request header
contains source, destination, and the hops count it takes to reach the
destination as illustrated in Figure 2. 12. Each node receiving the packets
checks if it knows the route to the destination [ 6 2]. If it does have a record
from a route request sent recently it discards the request and forwards the
request along its links. However, if it does not have a record it stores to its
own address and forwards the request along the outing links. In receiving
the route request packet the destination node responds by sending a route
reply (RREP) packet to the source node that carries the route incorporated
in the route request packet [5 0 ]. A route being established is stored in the
route cache where the source node explicitly lists these routes in data
packets header. This scheme allows a multi-hop route to the destination.
Figure 2. 12 : DSR route discovery
Route maintenance is executed when the source receives a route
error message (RERR) generated from a node that has transmission
problems. When receiving an error packet, the node that generated the error
packet is removed from the route cache and in all the route cache
containing hops to this node. DSR advantages include source node
alternative route awareness. DSR is quick and easy to recovery from link
failures. There are also no chances of routing loops as they are easily
detected and avoided. DSR works efficiently in lower mobility networks,
but there are disadvantages as well, like a large route acquisition delay due