MANET stands for Mobile Ad-Hoc Network. It is an infrastructure-less collection of mobile nodes that can arbitrarily change their geographic locations such that these networks have dynamic topologies which are composed of bandwidth-constrained wireless links.
MANET nodes are supplied with wireless transmitters and receivers. At a given time based on the nodes positions and their transmitter and receiver coverage designs and transmission power levels, wireless connectivity in the structure of a random, multi-hop graph or ad-hoc web exists between the nodes. The current applications of MANETs are in defense services, emergency search, and rescue services, meetings, and conventions, and other scenarios where quick sharing of information is acquired without any fixed infrastructure available.
There are common unpredictable topological changes in these networks, which creates the task of discovering and maintaining routes as tough. Conventional routing protocols depend on distance-vector or link-state algorithms cannot be used here, because the amount of routing associated traffic would waste a huge space of the wireless bandwidth, and such discovered routes would soon become obsolete because of the mobility of nodes.
AODV stands for Ad hoc On-Demand Distance Vector routing and is a type of reactive protocol. Its procedure is hop-to-hop routing. The node creates the Route Request (RREQ) if it requires understanding the route to a specific destination. Therefore the intermediate nodes forward the route request and thus simultaneously, these intermediate nodes generate a reverse route to the destination.
When the node gets the request that has the route to the destination, it creates a Route Reply (RREP) which contains a number of hops that are needed to appear at the destination. Each node that assists in sending this response to the source node makes a forward route to the destination.
There are three types of AODV routing messages which are as follows −
When a node requires to share a packet, and it doesn’t understand the route to the destination, it starts route discovery, by sharing an RREQ multicast message. The neighbouring nodes data where the message came from and forwards it to their neighbours until the message is received to the destination node.
The destination node responds with an RREP, which gets back to the source in the reverse direction along which the RREQ appears. Forward routes start in the intermediate nodes as the RREP carries back to the source. An intermediate node can also share an RREP in reply to a received RREQ if it understands the route to the destination, thus nodes can join in a current route.
The RERR message denotes the destination which is inaccessible. Nodes taking the message produce the route inactive (and usually the route is eliminated). The next packet to be sent triggers route finding.