10-06-2017, 06:45 AM
Ad hoc On-Demand Distance Vector (AODV)
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Ad hoc On-Demand Distance Vector (AODV) Routing is a routing protocol for mobile ad hoc networks (MANETs) and other wireless ad-hoc networks. It is a reactive routing protocol, meaning that it establishes a route to a destination only on demand.
AODV routing protocol is a reactive. AODV is based on-demand routing scheme which states that it (nodes) discovers a path only when the need arises. AODV requires host node to maintain only active routes. An active route is used to forward at least one packet within the past time out period. It is free from loops, by using the concept of sequence numbers to ensure that chosen route is always fresh enough for routing.
In AODV, each node maintains a routing table which contain one route entry for each destination that the node is communicating with. It has two phases: Route Discovery and Route maintenance.
Route Discovery: when the host node needs to send a packet to destination and doesn t contain an active route to the destination node in its routing table. It broadcast a route request (RREQ) packet to its neighbors. During the process of forwarding the RREQ packet, all the intermediate nodes record, in their routing tables, the address of neighbor from which the first copy of the broadcast is received, thereby establishing the reverse path. When the RREQ reaches the destination or an intermediate node with fresh enough route, the destination/intermediate nodes responds by unicasting a route reply (RREP) packet back to the neighbor from which it first received the RREQ .
The second phase for AODV is the route maintenance, where routes are maintained in the following manner: if a source node moves, it is able to reinitiate the route discovery process to find a new route to the destination node. Also if a node along a route moves, its upstream neighbors notice the move and propagates a ink failure notification or route error message (RERR) to each of its active neighbors so that they can update their routing table.
Working mechanism:
In AODV, the network is silent until a connection is needed. At that point the network node that needs a connection broadcasts a request for connection. Other AODV nodes forward this message, and record the node that they heard it from, creating an explosion of temporary routes back to the needy node. When a node receives such a message and already has a route to the desired node, it sends a message backwards through a temporary route to the requesting node. The needy node then begins using the route that has the least number of hops through other nodes. Unused entries in the routing tables are recycled after a time.