Ad hoc On-Demand Distance Vector Routing

The Ad-hoc On-demand Distance Vector Routing algorithm ( AODV ) is an algorithm for routing data through a mobile ad hoc network. The protocol is one of the topology- based, reactive routing method, that is, routes to specific destinations are determined only if necessary.

Operation

Each network node maintains its own monotonically increasing sequence number, so the loop-free routing is guaranteed. In each node route information is maintained in a route list. To this end, each node remembers the IP address of the next node toward the destination ( next hop ). Further, inter alia, the sequence number of the destination node, the distance to the destination node ( number of hops ), different state flags are recorded in an entry.

A AODV operation depends on certain network messages to distribute data through the network. The algorithm defines its different types of messages: Route Request ( RREQ ), Route Replies ( RREP ) and Route Errors ( RERR ).

As long as the endpoints of a communication connection have valid routes to each other, AODV does not matter. If a route is needed to a new destination, the source node sends a request message ( RREQ ) per broadcast. A route is determined when the RREQ reaches either the destination or an intermediate node with a route is that is " fresh enough ". A route is " fresh enough " if the route entry is valid and the registered destination sequence number is at least as large as the destination sequence number in the request message. This route is by reply message ( RREP ) unicast sent back to the origin of the RREQ. To this end, each node having received and forwarded the request stored the node from which it received the RREQ message.

Nodes monitor the connection status of neighbor nodes in active routes. When a disconnection is detected, an error message ( RERR ) is sent to notify the link breakage. This message indicates the nodes that are no longer reachable by the broken connection. This notification mechanism is provided by lists of " active neighbors " ( nodes that have received a packet for forwarding to the target within a period ) in the route entries.