Ad-hoc Mobile Routing ProtocolsTable Driven Protocols On Demand Protocols Hybrid Protocols ABR, DSR, AODV, DSDV, TORA WRP ZRP
Table Driven Routing Protocol ◦ Send periodic updates of the routes. ◦ Each node uses routing information to store the location information of other nodes in the network. On Demand Routing Protocols ◦ Establish routes only when required to route data packets. ◦ Route discovery process ◦ Have longer transmission delays
AODV is a packet routing protocol designed for use in mobile ad hoc networks (MANET) Intended for networks that may contain thousands of nodes One of a class of demand-driven protocols Each node maintains a routing table that contains information about reaching destination nodes.
The basic message set consists of: ◦ RREQ – Route request ◦ RREP – Route reply ◦ RERR – Route error ◦ HELLO – For link status monitoring
RREQ Messages ◦ A RREQ message is broadcasted when a node needs to discover a route to a destination. ◦ The RREQ also contains the most recent sequence number for the destination. ◦ A valid destination route must have a sequence number at least as great as that contained in the RREQ.
RREP Messages ◦ When a RREQ reaches a destination node, the destination route is made available by unicasting a RREP back to the source route. ◦ A node generates a RREP if: It is itself the destination. It has an active route to the destination. ◦ As the RREP propagates back to the source node, intermediate nodes update their routing tables (in the direction of the destination node).
Route Error Message: RERR are used mainly when nodes get moved around and connections are lost. If a node receives a RERR, it deletes all routes associated with the new error. Error messages are sent when a route becomes invalid, or if it cannot communicate with one of its neighbors.
HELLO Message:These are simple messages that nodes send at certain time intervals to all its neighbors to let them know that it is still there. If a node stops receiving hello messages from one of its neighbors, it knows that any routes through that node no longer exist.
Source G A RREQ RREQ RREQ RREP RREQ B D RREQ RREP RREQ RREQ RREP F Destination C RREQ RREQ E
There are two phases ◦ Route Discovery. ◦ Route Maintenance. Each node maintains a routing table with knowledge about the network. AODV deals with route table management. Route information maintained even for short lived routes – reverse pointers.
Broadcast RREQ messages. Intermediate nodes update their routing table Forward the RREQ if it is not the destination. Maintain back-pointer to the originator. Destination generates RREP message. RREP sent back to source using the reverse pointer set up by the intermediate nodes. RREP reaches source, communication starts.
Hello messages broadcast by active nodes periodically HELLO_INTERVAL. No hello message from a neighbor in DELETE_PERIOD,link failure identified. A local route repair to that next hop initiated. After a timeout ,error propagated both to originator and destination. Entries based on the node invalidated.
AODV route discovery latency is high AODV lacks an efficient route maintenance technique AODV lacks support for high throughput routing metrics