ABSTRACT
Vehicle ad hoc network (VANET) is the most important part of Intelligent Transport System[1]. In VANET, rapid movement leads to network topology change frequently. A high-reliability and high-performance routing protocol is required. Many routing protocols are used in VANET[2]. One of the most eective routing protocols is AODV[3]. AODV works on demand when the node wants to send packets. There are two phases of AODV: route discovery phase, route maintenance phase. When the node wants to send packets and there is no route to destination, route discovery phase works. The source node sends a broadcast routing packet called Route Request Packet (RREQ) to all of the neighbors. If the RREQ receiver node is the destination node or if the node has the route to the destination node, it sends a unicast packet called the Route Reply (RREP) to the RREQ sender. If the node that receives a RREQ does not have the route to the destination then it forwards the RREQ to all of its neighbors. The node receives RREP forward the RREP to the source. The route maintenance phase works when a route is established. Each node sends HELLO packet to its neighbors to keep alive. When a node detects not receiving a HELLO in a long time that means its link was broken, the node unicasts a Route Error (RERR) to the source node. Simulation of existing MANET routing protocols
(AODV, DSDV, DSR, TORA) shows that AODV is the best one[4]. However, there are two disadvantages of AODV in VANET. First, each node rebroadcasts the rout request packets (RREQ). This will reduce the network throughput. Second, the algorithm does not consider the stability of a link. When a node moves with high speed, the route failure happens frequently.
