# Impact of Direction Parameter in Performance of Modified AODV in VANET
## 2 AODV and Modified AODV Routing Algorithms
An AODV has three main phases of operation [15]:  
1. _Route discovery_ is initiated when a source node needs to communicate with another neighbor node. Each node keeps two counters: broadcast_id and node_sequence_number and (so that individual nodes can be recognized and the duplication of packets can be avoided) an RREQ. When the source node issues an RREQ, the broadcast_id is incremented. Each neighbor satisfies the RREQ by either sending back an RREP or rebroadcasting the RREQ after increasing the hop count in its neighborhood. 2. _Route maintenance_ does not have any impact on the route to the destination. It reinitiates the route discovery process when the source node moves. When the destination nodes or intermediate nodes move, an RREP is sent to the affected nodes. Periodic Hello messages or link-layer acknowledgments (LLACKS) (far less latency) can be used to determine node movements. If a node is not reachable, the special RREP is sent back toward the source, containing a new sequence number and hop count. 3. _Route message generation_ use a local connectivity to maintain a list of active nodes within its neighbors in one of two ways. First, if a node obtains a broadcast message from a nearby node, it updates its routing table, containing connectivity information. Second, when a neighbor does not send any packets within the Hello interval, it broadcasts a Hello message that includes its identity and its DSN. An AODV has a routing table management system where information about neighbor nodes is updated periodically. Information about short-lived routes is also stored in the routing table, such as the routes created to store reverse paths towards nodes originating RREQs temporarily. The route entry table in the AODV [15] includes the following information on its neighbor:  
* Destination sequence number
* Destination IP address
* Valid destination flag
* Next hop
* Hop count
* State and routing flags (e.g., repairable, being repaired, valid, and invalid)
* List of precursors
* Network interface
* Lifetime (i.e., deletion or expiration time of the route)  
In AODV, there is no special security to prevent attacks at high latency because the route discovery is reactive and requires more time. This results in high packet loss. Since it does not allow the handling of unidirectional links, a single route request packet may result in multiple route reply packets, leading to huge routing overhead. Periodic beaconing (to determine the active/alive state of a node) leads to unnecessary bandwidth consumption, which leads to low throughput. The high mobility of the vehicles may also cause more link breakage, which increases the delay in transferring the data packets. To maintain QoS and to overcome a flooding problem, low overhead is required when replying to a single route request. Moreover, the periodic beaconing time can be optimized depending on the size and number of nodes (cars) of the network. The route discovery phase can be modified to work more effectively with less time delay. The AODV routing protocols can be modified to give priority to a node to handle unidirectional links. Due to the highly dynamic nature of the network, the routing table can be modified and filtered to give priority to nodes based on the location information of each node.