AODV Routing Protocol: On-Demand Route Discovery Algorithm for Mobile Ad Hoc Networks

The AODV (Ad hoc On-Demand Distance Vector) routing protocol is a widely-used reactive routing algorithm for Mobile Ad hoc Networks (MANETs) that minimizes control overhead through its on-demand route discovery mechanism. Unlike table-driven protocols, AODV establishes routes only when required by source nodes, making it highly scalable for dynamic wireless environments. In code implementation, the protocol operates through two main processes: Route Discovery and Route Maintenance. When a source node needs to transmit data to an unknown destination, it initiates route discovery by broadcasting an RREQ (Route Request) packet containing source/destination IP addresses, sequence numbers, and hop count. Neighboring nodes receiving the RREQ implement a forwarding algorithm that checks their route caches - if no fresh route exists, they rebroadcast the packet while recording a reverse path to the source. The destination node or intermediate nodes with valid routes respond with unicast RREP (Route Reply) packets that traverse backward along the established reverse paths. Key functions in implementation include: - Sequence number management to ensure loop freedom - Route timeout mechanisms for stale route expiration - Hello messages for neighbor connectivity monitoring AODV efficiently handles network dynamics through route error (RERR) packets that propagate when link breaks are detected, triggering local route repairs or new route discoveries. The protocol's algorithmic design incorporates: - Bidirectional route verification - Hop-count-based metric for path selection - Expanding ring search for controlled flooding These features make AODV particularly suitable for resource-constrained mobile environments where bandwidth efficiency and adaptability to topology changes are critical requirements.