Q14Mobile Computing

AODV is a highly aggressive, reactive routing protocol engineered specifically for Mobile Ad-hoc Networks (MANETs). In a MANET, nodes are constantly moving, causing physical links to violently snap. Proactive protocols (like DSDV) waste massive battery power continuously broadcasting routing tables. AODV strictly calculates a mathematical route ONLY when a node explicitly demands it.

When Node S wants to send data to Node D, but has no route:

• Node S violently broadcasts a Route Request (RREQ) packet to all immediate neighbors. This packet contains (Source_ID, Dest_ID, Dest_Seq_Num, Hop_Count).
• The neighbors mathematically check if they have a route. If not, they increment the Hop Count and rebroadcast the RREQ, creating a massive expanding flood.
• To prevent infinite broadcast storms, nodes strictly maintain a temporary reverse-path pointer to the node they received the RREQ from.
• When the RREQ hits Node D (or a node with a fresh route to D), it violently fires a Route Reply (RREP) packet backward along the exact reverse path, mathematically locking the route into the routing tables.

The absolute genius of AODV. Every node maintains a monotonically increasing Sequence Number. When comparing two routes to D, a node will strictly choose the route with the highest Sequence Number (freshest data). This mathematically guarantees absolute immunity against catastrophic routing loops (the Count-to-Infinity problem).

If an intermediate node detects that the next hop has physically driven out of range, it violently blasts a Route Error (RERR) packet back to the Source. The Source immediately deletes the broken mathematical path and initiates a new RREQ flood.