Q18Mobile Computing

A MANET is a chaotic, self-configuring mathematical web of mobile routers (nodes) connected by fragile, temporary wireless links. Because there is absolutely zero fixed infrastructure (no cell towers), every single smartphone or laptop must violently act as a router for the entire network. Standard internet protocols (OSPF, BGP) fail catastrophically here due to extreme topology churn. MANET protocols are strictly divided into Proactive and Reactive architectures.

DSDV is a Proactive (Table-Driven) protocol. It mathematically forces every single node to maintain a complete routing table containing the exact distance to every other node in the entire network.

• The Mechanism: Nodes violently broadcast their routing tables to their neighbors periodically (e.g., every 15 seconds) or whenever a link state changes.
• The Innovation (Sequence Numbers): It modifies the classic Bellman-Ford algorithm by appending a strict Destination Sequence Number. Nodes only accept routing updates if the sequence number is newer. This mathematical genius completely annihilates the catastrophic "Count-to-Infinity" routing loop problem.
• The Demerit: In a highly mobile network of 10,000 nodes, 99% of the calculated routes will never be used. The constant violent broadcasting of routing tables completely saturates the wireless bandwidth and drains the battery of every device to zero, even if no actual user data is being transmitted.

AODV completely abandons proactive tables. It is Reactive (On-Demand). It mathematically calculates a route strictly ONLY when a node explicitly demands to send data.

• The Mechanism: When Node A wants to send data to D, it blasts a Route Request (RREQ) flood. When D replies with a Route Reply (RREP), intermediate nodes mathematically lock the route into their local tables.
• The Merit: It violently conserves bandwidth and battery power because it generates zero routing overhead when the network is idle.
• The Demerit: High latency for the very first packet. The application must mathematically wait for the RREQ/RREP flood to resolve before transmitting.

DSR is also Reactive, but its mathematical architecture is completely different from AODV. It utilizes Strict Source Routing.

• The Mechanism: During the RREQ flood, every intermediate node violently appends its own IP address to the packet header. When the RREQ reaches the destination, the packet mathematically contains the entire, absolute hop-by-hop path (e.g., A -> B -> C -> D).
• The Execution: The Destination sends this entire path back to the Source. The Source then violently injects this complete mathematical path into the header of every single data packet it sends. Intermediate nodes do not need routing tables; they simply blindly follow the list in the header.
• The Demerit: As the network scales, the path list in the packet header becomes massive, mathematically consuming 20% of the payload bandwidth just for routing overhead.