JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV ADHOC AND SENSOR NETWORKS Previous Question Paper (September - 2020 - R16)

DSDV (Destination-Sequenced Distance-Vector) and AODV (Ad hoc On-Demand Distance Vector) represent two fundamental approaches to routing in Mobile Ad hoc Networks (MANETs). DSDV is a proactive (table-driven) protocol, while AODV is a reactive (on-demand) protocol.

DSDV (Proactive):

• Maintains routing tables at all times for all possible destinations, ensuring low latency for route discovery.
• Uses sequence numbers to distinguish stale routes from new ones, preventing routing loops.
• Periodic updates are broadcast throughout the network, which consumes significant bandwidth and battery power, especially in highly dynamic networks.
• Scalability is limited due to the overhead of maintaining global topology information.

AODV (Reactive):

• Routes are discovered only when a source node needs to send data to a destination, reducing control traffic overhead during idle periods.
• Employs a route discovery process using Route Request (RREQ) and Route Reply (RREP) packets.
• Maintains active routes using periodic 'Hello' messages for local connectivity sensing.
• More scalable than DSDV in large, sparse networks, though it suffers from higher initial latency during the route discovery phase.

In summary, DSDV is suitable for networks with low mobility and predictable traffic patterns where immediate route availability is critical. Conversely, AODV is preferred for dynamic environments where bandwidth conservation and scalability are prioritized over instantaneous route availability.

Area-based broadcasting schemes are a class of routing protocols used in mobile ad hoc networks (MANETs) to reduce the broadcast storm problem by using location information to determine whether a node should rebroadcast a received packet. Unlike simple flooding, where every node rebroadcasts every packet, area-based schemes utilize the geographical position of the sender and the receiver to limit redundant transmissions.

The fundamental principle is that a node will only rebroadcast a packet if it determines that doing so will significantly increase the coverage area of the broadcast. If a node receives a packet from a neighbor and calculates that its own transmission would not cover a substantial new area, it suppresses the rebroadcast to save bandwidth and reduce packet collisions.

Common techniques within area-based broadcasting include:

• Distance-based scheme: A node calculates the distance between itself and the sender. If the distance is less than a predefined threshold, the node assumes its neighbors are already covered by the original transmission and drops the packet.
• Location-based (or Grid-based) scheme: The network area is divided into logical grids. A node rebroadcasts only if it is the first to receive the packet in its specific grid cell, ensuring that each grid area is covered exactly once.
• Area-based (or Coverage-based) scheme: A node estimates the additional coverage area it would provide by rebroadcasting. It compares this potential additional area against a threshold; if the additional coverage is below the threshold, the rebroadcast is suppressed.

These schemes rely on nodes having access to their own coordinates, typically via GPS or localization algorithms. By restricting rebroadcasts based on physical area, these protocols effectively mitigate network congestion, reduce energy consumption, and decrease the probability of contention and collisions in dense network environments.