JNTU B.Tech IV AD-HOC AND SENSOR NETWORKS Previous Question Paper (February/March - 2022 - R18)

Proactive (table-driven) routing protocols maintain up-to-date routing information by periodically exchanging routing tables. Advantages: Low latency for route discovery as routes are pre-computed, making them suitable for real-time traffic. Disadvantages: High overhead due to constant control traffic, which consumes significant bandwidth and battery power, and scalability issues in large or dynamic networks.

Reactive (on-demand) routing protocols establish routes only when a source node needs to send data. Advantages: Reduced overhead during periods of network inactivity and better scalability as they do not maintain global routing tables. Disadvantages: High initial latency for route discovery (route acquisition delay) and potential congestion during the flooding of route request packets.

The Zone Routing Protocol (ZRP) is a hybrid algorithm that combines the benefits of proactive and reactive approaches by dividing the network into local zones.

1. Intra-zone Routing Protocol (IARP): Within a node's defined routing zone (nodes within a specific hop count, 'd'), routing is proactive. This ensures immediate availability of routes to nearby neighbors.
2. Inter-zone Routing Protocol (IERP): For destinations outside the routing zone, ZRP uses a reactive approach. When a source needs to send data to a node beyond its zone, it initiates a route discovery process using bordercasting.
3. Bordercasting: Instead of flooding the entire network, IERP sends route requests only to peripheral nodes (border nodes) of the current zone. This limits the broadcast traffic to the edges of the zones.
4. Route Maintenance: If a link failure occurs within the zone, IARP updates the local topology. If a destination becomes unreachable via the reactive path, IERP triggers a new discovery process.

By limiting proactive updates to a local radius and using reactive discovery for long-distance communication, ZRP balances the low latency of proactive protocols with the bandwidth efficiency of reactive protocols.