Foundational
Principles of the AODV Routing Protocol in Mobile Ad-Hoc Networks
Dr.
Devendra Singh Chauhan*
Assistant
Professor, Computer Science, Tata College, Jamodi Khurd, Sidhi, Madhya Pradesh,
India
devendra.chauhan2005@gmail.com
Abstract: Mobile ad hoc networks (MANETs) depend on broadcast
mechanisms, such as probabilistic flooding, for route discovery, wherein source
nodes disseminate route request (RREQ) packets indiscriminately to all adjacent
nodes. This unregulated strategy induces superfluous retransmissions, thereby
exacerbating packet collisions, medium access contention, and the broadcast
storm problem, which in turn amplifies protocol overhead, routing burden, and energy
expenditure. Consequently, sophisticated flooding mitigation algorithms are
imperative.
The Ad hoc On-Demand Distance Vector (AODV)
protocol, a reactive routing paradigm, counters these inefficiencies by
establishing routes solely upon demand. It encompasses two principal phases:
route discovery, which utilizes controlled flooding to ascertain shortest paths
from source to destination, and route maintenance, involving link failure
detection and localized repair via route error (RERR) messages. By eschewing
proactive route upkeep, AODV substantially curtails signaling overhead, thereby
optimizing performance in highly dynamic MANET topologies.
Keywords: AODV, MANETs, RERR,
Broadcast Storm.
INTRODUCTION
The Ad hoc On-Demand Distance Vector (AODV) routing protocol represents a reactive framework optimized for mobile ad hoc networks (MANETs), establishing routes dynamically upon request to eliminate continuous topology broadcasts and minimize signaling overhead. Operating without centralized coordination, AODV exploits multi-hop relaying across mobile nodes with ephemeral topologies. Core operations include route discovery—triggered by the source broadcasting Route Request (RREQ) packets through bounded flooding to neighbors, culminating in the destination's unicast Route Reply (RREP) along the reverse path to forge the shortest hop-count route—and route maintenance, facilitated by Route Error (RERR) messages that disseminate link failure alerts, prompting fresh discoveries. RREQ dissemination inherently provokes the broadcast storm dilemma, characterized by redundant retransmissions, medium contention, and packet collisions that intensify overhead and power consumption; AODV mitigates this partially via sequence numbers to avert loops and suppress duplicates, with various extensions seeking further flooding suppression. This demand-driven approach ideally suits resource-constrained MANETs, balancing rapid path formation with attenuation of storm-related degradations.
REVIEW
OF LITERATURE
The
Ad-hoc On-Demand Distance Vector (AODV) protocol, formalized in RFC 3561
(2003), constitutes a reactive routing mechanism tailored for Mobile Ad-hoc
Networks (MANETs). It facilitates on-demand route acquisition in
infrastructure-less environments characterized by nodal mobility and
topological flux, thereby curtailing control overhead.
Operational Fundamentals
AODV
leverages route request (RREQ) broadcasts to initiate path discovery, followed
by unicast route reply (RREP) transmissions to confirm bidirectional routes.
Route error (RERR) notifications handle link failures, while destination
sequence numbers preclude loops by favoring elevated sequence values alongside
minimal hop metrics. Flooding is mitigated through expanding ring techniques
employing time-to-live (TTL) thresholds, augmented by periodic Hello messages
for neighborhood sensing and localized repair protocols for fault recovery.
These features accommodate unidirectional connectivity and subnet routing,
enhancing scalability.
Extensions and Empirical Insights
Scholarly
analyses affirm AODV's preeminence among reactive protocols, attributable to
diminished broadcast frequency and inherent loop prevention. Comprehensive
literature surveys reveal that enhancements predominantly target route
discovery (57% of investigations), selection (20%), and upkeep, incorporating
quality-of-service (QoS) provisions, energy conservation, and overhead
mitigation via machine learning/artificial intelligence integrations and
signal-strength heuristics. Persistent limitations encompass broadcast storm
amplification and power dissipation, prompting innovations such as AODV with
improvements (AODVI).
METHODOLOGY
AODV: A Reactive Routing Protocol for MANETs
Ad-hoc On-Demand Distance Vector (AODV) constitutes a reactive routing protocol tailored for dynamic Mobile Ad-hoc Networks (MANETs). Unlike proactive counterparts, AODV initiates route discovery solely upon demand, thereby curtailing control overhead. It integrates distance-vector principles with destination sequence numbers to avert routing loops, guarantee route recency, and mitigate pathologies such as the "counting-to-infinity" problem. Nodes sustain routing tables exclusively for active routes, facilitating rapid adaptation to topology perturbations induced by nodal mobility.
Route
Discovery Mechanism
Route establishment commences with the source node broadcasting a Route Request (RREQ) packet, encapsulating its sequence number and hop count. Intermediate nodes propagate the RREQ while caching reverse routes in their tables. Upon receipt by the destination or an intermediate node possessing a valid route, a Route Reply (RREP) is unicast back along the reverse path, thereby instantiating the forward route.
Route
Maintenance Procedures
Link failures prompt upstream nodes via Route Error (RERR) messages, initiating route rediscovery. Optional Hello packets enable neighbor discovery. Inactive routes undergo expiration, while sequence numbers embedded in control packets ensure selection of the most current, loop-free paths.
RESULTS AND DISCUSSION
Route Request Mechanism (RREQ)
AODV employs three primary broadcast control messages: Route Request (RREQ), Route Reply (RREP), and Route Error (RERR). These packets are retained with associated status metadata, as they are disseminated via broadcast rather than direct unicast to the destination.
The RREQ packet encapsulates the following fields:
· Source identifier (Ni), broadcast identifier, and destination identifier (Nj).
·
Source sequence number 
and destination sequence number 
).
· Time-to-live (TTL) value and routing table entry for the destination.
Sequence
numbers ensure route freshness through targeted increments:
· Prior to initiating new route discovery: sq(Ni)←sq(Ni)+1.
· Prior to transmitting RREP: sq(Ni)←max(sq(Ni), sq(Nj)) for i,j=1,…,m.
The
destination node increments sq(Nj) upon
receipt from a distinct source 
adopting the updated value, or when no valid
route exists.
Routing Table Entries and Neighbour Lists
Routing tables undergo updates under the following conditions:
· Establishment or modification of routes.
· Reception of control packets.
Sequence
number revisions adhere to:
· If incoming sq(Ni)′>sq(Ni), then sq(Ni)←sq(Ni)′.
·
If sq(Ni)′=sq(Ni) but
hop count is reduced: 
,
where 
.
·
If sequence number is
unknown: 
.
Tables maintain active routes alongside precursor lists (intermediate nodes) to facilitate error propagation.
Route Request Propagation and Maintenance
RREQ
dissemination occurs via broadcast for invalid or unknown routes. The
destination replicates the most recent sequence number and applies an increment
RREQ
identifiers increment sequentially: If 
Route maintenance leverages periodic "Hello" packets for neighbor discovery. Link failures trigger RERR dissemination and subsequent rediscovery.
Flooding in AODV and Optimization Strategies
AODV relies on blind flooding for route discovery: the source broadcasts RREQ to one-hop neighbors, which rebroadcast iteratively until the destination responds via RREP (along the reverse path) or RERR (route unavailable). This induces substantial control overhead, elevated energy consumption, and network congestion.
Mitigation
techniques encompass:
· EAODV: Mobility-aware RREQ broadcasting.
· Directional flooding: Reduced RREQ propagation volume.
· Density-based forwarding: Alleviated MAC-layer contention and power demands.
· Cluster-based approaches: Adaptive topology management with low-latency path establishment.
CONCLUSION
This Paper substantiates the selection of AODV as the baseline protocol, emphasizing its on-demand route discovery efficiency, while rigorously evaluating the ramifications of blind flooding on control overhead, energy expenditure, MAC-layer contention, and routing performance. Subsequent chapters delineate enhancements via AODV-EXT and AODV-EXT-BP protocols.
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