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Analysing AODV Protocol
Poulami Pal.
Formed by wireless hosts which may be mobile
Without (necessarily) using a pre-existing infrastructure
Routes between nodes may potentially contain multiple hops
Mobile Ad Hoc Networks
Ease of deployment
Speed of deployment
Decreased dependence on infrastructure
Why Ad Hoc Networks ?
Personal area networking◦ cell phone, laptop, ear phone, wrist watch
Military environments◦ soldiers, tanks, planes
Civilian environments◦ taxi cab network◦ meeting rooms
Emergency operations◦ search-and-rescue
Many Applications
◦ Ad-hoc Mobile Routing Protocols
Table Driven Protocols ◦ On Demand Protocols
Hybrid Protocols
◦ DSDV, WRP
ABR, DSR, AODV, TORA
ZRP
Adhoc Routing Protocol
Table Driven Routing Protocol◦ Send periodic updates of the routes. ◦ Each node uses routing information to store the location
information of other nodes in the network.
On Demand Routing Protocols◦ Establish routes only when required to route data
packets.◦ Route discovery process ◦ Have longer transmission delays
Table Driven & on demand routing Protocol
AODV is a packet routing protocol designed for use in mobile ad hoc networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols
Each node maintains a routing table that contains information about reaching destination nodes.
AODV Overview
The basic message set consists of:◦ RREQ – Route request◦ RREP – Route reply◦ RERR – Route error◦ HELLO – For link status monitoring
Overview (continued)
RREQ Messages
◦ A RREQ message is broadcasted when a node needs to discover a route to a destination.
◦ The RREQ also contains the most recent sequence number for the destination.
◦ A valid destination route must have a sequence number at least as great as that contained in the RREQ.
AODV Operation – Message Types
RREQ Message
B?
B? B
?B
?
B?
B?
B?
B
A
RREP Messages◦ When a RREQ reaches a destination node, the
destination route is made available by unicasting a RREP back to the source route.
◦ A node generates a RREP if: It is itself the destination. It has an active route to the destination.
◦ As the RREP propagates back to the source node, intermediate nodes update their routing tables (in the direction of the destination node).
AODV Operation – Message Types
RREP Message
B
A
A
A
A
A
A
A
Route Error Message: RERR are used mainly when nodes get
moved around and connections are lost. If a node receives a RERR, it deletes all routes associated with the new error. Error messages are sent when a route becomes invalid, or if it cannot communicate with one of its neighbors.
AODV Operation – Message Types
HELLO Message:These are simple messages that nodes send at certain time intervals to all its neighbors to let them know that it is still there. If a node stops receiving hello messages from one of its neighbors, it knows that any routes through that node no longer exist.
AODV Operation – Message Types
Message routing
A
B D
FC
G
E
RREQ
RREQ
RREQ
RREQ
RREQ
RREQRREQ
RREQ
RREQ
RREP
RREP
RREP
Source
Destination
There are two phases◦Route Discovery.◦Route Maintenance.
Each node maintains a routing table with knowledge about the network.
AODV deals with route table management. Route information maintained even for
short lived routes – reverse pointers.
AODV Routing
Broadcast RREQ messages. Intermediate nodes update their routing table Forward the RREQ if it is not the destination. Maintain back-pointer to the originator. Destination generates RREP message. RREP sent back to source using the reverse
pointer set up by the intermediate nodes. RREP reaches source, communication starts.
Discovery
Hello messages broadcast by active nodes periodically HELLO_INTERVAL.
No hello message from a neighbor in DELETE_PERIOD,link failure identified.
A local route repair to that next hop initiated. After a timeout ,error propagated both to originator and
destination. Entries based on the node invalidated.
Maintenance
AODV route discovery latency is high AODV lacks an efficient route maintenance
technique AODV lacks support for high throughput
routing metrics
Limitation of AODV protocol