This document discusses Ad-hoc On-Demand Distance Vector (AODV) routing protocol. AODV is a reactive routing protocol for mobile ad hoc networks that establishes routes on demand. It uses route discovery and route maintenance through broadcast of route request (RREQ), route reply (RREP) and route error (RERR) messages. AODV is efficient for networks with changing topologies but has higher latency for route discovery and lacks efficient route maintenance compared to proactive protocols.

1. Poulami Pal.

2.  Formed by wireless hosts which may be
mobile
 Without (necessarily) using a pre-existing
infrastructure
 Routes between nodes may potentially
contain multiple hops

3.  Ease of deployment
 Speed of deployment
 Decreased dependence on infrastructure

4.  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

5. Ad-hoc Mobile Routing Protocols
Table Driven Protocols On Demand Protocols
Hybrid
Protocols
ABR, DSR, AODV,
DSDV, TORA
WRP
ZRP

6.  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

7.  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.

8.  The basic message set consists of:
◦ RREQ – Route request
◦ RREP – Route reply
◦ RERR – Route error
◦ HELLO – For link status monitoring

9.  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.

10. A
B?
B?
B?
B?
B?
B? B?
B

11.  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).

12. A
A
A
A
B

13. 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.

14.  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.

15. Source
G
A RREQ RREQ
RREQ
RREP RREQ
B D RREQ
RREP
RREQ
RREQ RREP
F Destination
C RREQ
RREQ
E

16.  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.

17.  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.

18.  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.

19.  AODV route discovery latency is high
 AODV lacks an efficient route maintenance
technique
 AODV lacks support for high throughput
routing metrics