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