An AODV Tutorial

AODV协议概述

import from : http://www.soe.ucsc.edu/~ravindra/aodv.html

Last modified: Wed Apr 24 06:17:41 PDT 2002

An On-Demand Unicast routing protocol for Ad-Hoc Networks i.e. routing information maintained only for active nodes

Active nodes : Those nodes for which I am the origin or relay of traffic

Each node maintains a routing table with entries for each active destination

Each entry of the routing table has six fields

1. Destination
2. Next-Hop
3. Destination Sequence Number
4. Route Timeout
5. List of Neighbours who need me as next hop to destination (Along with last time they sent data)
6. Hop Count

RREQ's are broadcast to everybody

Each RREQ contains broadcast-id, src, dest, src-seq-no, dest-seq-no, hop count(incremented as RREQ is propagated)

Broadcast id is incremented for every new RREQ originating from the source

{src, broadcast-id} uniquely identifies a RREQ

An intermediate node may may respond to RREQ if it holds a route to the destination which has a seq-no equal to or greater than that specified in the RREQ

Among two RREP one with greater dest-seq-no is chosen. If they are equal then one with lower hop-count is chosen

As RREQ propagates its sets up a backward route with a timeout equal to rreq-expiration. This should be enough for a RREP to be received

Every time a packet is sent on a route, route timeout = current time + active route timeout

The neighbour which forwarded the packet also has its timer set to the same value (Active neighbours whose timer expires are no longer active neighbours)

Nodes periodically broadcast hello packets to tell neighbours that they are alive

If a next hop to a destination is dead then a RREP is sent to all neighbours who use me as a next hop. dest-seq number is incremented and hop count is set to infinity in the RREP

If an upstream node wants it may re-establish a route by sending a new RREQ with a higher destination-seq-number