Ad-hoc On-Demand Distance Vector Routing (AODV) and simulation in network simulator

1. Ad-hoc On-Demand Distance Vector Routing (AODV) and simulation in network simulator

2. Content • Introduction to ad-hoc networks • AODV : Concept • AODV : Mechanism • Simulation in Network Simulator • Conclusions

3. Introduction to ad-hoc networks • Network of mobile wireless nodes • No infrastructure (e.g., base stations, fixed routers, centralized servers) • Dynamic topology • Routing infrastructure created dynamically at intermediate node • Data can be relayed by intermediate nodes • Limited battery power and transmission range resources in the nodes • Usage: • Military environments, emergency and rescue operations, meeting rooms, etc

4. AODV : Concept • Reactive routing • Pure on-demand route acquisition system • The routes are created when needed, so called “on-demand” • A broadcast route discovery mechanism • RREQ (Route Request packet) broadcasting to find a route • RREP (Route Reply packet) is used to set up forward path • Dynamic establishment of route table entries • Nodes lie on active paths only maintain routing information • Destination sequence number • Prevention of routing loops • Avoidance of old and broken routes • Maintenance of timer-based states • A routing table entry is expired if not used recently

5. AODV : Mechanism • Path discovery Every node maintains two separate counters • Sequence number • Broadcast-id (increments whenever the suorce issues a new RREQ) • The source requests using RREQ broadcasting • <source_addr, source_sequence#, broadcast_id, dest_addr, dest_sequence#, hop_cnt> • Destination number of RREQ is the last known number to the source • The destination replies using RREP (Route Reply) unicasting • <source_addr, dest_addr, dest_sequence#, hop_cnt, lifetime> • The sequence number is first incremented if it is equal to the number in the request • RREP contains the current sequence number, hop count = 0, full lifetime • Intermediate nodes • Discard duplicate requests • Replies if it has an active route with higher destination sequence number • Otherwise broadcasts the request on all interfaces

6. AODV : Mechanism • Path discovery • Intermediate nodes • Setup reverse path • A node records the address of the neighbor who send RREQ • Keep track of some information • Destination IP address, Source Ip address, Broadcast_id, Expiration time for reverse path route entry, Source node’s sequence number • Setup forward path • Unicast RREP (Route reply) back to the reverse path • Each node along the path sets up a forward pointer to the node from which the RREP came • Update its routing table entry • Propagate the first RREP or the RREP if contains a greater destination sequence# or the same sequence# with a smaller hop count then contained in RREQ • Nodes that are not along the path determined by the RREP will timeout and will delete the reverse pointers

7. Example A L Y • <S, 11, 1, D, 0, 1> F J B K D P G S C E H I T Z RREQ

8. Example A L Y F J B K D P G S C E H I T Z Reverse Path Setup

9. Example A L Y F J B K D P G S C E H I T Z

10. Example A L Y F J B K D P G S C E H I T Z

11. Example A L Y F J B K D P G S C E H I T Z RREP

12. Example A L Y F J B K D P G S C E H I T Z Forward path setup

13. Example A L Y F J B K D P G S C E H I T Z

14. Example A L Y F J B K D P G S C E H I T Z

15. Example A L Y F J B K D P G S C E H I T Z

16. Route table management • Soft-state associated with the entry (useful information stored in route table management): • Route request expiration time (purpose of this timer is to erase reverse path routing entries from those nodes that do not lie on the path) • Route caching timeout (or the time after which the route is considered to be invalid) • Active route timeout (this information is maintained so that all active source nodes can be notified when a link breaks) • A neighbor is considered active if it originates or relays at least one packet to the destination

17. Path maintenance • Neighboring nodes with active routes periodically exchange hello messages • If a next hop link in the routing table fails, the active neighbors are informed • The RERR (unsolicited RREP) indicates the unreachable destinations • <source_addr, dest_addr, current sequence# + 1, infinity, lifetime> • The source performs a new route request when it receives a RERR

18. Simulation in network simulator • Now we are going to start simulation in Network Simulator • This example contains 30 nodes which are moving and use AODV routing protocol

19. Conclusion • AODV -- efficient algorithm for ad-hoc networks • Need for broadcast is minimized • Quick response to link breakage in active routes • Loop free routes

20. THE END