DSDV VS AODV
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DSDV is a proactive routing protocol that uses periodic routing table exchanges and sequence numbers to avoid loops. AODV is a reactive protocol based on DSDV that uses on-demand route discovery with broadcast RREQ and unicast RREP messages to find routes, and maintains routing tables at nodes instead of in packet headers like DSR. Both protocols aim to quickly adapt to dynamic links with low overhead.
DSDV VS AODV
- 1. DSDV & AODV 2/27/06
- 2. Last class • Basic classification of ad hoc routing – Proactive – Reactive, on-demand – Geographical routing – Hierarchical routing – … • DSR: dynamic source routing – Reactive protocol – Route discovery phase + maintenance phase. – Packet contains the path information.
- 3. This class • DSDV: Destination-Sequenced Distance- Vector – Proactive • AODV: Ad hoc on-demand distance vector routing – Reactive – Based on DSDV
- 4. Distance vector routing • Routing protocol in wired networks. • Distributed Bellman-Ford algorithm. – Each node maintains a hop count for each destination. – Nodes periodically send their routing tables to neighbors. – Nodes re-calculate shortest path upon the receipt of a routing table update. • Proactive protocol. • Shortest path routing.
- 5. Distance vector routing • Routing protocol in wired networks. – Continuously update the “reachability” information at all the network nodes – Low route request latency and high overhead • Problems in dynamic environment – Changes propagate slowly, slow convergence – Create loops – Count to infinity
- 6. Convergence of distance vector
- 7. Convergence of distance vector
- 8. Distance vector, count to infty
- 9. DSDV • DSDV: Destination-Sequenced Distance- Vector • Adds two things to distance-vector routing – Sequence number; avoid loops – Damping; hold advertisements for changes of short duration.
- 10. Sequence number Dest Nexthop Metric DestSequence InstallTime MN1 MN2 2 406 MN2 MN2 1 128 MN3 MN2 2 564 MN4 MN4 0 710 MN5 MN6 2 392 MN6 MN6 1 076 MN7 MN6 2 128 MN8 MN6 3 050
- 11. DSDV routing updates • Each node periodically transmits updates – Includes its own sequences number, routing table updates • Nodes also send routing table updates for important link changes • When two routes to a destination received from two different neighbors – Choose the one with greatest destination sequence number – If equal, choose the smaller metric (hop count)
- 12. DSDV full dump • Full Dumps – Carry all routing table information – Transmitted relatively infrequently • Incremental updates – Carry only information changed since last full dump – Fits within one network protocol data unit – If can’t, send full dump
- 13. DSDV link addition • When A joins network – Node A transmits routing table: <A, 101, 0> – Node B receives transmission, inserts <A, 101, A, 1> – Node B propagates new route to neighbors <A, 101, 1> – Neighbors update their routing tables: <A, 101, B, 2> and continue propagation of information
- 14. DSDV link breaks • Link between B and D breaks – Node B notices break • Update hop count for D and E to be infinity • Increments sequence number for D and E – Node B sends updates with new route information • <D, 203, infinite> • <E, 156, infinite>
- 15. DSDV routing updates • Each node periodically transmits updates – Includes its own sequences number, routing table updates • Nodes also send routing table updates for important link changes • When two routes to a destination received from two different neighbors – Choose the one with greatest destination sequence number – If equal, choose the smaller metric (hop count)
- 16. DSDV summary • Routes maintained through periodic and event triggered routing table exchanges • Incremental dumps and settling time used to reduce control overhead • Lower route request latency, but higher overhead • Perform best in network with low to moderate mobility, few nodes and many data sessions • Problems: – Not efficient for large ad-hoc networks – Nodes need to maintain a complete list of routes.
- 17. DSDV, DSR • DSDV performs well under low node mobility – High delivery rate – Fails to converge for increased mobility • DSR performs well at all mobility rates – Increased overhead of routing tables and control packets – Scalability for dense networks
- 18. AODV • DSR includes source routes in packet headers • Resulting large headers can degrade performance – When data content is small • AODV improves on DSR by maintaining routing tables (reverse paths) at nodes, instead of in data packets. • AODV retains the desirable feature of DSR that routes are only maintained between communicating nodes.
- 19. AODV • The Ad-hoc On-Demand Distance Vector Algorithm • Descendant of DSDV • Reactive • Route discovery cycle used for route finding • Maintenance of active routing • Sequence number used for loop prevention and route freshness criteria • Provides unicast and multicast communication
- 20. Goal of AODV • Quick adaptation under dynamic link conditions • Lower transmission latency • Consume less network bandwidth (less broadcast) • Loop-free property • Scalable to large network
- 21. AODV – unicast route discovery • RREQ (route request) is broadcast – Sequence Number: • Source SN: freshness on reverse route to source • Destination SN: freshness on route to destination – RREQ message • <bcast_id, dest_ip, dest_seqno, src_seqno, hop_count> • RREP (route reply) is unicast back – From destination if necessary – From intermediate node if that node has a recent route
- 22. AODV multicast route discovery • Message types – RREQ, with new flags: • Join and Repair – RREP – MACT (Multicast activation message) • Multicast routes have destination sequence number and multiple next hops – Multicast group leader extension for RREQ and RREP
- 23. AODV route discovery 1. Node S needs a route to D 2. Create a route request (RREQ) – Enters D’s IP address, sequence number, S’s IP address, sequence number – Broadcasts RREQ to neighbors
- 24. AODV route discovery, cont. 3. Node A receives RREQ – Makes reverse route entry for S • Dest = S, nexthop = S, hopcount = 1 – It has no route to D, so it broadcasts RREQ 4. Node C receives RREQ – Makes reverse route entry for S • Dest = S, nexthop = A, hopcount = 2 – It has route to D && seq# for route D > seq# in RREQ • Creates a route reply (RREP) – Enters D’s IP address, sequence number, S’s IP address, hopcount • Unicasts RREP to A
- 25. AODV route discovery, cont. 5. Node A receives RREP – Unicasts RREP to S – Makes forward route entry to D • Dest = D, nexthop = C hopcount = 2 6. Node S receives RREP – Makes forward route entry to D • Dest = D, nexthop = A hopcount = 3 – Sends data packets on route to D
- 26. AODV --- route maintenance (1) • Link between C and D breaks – Node C invalidates route to D in routing table – Node C creates route error (RERR) message • Lists all destinations with are now unreachable • Sends to upstream neighbors – Node A receives RERR • Checks whether C is its next hop on route to D • Deletes route to D, and forwards RERR to S
- 27. AODV --- route maintenance (2) – Node S receives RERR • Checks whether A is its next hop on route to D • Deletes route to D • Rediscovers route if still needed
- 28. AODV --- Optimizations • Expanding ring search – Prevents flooding of network during route discovery – Control Time to Live of RREQ • Local repair – Repair breaks in active routes locally instead of notifying source – Use small TTL because destination probably has not moved far – If first repair attempt is unsuccessful, send RERR to source
- 29. AODV --- Summary • Reactive / On-demand • Sequence numbers used for route freshness and loop prevention • Route discovery cycle • Maintains only active routes • Optimization can be used to reduce overhead and increase scalability