Landmark Routing for Large Ad Hoc Wireless Networks Globecom 2000 San Francisco, Nov 30, 2000

1. Landmark Routing for Large Ad Hoc Wireless NetworksGlobecom 2000San Francisco, Nov 30, 2000 Mario Gerla, Xiaoyan Hong and Gary Pei Computer Science Department University of California, Los Angeles http://www.cs.ucla.edu/NRL/wireless/

2. Single Hop (Cellular) Base Base Base Base Multihop (Ad Hoc) Ad Hoc vs Cellular Wireless Nets

3. Scalability in ad hoc wireless routing • Scalability to network size • Potentially, thousands of nodes (e.g., battlefield, sensor networks) • Scalability to mobility • mobility critical in battlefield and vehicular applications

4. Do Existing Routing Protocols Scale? • Proactive routing: • Distance Vector based: DBF, DSDV, WIRP • Link State Main limitations: routing table O/H; control traffic O/H • On-demand, reactive routing: • AODV, TORA, DSR, ABR etc Main limitations: search-flood O/H with high mobility and many short lived flows

5. Distance Vector 0 Routing table at node 5 : 1 3 2 4 Tables grow linearly with # nodes Control O/H grows with mobility and size 5

6. 1 Link State Routing • At node 5, based on the link state packet, topology table is constructed: • Dijkstra’s Algorithm can then be used for the shortest path 0 {1} {0,2,3} {1,4} 3 2 {1,4,5} 4 {2,3,5} 5 {2,4}

7. query(0) reply(0) query(0) reply(0) query(0) query(0) query(0) query(0) reply(0) query(0) On-demand Routing Advantages: • on-demand request & reply eliminates periodic update O/H (channel O/H) • routing table size is reduced (it includes only routes in use) (storage O/H) Limitations: • not scalable with traffic load • mobility may trigger frequent flood-searches 0 1 3 2 4 5

8. Hierarchical Routing • Traditional solution in large scale networks (eg, Internet): hierarchical routing • Unfortunately, hierarchical routing implementation problematic in ad hoc nets • In a mobile ad hoc network the hierarchical addresses must be continuously changed to reflect movements • Some ad hoc routing schemes recently proposed use an “implicit” hierarchy (eg, Fisheye, Zone routing, etc)

9. (2,3) (2,1) Level = 2 (1,2) HSR table at node 5 (1,3) DestID 1 6 7 (1,2) (1,4) (2,3) Path 5-1 5-1-6 5-7 5-1-6-(1,2) 5-7-(1,4) 5-7-(1,4)-(2,3) (1,1) Level = 1 (1,4) 2 8 9 6 3 1 Level = 0 10 11 7 5 4 Wireless Hierarchical Routing(addresses change with motion)

10. Implicit hierarchical routing: Fisheye State Routing 2 8 3 5 9 1 9 4 6 Hop=1 7 10 12 13 Hop=2 19 18 21 11 Hop>2 15 22 36 14 23 17 16 20 29 35 27 25 24 26 28 34 30 32 31

11. Fisheye Routing • In Fisheye routing, routing table entries for a given destination are updated (ie, exchanged with the neighbors) with progressively lower frequency as distance to destination increases • Property 1: the further away the destination, the less accurate the route • Property 2: as a packet approaches destination, the route becomes progressively more accurate • Major “scalability” benefit: control traffic O/H is manageable even for very large network size • Unsolved problems: route table size still grows linearly with network size; out of date routes to remote destinations

12. Update O/H Reduction in FSR (optional) LST HOP 0 LST HOP 0:{1} 1:{0,2,3} 2:{5,1,4} 3:{1,4} 4:{5,2,3} 5:{2,4} 1 0 1 1 2 2 0:{1} 1:{0,2,3} 2:{5,1,4} 3:{1,4} 4:{5,2,3} 5:{2,4} 2 1 2 0 1 2 1 3 LST HOP 2 0:{1} 1:{0,2,3} 2:{5,1,4} 3:{1,4} 4:{5,2,3} 5:{2,4} 2 2 1 1 0 1 4 5

13. Ad Hoc “Group” Hierarchical Solution: Landmark Routing • Main assumption: nodes move in groups • Three components in LANMAR: • (1) a “local ” proactive routing algorithm that keeps accurate routes from a source to all destinations within scope N (e.g., Fisheye alg truncated to scope N, Bellman Ford, DSDV, etc) • (2) a Landmark selection alg for each logical group • (3) a routing algorithm that maintains accurate routes to landmarks from all mobiles in the field

14. Landmark Logical Subnet • Logical subnet: group of nodes with functional affinity with each other (eg, they move together) • Node logical address = <subnet, host> • A Landmark is elected in each subnet Landmark Routing: the Concept • Every node keeps Fisheye Link State table/routes to neighbors up to hop distance N • Every node maintains routes to all Landmarks

15. Landmark Logical Subnet Landmark Routing (cont’d) • A packet to local destination is routed directly using Fisheye table based on MAC address • A packet to remote destination is routed to corresponding Landmark based on logical addr • Once the packet gets within Landmark scope, the direct route is found in Fisheye tables • Benefits: dramatic reduction of both routing overhead and table size; scalable to large networks

16. Landmark Routing: Dynamic Election • Dynamic landmark election a must in a mobile environment and in presence of enemy attacks • Node with largest number of group members in its scope proclaims itself Landmark for group; ties broken by lowest ID • “Oscillation” of landmark role is eliminated by hysteresis. • Multiple landmarks may coexist if group spans several “scopes” (they can be hierarchically organized)

17. Landmark Election (detail - may skip) • Landmark election algorithm: • No landmark exists initially, only FSR progresses. • A node proclaims itself as a landmark when it detects > T number of group members in its FSR scope. • An election is required to select the winner in the group. • Simple election winner algorithm • A node with the largest number of group members wins and the lowest ID breaks a tie. • Hysteresis election winner algorithm • The current election winner replaces the old landmark when its number of group members is larger than the old one by an extra fraction. • Or, the old landmark gives up the landmark role when its number of group members reduces to a value smaller than a threshold T.

18. Drifting nodes (detail - may skip) • Drifters are nodes outside of the scope of their landmark • Drifters periodically “register” with Landmark • Registration message creates reverse path from Landmark to drifter • A packet directed to a drifter must be first received by the Landmark and then forwarded to drifter • Routing table entries to drifters increase routing table OH; however, the extra O/H is low if drifter fraction is low

19. LM3 LM1 P O J K L D C I H LM4 LM2 B A Illustration by Example

20. Simulation Environment • GlomoSim platform • 100 nodes • 1000x1000 square meter simulation area • 150m radio range • UDP sessions between random node pairs • CBR traffic ( one 512 byte pkt every 2.5 sec) • # of logical groups = 4 • 2-level Fisheye with radius = 2 hops • IEEE 802.11 MAC layer; 2Mbps link rate • Reference Point Group Mobility model • random waypoint model is used for both individual and group component of the mobility vector

21. Throughput and Delay

22. Routing Load with and w/o Election

23. Conclusions • Accuracy of the route to Landmark nodes proves to be adequate • LANMAR exhibits good scalability with increasing communication pairs • LANMAR provides a dramatic reduction in routing table storage overhead with respect to FSR • Dynamic Landmark Election introduces only a moderate increase in routing O/H (with respect to fixed Landmark)

24. Work in Progress (optional) • Independent (instead of group) mobility • Very small groups (in the limit, all isolated nodes) • “Optimal” scope of local routing • Hierarchical Landmark organization • Membership change from one group to another • Landmarking in a heterogeneous structure: directive antennas, UAVs etc

25. The End Thank You ! www. cs.ucla.edu/NRL