Landmark Routing for Large Ad Hoc Wireless Networks Globecom 2000 San Francisco, Nov 30, 2000 Mario Gerla, Xiaoyan Hong and Gary Pei Computer Science Department University of California, Los Angeles /

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

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

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

Distance Vector Routing table at node 5 : Tables grow linearly with # nodes Control O/H grows with mobility and size

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 {1} {0,2,3} {1,4} {2,4} {2,3,5} {1,4,5}

query(0) reply(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

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)

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

Implicit hierarchical routing: Fisheye State Routing Hop=1 Hop=2 Hop>2 13

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

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

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

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

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 networksLandmark Logical Subnet

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)

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.

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

Illustration by Example A B C D H I J KL O P LM1 LM2 LM3 LM4

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 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

Throughput and Delay

Routing Load with and w/o Election

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)

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

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