1. Load Balanced Link Reversal Routing in Mobile Wireless Ad Hoc Networks Nabhendra Bisnik, Alhussein Abouzeid ECSE Department RPI Costas Busch CSCI Department RPI

2. Mobile Wireless Networks  Wireless nodes are mostly battery driven ) limited transmission range  Nodes act as relays  Often involves many-to-one communication  Multihop wireless mesh networks  Mobile sensor networks  Link reversal routing (LRR) is a good choice  Loop free routes  Low overhead  However LRR may lead to unbalanced distribution of load (traffic forwarded)

3. Contributions  Identify the causes of load unbalance in LRR  Propose three heuristic mechanisms that attack different causes of load unbalance  Evaluate the performance of the heuristics using simulations

4. Talk Outline  Link Reversal Routing  Causes of load unbalance  Load balancing problem  Heuristic mechanisms  Simulations

5. Talk Outline  Link Reversal Routing  Causes of load unbalance  Load balancing problem  Heuristic mechanisms  Simulations

6. Link Reversal Routing  Properties  Distributed  Loop free at every instant  Low overhead  Offers both proactive and reactive modes  Multiple routes to destination  Two phases  Route creation phase  Route maintenance phase

7. Route Creation Phase Destination Height = 0 0 1 2 2 3 4 5 11 1 1 1 1 QRY UPD 0 1 2 2 3 4 5 Directed Acyclic Graph (DAG)  Route creation phase assigns height to each node and transforms connected network into a DAG  a ! b exists in the DAG only iff h(a) > h(b)  Thus DAG is loop free  In general h(a) = [h 1 (a), h 0 (a) ] where h 1 (a) = height assigned by LRR and h 0 (a) = node id of a  Lexicographical ordering used

8. Route Maintenance Phase 0 1 2 2 3 4 5 0 1 2 2 3 4 5 0 3 2 2 3 4 5 0 3 6 4 3 4 5 0 7 6 4 7 4 5 0 7 6 8 7 8 5 Full Link Reversal Algorithm  Brings network from a bad state to a good state  Runs in  (n 2 ) time  Leads to increase in height of at least one node

9. Talk Outline  Link Reversal Routing  Causes of load unbalance  Load balancing problem  Heuristic mechanisms  Simulations

10. Causes of Load Unbalance  Traffic flows from higher height to lower height  Each time a node looses route to the destination, its height increases  The nodes with stable routes to destination tend to have lower height  Thus stable nodes relay large amount of traffic leading to  Battery exhaustion  Congestion

11. Load Unbalance - Example 0 7 6 8 7 8 5 0 7 6 8 7 8 5 Although alternate path is now available, most of the traffic is still routed through the node with height 5

12. Unbalanced Network State  If there exist routes to the destination in the undirected network graph whose use may lead to a more uniform spread of load, but the routes are absent in DAG  Characteristics of unbalanced network state  Selfish nodes (nodes with no incoming links)  High height gradients (h(a) – h(b) > 2 and a ! b exists in the DAG) C 0 B A D HE F I G J K 1 2 1 22 3 4 3 4 5 Selfish Node Isolated Routing Components L 6 High Height Gradient

13. Talk Outline  Link Reversal Routing  Causes of load unbalance  Load balancing problem  Heuristic mechanisms  Simulations

14. Load Balancing Problem  Two Components of the problem  Maintaining a good DAG (  )  Use good forwarding strategy over the DAG (S  )  Forwarding Strategy maps a link l of the DAG to traffic flowing over it, x S  (l)  Total traffic forwarded by a node where E  (i) is the set of outgoing links of node i  Load balance metrics  Balance Factor (BF)  Squared Sum (SS)

15. Load Balancing Problem  From optimization point of view, the load balance problem is to find and s.t.  This problem is NP-hard, distributed solution is even more difficult Or,

16. Talk Outline  Link Reversal Routing  Causes of load unbalance  Load balancing problem  Heuristic mechanisms  Simulations

17. Heuristic Mechanisms  Three heuristic mechanisms  Selfish Node Based Mechanism (SNBM)  Proactive Decrease in Height (PDH)  Reactive Increase in Height (RIH)  Height manipulation  Decrease height ) attract traffic  Increase height ) repel traffic

18. Selfish Node Based Mechanism  Aims to balance the size of isolated routing components  Periodically each node checks if it is selfish  If node selfish then  If h max – h min > 2 then  Sets height to minimum height that ensures path to the destination  Fix link directions  Update neighors

19. Selfish Node Based Mechanism C 0 B A D I E FJ H K L 2 7 1 2 2 3 4 3 6 8 G 5 0 C B A D I E FJ H K L 2 2 1 2 2 3 4 3 4 5 G 5 0 C B A D I E FJ H K L 2 7 1 2 2 3 4 3 6 5 G 5 C 0 B A D I E FJ H K L 2 2 1 2 2 3 4 3 4 3 G 5 0 C B A D I E FJ H K L 2 2 1 2 2 3 4 3 4 3 G 5

20.  However every instances of load unbalance does not involve selfish nodes  Example )  Solution – reduce height whenever it is possible in order to balance DAG  This observation leads to PDH C 0 B A D I E FJ H K L 2 1 2 2 3 4 3 6 8 G 5 M 9 7

21. Proactive Decrease in Height  Each node periodically compares its height with neighbors  If it is possible to decrease height without becoming a sink, then  Set height to minimum possible height that allows route to destination  Fix link directions  Update neighbors

22. Proactive Decrease in Height C 0 B A D I E FJ H K L 2 1 2 2 3 4 3 6 8 G 5 M 9 7 C 0 B A D I E FJ H K L 1 1 2 2 3 4 3 6 8 G 5 M 9 7 C 0 B A D I E FJ H K L 1 1 2 2 3 4 3 4 8 G 5 M 9 2 C 0 B A D I E FJ H K L 1 1 2 2 3 4 3 4 3 G 5 M 4 2

23. Reactive Increase in Height  Both SNBM and PDH are proactive in nature  RIH acts only when needed  Each node records the amount of traffic forwarded during an update window  If load served during an update window exceeds threshold then  Set height equal to h max + 1  Fix link directions  Update neighbors

24. Reactive Increase in Height 0 A B C D G F E 5 4 3 6 5 4 0 A B C D G F E 5 4 5 6 5 4 0 A B C D G F E 5 6 5 6 5 6 0 A B C D G F E 5 6 5 6 7 6 0 A B C D G F E 5 6 5 8 7 6

25. Forwarding Strategies  Load distribution is also affected by the forwarding strategies  Two forwarding strategies considered  Multi-path routing  Distribute load equally among all downstream links  Requires maintenance of forwarding records  Shortest path routing  Forward packets to downstream neighbor that lies on the shortest path available in the DAG  Requires no state information

26. Talk Outline  Link Reversal Routing  Causes of load unbalance  Load balancing problem  Heuristic mechanisms  Simulations

27. Simulation Setting  N mobile nodes, initially deployed randomly over 1000m £ 1000m area  Communication radius is m  Random waypoint mobility model used with v min = 2m/s, v max = 5m/s, pause time = 5s  Each node generates traffic at rate 1Kbps, destined to a sink node  Sink node located at (500m, 500m)  Models mobile wireless sensor network, multi-hop wireless mesh networks

28. Performance Metrics  Balance factor and squared sum for both multi-path and shortest path forwarding  Network lifetime  Routing updates

29. Balance Factor  PDH has highest balance factor  As number of nodes increases, path length increases leading to lower balance factor  Multi-path routing has larger balance factor Multi-path routingShortest path routing

30. Squared Sum Multi-path routing Shortest path routing  Again PDH has smaller squared sum  Multi-path routing leads to longer routes, hence larger squared sum

31. Network Lifetime  PDH leads to highest network lifetime  Lifetime decreases with increase in number of nodes

32. Height Update Rate  An update message is produced each time height of a node is updated  Thus routing overhead is proportional to the height update rate  RIH may cause a chain reaction of height updates, thus has much higher overhead

33. Conclusion and Future Work  All the proposed schemes achieve better load balance than basic LRR  PDH is the best, since it is most aggressive  Future Work  NS-2 implementation of the proposed schemes  Approximate algorithms based on optimization framework

34. Thank You!