Load Balanced Link Reversal Routing in Mobile Wireless Ad Hoc - PowerPoint PPT Presentation

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

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)

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

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

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

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

Route Creation Phase 3 3 4 4 1 1 2 2 1 2 2 1 5 5 1 1 1 1 0 Destination 0 Height = 0 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 QRY  In general h(a) = [h 1 (a), h 0 (a) ] where h 1 (a) = height UPD assigned by LRR and h 0 (a) = node id of a  Lexicographical ordering used

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

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

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Balance Factor Multi-path routing Shortest path routing  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

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

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

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

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

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