Load Balanced Link Reversal Routing in Mobile Wireless Ad Hoc Networks

Load Balanced Link Reversal Routing in Mobile Wireless Ad

Hoc Networks

Load Balanced Link Reversal Routing in Mobile Wireless Ad

Hoc NetworksNabhendra Bisnik, Alhussein

AbouzeidECSE Department

RPI

Costas BuschCSCI

DepartmentRPI

Mobile Wireless NetworksMobile 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)

ContributionsContributions

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 OutlineTalk Outline

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

Link Reversal RoutingLink 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 PhaseRoute Creation Phase

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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) = [h1(a), h0(a) ] where h1(a) = height assigned by LRR and h0(a) = node id of a Lexicographical ordering used

Route Maintenance PhaseRoute Maintenance Phase

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Full Link Reversal Algorithm

Brings network from a bad stateto a good state Runs in (n2) time Leads to increase in height of at least one node

Causes of Load UnbalanceCauses 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 - ExampleLoad Unbalance - Example

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Although alternate path is now available, most of the traffic is still routed through the node with height 5

Unbalanced Network StateUnbalanced 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)

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Load Balancing ProblemLoad 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, xS

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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 ProblemLoad 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,

Heuristic MechanismsHeuristic 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 hmax – hmin > 2 then

Sets height to minimum height that ensures path to the destination

Fix link directions Update neighors



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However every instances of load unbalance does not involve selfish nodes

Example ) Solution – reduce height

whenever it is possible inorder to balance DAG

This observation leads to PDH

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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



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Reactive Increase in HeightReactive 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 hmax + 1 Fix link directions Update neighbors

Reactive Increase in HeightReactive Increase in Height

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Forwarding StrategiesForwarding 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

Simulation SettingSimulation Setting

N mobile nodes, initially deployed randomly over 1000m £ 1000m area

Communication radius is m Random waypoint mobility model used

with vmin = 2m/s, vmax = 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 MetricsPerformance Metrics

Balance factor and squared sum for both multi-path and shortest path forwarding

Network lifetime Routing updates

Balance FactorBalance Factor

PDH has highest balance factor As number of nodes increases, path length increases leading to lower balance factorMulti-path routing has larger balance factor

Multi-path routing Shortest path routing

Squared SumSquared 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 LifetimeNetwork Lifetime

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

Height Update RateHeight 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 higheroverhead

Conclusion and Future WorkConclusion 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

Thank You!Thank You!

Load Balanced Link Reversal Routing in Mobile Wireless Ad Hoc Networks

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