Proceedings of the 10th International Conference on Computer Supported Cooperative Work in Design

Analysis and Countermeasure of Selfish Node Problem in MobileAd Hoc Network

Li Xu, Zhiwei Lin, Ayong YeDept. ofComputer Science, Fujian Normal University, Fuzhou, P.R. China

{xuli, 1w)(@flnu.edu.cn

Abstract

AIJNET (Mobile Ad Hoc Network) is a collection ofwireless mobile nodes forming a temporarycommunication network without the aid of anyestablished infrastructure. Because mobile nodes aretypically constrained by power and computing resources,a selfish node may not be willing to use its computing andenergy resources to forwardpackets that are not directlybeneficial to it, even though it expects others to forwardpackets on its behalf This paper not only analyzes theeffect of two typical kinds of selfish nodes throughsimulation methods, but also proposes resolving strategyrespectively. For type 1 selfish node, this paper proposesCI-DSR (cooperation inspirited dynamic source routing)protocol, which introduces an objective reputation-basedstrategy into the DSR protocol. For type 2 selfish nodes, aself-saving energy strategy is proposed. Simulationsindicate that both oftwo strategies can effectively tradeoffthe selfishness and cooperation.

Keywords: Mobile Ad Hoc Network, Selfish Node,Cooperation, Reliability, Energy Conservation.

damage other nodes. Malicious nodes aim at damagingother nodes by causing network outage by partitioningwhile saving battery life is not a priority. This papermainly focuses on the selfish nodes.

2. Stimulation-based Analysis of SelfishNodes

2.1 Selfish Node Models

In the type 1 model, the packet forwarding functionperformed in the selfish node is disabled for all packetsthat have a source address or a destination addressdifferent from the current selfish node. However, selfishnode participates in the Route Discovery and RouteMaintenance phases of the on-demand protocol.

The type 2 model selfish nodes do not participate inthe Route Discovery phase of the reactive protocol. Theimpact of this model on the network maintenance andoperation is more significant than the first one. A selfishnode of this type uses the node energy only for its owncommunications.

2.2 Simulations Model and Metrics1. Introduction

MANET (Mobile ad hoc network) is a multi-hopwireless network that is composed of mobile nodescommunicating with each other through wireless links [1].MANET is likely to be used in many practicalapplications, including personal area networks, home areanetworking, military environments, and search and rescueoperations. The wide range of potential applications hasled to a recent rise in research and development activities.

In emergency situations, all of the nodes in thenetwork belong to a single authority and therefore have acommon objective. As a result, cooperation among thenodes can be assumed. However, in emerging civilianapplications, cooperative behaviors such as forwardingeach other's messages, cannot be assumed. We canidentify two types of uncooperative nodes: maliciousnodes and selfish nodes. Selfish nodes use the networkbut do not cooperate, saving battery life for their owncommunications [2]. They do not intend to directly

Simulations use the wireless extension NS-2 [3]system provided by CMU. A network with 50 nodes isconfined in a rectangular region of size 670m X 670m. 50connections are established at random using CBR trafficso that each node has chance to connect to every othernode. MAC protocol uses IEEE802.11 and on-demandroute protocol in network layer uses the DSR [4]. Themaximum speed of mobile is lOm/s. The run-time is 200seconds. The percentage of selfish nodes is increased foreach simulation run and takes values range from 00O to70%o.

V = Vcooperative + Vselfish (1)

V is the set of network nodes. TheVcooperative represents the set of the cooperative nodes in

the network and Vselsh represents the set of the

1-4244-0165-8/06/$20.00 C 2006 IEEE.

Proceedings of the 10th International Conference on Computer Supported Cooperative Work in Design

uncooperative nodes in the network. The impact of selfishbehavior was measured in terms of aggregate networkthroughput and ABC (Average Energy Consumption),which are defined as Eq.(2) and Eq.(3).

Y,node i received packetsThroughput =

ACE =

Y,node i sent packetsViceV (2)

4

3.5

006 2

LU

0.

Y,Energy ConsumptionI

.,(node j received packets + node j sent packets)I

VjeV orVjeVcooperative selfish(3)

The percentage of selfish nodes is randomly selectedand increased for each simulation run and takes valuesfrom O0o to 7O0o.

2.3 Simulation Result and Analysis

Figi1, Fig.2 and Fig.3 respectively show thevariations of global network throughput and averageenergy consumption of each cooperative or selfish nodeas a function of the percentage of selfish nodes. Fig. 1points out that throughput degrade by 3500 when 500o ofthe nodes of the network become type 1 selfish node.Fig.3 illustrates that the ABC of cooperative nodeincreases linearly with the percentage of type 1 selfishnodes. Countermeasures for type 1 selfish nodes have tobe taken into account for the design of secure routingmechanisms. The secure scheme we propose is describedin section 3.

0.9

068

0.7

=086

0

.m 0.4

0.21

0.1

10 20 30 40 50 60 70

% of Selfish Node

Fig.1 Network Throughput

00w

1-t0 20 30 $ 40 50 6-0 70

Typof2SelfishhNodes

Fig.2 Average Energy Consumption

1 0 20 30 40 50% of Selfish Node

Fig.3 Average Energy Consumption

Fig. 1 also points out that throughput degrades onlyby 300 when 5000 nodes of the network become type 2nodes. Fig.3 illustrates the average energy consumptionof cooperative node increases no more than 1000 when5000 of the nodes become type 2 nodes. Fig.2 illustratesthat, in high density MANET, the type 2 nodes willreplaced by their neighbor node to construct a new route.So the average energy consumption is increase onlyslightly when the percentage of type 2 nodes is not toohigh. This phenomenon implies that a lower energy nodecan change his model to type 2 to conserve energy andprolong the network lifetime. The more discuss in detailis in section 4.

3. Cooperation Inspirited based DynamicSource Routing Protocol

Current reputation-based schemes utilize reputationin routing [5] or enforcing punishment [6]. However, theexisting reputation-based schemes suffer from lack ofeffective mechanisms to measure and propagatereputation. This paper introduces a quantity method toobjective measure reputation of a node. The new protocolis named as CI-DSR (cooperation inspirited dynamic

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Proceedings of the 10th International Conference on Computer Supported Cooperative Work in Design

source routing protocol), which introduces an objectivereputation-based strategy into DSR protocol [4]. The keyframework is illustrated in Fig.4, which including threemodels. Neighbor monitoring model is to collectinformation about misbehavior of neighbors. Reputationpropagation model counterpoise is aimed at sharinginformation among neighboring nodes to make thereputation more fairly. Punishment model is to encouragepacket forwarding and discipline selfish nodes.

3.1 Neighbor Monitoring

Neighbor monitoring is used to collect informationabout the packet-forwarding behavior of the neighbors.Suppose a node is capable of overhearing thetransmissions of its neighbors. With this capability, nodeK can maintain a neighbor node set N(k) and ReliabilityRK (X) for each neighbor node X defined as Eq.(4).

RK (X = FK(X)AK(X

VX E- N(k) (4)

Where AK (X) represents total number of packetsthat node N has transmitted to X except for the packetwhich destination is X. FK (x) represents the totalnumber of packets that have forwarded by X and noticedbyK.

3.2 Reputation Propagations and Counterpoise

Each node K periodically updates itS RK (X) for

each neighbor X if RK (x) has been significantlychanged. Then each node K must broadcasts the RK (X)to its neighbor to exchange information then calculates itsJoint Evaluation Reliability JERK (x) as Eq.(5).

JERK(X) =-(RK(X)+ iE )

F =N(K)flN(X) U{fN

(5)

3.3 Punishment

With the JERK (X) obtained, node k can punish itsneighbor X by probabilistic dropping the packet fromnode X. The probability of dropping is defined as Eq.(6).

=- -JERK (X) if JERK (X) < '-

otherwise(6)

3.4 Simulation Result and Evaluation

Simulation is set the same environment as section 2.The evaluation reference is throughput and average traffic.The maximum speed of mobile is tOm/s. The run-time is200 seconds. The percentage of selfish nodes is increasedfor each simulation run and takes values from 00o to 500o.

Fig.5 shows that with CI-DSR protocol and packetdrop ratio 10000, the network throughput can equal withthe DSR protocol packet drop ratio 5000. Thisphenomenon indicates CI-DSR protocol can efficientlyavoid the selfish node. Fig.6 illustrates the traffic ofcooperation node is higher than that of selfish nodes. Itindicates CI-DSR protocol can efficient punish the selfishnodes.

The main title (on the first page) should begin 1-3/8inches (3.49 cm) from the top edge of the page, centered,and in Times 14-point, boldface type. Capitalize the firstletter of nouns, pronouns, verbs, adjectives, and adverbs;do not capitalize articles, coordinate conjunctions, orprepositions (unless the title begins with such a word).Leave one blank line after the title.

0.95

0.9

0 85

=0.8

0.m 0.7

o 6

0.6

0.55

n.L~~~~~~~~~~

20 CBR Connections

-4-- DSR-CI. Packet drop rate or selfish node is 50%-li- DSR-CI. Packet drop rate or selfish node is iOO%-I'- DSR. Packet drop rate of selfishi node is 50%--W- DSR. Packet drop rate of selfish node is 100%

0 5 1 0 15 20 25 30 35 40 45% Selfish Node S.9

Fig.5 Network Throughput

20 CBR Connections, Packet drop rate of selfish node is 5O'%

CD 0.17

m 0.16

U 0.15

b-0.14

0.12

0.11

0. 1- 20 25 30

% Selfish Node

36 40 45

Fig. 6 Traffic under variation ratio of selfish node

-4- Well Node in DSR-CIA~ Everage Node in DSR

-JVL- Selfish Node in DSR-CI

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Proceedings of the 10th International Conference on Computer Supported Cooperative Work in Design

4. Selfish-based Energy ConservationStrategy

4.1 Self-Saving Energy Strategy

In MANET, the traffic and position of node randomlychange, so the network load is imbalance. On the otherhand, the initial energy of node is various, some lowerenergy nodes have to take on heavy transmit task, whilesome upper energy nodes are idle. The study result ofsection 2 tells us that, in density M\ANET, the lower nodecan change itself into type 2 selfish models in sometime.This Self-Saving Energy Strategy (SSE) defines a node kprobability p of change into type 2 models as Eq.(7) and(8).

p = 100 x(REk (t) - 0.2)21

if RE(t) > 0.2

if 0.1 < RE(t) <0.2

if RE(t) < 0.1(7)

Fig.8 indicate two examples, In Fig.7 and Fig.8, *represents using SSE strategy and * * represents not.Simulation result illustrates that using SSE can obviouslytrade-off network load. On the other hand, Without SSEstrategy, some of node, such as node 33 and node 83, useup their energy.

5. Conclusion

In this paper, based on the simulation we analyze theeffect of two kinds of selfish node in M\ANET. Theresults of throughput and Variation of Average EnergyConsumption prove that the type 1 selfish node affectsbadly the network capacity, while type 2 selfish nodescan conserve lower energy node in some conditions. Sothis paper not only proposes an Objective Reputation-based Countermeasure to find out and punish the type 1selfish nodes, but also proposes a Self-Saving EnergyStrategy to trade-off load among whole ad hoc network.

Re mainder Energy in time t

Initial Energy

Acknowledgement(8)

4.2 Simulations and Evaluation

This work is supported Partially by National NaturalScience Foundation of China (No. 60502047), ScienceFoundation of Fujian Province in China (No.A0440001).The authors would also like to express their cordialthanks to Prof. Zheng Bao-yu of Nanjing University ofpost and Telecommunication.

3l L; ^ _ _1References[1] Ram Ramanathan, Jason Redi. A Brief Overview of Ad HocNetworks: Challenges and Directions. IEEE CommunicationsMagazine. 50th Anniversary Commemorative Issue, May

Node [2] XU Li, ZHENG Bao-yu. Cross layer coordinated EnergySaving Strategy in MANET. Journal of Electronics.2003, 11,Fig.7 Comparison of each node's throughput In scene 20(6): 455-459

[3] NS-2. http:Hwww.isi.edu/nsnam/ns/doc/index.htmlScene - - [4] Johnson, D., Maltz, D., Dynamic Source Routing in Ad Hoc

Wireless Networks, Mobile Computing, Chapter 5, pp. 153-181,.t fi _Kluwer Academic Publishers, 1996.

r°rU::reb+_SMs1 S12 1 n t [5] s. Marti, T. Giuli, K. Lai, and M. Baker, Mitigating routingrE 17 g u u ~ n y m ^misbehavior in mobile ad hoc networks, Proceeding of

Mobicom 2000, Boston, MA, USA, Aug. 2000... T wt [6] S. Buchegger and J. Le Boudec. Performance analysis of the

,OTU DAN 5... i c l co p r to of node fa rnsin.COU4FTDAlNT1 prOIocol: cooperation Of nodes fairness inNode distributed ad hoc network. IEEE/ACM Workshop on Mobile

Ad Hoc Networking and Computing, Lausanne, Switzerland,Fig.8 Comparison of each node's throughput In scene 2 June 2002.

The simulation environment is set as in section 2.Node 0 and Node 1 are set as data sources. Theyrandomly select fifty CBR connections to destinationnode range from node 2 to node 49. Simulation executesin several random scenes, and run time is 400s. Fig.7 and