New Approach for Selfish Nodes Detection in Mobile Ad hoc Networks Djamel Djenouri CERIST, Basic Software Laboratory Algiers, Algeria ddjenouri@mail.cerist.dz Nadjib Badache USTHB, Computer Science Department Algiers, Algeria badache@wissal.dz Abstract A mobile ad hoc network (MANET) is a temporary infrastructureless network, formed by a set of mobile hosts that dynamically establish their own network on the fly without relying on any central administration. Mobile hosts used in MANET have to ensure the ser- vices that were ensured by the powerful fixed infrastruc- ture in traditional networks, the packet forwarding is one of these services. The resource limitation of nodes used in MANET, par- ticulary in energy supply, along with the multi-hop na- ture of this network may cause a new phenomena which does not exist in traditional networks. To save its en- ergy a node may behave selfishly and uses the forward- ing service of other nodes without correctly forwarding packets for them. This deviation from the correct be- havior represents a potential threat against the quality of service (QoS), as well as the service availability, one of the most important security requirements. Some solutions have been recently proposed, but almost all these solutions rely on the watchdog [13] technique in their monitoring components, which suffers from many problems. In this paper we propose a new approach to mitigate some of these problems, and we assess its per- formance by simulation. Key words: mobile ad hoc networks, security, self- ishness, packet forwarding, power control, GloMoSim simulation. 1. Introduction In some MANETs applications, such as the battle- field or the rescue operations, all nodes have a common goal and their applications belong to a single author- ity, thus they are cooperative by nature. However, in many civilian applications, such as networks of cars and provision of communication facilities in remote ar- eas, nodes typically do not belong to a single authority and they do not pursue a common goal. In such self- organized networks forwarding packets for other nodes is not in the direct interest of any one, so there is no good reason to trust nodes and assume that they al- ways cooperate. Indeed, each node tries to save its resources, particularly its battery power which is a pre- cious resource. Recent studies show that most of the nodes energy in MANETs is likely to be devoted to forward packets for other nodes. For instance, Buttyan and Hubaux simulation studies [5] show that; when the average number of hops from a source to a destination is around 5 then almost 80% of the transmission energy will be devoted to packet forwarding. Therefore, to save energy, nodes may misbehave and tend to be selfish. A selfish node regarding the packet forwarding process is a node which takes advantage of the forwarding service and asks others to forward its own packets but does not actually participate in providing this service. Some solutions have been re- cently proposed, but almost all these solutions rely on the watchdog [13] technique which suffers from many problems that will be presented later. The purpose of this paper is to propose a novel solution to monitor and detect selfish nodes, that overcomes some of these problems. The remainder of this paper is organized as follows: In the next section we present related work, and we briefly present the watchdog technique in section 3. Section 4 is devoted to the presentation and the analy- sis of our solution, followed by a simulation-based per- formance evaluation. Finally, section 6 concludes the paper and summarizes our perspectives. 0-7803-9469-0/05/$20.00 ©2005 IEEE