# Counteracting Selfish Nodes Using Reputation Based System in Mobile Ad Hoc Networks
## 1 Introduction  
A mobile ad hoc network (MANET) can be formed without the existence of centralized controlling authority or access points, every node acting in an autonomous mode, i.e., nodes are free to join or leave the network. Nodes can communicate to distant nodes via the intermediate nodes and can freely change location, but with the characteristic that mobility network topology changes regularly. Because of hardware malfunctions, malicious attacks, and environmental interference, the sensing nodes and wireless links in the network are prone to failure [1, 2]. Thus, MANETs require adaptive protocols that link mobile nodes after the changes induced by random topology. Such networks are robust and scalable because of their distributed nature and can be set up anywhere at any time [3]. Because of these features, a MANET is an effective key and can therefore beused in various applications, such as emergencies (e.g., natural disaster relief scenarios), military operations, vehicular networks, disaster management, underwater network, robot network [4; 5], personal area network, etc. [6; 7]. These networks play an integral role in the internet of things (IoT) paradigm [8]. Therefore, a MANET is the best option for social internet of things (SIoT) applications, which are characterized by mutual trust and interests [9]. Routing in MANETs depends on intermediary nodes because every node in the network performs the role of host and router [10; 11]. More specifically, they can function as sources, destinations, or intermediate routers to transmit and receive data or forward other node packets based on their movements in the network. This cooperative event of forwarding of packets is used to ensure the reliability of time-dependent tasks. If a node is within another node's transmission range, they can directly communicate; otherwise, they will communicate through intermediate nodes, thereby constituting multi-hop routing. This multi-hop communication makes it possible to solve the low range communication of nodes, but it may not be viable without node collaboration or cooperation [12; 13].  
One of the most important challenges in MANETs is the lack of cooperation in some nodes in multi-hop communications owing to limited resources (e.g., battery power) and mobility [14]. The noncooperative nodes, known as selfish nodes, selfishly drop packets from other nodes to save their resources and utilize network resources for personal gain. On the other hand, malicious nodes intend to harm the network and exploit its resources. As the number of such nodes increases, it severely disrupts network operations [15]. In order to counteract the effects of such nodes, they must be detected and isolated from the network. Different approaches have been proposed for detecting selfish and malicious nodes. Reputation-based schemes are one of the most popular methods to encourage nodes to cooperate for packet forwarding, in which each node earn a reputation value based on feedback from other nodes [16; 17; 18; 19]. Selfish nodes are discouraged by penalizing them with low reputation and ultimately isolating them from the network.