# Counteracting Selfish Nodes Using Reputation Based System in Mobile Ad Hoc Networks
## 2 Background and Literature Review
### Reputation-Based Schemes
The path manager decides to include or exclude a node from the path depending on the reputation rating of that node. Thus path manager selects a route with no selfish nodes and also rejects traffic from misbehaving nodes. In this scheme, the alarm messages has the disadvantage of rumors spreading, due to which the attacker node can spread false alarm messages indicating certain node(s) as being selfish. In this scheme, the alarm messages have the disadvantage of rumor spreading [32], due to which the attacker node can spread false alarm messages indicating certain node(s) as being selfish. The authors provided a solution to this problem in their work given in [32]. CORE (collaborative reputation mechanism to enforce node cooperation in mobile ad hoc networks) [25] is a reputation-based scheme that works on top of DSR protocol. This considers the MANET as a society to remain trusted and where nodes must be cooperative. CORE uses the following three types of reputation information:  
* Reputation considered through direct observations;
* Reputation information is received from one node concerning others;
* Functional reputations related to a certain function and the weight of the function depends on the priority or status of the function. At last, collective reputation is calculated based on these three sources of reputation information. Hence, a node with poor reputation value will be secluded from the network. However, if a node increases its contribution to the network, then the node may rejoin the network. [PERSON] et al. [26] proposed LARS (locally aware reputation system for mobile ad hoc networks). LARS uses local reputation information in which every node in the network monitors its one-hop neighbors for packet forwarding activities and calculates node reputation accordingly. Hence, a node having a low reputation value will be declared as selfish and its neighbors are notified through a warning message. To overcome the false accusation problem, the warning message must be received from multiple nodes to verify the warning message. OCEAN (observation-based cooperation enforcement in ad hoc networks) [27] considers only direct observations to decide a node's behavior. OCEAN uses five components to detect a selfish node, which are given below. * NeighborWatch: is used to observe neighboring nodes using the watchdog mechanism to determine whether or not a node forwards packets for others;
* RouteRanker: maintains a rating record of adjacent nodes. Initially, a neutral rating is assigned to all the nodes and then increases or decreases according to the receipt of positive or negative events, respectively, received from the NeighborWatch component;
* Rank-Based Routing: this component is responsible for selecting a path having no selfish nodes according to the information generated by the NeighborWatch component;
* Malicious Traffic Rejection: rejects all packets from selfish nodes to stop service provision to selfish nodes from other nodes;
* Second Chance Mechanism: this component periodically gives a second chance to nodes previously declared as selfish. The second chance mechanism is based on the assumption that the node forwards packets, but due to some technical problems or a bad environment the node was unable to maintain its reputation ratings, for example, accidental link errors. In [15], a central intelligent technique called SDA (separation of detection authority) is presented to consider network reliability. By utilizing three watchdogs, a payment punishment scheme (PPS) was proposed to send messages to the neighbor nodes, monitor them, and report on their behavior [33]. The method clusters nodes, and the cluster head uses a modified extended Dempster-Shafer model, watching out for selfish nodes with the use of watchdogs. Based on the Dempster-Shafer evidence theory, a trust model approach is proposed in [13], which is based on direct trust between nodes and indirect trust between neighboring nodes.