# Counteracting Selfish Nodes Using Reputation Based System in Mobile Ad Hoc Networks
## 2 Background and Literature Review
### Reputation-Based Schemes  
In reputation-based schemes, every node in the network monitors other nodes' packet forwarding activities; if a node forwards packets for other nodes it will be considered as a good node. On the other hand, if a node drops other nodes' packets, it will be considered a selfish or misbehaving node. Thus, a node's reputation will be increased upon the forwarding of packets for other nodes and decreased, otherwise. In such schemes, every node in the network evaluates and shares previous information of communications (experiences) with neighboring nodes and decides in collaboration regarding the behavior of a node, i.e., to establish whether a node is supportive or uncooperative. Reputation-based schemes define three objectives [30; 31]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Scheme** & **Reputation Based** & **Credit Based** & **Features** & **Limitations** \\ \hline [PERSON] et al. [23] & \(\surd\) & & Encourage good nodes & No punishing mechanism for selfish nodes \\ [PERSON] et al. [24] & \(\surd\) & & Punish selfish nodes & False alarm messages \\ [PERSON] et al. [25] & \(\surd\) & & Punish selfish nodes & Second chance mechanism \\ [PERSON] et al. [26] & \(\surd\) & & Local reputation information & False accusation problem \\ [PERSON] et al. [27] & \(\surd\) & & Direct reputation mechanism & Second chance mechanism \\ [PERSON] et al. [28] & & \(\surd\) & Trading among nodes & Wastage of nuglets \\ [PERSON] et al. [29] & & \(\surd\) & Centralized credit & Temper proof hardware, \\  & & \(\surd\) & management & fairness problems \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Existing works with pros and cons. * To provide evidence to distinguish between supportive and uncooperative events;
* To inspire the helpful performance of a node in a network;
* If a node is uncooperative, it must be stopped from consuming services of other nodes, or enforce it for assistance or cooperation. In these schemes, a node assesses the behavior of another node through local observations by using first-hand experience (i.e., through its direct interactions) or globally (using reports shared by other trustworthy nodes). Following are some of the reputation-based schemes. [PERSON] et al. [23] proposed a solution that consists of two methods, \"watchdog and pathrater\", to prevent selfishness and to increase good throughput of nodes. Watchdog is used to identify selfish nodes by overhearing in promiscuous mode, if the next node forwards a packet, then it will be considered as a good behaving node and vice versa; hence, a node rating can be increased or decreased accordingly. The pathrater is then used, which is responsible to constitute or select paths that do not include selfish nodes. There is no mechanism to punish selfish or misbehaving nodes; which is later addressed by the reputation scheme proposed in [24]. [PERSON] et al. [24] provide an extension to the DSR protocol named CONFIDANT (cooperation of nodes, fairness in dynamic ad hoc networks), which is a reputation-based scheme. The CONFIDANT uses four components to detect selfish nodes: monitor, reputation system, trust, and path manager. Monitor overhears its neighbor's activities using the watchdog mechanism, discussed above, and informs the trust manager accordingly. For the detection of untrustworthy nodes, trust manager keeps the record of the reputation rating of the nodes in the network. Whenever a misbehaving event occurs, the trust manager broadcasts alarm messages in the network. Moreover, trust manager uses the trust level of the sender nodes to confirm the trustworthiness of alarm messages. The reputation system maintains two lists, one is a rating list and the second is a black list; the rating list contains ratings of each node which is based on first-hand or second-hand information (information received from other nodes). The reputation system then recognizes selfish or malicious nodes based on reputation ratings. If a node rating falls below a predefined threshold, the reputation system then informs the path manager.