## 2 Related Work  
Cooperation enforcement in MANETs using the concept of reputation management systems has received considerable attention by researchers in the _ad hoc_ network community. Over the past decade, a lot of research works have been proposed and carried out on trust and reputation management (TRM) systems in MANETs, which employed price-based and reputation-based schemes to enforce cooperation among nodes in the network. The price-based schemes [18, 19, 20, 21, 22, 23] treat packet forwarding as a service that can be paid for and, thus, introduce a form of virtual currency to regulate packet-forwarding collaboration among nodes. Most of the price-based schemes require tamperproof hardware [18, 19] or virtual banks that all of the nodes in the network can trust [20, 21]. These price-based schemes use the virtual currency as a form of reward to nodes that participate in packet forwarding activities. In cases where a trust authority or virtual bank is required, it requires assistance from a fixed communication infrastructure to implement the reward schemes, which is not applicable for a pure _ad hoc_ network [24]. On the other hand, reputation-based schemes [7, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37] employ different monitoring techniques in gathering data, which are used in computing the reputation and trust of nodes in the networks [24]. A significant number of publications have proposed various reputation management-based techniques in which nodes in a MANET monitor the packet forwarding activities of their neighbours. If a node contributes in forwarding packets, the reputation of the node is increased. On the other hand, there is a decrease in the reputation of a node if it discards packets by dropping it. Subsequently, if a node's reputation drops below a certain threshold, the node is either punished or isolated from the network [3]. Several proposed TRM systems rely on first-hand and second-hand reputation information before computing the aggregated reputation of a node in their network. The second-hand reputation is obtained from their neighbouring nodes, while the data used in computing the first-hand reputation of nodes are derived using the watchdog mechanisms, as seen in several research works that are presented below. [PERSON] _et al._[7] proposed a reputation-based technique that employs a watchdog and path rater. Each node in their model employs the watchdog to overhear packet transmission and checks if the next-hop node forwards the packet or not. The watchdog mechanism is based on promiscuously listening to packet transmission emanating from the neighbouring node. A monitoring node maintains a buffer of recently sent packets and compares each overheard packet with the packet in the buffer to determine whether there is a match. If a match exists, the packet is removed from the buffer, and the node is determined to be a normal node. However, if a packet stays in the buffer for longer than the expected period and no transmission is overheard, a failure count is incremented. If the count exceeds a certain threshold value, it determines that the node is misbehaving, and the source node is notified. [PERSON] and [PERSON] [31] modelled reputation system for MANETs using a protocol known as CONFIDANT (cooperation of nodes: fairness in dynamic _ad hoc_ networks). The protocol specialises in the detection and isolation of nodes exhibiting anomalies in the network. The CONFIDANT protocol employs a monitoring system for observations. This includes a reputation system that specialises in knowledge creation based on first-hand and second-hand observations, a trust manager that manages incoming and outgoing second-hand reports from neighbouring nodes and a path manager that implements routing decisions through the elimination of paths containing misbehaving nodesand re-ranking of the other path based on the reputation of the nodes on the paths. Furthermore, CONFIDANT also utilises a passive acknowledgement scheme.