## 2 Related Work
This scheme confirms when the next-hop node in a routing path has forwarded a data packet. Although CONFIDANT ensures that low ranking nodes are denied data forwarding services, the monitoring scheme employed in the protocol will not be able to detect selfish nodes that do not participate in route discovery processes, because these nodes will never be presented packets for forwarding. He _et al._[29] proposed a secure and objective reputation-based incentive scheme for MANETs. The reputation of nodes in their proposed model is quantified by objective measures, and the propagation of reputation is efficiently secured by a one-way hash chain-based authentication scheme, which is computationally efficient and eliminates the need for a public key infrastructure (PKI) or other forms of authentication infrastructures. Their model uses punishment as a way of encouraging packet forwarding and disciplines selfish nodes by probabilistically dropping packets that originate from those nodes. In [38], the authors proposed a trust management system (TMS), which includes a reputation system and a watchdog. Watchdogs normally monitor the events of data forwarding and count the arrival of the acknowledgement packets (ACKs) with respect to the forwarded data. The watchdog in their model employs a positive feedback message (PFM) as the evidence of the forwarding behaviour of a node. The trust evaluation in their model is a combination of both direct and indirect observation of nodes activities. Their model aimed at detecting malicious nodes' attempts to degrade the network performance through dropping or arbitrarily forwarding data. [PERSON] _et al._[8] proposed a reputation-based trust management system for detecting and preventing vulnerabilities in MANETs. In their model, the node evaluates and exchanges the reputation values with its one-hop neighbours in the form of trust vectors. Trust vectors in their system signify the outcomes of previous transactions, and it is preserved for each neighbour that it had transactions with in the past. Every time a node intends to forward a packet, it checks the trust rating of the nodes connected downstream from its routing table. If the node is trusted, the packet is then forwarded. On the other hand, if the node is not trusted, a different downstream node is chosen randomly among the trusted nodes. Their proposed scheme works in a purely distributed manner, whereby attacks are detected by collaborative monitoring and information exchange among the nodes. The monitoring scheme employed in their model requires a node to monitor its upstream node, and trust computation is based on the received acknowledgement from the node. [PERSON] and [PERSON] [39] proposed a novel routing strategy that deals with nodes that, due to loss of power, become selfish after previously being classified as trustworthy. Their strategy assumes that the selfish nodes are not malicious in nature, thus ensuring that they are mandated to provide accurate information about their current energy level. The information containing the status of a node's energy level is exchanged through periodic updates with its neighbours. The knowledge about the power status of the neighbours helps a node to avoid those nodes with very low power. This is based on the assumption that a node with low energy level may drop the packets presented to it for forwarding in a selfish manner in order to save energy. [PERSON] _et al._[40,41] emphasized the importance of identifying selfish and malicious nodes to enable proper functioning of a MANET. They carried out critical reviews of some existing secure routing techniques and proposed an approach that incorporates a trust vector model within existing routing protocols. In their proposed model, each node monitors the traffic of its neighbours and evaluates its local trust vector about its neighbours. The nodes in their model monitor the packet forwarding activities using promiscuous listening of traffic.