## 2 Related Work
### Trust-Based Routing  
Trust-based routing is a technology that can discover and maintain routes by using trust values derived from trust evaluation and based on trust factors. In this paper, we introduce the proposed trust-based routing technology that can be utilized in MANETs and WSNs [14; 15; 16; 17; 18; 19]. Among the currently used schemes, ad-hoc on-demand multipath distance vector routing (AOMDV) [14] is an extension of ad-hoc on-demand distance vector routing (AODV) [15], which is a typical reactive routing protocol in MANETs. AOMDV is used for multipath routing because it is a search feature for linking disjoint multiple paths during path discovery. Ad-hoc on-demand trusted-path distance vector routing (AOTDV) [16] is a trust-based multipath routing protocol that extends AOMDV. Therefore, although the basic routing path discovery method of AOTDV is similar to that of AOMDV, the process in which the source node transmits the RREQ (route request) packet and the destination node that receives it transmits the RREP (route reply) packet is different. AOTDV considers both the hop count and the path trust value (\(PTV\))as routing metrics. To calculate the \(PTV\), it is necessary to evaluate the reliability of each node. In AOTDV, the ratio of the nodes that forward the target packet per unit time using the direct trust evaluation method is measured by considering both the control and the data packets. Based on this ratio, the \(PTV\) is accumulated by multiplying the trust values of all the nodes on the transmission path of the RREP packet, and each node updates the \(PTV\) in the routing table. After the trust path is created, the source node selects a path that satisfies the trust value required to transmit the important data packet and transmits the data. However, this can cause problems such as bottlenecks because it selects one path when transmitting data. Trust-based QoS routing (TQR) [17] introduced the concept of trust and QoS metric estimation. The authors demonstrated the performance of trust values and of discovering and maintaining the most reliable paths by properly considering trustworthiness and QoS metrics. They measured the \(ETX\), propagation delay, and transmission delay for calculating the QoS metric and calculated them with trust values. However, in the case of a bottleneck, the delay accumulated in the queue was not considered, and only a single path was used to transmit the data, making reliable communication difficult. This problem can be solved by creating an algorithm that periodically checks the trust value of the trusted multipath and efficiently transmits mission-critical data simultaneously over these paths. Centralized trust-based efficient routing with authentication (CENTERA) [18] introduced a gateway-assisted trust evaluation technique. CENTERA uses a base station (BS), which can effectively collect trust information from all the nodes in the topology, and calculates the best possible routes after detecting and isolating the malicious nodes. The BS creates a global view of the network topology and evaluates the trust value of each node by calculating three metrics: maliciousness, cooperativeness, and competency. The BS can detect malicious node types, such as those sending false or illogical information, those not reliably forwarding the packets from other nodes, or those unable to deliver the packets to the BS correctly. The malicious nodes are then isolated for a certain duration based on their history. The BS increases the level of bad reports or protective observation for all the nodes showing bad behavior while reducing the level of harm to well-behaving nodes. The BS then periodically distributes updated behavior-related information to all the nodes using an efficient method. However, CENTERA uses only the \(PFR\) to perform the trust evaluation of the nodes, therefore rendering the nodes vulnerable to denial of service (DoS) attacks that diminish the resources of the system and prevent its intended operations.