## 3 Proposed Scheme
### Trustworthiness and QoS-Based Path Discovery and Selection Procedure
\[PQTV_{p}(t)=\sigma_{p}(s)\times ETX_{p}\times(1-PTV) \tag{6}\]  
In general, multipath routing in traditional ad-hoc networks can be divided into two types. The first simultaneously transmits the packets over multiple paths to guarantee the transmission reliability of the data packet. The second primarily uses the best path from among multiple paths and then uses alternative paths if the link quality degrades owing to a bottleneck or a link disconnection. Our scheme proposes a multipath selection for mission-critical data to solve the problems of bottlenecks and degradation of link quality and to enable the simultaneous transfer of more important data over the trusted path. Trust path selection is based on the trust value of each path and the priority of mission-critical data. Transmission of data with high mission criticality requires the selection of a more reliable path. Figure 1 shows the overall process of path selection to satisfy the requirements of the proposed scheme. Here, the sensor node periodically updates and checks the trust value received. The requirements of mission-critical data are compared to the updated \(PTV\)s and E2E delay, and the \(PQTV\) of the valid paths are stored in the routing table. Finally, the sensor node can identify the best priority path over which mission-critical data should be transmitted and adaptively selects the path with the optimal trustworthiness and QoS. We compared the \(PTV\) requirements of each data packet with the actual measured \(PTV\) to determine the reliability of the path for transmitting mission-critical data. Because mission-critical data contain important information that should not be exposed to malicious nodes, they can be transmitted only when the trust value for the path meets the requirements. If the \(PTV\) is satisfactory, the delay time of the real-time data being sent is checked and compared with the required delay for the data. Mission-critical data transmission requirements are defined based  
Figure 1: Overall process for selecting paths that satisfy the trust requirements. ETX, expected transmission count. on communication status, priority/precedence, etc. If there is no path that satisfies the requirements, mission-critical data such as voice, which is real-time and important, are not transmitted through the network until a trusted path is guaranteed. Therefore, in this case, the operator should communicate using alternative methods, such as by using a separate voice communication frequency. For real-time data packets that satisfy the required performance parameters, the \(PQTV\) in the routing table is updated; for unsatisfactory performance, the packet is neither stored in the routing table nor transmitted. After successful fulfillment of the performance requirements, highly critical mission data are transmitted through the path with the minimum value among the stored \(PQTV\)s. Relatively low-critical mission data are randomly selected from paths that satisfy the requirements. In this study, it was assumed that the data packets A and B had high mission criticality, and the packets C, D and E had low priority, but the system could be operated according to the intention and preferences of the operator. Figure 2 shows an example of the methodology employed for assigning a path for transmission of mission-critical data from the sensor node to the gateway node. The \(PQTV\) evaluation in our experiment resulted in values of 0.068, 0.156, 0.025, 3.04, and 4.62 for Routes 1, 2, 3, 4, and 5, respectively. Therefore, transmission of the mission-critical data packet A was assigned to Route 3, which satisfied all the requirements. In the case of B, Routes 1 and 3 both satisfied all the requirements. For transmitting B, the node selected Route 3 with the lowest \(PQTV\) value.