## 3 Proposed Scheme
### Trustworthiness and QoS-Based Path Discovery and Selection Procedure
PHB, per-hop behavior; C2, command control; FO, FLASH OVERRIDE; EF, expedited forwarding; F, FLASH; I, IMMEDIATE; P, PRIORITY; R, ROUTINE; AF, assured forwarding; BE, best effort. In this study, we added the previous node ID information to the packet header to confirm whether the packet transmitted by node j had been received from node i only or from any other neighbor node. If a node exhibits malicious behavior that involves any arbitrary discarding of packets, such as a black hole or gray hole attack, the \(NTV\) for the node decreases. Thus, a node can be labeled as malicious if its \(NTV\) falls below a threshold value. The collected \(NTV\) values of all the nodes derived through the above method are then used to calculate the \(PTV\) in the trust path discovery process. Table 2 shows the meaning of the different node trust levels [16]. Before any interaction between the nodes, the initial trust value is 0.75 (less trustworthy node). A threshold value (\(\gamma\)) is assigned (considered as the blacklist threshold) and is used to pinpoint the malicious nodes. It can be set differently depending on the user and operator intentions. The threshold reflects the communication environment of the node and is flexibly calculated as shown in Equation (4). \[\gamma=\frac{Currentbandwidth}{Linkbandwidth}\times\mu\quad(0\leq\gamma<0.75) \tag{4}\]  
The reason for this calculation is to determine clearly whether the communication status is bad or an attack by a malicious node. The variable \(\mu\) is a constant \((1>\mu\geq 0)\). It can be set differently depending on the user and operator intentions. When the path bandwidth usage is low, the flexible threshold values are also reduced to allow the detection of malicious nodes with low packet drop attacks. If the path bandwidth usage is high, it is difficult to ascertain whether the network performance degradation is due to a bottleneck or a malicious node, and therefore, the flexible threshold is increased to help in the careful determination of path exclusions. We set the minimum \(NTV\) of the nodes in the path equal to the \(PTV\), as shown in Equation (5) [23]. \[PTV=minNTV\quad(0\leq PTV\leq 1) \tag{5}\]  
In tactical ad-hoc networks, mission-critical data have different requirements in terms of urgency and importance. Generally, the more mission-critical the data are, the more secure and trusted the required paths. Table 3 shows an example of the trust requirements of the data packets [16]. They can also be set differently depending on the user and operator requirements. In case of a delay, the network delays measured by each sensor node are accumulated and summed up at the gateway node. To prevent indiscriminate path generation, the sensor node receiving the plural of RREQs generates RREPs for up to three valid paths after considering the number of reliability levels of the data packets. The gateway node receiving the RREP updates k paths. The gateway node periodically checks the \(PTV\), \(ETX\), and E2 Edelay (\(\sigma_{p}(s)\)) values to calculate the path QoS and trust \begin{table}
\begin{tabular}{c c c} \hline \hline
**Level** & **NTV** & **Meaning** \\ \hline
1 & [0.9, 1] & Trustworthy node \\
2 & [0.75, 0.9] & Less trustworthy node \\
3 & [\(\gamma\), 0.75] & Suspect node \\
4 & [0, \(\gamma\)] & Malicious node \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Different node trust levels with their meanings. \(\gamma\) denotes the threshold value. NTV, node trust value. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Level** & **PTV** & **Meaning** \\ \hline
1 & [0.9, 1] & Extremely important data \\
2 & [0.75, 0.9] & Important data \\
3 & [0.65, 0.75] & Less important data \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Examples of the trust requirements for different data packets. PTV, path trust value. value (\(PQTV\)), as shown in Equation (6), and sends them to the sensor nodes. The sensor nodes can check the trusted paths based on the received value.