# Bio-Inspired Dynamic Trust and Congestion-Aware Zone-Based Secured Internet of Drone Things (SIoDT)
## 3 Preliminaries
### Drone Routing  
The traditional routing model is not suitable for drone routing; hence, hybrid routing [28] is used, which is the zone routing protocol (ZRP). This protocol is mainly designed to reduce the routing overhead, where the control packets maintain a static packet size. Here, connectivity is established using a prediction approach. The network coverage space is divided into several zones, and each zone is monitored by one or two drones. The major phases of the protocol are route request (RREQ), route reply (RREP), route expiration (RE), and route error (RERR). The packet structure of the ZRP routing protocol is shown in Figure 3.  
Figure 2: Communication among CH and Drone.  
In the ZRP protocol, the sender broadcast the RREQ packet, the control packet size ranges from 0 to 31, the S-DRONE-ADD represents the sender drone address, and the R-DRONE-ADD represents the receiver drone address. The inbuilt parameters, which are calculated directly from the control packets, are latency and efficiency. The possible pathway to reach the receiver is noted in the mobility pattern. Once the delay is so high or the efficiency of the packet reaches below its threshold, then the packet gets dropped automatically. Hop count represents the intermediate hops total count of the packet. Additionally, some other basic information is packet_ID, sequence number (Seq. No), and zone packets (Zone_Pac). After the broadcast of the RREQ packet, through certain hops, the packet must reach the receiver. Using certain parameters, the hops will update the packet such as momentum, latency, location, travel path, and efficiency. Here, RE represents the route expiration, and it happens on certain conditions when the efficiency of the route reaches below its threshold efficiency. Once the RREQ packet reaches the receiver, the total gain measurement (\(Gain_{M}\)) is calculated, which is mathematically expressed below:  
\[Gain_{M}=\left[\frac{RE}{Latency}\right]\times\left[\frac{RE}{ Efficiency}\right]\times\left[\frac{D_{path}}{1+\lambda}\right] \tag{1}\]  
In Equation (1), the \(Gain_{M}\) denotes the gain obtained during the connectivity of the route, \(D_{path}\) denotes the total number of routes measured by the single drone, \(\lambda\) denotes the actual allocation of the drone, and the latency and efficiency are the core parameters used for the measurement of gain. Following the gain measurement, the receiver generates the RREP packet and sends it back to the sender. The optimal path to transfer the RREP packet is chosen as the route with the highest gain measurements. The RREP packet also maintains the general information, such as packet_ID, sequence number (Seq. No), and zone packets (Zone_Pac). During the process of transmission of the RREP packet to route, expiration may occur at the time the route revival model is initiated and select the route with the next best gain measurement to transmit the RREP packet. If any connectivity issues occur due to the geographical changes of the drones at that time, a route error (RERR) packet is generated so as to recreate the route discovery. Due to this process of zone creation, link failures are easily identified. The process of drone routing is described in Algorithm 1.  
Figure 3: Packet Structure of ZRP Protocol.