## 4 Implementation and Discussion
### The Network Performance Result
#### 4.2.1 Delay  
To evaluate the behavior of the VANET protocol in terms of delay, Figure 9 has been plotted. AODV is used as the routing protocol with respect to suburban, urban with 1 TAS, and urban with 2 TASs scenarios. In VANETs, there are several parameters that are directly related to delays of the system. These includes simulation area, the vehicle's communication range, number of intermediary nodes (hops), number of vehicles and TASs, etc. If the density of the vehicles is more in a simulation area, it leads to more data and authentication requests within the network. As a result, the demand for authentication services rises, potentially increasing the overall network delay. The communication range of a vehicle denotes the farthest distance for direct communication with another vehicle. In a larger communication range, vehicles can communicate over greater distances without requiring intermediate nodes. As a result, this can reduce the number of hops needed to transmit data across the network, which reduces the overall network delay, as more hops can increase the overall delay due to the additional processing and transmission times at each hop. In a VANET, the relationship between the number of vehicles, TASs, and network delay are crucial. The TAS manages the authentication and security of the system. More TASs can help to distribute the load and handle requests more efficiently, potentially reducing network delays. In the same vehicle's communication range, if the number of TASs is fixed, then the delay of the system only depends on vehicle quantity. An increase in vehicle count correlates with a rise in system delay. We analyze three types of delay that happened in those three scenarios: authentication delay, handover delay, and end-to-end delay. The authentication delay encompasses both the transmission and processing time of messages, starting from when a vehicle sends the Request Authentication (RA) message until it receives the \(AU_{Sm}\) as the credential to enter the network through the RSU [35]. The authentication delay must not exceed 100 ms to satisfy VANET criteria [6]. Equation (12) quantifies the delay, with \(T^{i}_{BRA}\) indicating the duration for vehicle authentication requests. Vehicle \(i\) is assigned time \(T^{i}_{RFA}\) for receiving the message of service authentication from the RSU. The variable \(N\) signifies the total vehicle count in the simulation context [36]. The following is a breakdown of how the authentication delay is calculated:  
\[AuthDelay=\frac{1}{N}\sum_{i=1}^{N}{(T^{i}_{SRA}\ -\ T^{i}_{RFA})}. \tag{12}\]  
Figure 9 shows the delays, including the authentication, handover, and end-to-end delay for overall scenarios. In the suburban scenario, it shows that in a simulation involving 100 vehicles within a 5000 m \(\times\) 2500 m communication area, the authentication delay becomes 85 ms (<100 ms), indicating that this delay performance still meets the \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Units of Type** \\ \hline Communication model & IEEE 802.11p \\ Simulation area & 5000 m \(\times\) 2500 m \\ Communication range of RSU & 1000 m \\ Communication range of vehicle & 100 m \\ Data rate & 27 Mbps \\ Safety messages & Every 30 s \\ Mobility & Duaroute Mobility \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Simulation properties. requirement for VANETs [6]. However, when we tried to increase the number of vehicles from 100 to 200, considering the urban area, it effects the authentication delay of the network. In the urban area, we first considered 1 TAS. In this case, the authentication delay exceeds the VANET requirement and it reached 124 ms. This is because an increase in vehicles typically raises the demand of authentication services, potentially increasing the overall network delay, including authentication delay. Adding more TASs can mitigate this issue. For this, we considered 2 TASs in the same urban area without changing the other parameters and observed the effect of TASs in the overall network delay.