## 2 Methodology
### Communication Delay Parameters Between Vehicles and RSUs  
In addition, it should be ensured that the time for the vehicle OBU to reach the control plane is within a given threshold range. For the SDN architecture, a northbound interface is also required to connect the application deployment. Since the application deployment is completed in the IP network, to establish a secure channel between controllers, they must be situated on the same IP network. For Software-Defined Vehicular Networks (SDVNs), several crucial factors need to be taken into account. These include the physical positioning of the controllers, the interaction between the control plane and the data plane, and the functional demarcation within the system. This ensures that the SDVN can operate efficiently and securely, leveraging the proper placement and interaction of its components to manage network traffic and services effectively. The controller needs to process requests for network information in specific areas, such as vehicle statistics, road conditions, and network traffic statistics. The communication requests on the road are either redirected by the controller or received directly from the OBU that is not covered by the RSU. After processing the incoming requests, the controller will pass them to the OBU by controllingthe ordinary RSU or directly passing them through 4G/5G, depending on the type of request (such as real-time, non-real-time) and the reachability of the OBU (whether they are within the RSU coverage or not). The delay generated in the SDVN is mainly determined by the location and communication mode of the SDVN controller relative to the SDVN node. [PERSON] et al. [29] carried out a comprehensive comparison and in-depth analysis of the majority of the existing centralized Software-Defined Vehicular Network (SDVN) architectures. These architectures offer the advantage of endowing Vehicular Ad Hoc Networks (VANETs) with flexibility and programmability. However, this benefit is achieved by sacrificing latency. Therefore, in order to make SDVN more promising, it is necessary to consider the quality of service requirements of VANETs applications (such as the delay requirement of intelligent transportation system security applications being less than 100 ms); delay should be given a higher-priority consideration. As a solution to some of the above key issues, in order to reduce the communication delay, the control layer can be reduced to the vehicle and RSU end. This part discusses in detail the background knowledge related to the controller configuration problem, including the factors that affect the controller configuration, and the theoretical analysis of the time-delay parameters required to describe the problem. A simple method is to place a controller on each RSU so that the OBU can communicate directly with the SDN controller. Since the controller RSU needs to have both DSRC and LTE interfaces, the general cost is high and complicated. Obviously, placing the controller on all RSUs will increase the cost and complexity of the entire system. On the other hand, a single RSU may not have the minimum network topology state required for accurate routing decisions. At the same time, moving vehicles will only stay in an RSU coverage for a short period of time, which will lead to frequent switching between SDN controllers, which is not desirable. According to the research of [28], the communication contact characteristics between vehicles and intersections in SDVNs have been studied. The complementary cumulative distribution function (CCDF) for the contact duration is presented as follows:  
\[F_{duration}(t)=a_{1}\cdot e^{-a_{2}t} \tag{1}\]  
where \(a_{1}=1.41\) and \(a_{2}=0.73\). From the above equation, the average contact time \(\overline{E(t)}\) is given by Formula (2):  
\[\left\{ \begin{array}{l}\overline{E(t)}=\int_{0}^{\infty}t\cdot a_{1}\cdot e^ {-a_{2}t}dt\\ \overline{E(t)}=\frac{a_{1}}{a_{2}^{2}}\end{array} \right. \tag{2}\]  
It can be deduced that the average contact time \(\overline{E(t)}\) is 2.67 min.