## 3 Road-Based Multi-Metric Forwarder Evaluation Scheme
### Information Collection Stage
#### 3.1.1 Vehicle Density of the Road Estimation  
The Vehicle Density of the Road (VDR) estimation is considered as one of the metrics for achieving optimal NFV selection, because the higher the density on the road the better the options for optimal NFV selection. In the VDR, there exist two directional vehicles including In-Direction Vehicle Density (IDVD) and Opposite Direction Vehicle Density (ODVD) as in [22]. The vehicles in the direction of the DVN are considered as the suitable C-NFV. In this study, the density of the ODVD is given minimal consideration based on their status. The density of the road is estimated based on the C-NFV that exist on that particular road, which is within the coverage area of the PFV. In the hello message, each vehicle sends information of its road-id to the neighbors that have a two-hop link to itself. Therefore, the VDR is estimated as the number of vehicles that resides within a road, which is in the coverage area of the PFV based on the two-hop link. The vehicles are collated based on their respective road-id, which is stored in the TNI. The amount of vehicles that are neighbors to C-NFV is divided by the hop count (2 Hop), because every C-NFV collect information of vehicles in its two link coverage. It is presumed that the number of neighboring vehicles with their road-id can be used to determine which road has the highest vehicle density, in order to maintain connectivity. Even though, higher vehicular density might lead to congestion and wireless contention. However, the multiple paths considered have  
Figure 2: Information Packet Format.  
already separated the routes to avoid congestion based on route coupling. The VDR is computed as in Equation (1).  
\[\text{VDR}=\frac{(3\times\text{IDVD})+\text{ODVD}}{4\times 2\text{Hop}} \tag{1}\]  
The NFV is selected based on the C-NFV that has the highest value of VDR. However, the ODVD is given a smaller value by multiplying it with \(\frac{1}{4}\), which is three times lesser to the value of IDVD multiplied by \(\frac{3}{4}\). This ensures that C-NFV moving towards the direction of the DVN is given higher priority. Thus, a threshold has been assigned as \(\text{VDR}_{\text{max}}\), where the \(\text{VDR}_{\text{max}}\) is estimated based on the pilot simulation results obtained and the road density in [22]. Therefore, the \(\text{VDR}_{\text{max}}\) is set to 100 vehicles/km. The C-NFV that has a larger amount of vehicles than the \(\text{VDR}_{\text{max}}\) (\(\text{VDR}>\text{VDR}_{\text{max}}\)) is considered as a congested network. Therefore, it is related as follows in Equation (2).  
\[\text{VDR}=\ \left\{\begin{array}{l}1\ \text{VDR}\leq\text{VDR}_{\text{max}}\\ 0\ \text{VDR}>\text{VDR}_{\text{max}}\end{array}\right. \tag{2}\]  
The VDR is estimated for the two multiple paths independently since the paths are dispersed. The road density of a C-NFV is compared with the other road density of the neighbor vehicles of a C-NFV and the road with the highest density that is not greater than the \(\text{VDR}_{\text{max}}\), is considered for selection. Therefore, the vehicle density of the road is considered as one of the important metrics that enable optimal NFV selection. This, in turn, improves the quality of the video transmission since the faster selection of NFV has been considered based on density of the vehicle on the road. The vehicle trajectory is discussed in the next subsection.