## 4 Results
### Routing Performance Evaluation
#### 4.4.3 Impact of Network Size  
It was discovered in Section 4.4.2 that, at 0.5 Hz, there was moderate cost, utilization, latency, and PDR for the suggested routing approach; thus, we set \(f\), \(f^{\prime}\), and \(f^{\prime\prime}\) to 0.5 Hz in this experiment. We set \(C_{th}=0.5\) and \(T_{th}=0.2\), as experimentally found in Section 4.4.1. We modeled an urban mobility scenario with a maximum vehicle speed of 60 kph. The ratio of RSUs to vehicular nodes was kept constant at 1:3. The total number of nodes in the vehicular network, which could range from 4 to 256, was the variable in this experiment for all routing strategies. Figure 18 displays the results of evaluating the performance of routing techniques by adjusting the total number of nodes. As seen from Figure 18a, AODV has the highest average communication cost except in very small networks (network size less than or equal to eight). On the other hand, the proposed routing method has the lowest communication cost out of all routing methods for any network size, except for a network with four nodes. As evident from Figure 18, for the network size of four, there is zero DSRC utilization, zero latency, and zero packet delivery ratio, which is exactly the reason for observing least cost for all routing methods. Thus, a network size of four is a total isolated network in which none of the nodes are connected to each other (zero network link entropy). Note that the costs of routing methods for SDVN (proposed routing and Dijkstra) are non-zero even in a total-isolated network, since the controller collects metadata using cellular and Ethernet links. The communication cost for all routing methods increases with the increment of network size, having a gradient of increment in ascending order as the proposed routing, Dijkstra, and AODV. For large networks (e.g., a network size of 256), the proposed method is very effective in reducing average routing communication costs, as it had a gap of 33.5 with Dijkstra and a gap of 610.7 compared with AODV. It is very clear from Figure 18b that all channel utilizations, except LTE and Ethernet utilization of AODV, increase with the increase in the of number of nodes in the network. The DSRC utilization of routing methods is zero at a network size of four, since no packets are delivered in a totally isolated network. Another important fact to note is that the proposed method's Ethernet utilization is higher while the LTE utilization is lower than those of routing using Dijkstra, except at a network size of four, in which those utilizations overlap. Furthermore, the gap between LTE utilization and Ethernet utilization between the proposed routing and Dijkstra increases with the increment in network size. The increasing order of DSRC utilization for any network size is Dijkstra, then proposed routing, and then AODV. Another important fact to note from the channel utilization results in Figure 18b is that the DSRC utilization gap between the proposed method and AODV reduces with increments in network size. The reason for obtaining the highest DSRC utilization for AODV is due to the fact that it utilizes DSRC for both route discovery and packet routing. On the other hand, both Dijkstra and the proposed routing use DSRC for one-hop broadcast for metadata collection and then for packet routing in a given routing cycle, which yields lower utilization than AODV. The lowest DSRC utilization for any network size is observed for routing using Dijkstra, which can be explained due to its lower PDR, as evident from Figure 18d. Figure 18: Routing performance evaluation under diverse vehicular network sizes. (**a**) Communication cost fluctuation under various network sizes. (**b**) Channel utilization fluctuation for diverse network sizes. (**c**) Latency fluctuation for diverse network sizes. (**d**) Packet delivery ratio fluctuation for diverse network sizes.