# A Connectivity-Based Clustering Scheme for Intelligent Vehicles
## 6 Simulation Results and Discussions
### Assessment of the Connectivity-Based Clustering Overhead  
The overhead of the suggested protocol was evaluated with RRMs and average packet loss, as defined above. The overhead of suggested connectivity-based clustering was compared with reliability-based clustering [3] and Triple Cluster-based Routing Protocol (TCRP) [1]. Firstly, the metric for clustering in the previous TCRP was converted to link connectivity. In this experiment, we considered a congested traffic scenario on a highway, where continuous arrival of vehicles was in practice. The number of RRMs was massive to discover a strongly connected route towards a particular destination in a highly congested network. Since the suggested connectivity-based clustering and previous reliability-based clustering dynamically divide the network into an optimal number of clusters, the number of control messages is significantly lower compared to TCRP, as shown in Figure 3. The reliability and connectivity-based clustering use a heuristic approach for an optimal number of clusters; that is why the magnitude of the RRMs is also very low.  
In contrast, the TCRP forms a fixed number of clusters (i.e., three clusters); that is why the number of RRMs is significantly higher compared to the reliability and connectivity-based scheme. From Figure 2, we also notice that the number of clusters in our proposed connectivity-based clustering scheme is slightly more than the reliability-based scheme; thus, the magnitude of RRMs is also lower in Figure 3. The greater number of clusters enables our suggested clustering scheme to combine strongly connected vehicles in a cluster. The route discovery process in intra-cluster creates fewer RRMs due to the smaller number of clusters. Similarly, in inter-cluster discovery, the suggested FAP summarizes the reachability information of each cluster, which reduces significantly the number of RMMs. In a nutshell, due to the greater number of clusters, the suggested scheme has less overhead in discovering a particular destination.  
Figure 2: Temporal assessment of connectivity-based clustering (our suggested scheme) and reliability-based clustering scheme [3].  
Moreover, we also assessed the suggested protocol in terms of average packet loss. From Figure 4, it is noticed that the suggested scheme has less packet loss compared to the previous schemes. The packet loss in connectivity-based and reliability-based schemes are significantly less than TCRP. The reason behind a smaller number of packet losses in the aforementioned schemes is the evolving nature or the dynamic number of cluster selection. Additionally, we can see that our suggested connectivity-based scheme is slightly better than the previous reliability-based scheme because of its more dynamicity and application of FAP. It can also be seen in Figure 2 that our suggested scheme is fast evolving in the selection of clusters under various numbers of vehicles. Since TCRP forms only three clusters in all cases, i.e., the congested and non-congested scenarios, its performance is worse in terms of packet loss due to the highly dense clusters.  
Figure 4: Comparison of our suggested connectivity-based clustering packet loss with the previous reliability-based clustering [3] and TCRP [1].  
Figure 3: Comparison of our suggested connectivity-based clustering overhead/route request messages (RRMs) with the previous reliability-based clustering [3] and triple cluster-based routing protocol (TCRP) [1].