## Performance Evaluation
### Evaluation Results  
Figure 7 shows the number of cluster heads as a function of node mobility. The number of CHs is often around 10, as shown in Figure 7, that is, the average number of members in each cluster is 5. The reason is that the weighted function in Equation (8) is a combination of stability function, remaining energy ratio of node and speed ratio of node. This weighted function is then combined with Rules 1 and 2 in the CDS based clustering algorithm to provide a set of intermediate nodes (CDS) and the positions of intermediate nodes stably and reasonably. Figure 8 reveals the reused number of a cluster as a function of node mobility. As can be observed, the reused number of a cluster is decreased from 7.5 to 2.5 when the node's speed is increased. The reason is that the contribution of the weighted function and the CDS in the clustering phase provides stable clusters. In addition, the reused number of a cluster can reflect the stability of clusters in the networks, that is, the greater this number is, the higher the stability of clusters is. As can be seen Figure 8, when the speed of each node is increased, the stability of clusters is decreased. Figure 8: Reused number of a cluster versus node mobility. Figure 7: Number of cluster heads versus node mobility. Figure 9 shows the number of new cluster heads as a function of node mobility. The number of new CHs between two consecutive sessions is increased from 0.5 to 3.5 when the speed is grew. The reason is that the proposed CSD clustering algorithm is effective in supporting the stability of clusters and keeping all members of each cluster unchanged through sessions. Figure 10 indicates the number of switched channels of the CRD protocol as a function of node mobility. Its value is changed from 4.9 to 6.8, as shown in Figure 10. This result shows that the higher the speed is, the greater the number of switched channels is. It is also implied that the effects of speed on the proposed CRD protocol gives the number of switched channels is reasonable, that is, in both RREQ flooding and RREP replying processes, the average number of channel switching of mobile nodes is from 4.9 times to 6.8 times. Figure 11 illustrates the control overheads as a function of node mobility. The control overheads of CRD protocol (from 0.6 to 3.1) is smaller than that of CR-AODV (from 4.5 to 5.0). The reason is that the CDS based clustering algorithm helps to achieve an effective routing space and thus the clusters can be reused through multiple sessions resulting in the reduction of control overheads in CRD protocol. Moreover, the CFS algorithm with appropriate focus region and suitable sending channel help to establish a good route to decrease the control overheads in CRD protocol. On the other hand,  
Figure 10: Number of switched channels versus node mobility. Figure 9: Number of new cluster heads versus node mobility. CR-AODV protocol uses AODV routing as underlying technology without clustering and focus region and it sends packets in all channels leading to the severe control overheads. Figure 12 presents the delay as a function of node mobility. The delays of CRD and CR-AODV protocols increase slightly from 0.72 to 0.74 and from 0.76 to 0.78, respectively. This result shows that the delay of CRD protocol is better than that of CR-AODV protocol. The reason is that the proposed CRD protocol with efficient routing space and appropriate focus region mitigates the end-to-end delay during clustering and routing processes. Particularly, CRD protocol first initializes the clustering process to obtain a routing space. Thus, the routing space size of CRD protocol is smaller than the routing space size of CR-AODV. Moreover, with a stable routing space, CDR protocol does not need re-clustering in every sessions while CR-AODV spends more time in each session to exchange information packets. Figure 13 indicates the packet delivery ratio (PDR) as a function of node mobility. The PDR of CRD and CR-AODV protocols are decreased from 0.95 to 0.78 and from 0.85 to 0.65, respectively.