# Collision Avoidance Geographic P2P-RPL in Multi-Hop Indoor Wireless Networks
## 4 Performance Evaluation
As the average node degree increases, more one-hop neighbor nodes exist in the transmission range of the sender node, resulting in an increased number of received control packets. Figure 10 shows that the average hop count of P2P routes discovered by the Collision Avoidance Geographic P2P-RPL was very close to P2P-RPL when the average node degree was nine or more. P2P-RPL achieved the smallest hop count by discovering the P2P path through the whole network. Collision Avoidance Geographic P2P-RPL and Location-Aided P2P-RPL could not find a shorter route than P2P-RPL because these algorithms only search the location-constrained forwarding zone based on the location information of source and destination nodes. In this simulation network configuration, the network was fully connected. When the average node degree was 6, all algorithms discovered longer routes than when the average node degree was 9 or more. As the average node degree increased, shorter routes were discovered. The PDR performance under various average node degree is shown in Figure 11. As the average node degree increases, PDR increases. The PDR of Collision Avoidance Geographic P2P-RPL is observed about 90.9% at the average node degree of 6, 92.0% at the average node degree of 9, and 92.3% at the average node degree of 12. Although partial nodes participate in route discovery procedure, ER-RPL, Location-Aided P2P-RPL and Collision Avoidance Geographic P2P-RPL still achieve close performance to P2P-RPL when the average node degree is 9 and 12. Figure 12 shows the route discovery success ratio in the first route discovery attempt. As the average node degree increased, all algorithms could have a higher probability of finding the P2P route from the source node to destination node. Since P2P-RPL searches the P2P path throughout the entire network, ER-RPL, Location-Aided P2P-RPL, and Collision Avoidance Geographic P2P-RPL with limited search space for route discovery cannot improve the route discovery success ratio better than P2P-RPL. However, at the average node degree of 12, the route discovery success ratio performance of Collision Avoidance Geographic P2P-RPL was close to P2P-RPL with the accurate localization information. To improve the route discovery success ratio, Collision Avoidance Geographic P2P-RPL performed P2P-RPL by flooding the DIO control packets over the whole network if the route discovery failed in the first attempt. Figures 13 and 14 show the routing performance results under various numbers of active source-destination pairs. The number of active source-destination pairs varied from one to four. The size of network area was \(75\times 75\) m\({}^{2}\), and the average node degree was set to 12. Figure 13 shows that the network convergence time became longer as the number of active source-destination pairs increased. Due to the flooding nature,  
more collisions occurred as the number of active source-destination pairs increased. The network convergence time increased with the number of collisions. In Collision Avoidance Geographic P2P-RPL, the network convergence time is 38.7%, 46.7%, 48.8% shorter compared to P2P-RPL, ER-RPL, Location-Aided P2P-RPL, on average. Collision Avoidance Geographic P2P-RPL reduces the listen-only period up to 4 times shorter at each hop. A decrease in the listen-only period led to a decrease in the network convergence time. The proposed elastic trickle timer algorithm also allowed nodes to contend in longer intervals, resulting in a decreased probability of collisions. The network convergence time of Location-Aided P2P-RPL and ER-RPL was longer than for P2P-RPL. As shown in Figure 5, the non-deterministic suppression of standard trickle algorithm can cause a relay node to remain silent in the current trickle interval. This delays the DIO control packet in reaching the destination node, especially when high message suppression is performed (e.g., \(k=1\)). Figure 14 shows that, as the number of active source-destination pairs increased, the number of control packet overhead increased.