# Quantitative Study on the Impact of Energy Consumption Based Dynamic Selfishness in MANETs +
## 6 Experimental Results
### Impact of Selfish Node Densities  
In general, node density is defined as the number of nodes per unit area. It is reasonable to define node density as the number of nodes in the simulation because the simulation area is fixed. In order to evaluate the impact of selfish nodes in various density networks, the following experiments are conducted. For the purpose to assess the impact of different selfish thresholds on the performance of networks, the evaluation algorithm is executed with different selfish thresholds varying from 10% to 90% with the step size of 10% (0% and 100% are excluded because they mean altruistic and static selfish, respectively), and the number of nodes is fixed at 50. The results of the simulation are shown in Figure 6.  
In Figure 5(a), 5(b), it is obvious that the average packet loss rate increases with the increasing selfish thresholds. That means the higher threshold results in more selfish nodes in the  
Figure 6: Performance impact of various selfish thresholds (50 nodes). network. The average throughput decreases with the increasing selfish thresholds because of increments in packet loss rates. Figure 5(b) indicates there is little impact on average round-trip delay because average round-trip delay is mostly relevant to the packets successfully sent the destination (receiver). However, there are small fluctuations in the figure, which are because of dynamic selfishness and high mobility of the nodes. The dynamic selfish nodes in this work do not forward user data packets nor routing control packets. Therefore, the route discovery operations of the routing protocol are slightly influenced by the randomness of the selfish nodes. Because the residual energy level of each node is time-varying, the node states alternate between selfish and altruistic dynamically. Furthermore, it can be statistically deduced that the residual energy of most nodes is at a much higher level because the increments of average packet loss rates become larger with increasing selfish thresholds. Accordingly, the remaining experiments in following subsections are carried out with the fixed selfish threshold at 30%. Subsequently, the three evaluation metrics are compared in the MANET with various numbers of nodes, i.e., various node densities. The number of nodes varies from 10 to 50 with the step size of 10. Two sets of simulations are conducted for the purpose to compare the impact of selfish nodes to that of altruistic nodes on the network performance of the MANET. In the first set of simulations, all nodes are altruistic during the whole procedure. In the other set of simulations, all nodes are dynamic selfish (selfish threshold is 30%). The simulation results are shown in Figure 7.  
The increasing node densities give rise to increments in average packet loss rates in both sets of simulations (Figure 6(a)). This can be explained by the node mobility, which leads to dynamic topology changes and further results in link breakages in the network. However, there are relatively higher packet loss rates in the network with dynamic selfish nodes. In this case, nodes behave selfishly to refuse to forward packets for others, whenever the residual energy level comes down to less than the selfish threshold. The selfish behaviors lead to significant increases in the packet loss rate. The average round-trip delay in both networks with dynamic selfish and altruistic nodes increases with increasing node densities (Figure 6(b)). In MANETs, the more nodes involved in the network, the more complicated network topology is. Therefore, the routing protocol discovers and manages many possible routing paths in every node, which are time-consuming tasks in MANETs. However, the average round-trip delay of the network with dynamic selfish nodes is a bit smaller than that of the network with altruistic nodes. This is because selfish nodes refuse to cooperate with the routing protocol, which could reduce the number of nodes the routing protocol deals with. Figure 7: Performance impact of various node densities (selfish threshold: 30%).