## 5 Results and Discussion  
For each of the scenarios shown in Figure 12 (Section 4.1), three types of experiments were performed: \"_election without aggregation_\", \"_election with aggregation_\" and \"_without election_\". For each scenario and for each type of experiment, 10 rounds with duration of 15 min were performed. All experiments were conducted in the same environment under the same conditions. The results shown in Figures 13-15 refer to the average values of 10 rounds with a confidence interval of 95%. The margins of error of the experiments can be perceived only in Figure 15 because, in Figures 13 and 14, their values are very small and cannot be viewed. We first investigate the energy consumed by the monitoring network for transmitting the captured packets as a function of the number of sniffers. As shown in Figure 13, when the election mechanism is not used, the energy consumed by the monitoring network increases when the number of sniffers increases. This occurs because the packets sent by a given node of the target network are captured by a larger number of sniffers, thereby increasing the number of redundant captured packets and consequently increasing the energy consumed by the monitoring network for the transmission of these packets. In the two types of experiments in which the election mechanism is used, the energy consumption of the monitoring network remains almost constant, because, when the number of sniffers increases, each sniffer captures packets from a smaller number of nodes of the target network, but the total number of packets sent by the monitoring network changes very little. Figure 13 shows that, with 11 sniffers, the energy consumed by the monitoring network is 38.4 mJ when the election mechanism and the aggregation of headers are not used. When the election mechanism without aggregation of headers is used, the energy consumption is 11.8 mJ, which corresponds to a decrease of 69.3%. This decrease in energy consumption occurs because the use of the election mechanism significantly reduces the number of redundant packets transmitted by the sniffers. When the election mechanism and the aggregation of headers are used, the energy  
Figure 13: Energy consumed by the monitoring network number of sniffers. consumption is only 8.27 mJ, which corresponds to a decrease of 78.5%. These results prove the energy efficiency of the EPMOSt. Next, we study the average energy consumed by each sniffer for transmitting the captured packets as a function of the number of sniffers. Figure 14 shows that, for all types of experiments, a decrease in the energy consumed by each sniffer when the number of sniffers is increased, occurs. This is because sniffers constitute an independent mesh network. Thus, when the number of sniffers increases, sniffers are closer to each other and the power of their radio interfaces is reduced, thereby reducing the coverage area of each sniffer and, consequently, each sniffer captures packets from a smaller number of target nodes. It can also be seen that the use of the election mechanism considerably reduces the energy consumption of the sniffers and consequently prolongs the lifetime of the monitoring network. Finally, we study the percentage of distinct packets captured by the monitoring network as a function of the number of sniffers. Figure 15 shows that, for all types of experiments, when the number of sniffers increases, the percentage of captured packets also increases. This occurs because the sniffers are closer to the nodes of the target network and they receive the radio signals with higher strength (RSSI). When the election mechanism is not used, the percentage of captured packets is slightly higher than in the two types of experiments that use the election mechanism. This occurs because the same packet may be captured by more than one sniffer, thereby increasing the probability of it being captured. However, this difference between the captured packets decreases with increasing number of sniffers and it is only 0.62% at 11 sniffers.