## 4 Experiments
### Metrics  
For the evaluation of the experiments the following metrics are defined: percentage of distinct packets captured by the monitoring network (\(\%Pcaptured\)), energy consumed by the monitoring network for transmission of captured packets (\(Et\)) and average energy consumed by each sniffer for transmission of captured packets (\(EtSniffer\)). In the EPMOSt, as well as all monitoring systems analyzed in Section 2, sniffers \"listen\" to all packets traveling in their radio interfaces. Therefore, the energy consumed in the reception of packets  
Figure 11: Scenario used in the experiments. Figure 12: Distribution of sniffers: (**a**) 3 sniffers. (**b**) 5 sniffers. (**c**) 7 sniffers. (**d**) 9 sniffers. (**e**) 11 sniffers. in the proposed system is similar to the energy consumed by the systems described in related works, and so it was not used as a metric for evaluation. However, if the duty cycle of the target network is known, each sniffer can be programmed to activate its radio interface just before the duty cycle start and to deactivate its radio interface just after the end of the duty cycle of the target network. This strategy contributes to further reduce the energy consumption of the monitoring network. The total number of packets sent by the sensor nodes of the target network (\(PsentTarget\)) is obtained by Equation (1), where \(CountInitial_{l}\) and \(CountFinal_{l}\) are, respectively, the number of the first and last temperature measurements performed by node \(i\), and \(k\) represents the number of sensor nodes of the target network. In the scenario used in these experiments, the value of \(k\) is 21:  
\[PsentTarget=\sum_{i=1}^{k}\left(CountInitial_{l}-\ CountFinal_{i}+1\right) \tag{1}\]  
The number of distinct packets sent by node \(i\) captured by the monitoring network (\(Pcaptured_{i}\)) is determined by checking which packets from node \(i\) are in the interval [\(CountInitial_{l},CountFinal_{l}\)]. Therefore, the total number of distinct captured packets (\(Pcaptured\)) is obtained by Equation (2):  
\[Pcaptured=\sum_{i=1}^{k}Pcaptured_{i} \tag{2}\]  
The percentage of distinct packets captured by the monitoring network (\(\%Pcaptured\)) is determined by Equation (3):  
\[\%Pcaptured=100*Pcaptured/PsentTarget \tag{3}\]  
As explained in Section 3.3, the number of redundant packets from node \(i\) (\(Predundant_{i}\)) is determined by analyzing the DSN and the timestamp of the packets sent by the node. Therefore, the total number of redundant packets captured by the monitoring network (\(Predundant\)) is obtained by Equation (4):  
\[Predundant=\sum_{i=1}^{k}Predundant_{i} \tag{4}\]  
In order to calculate the energy consumed by the monitoring network for the transmission of packets, the energy model for MicaZ sensors defined in [34] and used in [20] was used. In this model, the energy consumed in the transmission (\(Et\)) is determined by Equation (5), in which \(Psent\) is the number of packets sent, \(Plength\) is the packet size in bytes, \(TB\) is the time spent for transmitting one byte, \(It\) is the value of current in the transmission mode and \(V\) is the electric voltage of the battery:  
\[Et=\ Psent\times Plength\times TB\times It\times V \tag{5}\]  
The values used for \(TB\), \(It\) and \(V\) were 32 mS, 17.4 mA and 3 volts, respectively. These values were obtained in the specification document of the MicaZ platform (datasheet), and are also equal to the values presented in [20,34]. By replacing these values in Equation (5), Equation (6) is obtained:  
\[Et=\ 1,\!6704\times 10^{-6}\times Psent\times Plength \tag{6}\]  
In the experiments \"_without election_\" and \"_election without aggregation_\", the number of packets sent by the sniffers is determined by Equation (7). In these two types of experiments, each packet sent by the sniffers has size (\(Plength\)) of 23 bytes, with 05 bytes of header and 18 bytes of the monitoring message (see Figure 4).