## 4 Experimental Evaluation
### Obtained Results  
As mentioned before, _Scenario 1_ shows the impact of the routing protocol on the region reliability, _i.e._, a single region and three different routing protocols: FLOODING, DIRECT and LEACH. The WSN reliability of each protocol is illustrated in Figure 18. Additionally, the strategy defined in Section 4.1 was considered.  
As expected, the WSN reliability is low when the FLOODING protocol is used as its power consumption is very high. The WSN reliability using DIRECT is lower than that of LEACH because the distance from the region to sink node has great impact on DIRECT than other protocols: the furthest nodes die sooner when the network uses the DIRECT protocol. Meanwhile, LEACH uses clusters that help to decrease the power consumption, balancing the power consumption of the network. Even though LEACH involves more links and sensor nodes in the path (which can decrease the reliability), the battery level is the key factor being considered. Additional factors, such as the quantity of sensor nodes and setup time, could be also considered.  
It is worth observing that FLOODING becomes a good alternative in the presence of failures of the sensor nodes and communication links, and when the sensor has enough energy. To show this situation, we carried out an experiment using _Scenario 1_, but considering the following setup: the  
Figure 18: Reliability of a region using three different routing protocols.  
battery level is constant (battery reliability set to 1.0); and the reliability of the sensor nodes and links was set to 0.1, _i.e._, they have a very low reliability.  
Figure 19 shows the results of this experiment. The DIRECT protocol had the best result, because it involved only two sensor nodes and one link. Furthermore, the reliability of the link does not consider the distance between the transmitter and receiver, what helped the DIRECT results. FLOODING had the second best result, because it created multiple paths, and LEACH had the worst result, because it used more sensor nodes than DIRECT and had a bottleneck (Cluster Head).  
_Scenario 2_ evaluates the impact of the number of sensor nodes of a region on its reliability. In this case, we consider a region containing 1, 3 and 5 nodes, and we adopted the LEACH routing protocol because it creates clusters in the network, which is ideal to evaluate the cooperation among sensor nodes. Finally, we also used the strategy defined in Section 4.1.  
As illustrated in Figure 20, the region with 1 sensor node has the worst reliability, whilst the difference between regions with 3 and 5 sensor nodes was not significant because they have a bottleneck in common (CH). If the CH fails, the region fails no matter the number of sensor nodes inside because the paths have the same CH as a common point (see Figure 15). However, the region with 5 sensor nodes was available for a longer time, because its reliability is only equal to zero when the battery level of all sensor nodes is less than 53.94%.  
Figure 19: WSN reliability when the sensor has enough energy.  
Figure 20: Reliability of the region considering different number of nodes.  
Last scenario, _Scenario 3_, shows that the location of the region impacts on its reliability. For that reason, the sensor nodes were placed between 10 to 100 m from the sink node. Each region has a single node and the DIRECT protocol was adopted. We choose this protocol, because the farthest sensor nodes die earlier when using this protocol (as mentioned before).  
As shown in Figure 21 (considering the strategy defined in Section 4.1), the reliability of the region closer to the sink node is the highest, whilst the reliability of the further region is the worst one. Moreover, this scenario highlights the importance of evaluating individual regions of a WSN instead of the entire network.