## 4 Performance Evaluation
It is useful to remind the reader that the delivery ratio is the ratio of the number of successfully-received packets to the number of sent packets. The end-to-end delay represents the interval between sending a packet from the application layer of the source and receiving it at the application layer of the destination. The jitter is the difference between the delays experienced by the packets. Even in this case, the performance has been compared with those obtained by the WN of [PERSON] _et al._ and [PERSON] _et al._ However, it is necessary to remind the reader that their WN is based on IEEE 802.15.4, and they have shown the impact of the variation in the packet size. In fact, they have varied the packet sizes from 32 bytes-128 bytes. For this reason, the packet size that obtains the best result in their approaches has been considered for the comparison. On the contrary, in this work, the WN is based on BLE 4.0, which supports only very short data packets, whose maximum size is 27 bytes. For this reason, the packet size has not been varied. Figure 10: The electricity consumption cost. As depicted in Figure 11, considering the results obtained by [PERSON] _et al._, the best results, about 77%, are obtained with a packet size of 32 bytes. This same packet size gets the best results in the approach of [PERSON] _et al._, about 80%. On the contrary, the packet delivery ratio of the BLE-based WN proposed in this work is almost 90%. In fact, BLE data packets are more efficient when sending small amounts of data infrequently. The end-to-end delay is shown in Figure 12. In the IEEE 802.15.4-based WN of [PERSON] _et al._, it is around 0.65 s, with a packet size of 96 bytes, while using the approach of [PERSON] _et al._, the delay is around 0.77 s with a packet size of 128 bytes. In BLE, it is possible to have a connection setup and data transfer as low as 3 ms. However, in the worst case, the delay can be also higher than 1.28 s. In order to make a direct comparison among the approaches with the same packet size, Figure 12 also shows the results obtained applying the approaches of [PERSON] _et al._ and [PERSON] _et al._ using the BLE protocol, whose end-to-end delay is around 0.33 s and 0.27 s, respectively. These values are lower than those obtained using the IEEE 802.15.4 protocol. On the contrary, the end-to-end delay measured in the proposed BLE-based WN is around 0.17 s, a value lower than that obtained in the best case by [PERSON] _et al._ and [PERSON] _et al._ This highlights the goodness of BLE, which allows an application to form a connection and then to transfer authenticated data in a few seconds for a short communication burst before quickly tearing down the connection. Figure 11: Delivery ratio of the wireless networks (WNs). The jitter is another important parameter, because high jitter values mean that consumers may experience variable end-to-end delays when they are communicating with the EMU. The jitter values are shown in Figure 8.0 In all of the approaches, the values are low, less than 0.05 s, which is negligible considering the human response times. However, even in this case, the proposed WN obtains a better result than the ones of [PERSON] _et al._ and [PERSON] _et al._.