# From Sensor Networks to Internet of Things. Bluetooth Low Energy, a Standard for This Evolution
## 8 Conclusions
In addition, our proposal uses the broadcast transmission mode, which allows us to take advantage over other alternatives that uses master-slave connections (see [28]), like a rapid network \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Evaluated Characteristics** & **CSR Mesh** & **Individual Mesh** & **Collaborative Mesh** \\ \hline Open protocol & No & Yes & Yes \\ \hline Bridge device needed & & & No \\ to use the network & & & No \\ \hline Master-Slave connections & Among new devices & & No \\  & and bridge devices & & No \\ \hline Necessary BLE version & 4.1 or higher for bridges & & \\  & 4.0 or higher for rest of nodes & & 4.0 or higher \\ \hline All devices retransmit & & & \\ mesh packets & No & No & Yes \\ \hline \hline \end{tabular}
\end{table} 
Table 19: Differences between CSR Mesh protocol, _Individual Mesh_ and _Collaborative Mesh_. establishment, a greatly device mobility and a greater reliability (the failure of a central device will not disconnect all attached devices). However, there are some shortcomings in our proposal, which are given by the type of data transmission, like security (packets are coded but not encrypted), and the impossibility of ensuring that a packet is received in its destination node, because there are no mechanisms implemented for that at this time. Future works regarding these weaknesses are required. In conclusion, our contribution regarding with Industry 4.0 requirements is summarised below:  
* Zero fails: our proposal improves the CSR Mesh PLR. In addition, the broadcast transmissions make our proposed mesh more flexible and reliable (a device failure does not cause a network failure). * Sustainability: the number of network devices in our mesh topology has been reduced in comparison with CSR Mesh, due to the use of bridge devices is not needed for new devices. For example, for a network with 8 sensor nodes and a BLE server we have used 3 CSR devices, while 9 CSR devices are needed as bridge devices in CSR Mesh. * Total coverage: in our proposal, all devices collaborate to retransmit mesh packets, increasing the network coverage range with the same number of devices. In addition, when mobile nodes are included, this coverage range will be total and dynamic, depending on users movement. Finally, there are still some points on which we must continue working:  
* To reduce the number of duplicated packets, and to ensure the packets are received by implementing some methods like packet priority or ACK mechanism. It will allow us to fulfil our Industry 4.0 aims: zero fails and sustainability. * To test the mesh network with a higher number of static devices (equipped with sensors). * To include mobile devices in the network (smartphones, smartbands, smartwatches, etc). * To include devices with actuators to check the correct transmission for different destinations. * To allow users to retransmit packets from other devices, varying the network in a dynamic way depending on the users movement and proving total network coverage for all users and devices. * To improve the collaborative mesh security. * To use LoRa devices to improve communications by extending the coverage range. **Acknowledgments:** This work was supported by the JCCM under grant POII-2014-010P, by the Spanish MEC under grants TIN2015-66972-C5-2-R (MINECO/FEDER) and TIN2015-65845-C3-2-R, and also by the I+D+i UCLM plan with the European Social Found. **Author Contributions:** Diego Hortelano, Teresa Olivares and M.Carmen Ruiz conceived and designed the experiments. Diego Hortelano, Celia Garrido-Hidalgo and Vicente Lopez performed the experiments. Diego Hortelano, Teresa Olivares and M. Carmen Ruiz analyzed the data; Diego Hortelano, Teresa Olivares, M. Carmen Ruiz wrote the paper. All authors have contributed to improve the paper after reviewers suggestions. **Conflicts of Interest:** The authors declare no conflict of interest.