# From Sensor Networks to Internet of Things. Bluetooth Low Energy, a Standard for This Evolution
## 5 Preliminary Evaluation: BLE Standard Topologies for Industry 4.0  
A preliminary study has been carry out to determine if the available network topologies are suitable for new Industry 4.0 challenge. For this study, Waspmote devices with a BLE radio module have been used to deploy our BLE network.  
Thus, a 10-BLE-device network was deployed in our institute, I3A. For data transmissions, devices use the broadcasting capability: the static BLE devices transmit packets as _broadcasters_, and an user equipped with a mobile device (which is a _observer_) receives these packets in different points while he is moving through the building (from P1 to P16 in Figure 9). Measurements relating to the number of packets and their RSSI have been taken in different points of the walk-through of the user to know if the deployed network works correctly. Figure 9 shows the situation of the static _BLE broadcasters_ (\(D1,...,D10\)) and _Testing Points_ (\(P1,...,P16\)). It has also been shown what we have called _Good Points_  
Figure 8: CSR1010 device [36].  
Figure 7: Waspmote devices equipped with BLE module.  
and _Bad Points_. In _Good Points_, the greatest RSSI corresponds to packets from the nearest device; _Bad Points_ show both, where the higher RSSI received packets do not come from the nearest device, or the observer has not received any packet from this nearest static device.  
As Figure 9 shows, only 68.75% of the testing points are _Good Points_, where the observer received packets from the nearest static device correctly. These results leads us to conclude that this topology does not fulfil the requirements of the Industry 4.0 identified above: there are several dead zones where there is not network coverage, and the PLR is too high.  
Furthermore, _connection_ topology has been dismissed due to the restriction in the number of slaves connected simultaneously to a master (this number depends on the memory of device, and, in practice, this number is 8 at maximum), and the impossibility of deploying a network hierarchy by means of connecting a master with other master devices working as slave (this characteristic was included in the specification 4.1 of Bluetooth [42], but most devices do not implement it). In most Industry 4.0 use cases, just 8 slave devices connected to a master device are not enough, because this is a very static and limited option, due to every slave device should be within the master slave range. In addition, these limitations affect the coverage of the network, and make hard to scale the network, which has a negative impact in its sustainability.  
Once the current topologies specified in the Bluetooth standard have been ruled out for use in Industry 4.0 due to it does not meet its requirements, a new BLE network topology is necessary: mesh topology. As seen before, there are already some initiatives to use this topology in BLE technology: However, these first versions have weaknesses which are necessary to solve. So that, in following sections, we will present our new topology proposal. Moreover, it will be compared with the current initiatives, evaluating its performance and demonstrating that its packet loss is lower.