# From Sensor Networks to Internet of Things. Bluetooth Low Energy, a Standard for This Evolution
## 6 Discussion
### CSR Mesh Evaluation
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sensor Nodes**} & \multicolumn{2}{c}{**CSR Devices Transmit**} & \multicolumn{2}{c}{**CSR Devices Transmit**} \\  & \multicolumn{2}{c}{**Each Packet Once**} & \multicolumn{2}{c}{**Each Packet Three Times**} \\ \cline{2-4} \cline{6-5}  & **Sent Packets** & **Packets Received** & **Sent Packets** & **Packets Received** \\  & & **by Server** & & **by Server** \\ \hline \multirow{2}{*}{W1} & 555 (to CSR2, & & 577 (to CSR2, \\  & master-slave connection) & 554 & master-slave connection) & 575 \\ \hline \multirow{2}{*}{W2} & 551 (to CSR3, & & 577 (to CSR3, \\  & master-slave connection) & 367 & master-slave connection) & 542 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Packets sent by sensor nodes and received by BLE server, for each CSR devices configuration. maintained in following evaluations. Thirdly, there is an increase in the number of packets received by CSR3 device higher than the increase in the number of packets received by CSR2. It is quite the opposite to what is expected since the CSR2 device is located in the middle of the mesh network, so that it must receive packets from all the rest nodes in the mesh. This behaviour is unsuitable and ends up in troubles when the network has a high number of devices. In Table 5 it can be observed the PLR of each sensor node, which are the source of the information. In the first configuration, CSR devices retransmitted each packet once, while in second configuration CSR devices repeated each packet three times. These packets could contain different data (including key data), therefore avoiding their loss can be crucial. The first conclusion we can draw is quite expected the results show a lower packet loss when CSR devices repeat each packet three times instead of one (3.21% against 16.73% on average). The second conclusion is related to the device positioning: the Waspmote 1 results are much better than the Waspmote 2 results due to the second one is farther from BLE controller (see positioning in Figure 11), so that, its packets need to be retransmitted by more devices (increasing their network hops). As stated above, an important parameter of this type of network is the number of packets which are moved by devices at any given time (network traffic). Therefore, the number of packets received in the CSR devices were measured. These packets could be repeated (either a repetition from the same device, or a retransmission from another device), so that, the CSR devices must filter them and remove the duplicate ones. Referring to this, Table 6 shows the number of packets per second in each CSR device, for two possible configurations: CSR devices retransmit each packet once or three times. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Configuration**} & \multicolumn{4}{c}{**Packets Received per Second**} \\ \cline{2-5}  & **CSR1** & **CSR2** & **CSR3** & **Average** \\ \hline CSR devices transmit & & & & \\ each packet one & 0.62 & 1.41 & 1.08 & 1.04 \\ \hline CSR devices transmit & & & & \\ each packet three times & 1.16 & 1.76 & 1.91 & 1.61 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Packets per second received by CSR devices in a network with 2 sensor devices and CSR mesh topology. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Configuration**} & \multicolumn{4}{c}{**Packets Received by**} \\ \cline{2-5}  & **CSR1** & **CSR2** & **CSR3** & **Server** \\ \hline CSR devices transmit & & & & \\ each packet once & 2186 & 4957 & 3778 & 921 \\ \hline CSR devices transmit & & & & \\ each packet three times & 3629 & 5542 & 6003 & 1117 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Packets received by CSR devices and BLE server in CSR Mesh evaluation, for each CSR device configuration.