# From Sensor Networks to Internet of Things. Bluetooth Low Energy, a Standard for This Evolution
## 7 Improving the CSR Mesh
### Collaborative Mesh Evaluation
#### 7.3.1 CSR Devices Retransmit Each Packet Three Times: Default Mode  
In this experiment, CSR devices were configured in default mode: retransmitting each received packet three times. Two available configurations were used for Waspmote devices: _Low Network Load_ (each packet is transmitted once by Waspmote devices, and the received packets in these packets are retransmitted once the first time that they are received) and _High Network Load_ (each packet is transmitted, or retransmitted if it is received, three times). Table 13 shows the number of packets received by CSR devices which make up the core of this mesh network. The number of packets received is increased, compared with the _Individual Mesh_, due to the fact that in this _Collaborative Mesh_ all devices collaborate for retransmitting packets and extending the network coverage range. In both cases, CSR2 has received the highest number of packets, due to its placement (see Figure 14), as in _Individual Mesh_ configuration. Further investigations regarding this lack of network load balance are required. Table 14 shows the number of packets sent by sensor nodes and the number of these packets received by the final device: the BLE server. In this case, the number of retransmitted packets has also been included, owing to sensor nodes also retransmit packets in this _Collaborative Mesh_, as explained above. Figure 17 shows the PLR for each Waspmote device using both configurations, _Low Network Load_ and _High Network Load_. The PLR for Waspmote devices is, on average, 2.06% for _Low Network Load_ and 0.11% for _High Network Load_. This network PLR is lower than CSR Mesh PLR, although the number of sensor devices was 8 in this experiment and 2 in CSR Mesh topology experiment. Comparing this configuration with _Individual Mesh_ configuration, whose PLR is 1.89% and 0.21% (for _Low Network Load_ and _High Network Load_, respectively), there is not a great difference. However, the main contrast is that this configuration allows increasing the coverage range of the network, due to all devices collaborate to retransmit the packets. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Number of Packets Transmitted** & \multicolumn{4}{c}{**Packets Received by**} \\ \cline{2-5}
**by Waspmote Devices** & **CSR1** & **CSR2** & **CSR3** & **Server** \\ \hline
1 (Low Network Load) & 36,917 & 49,824 & 34,377 & 6326 \\ \hline
3 (High Network Load) & 51,316 & 77,035 & 63,009 & 5411 \\ \hline \hline \end{tabular}
\end{table} 
Table 13: Number of packets received by CSR devices and BLE server for each Waspmote device configuration in Collaborative Mesh with CSR devices retransmit each packet three times. Table 15 shows the traffic network, measured in packet per second received in CSR devices. As seen before, using CSR Mesh configuration, devices received, on average, 1.61 packets per second when packets were retransmitted three times, for two sensor devices. In this experiment, the number of packets received was higher (8.44 for _Low Network Load_ and 11.76 for _High Network Load_), but also the number of sensor devices, which is 8 in this case. This configuration keeps the advantages of our proposal: its a PLR is close to zero, and increases the scalability of network regarding to CSR Mesh. Moreover, compared with the _Individual Mesh  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Sensor Nodes**} & \multicolumn{3}{c}{**Low Network Load**} & \multicolumn{3}{c}{**High Network Load**} \\ \cline{2-6}  & \multirow{2}{*}{**Sent Packets**} & **Packets** & \multirow{2}{*}{**Sent Packets**} & **Packets** & \multirow{2}{*}{**Retransmitted**} \\  & & **Received by BLE** & & **Packets** & **by BLE** & **Packets** \\  & & **Server** & & & **Server** & \\ \hline W1 & 817 & 800 & 2928 & 709 & 709 & 4334 \\ \hline W2 & 787 & 756 & 2889 & 690  
configuration, the coverage area is increased, although the traffic network for this configuration is slightly higher.