# Cyber Physical Systems Dependability Using CPS-IOT Monitoring
## 5 Performance Evaluation
### The Impact of INMP on the CPS Dependability
#### 5.5.2 Impact of Node Migration  
A second set of experiments was conducted to evaluate the benefits of moving nodes from one cluster to another in a multi-sink clustered configuration. An initial cluster configuration Configuration 1: (10, 21, and 17) was designed with each of the three clusters containing 10, 21, and 17 nodes respectively.  
This reflected a network with high variance in terms of number of nodes in the respective clusters. Thereafter, the initial configuration was adjusted by moving 5 nodes from the cluster 2 to cluster 1, thus leading to the second clustering: Configuration 2: (15, 16, and 17). A third and balanced configuration, Configuration 3: (15, 15, and 15) with equal number of nodes in each cluster was then built from Configuration 2 by moving a node from cluster 3 to cluster 1. The impacts of node migration are reported on Tables 4 and 5 in terms of energy consumption and nodes' interference respectively. As reported in Table 4, the energy consumption resulting from these network re-configurations reveals a balance in energy consumption due to node migration. A reduction in energy consumption variances of sink nodes was observed as we moved from an unbalanced network (Configuration 1, maximum energy variance of 0.4657) to a more balanced network (Configuration 3, maximum energy variance of 0.0009). Similarly, Table 5 reveals that besides energy conservation, the CPS-IoT reconfiguration using node migration also leads to a balanced profile in terms of interference. This in turn translates to a higher probability of prolonging the lifetime of the CPS-IoT.  
To test the scalability of our solution, we setup a bigger IoT network consisting of 86 nodes. We partitioned this into two clustering configurations--an unbalanced Configuration4: (49, 37) and a balanced Configuration5: (43, 43). Tables 6 and 7 further confirm previous results and reveal that node migration between clusters can increase the safety of the CPS-IoT by reducing energy consumption and can lead to a more balanced CPS-IoT in terms of an interference profile.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Configuration 1**} & \multicolumn{2}{c}{**Configuration 2**} & \multicolumn{2}{c}{**Configuration 3**} \\ \hline Energy & Highest & Average & Highest & Average & Highest & Average \\ Sink1 & 4.18\% & 2.09\% & 4.77\% & 2.51\% & 4.77\% & 2.58\% \\ Sink2 & 5.54\% & 2.89\% & 4.83\% & 2.66\% & 4.83\% & 2.66\% \\ Sink3 & 4.96\% & 2.44\% & 4.85\% & 2.71\% & 4.79\% & 2.61\% \\ Variance & 0.4657 & 0.1608 & 0.0017 & 0.0108 & 0.0009 & 0.0016 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Node migration: Energy consumption.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **5 Clusters** & **4 Clusters** & **3 Clusters** & **2 Clusters** & **1 Cluster** \\ \hline Sink1: & 4.55\% & 5.71\% & 3.18\% & 5.86\% & 6.60\% \\ Sink2: & 5.84\% & 3.86\% & 6.00\% & 4.27\% & none \\ Sink3: & 3.48\% & 3.40\% & 3.96\% & none & none \\ Sink4: & 3.35\% & 3.28\% & none & none & none \\ Sink5: & 3.93\% & none & none & none & none \\ Average: & 4.23\% & 3.92\% & 4.38\% & 5.07\% & 6.6\% \\ \hline \hline \end{tabular}
\end{table}
Table 3: Impact of clustering on energy consumption.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Configuration 1** & \multicolumn{2}{c}{**Configuration 2**} & \multicolumn{2}{c}{**Configuration 3**} \\ \hline  & 0 & 1 & 2 & 0 & 1 & 2 & 0 & 1 & 2 \\ Sink1 & 4 & 4 & 2 & 6 & 6 & 3 & 7 & 6 & 3 \\ Sink2 & 10 & 7 & 4 & 7 & 6 & 3 & 7 & 6 & 3 \\ Sink3 & 7 & 7 & 3 & 7 & 7 & 3 & 6 & 7 & 3 \\ Variance & 4.33 & 3 & 1 & 0.33 & 0.33 & 0 & 0.33 & 0.33 & 0 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Node migration: Node interference.