# Modeling and Fault Tolerance Analysis of ZigBee Protocol in IoT Networks
## 4 Analysis of the Simulation Results Concerning the Fault Tolerance Issues in ZigBee Protocol
### Results of the Research
Figure 7a shows the amount of management data received in the network expressed in bits per second. Figure 7b shows the amount of sent management data expressed in bits per second. Figure 8a shows the network throughput expressed in bits per second and Figure 8b shows the number of packets rejected during transmission. Table 6 shows the behavior of the network in the full state with the network with two failed nodes (Router2, Router4). As can be seen, the differences between the corresponding values are up to four thousand percent. The failure of two nodes drastically degrades the transmission parameters, but the network still works properly. The traffic is taken over by the functioning nodes. During the analysis of the third scenario results, two more nodes were removed (EndDevice9, EndDevice10). The analysis of the network with a total of four disconnected devices shows that the fluctuations are even greater and more noticeable than in the case of the second scenario test results. The amount of data sent is only 66 Kbps at the peak of the simulation. 25,920 packets were rejected. The results obtai  
Figure 8: (**a**) The network throughput in bits per second; (**b**) Number of packets rejected during transmission. Figure 7: (**a**) Received management data in bits per second; (**b**) Sent management data in bits per second. In the third scenario, there are larger differences between the values achieved during the simulation. In the fourth scenario, in addition to the devices that were damaged in the previous scenarios, two routers failed. This caused complete paralysis of the network so that it stopped functioning, as shown in Figure 9. Figure 9a shows the network throughput expressed in bits per second while Figure 9b shows the number of packets rejected during transmission. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Top Value II** & **Top Value II** & **The Ratio TI/TIII** \\ \hline Control traffic received & 8570 b/s & 188 b/s & 45.58 \\ \hline Control traffic sent & 1810 b/s & 55 b/s & 32.91 \\ \hline Received data & 109,200 b/s & 5850 b/s & 18.67 \\ \hline Sent data & 143,400 b/s & 91,500 b/s & 1.57 \\ \hline Received management data & 1750 b/s & 1535 b/s & 1.14 \\ \hline Sent management data & 570 b/s & 570 b/s & 1 \\ \hline Throughput & 24,025 b/s & 1360 b/s & 17.6. \\ \hline Rejected data & 8640 packets & 25,920 packets & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The statistics of the network operation in scenarios I and II. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Top Value I** & **Top Value III** & **The Ratio TI/TIIII** \\ \hline Control traffic received & 8570 b/s & 176 b/s & 48.69 \\ \hline Control traffic sent & 1810 b/s & 58.5 b/s & 30.94 \\ \hline Received data & 109,200 b/s & 5600 b/s & 33.96 \\ \hline Sent data & 143,400 b/s & 65,600 b/s & 2.18 \\ \hline Received management data & 1750 b/s & 1484 b/s & 1.17 \\ \hline Sent management data & 570 b/s & 1387 b/s & 2.43 \\ \hline Throughput & 24,025 b/s & 1530 b/s & 1.57 \\ \hline Rejected data & 8640 packets & 25,920 packets & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: The statistics of the network operation in scenarios I and III. Figure 9: (**a**) The network throughput in bits per second; (**b**) Number of packets rejected during transmission. In the fourth scenario, the amount of network management data is huge, several times higher than the previous scenarios. Also, the number of discarded packets is very large and is as high as 60,500 packets. The detailed traffic comparison is shown in Table 8. The differences between the results of the first scenario and the results of the fourth scenario are huge. The failure of several devices caused practical network malfunction. ZigBee transmissions can repeat up to two times (three times in total) and every node in the network or in the radius of that transmission repeats it. Transmissions can consume a lot of bandwidth.