# 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  
ZigBee is a communication protocol used for low-power devices. Frequently used on wireless monitoring and control systems. The 802.15.4 MAC layer is used for basic message handling and congestion control. The MAC layer includes mechanisms for forming and attachment to the network, a CSMA mechanism for pure channel listening devices, as well as a link-layer to handle retry and message acknowledgment for reliable communication between neighboring devices. The Zigbee network layer builds on these basic mechanisms to provide reliable end-to-end communication over the network. The efficiency of ZigBee and IEEE 802.15.4 may be evaluated with the use of relevant parameters. The most important parameters which were evaluated in this paper are:  
* Data Traffic Send--This measure contains all traffic sent by the MAC over CSMA-CA. It excludes any management, control, or ACK traffic. * Data Traffic Received--Consists of the total traffic that was successfully transmitted by the MAC from the physical layer in bits/sec. Includes retransmissions. * Throughput--it refers to the rate at which data is successfully transmitted from a source node to a destination node. * Rejected data--it refers to the rate at which data sent by the node ware rejected by the destination node In each of the designed test scenarios, several devices were selected after simulation and their statistics were analyzed. The baseline values for the optimal operation scenario (basic configuration--all connections active) are shown in Table 2. \begin{table}
\begin{tabular}{c c c c} \hline
**Scenario** & **Number of Operative Nodes** & **Number of Faulty Nodes** & **Nodes Failed in Each Scenario** \\ \hline I & 17 & 0 & — \\ \hline II & 15 & 2 & Router2, Router4 \\ \hline III & 13 & 4 & EndDevice9, EndDevice10 \\ \hline IV & 10 & 7 & Router1, Router3, EndDevice8 \\ \hline \end{tabular}
\end{table} 
Table 1: Analyzed scenario descriptions. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Parameter** & **Network Coordinator** & **EndDevice1** & **EndDevice4** & **EndDevice7** & **EndDevice8** \\ \hline Control traffic received & 892 b/s & 0.20 b/s & 880 b/s & 0.10 b/s & 0.10 b/s \\ \hline Control traffic sent & 918 b/s & 0.10 b/s & 0.10 b/s & 0.10 b/s & 0.10 b/s \\ \hline Received data & 13,530 b/s & 130 b/s & 13,250 b/s & 170 b/s & 360 b/s \\ \hline Sent data & 1.8 b/s & 12,950 b/s & 25,900 b/s & 12,950 b/s & 12,950 b/s \\ \hline Received management data & 57 b/s & 6 b/s & 78 b/s & 4 b/s & 7 b/s \\ \hline Sent management data & 2.7 b/s & 5 b/s & 3.5 b/s & 3 b/s & 5 b/s \\ \hline Rejected data & 11,940 b/s & 1.5 b/s & 1.8 b/s & 3 b/s & 9 b/s \\ \hline Delayed utility access & 892 b/s & 0.0012 s & 0.029 b/s & 0.0011 s & 0.0014 s \\ \hline Throughput & 918 b/s & 0.27 b/s & 0.27 b/s & 0.27 b/s & 0.27 b/s \\ \hline \end{tabular}
\end{table} 
Table 2: Device statistics—baseline parameters—scenario 1. The overall statistics of the network operation in the first scenario are shown in Table 3.  
At the peak of the simulation, the number of received as well as sent data are 109 Kb/s and 143 Kb/s, respectively. Also of special note is the high throughput of 24 Kb/s and the low number of rejected packets of 8640. The number of exchanged network management data is not high, and the network operates stably. The data of the network coordinator statistics in the scenario I are shown in Table 4.  
OPNET environment tool was used to run real-time scenarios to affirm our simulation results. Because of the random deployment, we ran more than 10 simulation replications for each scenario. Each simulation was run under the same conditions with the same input parameters. The benchmark state was assumed to be the state in which the standard deviation does not exceed 1 to 4% depending on the parameter. The result of the test series as multiple measurements of the same parameter, under the same conditions, was considered the arithmetic mean of the individual results, and their uncertainty (standard deviation of the mean value Sx) was verified.