# Modeling and Fault Tolerance Analysis of ZigBee Protocol in IoT Networks
## 2 Previous Works
This emphasizes the need for the coexistence of different techniques to implement a fault tolerance solution. Fault tolerance is the ability of a system to deliver a desired level of functionality in the presence of faults [30]. Effective fault tolerance mechanisms generate fewer control messages, thus limiting the generated traffic, requiring computing power of the node, which directly impacts its energy longevity and at the same time the reliability of the entire solution, the entire IoT structure. As the authors assure in [31], ZigBee technology provides more effective support compared to WiFi, Bluetooth, and Ultra Wide Band (UWB) standards in terms of transmission range. To confirm their thesis, they present the results of their research on the example of a medium-sized WSN. However, many works analyze specific routing algorithms for WSN structures. In [32; 33], the performance of a network running on ZigBee using the IEEE 802.15.4 protocol stack was evaluated using the parameters: throughput, delay, lost data, and received and sent data traffic. The obtained data show that it is possible to get a satisfactory reply by using a blend of star and tree topologies as well as mesh and hybrid topologies. It is observed that hybrid topology reaches maximum capacity while tree topology reaches minimum capacity and for mesh topology, the capacity is almost equal in all instances. It is also observed that the MAC latency of hybrid topology is maximized while the MAC latency of tree topology is steady. The Zigbee protocol is used extensively in domestic networks. According to the Ambient Intelligence model, heterogeneous devices can act collectively by exploiting contextual information and reconnaissance that is usually covert in such networks. As shown in [34], ZigBee device networks play an important role and require an easier interaction model with IP-based networks. The authors of this paper presented an open-source platform that integrates ZigBee devices with applications running on smartphones and other devices available in the home network. This makes it easier to manage such a network. With this platform, it can be placed on low-cost devices, such as Plug-PCs, using the OSGi execution environment to detect devices and notify the smart home of newly available services. The basis of the communication stack of most WSNs is the ZigBee protocol, and therefore it is important to know its properties in this area. The majority of network protocols rely on the idea of layers to divide various elements and features into autonomous units. The layers of the ZigBee protocol are based on the ISO/OSI basic reference model. There are seven layers in the ISO/OSI model, but ZigBee has implemented just the layers necessary for low power, low data rate wireless networks. Zigbee is built on the physical layer (PHY) and medium access control (MAC) sublayer defined in IEEE 802.15.4. The NWK (Network) and APL (Application) layers are defined by the ZigBee standard. Thisstandard provides a user-friendly framework for component-based software that supports client applications from multiple sources. The ZigBee network layer creates a mesh network that is able to route data around defective nodes. In our research, a two-tier ZigBee network is tested in different scenarios, simulating different failures triggered at the sensor and router nodes, simulating realistic failure conditions.