# Modeling and Fault Tolerance Analysis of ZigBee Protocol in IoT Networks
## 2 Previous Works
As the authors note, a drawback of the REDE system is that it does not have any fault-tolerance mechanism, which is essential in unsafe environments where connectivity and node failure is widespread. In [20], the authors investigated a fault-tolerant IoT and ML-based natural disaster detection and forecasting system called SENDI (system for detecting and forecasting natural disasters). The system was modeled and tested to be fault-tolerant and to maintain its ability to continue performing its planned functionality. The implementation was based on 6 LoWPAN standard modules and many classical routing mechanisms. However, there is a significant lack of analysis of another important protocol often indicated as the first choice protocol which is the ZigBee protocol. Zigbee is a wireless communication standard designed as an open global standard to satisfy the inimitable demands of low-cost, low-power wireless IoT networks. This standard is also based on the IEEE 802.15.4 physical radio definition and supports use in unlicensed frequency ranges, including 2.4 GHz, 900 MHz, and 868 MHz. The 802.15.4 standard underlying the Zigbee specification was approved by the IEEE in 2003. This standard provides a packet-based wireless protocol for cost-effective, battery-powered equipment. Thus, it enables nodes to be capable of transmitting over a wide diversity of network topologies, the protocol enables devices to communicate over a wide range of network topologies, and the battery life can last for several years [21]. The authors of [22] have shown that in WSN, limited energy resources for communication are a critical element. In order to achieve better WSN communication, appropriate schemes must be selected to describe the energy level and reliability of the system. In real-time low-latency industrial applications, one way to improve network reliability is scheduling. Next to routing, it is one of the most important problems to be solved. The authors of [23] proposed centralized scheduling algorithms for time slot channel hopping (TSCH) networks for real-time industrial applications, but they have some drawbacks such as schedulability and large data traffic. In work [24], the author shows that a resource-limited, single centralized ZigBee network cannot be deployed in very large-scale applications. To solve this problem, he presents a design strategy for a ZigBee network that can be centralized and decentralized, and distributed over a wide area. The author defines two types of network structure: independent mobile network and multi-scale multipoint network. Authors in [25] present a new real-time monitoring system for photovoltaic (PV) generation. This system allows remote monitoring of photovoltaic systems based on multi-node network communication based on the ZigBee protocol. Furthermore, in [26; 27], for intelligent remote control of maximum power point tracking and low power consumption, ZigBee modules were integrated into the PV inverter side. The experiments conducted confirmed the high usability and excellent real-time performance through the communication module and cloud server. In contrast, the work in [28] presents a wireless monitoring system by using Bluetooth to measure and collect data of the generated power. As the authors stated, Bluetooth is an open short-range wireless standard, but it has high latency and power consumption in large-scale networks. The IoT environment is highly heterogeneous in terms of hardware, software, functionality, observability, administrability, network, and communication models. As pointed out in the paper [29], network protocols are different from wired, Wi-Fi, Blue-tooth, Z-wave, or Zigbee and have their own characteristics. This involves extended capabilities in terms of means of observation, but also variability in the uncertainty of error detection. There may be many communication models implemented within the same application, such as message passing, publish-subscribe, or synchronous function calls.