## 2 Background and Related Works
### Related Works  
Substantial research is being conducted with the performance analysis of Zigbee under various constraints, scenarios, and applications. [PERSON] et al. have studied the throughput and latency of the Zigbee WSN under three different topologies and concluded that at 2.4 GHz, operating frequency tree topology achieves the highest throughput whereas the star topology performs with the least latency [17]. However, this study is based just on simulation, and is only focused on the performance of the latency and throughput. [PERSON] et al. conducted a study on the transmission range of the Zigbee communication with the XBee pro 2B module for both indoor and outdoor scenarios [32]. However, they did not consider other performance metrics beyond the transmission range. [PERSON] et al. conducted a performance analysis of Zigbee in various indoor setups to study different network Quality of Service (QoS)-delays, throughput, and packet loss [19]. Even though this study considered LoS and NLoS scenarios for the analysis, the performance with encryption and outdoor scenario was not addressed. [PERSON] et al. conducted a comparative analysis on the Zigbee QoS with three different topologies in an IoT lighting automation network [27], studied the performance of two different routing protocols--ad-hoc on-demand distance vector (AODV) and dynamic source routing (DSR)--and evaluated that star topology with DSR routing performs better in end-to-end delay, throughput, and latency with the trade-off of higher energy consumption. However, this study is based just on a simulation. [PERSON] et al. studied the superframe structure of the MAC sublayer of Zigbee and made a point that the performance of such a low-rate PAN network largely depends on the active portion of the superframe [33]. [PERSON] et al. conducted a study on different Zigbee topologies in the LoS scenario based on the performance in latency, throughput, and packet loss [34]. The study concluded that star topology performs better in short-distance communication, but tree and mesh topology would be necessary for larger network coverage. However, this study did not consider the parameters, such as RSSI and energy consumption, and the study was not compared with the NLoS scenario with data encryption, which would have provided a better understanding of the QoS performances. [PERSON] et al. conducted a study on the performance of two Zigbee-based mesh topologies, Zigbee mesh and Digi mesh, and concluded that Zigbee mesh performs better with time-critical applications due to lower latency and better link quality, but better throughput is achieved with Digi mesh [35]. This study is limited by the lack of different deployment scenarios, indoors and outdoors, where the performance might have varied significantly. Moreover, it did not study the power consumption and performance of encrypted communication, which is needed to reduce the security threat. [PERSON] et al. analyzed different Zigbee topologies with underground deployment by considering throughput, delay, energy consumption, delivery ratio, and packet delivery security [32]. This analysis is based on simulations whereas the real-world performance might vary from the simulated results. [PERSON] worked on a simulation-based performance analysis with Zigbee topologies using the Riverbed simulation [36]. This work analyzed how the network performance changes with the increase in the number of nodes in three different topologies, star, tree, and mesh, and their results showed that the throughput of the mesh topology was higher than that of the tree and star topologies. [PERSON] et al. also used the Riverbed simulator to analyze the performance of different topologies of Zigbee and concluded that cluster tree performs better in scenarios where the larger network coverage is needed [37]. Few other research works on the Zigbee performance analysis are stated in [38; 39; 40]. The discussed research works are summarized in Table 2.