## 2 Mechanisms of Initiating Device Communication  
To improve the comprehension of the communication complexities in the current IoT systems, we categorize the different methods through which a device can initiate communication. We identified three approaches, illustrated using sequence diagrams in Figure 2.  
* Cyclical communication relies on a time-based scheduling. Energy consumption is determined by the time frame. Depending on the primary optimization factor, which may include battery levels, sensor thresholds, time of the day, seasonality, and network activity, the period can be fixed or variable to accommodate application constraints related to process reactivity or energy consumption. * Event-based communication is triggered by either an external event, typically a sensor reading or data processing (e.g., temperature alert) or by hardware interruption generated by a process event (e.g., shock or body fall). Energy consumption is strongly influenced by the frequency of events, which can be roughly estimated according to previous occurrences and process variability. Reactivity reaches a peak as information transmission is solely dependent on the speed of data processing. * On-demand communication is initiated by a stimulus from an external process or device using a wireless wake-up mechanism, regardless of the device's ongoing task. Energy consumption is determined by the frequency of the stimulus, so it is mandated by external processes. The device's communication activity is driven by the external processes based on on-demand requests (e.g., for commissioning or sensing). Reactivity is entirely independent of process variability and solely dependent on external requests. Considering the wide variety of communication initiation mechanisms between the devices, edge-cloud components, and systems used in IoT communication architectures, we propose the following classification of these mechanisms, which is supported by three major principles: cyclical, event-based, and on-demand principles. The communication mode of a device can be analyzed and decomposed using these three mechanisms, either exclusively with one of the three or according to a combination, as presented in Figure 3. This classification helps to identify how the device interacts at the communication level with higher layers or other devices in the IoT architecture and how the communication process can be improved on the device to change latency, reactivity, and energy consumption to create a sustainable approach. Figure 2: Sequence diagrams of three identified communication initiation mechanisms. The trigger modes reference diagram can also be used to compare different device communication profiles. For instance, 80% of a device's communications can be event-based, whereas the remaining 20% can be used for either cyclical neighborhood detection or scheduled data upload (Figure 3(a)). The presence of event-driven communication increases reactivity at the cost of probabilistic energy consumption. Conversely, communication has fixed reactivity and deterministic energy consumption. The lack of on-demand communication means that the process cannot request data or wake up the device without relying on cyclical scheduling or probabilistic events. It also means that the energy consumption of the communication is not managed. In contrast, conventional radio frequency identification (RFID) devices fully perform on-demand communication activity (Figure 3(b)) and cannot initiate any communication on their own, relying entirely on the reader and having entirely managed energy consumption. Overall, the diagram in Figure 3 illustrates the impact of each initiation mechanism on the device's reactivity and energy consumption in the present application. The occupied area in each third of the graph represents this impact. Currently, the industry is mostly dominated by cyclical-based communication devices and applications.