## 8 Simulation Assessment
### Results and Discussion
Figure 20: Average consumed energy for the allocation schemes: (**a**) Unconditioned Scenario; (**b**) Conditioned Scenario. As it can be observed, the average end-to-end communication delay is significantly smaller when considering the reduction of the beacon interval, according to the reasoning previously presented in Section 4.1. In fact, a shorter beacon interval always corresponds to shorter end-to-end communication delays. It is clear that there is a significant improvement of the end-to-end communication delay for the SOA-SDA allocation scheme, compared to the case with longer beacon interval. This behaviour is due to the fact that considering a shorter beacon interval, messages can be dispatched in a shorter time interval, decreasing network congestion and message discards. However, the energy consumption will increase, due to the higher activation rate of the sensor nodes. Figure 23 illustrates the average total energy consumption for the allocation schemes, considering both unconditioned and conditioned allocation schemes with a shorter beacon interval. It can be concluded that, for the case of shorter beacon intervals, the Load-SDA, Nodes-SDA and SOA-SDA schemes have a better performance when compared to the STD-SDA schemes (similar energy consumption, but significantly smaller end-to-end communication delays). Finally, in order to highlight the differences between Load-SDA and Nodes-SDA allocation schemes, Figure 24 illustrates the superframe duration configuration (in terms of superframe order, respecting Equation (5)) provided by the Load-SDA allocation scheme, while Figure 25 illustrates the superframe duration configuration provided by the Nodes-SDA scheme for the same cluster-tree network, considering a conditioned scenario. Figure 23: Average consumed energy for the allocation schemes with a shorter beacon interval: (**a**) Unconditioned Scenario; (**b**) Conditioned Scenario. Figure 14:0 Average end-to-end delay for the monitoring traffic with a shorter beacon interval: (**a**) Unconditioned Scenario; (**b**) Conditioned Scenario. Figure 24 highlights that the Load-SDA scheme allocates higher values of Superframe Order for cluster-heads located in the high load zone, and lower values for cluster-heads located in the low load zone. On the other hand, the Nodes-SDA scheme allocates proportional values of Superframe Order for cluster-heads of the same depth (Figure 25), regardless of being located in low load or high load zone. Note that, as the Nodes-SDA scheme does not consider the load imposed by descendant nodes (it considers only the number of nodes), this allocation scheme may over-allocate superframe durations for cluster-heads. Importantly, this behaviour was observed for all the simulation scenarios. Table 8 presents the average superframe order values (per depth) defined by the Load-SDA and Nodes-SDA allocation schemes, for both high load and low load zones of the conditioned cluster-tree. In general, the Nodes-SDA scheme allocates similar superframe durations (in terms of the superframe order parameter) for cluster-heads of same depth for both zones, showing that the difference of message loads does not interfere in its allocation mechanism. In turn, the Load-SDA scheme allocates highest superframe duration values for cluster-heads located in the high load zone, while that cluster-heads located in the low load zone receive lower superframe duration values. Figure 14:1 An example of Superframe Order configuration for all cluster-heads, using Load-SDA scheme (conditioned Scenario). Figure 14:2 An example of Superframe Order configuration for all cluster-heads, using Nodes-SDA scheme (conditioned Scenario). From this simulation assessment, it can be concluded that proportional SDA schemes can adequately allocate the required communication resources for cluster-heads (active communication periods and buffer sizes), avoiding traditional problems that occur in cluster-tree networks, such as: network congestion, high end-to-end communication delays and discarded messages due to buffer overflows.