## 8 Simulation Assessment
### Results and Discussion
Considering that the beacon interval parameter can directly influence the behaviour of the network (refer to Section 4.1), we have  
Figure 16: Average message discard rate (per depth) due to buffer overflows for the SOA-SDA scheme: (a) Unconditioned Scenario; (b) Conditioned Scenario. Figure 17: Message loss rate for the SDA schemes: (a) Unconditioned Scenario; (b) Conditioned Scenario. assessed the different possibilities for the BI adjustment and its impact upon the network behaviour (end-to-end message delays and energy consumption of the nodes). As previously mentioned, the SOA-SDA allocation scheme was constrained to the use of a single beacon interval for all the clusters. Nevertheless, this would be the expected parameter settings for the case where all the supported traffic has the same periodicity. Firstly, we have considered the case where the beacon interval is set to a value close to the shorter message period (longer beacon interval). Figure 18 illustrates both the beacon interval and the average sum of superframe durations defined for each of the allocation schemes (absolute average values and the percentage of the sum of superframe durations regarding to BI). Figure 19 illustrates the average end-to-end communication delay for a network with longer beacon Interval. It can be observed that end-to-end delays for the SOA-SDA and STD-SDA schemes are remarkably higher than for the case of the Load-SDA and Nodes-SDA schemes. The main reason is that, as the network is congested, messages are remaining more time in the internal buffers of cluster-heads. Therefore, message transfers require more beacon intervals to be forwarded, increasing their end-to-end communication delays. As the network, with the proposed Load-SDA and Nodes-SDA allocation schemes, does not face any congestion, messages can flow along the tree until the sink node, being their end-to-end communication delays slightly smaller than the beacon interval. Figure 19: Average end-to-end communication delay for a network with a longer Beacon Interval in the: (**a**) Unconditioned Scenario; (**b**) Conditioned Scenario. Figure 18: Beacon Interval and average sum of superframe durations for a network with a longer beacon interval in the: (**a**) Unconditioned Scenario; (**b**) Conditioned Scenario. Figure 20 illustrates the average total energy consumption for a network with longer Beacon Interval. The energy consumption is mainly related to two factors: the time interval during which the nodes remain active, and the activities performed by them. As the active period (sum of superframe durations) of SOA-SDA is smaller than for Load-SDA scheme, it has a slightly better performance. Note also that, the average energy consumption for the Nodes-SDA scheme is larger than for both the Load-SDA and SOA-SDA schemes, considering both scenarios. In what concerns the STD-SDA allocation scheme, it is important to highlight that the energy consumption is proportional to the number of non-discarded messages. Therefore, as there is a large number of messages being discarded due to buffer overflows, there is a consequent reduction of the energy consumption of the overall network. Figure 21 illustrates the beacon intervals and the average sum of superframe durations defined for each of the allocation schemes, considering the shorter beacon interval (absolute average values and percentage of the sum of superframe durations regarding to BI). In this case, the adjustment of the beacon interval was performed for all allocation schemes (except for the Nodes-SDA scheme), being that the SOA-SDA scheme had the smaller average beacon interval. For the Nodes-SDA scheme, if the beacon interval (in terms of beacon order) is decreased, the protocol constraint would no longer be respected. Figure 22 shows the average end-to-end communication delay for a network with a shorter BI. Figure 21: Average sum of superframe durations and beacon interval for the allocation schemes with adjustment of BI: (**a**) Unconditioned Scenario; (**b**) Conditioned Scenario.