The Pareto-optimal sets (POSs) for scenarios 1 and 2 are composed of 5 and 4 optimal solutions respectively (see Fig. 6). The corresponding ETX and end-to-end delay values of all optimal solutions are listed in Table 5. In terms of the multi-objective optimization, two distinct goals should be considered: (1) solutions should be as close as possible to the POS and (2) solutions should be as diverse as possible in the obtained non-dominated set. In terms of the former goal, the set of non-dominated solutions presented were the best among all runs of the SPEA algorithm whose goal was to minimize both objectives (delay and ETX). Fig. 6 shows that solutions from scenario 2 are better distributed across the POS in comparison to those of scenario 1. Despite this, both sets of solutions satisfy the latter goal.