Each optimal path can possibly satisfy a particular QoS constraint not yet satisfied by any other path. QoS routing guarantees finding a path that satisfies the QoS constraints if it exists, by considering all QoS optimal paths. The number of optimal paths can grow exponentially with respect to the network size [19].
The WMSN QoS routing problem can be addressed meta-heuristically using multi-objective optimization algorithms, as explained in the following section.