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.
The WMSN QoS routing problem can be addressed metaheuristically using multi-objective optimization algorithms, as explained in the following section.