Nowadays WSNs support applications such as target tracking, environmental control or vehicles traffic monitoring. Generally, these applications have strong and strict requirements for end-to-end delaying and loosing during data transmissions. In this paper, we propose a practical scenario for application of the WSN field in order to illustrate selection of an appropriate approach for guaranteeing performance in a WSN-deployed application. The methodology we have used includes four major phases: 1) Requirements analysis of the application scenario; 2) QoS modelling in different layers of the communications protocol stack and selection of more suitable QoS protocols and mechanisms; 3) Definition of a simulation model based on an application scenario, to which we applied the protocols and mechanisms selected in phase 2; 4) Validation of decisions by means of simulation; and 5) analysis of results. This work has being partially developed in the framework of the CRISAL - M0700204174 project (partially funded by “Universidad Politécnica de Madrid” and “Comunidad de Madrid”, Spain).