Wireless Sensor Networks (WSNs) have revolutionised the design of emerging embedded systems and triggered a new set of potential applications. A WSN is typically composed of a large set of nodes scattered in a controlled environment and interacting with the physical world. This set aims at the collection of specified data needed for the monitoring/control of a predefined area/region. The delivery of sensory data for process and analysis, usually to a control station (also referred as sink), is based on the collaborative work of the WSN nodes in a multi-hop fashion (Fig. 2.1).