  Wireless sensor networks are conceived to monitor a certain application or
physical phenomena and are supposed to function for several years without any
human intervention for maintenance. Thus, the main issue in sensor networks is
often to extend the lifetime of the network by reducing energy consumption. On
the other hand, some applications have high priority traffic that needs to be
transferred within a bounded end-to-end delay while maintaining an energy
efficient behavior. We propose MaCARI, a time segmentation protocol that saves
energy, improves the overall performance of the network and enables quality of
service in terms of guaranteed access to the medium and end-to-end delays. This
time segmentation is achieved by synchronizing the activity of nodes using a
tree-based beacon propagation and allocating activity periods for each cluster
of nodes. The tree-based topology is inspired from the cluster-tree proposed by
the ZigBee standard. The efficiency of our protocol is proven analytically, by
simulation and through real testbed measurements.
