There is increasing demand for wireless sensor networks (WSN) to be able to carry real-time information. However, current WSN technologies are not yet capable of offering quality-of-service (QoS) guarantees, which are required to support these types of applications. Achieving QoS is especially challenging in WSNs due to their multi-hop nature and their processing-power, memory, and energy constraints. In this article, we propose a cross-layer architecture in which the medium access control

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... and routing protocols collaborate to organize nodes into clusters and to achieve a coordinated time-shared access to the transmission medium. The resulting protocol is called QUAlityof-service-capable clusTer-based Time-shared ROuting (QUATTRO)-assisted MAC protocol. Our performance evaluation results show that the protocol overhead observed in terms of configuration time, transmitted control messages, and consumed energy is very reasonable and that not only QoS is achieved but also great energy savings by eliminating collisions and considerably reducing idle listening.