Increasing interests in real-time applications involving delay and loss critical data, routing protocols that consider QoS have become more important for Wireless Sensor Networks (WSNs). Moreover, these applications may also have to deliver non-critical periodic data packets and thus, the mixture of periodic and aperiodic traffic types imposes new challenges in designing communication protocols for WSNs. Our endeavor in this work is to address the QoS provisioning challenges in large-scale WSNs.