In the paper, we propose an energy-efficient communication protocol, called Scheduling-based Low duty cycle Energy Efficient Protocol (SLEEP). The proposed protocol ensures that a node wakes up at specific times and transmits only when the receiving node is awake to receive a message, while ensuring that the channel capacity is fairly distributed among participating nodes. The protocol is simple and general enough to be embedded in any existing protocol stack concerned with energy management of sensor networks. The SLEEP protocol trades off energy efficiency with higher latency of packet delivery. SLEEP is implemented on TinyOS for CC2420 radio stack, and is compared against the existing Low Power Listening (LPL) scheme of the TinyOS stack. The experiment results show tangible improvement in energy consumption. The results further show reduction in medium contention leading to less packet collisions, and thus increased packet delivery ratio.