Wireless Sensor Networks (WSNs) are generally energy and resource constrained. As the traffic pattern in most WSN applications is from sensor-to-sink, in-network data aggregation methods are employed for effective utilization of available resources. As aggregated data packets contain correlated information, a significant amount of information is lost if a data packet is lost. In order to reliably transfer the aggregated data packets, there arises a need for data transport protocols that provide reliability at the packet level. Existing protocols that provide reliable data transfer for sensor-to-sink traffic either provide reliability at the event level or are not energy efficient. By employing duty cycles, energy-efficiency can be improved but it degrades the network performance in terms of latency. To provide energy-efficiency while enhancing the packet level reliability, we propose an energy-efficient reliable data transfer protocol. This protocol provides packet level reliability by extending the concept of monitors and improves the energy-efficiency by employing duty cycles. To further reduce the energy consumption and congestion in the network, only a subset of nodes is chosen as active nodes to transfer the data. We implemented our protocol using the NS2 simulator for evaluating its performance. Results show that our protocol has significant improvement in packet delivery ratio and energy savings.
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