RPL-based routing protocols for multi-sink wireless sensor networks

Recent studies demonstrate that the performance of a wireless sensor network (WSN) can be improved by deploying multiple sinks in the network. Therefore, in this paper we present different routing protocols for multi-sink WSNs based on the routing protocol for low-power and lossy networks (RPL). Our protocols use different routing metrics and objective functions (OFs). We use the available bandwidth, delay, MAC layer queue occupancy, and expected transmission count (ETX) as the tie-breaking metrics in conjunction with the shortest hop-count metric. Our OFs use the tie-breaking metrics on a greedy or end-to-end basis. Our simulation results demonstrate that the protocols based on the delay, buffer occupancy, and ETX metrics demonstrate best performance, increasing the packet delivery ratio by up to 25% and decreasing the number of retransmissions by up to 65%, compared to a version of the RPL protocol that only uses the hop-count metric. Another key insight is that, using the tie-breaking metrics on a greedy basis demonstrates a slight performance improvement compared to using the metrics on an end-to-end basis. Finally, our results also demonstrate that multiple sinks inside a WSN improve the RPL-based protocol performance.