A hybrid routing protocol for wireless sensor networks with mobile sinks

Low power and lossy networks have been an active area of research due to their large number of potential applications in different environments like health, environment monitoring and entertainment domain. Numbers of protocols have been proposed for routing in these networks using metrics like hop count, delay, bandwidth etc. The working group of IETF has done one major contribution in form of a proactive gradient based routing protocol for low power and lossy networks (RPL). However, for a network having few mobile sinks calculating gradients using proactive approach is costly in terms of energy. This paper proposes a hybrid routing protocol for wireless sensor networks with mobile sinks. It proposes a combination of reactive and proactive approach to enhance RPL for efficiently handling movement of multiple sinks. DAGs are only maintained by nodes close to the sink within a certain zone. While the nodes outside the zone use on demand sink discovery to find the closest possible sink, without maintaining DAG. The frequency of zone creation messages and zone sizes can increase or decrease depending on the speed of sink. This helps to decrease the number of retransmissions resulting in low standing cost for maintain DAGs and enhances the network life time especially under average or high mobility of sink.