An Efficient MOP Decision Method Using Hop Interval for RPL-Based Underwater Sensor Networks

In underwater wireless sensor networks (UWSNs), not only data packets but also sensor nodes can be lost due to ocean current, running out of battery and etc. Among various routing protocols, Routing Protocol for Low Power and Lossy Networks (RPL) is a promising routing protocol to overcome this problem since it provides multiple upward path establishments and path repair methods. However, unlike upward paths, downward routing in RPL have low reliability since it source routing technique for reducing routing table size. In order to increase the reliability of downward paths, RPL standard defines two operational modes (Mode Of oPeration, MOP) for intermediate nodes, i.e., storing mode and non-storing mode. A node which operates in storing mode can increase the reliability, however it cannot be operated in storing mode for the all instances due to the limited memory. In this paper, we therefore propose a hop interval based MOP decision method for intermediate nodes. In our proposed method, the sink calculates the hop interval between storing nodes based on the number of application and each intermediate nodes decide their MOP according to the calculated hop interval. In addition, we propose a QoS-based initial storing node decision scheme to reflect differences between swallow and deep water.