Achieving Hard Reliability in RPL for Mission-Critical IoT Applications

Routing Protocol for Low Power and Lossy Networks (RPL) is the de-facto routing standard for Internet of Things (IoT) applications. MRHOF and OF0 are the two standardized objective functions (OFs) in RPL for selecting optimal paths. However, the existing approaches are not suitable for Mission-Critical IoT (MC-IoT) applications. Strict reliability requirement is one of the significant challenges in such applications. Standard RPL and its different variants cannot provide strict reliability requirement. Therefore, this paper proposes a new OF and extends the default RPL to reliable multi-path RPL (RMP-RPL) based on the proposed OF. In RMP-RPL, each node forwards its data packet to k number of parents which are selected using the proposed OF and its strict reliability requirement. The OF calculates path cost of each potential parents based on three routing metrics: node mobility, alternative parent connectivity, and expected transmission count. Alternative parent connectivity is a new metric proposed in this work to select parents with more alternative parents, and thus, increases the reliability. RMP-RPL proves to be suitable for MC-IoT applications by producing results greater than 99% packet delivery ratio. In addition, it shows improved performance in terms of end-to-end delay and control packet overhead compared to the benchmark schemes.