Reliable and Delay Efficient Multi-Path 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. It has been designed to work with resource-constrained devices in constrained environment. In RPL, objective functions (OFs) play the role of selecting optimal paths. However, the existing OFs are not suitable for Mission Critical IoT (MC-IoT) applications. MC-IoT applications expect that the data should reach the destination within a strict deadline. So, reliability and delay are the two significant requirements in such type of applications. An existing work RMP-RPL achieves the hard reliability requirement for MC-IoT applications. However, it did not consider the delay requirement. Also, it was not tested for different traffic rates. Therefore, this paper proposes a reliable and delay-efficient multi-path RPL (RDMP-RPL) that optimizes both reliability and delay. It considers buffer and channel loss probabilities while calculating reliability. For delay calculation, it considers queueing and link delays. In addition, the protocol presents a method to select backup parents to meet end-to-end delay requirements. The results demonstrate that RDMP-RPL maintains a packet delivery ratio (PDR) of at least 99% and at most one second end-to-end delay (EED) considering a maximum of 5 hops for a packet to reach the destination from any of the source nodes for grid topology. But, for random topology, the number of hops can exceed 5. RDMP-RPL cannot achieve the strict requirements in situations where traffic rate, mobility and number of nodes cross a specific threshold. However, it outperforms other benchmark protocols by a significant margin.