Edinburgh Napier University

  An examination of existing studies in the area of Routing Protocol for Low-Power and Lossy Networks (RPL) implementation in wireless sensor networks (WSNs) reveals a consistent approach taken of optimal node distribution. This in order to best evaluate networking metrics such as Packet Delivery Ratio (PDR), latency and energy consumption. The tests detailed in this paper differ from previous work, in that there is no concerted effort to ensure the appropriate density of the network topologies. The intention being to `strain' the limits of the transmission ranges. Using the Cooja simulator, we take the approach of utilising nodes in less-than perfect, real-world scenarios. In this way the main factor at play is the ability to retain nodes as part of the Destination Oriented Directed Acyclic Graph (DODAG) build in environments with `strained' transmission ranges. In this regard we compare Objective Function Zero (OF0) Hop-count with The Minimum Rank with Hysteresis Objective Function (MRHOF) Energy and expected transmission count (ETX) metrics. In utilising the energy metric, a novel approach, we prove that it is ineffective in this scenario. Resultantly, the ETX metric outperforms Hop-count, producing results that improve over time, adjusting to `strained' environments to include more motes in the DODAG build as time passes. In conclusion, we propose future work to develop an extension to Cooja to utilise the ETX metric with an Energy constraint. This in order to better evaluate the use of node energy levels as part of a DODAG build in `strained' WSN implementations in the future.