Design and evaluation of routing metric for RPL routing protocol in WSN based on queue backlogs

Abstract

The current de-facto routing protocol over Low Power and Lossy Networks is developed by IETF Working Group (ROLL), and named as Routing Protocol for Low Power and Lossy networks (RPL). RPL in the network layer faces throughput challenges due to the potential large networks, number of nodes and multiple coexisting applications will be running in the same physical layer. In this study, a node metric for RPL protocol based on the node's Queue Backlogs is introduced, which leads to a better throughput performance while maintaining the delay and the ability to use with different network applications. This metric depends on the length of Packet Queue of the nodes with the consideration of other link and node metrics, like ETX or energy usage, leading to better load balancing in the network. To implement and evaluate the proposed metric compared to other RPL metrics, ContikiOS and COOJA simulator were used. Extensive simulations had been carried out in a systematic way resulting in a detailed analysis of the introduced metric namely W-metric, Expected Transmission Count (ETX) and Objective Function Zero (OF0) that uses hop-count as a routing metric. The analysis and comparison were based on five performance parameters, which are throughput, Packet Delivery Ratio (PDR), latency, average queue length, and power consumption. Simulation results show that the introduced W-metric has a good performance compared to other RPL metrics with regards to performance parameters mentioned above. At the same time, the results show that its latency performance is comparable with other RPL routing metrics. In a sample simulation of 500 seconds with 25 nodes and with nodes sending packets periodically to the network root at a rate of 1 packet per 4 seconds, W-metric shows a very efficient Throughput of 5.16 kbps an increase by 8.2% compared to ETX. Results show that it has a packet delivery ratio of 93.3%, which is higher as compared to 83.3% for ETX and 74.2% for OF0. Average queue length 0.48 packet shows improvement of 15.8% better than ETX. In addition, it exhibits an energy consumption of 5.16 mW, which is 2.1% less than ETX. In overall, W-metric appears to be a promising alternative to ETX and OF0 as it selects routes that are more efficient by working on load balancing of the network and by considering the link characteristics.