CA-RPL-QM: A Lightweight Congestion-Aware Objective Function for RPL using Link Quality and Queue Threshold Monitoring

RPL is the main IPv6 routing protocol for low power and lossy networks. These networks go under the name LLNs. It suffers from a serious problem. The default objective functions remain oblivious to congestion. They keep choosing parents through links that appear of high quality. For example, they prefer low ETX values. This is even if those parents are suffering from heavy overload. The result is a full performance breakdown. Buffer overflows are the cause. Packet loss follows. Delay spikes come in strong. Energy goes to waste too. Here, we present CA-RPL-QM. It is an lightweight objective function. It remains fully compatible with standards. This setting solves the problem. It does so by building on the parent selection. A basic additive score is used. It mixes the link quality from ETX. It adds the real time queue use, too. The key aspect lies in diffusing congestion information. It uses the usual DAG Metric Container for this. Queue triggered Trickle reset is of help. It speeds up the change in network conditions. The overhead remains low. Compatibility remains high. Tests ran in Contiki-NG and Cooja. CA-RPL-QM increases packet delivery ratio by up to 37%. It decreases end-to-end delay by twenty-nine percent. Energy consumption drops by 21%. Control overhead increases by mere 5.8%. The approach seems practical. It avoids complex states. No new packet types show up. It is easy to port into current RPL deployments.