Trust-based Neighbor Unreachability Detection for RPL

The IETF ROLL working group developed Routing Protocol for Low Power and Lossy Networks (RPL) for packet routing within Low power and Lossy Networks (LLNs) formed by resource constrained devices. RPL handles LLN issues such as unreachable parent and routing loops by triggering reconstruction of routing tree. For unreachable neighbor detection, RPL requires an external mechanism with very low communication overhead. This rules out the use of proactive mechanisms that employ keep-alive messages. Instead, RPL suggests to use IPv6 Neighbor Unreachability Detection (NUD), which is a reactive mechanism maintaining timers that trigger control messages. However, due to the use of fixed timeout intervals, NUD suffers from frequent premature timeouts and the communication overhead of NUD is still substantial. We propose a cross layer trust-based NUD mechanism, which adapts its timeout intervals based on network traffic without the need for explicit coordination among nodes. The proposed mechanism takes advantage of overhearing at the link layer and uses the statistics about packets that are not sent to the node itself, i.e. that would otherwise be discarded. Our evaluation shows that the proposed mechanism decreases the number of control messages significantly, while the packet delivery rate remains comparable to classical NUD.