On adaptive timers for improved RPL operation in low-power and lossy sensor networks

In this paper, we propose two adaptive algorithms to control Destination Advertisement Option (DAO) packet emissions in RPL non-storing mode: a centralized, or controlled by the DAG root, and a distributed. We propose new mechanisms to derive the most appropriate value for the DelayDAO Timer, a timer that determines how long a node should wait before transmitting its destination advertisement packet to the DAG root or collection point. We also propose similar mechanism for RPL-storing mode by implementing multiple destination aggregation in a single DAO packet. We show that instead of using a fixed universal timer to control DAO emissions, as recommended in the IETF standard, the use of an adaptive timer at each node allows the network to quickly adjust to topological changes. This is aimed at reducing congestion and packet drops, specially near the DAG root, which also impacts memory and buffer requirements, as well as data delivery delay. This is crucial for networks such as Urban LLNs or Smart Grid AMI networks, whose nodes have very limited resources with regards to energy and buffer space. We show how the proposed mechanisms outperform the default method in RPL with regards to these metrics.