Magnet: Robust and Efficient Collection through Control and Data Plane Integration

Despite being a core networking primitive, collection protocols today often suffer from poor reliability (e.g., 70%) in practice, and heavily used protocols have never been evaluated in terms of communication efficiency. Using detailed experimental studies, we describe three challenges that cause existing collection protocols to have poor reliability and waste energy: inaccuracies in link estimation, link dynamics, and transient loops. In this paper we present Magnet, a robust, efficient, and hardware-independent collection protocol. Magnet uses three novel techniques to address these challenges. Magnet’s link estimator addresses the inaccuracies in link estimation by using feedback from both the data and control planes, using information from multiple layers through narrow, platform-independent interfaces. Second, Magnet addresses link dynamics by using the Trickle algorithm for control traffic, sending few beacons in stable topologies yet quickly adapting to changes. Finally, Magnet addresses transient loops by using data traffic as active topology probes, quickly discovering and fixing routing failures. Magnet runs on six different mote platforms and we have tested it on four testbeds. In most experiments, Magnet achieves 99% reliability, and in some cases 99.9%. In the most challenging testbed, the state-of-the-art collection protocol today (MultiHopLQI) achieves 70% reliability: Magnet achieves 97%. Magnet achieves this ten-fold reduction in dropped packets with 25% fewer transmissions. Magnet works seamlessly on top of existing low-power MAC layers. Together, these results suggest that Magnet can be the robust, efficient collection layer that so many sensor network applications and protocols need.