The Internet of Things vision foresees billions of devices to connect the physical world to the digital world. Sensing applications such as structural health monitoring, surveillance or smart buildings employ multi-hop wireless networks with high density to attain sufficient area coverage. Such applications need networking stacks and routing protocols that can scale with network size and density while remaining energy-efficient and lightweight. To this end, the IETF RoLL working group has designed the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL). This paper discusses the problems of link quality estimation and neighbor management policies when it comes to handling high densities. We implement and evaluate different neighbor management policies and link probing techniques in Contiki's RPL implementation. We report on our experience with a 100-node testbed with average 40-degree density. We show the sensitivity of high density routing with respect to cache sizes and routing metric initialization. Finally, we devise guidelines for design and implementation of density-scalable routing protocols.
Abstract. Sensor networks are gradually moving towards full-IPv6 architectures and play an important role in the upcoming Internet of Things. Some mission-critical applications of sensor networks will require a level of reliability that excludes the presence of single points of failure, as it is often the case today for the gateways connecting sensor networks to the Internet. In this paper, we introduce RPL-6LBR, a 6LoWPAN border router that addresses mission-critical deployments through redundancy. The paper discusses how existing standards may be leveraged to enable redundant border router synchronization, while identifying certain of their shortcomings. We also propose innovative network architectures incorporating multiple border routers, which deal with redundancy and node mobility without requiring any synchronization among the border routers. We implement the proposed RPL-6LBR in the Contiki operating system and report on this implementation through trials on a small-scale testbed and simulator. Our results open new possibilities for real-world wireless sensor networks requiring reliable border routers, and guide further standardization efforts in emerging technologies in support of the Internet of Things.
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