Abstract—Internet of Things devices will by and large be battery-operated, but existing application protocols have typically not been designed with power-efficiency in mind. In low-power wireless systems, power-efficiency is determined by the ability to maintain a low radio duty cycle: keeping the radio off as much as possible. We present an implementation of the IETF Constrained Application Protocol (CoAP) for the Contiki operating system that leverages the ContikiMAC low-power duty cycling mechanism to provide power efficiency. We experimentally evaluate our low-power CoAP, demonstrating that an existing application layer protocol can be made powerefficient through a generic radio duty cycling mechanism. To the best of our knowledge, our CoAP implementation is the first to provide power-efficient operation through radio duty cycling. Our results question the need for specialized low-power mechanisms at the application layer, instead providing low-power operation only at the radio duty cycling layer. Keywords-Internet of Things; Web of Things; CoAP; embedded Web services; energy; radio duty cycling; I.

As sensor networks move towards general-purpose lowpower wireless networks, there is a need to support both traditional low-data rate traffic and high-throughput transfer. To attain high throughput, existing protocols monopolize the network resources and keep the radio on for all nodes involved in the transfer, leading to poor energy efficiency. This becomes progressively problematic in networks with packet loss, which inevitably occur in any real-world deployment. We present burst forwarding, a generic packet forwarding technique that combines low power consumption with high throughput for multi-purpose wireless networks. Burst forwarding uses radio duty cycling to maintain a low power consumption, recovers efficiently from interference, and inherently supports both single streams and cross-traffic. We experimentally evaluate our mechanism under heavy interference and compare it to PIP, a state-of-the-art sensornet bulk transfer protocol. Burst forwarding gracefully adapts radio duty cycle both to the level of interference and to traffic load, keeping a low and nearly constant energy cost per byte when carrying TCP traffic.

Ease of deployment has always been seen as a major selling point of wireless sensor networks, yet experience has shown deployment to be difficult. We argue that parts of these difficulties have come from the lack of a generic networking layer and of well-tested, generic transport protocols in traditional sensornet deployments. We believe that the use of low-power IPv6 can help by providing nodelevel addressing, point-to-point routing, and generic well-tested transport protocols. We evaluate the performance of HTTP/TCP and CoAP/UDP over a duty cycled radio layer, showing that with a small modification to the duty cycling layer results in a dramatic improvement in performance at a retained low power consumption. Based on our experiences, we introduce an in-network caching mechanism that significantly improves the performance of software updates in incrementally deployed sensor networks. Our results are the first steps towards a deployment tool for IP-based sensor networks. 1.

We make the case for a sensor network model in which each mote stores sensor data locally, and provides a database query interface to the data. Unlike TinyDB and Cougar, in which a sink node provides a database-like front end for filtering the current sensor values from a data collection network, we propose that each sensor device should run its own database system. We present Antelope, a database management system for resource-constrained sensors. Antelope provides a dynamic database system that enables run-time creation and deletion of databases and indexes. Antelope uses energy-efficient indexing techniques that significantly improve the performance of queries. The energy cost of a query that selects 100 tuples is less than the cost of a single packet transmission. Moving forward, we believe that database techniques will be increasingly important in many emerging applications.

Low-power wireless devices must keep their radio transceivers off as much as possible to reach a low power consumption, but must wake up often enough to be able to receive communication from their neighbors. This report describes the ContikiMAC radio duty cycling mechanism, the default radio duty cycling mechanism in Contiki 2.5, which uses a power efficient wake-up mechanism with a set of timing constraints to allow device to keep their transceivers off. With ContikiMAC, nodes can participate in network communication yet keep their radios turned off for roughly 99 % of the time. This report describes the ContikiMAC mechanism, measures the energy consumption of individual ContikiMAC operations, and evaluates the efficiency of the fast sleep and phase-lock optimizations. 1

The Internet of Things requires interoperability and low power consumption, but interoperability and low power consumption have thus far been mutually exclusive. This talk outlines the challenges in attaining low power operation for