High-level states with CoAP: Giving meaning to raw sensor values to support IoT applications

The number of sensors pervading our everyday life, e.g., in smartphones, cars, and buildings, is constantly increasing. These sensors, which are typically embedded into resource constrained devices such as sensor nodes or smartphones, allow measuring the state of the entities they observe or are attached to. If this information is accessible via the Internet, they contribute to the Internet of Things (IoT), where real-world objects have virtual representations. The standardization process to have a complete and efficient communication protocol stack for these constrained devices is in full swing. The Constrained Application Protocol (CoAP) on the application layer allows retrieving data from devices (e.g., metadata) and its sensors (e.g., sensor measurements). This information can be used in a variety of new real-time real-world applications. However, sometimes it is sufficient and desirable not to communicate raw sensor readings but abstractions, i.e., high-level states of the observed entities. Furthermore, as resource constrained devices will be accessible by everyone on the Internet, mechanism to reduce energy consumption play a key role. This paper presents a new option for CoAP which contributes to these two requirements as it allows the creation of high-level states from raw sensor readings. We show that the option can reduce the number of messages when observing a sensor resource which can substantially decrease energy consumption and thus increase device lifetime.