Observing CoAP groups efficiently

It is envisioned that by the year 2020 the Internet will contain more than 50 billion devices, among which the majority of them will have constraints in terms of memory, processing power or energy. As a consequence, they are often unable to run current standard Internet protocols, requiring special, optimized protocols. A number of these protocols, covering the different layers of the protocol stack, have been developed and standardized lately. At the application level, the Constrained Application Protocol (CoAP) is proposed by the IETF as an HTTP replacement that is suitable for constrained devices. CoAP is a very light-weight base protocol that can be extended with optional specifications to satisfy specific use case needs. Two important optional specifications are observe, allowing monitoring of a CoAP resource over a period of time, and group communication, supporting interactions with multiple CoAP devices at once. Currently, these two optional specifications do not work together, i.e., it is not possible to gain the benefits of both of them at the same time. In this paper we present an alternative and novel approach to CoAP group communication that works well with the CoAP observe extension. In addition, it enables to perform operations on the observed results, bringing intelligence closer to the data sources.