Efficient Proxying of CoAP Observe with Quality of Service Support

The Observing Resources extension of the Constrained Application Protocol (CoAP) is expected to play a major role in future Internet of Things (IoT) applications, since it enables asynchronous monitoring of IoT resources in an efficient manner. As the number of IoT applications will grow, solutions are needed to manage multiple observe relationships for the same resource, especially if hosted by a constrained IoT device. The problem is further exacerbated since multiple observers may have heterogeneous Quality of Service (QoS) requirements on the minimum and maximum frequency with which to receive notifications, while the resource-constrained server may only be able to provide notifications with one fixed period for all. In this work, we propose an efficient solution to support multiple CoAP observers with QoS requirements. In particular, we formulate the problem of finding the notification period which minimizes the amount of messages sent by the server, so as to reduce energy consumption of IoT devices and congestion in constrained networks, while ensuring all observers' requirements are met. We then propose an algorithm, named Observation Period Selection (OPS), which is proved to find the optimal solution to this problem. OPS is also evaluated experimentally to analyze its effectiveness in some simple scenarios.