Efficient Scheduling, Caching, and Merging of Notifications to Save Message Costs in IoT Networks Using CoAP

Internet-of-Things (IoT) devices are widely deployed and many of them have limited capabilities. Constrained application protocol (CoAP) is developed to integrate such devices into the Web environment. Specifically, client devices register their interested data with IoT devices, which will keep notifying them of the status of sensing data. However, client devices have different demands in terms of minimum and maximum periods to receive notifications, whereas IoT devices usually offer notifications at regular intervals. Some IoT devices would send many more notifications than necessary, which wastes bandwidth and energy. To conquer this problem, this article proposes a group-based message management (GMM) framework for CoAP proxies to efficiently coordinate the sending of notifications from IoT devices and forward them to client devices. GMM curtails superfluous notifications by three modules. The scheduling module groups client devices based on their demands and finds an optimal observation period for each group. The caching module adjusts the max-age value to allow a proxy reusing its cached notifications to answer requests. The merging module combines the notifications originated from different IoT devices queried by the same client device so as to save bandwidth. The simulation results show that GMM not only reduces unnecessary notifications but also conserves the energy of devices.