CoAP-XED: Enabling Relaxed Requests to IoT Sensing Resources

In the context of the Internet of Things (IoT), a new service model has emerged, namely, the Sensing as a Service (S²aaS). In such model, sensing data is available for external users as resources, and can be provided on demand, as services. Typically, the devices providing sensing resources are powered by batteries, thus the lifetime of devices becomes a concern to IoT service providers. A common strategy to reduce the number of tasks to be performed by the devices, thus saving energy, is caching data, reusing a prior response message to satisfy a current request. However, on the side of IoT service consumers, the freshness of the data is also a critical concern. That is, the time elapsed since the data is collected until it is delivered to the requesting user should be small. In high workload scenarios, addressing both lifetime and data freshness requirements may be challenging, mainly because commonly used application protocols, such as the Constrained Application Protocol (CoAP), only allow specifying the data freshness requirement in a strict way. This paper introduces an extension to CoAP, namely, CoAP-XED, aiming at supporting the relaxation of requests to sensing resources. Simulation results show that our approach supports maximizing the lifetime of devices and, at the same time, fulfill data freshness requirements.