Caching IoT Resources in Green Brokers at the Application Layer

In this paper, we propose to cache popular Internet of Things (IoT) resources in the brokers (which can be considered as application layer middlewares) by applying the CoAP Publish/Subscribe protocol in order to reduce the energy consumption of the servers (e.g., IoT devices), which host these resources. If an IoT resource is cached in a broker, all the requests to retrieve the content of the IoT resource will be delivered to the broker, which responses to the requests by sending related contents, thus increasing the power consumption of the broker. In order to reduce the operational expenditure of the broker provider, each broker is powered by green energy and uses on-grid energy as a backup. On-gird energy consumption of the brokers may be different. That is, some brokers with low green energy generation and more cached IoT resources may consume more on-grid energy consumption than brokers with high green energy generation and less cached IoT resources. In order to minimize the total on-grid energy consumption of the brokers, the Green Energy Aware Resource caching (GEAR) algorithm is proposed to balance energy demands by re-allocating/re-caching the popular IoT resources among the brokers. The performance of GEAR is validated via simulations.