Towards an interoperable Internet of Things through a web of virtual things at the Fog layer

A wide range of Internet of Things devices, platforms and applications have been implemented in the past decade. The variation in platforms, communication protocols and data formats of these systems creates islands of applications. Many organizations are working towards standardizing the technologies used at different layers of communication in these systems. However, interoperability still remains one of the main challenges towards realizing the grand vision of loT. Intergration approaches proven in the existing Internet or enterprise applications are not suitable for the loT, mainly due to the nature of the devices involved; the majority of the devices are resource constrained. To address this problem of interoperability, our work considers various types of IoT application domains, architecture of the loT and the works of standards organizations to give a holistic abstract model of loT. According to this model, there are three computing layers, each with a different level of interoperability needs - technical, syntactic or semantic. This work presents a Web of Virtual Things (WoVT) server that can be deployed at the middle layer of loT (Fog layer) and Cloud to address the problem of interoperability. It exposes a REST like uniform interface for syntactic integration of devices at the bottom layer of loT (perception layer). An additional RESTful api is used for integration with other similar WoVT servers at the Fog or the Cloud layer. The server uses a state of the art architecture to enable this integration pattern and provides means towards semantic interoperability. The analysis and evaluation of the implementation, such as performance, resource utilization and security perspectives, are presented. The simulation results demonstrate that an integrated and scalable loT through the web of virtual things can be realized. (C) 2018 Elsevier B.V. All rights reserved.