The Internet of Things (IoT) has many important applications in multiple domains that include home automation, smart cites, healthcare, agriculture, and environment. IoT comprises a wide range of sensors and actuators that communicate with each other over cloud, fog and edge level networks. Moreover, these devices use various communication protocols and are made by different manufactures. To deal with these diversities, IoT essentially needs interoperable communication interfaces among devices. Unfortunately, existing interoperability solutions are centralised and use fog or cloud level computing resources, making IoT communications latency-prone and poorly scalable. These issues could be handled effectively, if edge level devices could be made interoperable within the edge level and without needing fog or cloud level access. This paper proposes a decentralized interoperability solution that stays fully within the edge level. The solution relies on controller devices that work on the interface boundaries of the edge devices. Unlike existing solutions, the proposed solution adopts a hierarchical interoperability model to handle interoperability at network, syntactical, semantic, and organizational levels. Our solution is non-proprietary, generic over vendors and platforms, and easily extendable to new devices. We compare our proposed solution with existing interoperability solutions for edge devices and show its mobility, efficiency and flexibility.