Smart city offers a concept of interconnection of modern digital technologies in the context of a city that provides a solution to enhance the quality and performance of urban services. However, interconnection of the Smart city systems still is a challenging process due to incompatibility of systems that apply a plenty of appropriate technical solutions and protocols that cause collaboration between automation devices such as sensors, actuators, controllers. Introduction of Internet-of-Things (IoT) provides promising opportunities to develop new services and integrate different application domains. The Arrowhead Framework aims to apply Service Oriented Architecture to the embedded systems' world. This research is focused on the one of the Arrowhead Framework core systems - Event Handler. This system supports the handling of events, and enriches service-oriented applications with the capabilities of interacting via the publish/subscribe paradigm. We implemented the Event Handler system as a MQTT enabled service broker, and deployed data flow programming tool Node-RED for wiring together divergent hardware devices and nodes, and APIs for online services. A case study of the service broker implemented for control of utilities systems in urban environment is presented and discussed.