Demands for Internet of Things (IoT) platforms are increasing along with the expansion of data-driven sciences, and academic network infrastructure such as national research and education networks (NRENs) are now being encouraged to aggressively support diverse IoT research projects. In Japan, the National Institute of Informatics (NII) operates an NREN called "SINET5," which is an academic backbone network linking more than 900 universities and research institutions. In addition to SINET5's high-speed 100 Gbps backbone network, SINET5 also provides a mobile network called "Mobile SINET" as IoT infrastructure. To provide crucial support to IoT research projects and to facilitate the development and deployment of IoT applications, we present herein our experience with our software library, "SINETStream." In this paper, we provide an overview of SINETStream and discuss lessons learned from examples of application deployment over Mobile SINET. SINETStream provides a common and simple application program interface (API) for various message brokers, security functions, and performance tuning support features. These functions improve the portability of applications and help application developers to remove hindrances to the development of secure and efficient IoT applications. The experimental results provided herein show that application developers can use SINETStream functions within a reasonable overhead. We also show how the combination of SINETStream and Mobile SINET enables users to develop and deploy highly confidential and efficient IoT applications.