This thesis proposes and evaluates an Internet of Things (IoT) solution consisting of architectures and algorithms, which enable several heterogeneous devices to intercommunicate, providing support for their offered services. An IoT network needs to enable exchange of diverse data types including rich-media and sensor data and handle a large number of devices, offering services at high quality levels. These goals are achieved by innovative solutions, which improve the performance and quality of IoT services and allow exchange of rich-media content. The proposed architecture consists of IoT objects and their services, smart gateways, supporting IoT object network connectivity, and cloud platforms employed for resource management. The performance and quality of IoT services are improved through NETSMITS (NETworking Scheme for sMart IoT gatewayS), which contains an algorithm that uses Quality of Service (QoS) and service relevance metrics in order to efficiently cluster inter-communicating IoT objects, attach them to the most suitable smart gateway and improve the performance of their services. The IoT mobility challenges are addressed through REMOS-IoT (RElay and MObility Scheme for the Internet of Things), which introduces algorithms that use QoS and service relevance metrics, age of information, and objects location in order to provide the best connectivity for devices and achieve better overall performance and QoS. A higher layer in the architecture contains VRITESS (VR-IoT Environment Synchronisation Scheme), which allows virtualisation of the IoT devices to fulfil requirements of certain rich-media devices and platforms, such as virtual reality (VR) devices and social media, integrating them to the IoT network. The contributions presented in this thesis include simulation models and testbeds for the mobility-enabled networking scheme for rich-media IoT, demonstrating performance improvements in comparison with other baseline solutions. A survey of IoT architectures, applications, QoS, protocols and mobility solutions is also provided.