MQTT is a widely used application-layer protocol for Internet-of-Things (IoT) and Industrial IoT networks. However, its centralized architecture, which relies on a broker that mediates all data transmissions, can lead to traffic congestion and reduced network capability, particularly in networks with a large number of devices, such as edge networks. This paper proposes an optimized SDN-based real-time MQTT architecture for edge networks, called Multicast Real-Time MQTT (MRT-MQTT) that leverages multicast routing mechanisms to efficiently distribute data while supporting timeliness requirements and minimizing network usage. Extensive emulation experiments show the effectiveness of the proposed approach and its superiority over Direct Multicast-MQTT (DM-MQTT) and Standard MQTT (STD-MQTT). We achieved a reduction in transmission delay of 29% and 23% for QoS=0 and QoS=1, respectively, when compared to DM-MQTT and 55% and 43% compared to STD-MQTT. In this last case, MRT-MQTT also reduced network usage by 58.0% and 45.0% for QoS=0 and QoS=1, respectively.

Nowadays, custom components are increasingly being replaced by commercially available off-the-shelf hardware and standard protocols. Additionally, emerging industrial paradigms like Industry 4.0 and IoT place new demands on requirements like scalability, transparency, adaptability and efficiency. Accordingly, application layer protocols like the Message Queuing Telemetry Transport Protocol (MQTT) are becoming more and more popular in these fields, thanks to their simplicity, scalability, low resource-usage and decoupling between end nodes. However, these protocols are not deterministic, thus being unsuitable for real-time applications. Recently the authors proposed a set of extensions to the MQTT protocol, allowing applications to explicitly specify real-time requirements that are then used by a resource manager, implemented in Software Defined Networking (SDN), to create real-time channels. This paper extends the work, providing worst-case analysis using the Holistic and Trajectory approaches. The paper also includes a set of experimental results aiming to verify the correctness of both analysis and evaluate its performance in several scenarios.

MQTT is an application-layer protocol that eventually became popular in the Internet of Things (IoT) and Industrial IoT (IIoT) thanks to its simplicity and effective publisher-subscriber messaging model that enables its use in embedded resource-constrained devices. However, MQTT features a limited set of Quality-of-Service classes addressing exclusively message delivery, impairing its use in IIoT applications subject to timeliness requirements. This limitation of MQTT has been addressed in the literature, but with focus on the broker real-time operation, only. This paper adds to the state-of-the-art, by proposing a set of extensions to the MQTT protocol grounded on Software-Defined Networking (SDN) that enable, at the network level, attaining real-time communication services. Simulation results validate the benefits of the proposed extensions.