In industrial environments, publish/subscribe is essential for reliable and efficient machine-to-machine communication. Established protocols like Message Queuing Telemetry Transport (MQTT) and Advanced Message Queuing Protocol (AMQP), which implement this messaging pattern, have architectural limitations that hinder their ability to guarantee hard real-time requirements. To address this limitation, we propose combining MQTT for Sensor Networks (MQTT-SN), a lightweight UDP-based variant of MQTT, with Time-Sensitive Networking (TSN), a set of IEEE standards that enhance Ethernet with real-time capabilities. The resulting protocol, designated as MQTT-TSN, enables time-triggered publish/subscribe using the Time-Aware Shaper (TAS) and guarantees hard real-time compliance for MQTT-SN messages. In this work, we present a conceptual framework for the mapping of real-time MQTT-SN traffic to periodic time-triggered (TT) streams, incorporating configuration and adaptation at runtime. A case study demonstrates the feasibility and limitations of our approach in a simplified scenario.

In Time-Sensitive Networking (TSN), Time-Aware Shaping facilitates the convergence of deterministic and lowpriority traffic in Ethernet networks. The allocation of bandwidth for low-priority traffic is crucial when scheduling timetriggered (TT) streams to prevent starvation and packet loss caused by queue congestion. This issue is particularly pertinent in online scheduling scenarios, where the deletion of streams can lead to schedule fragmentation. To prevent this issue, the time slots of the TT streams must be compressed to provide larger contiguous gaps for low-priority traffic in the schedule. In this paper, we present a novel heuristic approach for compressing schedules, which facilitates the grouping of time slots into units, thereby increasing the bandwidth for low-priority traffic and improving the schedulability of future streams. The proposed heuristic can be tailored to specific use cases through adaptive weighting, allowing a comprehensive evaluation of time slots according to the properties of the associated time slot units, TT streams, and the network.

In this paper, we present the integration of MQTT for Sensor Networks (MQTT-SN) into OPC Unified Architecture (OPC UA) as a novel publish/subscribe (PubSub) protocol binding in order to enhance the industrial communication stack. By leveraging the lightweight MQTT-SN protocol, which is currently not considered in the architecture, we improve OPC UA's capability for high-frequency, low-latency messaging, which is essential for Industrial Internet of Things (IIoT) applications. We discuss related work and describe the design and implementation in detail. Our hybrid approach combines the rich data modeling and security capabilities of OPC UA with the communication efficiency of MQTT-SN, providing a scalable solution for real- time data management in industrial automation systems.

Real-time capability plays an important role in modern factory communication systems. However, protocols such as MQTT, CoAP, and MQTT-SN, which are increasingly finding their way into industrial environments alongside industrial-grade protocols such as OPC UA and DDS, cannot fulfill the timing requirements without further optimization. In this paper, we present extensions of MQTT-SN to improve the real-time behavior in combination with PREEMPT_RT, which provides different real-time mechanisms for the Linux kernel. We address general, operating system-based, and hardware-specific optimizations. Their benefits are demonstrated by measurements in a practical testbed. The proposed extensions reduce delay and jitter, but do not aim to guarantee an upper bound on end-to-end delay.

The Message Queuing Telemetry Transport (MQTT) protocol is a de-facto standard for machine-to-machine (M2M) communication in the Internet of Things (IoT) domain. However, since it is limited to TCP at transport layer, it is not possible to run MQTT over UDP, which would be desirable for real-time capable publish/subscribe. MQTT for Sensor Networks (MQTT-SN), which is a lightweight version of MQTT, allows the use of UDP, however, is strongly coupled to MQTT by the current specification and cannot be operated independently of it. In this work, we therefore propose a standalone broker implementation of MQTT-SN. In initial measurements, we can show that our approach is much more performant than the approach described in the specification and that our implementation compares very well with the protocols CoAP Pub/Sub and MOTT.

In the age of digitalization, data protection plays an important role. Data is created, modified and shared over the Internet between data owners and data users. A key issue in this context is the respect of data sovereignty. The International Data Spaces (IDS) Reference Architecture has been developed in order to preserve data sovereignty. In this regard, Internet of Things (IoT) devices, such as sensors, play an important role for providing data. However, an IoT device is not capable of being integrated directly into the IDS by default. We propose an approach to enable the IDS for vendor independent IoT devices, using an open interoperability standard for the IoT specified by the Open Geospatial Consortium (OGC). This allows data owners to benefit from providing their own data while retaining control over it.