Improving the Real-Time Capability of MQTT for Sensor Networks (MQTT-SN) Using PREEMPT_RT

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.