Speaker
Description
The Synchronous Databus Network (SDN) is the real-time communication protocol used in the Instrumentation and Control (I&C) systems of the ITER nuclear fusion reactor. The goal is to guarantee a maximum latency of 50 µs between two computers through a dedicated 10 Gbps network. This contribution evaluates SDN performance in a 1 Gbps network using two optimization strategies: Time Sensitive Networking (TSN) and real-time enhancements to the Linux kernel. The experimental setup involves two computers connected via a TSN-enabled switch and synchronized using a grandmaster clock through the Generalized Precision Time Protocol (gPTP, IEEE 802.1AS). TSN protocols such as IEEE 802.1Qbv and VLAN priority tagging (IEEE 802.1Q) are used to isolate SDN traffic in dedicated NIC queues, minimizing interference from low-priority traffic. Linux kernel version 6.12 is configured with PREEMPT RT patches to improve system determinism. A CPU core is isolated for SDN processes, and real-time scheduling (SCHED_FIFO) ensures priority execution. The SDN library is modified to support TSN queuing and enable timestamp tracing via socket options, without altering its core functionality. Performance was measured across multiple configurations. The most optimized setup achieved an average round-trip latency of $99.952 \mu s$ with a deviation of $2.278 \mu s$. Under saturated traffic, latency rose to $214.018 \mu s$ with a $27.259 \mu s$ deviation. These results confirm that the combination of TSN, utilizing a 1 Gbps network, and real-time Linux optimizations enables latency to be limited to values that approximate the performance achieved using SDN over 10 Gbps.
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