PROFINET
Industrial Ethernet protocol developed by Siemens — drives factory floors worldwide. Real-time extensions go down to 31 µs cyclic updates.
PI Consortium maintains the spec. Three performance classes: PROFINET RT (soft real-time, ~10 ms), PROFINET IRT (Isochronous Real-Time, hard real-time, software-managed switches), PROFINET TSN (Time-Sensitive Networking, IEEE 802.1-based). Competitors: EtherCAT (Beckhoff, faster for servos), Ethernet/IP (Allen-Bradley/Rockwell), POWERLINK (B&R), Modbus TCP (universal but slow). Common confusion: "PROFIBUS ≠ PROFINET" — Profibus is the old RS-485 bus.