PROFINET

showstack / protocols / profinet

Also called PROFINET IO, PROFINET CBA.

PI's real-time industrial Ethernet standard for connecting PLCs, drives and I/O, spanning acyclic RPC parameter access over UDP/TCP up to sub-millisecond isochronous real-time (IRT) cyclic I/O carried as raw Ethernet frames. In entertainment it shows up where show control hands off to venue or stage-machinery automation, such as fixed-theatre stage-technology installs.

Machinery and motionPaid specPIReported

Stewarded by PI (PROFIBUS & PROFINET International).

Control Small, urgent, must arrive

Small messages that either repeat constantly or fire once. Bandwidth is almost never the problem.

What kills it. Latency and loss on the messages that fire once. A repeating level survives a dropped packet; a GO does not.

The four flows, and why the model is worth having →

Ports

udp/34962 PROFINET RT unicast (registered alternative to raw-Ethernet RT; rarely used in practice)

udp/34963 PROFINET RT multicast (registered, rarely used in practice)

udp/34964 RPC Context Manager — acyclic connection setup, parameter/record read-write, diagnostics
Connection setup on this port must complete before cyclic I/O starts on Ethertype 0x8892.

What goes wrong

Cyclic real-time I/O (Ethertype 0x8892) runs on raw Ethernet frames with no IP address and does not route, while the RPC Context Manager handshake on UDP 34964 is ordinary routable traffic; a capture from a router or a different VLAN shows the setup but never the actual cyclic data.

IRT (isochronous real-time, sub-1ms cycles used for drive/motion applications) requires PROFINET-aware switches with synchronized scheduling; dropping a standard unmanaged switch into an IRT segment breaks the timing guarantee even though the link still passes traffic.

The full specification set sits behind a paid PI membership (PI North America lists annual dues from roughly $800 for integrators up to $8,000 for larger device manufacturers) or individual purchase of the equivalent IEC 61158/61784 documents from the IEC Webstore — there is no free public PDF.

What speaks PROFINET (2)

Product	Direction	Notes
TwinCAT Beckhoff Automation	bidirectional	Via supplementary functions.
Beckhoff CX5140 Embedded PC Beckhoff Automation	bidirectional	With the relevant supplement.

Typical use

Machinery-level integration between venue/stage-automation PLCs and drives
Theme-park and large fixed-venue control architectures run alongside EtherNet/IP on redundant switch infrastructure
General industrial machine and drive networking behind scenic automation, rigging and building-adjacent equipment

Sources

Which TCP/UDP ports are used by PROFINET? (34962 RT unicast, 34963 RT multicast, 34964 RPC Context Manager) — HMS Networks
PROFINET Port Numbers Explained (Ethertype 0x8892 cyclic data vs UDP 34964 acyclic RPC handshake) — SCADA Protocols
PROFINET Specification — Official Downloads (PI member login required) — PI (PROFIBUS & PROFINET International) primary
Become a Member — PI North America (membership fees by category) — PI North America primary
Profinet (history and first release circa 2003, real-time classes and cycle times) — Wikipedia
Advanced Control System Architecture for Theme Parks (PROFINET named alongside EtherNet/IP on redundant switches) — Pacific Blue Engineering

Understand the mechanism

Code on a show

Something wrong, or missing?

Known gaps on this entry: implementations. If you can source one of them, that is a ten minute pull request.

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