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I understand that Profinet builds on Ethernet, but I am not quite sure how.

Ethernet has a lot of different standards for the physical layer, eg 10Base2 (coaxial, 10 Mbit/s), 100Base-TX (twisted pair, 100 Mbit/s) and 1000BASE‑SX (fiber, 1Gbit/s).

Let's say I have full access of a 10Base2 (coaxial) NIC, including writing a new driver for it if necessary, so that such NIC's can send frames back and forth, and the frames conform to PROFINET standard and the NIC's deal appropriately with Profinet frames. Can I call this Profinet?

If not, then what is the requirements for the physical layer in order to call the network Profinet? Perhaps the allowed physical layers are specified individually in the Profinet standard specifications? If so, where can I find a complete list of the physical layers that are part of Profinet?

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Profinet's many things. Mainly a suite of standards, developed by Siemens.

The different things described as Profinet, that you're likely to meet:

  • S7-protocol
    • This is a TCP protocol, running on Port 102, used for communication to and between PLC's. This includes HMI to PLC, PLC to PLC, and PG (Programming computer) or other PCs. This protocol can be routed. It's not real time.
  • I-Device is a real time protocol. I-Device is not IP; it uses L2 addressing. It cannot be routed. It's used between PLCs, and to IO-system (e.g. ET200SP racks).
  • Isochronous profinet. This requires special network devices. There's a time slice reserved for important communication, e.g. position control, at a fixed time and length.
    • This may be useful when trying to do stuff in real time, for example position control, where you have tight time constraints. The network devices will drop other communications for the time slice assigned to (Isochronus Real Time).
  • The same network devices can be used for regular TCP/IP at the same time.

For the two first categories, you can use commodity hardware. For the last, IRT, you have to use hardware that supports IRT, typically from Siemens.

If you work with Profinet you'll probably come across concepts such as MRP, which is a ring topology with the ring kept open by the master. On failure, the ring will close.

In addition you have various standards for running Profinet (with real time support AFAIK) over WiFi.

  • If you're more specific, I can try to add more information to my answer. As for now it's rather general, but it's a broad topic – vidarlo Jun 18 at 18:02
  • Thanks a lot :) Here is some feedback that I hope you will either confirm or dismiss. 1) Profinet is officially an open standard, administered by PI International, though perhaps Siemens is pulling the strings behind the scenes. 2) I just read about S7 for the first time, and it does not appear to be part of Profinet. Instead I believe Profinet is solely an adaption of ethernet, so OSI level 2 (ethernet covers level 1 too, but I believe the changes made in Profinet are only on layer 2). – Mads Skjern Jun 19 at 8:34
  • 1 is true, yes. It's controlled by an independent association. Commonly in Siemens documentation, you'll find S7 protocol refered to as Profinet. And I'd say there's changes to L1 as well, for instance due to the reserved timeslots. – vidarlo Jun 19 at 8:48
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PROFINET uses Industrial Ethernet for the lower layers - so basically, if a piece of hardware can support the technical specifications of IE you could use it. That however is not likely for ancient 10BASE2 hardware.

Industrial Ethernet expands the standard Ethernet definition such that deterministic and real-time processing can be guaranteed. Hardware usually features ruggedized connectors and cases. Protocol families like PROFINET sit on top of that.

As physical layers, you could probably use any Ethernet PHY with 100 Mbit/s or faster - provided you find hardware that suits the specs.

  • Exactly what do you mean by "Industrial Ethernet"? Also, I believe Profinet is an adaption of Ethernet. It is not a protocol on a higher OSI level than Ethernet. Eg Profinet (at least in some configurations) changes even the max length of the frame and changes the system for when NIC's are allowed to send frames from CSMA/CA to some cyclic scheme. Please correct me if I am wrong. – Mads Skjern Jun 19 at 8:52
  • "Industrial Ethernet" is a collective term for various extensions and modfications made to Ethernet 802.3 and 802.1. The exact definition depends on the vendor at hand. PROFINET is a higher layer protocol suite that sits on top of (industrial) Ethernet, TCP/IP, or some other supported protocol. – Zac67 Jun 19 at 17:07

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