Physical Layer Requirements


The physical layer requirements for PROFINET are simple: PROFINET lays directly on top of standard IEEE 802 Ethernet.  Any PROFINET device can be placed on a standard Ethernet network in a home or an office, and it will communicate just the same as it would on the factory floor.

Physical Layer

But underneath that simple description, Ethernet is a complex protocol with a dizzying assortment of amendments, clauses, and revisions.  This section breaks them down to help identify some of the most basic features each PROFINET device has to implement.  To do that, we’ll break the monolithic IEEE 802 specification in to two parts: the wired physical layer (802.3), the wireless physical layer (802.11).  The exact requirements for a PROFINET device are described in the PROFINET Cabling and Interconnection Technology Guideline, available as part of the PROFINET IO Test Bundle or as a stand-alone download from the PI Website.  But that makes for slow reading, so we’ll summarize the main points here.

Wired Network Interface

According to the Cabling and Interconnection Technology guideline, there are four approved connector types for PROFINET devices: RJ-45, M12, SC-RJ and LC.  Of these, RJ-45 and LC connectors seem to be the most popular on IP-2x (regular electronics cabinet) hardware, while M12 and the SC-RJ connectors are more commonly found on IP-6x (washdown, exterior or waterproof) hardware.

Canonical interface types for PROFINET devices with copper or fiber-optic media.

But that’s just the physical connector.  PROFINET requires a host of protocols to get devices to agree on what voltages represent logical bits on the media (802.3 or 802.11) and how to pass those bits between nodes on the network (802.1).  These protocols are specified in the How to Get a Certificate for a PROFINET Device document, available as part of the PROFINET IO Test Bundle or as a direct download from the PI website.

Copper Interface (RJ-45 or M12 connectors)

PROFINET uses a subset of the full Ethernet feature set to ensure interoperability between devices.  The table below lists the minimum requirements to make nodes work together, but it’s possible that a PROFINET node may implement additional protocols.  For instance, it’s common for a remote sensor to implement Power Over Ethernet (IEEE 802.3at) in addition to these protocols:

Standards Required for Copper Interface

Fiber Optic Interface (SC-RJ or LC connectors)

The requirements for a Fiber Optic interface are nearly the same as those for a copper interface.  But instead of referencing Clause 25 for 100BaseTX operation in IEEE 802.3, the PROFINET protocol references Clause 26 for 100BaseFX operation.

Standards Required for Fiber Optic Interface

Wireless Network Interface

A wireless connection must comply with one of the IEEE 802.11 flavors (a, b, g, n, ac, etc..), or it may comply with one of the 802.15 family of protocols, such as Bluetooth.  However, in order to be certified in a PI Test Lab, the device must at least support an 802.11 flavor, along with a few other protocols.  Unlike the requirements for a wired interface, there are no provisions for switching or neighborhood detection functions.  Those are’t necessary once you switch to a shared medium like an air interface.

Standards Required for Wireless Interface

Summary

PROFINET is a protocol that runs on top of standard Ethernet.  But even when you break it down to the specific parts of Ethernet that PROFINET relies on, it’s just a small subset of the larger Ethernet specification, and it’s a subset that allows a huge range of interoperability over a diverse set of networks.