Profinet
Profinet is the Siemens-originated industrial Ethernet protocol that succeeded Profibus DP for deterministic communication between PLC or DCS and field devices. It runs on standard Ethernet hardware while adding three performance classes, TCP, RT, IRT for soft real-time, real-time, and isochronous real-time traffic. PROFIsafe layers SIL-rated safety on top.
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Profinet was introduced by Siemens and the Profibus & Profinet International organization in 2003 as the Ethernet-era successor to Profibus DP. Where Profibus DP used RS-485 serial at up to 12 Mbit, s with a master-slave token-passing scheme, Profinet runs on standard 100 Mbit, s or 1 Gbit, s Ethernet with managed switches and uses Ethernet frames with real-time extensions. It is not simply Modbus or EtherNet/IP reimplemented. Profinet has its own frame priority mechanism, topology discovery, using LLDP-based device identification, and diagnostic architecture based on GSDML device description files. Three performance classes exist. Profinet RT for standard I/O, millisecond cycles, Profinet IRT for synchronized motion control, sub-millisecond jitter, and the emerging Profinet TSN that aligns with IEEE 802.1 Time-Sensitive Networking for deterministic shared-network operation. The critical point for process instrumentation is that Profinet does not natively reach into hazardous areas the way Profibus PA or Foundation Fieldbus does. The APL, Advanced Physical Layer, IEC 63171-6 standard fills this gap by delivering 10 Mbit, s Ethernet over two-wire intrinsically-safe cable runs. APL allows Profinet to reach field instruments in Zone 1 and Zone 2 areas, giving a migration path from Profibus PA to Ethernet-native field devices. The installed base of Profibus PA remains larger in 2024, but new Siemens-platform projects increasingly specify APL for field instruments.
What are the three Profinet performance classes..
Profinet RT, Real-Time. Millisecond-class cycles for general I/O and motor control. Profinet IRT, Isochronous Real-Time. Microsecond-class jitter for motion-control axes. Profinet TSN, Time-Sensitive Networking. The IEEE 802.1 TSN-aligned future direction, providing deterministic traffic over standard switched Ethernet. Most installed Profinet today is RT on standard managed-switch infrastructure.
Profinet vs EtherNet/IP.
EtherNet/IP, Rockwell-originated and Profinet, Siemens-originated are the two dominant industrial Ethernet protocols. They occupy roughly the same architectural niche but are not interoperable. Gateway modules bridge between them. Project selection follows the PLC platform. EtherNet/IP on Allen-Bradley ControlLogix and CompactLogix, Profinet on Siemens S7. Both share standard Ethernet wiring and switching.
How are Profinet devices configured..
Every Profinet-capable device ships a GSDML, Generic Station Description Markup Language file that describes its I/O modules, parameters, and diagnostic capabilities. The engineering tool, TIA Portal for Siemens, or a third-party Profinet configurator imports the GSDML, places the device in the network topology, and assigns slot and subslot addresses to each I/O module. During commissioning the controller downloads the configuration and the device responds to cyclic I/O exchanges. Faulty devices are identified by device name, set in the GSDML rather than by IP address, which is assigned automatically by the controller at startup using the DCP, Discovery and Configuration Protocol. This tooling workflow is one of the reasons Profinet adoption is strongly correlated with TIA Portal usage. The configuration workflow is integral rather than bolted on.
How does PROFIsafe extend Profinet for SIS..
PROFIsafe is the safety profile that runs over standard Profinet infrastructure. Safety frames include a consecutive number, to detect lost or reordered frames, a CRC over the safety payload, to detect data corruption, and a watchdog mechanism, to detect communication loss. The logic solver, an F-CPU or a certified safe PLC checks these fields on every safety message cycle. A detected fault causes the safe-state output without depending on the underlying Ethernet switch or network to be fault-free. PROFIsafe is certified for use up to SIL 3 per IEC 61508 and PLe per ISO 13849. The SIS I/O list for a PROFIsafe project flags the communication path as PROFIsafe alongside the signal class.
What is Profinet APL and how does it work..
Standard Ethernet cable is unsuitable for Zone 1 hazardous areas. The connector and cable standards do not support intrinsic safety. APL solves this with a two-wire physical layer rated for Zone 1 IIB T4 that delivers power and 10 Mbit, s Ethernet to a field device over cable runs up to 200 m, with field switches extending further. An APL field device exposes a Profinet interface directly on the plant Ethernet segment. There is no DP, PA coupler or linking device as in a Profibus PA architecture. The I/O list entry for an APL-connected transmitter such as PT-101 includes the APL port IP address and the Profinet device name in place of the terminal-block reference used for 4-20 mA wiring.
Profinet vs EtherNet/IP at a glance.
The two dominant industrial-Ethernet protocols. Both run on the same physical layer. They differ in vendor ecosystem and real-time mechanism.
| Aspect | Profinet | EtherNet/IP |
|---|---|---|
| Origin | Siemens, PROFIBUS user group, PI | Rockwell Automation, ODVA |
| Standardization | IEC 61158, IEC 61784 | IEC 61158, CIP Common Industrial Protocol |
| Real-time mechanism | Three classes. TCP/IP, non-real-time, RT, real-time, no IEEE 1588, IRT, isochronous via switched fabric | Standard TCP/IP plus CIP Sync for time-critical, IEEE 1588 |
| Typical PLC ecosystem | Siemens S7-1200, S7-1500, ET 200SP | Rockwell ControlLogix, CompactLogix, Micro 800 |
| Safety extension | PROFIsafe, SIL 3 certified | CIP Safety, SIL 3 certified |
| Process-instrument variant | APL, Advanced Physical Layer, 2-wire bus power, intrinsic safety | No equivalent bus-powered IS variant. Uses gateways to HART or Foundation Fieldbus |
| Device discovery | DCP and LLDP | BootP, DHCP, ACD |
| Topology | Line, star, ring, MRP, tree | Star, ring, DLR, linear |
| I/O list flag | GSDML device file, slot, subslot, IO module type | EDS device file, vendor, product, catalog number, assembly instance |
Frequently asked.
Can Profinet carry process-instrumentation traffic at PA-equivalent scale.
Profinet over APL, Advanced Physical Layer Ethernet is the answer the standards bodies have converged on. APL delivers two-wire Ethernet to intrinsically-safe areas with adequate cable lengths. APL deployments are growing but Profibus PA remains the larger installed base in 2024.
Does Profinet need certified-safe components for SIS use.
Yes. Profinet has a safety profile, PROFIsafe that runs over the same Ethernet wires and is certified for SIL 3 use. Safety frames travel with extended sequence numbering and CRC discipline so a non-safe network fault cannot disable a safety-critical message.
What is APL and how does it relate to Profinet.
Advanced Physical Layer, APL, IEC 63171-6 is a two-wire Ethernet variant designed for intrinsically safe process-instrumentation areas. It runs standard Ethernet protocols including Profinet at 10 Mbit, s over the same type of cable used for 4-20 mA wiring. APL is the path the industry standardized on for bringing Profinet into Ex areas, replacing the Profibus PA role in new installations.
Is Profinet the same as Profibus.
No. Profibus is a serial fieldbus, RS-485 at up to 12 Mbit, s for DP. 31.25 kbit, s for PA. Profinet is industrial Ethernet, 100 Mbit, s or 1 Gbit, s. They are different physical layers and different protocols. Profinet is the successor to Profibus DP for device-level communications on Siemens-platform projects. Profibus PA remains in service for process-instrumentation bus segments where intrinsic safety and existing wiring limit migration.
How does Profinet topology discovery work.
Profinet uses LLDP, Link Layer Discovery Protocol for topology detection. Each device advertises its port connections, allowing the engineering tool to map the physical network topology. This topology map is used during diagnostics. A port fault or a missing device can be localized to a specific switch port and cable segment without physical inspection. TIA Portal displays the live topology and highlights deviations from the configured topology.
What I/O list columns are specific to a Profinet project.
A Profinet I/O list adds a device name, the GSDML name assigned to the device, a slot and subslot address, the module position within the device, and a Profinet RT or IRT classification alongside the standard signal class. For APL devices the list includes the APL segment reference. For PROFIsafe devices the list includes a PROFIsafe F-address. These columns replace the terminal-block and multicore-cable columns used in conventional 4-20 mA I/O lists.