Industrial networks — PROFINET, PROFIBUS, EtherCAT, Modbus, OPC UA…
Exhaustive overview of industrial communication protocols: legacy serial buses (Modbus, PROFIBUS, HART, AS-i…), deterministic Industrial Ethernet (PROFINET, EtherNet/IP, EtherCAT, POWERLINK), application layers (OPC UA, MQTT Sparkplug), utility/SCADA protocols (DNP3, IEC 60870, IEC 61850), safety variants (PROFIsafe, CIP Safety, FSoE) and wireless (WirelessHART, ISA100, industrial 5G). Parent standard: IEC 61158 + IEC 61784.
Core principles
An industrial bus is not an IT network. It has specific constraints that explain why ~40 variants exist instead of a single Ethernet.
Determinism
An industrial bus must deliver each frame at a predictable instant — to the µs in motion control. Different from "best effort" IT Ethernet. Achieved by strict cyclic polling (PROFIBUS, AS-i) or by real-time Ethernet mechanisms (PROFINET IRT, EtherCAT, TSN).
Environmental robustness
Shielded cables, differential coding (RS-485, Manchester), galvanic isolation, EMC immunity per IEC 61000-6-2. Designed for −40 °C to +85 °C, vibration, corrosive atmospheres, ATEX (PROFIBUS PA, Foundation Fieldbus H1).
Addressing and topology
Master-slave (PROFIBUS DP, Modbus RTU), producer-consumer (Foundation Fieldbus), pub/sub (OPC UA PubSub, MQTT). Topologies: bus, star, redundant ring (MRP, PRP, HSR), mesh.
Functional safety on top
No dedicated safety bus — a certified IEC 61784-3 protocol (PROFIsafe, CIP Safety, FSoE, openSAFETY) is overlaid on a standard bus. End-to-end integrity check independent of the transport ("Black Channel").
1. Serial / legacy buses (1980–2000)
The first industrial generation, still omnipresent. RS-485 differential for EMC robustness, master-slave polling, modest bandwidth but strict determinism. Many plants still run on these in 2026.
| Bus | Year | Organization | Physical layer | Speed | Nodes | Use case | Status |
|---|---|---|---|---|---|---|---|
| Modbus RTU | 1979 | Modbus Org | RS-485 / RS-232 | 9,6 – 115,2 kbps | 247 | The grandfather. Universal, simple, open. Still everywhere. | Active |
| HART | 1986 | FieldComm | 4-20 mA + digital overlay | 1,2 kbps | 15+ (multidrop) / 1 (point-to-point) | Sensor configuration & diagnostic without changing analog wiring | Active (massive legacy) |
| PROFIBUS DP | 1989 | PI | RS-485 | 9,6 kbps – 12 Mbps | 126 | PLC ↔ actuators / remote I/O. Siemens de-facto standard. | Declining — replaced by PROFINET on new installations |
| PROFIBUS PA | 1995 | PI | MBP-IS (2 fils) | 31,25 kbps | 32 (segment) | Process instrumentation in zone 1 ATEX — power and signal on the same pair | Stable — gradual replacement by Ethernet-APL |
| Foundation Fieldbus H1 | 1996 | FieldComm | IEC 61158-2 (2 fils) | 31,25 kbps | 32 | Direct competitor of PROFIBUS PA in petro-chemicals ATEX. Producer-consumer. | Stable, large installed base |
| AS-Interface (AS-i) | 1993 | AS-i Consortium | 2 yellow wires (signal + 24 V power) | 167 kbps (AS-i 3) / 600 kbps (AS-i 5) | 62 | Low-cost binary sensors/actuators. Vampire-tap flat cable. | Active — AS-i 5 (2020) adds IO-Link & safety |
| DeviceNet | 1994 | ODVA | CAN | 125 / 250 / 500 kbps | 64 | CAN variant of CIP. Tied to Rockwell. | Legacy, North American installed base |
| CANopen | 1995 | CiA | CAN | 1 Mbps max | 127 | Machine tools, embedded automotive, medical. Excellent cost/feature ratio. | Active — CANopen FD emerging (CAN-FD) |
| CC-Link | 1996 | CLPA | RS-485 différentiel | 10 Mbps max | 64 | Mitsubishi. Dominant in Asia on Mitsubishi installations. | Active, but migration to CC-Link IE (Ethernet) |
| INTERBUS | 1987 | Phoenix Contact | RS-485 / fibre | 500 kbps – 2 Mbps | 512 | Serial ring. Strong historic presence in European auto and special machinery. | Legacy — not recommended on new installations |
| ControlNet | 1995 | ODVA | Coaxial / fibre | 5 Mbps | 99 | PLC-to-PLC backbone at Rockwell — superseded by EtherNet/IP | Legacy |
2. Intelligent single-drop — IO-Link and Ethernet-APL
Not really a bus — an intelligent point-to-point link between a sensor/actuator and a master. The big innovation of the 2010s-2020s: cheap cable carrying power + measurement + diagnostic + parameterization.
| Protocol | Year | Organization | Physical layer | Speed | Nodes | Use case | Status |
|---|---|---|---|---|---|---|---|
| IO-Link | 2009 | PI / IEC 61131-9 | 3 unshielded wires (24 V) | 4,8 / 38,4 / 230,4 kbps | 1 (point-to-point) | Intelligent sensor: measurement + diagnostic + parameterization on the same wires. Plug-and-play. | Strong growth — standard on new installations |
| IO-Link Safety | 2022 | PI / IEC 61131-9 | Same as IO-Link | Idem | 1 | Safety extension of IO-Link for SIL 2 sensors | Emerging — first products 2024 |
| Ethernet-APL | 2021 | Multi-vendor (APL Project Group) | 2 wires (power + signal), IEC 61158-2 long distance, intrinsically safe ATEX | 10 Mbps full-duplex | 1 (point-to-point) | Replacement for ATEX zone 0/1 process — Ethernet down to the sensor inside the vessel. Natural successor of PROFIBUS PA / FF H1. | Emerging — first industrial deployments 2024-2025 |
3. Industrial Ethernet (deterministic)
The 2000s evolution: take standard IT Ethernet (IEEE 802.3) and add the missing real-time guarantees. Every vendor cooked up its own recipe; TSN is now trying to unify everything.
| Bus | Year | Organization | Main vendor | Speed | Latency | Use case |
|---|---|---|---|---|---|---|
| PROFINET | 2003 | PI | Siemens | 100 Mbps – 1 Gbps | Standard <10 ms, IRT <1 ms, Isochronous <1 µs jitter | Most used in Europe. 3 classes: Standard (TCP/IP), RT (L2), IRT (motion control) |
| EtherNet/IP | 2001 | ODVA | Rockwell | 100 Mbps – 1 Gbps | < 10 ms typique, < 1 ms avec CIP Sync | Dominant in the US. Wraps CIP over TCP (explicit) and UDP (implicit cyclic). |
| EtherCAT | 2003 | ETG | Beckhoff | 100 Mbps | <100 µs (32 axes), unique on-the-fly circulating frame | Highest-performance motion control. Circulating frame. Line/ring/tree topology. Hot-connect. |
| POWERLINK | 2001 | EPSG | B&R | 100 Mbps | < 200 µs | Open source (LGPL). Strict isochronous cycle. European industrial niche. |
| Sercos III | 2003 | IGS | Multi (Bosch Rexroth, Indramat) | 100 Mbps | <31.25 µs (synchronous motion control) | Machine tool & robotics motion control |
| Modbus TCP | 1999 | Modbus Org | Multi (open) | 100 Mbps – 1 Gbps | Best-effort (non-deterministic) | Universal and simplest to implement. Not deterministic, but ubiquitous. |
| CC-Link IE | 2007 | CLPA | Mitsubishi | 1 Gbps | < 1 ms | Gigabit from the start. Mainly Asia. |
| TSN (IEEE 802.1) | 2018 | IEEE / IEC | Multi-vendor | 1 – 10 Gbps | < 100 µs (déterministe garanti) | Not a bus but a set of Ethernet extensions (802.1Qbv shaping, 802.1AS PTP, 802.1Qbu preemption) making Ethernet deterministic. Future convergence layer. |
4. Application layers — IT/OT interoperability
On top of transport (Ethernet, serial), application layers define what the data means. OPC UA is becoming the modern IT/OT lingua franca; MQTT Sparkplug B plays the same role on the IIoT cloud side.
| Protocol | Year | Organization | Transport | Use case |
|---|---|---|---|---|
| OPC UA | 2008 | OPC Foundation / IEC 62541 | TCP, HTTPS, WebSocket | De-facto IT/OT interop standard. Rich information model, native security (Sign + Encrypt + X.509). |
| OPC UA Pub/Sub | 2018 | OPC Foundation | UDP multicast, MQTT, AMQP | Publisher/subscriber extension of OPC UA — participant decoupling, IIoT scalability. |
| OPC UA over TSN | 2020 | OPC + IEEE | Ethernet L2 + TSN | Convergence target: OPC UA for information, TSN for real-time. PLC and motion on the same cable. |
| OPC Classic (DA/HDA/A&E) | 1996 | OPC Foundation | DCOM (Windows) | Windows-only legacy. Avoid in new projects — replaced by OPC UA. |
| MQTT | 1999 | OASIS / ISO 20922 | TCP (broker) | Ultra-light pub/sub. Worldwide IIoT standard. Cellular and NB-IoT compatible. |
| MQTT Sparkplug B | 2019 | Eclipse Foundation | MQTT broker (Mosquitto, HiveMQ) | Industrial profile of MQTT — state machine, rich metadata, auto-discovery. IIoT cloud reference. |
| AMQP | 2003 | OASIS | TCP (broker) | Rich queue messaging. More used in finance than industry. |
5. Utility / SCADA protocols — energy, water, gas
For wide infrastructure (power grids, pipelines, water utilities), floor buses are not enough. A specialised family of long-distance protocols, designed to poll hundreds of remote RTUs/PLCs.
| Protocol | Year | Region | Transport | Use case |
|---|---|---|---|---|
| DNP3 / IEEE 1815 | 1993 | North America | Serial RS-485 or TCP/IP | Power distribution, water. RTU time-stamping, event classes, strong integrity. |
| IEC 60870-5-101 | 1995 | Europe | Serial | Historic European electrical telecontrol. Low-bandwidth long-distance serial. |
| IEC 60870-5-104 | 2000 | Europe | TCP/IP | Ethernet evolution of -101. Modern European and Asian power grids. |
| IEC 61850 MMS | 2003 | Worldwide | TCP (ISO 9506) | Substation station-bus communication. XML / SCL data model. |
| IEC 61850 GOOSE | 2003 | Worldwide | L2 multicast (Ethernet) | Real-time exchange between protection relays in a substation. <4 ms. NEVER routed between sites. |
| IEC 61850 Sampled Values | 2003 | Worldwide | L2 multicast (Ethernet) | Digital current/voltage samples replacing analog CT/VT. Process bus. |
6. Functional safety on top — IEC 61784-3
None of these buses is natively "safety". For SIL 2/3 functions, a certified protocol is overlaid that adds end-to-end integrity (CRC + sequence + timestamp + connection ID). The underlying transport may lose / duplicate / reorder messages — the safety receiver detects and enters the safe state.
| Protocol | Underlying transport | Organization | Use case |
|---|---|---|---|
| PROFIsafe | PROFINET / PROFIBUS | PI | Safety standard for Siemens/PI environments. SIL 3. |
| CIP Safety | EtherNet/IP, DeviceNet | ODVA | Safety for Rockwell environments. SIL 3. |
| FSoE (Fail Safe over EtherCAT) | EtherCAT | ETG | Native EtherCAT safety. SIL 3. Very low overhead. |
| openSAFETY | POWERLINK and others | EPSG | Open-source safety, transport-independent. SIL 3. |
| CC-Link IE Safety | CC-Link IE | CLPA | Safety for Mitsubishi environments. SIL 3. |
7. Industrial wireless
Wireless remains a minority in core process (harder determinism and reliability), but is gaining ground for: hard-to-reach remote sensors (vibration, temperature), mobile AGVs/AMRs, tele-operation. 5G URLLC may change the game for wireless motion control from 2026-2027.
| Protocol | Year | Standard | Band | Range | Use case |
|---|---|---|---|---|---|
| WirelessHART | 2010 | IEC 62591 | 2,4 GHz | 100 m typical, mesh-extendable | Wireless process sensors — typically vibration, temperature. Self-organizing mesh. |
| ISA100.11a | 2009 | ISA / IEC 62734 | 2,4 GHz | 100 m typical | Competitor of WirelessHART. More flexible (native IPv6) but less widespread. |
| 5G industriel (URLLC) | 2020 | 3GPP Release 16+ | Sub-6 GHz, mmWave | km (private campus coverage) | Wireless motion control, AGVs, tele-operation. URLLC: <1 ms and 99.9999% reliability. |
| Wi-Fi 6/6E/7 | 2020 | IEEE 802.11ax/be | 2,4 / 5 / 6 GHz | 100 m | AGVs, operator tablets, mobile HMI. Not deterministic — not for motion control. |
| LoRaWAN | 2015 | LoRa Alliance | Sub-GHz (868 MHz EU, 915 MHz US) | 2–15 km | Very low-power, long-range, low-bandwidth sensors. Metering, environment. |
| NB-IoT | 2017 | 3GPP Release 13 | LTE / 4G existing bands | Cellular coverage | Outdoor IIoT — pipelines, water meters, urban sensors. Operator-provided coverage. |
How to choose a bus?
No universal answer. Questions to ask, in order:
- What latency is required? Motion control <1 ms → EtherCAT / PROFINET IRT. Process control <100 ms → PROFINET / Modbus TCP / OPC UA. Reporting >1 s → MQTT Sparkplug.
- Which PLC vendor? Siemens → PROFINET + PROFIsafe. Rockwell → EtherNet/IP + CIP Safety. Beckhoff → EtherCAT + FSoE. B&R → POWERLINK + openSAFETY. Mitsubishi → CC-Link IE. For a vendor-neutral site, Modbus TCP or OPC UA.
- ATEX zone 0/1? PROFIBUS PA, Foundation Fieldbus H1, Ethernet-APL (future). Intrinsically safe sensors (Ex ia).
- Inter-site / cloud exchange? NEVER PROFINET / EtherCAT / GOOSE between sites. Always OPC UA encrypted or MQTT Sparkplug B with TLS.
- SIL 2/3 safety required? Choose the standard bus first, then add the matching safety profile (PROFIsafe, CIP Safety, FSoE…).
- Cost-sensitive? Low-cost binary sensors → AS-i. Intelligent sensor → IO-Link (most cost-effective since 2020).
Reference standards
- IEC 61158 — Parent standard — OSI layers 1, 2, 7 of ALL industrial buses (40+ types)
- IEC 61784 — Communication profiles (CPF) — 18 families mapping the market's buses
- IEC 61784-3 — Safety profiles (PROFIsafe, CIP Safety, FSoE, openSAFETY)
- IEC 62541 — OPC UA — IT/OT application layer
- IEC 61131-9 — IO-Link single-drop
- IEEE 802.1 TSN — Time-Sensitive Networking — deterministic Ethernet
- IEC 62591 — WirelessHART
- IEC 62734 — ISA100.11a