table of contents
- Introduction
- What is industrial Ethernet?
- Basic structure of industrial networks
- 1. EtherCAT (Ultra-high speed, low latency orientation)
- 2. Profinet (Flexibility/Interoperability)
- 3. Ethernet/IP (IT affinity/standardization)
- summary
Introduction
This article focuses on three widely used protocols and clearly explains the differences in their technical structure and design philosophy .
- EtherCAT
- PROFINET
- EtherNet/IP
(※Evaluation and implementation methods will be explained in a separate article.)
What is industrial Ethernet ?
- This is a best-effort communication method, and the delay varies depending on the load and switching processes.
- Frame loss (packet loss) may occur.
- TCP/UDP/IP is not designed for real-time control.
- Real-time communication
- Synchronization control
- Redundant configuration
- Diagnostic function
■ Key points for understanding industrial Ethernet: OSI model
Industrial Ethernet achieves real-time performance and reliability by using each of the OSI layers as a base and extending and optimizing specific layers for each protocol.
OSI reference model in industrial Ethernet:
| hierarchy | name | The role of industrial Ethernet |
| 7 | application | Contents of communication data (device control, status, settings) |
| 6 | presentation | Data encoding, compression, and encryption |
| 5 | session | Establishing, maintaining, and terminating communications |
| 4 | transport | Communication quality control (TCP/UDP), data delivery assurance. |
| 3 | network | Routing by IP address (determining packet destination) |
| 2 | Data Link | Data delivery by MAC address, creation of Ethernet frames |
| 1 | physics | Cables (Cat5e/6, etc.), connectors, and physical signal transmission. |
Layers used for each industrial Ethernet protocol:
Characteristics of each Ethernet protocol:
| protocol | hierarchy | Features |
| EtherCAT | 2 | High speed without using IP |
| PROFINET | RT/IRT is L2 NRT L3/4 |
Differentiated usage between RT and IRT. |
| EtherNet/IP | 3/4 | Standard Ethernet based |
These differences in characteristics directly lead to the following:
- Speed (real-time performance)
- Implementation cost
- Applicable use
Basic structure of industrial networks
■ System and Device Structure
Main device (controller):
It plays a central role in controlling the entire network.
- Starting communication and setting connection parameters
- Sending output data and receiving input data
- Communication management and termination process
Typical examples: PLCs, industrial PCs
Sub-device (device):
- Respond to connection requests and send and receive necessary data.
- Receiving output data and transmitting input data
- Self-notification on the network
- Alarms sent as needed
Typical examples: sensors, servos, actuators
■ Communication method: cyclic communication vs. aperiodic communication
Once a connection is established, I/O data is continuously exchanged between the MainDevice and SubDevice at very short intervals. This communication is divided into "periodic communication" and "aperiodic communication" depending on the application.
Cyclic communication (periodic communication)
Application: For real-time control
- Essential for applications requiring real-time performance, such as motor control and I/O control.
Acyclic communication
Uses: Configuration, diagnostics, and event management.
- Used for reading and writing configuration data, diagnostic information, and notifications of unexpected events.
■Key concept supporting real-time performance: Synchronization ( Clock )
In industrial systems, it is extremely important that "all devices operate on the same time standard."
For example, if multiple devices acquire data at different times, Δt₁, Δt₂, and Δt₃, as shown in the diagram below, the information received by the controller (PLC) will not be data from the same time, but rather "separate snapshots" that are staggered in time.
the result:
- Occurrence of positional misalignment
- Incorrect control judgment
- In particular, critical synchronization errors in motion control
This can lead to problems like these.
Therefore, in Industrial Ethernet , a mechanism for synchronizing clocks between devices is a crucial element.
Summary of the technical comparison of the three protocols
| EtherCAT | PROFINET | EtherNet/IP | |
| Operating Organization | Bechoff / ETG (EtherCAT Technology Group) |
Siemens / PNO (PROFIBUS & PROFINET International) |
Rockwell / OVDA (Open Device Net Vendors Association) |
| Communication method | Summary frame (SubDevice reads and writes data as it passes through the frame) | Layer 2-based real-time communication (RT/IRT) | CIP: Explicit (TCP) / Implicit (UDP) communication model |
| Main use | Motion control, ultra-high-speed control | General-purpose FA, process control, and a wide range of industrial applications | Factory automation, PLC networks, robots |
| Cycle time | ~31.25μs level (implementation dependent, very fast) | RT: A few milliseconds IRT: 31.25μs (implementation-dependent, TSN/IRT) |
Generally, 10ms level (UDP-based) |
| Synchronization method | Distributed Clock (DC) | IRT: Precision Synchronization (PTCP) | CIP Sync (IEEE1588) |
| Device Model | PDO / SDO (CANopen over EtherCAT) | Slot / Subslot (GSDML) | Class / Instance / Attribute Object Model |
| topology | Line, tree, ring (low latency) | Line, Star, Ring (MRP/MRPD) | Line, Star, Ring (DLR) |
| advantage | In short, high speed and low latency / hardware processing. | Various classes and diagnostic functions, high interoperability | Widely used in standard Ethernet infrastructure, easy to understand. |
From here, we will explain the technical characteristics of each.
1. EtherCAT (Ultra-high speed, low latency-oriented)
■ EtherCAT Overview
- Developed by Beckhoff Automation, managed by ETG.
- It operates at Layer 2 and has no IP/TCP/UDP overhead.
- Cycle time: ~ 31.25 μs ( implementation dependent )
- Synchronization accuracy: ±1μs or less
■ Network Configuration
- Main device (master) and Multiple sub-devices (slaves)
- The sub-device is equipped with an ESC ( EtherCAT Slave Controller ) and uses dedicated hardware for high-speed processing.
- While a line configuration is the basic setup, it also supports redundant configurations using a ring structure.
Figure: EtherCAT network configuration image
The most distinctive feature of EtherCAT is "on-the-fly processing. " A single frame is processed as it passes through all devices, with each device reading and writing data during transit. Because processing is handled by dedicated hardware (ESC) without involving the CPU, it achieves extremely low latency.
Figure: EtherCAT network transfer image
■ Related protocol conversion: EtherCAT (IEC 61784-2-12)
• CoE (CAN over EtherCAT): Enables CANopen communication to be used by tunneling it over an EtherCAT frame.
• FoE (File over EtherCAT): A protocol for transferring files via EtherCAT.
EoE (Ethernet over EtherCAT): A mechanism for encapsulating and transmitting regular Ethernet frames (such as TCP/IP ).
Figure: EoE protocol conversion by master device (MDevice)
2. PROFINET (Flexibility/Interoperability)
■ PROFINET Overview
- Developed by Siemens, managed by PNO.
- Standard Ethernet based
- Use RT/IRT/NRT depending on the application.
- Producer/Consumer Model
■ Network Configuration
- Flexible support for various topologies such as line, star, and mixed configurations.
- It also supports ring redundancy via MRP ( Media Redundancy Protocol ) / MRPD (IRT) .
- PROFINET 's communication performance is classified by " Conformance Class ( CC )".
CC-A : Basic real-time, all IT services (e.g., TCP/IP ) can be used without restrictions.
CC-B : Adds network diagnostics and other features to the general FA 's RT .
CC-C ( IRT
■ Communication type
- NRT: Record Read/Write: Sends and receives parameters and settings aperiodicly. Alarms: Notifies of abnormalities from the device.
- RT: Periodic I/O communication, generally 1ms
- IRT (Isochronous): Time-synchronized high-speed periodic communication , typically 31.25us.
→ Achieves high flexibility, detailed diagnostics, and high interoperability.
3. EtherNet/IP ( IT compatibility/standardization)
■ EtherNet/IP Overview
- EtherNet/IP is managed by ODVA (Open DeviceNet Vendors Association).
- It adopts CIP (Common Industrial Protocol), which operates at a layer above TCP/UDP/IP (L3/L4).
- Object-Oriented Model
■ Network Configuration
- Supports line, star, and ring topologies.
- Supports high-speed redundancy using DLR ( Device Level Ring ).
Main device → Scanner : Functions as a controller and typically initiates requests.
Subdevice → Adapter : The device that responds to that request.
■ EtherNet/IP's key feature: "Object-Oriented Model"
Each device is defined as a collection of objects consisting of " Class ," " Instance ," " Attribute ," and " Service ."
- Class : Type of function (e.g., Identity , Assembly )
- Instance : A specific instance of that class.
- Attribute : The specific value that each instance possesses.
- Service : Operation details such as reading and writing.
This results in a very clear structure for the device's functions, enabling high compatibility across manufacturers.
■ Communication type
Explicit Messaging Connection
- Uses TCP , reads and writes configuration values, performs self-diagnosis, and logs.
- Give instructions such as "Read" and "Write" once each.
Implicit Messaging- I/O Connection
- Using UDP , it enables real-time communication such as cycle I/O , with the scanner sending and receiving I/O data at regular intervals.
- The key feature of EtherNet/IP is its ability to enable high-speed I/O communication using implicit ( UDP ) protocols.
summary
Industrial Ethernet is not just a communication tool; it's a system technology that enables real-time control . The three protocols introduced here each achieve this through a different approach.
| protocol | design philosophy | Main uses |
| EtherCAT | High speed, low latency | Motion control |
| PROFINET | Flexibility and Integration | General-purpose factory automation (FA) |
| EtherNet/IP | IT integration | PLC Network |
As a future trend, industrial networks will move in the following direction.
- TSN ( Time Sensitive Networking )
- Security (including CRA compliance)
- Integration with OPC UA
In other words, the key lies in the fusion of "real-time × IT integration × security" .
Next time,
- Why is the i.MX RT1180 suitable for industrial Ethernet protocols?
- Actual implementation and evaluation procedures
We will explain this in detail.
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This article focuses on three widely used protocols and clearly explains the differences in their technical structure and design philosophy .
- EtherCAT
- PROFINET
- EtherNet/IP
(※Evaluation and implementation methods will be explained in a separate article.)
(Reading time: 15 minutes)