The demand for high performance, integration with factory equipment and IT systems, and the Industrial Internet of Things (IIoT) has driven the growth of Industrial Ethernet. According to HMS's 2017 Industrial Networking Market Share Report, Industrial Ethernet grew faster than in previous years, with a growth rate of 22%. Industrial Ethernet now accounts for 46% of the global market, compared to 38% last year. In specific communications, EtherNet/IP and PROFINET have the largest market share, with PROFINET primarily in Central Europe and EtherNet/IP dominating North America. Following closely are EtherCAT, Modbus-TCP, and EthernetPOWERLINK.
In real-time industrial Ethernet, EPA, EtherCAT, EthernetPowerlink, PROFINET, Ethernet/IP, and SERCOSIII are the main competitors. A brief comparison is provided below.
Ethernet/IP
Ethernet/IP is an industrial Ethernet standard jointly developed by ControlNet International and ODVA (Open Device Network Vendors Association) in March 2000.
Methods to achieve real-time performance
Ethernet/IP
Ethernet/IP is an industrial Ethernet standard jointly developed by ControlNet International and ODVA (Open Device Net Vendors Association) in March 2000.
Ethernet/IP achieves real-time performance by adding the CIP (Common Industrial Protocol) protocol on top of the TCP/IP layer for real-time data exchange and running real-time applications.
Ethernet/IP uses standard Ethernet technology at the physical and data link layers, and uses IP, TCP, and UDP protocols to transmit data at the network and transport layers. UDP is a connectionless protocol that can operate in unicast and multicast modes, providing only the ability to send datagrams between devices. UDP/IP is used for sending high-real-time I/O data, motion control data, and functional safety data. TCP, on the other hand, is a reliable, connection-oriented protocol. TCP/IP is used for sending data with less stringent real-time requirements (such as parameter settings, configurations, and diagnostics).
Ethernet/IP employs a producer/consumer data exchange model. Producers send data packets with unique identifiers to the network. Consumers receive the data they need from the network using these identifiers. This way, the data source only needs to transmit the data to the network once, and other nodes selectively receive the data, thus improving communication efficiency.
Ethernet/IP enables the transmission of both non-real-time and real-time data under the control of the CIP protocol. CIP is an end-to-end object-oriented protocol for industrial devices, independent of the physical and data link layers, allowing devices from different vendors to interact effectively. Furthermore, to achieve better clock synchronization performance, in 2003, ODVA introduced IEEE 15888 into Ethernet/IP and developed the CIPsync standard to improve the clock synchronization accuracy of Ethernet/IP.
EPA
The EPA was jointly developed by Zhejiang University, Tsinghua University, Zhejiang Supcon Technology Co., Ltd., Dalian University of Technology, and the Institute of Automation of the Chinese Academy of Sciences, with the support of the "863" Program. It is a real-time Ethernet standard for industrial measurement and control systems.
Methods to achieve real-time performance
The EPA achieves real-time performance by adding an EPA-CSME (communication scheduling management entity) on top of the data link layer specified in the ISO/IEC 8802.3 protocol.
The EPA-CSME is added for scheduling and management of data packets. It supports two communication scheduling modes: non-real-time communication uses the CSMA/CD communication mechanism, where non-real-time data is directly transmitted between the DLE layer and DLS-Use without any buffering or processing; real-time communication uses a deterministic scheduling mode, where the EPA transmits DLS-User data to the DLE according to the control timing and priority, and then sends it out through the PHY, thus avoiding packet collisions in the network.
Furthermore, to avoid collisions, the EPA network divides the control network into several isolated control areas—micro-segments—each separated by bridges. Communication within each micro-segment is independent. Communication between devices in different micro-segments is achieved through bridge forwarding. This ensures that all packets in the network are strictly monitored, thus preventing broadcast storms.
Currently, some companies, such as Zhejiang University Control System Co., Ltd. (ZJUCC), have developed a variety of EPA-based products, including EPA-based control systems, EPA-based transmitters, actuators, remote distributed control stations, data acquisition units, field controllers, and paperless recorders. EPA-based distributed network control systems have been successfully applied in factories.
EthernetPowerlink
EthernetPowerLink (EPL) is a real-time Ethernet solution developed by B&R (B&R) of Austria in 2001. In 2003, EPSGCEthernetPowerLink, a standardization organization, was established by leading companies in the global automation and drive industry to standardize and enhance PowerLink technology.
Methods to achieve real-time performance
The EPL standard was developed based on CANopen. Its real-time approach involves extending the TCP/IP protocol stack in real-time and introducing the SCNM (slot communication network management) mechanism to eliminate the uncertainty of CSMA/CD.
The SCNM principle involves network communication following a fixed cycle. Each cycle is divided into three time slots: a synchronous time slot, an asynchronous time slot, and an idle time slot. Data with strict real-time requirements is transmitted in the synchronous time slot, while data with less stringent time requirements is transmitted in the asynchronous time slot. Within each of these three time slots, further subdivisions are made based on the number of communication nodes in the network. This ensures the real-time transmission of data while preventing network collisions.
PROFINET
PROFINET is an industrial Ethernet standard proposed by PI (Profibus International). Starting in April 2004, PI partnered with Interbus Club to collaboratively develop and define the relevant standards for PROFINET. PROFIBUS and Interbus technologies can be seamlessly integrated into the entire control system.
Currently, PROFINET has three versions, enabling three types of communication: standard TCP/IP communication and two types of real-time communication. In these versions, PROFINET proposes technical solutions for real-time extensions of IEEE 802.1D and IEEE 1588, and employs different real-time channel technologies according to different real-time requirements.
PROFINET provides standard channels that use the TCP/IP protocol for non-real-time communication, used for transmitting device parameterization, configuration, and diagnostic data. There are two real-time channels: Real-Time Channel (RT) and Real-Time Channel (IRT).
Real-time (RT) channels are a type of software real-time solution with a typical response time of 10ms. They are primarily used in factory automation for high-performance cyclic transmission of process data, event control signals, and alarm lights.
Isochronous Real-time (IRT) channels utilize dedicated ASIC chips to parse data frames, thus reducing processing time. This approach is particularly suitable for high-performance transmission, isochronous transmission of process data, and motion control applications requiring rapid clock synchronization.
In addition, depending on the application, PROFINET has two networking modes: PROFINETIO and PROFINETCBA.
SERCOSIII
SERCOS (Serial Real-Time Communication System) was developed in 1989 and became the international standard IEC 61491 in 1995. To date, SERCOS has undergone three generations of development: SERCOS I, SERCOS II, and SERCOS III, with SERCOS I and SERCOS II collectively referred to as SERCOS. SERCOS III is a product of combining the mature communication mechanism of SERCOS with industrial Ethernet, possessing both the real-time characteristics of SERCOS and the characteristics of Ethernet. Compared to SERCOS, SERCOS III has the following advantages:
Based on industrial Ethernet, the data transmission rate is up to 100 Mbit/s;
It can achieve standard TCP/IP communication;
Capable of using CATSE twisted-pair copper cables and fiber optic communication;
It has linear and ring-shaped topologies;
Supports cross-communication between slave stations;
Supports hot-swapping of slave stations; supports security-related data transmission;
It is backward compatible with the previous SERCOS bus protocol.
Methods to achieve real-time performance
SERCOSSIII uses a TDMA (Time Division Multiplexing) communication mechanism to achieve real-time and deterministic Ethernet connectivity. It can connect to drivers, I/O devices, and sensors using linear or ring topologies, but does not support star topologies.
EtherCAT
EtherCAT is a real-time industrial Ethernet technology proposed by Beckhoff GmbH in 2003. To provide EtherCAT technical support to automation professionals and product suppliers worldwide, the ETG (EtherCAT Technology Group) was established at the end of 2003. To date, this organization is the world's largest industrial Ethernet organization with 2705 members, and its membership is growing rapidly, demonstrating the increasingly important role and status of EtherCAT technology in the industrial control field. After several years of development, EtherCAT has gained widespread recognition and is now included in several relevant international standards: Type 12 in IEC 61158; CPF12 in IEC 61784; in IEC 61800, EtherCAT supports the CANopen DS402 and SERCOS specifications; and in ISO 15745, EtherCAT supports DS301.
Key features of EtherCAT
Fully compliant with Ethernet standards
1
Common Ethernet technologies can be applied to EtherCAT networks. EtherCAT devices can coexist with other Ethernet devices on the same network. Standard components such as Ethernet cards, switches, and routers can all be used in EtherCAT.
Supports multiple topologies: linear, star, and tree.
2
It can use standard Ethernet cables or fiber optic cables. When using 100Base-TX cable, a communication distance of up to 100m is allowed between two devices. In 100BASE-FX mode, using two pairs of optical fibers in full-duplex mode, single-mode fiber can achieve a transmission distance of 40km, and multimode fiber can achieve a transmission distance of 2km. EtherCAT can also use Beckhoff's proprietary Low Voltage Differential Signaling (LUDS) cable for low-latency communication, with a communication distance of up to 10 meters.
Wide applicability
3
Any device with a standard Ethernet controller can function as an EtherCAT master, such as embedded systems, ordinary PCs, and control boards.
High efficiency and short refresh cycle
4
In EtherCAT, the reading, parsing, extraction, and insertion of process data by the slave station are entirely implemented in hardware. This makes data frame processing unaffected by CPU performance or software implementation, resulting in minimal latency and high real-time performance. Furthermore, EtherCAT can achieve a data refresh cycle of less than 100µs.
Capable of compressing large amounts of device data
5
EtherCAT Ethernet frames can compress a large amount of device data, enabling EtherCAT networks to achieve an effective data rate of over 90%. Official tests show that 1000 I/O updates take only 30µs, including I/O cycle time. A single Ethernet frame containing 1486 bytes (equivalent to 12000 I/Os) refreshes in just 300µs.
Excellent synchronization performance
6
EtherCAT uses a high-resolution distributed clock to enable synchronization accuracy between slave nodes to be much less than 100 ms.
No need for subnets
7
Even very complex nodes or digital I/O with only one or two bits can be used as EtherCAT slaves.
Multiple application layer protocol interfaces
8
EtherCAT offers multiple application layer protocol interfaces to support various industrial equipment standards: CoE (CANopen over EtherCAT) supports the CANopen protocol, SOE (SERCOE over EtherCAT) supports the SERCOE protocol, EOE (Ethernet over EtherCAT) supports common Ethernet protocols, FOE (File over EtherCAT) is used for uploading and downloading firmware programs or files, and AOE (ADS over EtherCAT) is used for aperiodic data access services between master and slave stations. This support for multiple standards makes it easy for users and equipment manufacturers to transition from fieldbus to EtherCAT.
