Research results: Protocols for Industrial Ethernet

Need for wide-ranging application capability and the ability to handle diverse environments drives protocol development, sparks user interest, survey results suggest.

Dick Johnson, Control Engineering -- Control Engineering, 5/1/2008

Ah, the digital era! It seems it was only a short time (actually it was a couple of decades or so) ago that control engineers sought to replace the old analog 4-20mA control system protocol with a digital one. The advantages of digital control certainly were tantalizing — determinism, simplified wiring, speed, the ability to remotely calibrate and check the health of instrumentation, just to name a few. The effort got off to a great start and standardization seemed to be in the grasp of the control engineering community when innovation reared its ugly head. As reality would have it, industrial Ethernet protocols have become true tools of digital control and, as such, have adapted to suit a variety of applications.

Supervisory control and data acquisition (SCADA) is easily the most important plantfloor application for Ethernet, according to respondents, being cited nearly half again as often as the second-most important: diagnostics, testing and maintenance.

According to Reed Corporate Research studies of control products as recent as five years ago, products using the 4-20mA standard were still dominating the control scene. That’s changing. In the most recent survey, 295 answered online questions about industrial Ethernet protocols. Since intra-company connectivity is one of the major benefits of Ethernet, it is not surprising that 53% of respondents indicated that engineering was involved most on industrial Ethernet cross functional teams, along with information technology (34%), plant engineering (23%), manufacturing management (22%) and, to a lesser extent, customer/tech support (8%), QC/QA (8%) and others.

Applying the network

Control engineers use Ethernet for a wide variety of in-plant functions. (See accompanying graphic.) The lineup was essentially similar to those indicated in the survey done in 2006, with one important exception: Ethernet use in business management applications has become more prevalent in just a few short years, signaling increasing involvement of all levels of management in the day-to-day manufacturing that is the hallmark of multinational operations in a global economy.

Specific uses for Ethernet protocol exist within these applications at a number of levels. These include monitoring or data acquisition (78%), control (68%), manufacturing operations or execution (63%), and enterprise operations (58%). Lower-level applications included I/O (48%), actuation (37%), and sensor (24%). Within control systems, industrial Ethernet network connectivity remains concentrated in logic (PCs 89%, PLCs 79%, and programmable automation controllers 66%), compared to sensors (vision 37%, temperature sensors/transmitters 18%, and flow sensors/transmitters 17%) or actuators (such as block valves 18% and control valves 14%).

Most used protocols

According to survey respondents, the top 10 industrial Ethernet protocols being used for industrial applications are (in descending order):

• TCP/IP (native)—95%

• EtherNet/IP—88%

• Modbus TCP—81%

• UDP (native)—79%

• Fieldbus Foundation High Speed Internet (HSE)—43%

• EtherCAT—41%

• SERCOS III—38%

• Profibus Profinet—36%

• CC-Link IE (Gigabit Ethernet)—31%

• Ethernet Powerlink—27%

Other industrial Ethernet protocols listed included VARAN (Versatile Automation Random Access Network), FL-net (OPCN-2) from Japan Electrical Manufacturers Association, synqNet, Mechatrolink III, and SafetyNet. See the product section below for descriptions of the top 10 protocols and others.

All of these protocols are being considered for standards and/or are represented by organizations, an attribute that is relatively prominent on the lengthy list of issues control professionals deemed very important in the industrial Ethernet protocols they seek. (See accompanying graphic.)

Of the 34 mentioned attributes, high speed capability (66%) was listed as the most important. This was followed closely by availability of devices that use that protocol (65%), upgradeability (60%), the ability to use commercial-off-the-shelf componentry, and the ability to use it for control applications (60%).

Respondents ranked many "very important" traits nearly equally, with the top 7 separated by 7 percentage points.

These top five reflect the same results as those collected in the last survey done in 2006 with one exception: The importance of using 10/100 base T/TX Ethernet media fell from the top five to tenth place. It was replaced by ease of data transfer to higher level systems, inferring the expansion of Ethernet protocols into more expansive and ever more complex enterprise systems.

According to survey respondents, 92% have already started using Ethernet on the plant floor. The remaining 8% have yet to start, but are planning to. Of those planning to start, 59% stated they will within the next year, and 41% will do so within the next 13-24 months.

Of control systems using Ethernet, many have been around for some time. Control professionals using it for more than 10 years or more account for 17% of the responses. Many may not have been separately installed systems, but part of existing DCS-based control; DCSs have long used Ethernet-based systems. Systems that were 6-10 years old accounted for 29% of the total. Systems that were 2-5 years old accounted for 34%. Those starting 13-24 months ago or within the past year accounted for 12% and 8%, respectively.

Despite the variety of Ethenet-based control protocols available and the complexity of commissioning on the plant floor, control professionals said they were overwhelmingly satisfied with their Ethernet protocol compared to another favorite industrial network. Sixty-three percent said they were very satisfied and 36% stated that they were somewhat satisfied. Only 1% stated they were unsatisfied with their choice.

When asked for advice on installing an Ethernet-based control system, control engineers were not shy about the amount of learning and effort it requires. Verbatim responses such as “do your homework first” and “have your own knowledge of real-time Ethernet“ were common. “Take time to thoroughly investigate all available choices,” was another idea frequently echoed. With a 99% satisfaction rating on industrial Ethenet protocol usage, it seems the time it takes to specify, recommend, purchase, and install Ethernet-based control variants is worth the effort.

TCP/IP: Straying from intent?

TCP/IP, the original Ethernet protocol, is considered the dominant protocol by the Internet Engineering Task Force (IETF). Conceived for data networks in commercial applications, it has become one of the predominant transport protocols for industrial Ethernet use. Ethernet TCP/IP is a suite of communications protocols used to connect hosts on the Internet and has become the de facto standard for transmitting data over networks. www.ietf.orgInternet Engineering Task Force

EtherNet/IP: Manufacturing

EtherNet/IP is a member of a family of networks that uses Common Industrial Protocol (CIP) at its upper layers. CIP uses a suite of messages and services for manufacturing automation applications (control, safety, synchronization, motion, configuration, and information). It is media-independent, supported by hundreds of vendors, and unifies manufacturing communications. Producer-consumer services let the user simultaneously control, configure, and collect data from intelligent networked devices or use one network as a backbone for multiple distributed CIP networks. It is compatible with standard Internet protocols and standard industrial protocols such as OPC for data access. www.odva.orgODVA

Modbus TCP: Up a notch

Modbus TCP Protocol is a messaging structure originally introduced to the market 1979. It is used to establish master-slave/client-server communication between intelligent devices. As a simple messaging structure, Modbus is independent of the underlying physical layer. It combines a versatile, scalable, and ubiquitous physical network (Ethernet) with a universal networking standard (TCP/IP) and a vendor-neutral data representation. Ethernet port 502 is assigned for the Modbus TCP protocol. Modbus TCP is implemented over Ethernet; fiber and major wireless technologies including Wi/Fi, radio, GPRS, and Bluetooth. Modbus TCP wraps TCP/IP around Modbus. www.modbus.orgModbus-IDA

UDP: Transactions up front

User diagram protocol (UDP) makes available a datagram mode of packet-switched computer communication for an interconnected set of computer networks. UDP assumes the Internet protocol (IP) is the underlying protocol and provides a procedure for application programs to send messages to other programs with a minimum of protocol mechanism. The protocol is transaction-oriented, and delivery and duplicate protection are not guaranteed. www.ietf.orgIETF

HSE: Total plant control

High Speed Ethernet (HSE) is said to be a key enterprise integration technology for mission-critical applications. HSE is the Fieldbus Foundation’s high-performance network running Ethernet and TCP/IP, suited for use as the plant control backbone. At 100 Mbit/s, HSE is designed for device and subsystem integration. It enables integration of data server technology such as OPC. It supports fieldbus capabilities (standard function blocks, electronic device description language, and application-specific flexible function blocks for advanced process and discrete/hybrid/batch applications). www.fieldbus.orgFieldbus Foundation

EtherCAT: Fast, cost effective

EtherCAT is an open, real-time Ethernet network that can update 1,000 distributed digital I/O points in 30 µs or 100 axes every 100 µs using twisted-pair or fiber-optic cable. Fast and cost effective, it features almost unlimited network size and optimum vertical integration due to open Ethernet and Internet technologies. EtherCAT does not require switches or hubs, reducing cost. EtherCAT is an IEC, ISO and SEMI standard. www.ethercat.orgEtherCAT Technology Group

SERCOS III: Motion, I/O

SERCOS III is an open real-time industrial Ethernet protocol--part of standards IEC 61784-2 and IEC 61158. It provides high-precision deterministic control with low cycle times and network jitter, is backward compatible with prior SERCOS versions, and can operate without switches or hubs. New features include synchronization and communication between multiple motion controls and a powerful device profile for decentralized I/O modules. www.sercos.comSERCOS North America

Profinet: Compatibility

Profinet is said to be applicable in virtually any function required in automation: discrete, process, motion, peer-to-peer integration, vertical integration, safety, and others. It uses standard IEEE 802.3 Ethernet, so works over IEEE 802.11 wireless. It controls 150 axes of motion in 1 msec with 1 μsec of jitter. It is said to be the only industrial Ethernet standard that defines communication of plant asset management and other information needed by manufacturing execution systems. www.us.profinet.comProfibus Trade Organization

CC-Link: New, gigabit Ethernet

CC-Link Partner Association (CPLA) has developed a gigabit industrial Ethernet (IE) protocol, CC-Link IE, allowing network communications at near backplane speeds. It is the first open standard, 1 gigabit/sec manufacturing network released globally. It uses standard Ethernet IEEE 802.3z multimode fiber-optic cable in dual-loop topology. It is deterministic with network common memory, without hubs or switches. www.cc-linkamerica.orgCC-Link Partner Association

Ethernet-Powerlink: More value, top speed

Ethernet-Powerlink Standardization Group (EPSG) says its protocol adds value, including the following features for machine and plant operators: Safety (TÜV Rheinland certified, usable with systems requiring SIL 3 protection), redundancy capability, compatibility with CANopen, freedom of users to choose network topology, hot plugging capability, cross-traffic capability, and easy system diagnostics. www.ethernet-powerlink.orgEthernet Powerlink Standardization Group

FL-Net: Connecting the factory floor

FL-net (OPCN-2) protocol, developed by the Japan Electrical Manufacturers’ Association (JEMA), connects PLCs and numerical control units using Ethernet cable and enables mutual exchange of control data among controllers at high speed. FL-net (OPCN-2) supports a number of protocols including UDP/IP and the FA link, located in the upper layer of UDP/IP. www.jema-net.or.jp/EnglishJapan Electrical Manufacturers Association

ONLINE extra

Ethernet protocols in use for industrial applications

Significantly more people are using Ethernet for industrial applications. The following shows the percentage of survey respondents who currently (May 2008) use the following Ethernet protocols, compared to current and planned use among survey respondents in December 2006.

95% TCP/IP (native) up from 73% in December 2006

88% EtherNet/IP up from 73%

81% Modbus TCP up from 48.5%

79% UDP (native), up from 23.6%

43% Fieldbus Foundation High Speed Internet (HSE), up from 20%

41% EtherCAT, up from 10.6%

38% SERCOS III, up from 11.4%

36% Profibus Profinet, up from 20%

31% CC-Link IE (Gigabit Ethernet), new

27% Ethernet Powerlink, up from 8%

 

Read the December 2006 article about these protocols…

Industrial Ethernet Protocols: Survey results show who's winning and why

www.controleng.com/article/CA6396565.html

 

Related reading: Ethernet hardware

Dozens of new Ethernet products are introduced weekly. Here’s a sampling of some recent introductions.

Ethernet hardware: Switches and more

www.controleng.com/article/CA6555610.html

 

More about Ethernet protocols

More Ethernet protocol information follows.

 

TCP/IP: The IETF regularly updates the protocol and congestion control algorithms that help stabilize the Internet and deals with other issues that include updates, maintenance, standards, and protocol changes as needed.  It is a layered protocol, with each layer solving a set of problems involving the transmission of data and providing well-defined service to the upper-layer protocols based on using services from the lower ones.

 

Modbus TCP: With a Modbus driver and an understanding of Ethernet and TCP/IP sockets, a user is said to be able to have a device up and communicating in a few hours with minimal hardware. No licensing fees are required for using Modbus over serial line. Modbus TCP specifications and implementation guides may be downloaded for free at the Modbus Organization Website. In fall 2007, ODVA extended the CIP standard to provide seamless access to Modbus devices, requiring no change for Modbus TCP target devices or EtherNet/IP target devices, thus opening the market further for Modbus device

suppliers as well as offering users, whose applications include CIP networks, the opportunity to specify product from among the thousands of Modbus devices available.

 

UDP: Not suitable for applications requiring ordered, reliable delivery of streams of data, the UDP module must be able to determine the source and destination Internet addresses and the protocol field from the Internet header. One possible UDP/IP interface would return the entire Internet datagram, including the Internet header, in response to a received operation. Such an interface would also allow the UDP to pass a full Internet datagram complete with header to the IP to send. The IP would verify certain fields for consistency and compute the Internet header checksum. As with the the TCP/IP protocol, information is also available at

 

Profinet: Wireless is a necessity when untethered devices, like automatic guided vehicles, must be controlled. Profinet also is said to protect users’ investments in their current plant equipment and networks by seamlessly assimilating existing Profinet installations and installations of other fieldbuses. While embracing industry standards like Ethernet, TCP/IP, XML, and OPC, Profinet is an open, industrial standard.

 

CC-Link IE features token-passing collision avoidance, 256k bytes network common memory, 120 stations per network capability, 550 m maximum cable length between two stations, and the ability to handle 239 interconnected networks. Other protocols in the family are CC-Link, which can connect controllers, and CC-Link/LT, for smaller devices; field and motion protocols are planned, the organization says. Core technology was donated by Mitsubishi Electric Automation.

 

HSE: Supports interoperability between disparate controllers and gateways from multiple suppliers. HSE is designed to support fault-tolerant networks and devices used in mission-critical monitoring and control applications. All or part of the HSE network and devices can be made redundant to achieve the level of fault tolerance required for any given application.  It supports complex logic functions for data-intensive process devices and enables plant optimization. It is an international standard (IEC 61158).

 

EtherCAT: Because of its inherent cabling flexibility, EtherCAT can be implemented in any topology (star, line, tree, or ring) needed for an application. All types of Ethernet devices can be integrated via a switch or switch port, and other fieldbus devices can be used with simple gateways. It operates with cost-effective, standard Ethernet cards (NICs). EtherCAT technology is used to ensure compatibility and continuity throughout an I/O system in existing industrial infrastructure as well as for future system revisions and expansion. Automation software, industrial PCs, control panels, Ethernet PCI cards, and servo drives are available with built-in EtherCAT connectivity, along with a selection of other drives, controllers, and sensors.

 

SERCOS III:  Non-SERCOS III Ethernet frames can be transmitted in parallel to the real-time communications. Any standard Ethernet device can be connected to an unused port on the ring and communication is possible even when real-time communication is not active. It works with prior SERCOS servo and motion profiles, cyclic and non-cyclic communication, and synchronization mechanisms. Other new features include fast independent cross communications between slave devices, hardware redundancy for fault tolerance in case of a break in the ring, hot plugging for connection and removal of nodes during operation, and safe communication using CIP Safety on SERCOS. To work without switches or hubs it uses either low-cost FPGA communications controllers or SoftMasters for operation with standard commodity hardware.

 

Ethernet-Powerlink: EPSG says the search for the “best” real-time fieldbus tends to be dominated by the one criterion: speed. As a result, other technical features that may be of greater importance depending on planned application and that provide additional benefits may receive too little attention. Users must take them into account, however, to get the full picture needed to support their decision-making process.

 

Links to other industrial Ethernet networks:

 

Mechantrolink III … www.mechatrolink.org/en/about/mecha4.html

SafetyNet www.safetybus.com

VARAN www.varan-bus.net/index_en.htm

synqNet www.synqnet.org

 

FL-Net: FL-Net: Connecting the factory floor

FL-net (OPCN-2) protocol, developed by the Japan Electrical Manufacturers’ Association (JEMA), connects PLCs and numerical control units using Ethernet cable and enables mutual exchange of control data among controllers at high speed. FL-net (OPCN-2) supports a number of protocols including UDP/IP and the FA link, located in the upper layer of UDP/IP. Ethernet connects the controllers with an upper layer or personal computer and is used for transmission and control of production information. An FL-net (OPCN-2) unit is implemented in a controller, such as a PLC or CNC and transmits and receives data cyclically among controllers only by assigning a node number and common memory for linking in the same manner as the CPU link unit of a normal PLC, making a particular communication program for the PLC is unnecessary.

www.jema-net.or.jp/English

Japan Electrical Manufacturers Association

 

Other resources for, information about Industrial Ethernet… Links and online extra material for May 2008 PR   Industrial Ethernet Protocols: Survey results show who's winning and why http://www.controleng.com/article/CA6396565.html   CC-Link IE: First, open, industrial Gigabit Ethernet protocol www.controleng.com/article/CA6493699.html   Wikipedia list of automation protocols http://en.wikipedia.org/wiki/List_of_automation_protocols   Wikipedia list of industrial Ethernet http://en.wikipedia.org/wiki/Industrial_Ethernet   Real-time Ethernet options… http://www.real-time-ethernet.de/   Virtual Automation Networks… www.van-eu.eu