industrial ethernet
November 2013
Essentials of
Industrial ethernet
A Control Essentials Guide, by the editors of Control
About the Control Essentials Series
The mission of the Control Essentials series is to provide process industry professionals with
an up-to-date, top-level understanding of a range of key process automation topics. Our intent
is to present essential engineering concepts in a practical, non-commercial fashion, together
with a review of the latest technology and marketplace drivers—all in a form factor well suited
for onscreen consumption. We hope you find this edition on Industrial Ethernet useful. Check in
at ControlGlobal.com/Essentials for other installments in the weeks to come.
—The Control Editorial Team
This Control Essentials guide made
possible by TURCK. See page 8 for
more information on TURCK’s full
range of Industrial Ethernet
products and services.
EXECUTIVE SUMMARY
E
thernet just celebrated its 30th birthday. In
1983, IEEE published the 802.3 standard
as a draft and, ever since, Ethernet has
come to dominate the commercial and consumer
world. Every home PC comes with an Ethernet
port, and virtually all communications are done
via Ethernet—except in the industrial world.
For years, industrial users criticized Ethernet’s
lack of determinism—that is, its inability to guarantee a response time, which is critical for realtime control and monitoring systems. Critics also
took issue with using an “office” network in an
industrial environment, the lack of redundancy,
problems with electrical noise, and so on. Ethernet
simply couldn’t be used, they said.
In 1999, the IEC decided that industrial networks needed to be defined and standardized, so
they wrote the IEC 61158 fieldbus standard, and
said eight networks met the standard. Some of the
approved networks have more or less disappeared
from the scene (P-Net, SwiftNet and WorldFIP)
and some new ones joined, leaving Foundation
fieldbus H1, HART, ControlNet, Profibus, DeviceNet, Modbus, Interbus and AS-I as the primary
non-Ethernet device-level networks.
Ethernet wasn’t ready for industrial applications
in 1999, so the industrial world was content to follow major automation vendors down the fieldbus
and device network path. But things have changed.
According to IMS Research, Industrial Ethernet
is growing fast and will become the dominant
networking technology within 10–15 years. ARC
Advisory Group says that Industrial Ethernet is
establishing itself as the common industrial network, displacing application-specific fieldbuses
across a broad spectrum of industries.
What is Industrial Ethernet? Simply put, it’s
just standard Ethernet with rugged connectors, devices that can withstand environmental
conditions found in industrial environments,
redundant configurations, and a few other
changes that make Ethernet more deterministic for industrial use. Because of this, Industrial
Ethernet is crowding into virtually every area of
a factory or process plant.
The most popular Ethernet-based industrial networks include EtherCAT, EtherNet/IP,
Foundation Fieldbus HSE, Profinet, Sercos,
CC-Link, and standard Ethernet TCP/IP. The
beauty of Ethernet is that it’s like an “information super highway”; that is, the highway can accommodate plenty of different types of traffic
at the same time. For example, a single Ethernet cable might have EtherNet/IP connecting to
a f lowmeter, Profinet connecting fieldbus systems, and Sercos connecting to motor drives.
Industrial Ethernet is a force to be reckoned
with.
THE PLAYERS
F
igure 1 shows the predicted use of Industrial Ethernet networks in
2015, according to IMS Research. It’s interesting to note that standard Ethernet TCP/IP is predicted to be the most popular, at 40.2%.
The next two most popular are Profinet and EtherNet/IP — in no small
part because of ardent support from Siemens and Rockwell Automation,
respectively.
Most Industrial Ethernets were first developed by vendors to support their
own products. The vendors helped form support groups, then turned their
proprietary network over to the support group as an “open” network available to all. To the right is a capsule summary of the major players.
Others, 9.5%
HSE, 0.7%
sercos III, 2.1%
Ethernet
TCP/IP, 40.2%
EtherCAT, 3.1%
POWERLINK,
4.2%
CC-Link—Originally developed by Mitsubishi Electric, CC-Link became an “open” network, and is supported by the CC-Link Partner Association (CLPA).
EtherCAT—Originally developed by Beckhoff, EtherCAT is now an
open network that uses “pass-through reading.” That is, EtherCAT messages are passed on before processing in each network node, providing for
very short cycle times. EtherCAT is supported by the EtherCAT Technology Group (ETG).
EtherNet/IP—Originally developed by Rockwell Automation, EtherNet/
IP is now an open network supported by the Open DeviceNet Vendors Association (ODVA). It is built on standard Ethernet TCP/IP protocols, and
can be used for both discrete automation and process control.
Ethernet Powerlink—Originally developed by B&R Automation, Powerlink is supported by the Ethernet Powerlink Standardization Group
(EPSG). It uses a “time slicing” method to guarantee transfer of timecritical data.
Ethernet TCP/IP—Ethernet consists of physical hardware, such as cables, connectors, routers and switches, which are all the same no matter
what Industrial Ethernet is being used. TCP/IP is a protocol that defines
how data in the packets is arranged and interpreted. Modbus TCP/IP, for
example, simply embeds its packets into the TCP/IP protocol. Other industrial Ethernets define their own protocols.
Foundation Fieldbus HSE—Developed to support Foundation Fieldbus
(FF) applications, HSE uses standard Ethernet hardware to connect systems and subsystems in a FF system.
Modbus
TCP/IP, 6.4%
EtherNet/IP,
13.9%
Gigabit Ethernet,
5.5%
PROFINET, 14.5%
Figure 1. Estimated use of Industrial Ethernet by 2015.
Source: IMS Research.
Profinet—Originally developed by Siemens and the Profibus User Organization, Profinet—like FF HSE—was initially established to provide
high speed communications for Profibus fieldbus systems. Profinet has
since expanded into direct device communications and can be used for
both automation and process control.
Sercos III—Developed by Bosch Rexroth and the German Machine Tool
Builders Association (VDW), Sercos III is primarily used for fast motion
control applications. Sercos is supported by Sercos International (SI). It
uses the CIP safety protocol, making it compatible with EtherNet/IP.
HOW ETHERNET WORKS
F
ollowing is a vastly simplified explanation of how Ethernet and Industrial Ethernet work. The IEEE 802.3
standard defined the OSI Reference Model,
which describes how information moves
over Ethernet. The OSI model has seven
layers, which include:
• Application layer, which consists of application programs that use the network
• Presentation layer, which standardizes data
presentations to the applications
• Session layer, which manages sessions between applications
Figure 2. Industrial Ethernet can be set up in star, line (bus) or ring topologies.
• Transport layer, which provides end-to-end
error detection and correction
along the cable. If one exists, it sends incoming messages to it. If no device exists, the NIC
• Network layer, which manages connecsends the message back. This allows Ethernet networks to be assembled in several different
tions across the network for the upper layers
topologies: star, line (bus) or ring (Figure 2).
• Data Link layer, which provides reliable data delivery across the physical link
In a star topology, a central Ethernet switch connects to one or more devices over a bidi• Physical layer, which defines the physical characteristics of the network media
Ethernet hardware at the physical level is essentially the same for all versions of Ethernet. rectional cable. The advantages of a star network are speed of transmission, isolation of critiThis includes cables, connectors, routers, switches, etc. Any computer, PLC, flowmeter, ro- cal devices, and the ability to easily diagnose problems. Star connections are often used in
bot or device that has an Ethernet Network Interface Card (NIC) can connect to Ethernet. fast real-time applications, such as motion control or machine safety, where response time
In almost all cases, the NIC function is built into devices these days. Each NIC has a unique is critical.
Ring networks are used to connect multiple devices, and overcome the distance limita48-bit MAC (media access control) address.
The data format or protocol for standard Ethernet is contained in the Data Link layer. In- tions of wired Ethernet (100 m maximum). Because a disruption in the ring—such as a forkdustrial Ethernet encompasses the physical, data link, network and transport layers by using lift running over a cable—can disrupt communications, a ring can be set up to send data in
Internet Protocol (IP) addressing in the network layer and Transmission Control Protocol both directions.
A bus network connects multiple devices along a single bidirectional cable. A bus
(TCP) in the transport layer. This is also known as the IP suite, or TCP/IP.
The NIC has intelligence that can analyze incoming data; if the device sees that an in- network is simple, inexpensive and minimizes the amount of cable needed for a netcoming message is addressed to its MAC address, it will process the data; otherwise, it passes work. If one device fails, however, the entire network can fail unless a redundant systhe message to the next device on the cable. A NIC knows if another device exists farther tem is established.
INDUSTRIAL ETHERNET HARDWARE
O
ne of the biggest differences between “office” Ethernet and Industrial Ethernet is the
hardware. Although both use the same types
of plugs, cable, cords, switches and routers (Figure 3),
equipment built for Industrial Ethernet is more robust,
and able to withstand industrial environments.
Connectors and Cordsets — The two types of connectors for Ethernet copper cable are RJ45 and M12. The
RJ45 connector is the same connector that plugs into your laptop,
but the M12 connector is a round,
8-pin device that supports data
rates up to 10 GB/sec. The M12 is
best for harsh environments. SC
and LC connectors are commonly
used with fiber. Cordsets are Ethernet cables that come with connectors at both ends. With raw
cable, on the other hand, technicians must cut cable to length
in the field and attach connectors. Cables are rated for
speed and susceptibility to noise. Category 5 cables are
used in offices, but industrial applications call for Category 6 or 6E cables, which can carry 10GB, are less susceptible to crosstalk and EMI noise, and resist physical
deterioration in industrial environments.
Switches, Gateways and Routers — A switch is
a multi-port device that receives a transmission at one
port and sends it to the targeted device. The switch learns
the MAC addresses of all devices, builds a MAC address
Figure 3. Typical Industrial Ethernet hardware configuration. A is cordsets, B is cable, C is I/O, and
D is interconnect products, such as switches and routers.
table, watches for traffic intended for that MAC address,
and sends the message directly to that device. A managed
switch has features that allow for
redundant configurations, management of network traffic, diagnostics, etc., while an unmanaged switch is simpler, for use in
smaller networks. While a switch
connects to devices, a router links two or more Ethernet
networks, each having independent IP addresses. A router
often has interfaces for different physical types of network
connections, such as copper cables, fiber optic, or wireless. The larger the network, the more routers are needed
to manage Ethernet traffic. A gateway is a type of router
that connects two different types of networks with different protocols, such as Ethernet and DeviceNet. Gateways
allow legacy or proprietary networks to gain access to the
main Ethernet network.
Ethernet I/O — Although Ethernet is slowly but surely getting embedded into many types of sensors, transmitters, motor
drives, robots and
other I/O devices,
millions of sensing
and control devices
are still not connected. Ethernet
I/O systems connect to these devices, accept their mV, 4-20mA and other outputs, and put them into an Ethernet packet for transmission.
Likewise, they accept data values from a packet and convert
them to outputs suitable for the control device.
ISSUES & TRENDS
A
recent study by the Aberdeen Group notes that manufacturers need real-time visibility into plant floor operations to optimize production, maintenance and safety.
Networks provide this data, but many manufacturers are managing multiple networks, which entails extra levels of hardware and software that do the same thing. Aberdeen
sees a major trend toward the adoption of industrial Ethernet across entire manufacturing
operations. “The opportunity exists now more than ever to overcome the historic isolation
of the control platform from the enterprise,” says the study. “Moving forward, it is time for
manufacturers to visualize the real-time enterprise and take steps to lay the real-time network foundation that they need to support it.”
Aberdeen agrees with IMS Research and ARC that Industrial Ethernet is growing at a
remarkable rate, and may soon take over manufacturing. This may come at the expense of
fieldbus networks, as ARC noted. For example, EtherNet/IP is now available in flowmeters,
where it provides the same functions as fieldbus—device diagnostics, operation in hazardous environments, and multiple flowmeters on a single “segment.” However, EtherNet/IP
does not require the expense and overhead of fieldbus, and its data is readily available to any
device with an Ethernet connection, such as a PLC or PC.
Devices on EtherNet/IP can be polled by a condition monitoring system to determine if
there are any diagnostic messages that need to be sent to maintenance personnel. An industrial
PC equipped with asset management, maintenance, condition monitoring or HMI/SCADA
software can access all the I/O and diagnostic information it needs directly from the devices
via the Ethernet interface. Ethernet devices can now operate in hazardous areas. Intrinsically
safe power-over-Ethernet (PoEX) allows Ethernet devices to be used in Zones 1 and 2.
Managing Multiple Networks
When a manufacturer has multiple networks in a plant—such as Ethernet, fieldbus, wireless
and dedicated device networks—it must support and maintain all of them. Each network
requires training that cannot be applied to the others. One of the advantages to adopting
Industrial Ethernet across a plant is that it simplifies maintenance and training, and allows
the plant’s IT technicians to service, diagnose and maintain automation networks without
additional training.
For example, most Ethernet devices support Simple Network Management Protocol
(SNMP). This enables IT technicians to monitor, troubleshoot and administer network devices using standard network management tools. This leverages the investments a company
has made in their IT support infrastructure, and minimizes the need for an automation or
process control engineer to also be an IT support engineer.
The Challenge of Cyber Security
Security can be a nightmare with multiple networks, as each one has to be protected against
intruders. With the increasing use of wireless networks, RTUs with maintenance ports, and
remote systems in unattended locations, intruders have many more opportunities to get in—
as was illustrated by the Stuxnet virus, which got into systems from infected PLCs.
Cyber security has become a major issue affecting manufacturing and process control.
President Obama issued Executive Order 13636 “Improving Critical Infrastructure Cyber Security” on February 12, 2013. The National Institute of Standards and Technology
(NIST) is currently working with industry leaders—such as the Automation Federation— to
finalize a comprehensive cyber security framework
While this guide cannot address security in depth, suffice it to say that Industrial Ethernet
users can employ the latest security devices and techniques, such as firewalls, demilitarized
zones (DMZs), and defense-in-depth security strategies as they become available. The same
cannot be said for non-Ethernet networks.
Over the past 30 years, Ethernet has overcome numerous obstacles, eliminated proprietary commercial and industrial networks, and is now moving into the industrial world at
its 10 GB/sec speed. While there will continue to be a need for certain kinds of specialized
networks—such as fieldbus or dedicated device level networks that are more deterministic,
cheaper, less sensitive to electrical noise, or work over longer distances—Ethernet’s penetration of the industrial market is just getting started.
ACRONYMS & DEFINITIONS
• Broadcast message—A communication from one device on a network to all
devices on the network.
• Bus topology—a network configuration where all devices are connected by a
single cable, which ends at the last device (see Ring and Star topologies).
• Collisions—Ethernet devices “listen” to the network to ensure they are the only
device transmitting at the time. If two devices transmit at the same time, a “collision” occurs, which garbles the messages (see CSMA/CD).
• Connectors—Two types of connectors for copper cable are RJ45 and M12. The
M12 connector is best for harsh environments. SC and LC connectors are commonly used with fiber.
• CSMA/CD (Carrier Sense Multiple Access/Collision Detection)—A
method for detecting collisions, and retrying messages until correct.
• DMZ (Demilitarized Zone)—A separate or perimeter network that isolates
vulnerable services such as email or web servers from the rest of the system.
• Firewall—Hardware or software that analyzes packets and determines if it should
be allowed through based on rules established by the user.
• Gateway—A routing device that connects two different types of networks with
different protocols, such as Ethernet and RS-485.
• Hub—Network device that receives a transmission at one port and sends it out all
its other ports. Hubs are rarely used. Switches are preferred.
• Logical address—a configurable network address, or a device’s IP address. IP
addresses can be assigned by an administrator.
• MAC (media access control) address—the unique, 48-bit physical address
for an Ethernet device.
• Managed Switch—A switch with features that allow for redundant configurations, management of network traffic, diagnostics, etc.
• Multicast message—Communication from one device to multiple devices on
a network (but not all—see Broadcast messages)
• Redundant configuration—A network that provides for an alternate communication path in case of network failure. This typically involves a duplicated cable, two Ethernet ports per device, and a switch that supports a redundancy protocol.
• Ring topology—Network configuration in which multiple devices are connected by
a single cable arranged in a “ring”; that is, the cable goes from device to device in a circular fashion, returning to its point of origin.
• Router—Links two or more Ethernet networks, each having independent IP addresses.
• Switch—Multi-port device that receives a transmission at one port and sends it to the
targeted device, based on its MAC address. The switch learns the MAC addresses of all
devices connected to its ports.
• Star topology—A network configuration where a central device—such as a PLC—
connects to single devices via separate cables; i.e., one device per cable.
• Unmanaged Switch—A simpler type of switch, used in smaller networks. It has few
of the features of a managed switch.
• Unicast message—Communications between two devices on a network.
MAde possible by
This Control Design Essentials guide on Industrial Ethernet was
made possible by TURCK, which manufactures a full range of
Industrial Ethernet distributed I/O products in a variety of
mechanical and field wiring formats and supporting a range
of Industrial Ethernet protocols.
Learn more about TURCK’s industrial Ethernet offerings.
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