Industrial Networking Explained: EtherNet/IP, PROFINET and Modbus TCP
Modern industrial machinery relies on communication.
A PLC may need information from remote I/O located elsewhere on a production line. A variable speed drive needs to receive speed commands. An HMI needs access to machine data. A SCADA system may collect information from multiple PLCs, while different pieces of production equipment need to exchange status information with one another.
Industrial networks make these connections possible.
Three names frequently encountered in industrial automation are EtherNet/IP, PROFINET and Modbus TCP.
All three can operate over Ethernet-based networks, but they are not simply different names for the same technology. They have different architectures, capabilities and typical applications.
Understanding the basics can make it much easier to specify new equipment, integrate machinery and diagnose communication problems.
What is an industrial network?
An industrial network allows automation devices to exchange data.
Historically, many control systems relied heavily on individual hardwired signals. A device requiring ten separate pieces of information could potentially require multiple individual wires connected back to the control panel.
Industrial communication networks allow large amounts of information to be transmitted digitally between compatible devices.
A PLC might communicate with:
Remote I/O
Variable speed drives
Servo systems
HMIs
SCADA systems
Other PLCs
Instrumentation
Robots
Safety devices
Intelligent sensors and field equipment
This can reduce the amount of point-to-point wiring required while providing significantly more information about the equipment.
The network effectively becomes part of the control system's nervous system, carrying information between the devices responsible for controlling and monitoring the process.
Isn't industrial Ethernet just normal Ethernet?
Not quite.
Industrial Ethernet technologies use many of the principles and technologies associated with standard Ethernet, but industrial automation creates requirements that an ordinary office network does not necessarily have.
If an office printer receives information slightly later than expected, the impact is usually insignificant.
On a production machine, timing can be considerably more important.
A PLC may be coordinating motors, drives, remote I/O and other equipment where predictable communication is required for the process to operate correctly.
Industrial environments also introduce practical challenges such as electrical interference, vibration, temperature, long operating periods and the need for equipment that can be maintained reliably in production environments.
The network therefore needs to be designed around the requirements of the industrial application, rather than treated as ordinary office IT infrastructure.
What is PROFINET?
PROFINET is an Industrial Ethernet communication technology widely used within automation and particularly associated with Siemens automation systems.
It allows controllers such as PLCs to communicate with devices including distributed I/O, drives, HMIs and other industrial equipment.
In a typical Siemens-based automation system, for example, a PLC may use PROFINET to communicate with remote I/O stations distributed around a machine.
Instead of every sensor and actuator being individually wired back to the main PLC panel, devices can connect to remote I/O located closer to the equipment. The PLC then exchanges data with those I/O stations over the network.
PROFINET can also support applications where communication timing is particularly important, including motion and other time-sensitive automation requirements.
For facilities already using Siemens PLCs, HMIs and drives, PROFINET is commonly a natural part of the overall control architecture.
What is EtherNet/IP?
EtherNet/IP is another widely used Industrial Ethernet protocol.
Despite the name, the “IP” refers to Industrial Protocol, although EtherNet/IP also uses standard Ethernet and TCP/IP technologies as part of its architecture.
EtherNet/IP uses the Common Industrial Protocol, or CIP, for communication between industrial devices.
It is particularly common within automation systems built around Allen-Bradley and Rockwell Automation equipment, although the protocol is supported by equipment from numerous manufacturers.
A PLC might use EtherNet/IP to exchange data with remote I/O, drives, HMIs, robots or other controllers.
As with PROFINET, this allows devices throughout a machine or production environment to exchange both control and diagnostic information.
What is Modbus TCP?
Modbus TCP is the Ethernet-based version of the Modbus communication protocol.
Modbus has been used in industrial environments for decades and remains common because of its relatively straightforward approach and widespread support.
Modbus TCP allows devices to exchange data over Ethernet using TCP/IP.
It is frequently encountered when connecting PLCs to instrumentation, energy meters, drives, third-party equipment and other devices where relatively straightforward data exchange is required.
One of the advantages of Modbus TCP is its broad availability across equipment from many different manufacturers.
However, communication often depends on understanding exactly where particular information is stored within the device.
For example, an engineer integrating a third-party energy meter may need to know which Modbus registers contain voltage, current, power or energy values and how those values are formatted.
The network connection may be working perfectly while the PLC still displays incorrect information because the data has been interpreted incorrectly.
EtherNet/IP vs PROFINET vs Modbus TCP
It is tempting to ask which of these protocols is best.
As with choosing between PLC platforms, there is rarely a useful universal answer.
PROFINET is particularly common within Siemens-oriented automation environments and provides extensive capabilities for industrial control and device integration.
EtherNet/IP is widely associated with Rockwell Automation and Allen-Bradley environments and provides comprehensive communication between controllers and industrial devices using CIP.
Modbus TCP offers a comparatively straightforward method of exchanging data and is supported by a very wide range of industrial equipment.
The right protocol depends on the application, the PLC platform, the equipment being connected, performance requirements and the existing automation infrastructure.
In many factories, the answer may actually be more than one.
Can different industrial protocols exist on the same site?
Absolutely.
A factory does not necessarily operate one communication protocol throughout the entire facility.
One production line may contain Siemens PLCs communicating over PROFINET, while another uses Allen-Bradley controllers and EtherNet/IP.
Elsewhere, a PLC might use Modbus TCP to collect information from an energy meter or third-party process instrument.
This becomes particularly common in facilities that have expanded over many years.
New machines arrive from different OEMs. Production lines are upgraded at different times. Automation platforms change, and individual pieces of equipment are replaced.
Eventually, the site can contain several generations of automation equipment and multiple industrial networks.
This is one reason why good network documentation becomes increasingly important.
What happens when two systems use different protocols?
Sometimes two pieces of equipment need to exchange information but do not communicate using the same protocol.
There are several ways this can be addressed depending on the equipment and application.
A gateway or protocol converter may be used to translate information between different communication systems. In other situations, a PLC or another automation device may support both protocols and act as the connection between the systems.
The right approach depends on factors such as how much data needs to be exchanged, how quickly it needs to move and how important that communication is to the operation of the machinery.
Simply making two devices capable of exchanging data is not always enough.
The integration also needs to remain reliable, understandable and maintainable.
Why industrial network problems can be difficult to diagnose
A communication fault does not always look like a network problem.
An operator may simply report that a drive will not start.
The drive itself could be perfectly healthy, but the PLC may have lost communication with it.
A remote I/O station dropping offline could cause multiple sensors to appear faulty simultaneously. An incorrectly configured device address could prevent a replacement component from communicating. A damaged network cable or connector could produce an intermittent fault that only appears when the machine is operating.
Other problems can arise from network configuration, incompatible settings, device replacement, electrical interference or modifications made without updating the documentation.
This is why effective automation fault finding often requires engineers to look beyond the individual device displaying the fault.
Industrial networking makes diagnostics more powerful
The same networks that introduce another layer of complexity can also provide considerably better diagnostic information.
Traditional hardwired equipment may provide little more than an ON or OFF signal.
An intelligent device connected through an industrial network can potentially provide much more information.
A drive, for example, may communicate operating status, speed, current, fault information and other diagnostic data directly to the PLC.
That information can then be made available through the HMI or SCADA system.
When properly designed, this gives operators and maintenance teams much greater visibility into what the machinery is doing and why it has stopped.
The value of industrial networking is therefore not simply reduced wiring. It is also the ability to make more information available throughout the control system.
Network design should consider maintenance
A network that works perfectly during commissioning can still become difficult to maintain if nobody understands how it has been constructed.
Industrial network documentation should make it possible to identify devices, network connections and important configuration information.
Device naming should also be consistent and meaningful.
This becomes especially valuable several years after installation when the engineer who originally commissioned the equipment may no longer be available.
When a replacement PLC, drive or remote I/O module needs to be installed, accurate information about the network can significantly reduce the time required to restore the system.
Cybersecurity also matters
As industrial systems become increasingly connected, industrial networking also introduces cybersecurity considerations.
A PLC network should not automatically be treated in the same way as a general corporate network, nor should industrial equipment be connected to wider networks without understanding the consequences.
Network segmentation, access control, remote-access arrangements, device configuration and collaboration between engineering and IT teams can all form part of an appropriate industrial cybersecurity approach.
The objective is not to prevent useful connectivity.
It is to make sure connectivity is introduced deliberately and managed appropriately for the operational environment.
Choosing an industrial network
When designing or upgrading an automation system, protocol selection should normally follow the requirements of the application rather than starting with a preferred protocol.
Consider what equipment needs to communicate.
Which PLC platform is being used?
Which protocols are supported by the field devices?
How quickly does information need to be exchanged?
Does the system require deterministic or time-sensitive communication?
Will third-party equipment need to be integrated?
How will engineers diagnose network faults?
What equipment and expertise already exist on site?
How is the network likely to expand in the future?
Answering these questions usually makes the appropriate communication architecture much clearer.
Industrial networks are part of the control system
EtherNet/IP, PROFINET and Modbus TCP ultimately perform the same broad job: allowing industrial devices to exchange information.
But the way they achieve that, their capabilities and the automation environments in which they are commonly used differ.
For engineering teams, understanding these differences becomes increasingly important as machinery becomes more connected.
A reliable industrial network is no longer simply an infrastructure consideration. It directly affects machine operation, diagnostics, maintenance and the ability to integrate future automation equipment.
At Stratos Control Systems, we work with PLCs, HMIs, SCADA systems, drives, remote I/O and industrial communication networks across Siemens, Allen-Bradley and Mitsubishi automation environments.
Whether you are integrating new equipment, diagnosing an intermittent communication fault or modernising an existing control system, the network needs to be considered as part of the complete automation architecture.
Speak to Stratos Control Systems about PLC integration, industrial networking, fault finding and control system upgrades.
