What Is PROFINET?
PROFINET, based on the TCP/IP model, adopts the real-time mechanism and communications protocols at the application layer. Therefore, PROFINET has the same features as standard Ethernet, such as full duplex and support for multiple topologies. PROFINET can transmit data at a rate of 1 Gbit/s. In addition, it has its own unique features. For example, it can exchange data in real time, and it is a next-generation automation bus standard for data communication over industrial Ethernet. PROFINET provides a complete network solution, including real-time Ethernet and motion control, for the automation communications field. This document describes why PROFINET is required, what the components of the PROFINET IO system are, and how PROFINET works.
Why Do We Need PROFINET?
In recent years, new network technologies have driven rapid developments in fields such as industrial automation, process control, robot control, and smart manufacturing. These fields are raising their requirements on data transmission speed as well as network interconnection and scalability. However, traditional industrial Ethernet technologies cannot meet such requirements.
Industrial communications forms the "nervous system" of the connected world. As innovations keep emerging and product lifecycles are shortening in various industries, fast response and process optimization become critical to ensuring long-term competitiveness. By combining industrial Ethernet with Internet technologies, PROFINET optimizes and expands the standard Ethernet. Therefore, PROFINET has the same features as standard Ethernet, such as full duplex and support for multiple topologies. PROFINET can transmit data at a rate of 1 Gbit/s. In addition, it has its own unique features. For example, it can exchange data in real time and supports multiple network topologies for greater openness, flexibility, efficiency, and performance. This helps meet the requirements of modern industries for low latency as well as high reliability, flexibility, and real-time performance.
The following figure shows the OSI reference model of PROFINET.
OSI reference model of PROFINET
Different protocols exist at the physical layer, link layer, network layer, transport layer, and application layer of PROFINET. The transmission rate at the physical layer can reach up to 1 Gbit/s, and the protocols in the TCP/IP protocol suite are used at the network layer and transport layer. The specifications of the PROFINET link layer and application layer are unique.
The PROFINET link layer complies with standards such as IEEE 802.3, IEEE 802.1Q, and IEC 61784-2 to ensure full duplex, priority tagging, and expansion capabilities, respectively. In this way, real-time communications (RT) can be implemented, which provides optimized real-time channels based on the Ethernet link layer and has a response time ranging from 5 ms to 10 ms.
At the application layer, PROFINET uses multiple protocol standards, such as IEC 61784 and IEC 61158, which ensure the PROFINET IO services.
Nodes from different manufacturers exist in a current industrial automation system. To ensure error-free data exchange between nodes from different manufacturers, all devices in the system need to support the PROFINET function, and support for PROFINET becomes a necessary condition.
What Are the Components of the PROFINET IO System?
Communications between devices supporting PROFINET is implemented based on the PROFINET IO system, a distributed control system comprising three components: IO Controller, IO Device, and IO Supervisor. A PROFINET IO system consists of at least one IO Controller and one IO Device, and IO Supervisor is typically used as a temporary component for debugging or diagnosis, as shown in the following figure.
PROFINET IO system model
IO Controller: is the master station of the PROFINET IO system. The CPU module of the programmable logic controller (PLC) which supports PROFINET typically functions as the IO Controller. The IO Controller carries out various control tasks, including executing user programs, exchanging data with the IO Device, and processing various communications requests.
IO Device: is the slave station of the PROFINET IO system. A field device (such as a robot arm or switch that supports PROFINET) typically functions as the IO Device. It is controlled and monitored by the IO Controller and consists of IO modules that are distributed on site and used to obtain data.
IO Supervisor: connects devices and programs the system. It downloads related data to the IO Controller as well as diagnoses and monitors the system. A user's programming computer functions as the IO Supervisor in most cases.
The IO Controller serves not only as a data producer to output data to the IO Device, but also as a data consumer to receive data provided by the IO Device. Likewise, the IO Device consumes output data of the IO Controller and also provides data for the IO Controller.
The following figure shows the basic PROFINET networking in which all terminals support PROFINET.
Basic networking diagram of PROFINET
In industrial scenarios, terminals 1, 2, and 3 often transmit PROFINET packets to devices using PLC. When DeviceA, DeviceB, and DeviceC all support PROFINET, they forward PROFINET packets to terminals 4, 5, and 6 through IP networks. In this way, PLC can be used to control terminals 4, 5, and 6.
If a device does not support PROFINET, for example, DeviceA does not support PROFINET but DeviceB does, DeviceA can only forward PROFINET packets sent by PLC, and real-time data exchange is unavailable between DeviceA and DeviceB and between PLC and DeviceA. As a result, DeviceB and PLC cannot obtain information about DeviceA.
How Does PROFINET Work?
After the IO Controller on PROFINET uses DCP to discover an IO Device, an Application Relation (AR) and a Communication Relation (CR) are created between them and device parameter settings are exchanged. Data can then be forwarded in the PROFINET IO system.
DCP
The Discovery and Basic Configuration Protocol (DCP) is a link layer protocol that provides multiple services for PROFINET, such as discovering and identifying devices, setting device names, and configuring IP addresses.
To implement these services, DCP provides the Identify All, Identify, Set, Set-Flash, Set-Reset to Factory, and Get functions. The PROFINET engineering tool, controller, and device all support the DCP service, but they deliver different functions. For example, the IO Device needs to respond to the commands released by the IO Controller and proactively use the Hello function to send messages to the IO Controller, while the IO Controller must be able to use the Identify function to search for specific devices. The main functions are described as follows:
Identify All: identifies all devices. Messages are broadcast to the entire network, and all devices must respond to the received messages. The engineering tool can use this function to obtain the information list of all devices to check the following issues on the network:
1. Whether the devices are connected.
2. Whether the device names are set.
3. Whether there are duplicate IP addresses or device names.
4. Whether the device names and IP addresses are properly set.
5. Whether the device types or suppliers are properly set.
The Identify All function enables the engineering tool to easily implement network management.
- Identify: searches for a specific device and checks device parameter settings. Before the system is started, the IO Controller uses this function to identify a device by name, and the corresponding device responds. If the length of a device name is set to 0, all devices that are not assigned names respond.
- Get: obtains device information. For example, to obtain the name, IP address, and manufacturer information of a device, you can set multiple conditions in a request frame in sequence to find the matching device.
- Set: writes parameters to a device. This function writes the name, IP address, and factory settings to the device.
- Set-Flash: enables the LED indicator of a specified I/O device to blink. When multiple devices of the same type exist on the same network, you can determine the object to be operated by making the LED indicator blink.
AR and CR
AR: Data is transmitted between the controller/monitor and a device through a precisely defined communications channel. Based on the received connection information, the controller establishes a communications channel, and must do so before data is exchanged. Each data exchange is embedded in an AR. A device can connect to only one controller, and an AR can be established between them.
CR: A CR specifies a clear communications channel identifier between a consumer and a producer. A CR must be established in an AR so that data can be exchanged. Multiple CRs can be created in an AR.
Data Forwarding
The following figure shows the data forwarding process of PROFINET.
Data forwarding process of PROFINET
- Device startup: After a device is powered on, the system is initialized and the IO Supervisor discovers the device using the LLDP protocol.
- System configuration: The system engineer needs to import the GSDML file (general station description) of the IO Device to the IO Supervisor on the TIA Portal. The GSDML file is provided by the device manufacturer and describes the device attributes, including the device identification information (device ID, manufacturer ID and name, product series, and number of ports), number and type of pluggable modules, definition of diagnostic information, communications parameters of the IO Device (including the minimum cycle time and reduction ratio), and configuration data (including the speed, duplex mode, VLAN, and port security information) of the IO Device module. After obtaining the information, the system engineer allocates the corresponding IO Controller to the IO Device.
- Station name setting: After discovering an IO Device, the IO Supervisor assigns it a station name and an IP address. The station name indicates the function or installation location of the IO Device in the system, and is sent to the IO Device through the DCP protocol.
- Information download: The IO Supervisor downloads the system configuration information to the IO Controller.
- Device discovery: The IO Controller uses the obtained system configuration information to discover the IO Device through DCP and assigns it an IP address.
- AR and CR establishment: After the IO Controller is started or restarted, it always starts the system using the configuration information. During the system startup, the AR and CR are established between the IO Controller and IO Device, and related objects are parameterized.
- Data exchange: After the system is started successfully, the IO Controller exchanges process RT data with the IO Device.
- Author： Meng Xianhai
- Updated on： 2024-06-14
- Views： 1397
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