PROFINET over TSN
Roadmap of PROFINET over TSN
Now that the PROFINET specification V2.4 with integrated TSN (Time Sensitive Networking) functionality has been published, PI (PROFIBUS and PROFINET International) is consistently working on the implementation of further modules for a successful market launch.
The TSN profile for "Industrial Automation" is currently being developed on the basis of use cases using the relevant IEEE Ethernet standards. Within "IEC/IEEE 60802", a Joint Working Group between the IEC and the IEEE, both the suitable functions of TSN and the configuration mechanisms for a convergent TSN network, are being defined.
In addition, the current version of the PROFINET specification is being updated as part of the IEC-61158 maintenance cycle. This specification forms the basis for creating test cases and implementing the PROFINET Tester for certification.
On this basis, manufacturers are working at full speed to implement their PROFINET solutions. In addition to demo installations at trade shows, various training courses and developer workshops are also being held to provide details and background information, as well as about the next steps in the specifications.
What remains exciting about the TSN mechanisms is its application.
Open questions are, for example:
- How to build a TSN network and how it must it be configured?
- What does GBit mean, and how can existing devices and system components be connected?
- How can vertical communication to superimposed systems, such as Cloud/Edge, be achieved in the same step?
PI provides answers to these questions so that TSN provides a future-proof common Layer2 technology for PROFINET communication in the field.
PROFINET over TSN
How does the integration of TSN in PROFINET work?
Many users are currently asking themselves why TSN (Time-Sensitive Networking) is the communication platform for future automation tasks.
To put it in a nutshell: Among other things, TSN aims to enable the convergent and robust use of a common Ethernet network for IT and OT applications.
Why is TSN even necessary?
As factories evolve, many additional components are being integrated in a plant, such as virus scanners. Such actions, such as a virus scan, stress the network because standard Ethernet (TCP/IP) can contain very large data packets and is not real-time capable. If larger TCP/IP data packets are present, they can block communication paths and it is not possible for real-time data packets to overtake them. This not only delays the delivery of the data packets in each switch, but also causes a real jam in the devices.
TSN offers advantages such as future-proof IEEE Ethernet technology with higher bandwidth, determinism, flexible network configuration, and a wide variety of chips. However, the declared goal of users is to continue to use proven PROFINET applications and existing architectures. For this reason, PI is not only working on integrating TSN, but also on making this new migration path as simple as possible for the user while remaining flexible for future I4.0 use cases.
Relief for the user
The good news is that it actuallymakes things easier for the user.
Today, network configuration (i.e. defining the communication paths from the controller to the device) is part of the engineering.
In the future, this task will be transferred to the software of the PROFINET devices and is thus part of the runtime in the controller or device.
This not only relieves the user; it also increases flexibility. The user only has to define simple rules for the network for the configuration calculation.
- Selection of a Working Clock Master (typically the PLC)
- Data rate (e.g. 100 Mbit/s or 1 GBit/s)
- Domain name
- Scheduling the update cycles
These settings are quickly done, especially since they are set for the entire network (the entire domain) and not per device. This reduces effort considerably. It is also no longer necessary to create a target topology during engineering - but this is still possible if required. In the meantime, the development and integration of the corresponding TSN mechanisms for use in today's automation world is quite advanced. Important functions, i.e. those relevant for industrial automation, have already been included in the standards and - or will soon be - integrated into standard chips. This opens up new application areas and hardware designs for controllers; in addition, field devices can be implemented more flexibly with these standard chips.
The goal set by PI of integrating TSN as an additional layer 2 technology in the PROFINET architecture has been achieved with the current PROFINET specification V2.4. The specification work has been completed and the three parts of the document can be downloaded from the PI website.
This enables both manufacturers and users to implement the advantages of TSN in an interoperable manner. The manufacturers of a PROFINET field device then simply use the corresponding modules and stacks or ready-made technology modules. This means they do not have to understand the details or even implement them themselves, as is the case today. As a result, device manufacturers can easily add TSN to their existing PROFINET portfolio.
Of course, the specification will continue to be maintained in the familiar annual maintenance process, so that new customer requirements, field experiences, or technology developments can be integrated openly and comprehensively comprehensibly.The TSN-Guidline also offers asimple explanation of the application of TSN.
Since TSN is to be classified in Layer2, the layers of the communication model arranged above it are unchanged. For this reason, the user view of PROFINET with parameterization, diagnostics or device model is also unchanged; the profiles arranged above it, such as PROFIsafe, are not affected.
Device manufacturers can either integrate PROFINEToverTSN, which is summarized in ConformanceClass D, into existing devices as an additional function or launch new devices with only CC-D.
Here you can find several frequently asked questions:
Ethernet with TSN essentially extends the existing mechanisms of Ethernet by the topics "Quality of Service" (e.g. bandwidth reservation), time synchronization as well as low latency and even bumpless redundancy. The applications register their communication requirements on the network and are assured of the respective requested QoS by the network.
The respective connections then run in so-called streams, which then enjoy bandwidth protection via the resource allocation in the switches' memories. In principle, each of these streams can be given a real-time capability. Due to the encapsulated streams, it is also possible with TSN that several real-time capable protocols can be operated in parallel in a single network. This is also known as network convergence.
This is a fundamental difference to today's Ethernet-based real-time protocols such as PRFOINET, where the network only allows PROFINET as the only real-time-capable protocol (besides TCP/IP-based traffic).
No, TSN does not replace PROFINET.
Since PROFINET relies on IEEE standards from the very beginning, we also see the TSN technology to be standardized in the IEEE as a useful extension of Layer 2 of PROFINET. PROFINET offers services necessary for automation, such as cyclic and acyclic data, alarms/diagnostics, parameterization, etc., which the IEEE mechanisms such as TSN alone cannot provide.
TSN is therefore not a competitor to PROFINET but describes IEEE basic mechanisms that can use communication protocols such as PROFINET or OPC UA. PROFINET will be able to use the possibilities of a TSN network for itself and benefit from them.
TSN alone will never be able to replace PROFINET because it is a basic technology on which communication protocols can be based.
PI is already working on using PROFINET based on TSN in addition to RT and IRT.
TSN standardizes the real-time mechanisms on Layer 2, which are typically solved via special hardware in today's Ethernet-based fieldbus systems, such as PROFINET with IRT. Protocols based on TSN will therefore be able to run with hardware standardized via IEEE in the future, even for clock-synchronous applications. Thus, PROFINET with TSN offers the advantages already known from PROFINET with IRT (time accuracy, reproducibility, bandwidth reservation, diagnostics) but on the basis of standard hardware.
Of course, the RT and IRT mechanisms will continue to be part of the PROFINET specification and benefit from PROFINET innovations.
By the way:
PROFINET based on TSN addresses not only the IRT applications (clock-synchronous motion control applications) but also the application area addressed with RT.
When the industrial profile IEEE/IEC 60802, which defines which TSN services are used for industrial automation, is adopted (from 2021).
TSN requires a "TSN-capable" hardware component; the Ethernet components installed today cannot usually be extended to TSN by software.
However, it is foreseeable that in future the "standard Ethernet module" will be a TSN-capable Ethernet module. This is a motivation for PI to set up PROFINET on TSN.
All well-known device manufacturers have already started or at least announced the development of hardware devices with TSN mechanisms. This opens up a wide range of possibilities for device manufacturers for their various hardware designs of the devices.
PROFINET over TSN Guideline:
This guideline provides initial guidance for device and stack developers to expedite the development of new devices supporting PROFINET over TSN.