TSN Update
The path to TSN offers key technology for IIoT applications Josep.Ng@shutterstock.com
Comprehensively networking everything with everything is the basis for future scenarios such as Industry 4.0 and the IIoT. To achieve this, currently separate fields of automation and information technology will have to be integrated even better. Time Sensitive Networking (TSN) standards can play a key role. WHAT IS TSN, WHICH STANDARDS ARE relevant, and how can the development work be assessed? At this point, it’s time for an overview. The classic bus systems, such as Profibus and CANopen, can still be found at the field level in current automation architectures. These systems and their use are currently proving to be a key discipline in automation technology (Operational Technology - OT). Any additional TCP/IP communication necessary, for example between the field and the control level or image transmission via webcams, is currently via separate Ethernetbased networks (Information Technology - IT). Such a split means that users have to master both specialist fields, which brings with it a corresponding level of complexity and the need for further qualifications.
IT and real-time critical applications
One huge advantage of Ethernet, however, is the cross-market and cross-application standardization work of the responsible body, the IEEE (Institute of Electrical and Electronics Engineers), and in this case the IEEE 802 project. This standardization ensures the broad, cost-effective, and interoperable availability of foundational Ethernet technologies and blocks. Systems based on Ethernet, such as Profinet RT and Modbus/TCP, benefit from these advantages because every IEEE 802-compliant end device and every switch can be used for data exchange. However, the IEE 802 work so far has not focused on the use of Ethernet in applications with hard real-time requirements, such as motion control applications. As a result, there are now special configurations available for such application scenarios, such
as Profinet IRT, that are not standardized through IEEE 802, and in part only support data rates up to 100 Mbps, and that also require special device hardware. This situation can change with TSN. With an appropriate bundle of mechanisms that are standardized through IEEE 802, Ethernet becomes real-time capable and allows bandwidths higher than 100 Mbps with simultaneous use of the network for both IT and automation applications. This means that the network can be used for all IT and real-time critical applications. This characteristic is known as convergence and provides a series of additional advantages. For users and applications, these include bandwidths of 1 Gbps and more, transmission guarantees, seamless media redundancy, the use of standard switches, short cycle times,
IEEE
Designation
Details
802.1Q
Streams
Robust routing through the network
802.1AS
Time synchronization
One synchronous time in the system
802.1Qbv
Scheduled Traffic
Communication according to timetable
802.1Qbu
Frame Preemption
High priority interrupts low priority
802.1Qcc
Stream Routes Configuration
Configuration options for TSN Networks
802.1Q ...
...
...
IEEE 802 TSN standards: All standards have now been released. 04.202 1
i n d u str i a l e th e r n e t b o o k
and, prospectively, comparable device costs. Manufacturers benefit from the use of standard chips in controllers, switches, and field devices, and one product hardware system for all TSN use cases. It has become clear that the TSN standards apply to the lower Ethernet layers. The user layer is largely independent and can be retained as it is for existing standards such as Profinet.
Profiling TSN standards for OT use
One important and necessary characteristic of the current fieldbus systems is their crossmanufacturer interoperability. Automation experts have become used to combining devices from different manufacturers to create workable solutions in a machine or system. This interoperability is assured by the large fieldbus organizations via specific measures, such as certifications. The convergent use of a TSN network can only be successful if it also provides a comparable level of interoperability. To achieve this, a cross-manufacturer definition of which mechanisms from the TSN bundle are to be used and how is necessary. Here, IEEE 802 does not make any provisions to guarantee the cross-sector use of Ethernet. Therefore, the IEC organization responsible for the fieldbus systems has joined forces with the IEEE 802 body responsible for Ethernet to establish the joint IEC/IEEE 802 60802 activity. This cooperation is targeted at
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