Time Sensitive Networking — An Introduction to TSN

Dr. Andreas Weder | Fraunhofer IPMS
Time Sensitive Networking — An Introduction to TSN


Ethernet has been equally established as a dependable wired solution in both computer and automation networks. The open standard allows terminals to be quickly and simply connected as well as easily scaled to exchange data with relatively inexpensive hardware.

Ethernet was, however, not originally designed to meet the requirements posed by automation technology, particularly in regard to guaranteed and real-time communication. Therefore, various bus systems in automation have evolved using Ethernet on a physical level while implementing proprietary real-time protocols on top. These systems often lead to the exclusive use of the network infrastructure as well as vendor dependencies. Such networks handling time-critical data traffic are today separated from networks directing less-critical data traffic in order to eliminate reciprocal negative interference.

In the future, Industry 4.0 applications will require increasingly more consistent Ethernet networks.  Such networks can only be produced at great cost with the traditional structure. Time-Sensitive networking (TSN) provides a solution aiming to change these current conditions. 

Real-time Communication 

Guarantees regarding cycle times and fluctuations in cycle times are prerequisite for a range of application fields in automation, including, for example, drive, control, and conveyor technology. The data transfer times demanded in these application fields are significantly less than 1 ms.

In addition to these applications requiring “hard” real-time capability, other applications such as process automation implement “soft” real-time capability with longer cycle times. Nevertheless guaranteed latencies are required for these applications as well. Various real-time communication methods such as EtherCat or Profinet IRT have been specially developed to provide guaranteed cycle times. Although they are based on conventional Ethernet, they are not compatible with each other. This incompatibility has resulted in fragmented networks.

Why TSN?
In most cases, traditional Ethernet networks involving automated sectors such as manufacturing are based on the hierarchical automation pyramid which separates information technology (IT) from operational technology (OT). IT includes classic office communication with typical end devices such as printers and personal computers. OT is made up of systems, machines and software used for process control and automation. The two areas are fundamentally different in how they communicate, with IT dependent on bandwidth and OT focused on high availability. Data traffic at the IT level is therefore often classified as non-critical while data traffic is designated (time-) critical at the OT level. As a result, each level uses a particular communication standard. While the Ethernet bus system with TCP/IP has largely prevailed at the IT level, various bus systems, also known as fieldbus systems, that particularly meet requirements for guaranteed latency times are widespread at the OT level. Each control vendor usually promotes a specific fieldbus system. For the user, this means that selecting the controller basically also determines the selection of the bus. The end user is thus often in a manufacturer's dependence, since the different bus systems are incompatible with each other.

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Published By CAST Inc on 18/07/2019