The benefits of TSN Ethernet for automation networks
13 November 2015
Dr. Oliver Kleineberg, Manager Advanced Development, Hirschmann Automation and Control GmbH at Belden, comments on the Time Sensitive Networking (TSN), a set of standards developed by the Time Sensitive Networking Task Group (IEEE 802.1).
This group was formed in March 2013 – and it continued the work of the Audio / Video Bridging Task Group. The name changed as a result of a scope extension of the of the standardization group. From home and professional audio and video networks, the scope of the working group was extended to encompass control networks for mission-critical applications, such as networks for Power Transmission and Distribution, Industrial Automation or automotive in-vehicle networks. The standards define mechanisms for the time-sensitive transmission of data over Ethernet networks in order to provide reliable worst case end-to-end latency and jitter values.
TSN consists of various IEEE 802.1 and 802.3 specifications. Some projects have already been worked on since 2012, whereas some projects were started at the beginning of 2015. Taking the permitted project durations of IEEE 802 into account, TSN in its various specifications will allow first operational systems by the end of 2016/beginning of 2017.
The key benefits
Once implemented, the full TSN IEEE 802 standard real-time Ethernet solution is set to provide the following benefits:
• TSN as an IEEE 802 specification ensures, that multiple vendors will offer the technology in their products. In addition, adherence to the technical specification guarantees cross-compatibility between different vendors. This leads to investment security as well as low equipment and overall system costs, given that virtually all devices and chip manufacturers will be adopting the technology.
This is the exact same reason why Ethernet has become the dominant networking technology in corporate datacenters and home networks.
• Real-time communication with Ethernet, even for the most demanding of application requirements (e.g. motion control & and safety).
• Full compatibility with the existing standard Ethernet technology (zero use of gateways or protocol converters is required).
IEEE 802.1 – from AVB to TSN
The TSN initiative arose during the specification of the AVB (Audio and Video Bridging) technology.Beldens participation and active collaboration in the IEEE 802.1 AVB workgroup commenced back in 2009. At Hirschmann, the subject of "AVB" was already being discussed internally as an option for a standardized real-time Ethernet.
The first official presentation of the idea to utilze the AVB technology for industrial automation took place during a meeting of the IEEE 802.1 working group in 2010, as part of a joint, coordinated approach between Siemens and Hirschmann. The official acceptance of the topic by the working group followed shortly thereafter, opening up the possibilities to present proposals for future work items.
Requirements were presented and projects commenced for the diverse requirements and specific challenges introduced by use cases from the industrial automation and automotive environments. This not only includes real-time schedulers in Ethernet switches, but also includes mechanisms for bandwidth reservation on the network and explicit ingress protection , a mechanism to prevent overloading the network medium and to ensure availability. The capabilities of TSN, in relation to the state of the art, extend well beyond what Ethernet and even a number of specifically adapted Industrial Ethernet variants are able to deliver.
Garnering full industry support
The work of the IEEE 802.1 TSN working group is being supported by a number of well-established companies from the fields of industrial automation and the automotive industry. These include Bosch, Siemens, General Motors, General Electric and National Instruments as well as Hirschmann, just to name a few.
The major producers of switching chips (e.g. Marvell and Broadcom) are also very active in IEEE 802.1 standardization and they offered their expertise in the standardization process from day one – and, in turn, learned about the demanding requirements from the industrial and automotive application fields. It is therefore to be expected that functional chips for general use, as well as chips that are fit for use in industrial and automotive applications will be available soon after the final specifications have been ratified.
Performance and technology
As the specifications are not yet final, performance cannot be predicted with 100% accuracy. The target for cycle times is in the low, two-digit microsecond range. Unlinke many Industrial Ethernet variants, TSN itself is not tied to a specific bandwidth of the network. 100 MB/s full duplex is a minimum requirement, and the initial implementations are expected to be introduced on the basis of 1,000 MB/s. If required, this can be extended to 10 GB/s networks - possibly larger at a later stage.
This performance will be achieved with a combination of time synchronization on all devices in the network and a time slot procedure for media access. This is being complemented by, a method for registering communication flows and bandwidth reservations, along with a process for uninterrupted fault tolerance.
A broad range of applications
Target application areas are those in which there are requirements for absolute guarantees for end-to-end latency, combined with very high levels of availability. Concrete examples are motors that change the blade angle of rotor blades synchronously in a modern wind turbine or in closed-loopcontrol of manufacturing robots. High performance in bandwidth and latency, combined with high availability and the ability to manipulate communication streams dynamically means that this technology is also a very good fit in future Industry 4.0 / Smart factory networks. This is due to the fact that it is precisely these networks that place increased demands on dynamics and the ability to reconfigure communication flows as the manufacturing equipment rearranges itself. TSN will also be used outside of industrial automation technology. TSN will play an important role in future communication solutions for automobiles and a significant number of automobile manufacturers are already active in TSN standardization.
You may wonder whether established Industrial communication protocols, such as PROFINET, EtherCAT and Powerlink, will cease to exist as a result of the emergence of TSN. The actual value of an established industrial Ethernet protocol such as PROFINET I/O or EtherNet/IP is not its capability to transfer data deterministically on ISO-OSI layer 2 through an Ethernet switch. The real value can be found inside the device modelling, the machine-to-machine communication, HMI tools and a number of others. Existing industrial Ethernet ecosystems will not cease to exist; they will be augmented by TSN:
TSN provides all of the technology that is required for deterministic and reliable data transfers. Established protocols such as PROFINET can saddle up onto TSN. This combines the benefit of a well-developed industrial Ethernet solution along with the efficiency and sustainability of standardized IEEE 802.1 layer 2 technology.
The OPC Foundation has chosen exactly this way for good reason: They chose to combine OPC UA with TSN. This is in a new OPC UA project where communication interfaces are specified and which allow the use of OPC Machine-to-Machine communication via TSN, as well as for configuring the devices via an OPC UA.
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