Time Sensitive Networking (TSN) Vision: Unifying Business & Industrial Automation | Automation.com

Time Sensitive Networking (TSN) Vision: Unifying Business & Industrial Automation

Time Sensitive Networking (TSN) Vision: Unifying Business & Industrial Automation

By Bill Lydon, Editor, Automation.com

Time management of all traffic on the network is a fundamental function to meet the time and determinism requirements of applications that are sharing the network.   This is why Time Sensitive Networking (TSN) was envisioned, to create single network to meet all requirements including audio, vision, and data with guaranteed speed and determinism for all applications.  Given all the requirements, and with all parts of the standard are not yet finalized, TSN is quite complex and the architecture is still being defined by IEEE.

 

Biggest TSN Advantages

Guaranteed Determinism

TSN is a centrally managed and time scheduled network architecture, with the goal of achieving deterministic communications with guaranteed end-to-end latencies and highly limited latency fluctuations (jitter).

 

A Data Highway for All Traffic

Think of a crowded highway with smoothly moving traffic. With TSN, all traffic can be run, including business information, operations information, and industrial protocols, all applications independently coexisting on the network.  There were many demonstrations at Hannover Fair 2018 in April which illustrated multiple independent networking streams over TSN including industrial automation protocols such as EtherCAT, PROFINET, EtherNET/IP, SERCOS, and others.

 

Network Protocol Agnostic

TSN is network protocol agnostic. Much like today’s standard ethernet networks, it can be used simultaneously to transport multiple industrial automation protocol traffic, IT data, OPC UA, video, and all other network traffic.

 

The Biggest Challenges/Headwinds for TSN

Finalize IEEE Standards

One of the biggest challenges for TSN is that the group of IEEE standards that are all not finalized, though the speculation I’ve gathered from industry experts is they should all be finalized in 2020.  TSN is a set of standards under development by the Time-Sensitive Networking task group of the IEEE 802.1 working group. The TSN task group was formed in November 2012 by renaming the existing Audio/Video Bridging Task Group.  The standards define mechanisms for the time-sensitive transmission of data over Ethernet networks.  To state that TSN is complicated is an understatement. With multiple elements, it includes several parts still under development including:

  • IEEE 802.1AS-Rev – Enhanced Generic Precise Timing Protocol: Adds support for Performance, Redundancy, Aggregation.
  • IEEE 802.1Qbv – Time Aware Shaper: Achieves the theoretical lowest possible latency in engineered networks.
  • IEEE 802.1Qbu & IEEE 802.3br – Packet Pre-emption: Reduces latency of time-sensitive streams in non-engineered networks.
  • IEEE 802.1CB – Frame Replication & Elimination: Supports zero switch over time when a link fails, or frames are dropped (aka: Seamless Redundancy).
  • IEEE 802.1Qcc – Enhanced Stream Reservation Protocol: Adds support class configurations, shaper and replication.
  • IEEE 802.1Qci – Per Stream Filtering & Policing: Assigns flows to policer.
  • IEEE 802.1Qch – Cyclic Queuing & Forwarding: Supports known latencies, no central controller needed, limits hops.
  • IEEE 802.1Qcr – Asynchronous Traffic Shaping: Supports zero congestion loss for asynchronous traffic, and deterministic latency without using network topology information.

 

Time Management

Another issue is that there is no defined, vendor-independent time management and shaping standard, which will be critical in enabling TSN to be the data highway for all network traffic including IT, multimedia, industrial & process automation, and VOIP.  Known as an engineered network, this is the most fundamental element of TSN: For all applications to communicate with a time manager that defines how those applications and network nodes will communicate.  Belden’s Stephan Kehrer explained the central network manager as a logical instance that has a global view of the network.  This manager will know the devices in the network, their capabilities, links and link speeds with which the devices are connected and so on. With this knowledge of the network topology and device capabilities of the devices on the network, together with additional application specific knowledge regarding communication relations and requirements between end devices, the central network manager then determines and specifies the data streams within the network.  This allows for an optimal utilization of the network and the coexistence of different types of traffic, i.e. real-time traffic, shaped traffic and best-effort traffic. As TSN is a technology providing communication at the data link layer (layer 2 of the OSI model), all higher layer protocols utilizing TSN for communication can be handled by the central network manager. In fact, the coexistence of the different classes of network traffic in one converged network is one of the great advantages TSN has to offer.

There is also a notion of an autonomous scheme where every node will communicate with the network and collectively generate the network management operating specification and application. Further, with industrial automation applications, usually when a change is made in the system there will be a latency time that is currently unclear for reconfiguration of the network operation.

Reference: Digging into the Details: Time Sensitive Networking (TSN)

 

TSN Independence

One of the keys of successful TSN implementation and the goal of a universal networking utility is that TSN needs to be independent of applications, including industrial automation protocols.  The manufacturing and process industries have experienced issues with various industrial automation protocols running over Ethernet networks

 

Complexity

TSN requires more and higher speed processing throughout the network, including Ethernet switches, routers and at every node (PLC, Process Controllers, Sensors; edge devices). In addition, software configuration requires more user interaction to specify time and determinism requirements that need to be integrated into the time and network management scheme.  This complexity, over time, could be integrated into silicon in high volume and plug ‘n play software similar to the evolution of the Ethernet, which required expensive computer boards and complex software configuration in the early days following its 1980 introduction.

 

Cyber Security

This complexity may also have security issues that may hinder adoption. In many ways, TSN drives against core cybersecurity concepts, such as Defense in Depth, plus it’s complexity may put more burden on protective procedures and measures.

 

Broad Adoption

Success will only come with the commercialization of TSN based on broad adoption as a proven, reliable networking scheme that delivers data at a defined and deterministic time to meet any application requirements. 

Through several presentations and discussions with industry experts and vendors, I found that several believe that a big part of the success of TSN will be adoption by the automotive industry. Potentially used for in-vehicle communications, this would legitimize the technology and drive down the cost due to volume.   There are various technologies competing for this position in the automotive industry and the winners are not clear at this point. In addition, in the automotive industry is hindered by differing philosophies regarding large networks in vehicles, or multiple application specific networks (i.e. Anti-lock Braking).   Automotive applications need to pass rigorous conformance and certification that may well drive network architecture design.

 

Will TSN Be the Answer?

If implemented successfully to achieve, performance, configuration, and cost goals, TSN may be the unifying real-time network for manufacturing and process automation businesses. Especially considering that industrial automation protocols were specifically invented to overcome the issues that TSN can solve.

 

Industrial Protocol Change

With more powerful industrial controllers, process controllers, PLCs, and smart edge devices, the need for industrial automation protocols may go away. Some might argue that the industrial and process automation messages need to be highly compact to be effective, but I don’t think this is consistent with the trend in computing.  There was a time that Voice Over Internet Protocol (VOIP) was considered impossible because of the amount of data involved, but with higher bandwidth networking coupled with Ethernet Quality of Service (QOS) functions it was accomplished. Also, the volume of web services traffic on intranet and the Internet has clearly benefited from providing clean and clear data messaging, with context improving the reliability of systems and interactions. In the industrial arena OPC UA provides the context and open data models for the wide range of industrial and process automation applications.  

 

Multi-vendor Interoperability

All that said, TSN does not solve the problem of multivendor interoperability of controller to controller communications, which users have been complaining about for years.  This is starting to be accomplished by progressive vendors, using OPC UA communications for controller to controller, leveraging the joint OPC Foundation/PLCopen standards. 

 

Bill's Final Thoughts

The concept of a single network, integrating real time industrial control, IT, OT, video, and other data communications sounds appealing but as emphasized throughout this article, it would be a very complex network scheme.  Complexity tends to negatively impact quality, reliability, and availability, and this could prove to be a deadly barrier to the implementation of Time Sensitive Networking as the universal data/information highway.

Industrial automation protocol groups including EtherCAT, ODVA (EtherNET/IP), and PROFIBUS & PROFINET International (PI) all have activities to demonstrate they can communicate using TSN technology, which is good.  The danger lies in if they create special dependencies within TSN for their respective protocols. This would drive directly against the spirit and vision of TSN.

One joint project of IEC SC65C/MT9 and IEEE 802 - to define TSN profiles for industrial automation - shows promise for convergence.  This joint work will provide a standard that is both an IEC and an IEEE standard, i.e., a dual logo standard.   This standard will define time-sensitive networking profiles for industrial automation. 

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