A Single Network for Industrial Ethernet: Will Time Sensitive Networking (TSN) Accomplish Convergence?

A Single Network for Industrial Ethernet: Will Time Sensitive Networking (TSN) Accomplish Convergence?

By Bill Lydon, Editor, Automation.com

Connecting the manufacturing plant floor with the business enterprise through a single, open network. That has been the elusive goal behind many of the rallying cries in today’s industry. Proponents of Time Sensitive Networking (TSN) believe they may have the answer.  TSN has been a major point of discussion at multiple events over the year, with presentations touting it as a potential technology to integrate real time industrial control, IT, OT, video, and other data communications.  Likewise, increasing numbers of companies are exploring and supporting the development of the TSN standard.   The 18th annual ODVA industry conference & annual meeting in Florida this past Febrary was a stellar example of this latest push. At this event and through my travels this year, I’ve learned that many industrial automation people believe that TSN will become a high volume, low cost technology with adoption by automotive and consumer industries.   So what’s the hold up? Currently, Time Sensitive Networking (TSN) standards are still under development and not yet finalized.  Still, TSN is already making inroads into our future. Already, TSN is being designed into some car models that may appear on the market as soon as the early 2020s.

Today, the automobile industry has a mix of networks including Control Area Network (CAN), Local Interconnect Network (LIN), and new forms of Ethernet. Further, MOST Cooperation is another industry initiative designed to define and adopt a common multimedia network protocol and application object model.

The fruits of high volume leading to low cost technologies, which has been seen in other markets, was the driver behind the development of CAN based industrial protocols including DeviceNet, and CANopen.   New industrial Ethernet protocols are saturating today’s market, making Ethernet options increasingly lower cost and ubiquitous.

What is Time-Sensitive Networking (TSN)?

Fundamentally, 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).  The key is that TSN requires a network-wide precision clock reference for all nodes to maintain synchronization. 

Standard, unmodified Ethernet is based on collisions which create an inherent non-determinism. This non-determinism is overcome using high-bandwidth connections relative to industrial protocol communications traffic.  There are variants that use time-synchronization techniques over standard Ethernet, in order to accomplish high-performance control for applications such as synchronized servos including SERCOS III, EtherCAT, CIP Sync and PROFINET IRT.

As a time-scheduled, synchronized network, TSN requires more processing at every node. Yet, as solutions are integrated into silicone in high volume, costs could become more insignificant.  Put this into perspective: Consider Ethernet, introduced in 1980 and first standardized in 1983. IEEE 802.3 required expensive computer boards full of electronics for a network connections.  Thankfully, this was eventually all integrated into single-chip solutions.

1990 vintage Ethernet interface card.

TSN requires a Centralized Network Configuration (CNC) policy engine software, running on a processor that receives all network and policy requirements, and calculates both the network calculus as well as the schedule for the network.    A Centralized User Configuration (CUC) entity provides the CNC with network loading and timing requirements necessary for the successful management of traffic across any given connection.

For a more instructive, technical view on TSN, I recommend checking out this in this keynote on Deterministic Time Sensitive Ethernet Standards from TSNA 2015, by Michael Johas Teener

Focal Point Organizations

There have been two organizations involved in the development of TSN, that have proven key in its rise in popularity

IEEE

In 2012, a group of people from the automotive industry, working in conjunction with long-time experts in the IEEE 802.3 Ethernet working group, started a project for a special version of 1Gb/s Ethernet. Specifically tailored for the automotive market, the project involved individuals from major auto companies, Tier 1 automotive suppliers (the major companies that build subsystems for cars), and the major Ethernet semiconductor vendors.  This effort resulted in the 2016 approval of 802.3bp-2016 - IEEE Standard for Ethernet Amendment 4: Physical Layer Specifications and Management Parameters for 1 Gb/s Operation over a Single Twisted-Pair Copper Cable and its current use: being designed into the cars that may appear in the early 2020s.  These efforts have been expanded in order to potentially provide DC power over the same single twisted wire pair used for 802.3bp-2016. This work is expected to be completed in early 2017, along with a 1Gb/s solution on plastic optical fiber (POF).

Avnu Alliance

The Avnu Alliance Industrial Control & Monitoring Group has been working to define compliance and interoperability requirements for TSN networked devices. Industrial suppliers, IT vendors, and silicon providers have been collaborating in IEEE 802 and Avnu, in order to create updates to standard Ethernet which will provide:

  • Bounded, low latency data transfer for control
  • Shared synchronized time
  • High bandwidth
  • Convergence of control traffic and standard Ethernet traffic
  • Security enhancements aligned with IT standards

These improvements are focused on enabling a single network to support reliable, multi-kHz closed loop control and dynamic, un-managed, standard Ethernet traffic. Because these capabilities are being incorporated in the core Ethernet standard, these upgrades promise broad adoption, increased flexibility, increased bandwidth, multi-vendor interoperability, and decreased cost.

Notable Avnu Alliance organization members include Cisco, Intel, Analog Devices, Belden, Bosch, National Instruments, Rockwell Automation, Schneider Electric, and General Electric.  Rockwell joined the organization in February 2016. Joe Kann, the Vice President of Global Business Development, for Rockwell Automation shared why. “We continue to evolve our industrial control and information solutions to help customers drive real-time productivity and innovation as they strive toward building a Connected Enterprise,” Kann explained, “By participating in the Avnu Alliance, we plan to share our industry knowledge and work together with other members toward further enhancing standard, IP-based Ethernet for manufacturing.”

More Industrial Organizations Are Exploring TSN

All these efforts have led to an atmosphere where several prominent industrial automation organizations are working to leverage TSN. These organizations include:

ODVA

In November of 2015, the ODVA Distributed Motion SIG (Special Interest Group) changed its name to the Distributed Motion and Time Synchronization SIG (DM & TS SIG) in order to respond to the market’s movement toward Time Sensitive Networking Technologies.  The primary focus and priority for the DM & TS SIG, with regard to TSN, is to develop approaches and migration mechanisms that minimize impact of TSN integration on current product designs and existing installations.  The DM & TS SIG seeks to enhance and maintain ODVA specifications in the manner needed to serve industrial automation applications. This includes high performance motion control work, which is executed by distributed intelligent controllers and drives, and systems requiring time synchronization of multiple devices including, but not limited to, drives.  As stated, the recent ODVA meeting contained several presentations based around TSN. These presentations were made at the ODVA 18th Annual Meeting and can be downloaded here.

PROFINET

PI (PROFIBUS & PROFINET International) established a new "I4.0" working group, in order to prepare relevant Industry 4.0 use cases from the perspective of industrial communication. This group works to assess existing and new technologies in order to identify requirements for communication, which are important in the Industry 4.0 environment, and bring them to standardization consistently as part of the further development of PI technologies.   One of the group’s first activities was a new sub-project regarding the merging of IT (Information Technology) and OT (Operations Technology).  PI has the potential opportunity to combine the strengths of PROFINET and TSN and to generate further added value.

OPC UA

At the November 2016 SPS IPC Drives show in Germany, a number of companies announced their intent to support OPC UA over TSN in future products, with the intent of enabling fully interoperable devices from multiple vendors. 

Leading automation suppliers ABB, Bosch Rexroth, B&R, Cisco, General Electric, Kuka, National Instruments (NI), Parker Hannifin, Schneider Electric, SEW-Eurodrive and TTTech announced support for OPC UA over TSN in products at the November 2016 SPS IPC Drives show in Germany.  Photo courtesy of B&R.

Multiple companies have gotten involved to begin an open technical collaboration under the umbrella of the Industrial Internet Consortium (IIC) and the OPC Foundation. With the goal of an open, unified, standards-based and interoperable IIoT (Industrial Internet of Things) system that will be suitable for deterministic and real-time peer-to-peer communications between industrial controllers and to the cloud, the group invites other similarly vision-focused companies to join the effort.

Bill’s Thoughts & Observations

I find TSN to be especially interesting. As a long proponent of the goal of a complete connected enterprise which connects manufacturing plant floor through a unifying open standard network, I am fascinated with the potential of TSN to realize this very elusive vision. 

Intriguingly, since TSN is a totally-managed network, all industrial protocols in the plant would need to conform and be compliant with the TSN set of standards in order to achieve deterministic and reliable communications.

The issue is: While the concept of a single network, integrating real time industrial control, IT, OT, video, and other data communications sounds very appealing, this is a complex network scheme.  Complexity has a tendency to negatively impact quality, reliability, and availability, and this could prove to be a deadly barrier to the implementation of Time Sensitive Networking. Still, only time will tell.

These demonstrations and testbeds should prove very interesting to watch, and will give us an idea of where TSN is headed:

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