Andy Pye investigates whether Ethernet can step up to the rigours of time sensitive networking for industrial systems.
As we scale to a world of billions of intelligent, connected devices, crucial differences are emerging between the Internet of Things (IoT) and its subset, the Industrial Internet of Things (IIoT). The biggest difference between them is time sensitivity.
Manufacturing operations require tight coordination of sensing and actuation to safely and efficiently perform closed loop control. Industrial automation approaches have traditionally been differentiated and separated from one another by different incompatible and non-interoperable standards used for communication between devices. As a result, customers have often found themselves locked into proprietary systems, while vendors have had to develop multiple versions of essentially the same product.
Recognising the inadequacy of most network infrastructures for handling such time-sensitive data, industrial suppliers, IT vendors and electronics manufacturers are collaborating to update the standard Ethernet protocol. The outcome is a next-generation Ethernet standard called Time-Sensitive Networking (TSN).
A group of major automation players – ABB, Bosch Rexroth, B&R, CISCO, General Electric, KUKA, NI, Parker Hannifin, Schneider Electric, SEW-EURODRIVE and TTTech – have started an open technical collaboration under the umbrella of the Industrial Internet Consortium (IIC) and the OPC Foundation. This group is aiming for open, unified, standards-based and interoperable IIoT for deterministic and real-time peer-to-peer communication between industrial controllers and to the cloud. Based on open standards, this enables devices from different vendors to be fully interoperable.
TSN is an attempt to answer some of the challenges for the transmission of large amounts of data deterministically. It enables a standard, single, open network infrastructure, supporting multi-vendor interoperability, with real-time control and synchronisation of high performance machines over a single, standard Ethernet network.
It is under development by the Time-Sensitive Network Task Group (IEEE 802.1), an initiative created by the Institute of Electrical and Electronics Engineers (IEEE). Precise time synchronization for 802.1AS, deploys the IEEE 1588 Precision Time Protocol to support synchronisation of multiple data streams; and to combine time synchronisation with traffic management to deliver latency guarantees – this means that each switch identifies time-critical data packets and puts them in a special queue. These packets are forwarded at specific times to create a network flow between the talkers and listeners across the network.
Support of fast control applications means the network needs to support communications with low latency – the time delay between an action and a reaction – and low jitter – the variation in delay time of received packets of information. Mechanisms are needed for distributed coordination – this is the collision-avoidance and time synchronisation strategy specified in the IEEE 802.11 based WLAN standard. In the past, fulfilling these requirements have resulted in non-standard network infrastructure or unconnected standard networks where devices and data are not accessible throughout the infrastructure.
TSN will open up critical control applications such as robot control, drive control and vision systems to the Industrial Internet. This connectivity then enables customers, suppliers and vendors to more readily access data from these systems and to apply preventative maintenance and optimization routines to these systems.
Time Sensitive Networking (TSN) is envisioned to be useful in a wide range of applications, including in addition to manufacturing, utilities, transportation, and oil & gas.
To address these needs of IIoT all the way to the control system, the IEEE 802 standards group has been adding new capabilities to the Ethernet and wireless standard to enable it to support time sensitive networking. These features will allow standard IT traffic to converge with time-sensitive control traffic. The new capabilities will support time synchronisation, low latency communications and high network reliability.
Other standards bodies to note in this area are the AVnu Alliance and the Industrial Internet Consortium (IIC). The former covers certification for TSN-based Ethernet. The latter develops “the standards, best practices and processes of the Industrial Internet” to help simplify multi-vendor systems targeted at vertical applications; it also hosts testbeds.
OPC UA TSN is the proposed unified standard for industrial automation and IIoT connectivity, and the participating companies intend to support OPC UA TSN in their future generations of products. OPC UA TSN is the combination of enhanced OPC UA Publisher/Subscriber (Pub/Sub) technology with the IEEE TSN Ethernet standards. It provides all of the open, standard building blocks required to unify communication for industrial automation and it enables the broad convergence of information technology (IT) and operation technology (OT) that is fundamental to realising the Industrial Internet of Things (IIoT) and Industrie 4.0.
The technology will be used to support real-time control and synchronisation of high performance machines over a single, standard Ethernet network, supporting multi-vendor interoperability and integration.
First pilots of these products are already being integrated in an IIC testbed. The group’s objective is to show compatible controller-to-controller communication between devices from different vendors using OPC UA TSN over standard IT infrastructure. Other companies that share this common vision of unified communication between industrial controllers and to cloud are welcome to join and contribute to this collaboration.
The testbed shows the value of the technology as well as some of the challenges in implementations from a number of vendors. It will not only document some of the value, but will provide feedback to the relevant standards organisations on areas of further clarification or improvement.
“Testbeds are a major focus and activity of the IIC and its members. Our testbeds are where the innovation and opportunities of the industrial Internet – new technologies, new applications, new products, new services and new processes – can be initiated, thought through and rigorously tested to ascertain their usefulness and viability before coming to market,” said Dr Richard Soley, executive director of the IIC.
Member participant National Instruments (NI) is hosting the testbed. Speaking at NIDays 2016, Sacha Emery, Senior Systems Engineer (ATE) at National Instruments UK, covered the main elements needed to the required support time sensitive networking: time synchronisation, traffic scheduling and system configuration. Customers that want to access the technology platform can join the NI Community “Time Sensitive Networks.”
In coordination with Cisco and Intel, NI has announced that there is to be an Early Access Technology Release to support TSN. This involves two new NI parts (cRIO-9035 and cRIO-9039, featuring Intel Atom processors and the Intel i210 TSN-enabled NIC), TSN software and a Cisco switch (to cover the IT piece), with under 100ns comms between CompactRIO controllers on the network and deterministic comms over standard Ethernet.
This will enable customers to build distributed systems that perform synchronised I/O, code execution and deterministic communication for distributed control and measurement loops, all using standard Ethernet.
These controllers use LabVIEW system design software to maintain synchronised time to the network and expose that time to code running on the real-time processor, as well as the code running on the FPGA. LabVIEW is already designed with time as a core concept, which makes it simple for users to tightly coordinate signal processing, control algorithms and I/O timing with scheduled network transmission and between multiple systems distributed across a network.
Extending security to lower levels
Most lower-level fieldbuses implement security through physical isolation (air gapping) and obscurity. However, today’s frequent security breaches highlight the need to fully extend security into the critical lower levels of control infrastructure.
TSN enables adoption of top-tier IT security provisions to protect critical control traffic and adds additional features that can be used to build additional security provisions. TSN’s ability to guarantee network delivery and timeliness limits the impact of attack by protecting critical control traffic. In addition, synchronicity between the various devices in the system can form a basis of trust so systems can detect intrusions by checking for synchronicity disruption.
What is a time-sensitive network?
By defining queues based on time, time-sensitive networking ensures a bounded maximum latency for traffic through switched networks. According to TTTech Computertechnik AG, this means that standard Ethernet will now allow:
* Message latency guaranteed through switched networks
* Critical and non-critical traffic converged in one network
* Higher layer protocols sharing the network infrastructure
* Real-time control extended away from the operations area
* Sub-systems integrated more easily
* Components added without network or equipment alterations
* Network faults diagnosed and repaired faster
The testbed is designed to demonstrate how to fo the following:
* Combine different critical control traffic (such as OPC UA) and best-effort traffic flows on a single, resilient network based on IEEE 802.1 TSN standards
* Demonstrate TSN’s real-time capability and vendor interoperability using standard, converged Ethernet
* Assess the security value of TSN and provide feedback on the ability to secure initial TSN functions
* Show ability for the IIoT to incorporate high-performance and latency-sensitive applications
* Deliver integration points for smart real-time edge cloud control systems into IIoT infrastructure and application
Early applications of Time-Sensitive Ethernet
* Advancements in next-generation computer numeric control machining (The Laboratory for Machine Tools and Production Engineering of RWTH Aachen University)
* Novel semiconductor processing machines (EUV Tech)
* Future electrical grid research (Oak Ridge National Laboratory (ORNL))