The Road to Deterministic Ethernet for Industrial Automation

Summary

Ensuring a real-time, deterministic response is a must for next-level Smart Manufacturing and the Industrial Internet of Things (IIoT). While standard Ethernet cannot support this goal per se, different solutions have been developed to build suitable industrial communication networks.

Thomas Burke, global strategic advisor for CLPA, gives an overview of the history of deterministic Ethernet technologies and how TSN can be a gamechanger in industrial communications.

First, there were protocols

Over time, industrial Ethernet has replaced fieldbus networks due to its ability to offer a standardized physical layer combined with greater bandwidth. This allows multiple devices to be connected over one network while ensuring high-speed data transmission. However, standard Ethernet, as defined by IEEE 802.3 specifications, is intrinsically a non-deterministic technology, as it cannot prevent message collisions.

While the limitations of standard Ethernet haven’t been an issue in the past, they can affect future factory operations, which demand increasingly powerful communications that can support real-time, time-critical transmission of control data.  Different solutions have been developed to make this network technology more deterministic, thus futureproof. For example, CC-Link IE open industrial Gigabit Ethernet was created to ensure deterministic communications by offering 1Gbit bandwidth.

This large bandwidth can minimize non-time-critical traffic interference for real-time control data.  In addition, to guarantee a stable data transfer cycle for control data while creating room for other types of traffic, CC-Link IE actively assigns a portion of bandwidth for non-time-critical communications. Finally, CC-Link IE uses token passing for data transmission control. This results in increased communication throughput and provides deterministic data exchange as well as constant link cycle time by eliminating the possibility of data collision.

Moving away from ‘disconnected’ industrial Ethernet protocols

The different solutions to achieve determinism often consisted of custom, “proprietary” industrial Ethernet protocols aimed at addressing specific tasks or domains. Thus, their scalability was limited, as each was tailored for a specific application area. Furthermore, while many of them could be considered open, they would not be compatible with each other.

To address these issues, some of the major developers of industrial Ethernet protocols have partnered to ensure interoperability between their solutions. For example, the CC-Link Partner Association (CLPA) and PROFIBUS & PROFINET International (PI) created a joint specification to allow for easy interoperability between CC-Link IE and PROFINET.

Recently, efforts have been made to build real-time determinism in standard Ethernet. More precisely, a set of IEEE 802.1 standards operating at Layer 2 of the OSI model (data link layer) is currently being developed. The result is a new technology, known as Time-Sensitive Networking (TSN), that helps industrial Ethernet to deliver deterministic communications and ensure a reliable delivery of data between endpoints.

Standardizing determinism

Key TSN standards that are currently available define time synchronization (IEEE 802.1 AS) and time-aware shaping functions (IEEE 802.1 Qvb). By implementing these elements, TSN offers a way to send both time-critical and non-time critical traffic in real-time over a standard Ethernet infrastructure deterministically.

The first function, time synchronization, sets up a “Time-Aware System” where all the real-time clocks in the nodes can be synchronized to an accuracy of 1μs or less. This makes the networks suitable for even the most demanding applications, such as motion control, where cycle times may be as short as a few microseconds.

Time awareness relies on this accurate synchronization to effectively schedule network traffic and deliver real-time, deterministic responses. Time-aware shapers (TASs) check the priority of each message and assign a suitable priority queue. The transmission of data in each queue is executed during scheduled time windows, while the other queues are blocked from transmission.

In this way, TASs ensure that cyclic messages are prioritized and protected against collisions and interference from non-time-critical traffic. Even more, communication cycle times are optimized, as different frames with similar priorities can be transmitted simultaneously.

Real-time, deterministic response without losing additional functionalities

TSN technology has huge potential, providing a robust and reliable infrastructure and supporting control-based applications from the embedded world to the Cloud, and is being developed rapidly to accommodate for higher level functions as well as network safety and security. It can already provide substantial benefits to manufacturers, supporting the creation of highly interconnected plants. Therefore, businesses that want to prepare their factories for the future of manufacturing and implement IIoT strategies should act now, combining
TSN with high-performance Ethernet.

A solution that offers precisely this is CC-Link IE TSN. It is an open industrial Gigabit Ethernet that incorporates TSN functionalities to ensure deterministic communications. In this way, it can handle all control needs, while also effectively transmitting time-critical and other types of traffic on the same network. Moreover, CC-Link IE TSN can support high-performance motion control and safety applications.

By choosing this technology, businesses can continue to support–or even improve–existing applications while also creating a system that will address future needs. Ultimately, this solution will allow forward-looking companies to get into the future of manufacturing today, fast-tracking the gains of creating interconnected, IIoT-driven Smart Factories.