Sercos Working Group Evaluates a New Standard for Time-Sensitive Networks

Sercos International recently announced that a working group will evaluate the future real-time Ethernet standard IEEE 802.1 TSN (Time-Sensitive Networks) in regards to its suitability for real-time machine communication.

Sercos International is an association of users and manufacturers that determines the technical development, standardization, certification, and marketing for the Sercos automation bus.

The group at Sercos is aware that Ethernet is an indispensable part of industrial automation technology, as it has gained wide acceptance due to its uniform technical basis, associated interoperability, and suitable scalability properties. However, it has not been able to penetrate network communication with hard real-time requirements.

“For the first time in the history of Ethernet, Ethernet TSN allows a time-triggered transmission of real-time critical messages via standard Ethernet components.” —Peter Lutz, Sercos International Managing Director

To cover this field of application, the TSN task force has come up with IEEE 802.1. This aims to extend existing Ethernet standards and meet the real-time requirements of modern control networks in industrial automation and the automotive industry. The new Ethernet TSN standards include but are not limited to time-triggered data transmission, bandwidth reservation, and measures to interrupt non-time-critical data streams. Within these updated standards, a deterministic communication is made possible and additional protocols can be transmitted over the same medium without impacting the real-time characteristic of the network.

To achieve these standards for high-precision time synchronization, TSN uses the newly developed IEEE P802.1AS-Rev standard. Priorities in accordance with IEEE 802.1Q are used for enabling the coexistence of different traffic categories. However, further prioritization mechanisms are needed as the sequence for data packets of equal priority cannot be influenced using this technology. In TSN, IEEE 802.1Qav, a related standard, employs a credit-based shaper (CBS), which can prioritize soft real-time flows over best-effort traffic. Cyclic transmission time windows (IEEE 802.1Qbv) are installed along with this, which allows time-critical data flows to be transmitted without hindrance. A guard band is also set up which ensures that no data is allowed on the transmission path prior to the time-critical transmission. This is especially useful particularly in the areas of industrial automation and the automotive industry as they require smaller and guaranteed worst-case latencies and jitter.

The identification, registration, and management of suitable paths is supported as TSN defines a set of mechanisms and interfaces in IEEE P802.1Qcc. Replication and redundant transmission of data is also allowed over several disjunctive paths, and the redundancy properties of these mechanisms are transparent for the communicating applications.

The combined standards of TSN fulfill the requirements of hard real-time data transmission. This new Sercos TSN working group will also evaluate the future IEEE 802.1 TSN standard, in addition to the required network management associated with different network configurations.

The benefits of using Ethernet TWN are numerous, as it can result in low cost and a wide range of products and manufacturers, and can make a significant contribution to the implementation of consistent IoT solutions and the improvement of the coexistence of real-time Ethernet and Internet protocols. Peter Lutz, managing director at Sercos International, commented on the suitability of this new standard saying, “For the first time in the history of Ethernet, Ethernet TSN allows a time-triggered transmission of real-time critical messages via standard Ethernet components.”

A full overview of the key components that are being developed within these TSN activities can be found at Sercos in connection with TSN webpage.