In the last few years, Time Sensitive Networking (TSN), a family of IEEE 802.1 standards to enable time synchronization and data delivery with strict latency bounds, has seen stable growth in Ethernet-based wired networks.
As the benefits of wireless communication are becoming increasingly apparent, e.g., greater flexibility, higher mobility and reconfigurability, and lower maintenance costs, interest in extending TSN to wireless is also growing.
As TSN becomes more widely implemented in Industrial Internet of Things (IIoT) applications, with more TSN-enabled devices being deployed, it’s no surprise that the industry is now looking to enable extensions of similar capabilities over equally advancing wireless technologies, like 5G.
With the potential to enable wireless connectivity for a variety of industrial applications, 5G use cases will be a boon for manufacturers of end-devices and systems across IIoT, enabling them to easily reconfigure industrial automation, control systems, factory automation, and other elements of Industry 4.0. We can expect wireless TSN and 5G to completely transform the future of wireless networks with high reliability, resiliency, and security.
Why TSN can be impactful for wireless standards
Already, some existing TSN standards and capabilities have been extended to operate over wireless, 802.11 (Wi-Fi) and 5G, for example: time synchronization (802.1AS).
"Arguably the market with the most diverse set of use cases and requirements for wireless TSN, the industrial segment has already received significant interest from the TSN community."
Alon Regev, Keysight Technologies.
Time synchronization is a fundamental TSN capability and is used by TSN-enabled applications to enable other TSN capabilities, e.g. Time-Aware Scheduling. The standard extensions to distribute time over 5G systems have been developed, enabling a single reference time can be distributed between wired (Ethernet) and wireless TSN domain across a 5G System. Another capability fundamental to TSN is the ability to identify and differentiate time-sensitive traffic streams. With IEEE 802.1Q-2014, mechanisms are defined to classify time-sensitive streams and differentiate them from other traffic across the TSN-enabled nodes and end stations.
Both time synchronization and traffic classification, shaping, and scheduling over 802.11 and 5G prove that some standards have already been successfully developed to extend TSN capabilities over wireless domains.
As the industry continues efforts to adopt and deploy more wireless capabilities within TSN domains, we can expect this transition to be gradual; however, this endeavor is, indeed, worthwhile, as there are many applications that can directly benefits from TSN capabilities over wireless.
Arguably the market with the most diverse set of use cases and requirements for wireless TSN, the industrial segment has already received significant interest from the TSN community. Closed loop control, for example, is one of the most widely applicable use cases due to its generic control loop model (input + compute + actuation). Mobile robots are another industrial use case for which wireless will prove beneficial, as wireless is fundamental for mobile’s requirements for mobility, flexibility, and reconfigurability of tasks; its latency and reliability requirements are also compatible with capabilities of the latest wireless technologies.
As TSN features continue to extend to wireless, we will see future use cases abound. For example, emerging applications, like gaming and augmented/virtual reality, will benefit from wireless and also wireless TSN features, as avoiding high latency and jitter is paramount for providing a quality user experience. Automotive and transportation applications, too, could benefit from wireless: The wiring harnesses in vehicles, airplanes, and trains add high costs to production; should wireless technology provide the same time-sensitive performance as these harnesses, they could significantly reduce production costs. At present, however, these industries have specific safety critical requirements that are beyond the current scope of the wireless standards in 802.11 and 5G.
Bringing TSN capabilities to 5G
"As we begin the gradual transition to adopt and deploy more wireless TSN capabilities within various domains, there is also work underway to introduce TSN support over 5G."
Alon Regev, Keysight Technologies.
As we begin the gradual transition to adopt and deploy more wireless TSN capabilities within various domains, there is also work underway to introduce TSN support over 5G. Unlike 802.11, 5G is not a native 802 LAN technology and, thus, cannot be directly integrated with Ethernet TSN standards at Layer 2; however, the 3GPP Rel-16 has started to introduce TSN support over 5G. This 3GPP approach to integration is over-the-top (i.e., TSN-related functionality is confined to TSN Translator (TT) functions at the 5G system ingress and egress points), but more work is expected to continue in the 3GPP Rel.17 specification. To help coordinate the development of these 3GPP standards and to foster industry adoption of 5G technology in industrial markets, the 5G-ACIA (Alliance for Connected Industries and Automation) has been formed. The group also expects to help evaluate 5G technology and explore spectrum needs operator models for industrial 5G networks.
Opportunities and challenges
As the industry charges forward towards extending TSN capabilities over wireless, we must be prepared for new challenges. For one, we can expect that future TSN domains will be extended with both IEEE 802.11 and 3GPP-based wireless solutions; however, in order to continue leveraging existing TSN standards and ecosystems, we’ll also need to define a common model with clear service requirements and capabilities to integrate wireless technologies with a TSN domain. Next, ongoing configuration and management of TSN features will also require attention, as we must consider the capabilities of underlying communication tasks, e.g. the CNC (Computer Numerical Control) task that defines and configures a time-aware schedule for a set of time-sensitive streams across the network; because the CNC task assumes a constant data rate for each Ethernet link in order to compute the proper gate operation schedule across the bridges, we need to consider what will happen when wireless links are introduced, as the CNC will need to consider the possibility of dynamic changes in link speed/bandwidth due to wireless channel dynamics, interference, etc.
Meanwhile, interference—typically the number one concern for wireless TSN extensions—will also need to be addressed, as the industry will require tools to mitigate the potential impact of interference in a wireless TSN domain. Because TSN is based on Ethernet and wireless standards (IEEE 802.11/Wi-Fi and 5G), networks can take advantage of security best practices and standards that have already been developed for Ethernet, 802.11, and 3GPP systems. Finally, it’s also worth noting the mobility and roaming challenges that will arrive. Mobility is a unique benefit of wireless connectivity, enabling flexible deployment and easy recognition of devices and applications; however, current roaming procedures in cellular and Wi-Fi networks cannot meet the stringent latency and high reliability requirements in TSN domains. For future wireless connectivity standards, thus, it will be important to provide TSN-grade latency and packet loss performance during roaming.
Conclusion
Moving forward, it is important for the TSN community to gain a deeper understanding on how wireless networks can schedule time-sensitive traffic. As the need for time-synchronized communications continues to grow, the Avnu Alliance and its WTSN Working Group remain committed to accelerating the adoption of the TSN interoperable foundation with extensions over wireless technologies to ensure maximum benefits for the industry.
About the Avnu Alliance
Avnu Alliance is a community creating an interoperable ecosystem of low-latency, time-synchronized, highly reliable networked devices using open standards, supporting the foundational technology of IEEE Audio Video Bridging (AVB)/Time Sensitive Network (TSN) base standards. Avnu creates comprehensive certification tests and programs to ensure interoperability of networked devices. The Alliance, in conjunction with other complementary standards bodies and alliances, provides a united network foundation for use in professional AV, automotive, and industrial control.
