Extending TSN capabilities over 5G and other wireless networks

Time-sensitive networking (TSN) is gaining traction in manufacturing applications as capabilities like 5G become more accessible. Fast and precise communications are needed. Dave Cavalcanti, principal engineer, Intel; Stephen Bush, senior scientist, GE; Alon Regev, senior director, product development, Keysight Technologies, who are members of the Avnu Alliance, offer some insight on TSN’s benefits for manufacturers and what the future holds.

Question: Why is time-sensitive networking (TSN) receiving attention from the wireless standards and protocols industry? What does the market look like?

Cavalcanti: The IEEE 802.1 Time Sensitive Networking (TSN) standards have seen a lot of growth in the past three to five years in the industrial space, becoming a more frequently implemented technology in the IIoT and on factory floors. At the same time, other markets, like professional media (audio/video), are also expanding the adoption of TSN capabilities, with solutions like the Milan protocol, creating a link between AV, IT, and silicon to enable a true IT convergence.

Recent advances in 5G and IEEE 802.11 wireless connectivity technologies in providing low latency and high reliability have generated significant interest in extending TSN capabilities over wireless. Wireless communication systems are beneficial for many reasons, including enabling flexibility and reducing wire costs, while also enabling mobility.

Question: TSN has been a standard based on Ethernet. What is meant by “wireless TSN?”

Cavalcanti: Although a few of the IEEE 802.1 standards exist for wireless, most implementations, market-specific profiling, interoperability testing and certification efforts, which are enabled by Avnu, have focused on Ethernet as the main transport media. As TSN-enabled devices and networks start to be deployed, enabling extensions of similar capabilities over wireless is a natural next step.  It is envisioned that TSN-enabled networks will extend from wired (Ethernet) to wireless domains. The term “Wireless TSN” is used to refer to a wireless network that extends IEEE 802.1 TSN capabilities over wireless media. The Wireless TSN links can enable wireless access to end devices and computing resources as well as extend the range of wired TSN networks. But not every wireless technology can support TSN features. Therefore, the Wireless TSN group within Avnu have decided to narrow our focus to the IEEE 802.11/Wi-Fi and 5G standards, given the recent advances and features available to enable TSN-grade performance from these two technologies.

Bush: To leverage the IEEE 802.1 TSN standards and ecosystem developed around them, it is important to enable seamless operation and interoperability from wired to wireless TSN domains. Some challenges associated with mapping TSN capabilities to wireless include fundamental differences between wireless and wired communications – the variable capacity of wireless links and the packet error rate (PER) being typically higher in wireless. The broadcast nature of the wireless medium is another important aspect to be considered. While it may open up the possibility to reach more devices with a single transmission, it also is more susceptible to interference. Coordinated medium access, as well as resilience to interference, is very important.

Question: What are some of the benefits of implementing wireless TSN?

Cavalcanti: The 802.1 TSN family of standards can be grouped into four main areas, most of them directly related to a performance vector; time synchronization, bounded latency, reliability, and resource, or network management capabilities. Each of these areas provide unique performance benefits that also lend themselves to success in a wireless network such as those enabled by Wi-Fi or 5G. These wireless TSN capabilities will enable time-sensitive communication performance with the flexibility and mobility benefits of wireless.

For example, given that traffic streams can be uniquely identified from Ethernet to Wi-Fi and 5G domains, it is possible to apply traffic shaping mechanisms to 802.11 and 5G networks. The TSN concept of 802.1Qbv time-aware scheduling can then be applied over the wireless networks to prioritize traffic and avoid congestion delays. A time-aware schedule must consider the feasible data rates that can be achieved across each wireless link as well as overhead due to medium access procedures. Therefore, the minimal latency bounds as well as number of traffic streams that can be supported over wireless TSN link will differ from a wired (Ethernet) TSN link. We dial down deeper into each of these benefits related to TSN in our white paper on the topic.

Regev: It’s important to consider that as multiple wireless standards develop TSN-enabling capabilities (such as IEEE 802.11 and 3GPP), it is expected that future TSN domains will be extended with both 802.11 and 3GPP-based wireless solutions. To leverage existing TSN standards and ecosystem, it is important to define a common model to integrate wireless technologies with a TSN domain. A new abstraction interface for wireless TSN should define clear service requirements and capabilities expected from wireless standards, such as IEEE 802.11 and 5G.

Question: Can you explain a few example use-cases of wireless TSN at work in a system?

Bush: In an industrial automation system, mobile robots are an important use case as wireless is fundamental for mobility, flexibility and reconfigurability of tasks and routes. Mobile robots’ latency and reliability requirements are compatible with capabilities of the latest wireless technologies. Electrical power grid systems are another interesting use-case for wireless TSN, as these systems have varied coverage areas which may vary from local (such as a substation) to wide areas (distribution and transmission). Industrial control systems also could benefit from wireless connectivity, but they will require the highest level of determinism and reliability and rely exclusively on IEEE 802.1Qbv for scheduling over wireless links.

Regev: Other use cases that require TSN-enabled networks, such as automotive and transportation applications, also may benefit from wireless. For instance, the wiring harness within vehicles, airplanes, and trains add significant production costs. If wireless technologies can provide the required time-sensitive media performance, it would bring value to such systems. However, the transportation market also comes with stringent latency, safety requirements and regulations, and use cases that require under 100 microsecond level cycle times are currently considered out of scope for wireless, but this is expected to change as wireless technologies evolve.

Question: How is wireless TSN beneficial for industrial systems?

Bush: The industrial market has the most diverse set of use cases and requirements for wireless TSN and has received significant interest. It has motivated the development of the 5G Ultra-Reliable Low Latency Communications (URLLC) mode and recent enhancements in IEEE 802.11 (such as IEEE 802.11be), with several industrial use cases having already been captured in detail by 3GPP, 5G ACIA, and IEEE 802.11 standard groups. Closed loop control is one of the most widely applicable use cases given its generic control loop model (input + compute + actuation), but specific latency and reliability requirements varies significantly depending on the application.

Use cases related to control of Power Grid components also have been described in the IETF DetNet group. One unique aspect to be considered in some electrical power grid systems is the required coverage area, which may vary from local (substation) to wide areas (distribution and transmission). Industrial control systems require the highest level of determinism and reliability and rely exclusively on scheduled communications enabled by the IEEE 802.1Qbv standard.

Question: What are some of the goals of the wireless Avnu Alliance TSN workgroup?

Regev: Despite the significant momentum and progress, more work is needed to bring wireless TSN capabilities to market. For instance, wireless specific TSN configuration interfaces, parameters, and test procedures still need to be developed. That is why we’ve put together the wireless TSN working group within Avnu Alliance. The WTSN workgroup work has highlighted that it is important to start early discussions and alignment on topics such as consistent TSN interfaces for wired and wireless technologies, interoperability testing, and certification efforts. These and other ecosystem activities will need to be addressed to provide consistent TSN services across wired and wireless physical layers that address real user needs across industries.

Cavalcanti: We also recently wrote an  Avnu Alliance white paper on wireless TSN to discuss the various opportunities for wireless TSN across numerous markets titled “Wireless TSN – Definitions, Use Cases & Standards Roadmap,” published by Avnu Alliance. The white paper introduces the basic terminology, use cases, and standards for extending TSN capabilities over wireless networks and aims to serve as an introduction to the concept of wireless TSN, and to start defining the work required in Avnu to test, certify and get the technology ready to market.

Dave Cavalcanti, principal engineer, Intel; Stephen Bush, senior scientist, GE; Alon Regev, senior director, product development, Keysight Technologies. Edited by Chris Vavra, associate editor, Control Engineering, CFE Media and Technology, cvavra@cfemedia.com.

MORE ANSWERS 

Keywords: time-sensitive networking, wireless networks, 5G wireless

Wireless time-sensitive networking (TSN) standards can improve communication and coordination on the manufacturing floor.

IEEE 802.1 TSN standards can be grouped into four main areas: time synchronization, bounded latency, reliability and resource, or network management capabilities.

While progress has been made, more work bringing wireless TSN to the market.

ONLINE 

Read more articles about wireless networks in the “wireless” sub-channel page under networking and security at www.controleng.com.

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