For most uses of Ethernet technologies, the latency, or time it takes data to traverse a network from point A to point B, is generally not an issue in modern network deployments if all components are working. The difference of either 5 ms of latency or receiving a few packets out of order when streaming a video, downloading a file, or even playing an online video game often go unnoticed by individuals. In systems where the tight coupling of distributed components is necessary, such as scientific computing, high-frequency stock trading systems, or manufacturing line operations, milliseconds matter. No misses or out-of-order data transmissions can occur. To meet these needs and others like it, the IEEE developed a task force to research time-sensitive networking (TSN) .
Traditional Ethernet transmission can be thought of as best-effort; the sender transmits data in slices, and the receiver reassembles the slices into the original data. If a slice is missing or arrives out of order, the receiver knows how to request another copy of the slice(s) and/or put them into the correct order. These actions of resending and out-of-order assembly take time and can create a delay in the receiving system having the data available for use. Network device vendors know these limitations in traditional Ethernet and have created proprietary communication protocols such as EtherCAT  and Profinet  to address them. While these implementations are very good at expanding the functionality of Ethernet to meet the needs of manufacturing, components and devices need to meet standard specifications from the associated trade groups for easier integration.
TSN: Synchronization, quality of service, scheduling
The IEEE 802.1 Task Group developed TSN with several specific goals. Synchronization of clocks to nanosecond levels of accuracy is accomplished in conjunction with the precision time protocol (IEEE 1588) . Bandwidth reservation and network traffic shaping allow specific types and classifications of communications to pre-empt others, similar to the application of quality of service (QoS) on standard Ethernet networks. Due to industrial communications requirements, the tactics used in the scheduling and reservation systems are much more complex in design and implementation. Efforts are underway to make these features more robust and accommodating to different communication workloads, such as automotive and safety systems . Today there are eight priority values that can be assigned to network communications that aid in devices sending and receiving data based on significance.
When analyzed through the framework of the seven-layer OSI model, many of the changes TSN brings occur within Layer 2. These Layer 2 changes have some dependencies on the physical interfaces that comprise Layer 1, such as support for time-stamping.
Due to the fundamental differences in how communications are structured and sent, TSN requires pairing supported hardware and operating systems. A brief overview of how this impacts the OSI model is shown in the table. The joint project with IEC is referred to as IEC/IEEE 60802 TSN Profile for Automation . Find more details in IEEE 802.1AS, 802.1Q (at, av, br, bu, bv, ca, cc, ch, ci, cp, cr) .
Part 2 – Current challenges with TSN: Hardware
The digitization of industrial processes often referred to as “Industry 4.0,” has been underway for years. Different industries are embracing the concept at different speeds. Many of the potential challenges they face can be reduced by adopting and integrating software and devices that support TSN. The time-series data critical for applications, such as machine learning (ML), requires all components that time-stamp their data have accurate and synchronized timings measured on the order of nanoseconds due to the high speeds at which today’s lines perform actions.
Safety or control systems must have assurances of available bandwidth through which critical commands can be sent and reliably received by downstream equipment. The innovation brought into facilities through customized or specialty devices must work with existing protocols to avoid the vendor lock-ins of the previous generation. The Industrial Internet of Things (IIoT) movement provides solutions to many different data collection use cases at various price points, enabling cost-effective monitoring and data collection of previously unviewed equipment or line operation aspects.
To use TSN features, the hardware must support it. The chips and components related to Ethernet communication must support built-in features, such as time-stamp generation. Unfortunately, this means many of the devices in use today do not support TSN and would need to be upgraded, including programmable logic controller (PLC) communication modules, servers, workstations, and sensors. This also requires a new networking code implementation that handles network communication as the shaping and priority functionality does not exist in standard Ethernet. These features and functions will consume more processor time.
As a result, this firmware may be limited to more current hardware with more available resources for use by TSN features, which will be another driver for upgrading hardware. A complete TSN implementation in a location would require TSN-supported network switches, Ethernet controllers with TSN support, servers or devices with TSN-supported chipsets and software and possibly TSN-gateways if transition or translation from proprietary deterministic networks is needed. The Avnu Alliance is an organization working on evaluating and certifying devices to ensure compatibility and conformance to the standards .
TSN research on IEEE 802.11 wireless, 5G
Connectivity is another consideration in adopting TSN as part of Industry 4.0. Today, implementing TSN is achieved via wires and cable. Research on how to bring TSN capabilities to wireless devices is underway, but organizations should not plan on these technologies being available for another few years . This research is already bringing forward proof-of-concept products that operate in the standard IEEE 802.11 wireless space but also the 5G cellular network spectrums . For the time being, wireless devices cannot support the features or functions of TSN. Network designers or engineers should understand these limitations when evaluating the equipment they plan to deploy and connectivity needs. The Industry 4.0 approach to wireless currently has other technologies under consideration, such as LoRaWAN and Bluetooth Low Energy (BLE).
Part 3 – TSN uses, benefits for Industry 4.0: Standards, determinism
The benefits of TSN-enabled equipment to drive solutions, such as predictive maintenance, machine performance metrics, quality, and efficiency modeling, which leverages artificial intelligence or machine learning, and cannot be overstated. Having one interface that can enable high-speed control, data acquisition, and supervisory functions will simplify applications that used to require multiple interfaces and much more complex implementations, enabling faster development and deployment.
As an IEEE standard, the concerns for vendor lock-in and proprietary protocols become less of an issue for organizations looking to adopt new communications technologies and capabilities. Network switches with TSN support will be available from various vendors. Devices can be purchased from any vendor implementing TSN into its products. The use of standard Ethernet cabling removes some complexity and may allow IT and OT to share technical resources responsible for supporting infrastructure. As an end-user of TSN, there are no licenses, fees, or other annual costs imposed by IEEE to be concerned about as the products are developed against the published standards, and interoperability is the primary goal.
The ability to have deterministic data traversing standard networking solutions should reduce the complexity of solutions going into facilities. With the added reliability of the scheduling and priority functionality, TSN may be a path forward for upgrading from legacy solutions. Vendors will also introduce gateways that allow time-sensitive communication protocols such as SERCOS to TSN to transition to TSN-based Ethernet, allowing them to have the benefits of Ethernet without requiring a complete replacement of components at a considerable cost .
The current methods of redundancy achieved through Device Level Ring (DLR), Parallel Redundancy Protocol (PRP), Media Redundancy Protocol (MRP) may be replaced with additional features added to TSN. While these are not in place yet, they are being discussed and, if brought into the standard, would further reduce the complexity and proprietary structure of industrial networks. Organizations using these existing technologies should continue to stay informed on the developments in these areas as they may impact the design and technology choices for upgrades for projects 5 to 7 years from now.
Part 4 – Time for TSN features, functions
The short and long-term futures of industrial networking are shaping up to be exciting. It may take a few years for all of the features and functions discussed in this article to mature and be present in the equipment. Some features, such as precision time protocol, are used today and are already creating value. Time-sensitive networking is a key component to the transformative movement of Industry 4.0. The uses and applications that may now be possible with the accuracy and consistency of TSN are held back by the user’s imagination.
This article was originally published on Control Engineering.