Time-sensitive networking (TSN) is the most recent leg of the journey that will make critical data available where and, most importantly, when it’s needed. The automotive industry’s use of audio video bridging has evolved into time-sensitive networking for in-vehicle and out-of-vehicle communications.
But what exactly is TSN, and why does it matter?
“On the one hand, time-sensitive networking denotes a set of IEEE 802 standards, which extends the functionality of Ethernet networks to support a deterministic and high-availability communication on Layer 2,” explains Dipl. Ing. André Hennecke, researcher at DFKI, a research center in Kaiserslautern, Germany. “In particular, this includes an improved timing synchronization and a real-time scheduling method, enhancements of the stream reservation protocol, explicit path control and network policing procedures.”
On the other hand, the term “time-sensitive network” is also used to designate a series of acts from different organizations to enable a deterministic communication via Ethernet, not only with a focus on Layer 2, but also with a view on Layer 3 (DetNet), applications and certification processes, such as those from AVnu Alliance, says Hennecke.
“It’s possible to have a network that offers no value to a customer, even though it conveys 100% of the requested information, simply because of the transmission latency it introduces,” warns Doug Taylor, principal engineer, Concept Systems, a system integrator in Albany, Oregon. The aim of TSN is to eliminate that latency for critical data by reserving a traffic lane for those packets.
At one level, time sensitive networking it is a set of IEEE 802.1 and 802.3 standards, explains Paul Didier, solutions architect manager at Cisco. “The objective is to enhance Ethernet and core standard networking to better support time-sensitive applications, such as industrial automation control,” he says.
“We’re trying to match up standard networking with a lot of the requirements coming out of industrial automation and control. The concept of these control transactions or messages is a little challenging. Control engineers think they’ve got a controller or motor, and there’s a wire between the two of them. Technically, they understand that moving to standard networks and being able to do things in those models makes things a lot easier. Queuing the stuff up is counter-intuitive. They’re looking for deterministic network performance characteristics around latency, jitter and reliability that are easy to implement and use. It gives them an open and interconnected network that allows much more freely flowing information from those devices and to enhance and add to those devices over time, which drives the overall story of the IoT, where you can do off-line or close-to-the-machine. You need access to the data without having to drop extra lines in. It’s about convergence. There’s all of this IIoT, and it’s all about these things using the Internet. Aren’t there different requirements? Isn’t there a reason they haven’t used the Internet? Should we make some modifications?”
At the heart of TSN are mechanisms that provide time synchronization for networked devices and scheduled forwarding of defined traffic flows through the network, explains Markus Plankensteiner, vice president, sales industrial, North America, and global alliance manager, TTTech Computertechnik (www.tttech.com). “Through time synchronization and scheduling, TSN delivers deterministic communication over standard Ethernet, thereby enabling the convergence of critical control traffic with data traffic over one infrastructure without the need for gateways or proprietary solutions,” he says.
“The TSN standards define mechanisms for the time-sensitive transmission of data over Ethernet networks; these in particular address the transmission of data at very low latency and high availability, allowing for time-determination communication and synchronization,” says Sari Germanos, open automation business development manager, B&R Industrial Automation.
Time-sensitive networking is a collection of projects aimed at improving Ethernet, and specifically Internet technologies for time synchronization, explains Joey Stubbs, P.E., North American representative, EtherCAT Technology Group. “These projects are intended to improve routing, pre-emption, time synchronization, security and throughput of Ethernet traffic for A/V streaming and bridging,” he says. The IEEE 802.1 standard encompasses the work of the TSN Task Group, which used to be called the AVB Task Group for audio video bridging.
Fieldbuses are proprietary, well-designed for the applications they support, but getting data out of them is a bear, says Didier. “We can support that much better than the much-less-deterministic methods that we currently have,” he explains. “They have control problems they’re trying to solve. We’ve got an ecosystem we’re trying to build this into. This isn’t going to be a separate network configuration. It’s simply incorporated in the standard tools that you use. The idea is those programs understand the control loops and what information needs to come in and leave. The network will say it can handle it, sometimes with modifications, and push it out into the network. That’s the architecture we’re putting together on top of the IEEE standards.”