Ethernet evolution: The rise of SPE and TSN in automotive and industrial applications
The Ethernet era
IT professionals quickly recognized the benefits of networking computers and peripherals as the burgeoning computer industry established itself in the 1980s. However, making it a reality was another matter. Multiple proprietary protocols emerged, with each aspiring to become an industry standard. Consequently, networking computers was a rather complicated task. Roll forward four decades, one of these protocols, Ethernet, has become the dominant and widely adopted computer networking standard. Ratified by the IEEE in 1983 as the IEEE 802.3 networking standard, Ethernet has constantly evolved and spread beyond its legacy roots for enterprise computing. Figure 1 shows how Ethernet's bandwidth capabilities have evolved to meet application demand and use cases.
Today, Ethernet-based networking is omnipresent, serving industrial operational technologies (OT), automotive in-vehicle networking, media streaming, and traditional IT applications. Ethernet's characteristics of flexibility, ease of deployment, and resilience have firmly established it as the ideal candidate for virtually any wired or optical networking requirement. Ethernet is traditionally implemented using four unshielded twisted pairs (UTP) of conductors, all packaged into a single cable. The cable and its associated RJ45 terminations are ubiquitous.
Figure 1 - Ethernet speed evolution and diversity of use cases
Single-Pair Ethernet delivers Ethernet connectivity to the OT edge
The industrial landscape of operational technology machinery and equipment has long been fragmented. Multiple legacy serial protocols such as Modbus, RS232/RS422 and Profibus have traditionally served the needs of industrial automation systems. However, as Ethernet became the perfect way to connect IT and OT domains as industrial performance improvement initiatives such as Industry 4.0 progressed, deploying bulky four-pair cables in space-constrained equipment racks became challenging. To overcome the cabling challenges of four paid cables and to deliver Ethernet connectivity from the data centre to the edge, single-pair Ethernet (SPE) was announced in 2011. Consisting of a slim and lightweight cable containing a single twisted pair, SPE has continued to evolve with gigabit single pair Ethernet (SPE) IEEE 802.3bp (1000BASE - T1) standard ratified in 2019. With a maximum link run of 15 metres for unshielded cables and 40 metres using shielded cables, an SPE cable is up to 60 % lighter than its four-pair legacy. With SPE, Ethernet connectivity is assured across IT and OT systems, from the data centre to the edge - see Figure 2.
Figure 2 - Single-pair Ethernet connects IT and OT networks across the enterprise
Achieving determinism in Ethernet networks
As Ethernet has expanded its foothold outside traditional IT applications, some new use cases introduce the need for a deterministic communication behaviour. Most consumer and enterprise use cases of Ethernet and the way it had previously developed have been focused on an ever-increasing bandwidth requirement. When streaming video over the internet, for example, as users, we are aware of a slight delay or pause before the video starts to stream. However, the introduction of industrial IoT and automotive applications that work with actuators and sensors in real-time challenged the underlying processes of Ethernet, which is not aware of time. Unfortunately, such infrequent and variable delays in network traffic flow are unacceptable for most real-time industrial and automotive applications. To overcome the impact of latency and network jitter for real-time communications, the IEEE established a time-sensitive networking (TSN) task group in 2012 to define standards that bring predictable and deterministic behaviour to Ethernet networking. The result is a broad set of standards under IEEE 802.1 - see Figure 3 - that offer time synchronisation, determined latency, and high-reliability communications across all supported base Ethernet standards, including SPE.
Figure 3 - Time-sensitive networking standards for industrial, automotive, and media use cases
Single-pair Ethernet and Time-sensitive networking: A game-changing combination
The ability to deliver a deterministic, time - synchronised network link using lightweight, flexible, single-pair Ethernet cables offers significant benefits to industrial and automotive networking. Most importantly, Ethernet's IEEE 802.1 TSN protocols can co-exist alongside non-deterministic network traffic. The TSN standards highlighted in Figure 3 provide the means to solve whatever deterministic networking requirements the use case needs, from a shared and standard view of time through to an assured maximum latency metric.
Another benefit to SPE is that it also features a power delivery capability, power over Ethernet (PoE), that already exists across the IEEE 802.3 standard. For many applications, particularly in large-scale industrial IoT deployments, the ability to power an edge device, such as a sensor, and provide resilient network communication saves significant time and cost.
SPE and TSN: Revolutionising the automotive sector
As automotive systems migrate from distributed to domain and zonal architectures, single-pair Ethernet yields considerable advantages. Firstly, with its compact, lightweight and flexible cabling, SPE for zonal architectures helps reduce the vehicle's cabling weight, an essential aspect of electric vehicles. Secondly, with a multi-drop network architecture, SPE connects the growing number of vehicle systems, such as advanced driver assistance systems (ADAS). SPE also significantly aids the unification of in-vehicle networking protocols by providing a single network protocol stack, reducing system complexity. Coupled with its ability to support TSN, SPE addresses the real-time needs of ADAS and other semi or fully autonomous vehicle networks. For example, real-time data from a forward-facing radar or lidar sensor must arrive at the adaptive cruise control (ACC) electronic control unit (ECU) within a maximum latency window. Likewise, video streaming from a front-mounted camera for collision avoidance detection must arrive at the corresponding ECU within a narrow latency window. Excessive network traffic latency, for example, due to a music stream to the infotainment system, is unacceptable and could result in erratic vehicle behaviour or even an accident.
Industrial advancements with SPE and TSN
As industrial automation deployments advance, factory floor space becomes a premium. With typically only room for one control cabinet per production process, squeezing more technology into a single cabinet is imperative. With its thinner cable dimensions and improved bending radius compared to a four-pair Ethernet cable, SPE offers significant gains. As highlighted, SPE delivers enterprise-grade interoperable and unified Ethernet communications from IT to OT and right down to edge devices. Combined with TSN's deterministic and bounded latency attributes, SPE and TSN enable a new generation of real-time industrial automation use cases. Also, with production and manufacturing efficiencies increasing under the spotlight, monitoring and controlling increasingly diverse and connected production assets as a single entity requires resilient, robust and deterministic communications. Examples include cobots, high-throughput production processes, real-time video-based machine-learning quality assurance, and increased conformance to functional safety requirements. SPE and TSN are particularly suited to high-speed, closed control loops, where everything from process control motor drives, AI-driven sensors and fast cycle-time actuators require low jitter, deterministic communications latency, and time - synchronisation to operate reliably, safely and efficiently.
SPE and TSN - Leading the way to deterministic Ethernet networking
Ethernet has come a long way these past forty years. Long respected by IT professionals for delivering robust and reliable networking infrastructures, it was only a matter of time before other market sectors benefited from Ethernet's impressive capabilities. As Ethernet's use cases expanded, so did the need for provisioning time-aware synchronised and ultra-low latency determinism. Single-pair Ethernet and time-sensitive networking are examples of how Ethernet has evolved to satisfy an ever-increasing demand for network communications. Together, SPE and TSN are transforming wired communications for a new breed of applications, such as industrial automation and in-vehicle networking, just as Ethernet did for the evolving IT industry.
Sources
Figure 2: https://ethernetalliance.org/wp-content/uploads/2021/01/EA-SPE_infographic2-brewery-DEC2020.png
Figure 3: https://www.ieee802.org/1/files/public/docs2023/admin-tsn-summary-0823-v01.pdf
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