Why 10BASE-T1S is the missing Ethernet link in automotive communications

[Introduction]New IEEE Automotive Ethernet standards are emerging, and 10BASE-T1S Ethernet is one of the newest. This article discusses trends in the automotive industry that reflect changes in automotive electronics/electrical (E/E) architectures and how the new 10BASE-T1S standard supports and drives the deployment of this new architecture.

Megatrends offer new opportunities

The automotive industry is currently undergoing major changes. Automakers need to quickly provide solutions for several megatrends such as personalization, electrification, automation and total connectivity. OEMs need to overhaul their E/E architectures to support new features. While this change poses significant technical challenges, it also presents an opportunity for OEMs to start considering moving away from standalone domain-based solutions in E/E architectures, as such The solution became unwieldy with the increasing number of control modules. With this major change in architecture, OEMs can focus on developing better technology solutions while increasing aftermarket revenue through features such as vehicle personalization, sales service and over-the-air (OTA) upgrades. The industry is moving to a common new architecture, often referred to as a regional architecture, and is looking to leverage technology and experience from other industries, especially IT, to make the car a computer on wheels.

Regional architectures determine connectivity by actual physical location, not by function, with standalone domain-based architectures of the latter (connectivity by function). This change greatly reduces the number of Electronic control units (ECUs) in the car and reduces the overall cable length by up to 1 km1. Second, it decouples hardware and software, providing a service-oriented architecture (SOA). Many OEMs are investing heavily in their own software development, hoping to provide end-to-end solutions that simplify platform integration and provide more cross-functional capabilities. 2 This scalable software platform approach can minimize design changes, add new revenue streams, help reduce long-term R&D investments, shorten development cycles, and support multiple model families simultaneously.

These revolutionary architectural changes have created challenges that have prompted many OEMs to reorganize their entire organization, moving away from individual divisions responsible for specific independent domain function controllers to a more integrated, cross-functional organization.

Automotive is fast becoming the dominant area for using Ethernet devices, and widespread deployment of Ethernet in cars is one of the key foundations for the successful rollout of these new architectures. Ethernet brings the required scalability, supports multiple speed classes, is a mature and reliable transmission medium, supports a service-based architecture, and employs well-developed security and protection building blocks. Ethernet uses a well-defined, easy-to-understand OSI model to more easily manage complex networks throughout the vehicle.

Why 10BASE-T1S is the missing Ethernet link in automotive communications

Figure 1. The regional architecture of the car

Unique needs of the automotive sector

While many basic Ethernet concepts from other industries can be leveraged, automotive E/E architectures have some unique requirements that require the development of new technologies. For cars, a key factor is reducing the weight of the car, which directly affects the mileage of the car. The cable harness used today is one of the three heaviest subsystems in a car (up to 60 kg). 3 Traditional Ethernet cables use four differential pairs for data transmission, which adds weight and wiring complexity to the car and is not optimal for automotive applications. To address this, a new IEEE standard was developed that supports Ethernet transmission over a single twisted pair, in addition to shortening the length of the cable harness through a zone architecture, resulting in significant savings in cable cost and weight.

What factors are driving the demand for 10BASE-T1S?

As the concept of zone-based architectures continues to evolve, in order to take full advantage of this new architecture, it is clear that Ethernet connectivity needs to be extended to end sensors and drives. Existing legacy connectivity technologies such as FlexRay and CAN often require protocol conversion in the gateway, which can lead to increased cost, complexity and latency. Existing automotive Ethernet technologies such as 100BASE-T1 require the use of point-to-point switched connections and cannot meet the system cost requirements to support the transition to Ethernet in end-connection applications. So, IEEE calls for a solution to this problem. Some key requirements include: 4

● Enables faster communication speeds than existing technologies; eg, CAN(FD)

● Replacing traditional in-vehicle network technologies such as FlexRay

● If using 100BASE-T1 to connect the ECU is not cost-effective, an alternative to 100BASE-T1 is required

● Ability to support simple, redundant sensor network connections

What is 10BASE-T1S?

The 10BASE-T1S specification is part of the IEEE 802.3cg standard and was published in February 2020. 10BASE-T1S provides the missing link in the automotive Ethernet ecosystem, enabling true Ethernet-to-edge connectivity and addressing the needs of regional architectures.

10BASE-T1S is unique from other automotive Ethernet technologies: it supports a multipoint topology, where all nodes are connected by the same unshielded twisted pair. This bus configuration provides an optimized BOM with only one Ethernet PHY deployed on each node, eliminating the need for switching or star topologies associated with other Ethernet technologies. The standard stipulates that at least 8 nodes must be supported (more nodes can be supported), and the bus length must reach 25 meters.

Why 10BASE-T1S is the missing Ethernet link in automotive communications

Figure 2. 10BASE-T1S bus topology

Another new feature of the standard is Physical Layer Conflict Avoidance (PLCA), which, as the name suggests, avoids conflicts on shared networks. This configuration ensures that the deterministic maximum latency is mainly determined by the number of nodes in the network and the amount of data to be transmitted. Each node gets a transmission opportunity. If a node has no data to transmit at that time, it will hand over the transmission opportunity to the next node to fully utilize the available 10 Mbps bandwidth.

Since it is an AC coupled system, it also supports 10BASE-T1S network power supply. This results in further cable savings, reduced connector size, and higher reliability due to cable savings and reduced connector complexity. Power over Data Lines (PoDL) can be used for point-to-point configurations, and now as part of an improvement to the IEEE standard, multipoint topologies are also supported.

10BASE-T1S has a wide variety of applications in the automotive sector, with multiple sensors and actuators still being explored across multiple functions in body, comfort, infotainment, and ADAS systems.

in conclusion

Automotive E/E architecture is undergoing a major change. The transition to a regional E/E architecture is imminent. 10BASE-T1S provides the missing link, supporting this transition with optimized Ethernet-to-edge connectivity. During this deployment, there are still some issues to overcome, such as Ethernet connectivity adding component cost and complexity to the module implementation. 10BASE-T1S addresses these issues by reducing system cost and offering a wide selection of products that support different types of signal chain partitioning. Analog Devices is actively involved in standardization activities and works closely with OEMs to actively promote and deploy 10BASE-T1S to ensure that their system requirements are met.

Contact Analog Devices to learn about our 10BASE-T1S products and how we plan to help promote and deploy 10BASE-T1S in the automotive space.


1 Cariad. May 2021.

2Ryan Fletcher. “End-to-End Automotive Software Platform Use Cases.” McKinsey & Company, January 2020.

3 Dan Scott. “Wire Harness Development in Today’s Automotive Sector.” Siemens AG, July 2020.

4 Calls for 10Mb/s single twisted pair Ethernet. IEEE 802.3 Ethernet Working Group.

About the Author

Fionn Hurley is Marketing Manager for Analog Devices’ Automotive Cockpit Electronics business unit in Limerick, Ireland. He joined Analog Devices in 2007. Previously worked as an RF design engineer. He is a graduate of the University of Cork (UCC) in Ireland with a BA in Electrical and electronic Engineering. Contact: [email protected]

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