This article is part of the TechXchange: Single Pair Ethernet.
What you’ll learn:
- What is 10BASE-T1S and how does it work?
- How 10BASE-T1S can benefit automotive systems and increase scalability in the industry.
- The challenges that still need to be addressed before 10BASE-T1S is implemented across the entire automotive spectrum.
Today's automobiles come packed with numerous technological improvements designed to make vehicles perform better and operate more safely, while adding features to keep drivers and passengers safe while presenting them with richer entertainment options. To that end, modern vehicles come outfitted with advanced driver-assistance systems (ADAS) such as adaptive cruise control, collision warning systems, and automatic emergency-braking systems, along with advanced infotainment systems and more.
All of those platforms are driven by embedded systems with advanced microcontrollers that rely on communicating with each other for seamless operation. For example, data gathered from sensors dedicated to collision avoidance are useless unless shared in real-time with vehicle control systems. That's only one of the innumerable interactions among automotive subsystems that justify a robust in-vehicle network (IVN)—a network more robust than what’s presently in use.
Most vehicles come equipped with a Controller Area Network (CAN) bus to handle communication between those embedded systems without the need for a host computer. CAN is a message-based protocol and functions by transmitting data serially to another device at a maximum of 1 Mb/s. CAN began showing its age over the last decade and is no longer able to handle the large data throughput required for today's embedded systems.
When CAN Can't
As mentioned earlier, CAN tops out at 1 Mb/s, and the faster variant CAN-FD maxes out at 8 Mb/s. The limits are a serious impediment to a number of automotive capabilities that are already standard features as well as other proposed options. Data from cameras, radar, and LiDAR used in current collision-avoidance systems and other ADAS features demand far more bandwidth than is available through the CAN bus. For example, the data stream from a single LiDAR sensor can be upwards of 70 Mb/s.
The automotive industry needed a replacement for the aging CAN protocol and decided to adopt Ethernet to handle in-vehicle communication. Ethernet is widely used in data centers, manufacturing, home networks, and more to transfer large data throughput.
However, the auto industry uses another form known as automotive Ethernet (AE). Vehicles employ the AE protocol as it adds a physical layer for specific use cases, and the cost of the cables is reduced by using PHY transceivers that stand up to challenging road conditions. It provides a higher baud rate over traditional Ethernet and allows for the reuse of IP technologies from other industries.
AE supports data transfer at roughly a gigabit per second. Subsequent versions include IEEE 802.3cg, which specifies up to 10 Mb/s on a single pair, and 802.3ch, which specifies 2.5, 5, and 10 Gb/s, also on a single pair. AE ordinarily specifies the use of twisted-pair cables to reduce weight and costs, but fiber optics are typically more resistant to noise and more conducive to signal integrity.
That being said, automotive Ethernet isn't without its challenges, as the demands for higher bandwidth increase as technology and applications evolve.
Several of those key challenges include maintaining multi-gigabit transmission of data within the vehicle in the near term while aiming for much higher throughput in the long term. Trying to maintain electromagnetic compatibility and reliability with increasingly noisy environments is another concern, along with maintaining low weights and costs associated with wire harnesses to support a data center on wheels.
Enter 10BASE-T1S
New IEEE automotive Ethernet standards are starting to emerge to address those challenges. One of the latest is 10BASE-T1S, which is designed to support new architecture rollouts. Vehicle manufacturers are continuously looking to provide solutions to the latest megatrends in personalization, autonomy and full connectivity as OEMs continue to modify their electrical/electronic (E/E) architectures to support increased functionalities.
10BASE-T1S, which is specified in the IEEE 802.3cg standard, defines a physical layer and data link layer for MAC addresses within Ethernet networks. The physical layer provides connections to nodes or devices such as routers, switches, and hubs.
Broken down, the “10” represents the maximum transmission speed (10 Mb/s), “BASE” refers to baseband signaling, and “T1” denotes single twisted-pair cabling. The specification is designed to provide a multi-drop transmission medium that can handle at least eight transceiver nodes or devices at distances of 25 meters or more. The “S” means a short length or short reach.
With 10BASE-T1S, standard Ethernet communication no longer needs gateways to connect incompatible communication or embedded systems. It also increases scalability, as several nodes can operate on the same bus line without sacrificing data throughput.
One of the unique aspects of the standard is a physical-layer collision-avoidance ability, which prevents data traffic from jamming or overwhelming nodes. This provides maximum latency for data throughput dictated by the number of nodes on the network and the amount of data to be transmitted.
Each node in the network is assigned an opportunity to transmit. However, if that node has no data to transmit, it hands over priority to the next node, ensuring maximum utilization of speeds and throughput.
It’s also possible to provide power over the 10BASE-T1S network (known as PoDL/Power over Data Lines) as it's an ac-coupled system, which reduces the amount of cable needed for vehicle networks. It also shrinks connector sizes and increases reliability to the system.
10BASE-T1S Will Drive AE into the Future
The 10BASE-T1S standard will allow automotive Ethernet to expand and evolve along with embedded electronics. This, in turn, will enable vehicle E/E systems to evolve as well with new feature sets, such as multi-drop physical layers, low latencies, and efficient bandwidth utilization.
Automotive suppliers have already started producing 10BASE-T1S components, and new system designs are underway to implement those new devices, as the necessary tools are already available.
10BASE-T1S also allows manufacturers to implement Ethernet-to-the-edge connectivity. One of the key connections in some modern vehicles includes telematics control units (TCUs), an embedded system that handles wireless connectivity to cloud services for any number of applications. The standard optimizes that connectivity; thus, connected nodes can send and receive data in the cloud for everything from tracking to firmware updates.
That said, hurdles must be overcome before the 10BASE-T1S standard is implemented across the entire automotive spectrum, including the notion that the standard will add cost and complexity when designing embedded systems and devices. Suppliers are, of course, working with OEMs to make sure system requirements are addressed before heading to the market.