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Modern vehicles are increasingly evolving into software-defined vehicles (SDVs) – systems dominated by software, where innovations and new functions are primarily delivered via updates and applications. This transformation requires a powerful, scalable, and cost-effective in-vehicle network that provides both high-speed data streams for sensor fusion and advanced driver assistance systems (ADAS) as well as reliable, robust communication channels for basic functions.
While high-performance computers (HPCs) assume the role of central data nodes, a robust, cost-effective, and easy-to-implement network is required for numerous peripheral components. Here, the 10BASE-T1S automotive Ethernet variant offers an attractive alternative to established fieldbuses such as CAN CC, LIN, or FlexRay. Along with other high-speed solutions such as 1000BASE-T1 or 2.5GBASE-T1, 10BASE-T1S (Single-Pair Ethernet, SPE) is a crucial building block for networking simple control units, sensors, and actuators. The standard was specified in 2019 by IEEE 802.3cg and has since become an integral part of discussions surrounding zonal vehicle architectures.
Figure 1: From domain-oriented to zone-oriented system structures.
10BASE-T1S enables data transmission at 10 Mbps over a single twisted-pair cable and supports a multi-drop topology in which up to eight nodes can be operated on a single line. Because it uses the Physical Layer Collision Avoidance (PLCA) bus access method, communication occurs in half-duplex mode. This ensures real-time communication even with multiple nodes.
Figure 2: Transmission sequence of the nodes via PLCA.
The PLCA method is the heart of 10BASE-T1S and ensures that data collisions do not occur in half-duplex operation. Each node in the multi-drop network receives a fixed node ID. A so-called coordinator distributes the "beacons," or synchronization signals, at regular intervals, and the resulting "transmit opportunities" (TOs) are then derived individually by each node. A node is only allowed to transmit when it is its turn; otherwise, it remains silent.
The minimum and maximum cycle time in the PLCA process depends on the data volume. In the minimum case – when hardly any data is sent – the cycle runs very quickly, as unused transmit opportunities are immediately skipped. In the maximum case, however, all nodes use their transmit opportunity with full frames. This lengthens the cycle, but remains deterministic: A packet waits at most until the next round. Thus, PLCA guarantees short response times under low traffic conditions and a clear upper latency limit under high load conditions.
This procedure is similar to an “ordered broadcast” and guarantees a deterministic transmission with minimal delays, even if several control units want to send data at the same time.
Figure 3: Multi-drop network topology
Cabling is particularly simple: Up to 15 meters can often be implemented using unshielded twisted pair, which significantly reduces costs and weight. Furthermore, Power over Data Line (PoDL) allows the simultaneous transmission of power and data – a particular advantage in sensor-actuator networks. In the future, 10BASE-T1S will be expanded to include functions such as MACsec for encrypted communication. This makes it an attractive alternative to traditional bus systems such as CAN CC or LIN and a key building block for a unified Ethernet-based vehicle network.
The advantages of 10BASE-T1S lie primarily in the reduction of cabling complexity and thus vehicle weight, as well as in the possibility of gradually replacing existing CAN or LIN topologies with Ethernet. Typical areas of application:
A key advantage: The Ethernet basis enables seamless integration into zonal architectures. This allows simple devices to be connected directly to HPCs without the need for additional gateways.
While CAN and LIN have set the standard for low-speed communication for decades, they are increasingly reaching their limits in modern architectures. Scalability and service-oriented communication (e.g., via SOME/IP) are also limited. 10BASE-T1S can advance the homogenization of Ethernet—with uniform diagnostic tools, security mechanisms, and protocol stacks.
Figure 4: Development of network technologies in the automotive sector
With years of experience in the automotive sector, HMS Networks is already addressing the growing importance of 10BASE-T1S with high-performance automotive gateways specifically designed for test engineers at automakers and suppliers.
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