Why use 10BASE-T1S instead of CAN and its variants?
In modern vehicles with legacy CAN or FlexRay and automotive ethernet networks designed, the architecture tends to be heterogeneous. We might see a mixture of legacy network and automotive ethernet 100BASE-T1 or 1000BASE-T1 employed in a domain within the vehicle. This makes sense for that specific type of application; for example, you will see in modern vehicles many of the infotainment networks are automotive ethernet-based, whereas their control networks, like engine transmission controls, tend to be legacy networks, specifically CAN/CAN FD or FlexRay. The situation as we stand now is that there’s a heterogeneous type of network architecture in vehicles where we have many different types of technologies employed within a single vehicle. The industry looks forward to a homogeneous network where one type of network is used throughout the vehicle.
One reason automotive ethernet cannot replace CAN FD and FlexRay is its high cost and architecture limitations. Automotive ethernet with 100BASE-T1 and 1000BASE-T1 is only a point-to-point network, meaning that if you want to have more than three nodes in the bus to communicate with each other, you must include a switch in the network, which is an expensive device that prohibits the use of higher speed ethernet networks throughout the vehicle because of cost and wiring flexibility. CAN/CAN FD, FlexRay, and most other legacy in-vehicle networks are based on multi-drop bus architecture. All nodes are connected over the same unshielded twisted pair cable in the all-Ethernet network, giving wiring flexibility. It lets you connect many ECUs with a single pair of wires instead of the point-to-point form with mixed topologies.
Figure 1. Example of an all-Ethernet Network in a car, reducing the number of different communication bus topologies.
Multi-drop mode
The motivation for the 10BASE-T1S standard is to overcome some of these limitations. It should also be noted that for many of these legacy networks, a recent study concluded that >80 % of communications within a vehicle are less than ten megabits per second. The 10BASE-T1S is 10Mbits per second with a single twisted pair, and it also supports a multi-drop bus mode and point-to-point mode. The support for the multi-drop technology is fundamentally different from other types of automotive ethernet. When we have a heterogeneous type of network to bridge data between the different networks, for example, between CAN FD and 100BASE-T1, we must introduce a gateway, which is essentially a powerful ECU with a built-in switch network, to be able to handle network traffic. Moving toward a homogeneous network that is all ethernet-based, addressing or sending data back and forth between nodes is much simpler because we’re using the same addressing method, which has proven reliability, flexibility, and robustness within ethernet. From the development perspective, the same software stack used for connecting higher-speed automotive ethernet nodes can be leveraged to connect 10BASE-T1S, speeding up the development time and cost and improving reliability.
Figure 2. Visualization of a zonal network and where the different speed grades of automotive Ethernet would be used.
The impact of zonal architecture
Another driver for 10BASE-T1S technology is associated with zonal architecture. As the concept of zonal-based architectures evolved, it became evident that automotive ethernet connectivity to edge sensors and actuators would be required to leverage this new architecture's advantages fully.
Applications for 10BASE-T1S in automotive are broad and varied, with many sensors and actuators across multiple functions in the body domain, including comfort, infotainment, powertrain, and ADAS, under discussion. It can replace CAN, CAN FD, CAN XL, LIN, FlexRay, and A2B in the future. Below is a Screenshot from Keysight D9020AUTP decode software.
Figure 3. Application from Keysight that can trigger and decode on 10BASE-T1S protocol level messages.
A true homogeneous Ethernet network
In the automotive industry, there is a push for a more simplified network covering low-speed buses, and 10BASE-T1S is an answer that enables a homogeneous ethernet or IP-based network solution, reducing the complexity and cost of heterogeneous architecture. 10BASE-T1S provides the missing link in the automotive Ethernet ecosystem, enabling proper Ethernet-to-the-edge connectivity and addressing the needs of zonal architecture.
Keysight offers a way to access integrated protocol-level triggers, view packets at the protocol level, and then utilize time-correlated views to troubleshoot protocol problems back to timing or signal integrity root cause for 10BASE-T1S as well as CAN, CAN FD, CAN XL, and LIN on our new MXR B oscilloscope.
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