How to Achieve Efficient Communication Between ECUs via Switches?

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In today’s smart vehicles, the number of in-vehicle ECUs (Electronic Control Units) is increasing, ranging from dozens to hundreds. Faced with such a complex network communication scenario, the switch has become a core component connecting these ECUs. So, how do ECUs communicate efficiently through switches? This article will comprehensively break down the underlying principles and engineering practices!

From CAN Bus to Ethernet: Why Do We Need a Switch?

Traditional ECU communication mainly relies on bus technologies such as CAN, LIN, and FlexRay, but these buses have inherent bandwidth limitations (e.g., CAN has a maximum of 1Mbps). With the emergence of new features like autonomous driving, infotainment, and OTA, Ethernet has become the preferred choice for the next generation of in-vehicle communication backbone networks.

In Ethernet networks, the switch (Ethernet Switch) is the key device for achieving efficient communication between multiple ECUs, similar to the switching chip in a home router.

Working Principle of the Switch: Forwarding, Filtering, and Broadcasting

Automotive Ethernet switches follow the second layer (Data Link Layer) protocol of the OSI model, primarily based on MAC addresses for packet forwarding. Their core functions include:

🔹 Forwarding: Accurately forwarding packets to the corresponding ECU port based on the destination MAC address of the data frame.

🔹 Filtering: Only allowing data that meets configured rules to pass through, such as filtering strategies based on VLAN, priority, etc.

🔹 Broadcast/Multicast Control: Controlling broadcast storms and supporting multicast-based protocol communications like DoIP and SOME/IP.

🔹 Flow Control: Supporting rate limiting, congestion management, time-sensitive networking (TSN), etc., to ensure critical ECU communications are not disrupted.

Three Modes of Communication Between ECUs

With the support of Ethernet switches, the communication modes between ECUs can be roughly divided into the following three types:

1) Point-to-Point Communication (Unicast)

ECU A and ECU B communicate directly, with the switch accurately forwarding data based on MAC address mapping, without occupying bandwidth on other ports.

2) Multicast Communication

Multiple ECUs listen to the same multicast address (commonly used in protocols like SOME/IP and TSN), suitable for one-to-many publish-subscribe communication.

3) Broadcast Communication

One communication is sent to the entire network, commonly used for initialization and addressing (e.g., DoIP broadcast discovery), but the frequency needs to be controlled to avoid congestion.

Engineering Practice: Connection Configuration Between ECU and Switch

In actual projects, ECUs connect to switches and achieve efficient communication in the following ways:

🔧 PHY Chip Connection: The Ethernet controller of the ECU connects to the switch via a PHY chip, supporting interfaces like RMII and RGMII.

🔧 VLAN Configuration: Static or dynamic VLAN configurations can be used to isolate communication between ECUs in different functional domains (e.g., ADAS, infotainment, power systems).

🔧 TSN Support: Critical communications can enable TSN mechanisms to ensure real-time performance, supporting time synchronization (802.1AS), bandwidth reservation (802.1Qbv), and other functions.

🔧 SOME/IP Configuration: Through the Service Discovery mechanism, ECUs can automatically publish and discover services in the network, enhancing flexibility and modularity.

Future Trends: From Static Configuration to Software-Defined Networking (SDN)

As automotive software architecture evolves towards centralized computing platforms and SDN, future switches will support smarter control and dynamic configuration:

Centralized Configuration: Dynamically issuing communication policies through a central gateway or SDN controller.

Virtual Switching Function: Implementing virtual switching logic in SoC, combined with hypervisor support for multi-domain isolation.

Visual Management: Supporting remote diagnostics, traffic statistics, QoS monitoring, and other functions for easier development and debugging.

In-Vehicle Switches: The Hub of Future Communication

In-vehicle switches play a crucial role in the automotive Ethernet architecture, making communication between ECUs more efficient, flexible, and controllable. With the development of autonomous driving and smart cockpits, understanding the working principles and engineering applications of switches will become an essential skill for every automotive electronics engineer.

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