Time Synchronization in Automotive Ethernet Networks

There are many different time-critical Ethernet applications in the automobile. They include advanced driver assistance systems (ADAS) with cameras and (radar) sensors, real-time audio and video streams, and backbones for synchronizing various physical domains (Figure 1). Another use case is on-board data logging. Moreover, devices networked via Ethernet must naturally also be synchronized with other physical systems such as CAN and FlexRay. Originating from the computer networking and office environment, Ethernet lacks the real-time capability necessary for technical applications. Although switched Ethernet topologies reduce unwanted collisions during network access, a fully deterministic behavior cannot be realized by this alone. In particular, the sensitive task of time synchronization requires complete information along the transmission path on the run times and latencies that are inherent in switches and gateways. Anyone wanting to control processes in connection with Ethernet is confronted with these challenges. This explains why various standards development organizations are working in parallel to add real-time capability to Ethernet, including mechanisms for time synchronization. The principal methods for time synchronization in the automotive industry are currently based on AUTOSAR 4.2.2, IEEE 802.1AS, and the revised IEEE 802.1AS-ref, which was developed by the Audio/Video Bridging Task Group, which is now known as the TSN (Time Sensitive Networking) Task Group.