A comparison of time synchronization in AVB and FlexRay in-vehicle networks

Ethernet gains more and more interest by the automotive industry which uses already a couple of different in-vehicle networks. Together with an demand for the integration of the IP protocol and a steadily increasing bandwidth requirements, Ethernet based networks are researched for the usage in this area to cope with future needs [1]. Especially Ethernet AVB promises an interesting networking solution for multiple application areas. In addition to the continuously rising communication demands of different industry´s AVB provides different enhancements for Quality of Service (QoS) within Ethernet based networks. Timing sensitive applications, e.g. synchronous multimedia transport or real time control loops, require the predictable behavior that is addressed by this standard. The authors built up a QoS-based gateway interconnecting FlexRay and AVB. Most automotive network technologies used within automotive are time-triggered since many applications require a timely handling. Therefore the time synchronization methods are an essential part and the evaluation starts with the comparison of both time synchronization protocols. Since AVB is not originally designed to be used in in-vehicle networks yet, it has also to be proven if the protocol is able to fulfill the demands for automotive networks. The authors focus mainly on the average speed of time message distribution since vehicle network communication have to be established very fast. The comparison of the time accuracy shall shown if it is possible to keep the timing constraints of FlexRay when embedding those frames within Ethernet frames and to built up a global common time base. The results show that 802.1AS together with certain requirements to the AVB environment can provide almost similar timing guarantees in comparison to FlexRay which was proved by a demonstrator system.