2. Evolution towards automotive Ethernet
Ethernet is an open LAN standard and defines the two lower layers of the OSI reference model. Over the past decades, the IEEE 802 standardization committee has specified several physical layers from 10Mbps up to 10Gbps. IEEE 802.3u (100Base-TX) is widely used in consumer and industrial domains and has recently been selected for car diagnostics over IP as described in ISO 13400.
Higher layers have to be taken into account besides data link and physical layer, as shown in Figure 2
. The Audio/Video Bridging (AVB) Task Group of AVnu alliance [1
] has defined IEEE standards covering higher-level services for IEEE 802-compliant networks. The protocols IEEE 802.1 AS, QAT, QAV and BA cover address timing and synchronization, streaming reservation, forwarding and queuing in Audio/Video Bridging systems. In addition, transport protocol layer standards like IEEE 1722 facilitate stream-time-sensitive audio and/or video across Ethernet AVB networks and interoperability between end stations.
Driver Assistance Systems are increasingly using video cameras for applications like surround view. Activities for the standardization of the communication protocol and physical layer have recently been started in ISO 17215 called “Video Communication Interface for Cameras”. In order to further develop the Automotive Ethernet technology, an industry-wide Special Interest Group named One Pair EtherNet Alliance has been formed for the physical layer. The so-called “OPEN Alliance” will work on standardization for components and compliance tests based on the Broadcom BroadR-Reach technology [2
]. A further intention of the interest group is to gather requirements for future technologies such as “Reduced Pair Gigabit”. Finally, AUTOSAR addresses Automotive Ethernet in their software layer stack.
Figure 2: Ethernet roadmap, generations and layers
Ethernet has not been developed for TDMA networking, and one topic that still needs to be addressed for automotive systems is a suitable solution to achieve the required real-time performance and Quality of Service. AVB already includes measures to ensure the timely delivery of media streams.
For the Automotive AVB Gen2 Work Group, latency time improvements are one of the major targets. First applications for Time-Triggered Ethernet took place in Avionic systems [3
] with highest safety level requirements. Defined in SAE AS6802 and different to Audio/Video Bridging, TTEthernet is based on a distributed clock-synchronization algorithm that finally results in an exact schedule with deterministic behavior.
Although the integration of both AVB and TTEthernet is possible [4
], further investigations are needed to allow its use in automotive applications where multimedia streams, real-time control data as well as diagnostic information and software updates will be transmitted on the same network.