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Employing IP, Ethernet in automotives

Posted: 09 May 2013     Print Version  Bookmark and Share

Keywords:CAN bus  IP development  protocol analysis 

Until just a few years ago, the popular opinion was that Ethernet would never be utilised for in-vehicle applications, with the exception of diagnostic access. Soon, however, camera-based driver assistance systems will be the first applications to utilise Ethernet technology as a system network. This presents new challenges to automotive OEMs, suppliers and development tool producers, because the Internet Protocol and Ethernet represent a new network technology for motor vehicles. Nonetheless, many of the issues can already be solved.

After the debut of the CAN bus in the Mercedes S-Class in 1991, the LIN, MOST and FlexRay bus systems also became established in the motor vehicle. Today, CAN continues to be used in automotive network architectures in all domains (from powertrain to body). LIN bus technology is ideal for simple and cost-effective data exchange of noncritical signals in the convenience area. Where bandwidths and real-time requirements run into limitations, CAN is replaced by FlexRay or MOST – in cases where it is economically justifiable. In today's vehicles, one often finds all of the named bus systems, segmented and networked via gateways.

Motivation for Ethernet
Ethernet has long been an established standard technology in office communications, industrial engineering (ODVA standards, Ethernet/IP and ProfiNet) and in the aerospace industry (AFDX). In the automotive field, Ethernet had already proven itself in the vehicle for diagnostic access. In recent years, other use areas have increasingly been discussed in automotive research and development departments, because Ethernet's scalable bandwidth and flexibility spoke strongly in its favour. Nonetheless, a suitable and economical wiring technology was lacking for the motor vehicle.

Currently, the main drivers for Ethernet usage in the vehicle are camera-based driver assistance systems. In camera applications in the vehicle, LVDS technology (Low Voltage Differential Signaling) has been used until now. The shielded cable that is generally used there does indeed assure electromagnetic compatibility, but it is expensive by industry measures, and it is very impractical to install in the motor vehicle. Most recently, a physical layer is available that offers full-duplex transmission at 100 Mbit/s on a CAN-like, two-wire cable (unshielded twisted pair), and in the opinion of various publications it is suitable for use in the motor vehicle [1], [2], [3].

Requirements of an IP development tool
First, known requirements of previous bus systems still apply to the development tool. Initially, what is required is a detailed protocol analysis with stimulation option that extends to script-based testing with automatic generation of test reports. The user also expects that the market-proven multi-bus capability will of course be extended to include Ethernet and IP, so that dependencies between events on different bus systems can be studied. Currently, for example, there is interest in correlation between LIN and CAN, and in the future interest will be between CAN and IP.

As previously, in protocol analysis the user needs easy symbolic access to all relevant application signals as well as the ability to further process them in any desired way – logically and graphically. However, there will also be new requirements, which on the one hand are imposed by the bus physics and on the other by the wide variety of IP protocols. The article explains – based on the current camera example and four other application areas of IP and Ethernet in the motor vehicle – how these measurement tasks present themselves in product development departments from the perspective of the system manager, and which special requirements result for the development tool.

Camera: Ethernet as system network
A camera-based driver assistance system at BMW will be the first production implementation in the motor vehicle to utilise IP and Ethernet as the system network in the vehicle [1]. OEMs and suppliers will use the new BroadR-Reach physical layer to save on weight and costs compared to currently used LVDS technology [1], [4], [5]. BroadR-Reach will be licensed by other producers [6].

Figure 1: Reliable analysis of camera-based driver assistance systems requires monitoring the data traffic at multiple points of the Ethernet network, ideally via "tee-couplers" with as little time offset as possible and with a common time base.

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