Payload efficiency and network considerations of MOST and Ethernet

May 12, 2011 // By Josef Nöbauer, Helge Zinner
This paper discusses the payload efficiency of MOST and Ethernet and the derived influence on the network architecture of vehicles with high bandwidth needs. Furthermore, ideas for coexistence of these competing technologies are described.

MOST Technology is nowadays dominating the upper class infotainment systems due to its support of high bandwidth data. Fostered by the integration of consumer devices and the worldwide success of the Internet Protocol (IP), the research for the usage of IP as the common network layer in an automotive environment has already started. The results presented in this paper have been prepared within the publicly funded project SEIS (1). In combination with IP, Ethernet is the most commonly used physical layer.

Actually, the usage of a cost efficient and automotive-qualified Ethernet solution is already scheduled for implementation in series production (2). So the competition between MOST and Ethernet is already fully ongoing. This paper will focus on a specific part of this competition. The payload efficiency of MOST and certain transport protocols of Ethernet AVB (3) are compared, since Ethernet AVB defines provisions to achieve Quality of Service (QoS) within an Ethernet network. However, simply looking at the payload efficiency is not sufficient, since MOST is a bus system, while today's Ethernet is a switched network that leads to a multiplication of the system-wide available bandwidth by the number of point-to-point links in the system. Hence, network utilization will also be discussed in this paper.

Description of problem/challenge

Automotive infotainment networks are becoming more open to non-automotive devices like mobile phones and are supporting IP/Web based applications. High-definition video and camera based applications create higher data rates that already need to be handled today. The bandwidth requirements of certain applications, compared to the bandwidth offered by networks, is shown in . The continuously increasing bandwidth requirement is a clearly visible trend.

Figure : Bandwidth requirements and network capabilities over time. For better resolution, click here

One of the core requirements for a network is that it will deliver application data reliably and will provide reasonable response times between any nodes. In order to support QoS in asynchronous Ethernet networks,