Choosing the right transport method for automotive data

June 07, 2012 //By Henry Muyshondt, SMSC
Choosing the right transport method for automotive data
Much ado has been made recently about high speed networking in cars. A battle is presented between the existing de facto high speed networking standard in the car (MOST, which stands for Media Oriented Systems Transport) and the standard for the IT infrastructure in the commercial world, Ethernet. The technologies are presented as if you have to make a hard choice between them and only one technology can deliver everything that automotive systems require. This article explores the issues and shows how a combination of technologies is actually a better solution rather than trying to force-fit everything under one type of transport.

A car is made up of subsystems that may communicate with each other but have very different requirements for the data transports that they use. For example, a simple button to lower and raise a window has very low data communications requirements and is extremely cost sensitive. You won't be running a full TCI/IP stack or even a CAN (Controller Area Network) controller to keep track of the window. Instead, many cars use an inexpensive serial bus called Local Interconnect Network (LIN). CAN also provides many useful functions in the vehicle and, though more complex than LIN, is easy to implement in a variety of automotive microcontrollers. Many diagnostics functions, body and engine control communications flow over CAN, which uses a message based protocol.

As the amount of data that needs to be transported increases, faster and more complex networks are needed. Those networks are the subject of this paper. These networks require significantly more processing power than the ones previously described and also use orders of magnitude more bandwidth due to the amount of data that needs to be moved from one place to another.

Over the last decade the automotive industry has gravitated towards MOST for its audio and video communications needs. The network was conceived from the beginning to stream data to various devices, with the primary intention of simplifying automotive entertainment systems. There are now over 115 car models with MOST networks in them, according to the MOST Cooperation, the association of car makers and their suppliers that is the caretaker of the standard. There are over 100 million devices that implement the technology, with some high end cars including up to 15 devices in one vehicle.

As the car becomes connected to the outside world, Internet Protocol (IP) communications have become more important. Most of the traffic in the IT world uses various protocols geared around IP packets and many applications rely on this standard

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