Who would have thought 10 years ago when the MOST Cooperation was formed that today’s automobiles, with all of their multimedia features, would turn into home entertainment centers on wheels? In fact, two years prior in 1996, U.S. automotive manufacturers weren’t even keen on adopting the MOST (Media Oriented Systems Transport) protocol.
Such wasn’t the case with their European and later their Asian counterparts, who began discussing the concept (Fig. 1). Subsequently, Germany-based Becker (now Harman/Becker), U.S.-based OASIS Silicon Systems (now SMSC), and German companies BMW and Daimler Benz founded the MOST Cooperation. German automaker Audi later joined the group.
Today, more and more Korean, Japanese, and European car makers are joining the MOST Cooperation as associated partners. So are suppliers of semiconductor IC chips, software products, components, test equipment, development platforms, and subsystems. They now number more than 80.
The big three U.S. automakers—General Motors (GM), Ford, and Chrysler—are actively evaluating the MOST system for their future cars, with GM reportedly now moving beyond the evaluation stage. Some 58 car models worldwide are using MOST, including five recently introduced Asian models. Many of the parts required for the electrical and optical physical layers of the protocol are in production.
Today, about 10% of cars worldwide in production use MOST. Most of these cars are high-end vehicles. The next-generation low- and mid-range cars are expected to subscribe to the MOST concept as manufacturing efficiencies of supplied parts increase, decreasing OEM costs. Another key is the automotive industry’s adjustment to working with the optical fiber technology that forms MOST’s backbone.
The MOST Cooperation is also working with the Consumer Electronics Association (CEA) to bring together the consumer electronics and automotive worlds. Many OEM suppliers are working with the CEA to achieve this goal. MOST supports up to 64 nodes of plug-and-play devices, which can be arranged in a ring, star, or chain topology.
“Cost was a major reason why the MOST concept did not catch on in the U.S. auto market, driven by the difficulty of dealing cost-effectively with the opticalto- electrical and electrical-to-optical (OEO) conversion circuitry required. But that’s no longer the case, since many improvements have been made in the manufacture of OEO components. The 58 car models mentioned previously are now all using plastic optical fibers,” explains Henry Muyshondt, senior director of business development for SMSC.
“Another factor has been the industry’s reticence to work within an optical environment, since such systems require a new way of servicing optical components like cutting, splicing, tapping into optical lines, and measuring their signals, requiring new types of tools to do so,” adds Muyshondt.
“The electronics industry has gained more confidence in the optical communications approach. Besides, the MOST protocol is also compatible with using shielded or unshielded copper wiring,” he says. In fact, Toyota embraced the MOST concept this year, using copper wiring in its 2008 model cars.
Many published comparisons stack MOST up against other popular automotive protocols like FlexRay, the Controller Area Network (CAN), the Local Interconnect Network (LIN), Byteflight, Bluetooth, and IEEE-1394 (FireWire). Each of these network protocols was conceived for a specific function and does a good job of satisfying those applications.
However, they aren’t necessarily optimized for many automotive functions, like X-by-wire, passive and active safety, chassis, power-train, car body, and infotainment applications, whose requirements are very different. Thus, comparing them against each other really isn’t a valid exercise.
Many of these network protocols, though, can often coexist with MOST. Each excels at one or more tasks, with MOST having progressed from 25 to 150 Mbits, providing the bandwidth required for modern automotive infotainment systems. The latest version of MOST150 serves as the automotive-grade physical layer for 100BaseT Ethernet (Fig. 2).
Much has been said about 100-Mbit Ethernet’s usefulness for automotive infotainment networks. “When you take into consideration the messagetransmission mechanism of Ethernet, i.e., carrier-sense multiple-access with collision detection (CSMA/CD) and other load factors, the 100-Mbit/s bandwidth drops down considerably for infotainment applications,” says Muyshondt.
MOST is a high quality-of-service (QoS) network with its packet-based communications approach. It doesn’t suffer from message collisions, and it isn’t affected by interference thanks to its optical fiber backbone. And, it offers close to 100% utilization of its nominal data rates.