Media Oriented Systems Transport (MOST)

Media Oriented Systems Transport (MOST) is an automotive multimedia communication protocol jointly developed in 1998 by carmakers including BMW and DaimlerChrysler alongside Harman/Becker. Tailored to meet high-speed transmission requirements for streaming media such as in-car audio and video, this bus system once served as the backbone of infotainment systems and stood as a benchmark technology in the "audio-visual era" of in-vehicle networking.

Technical Principles and Key Features

The defining characteristic of MOST is its reliance on plastic optical fibre (POF) as the physical transmission medium, carrying data over a 650 nm wavelength red light carrier. This approach delivered distinct advantages over conventional copper wiring: complete immunity to electromagnetic interference (EMI), uncompromised signal integrity amidst complex on-board electrical environments, and a significant reduction in overall wiring harness weight.

In terms of communication architecture, MOST typically adopts a ring topology where data circulates unidirectionally along the optical fibre loop, supporting up to 64 nodes. It operates via synchronous transmission, in which a designated "timing master" node generates a 44.1 kHz system clock (strictly aligned with the audio CD standard); all slave nodes synchronise to this reference clock to send and receive data, ensuring jitter-free audio and video playback.

To keep pace with growing data demands, MOST technology evolved across three distinct generations: MOST25 (25 Mbps), MOST50 (50 Mbps), and MOST150 (150 Mbps). Notably, MOST150 incorporated an Ethernet channel to support IP-based data communications, acting as a crucial stepping stone towards next-generation in-vehicle networks.

Rise and Eventual Decline

Leveraging its robust noise immunity and synchronised streaming capabilities, MOST was once the undisputed standard in automotive infotainment. It was deployed across more than 200 vehicle models globally—making its debut on premium German flagships like the BMW 7 Series and Audi A8 before trickling down to the Volkswagen Magotan, Porsche, and diverse platforms across mainstream manufacturers like Toyota and General Motors.

However, as vehicles evolved into software-defined, highly automated machines, network demands shifted from basic multimedia streaming to massive data pipelines driven by multiple HD cameras and LiDAR sensors. Hamstrung by a closed proprietary ecosystem and rising licensing costs, MOST steadily lost ground to high-bandwidth, cost-effective, and open-standard Automotive Ethernet. In modern centralised computing and zonal electronic/electrical (E/E) architectures, Automotive Ethernet has firmly established itself as the dominant backbone network.

Note: While MOST served as a pivotal automotive communication standard that successfully proved the viability of optical fibre in vehicular applications, it has largely been superseded by open, high-bandwidth Automotive Ethernet. In today's intelligent connected vehicles, its technological footprint has effectively been relegated to history.