The MOST bus(Media Oriented System Transport) is a field bus used in automotive technology for in-vehicle infotainment( IVI). Originally designed for the transmission of audio and for control signals from CD players and radios, the MOST bus can also be used for video and digital TV due to its large bandwidth.
Three standardized data transmission rates of25 Mbit/s (MOST25), 50 Mbit/s (MOST50) and 150 Mbit/s (MOST150) are available for transmission, which can be divided up for the various applications by means of scaling or budgeting. For example, several audio, broadcast, video and camera signals could share the bandwidths, with the bandwidth requirement depending largely on video compression and screen resolution.
The MOST bus uses a polymer fiber( POF) for transmission, thus reducing the previous extensive cabling for the individual services and their control signals. It can be set up in ring or star topology with up to 64 stations and a timing master sharing the data rate. For safety reasons, double rings are used, which also provide redundancy in the event of a fault. Interference-free data transmission is carried out using the MOST transmission protocol.
The Most bus conforms to the OSI reference model and covers all seven layers, from the physical layer to the application layer. In terms of services, the Most protocol offers "Low Level System Services" in the link layer, "Basic Layer System Services" in the network layer, transport layer and communication control layers above it, and application sockets in the presentation layer.
To ensure the security of the transmitted data, it can be encrypted using Digital Transmission Copy Protection( DTCP). Before two or more devices exchange data over a secure connection, an Authentication and Key Exchange (AKE) takes place.