MOST Bus
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MOST (Media Oriented Systems Transport) is a high-speed multimedia network technology for the automotive industry. It can be used for applications inside or outside the car. The serial MOST bus uses a daisy-chain topology or ring topology and synchronous serial communication to transport audio, video, voice and data signals via plastic optical fiber (POF) (MOST25, MOST150) or electrical conductor (MOST50, MOST150) physical layers.
MOST technology is used in car brands worldwide, including
]MOST is a registered trademark of Standard Microsystems Corporation (SMSC), now owned by Microchip Technology.
Principles of communication
The MOST specification defines the physical and the
MOST networks
A MOST network is able to manage up to 64 MOST devices in a
In a MOST network, one device is designated the timing master. Its role is to continuously supply the ring with MOST frames. A
MOST25
MOST25 provides a bandwidth of approximately 23
MOST25 supports up to 15
MOST also provides a channel for transferring control information. The system frequency of
MOST50
MOST50 doubles the bandwidth of a MOST25 system and increases the frame length to 1024 bits. The three established channels (control message channel, streaming data channel, packet data channel) of MOST25 remain the same, but the length of the control channel and the sectioning between the synchronous and asynchronous channels are flexible. Although MOST50 is specified to support both optical and electrical physical layers, the available MOST50 Intelligent Network Interface Controllers (INICs) only support electrical data transfer via a three copper conductor configuration; consisting of an Unshielded Twisted Pair (UTP) set and a single additional control line. The additional control line is connected to each MOST50 network device in a parallel single shared bus configuration. Each MOST50 device would contain five copper wire connections in this configuration. Control line (for signals sent from the master) and two UTP sets (each containing D+ D−). One set is used for data input (outputted from the preceding device on the network ring) while the other is used for data output to the next device on the ring. As with its fiber counterparts, closing or completing the ring (termination at the originating device) is required for any and all network operation.
MOST150
MOST150 was introduced in October 2007. It increases the frame length up to 3072 bits. It includes an Ethernet channel with adjustable bandwidth in addition to the three established channels (control message channel, streaming data channel, packet data channel) of the other grades of MOST. MOST150 also permits isochronous transfer on the synchronous channel.
Physical layer
MOST uses
MOST Cooperation
The MOST Cooperation, a partnership of carmakers, AV equipment designers, system architects, and key component suppliers, was founded in 1998. Their objective was to define and adopt a common multimedia network protocol and application object model.[2]
Infrastructure
The MOST Cooperation has published specifications for the MOST Bus for a number of years. However, these specifications do not include details on the data link layer. In March 2008,
At this time MOST chip solutions are available from SMSC, Analog Devices and some FPGA intellectual property vendors. Development tools are offered by K2L, Ruetz System Solutions, SMSC, Vector Informatik GmbH and Telemotive AG.
Competing standards
- BroadR-Reach has taken a chunk of the automotive communication bus network for Infotainment. First with 100 Mbit/s, then 1 Gbit/s and now 10 Gbit/s for domain controller backbone links.
- The IEEE has standardized single pair Ethernet variantsat speeds up to 10 Gbit/s.
- IEEE 1355 has a slice (combination of network medium and speed) TS-FO-02, for polymer optical fiber operating at 200 Mbit/s. The specification is faster than MOST, well tested, and open. However, it lacks industry advocates.
- Cat 5 cable may be too expensive or heavy for automotive applications. Also, standard Cat 5 plugs do not resist vibration. The thin layers of gold rapidly rub off, and corrosion then causes failure. Standard ruggedized connectors exist, which hold the connectors steady, but are more expensive.[3]
- CAN (Controller Area Network), LIN (Local Interconnect Network) and other automotive OBDstandards are not suitable because they are too slow to carry video.
- FlexRay, also an automotive bus standard, though faster than CAN, is intended for timing critical applications such as drive by wire rather than media.
References
Further reading
- Grzemba, Andreas (2007). MOST: Das Multimedia-Bussystem Für Den Einsatz Im Automobil (in German). Poing: Franzis. ISBN 978-3-7723-4149-6.
- Grzemba, Andreas (2011). MOST: The Automotive Multimedia Network; from Most25 to Most150. Poing: Franzis. ISBN 978-3-645-65061-8.
- Zimmermann, Werner; Schmidgall, Ralf (2008). Bussysteme in der Fahrzeugtechnik: Protokolle und Standards; Mit 96 Tabellen (in German) (3rd ed.). Wiesbaden: Vieweg + Teubner. ISBN 978-3-8348-0447-1.