Media Oriented Systems Transport: Difference between revisions

{{Update|date=May 2011}}

'''Media Oriented Systems Transport''' (MOST) is a [[vehicle bus]] standard, intended for interconnecting [[multimedia]] components in [[automobile]]s and other [[vehicle]]s. First conceived in 1997, it differs from existing [[vehicle bus]] technologies, in that it's intended to be carried largely on an [[optical fiber]] bearer, thus providing a bus-based networking system at bit-rates far higher than available on previous vehicle-bus technologies. MOST was publicly debuted in the [[BMW]] [[BMW 7 Series|7 Series]] [[iDrive]] system at the [[2001]] Frankfurt Auto Show.<ref>[http://www.mostcooperation.com/news_and_events/press_releases/index.html?year=2001 "2001 Debut Press Release"]</ref>

The MOST specification defines all seven layers of the [[ISO/OSI Reference Model]] for data communication. The MOST network often employs a ring topology, but star configurations and double rings for critical applications are possible and may include up to 64 devices or nodes. A [[plug and play]] feature enables easy adding and removing of devices. A Timing Master is one of the nodes which continuously feeds data frame into the ring or acts as the gate for data. The [[preamble]], or [[packet header]] repeatedly synchronizes the rest of the nodes called Timing Slaves. The total bandwidth (including streaming data and packed data) is approximately 23 M [[Baud]]. 60 channels, 15 MPEG1 channels are available to the user for configuration.

MOST development is done by the ''MOST Cooperation'', an industry-standards body consisting of automotive manufacturers (including [[Ford Motor Company|Ford]], BMW, [[DaimlerChrysler]], and [[General Motors Corporation|General Motors]]), tier-1 automotive electrical suppliers (including [[Infineon Technologies]], [[Yazaki]], [[Delphi (auto parts)]] E&S (former [[Delco Electronics|Delco]]), [[Denso]] (a division of [[Toyota]]), [[Robert Bosch GmbH|Bosch]], and [[Hamamatsu]]<ref>[http://sales.hamamatsu.com/assets/pdf/parts_L/l8628-01b_etc_kpic1048e05.pdf "Transmitter/receiver for MOST automotive network, POF communications"]</ref>), and audio-video manufacturers (including [[Sony]], [[Philips]], [[Linn Products]], and [[Motorola]]). SMSC, MediaLB, and MOST are registered trademarks of SMSC. The MOST Cooperation has authorization to use it free of charge.

==Protocol==

===Physical layer===

MOST can use both optical and electrical interconnects.

[[Biphase mark code]] is used to encode data on either physical medium, such as used in [[S/PDIF]]. All bits are transmitted in a single clock cycle. A zero bit has a single transition at the end of the clock cycle. A one bit is encoded with two transitions both in the middle of the clock cycle and at the end of the clock cycle. The preamble is encoded using a clock cycle after the third clock cycle.<ref>[http://www.mostcooperation.com/publications/mostbook/index.html?do173194=download "MOST book"]</ref>

===Link layer===

A most block comprises 16 "frames".

A most Frame comprises

* A 4 bit preamble

* A 4 bit boundary descriptor

* 15 quad-byte payload that are split into a synchronous and asynchronous part, the split point is specified by the boundary descriptor.

* A 2 byte control pay-load; the control payload of 16 frames are concatenated to form a single 32 byte control message.

* 7 bits frame control

* A parity bit.

==References==

{{Reflist}}

==External links==

* [http://www.mostcooperation.com/publications/Specifications_Organizational_Procedures/index.html?doc=3532&dir=291 MOST Specification Rev. 3.0]

* [http://www.mostcooperation.com/ MOST Cooperation homepage]

* [http://www.telos.de/most/ MOST history]

* [http://www.automotivedesignline.com/howto/198001031 Consumer and automotive electronics converge: A MOST implementation]

* [http://www.atmel.com/journal/documents/issue6/pg29_32_autobussyste.pdf Automotive Bus Systems]

{{Computer-bus}}

{{List of Automation Protocols}}

[[Category:Computer buses]]

[[Category:Automotive technologies]]

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