[1] For OGF, the media sources are connected by repeaters[citation needed] (signal generators) being joined on a central star coupler.
[1] MVB was derived from the P215 bus developed by Brown Boveri Cie, Switzerland (now ABB), incorporating the publisher/subscriber principle from early field busses (DATRAS)[citation needed].
MVB presents many similarities with the FIP field bus (originally from French "Flux d'Information vers le Processus", relabeled as Factory Instrumentation Protocol or some references also use the hybrid "Flux Information Protocol") that was developed in the French NFC 46602 standard series.
Despite the advantages of the MVB field bus, many vehicle buses are still built from CANopen, WorldFIP (in France), LonWorks (in the USA) and Profibus components.
This is not due to the communication technology: most devices implement the MVB protocol machine in a small area of an FPGA which is today anyhow present, and the costliest component remains the connector[citation needed].
Running FlexRay with 2.5 Mbit, an RS-485 physical layer and only one "coldstarter" would lead to a very similar behavior in respect to the application.
Conversely, in 1999, the automotive industry evaluated MVB[citation needed] (in an extended 24 Mbit/s version), but dropped it because of the costs, which should be unreasonably low for the mass-market of millions of vehicles.
The encoding uses a Manchester II code and a HDLC frame protocol with proper voltage balancing to avoid DC components in the galvanic isolation transformers.
The Manchester decoder uses a phase/quadrature demodulation (not RS-485, that operates with zero-crossings) which allows to span 750 m under worst-case conditions, especially when only the two extremity vehicles are equipped, as is the case with multiple traction for freight trains.
[4] Since frame size is limited, a version of TCP with reduced overhead was used for message segmenting and reassembly, that at the same time allows to cope with changes in composition, called RTP (Real-Time Protocol).
The physical layer of WTB shows similarities with the WorldFIP field bus (EN 50170 part 4) - its "voltage mode" did use 1 Mbit/s and a maximum of 32 stations on the bus with a maximum length of 750 meters, the use of FIP transceivers was studied early[citation needed] in the TCN evaluation, but the Phase/Quadrature decoding was used instead.
The TCN is used in most of the modern train control systems usually connecting the vehicles with an 18-pin UIC 558, including: IEC 61375 is a suite of standards.