A slave is a MOST device, which is controlled by a Controller. It provides its functionalities by means of properties and methods of its function blocks. A slave has no system knowledge at all, i.e., information about other devices is not stored statically and consequently the slave does not control other slaves either. They can easily be added to or removed from a MOST system, without the software being modified or other slaves being influenced. This means that a CD changer or amplifier, can easily be used in different vehicle platforms, if they are implemented as slaves.
   A Controller is an application for administration of a functional part of a MOST system, i.e., it controls the function blocks of one or more slaves . A tuner, for example, can control its corresponding amplifier. For this purpose, the Controller requires partial system knowledge, which means that it must know the function blocks to be controlled. The Controller uses an application protocol to control a function block. It is transmitted via the Control Channel .The device address of the addressed function block does not need to be known, as it is ascertained by the Network Service.
  The Human Machine Interface (HMI) is the interface to the user of the MOST system and thus presents the system function on a high abstraction level. It coordinates the various Controllers. [16]

I. Most Frame

  The synchronous transmission of multimedia data, is directly reflected in the frame structure. A frame contains one channel for the synchronous  transmission of streaming data, one channel for the asynchronous transmission of packet data, and one channel for the transmission of control data. In the Streaming Data Channel, static connections between a streaming source and one or several streaming sinks can be built up with the sampling rates 44.1 kHz (MOST25 and MOST50) and 48 kHz (MOST150). The control of the connection set-up and disconnection, and the exchange of the control messages for the function blocks are effected via the Control Channel. The data for the commands transmitted via the Control Channel are distributed over several subsequent frames. Packet data is transmitted in the Packet Data Channel without influencing the synchronous data transmission at all.  A MOST25 frame contains 64 bytes in total. MOST50 can transport 128 byte at the same time due to the double bandwidth, and MOST150 carries 384 bytes.