Explain the distinctions between the three forms of synchronization (synchronous distributed state, media synchronization and external synchronization) that may be required in distributed multimedia applications. Suggest mechanisms by which each of them could be achieved, for example in a video conferencing application.

What will be an ideal response?

synchronous distributed state: All users should see the same application state. For example, the results of operation on controls for a video, such as start and pause should be synchronized, so that all users see the same frame. This can be done by associating the current state (sample number) of the active multimedia streams with each state-change message. This constitutes a form of logical vector timestamp.
media synchronization: Certain streams are closely coupled. E.g. the audio that accompanies a video stream. They should be synchronised using timestamps embedded in the media data.
external synchronization: This is really an instance of synchronous distributed state. The messages that update shared whiteboards and other shared objects should carry vector timestamps giving the states of media streams.