Editing Session layer (section)

=== Synchronization points and resynchronization ===

The session layer may also allow the two sides to insert ''synchronization points'' into the dialogue, and allow them to do a ''resynchronization'', which aborts the current transmission, sets the synchronization point to a certain value, and restarts transmission from that point.

This may be used in real-time audio/video transmission. Synchronization points can be used to insert timestamps to the data flow, and a resynchronization may be used to reset the transmission to start from a new timestamp. For example, if the video stream lags behind the audio stream too much, the receiving side may issue a resynchronization request on the video stream, restarting its transmission from a later timestamp.

This may also be used by the application to do checkpointing. Synchronization points can be used to indicate that a checkpoint has been committed by the application, and after an application crash or a power failure, a resynchronization can be used to indicate that the application has recovered from a checkpoint and the transmission can be resumed from that point.

This may also be used to interrupt / resume a dialogue at any time, not due to an application failure, but as planned by the application. The application may interrupt a dialogue, start another dialogue in the same session, and resume the previous dialogue in the same session or in another session.

The session layer may also provide explicit support for managing multiple interruptible dialogues over one or more sessions. These dialogues are called ''activities''. Activities can be interrupted and resumed explicitly. Compared to implicitly interrupting and resuming dialogues by resynchronization, activity support gives the application simpler control of these dialogues.