Message sequence chart

A message sequence chart (or MSC) is an interaction diagram from the SDL family standardized by the International Telecommunication Union.

Since in MSCs the communication behaviour is presented in a very intuitive and transparent manner, particularly in the graphical representation, the MSC language is easy to learn, use and interpret.

In connection with other languages it can be used to support methodologies for system specification, design, simulation, testing, and documentation.

The existing symbols are: UML 2.0 Sequence Diagram is strongly inspired by the ITU-T MSC.

Still, for historical reasons, the default basic principles are quite different: It has been said that MSC has been considered as a candidate for the interaction diagrams in UML.

The diagram shows three entities. At start the phone is disconnected. A user tries to establish a connection. A connection request is sent to the switch and a timer is started. An alternative deals with two possibles responses: 1 - The timer goes off because the switch did not reply and the phone goes back to the disconnected state.2 - The switch grants the connection and the call is established.
Dynamic process creation in an MSC
Call operation in an MSC
Time constraint in an MSC
MSC Reference in an MSC
SDL-RT Semaphore extension to MSC