There are many systems, which need synchronisation between their components. Typical examples are concurrent task synchronisation, or synchronisation of multimedia streams during their transmission and presentation.
UML (Unified Modelling Language) is a specification language elaborated for object-oriented modelling. The UML enables explicit specification of peer-to-peer synchronisation only. The specific feature of the UML is its extensibility, allowing adaptation of it to a given domain.
In the paper, a new mechanism for a specification of a multicast synchronisation is presented. First, we extend the UML metamodel by introducing new metaclasses. Next, we define a new stereotype Synchroniser. Synchronisers have instances called synchronisation points. Synchronisation points offer synchronisation services to objects that may use them. The paper describes informally semantics of synchronisation points and demonstrates their expressive power by analysis of three examples.