Abstract: The inner logical structure of multimedia conferencing is studied. A logical description model basing on media relationships and dependency relationships is proposed with both formal and non-formal methods. The semantic rules of the model are also given. Then the expansion mechanisms of themodel are studied, including both semantic extensions and structural extensions.As a verification, a sample multimedia conference scenario is described using proposed model. Both practices and analyses have shown that this model can fullymeet the requirements on its functionality, expressivity and extensibility.

Key words: multimedia conferencing/conference, description model, formal methods