Multimedia multicasting brings together two technologies considered to be cornerstones of the future Internet, where rich media content will be distributed to a mass audience. It is obvious that unicasting will not be adequate for such content distribution due to the unacceptable stress imposed on network resources. Multicasting is a solution to this problem, and thus multicast routing and group management are now receiving high attention. However, so far, conditions on the composition of multicast groups have been kept rather simple. Requirements on group membership, member roles and group organization, commonly referred to as group integrity conditions, are rarely addressed or even enforced. Furthermore, the traditional multicasting model has been flat, with no finer granularity than a group, lacking any inter-group relationships. In our work, we address both issues that we see as shortcomings of current models. Our framework allows us to subdivide multicast groups into subgroups (e.g. for high and low quality versions of a media stream) and to form and manage meta groups from groups, integrating inter-related "multi" media groups. On all three levels, we specify a variety of integrity conditions as part of our comprehensive policy framework, including integrity on state and state transition, as well as group management action and transition policies.
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