Spatial Scope and Multicast in Large Virtual Environments

This paper considers the use of multicasting and spatial scoping in creating large-scale multi-user virtual environments. The asymmetry of network multicasting with respect to producers and consumers is discussed. Five approaches are described for using multicast groups in systems with spatially scoped interaction: one group per object, one group per world, location-based groups, content-associated groups and dynamic groups. Some illustrative aspects of the design of MASSIVE version 2 are described. Specific strengths and weaknesses of each approach are identified together with appropriate areas of application. Finally some generalisations of multicast-style functionality are suggested.