IP Multicasting has been a crucial requirement of many scalable networked virtual environments by providing an efficient network mechanism through which a sender can transmit its information to a large number of receivers without having to send multiple copies of the same data over a physical link. The widespread deployment of IP Multicast has been slow due to some yet unresolved issues, prompting recent efforts in the development of multicasting protocols at the application layer instead of at the network layer. Most of these protocols address the case of a single source streaming media to a large number of receivers in applications such as video-on-demand or live broadcast. Collaborative and distributed virtual environments exhibit different characteristics that in turn necessitate a different set of requirements for application layer multicast protocols. This paper presents an introduction to application layer multicasting as it relates to distributed and collaborative virtual environments and the development of our own end system multicast protocol for multi-sender virtual teleconference applications.

Collaborative virtual environment (CVE) concepts have been used in many systems in the past few years. Applications of such technology range from military combat simulations to various civilian commercial applications. The architectures available today provide support for a number of users, but they fail if too many users are together in a small “space” in the virtual world. This paper introduces VELVET, an adaptive hybrid architecture that allows a greater number of users to interact through a CVE. This is accomplished through an adaptive filtering scheme based on multicasting. VELVET also supports small groups of users, but its use in large environments shows the greatest potential, better handling local concentrations of activity than region-, cell-, or locale -based approaches. VELVET introduces a novel adaptive area of interest management that supports heterogeneity amongst the various participants. This allows users in a supercomputer with high-speed networking to successfully collaborate with others in not-so-powerful systems behind a slow dial-up connection.