Multi-source Multimedia Conferencing over Single Source Multicast: An Application-Aware Approach

A key issue for the establishment of large-scale multimedia conferencing in the global Internet is the provision of a ubiquitous IP multicast service. Despite extensive research and standardization efforts, worldwide availability of IP multicast is still limited. Single-source multicast constitutes an alternative that achieves to alleviate many of these problems. However, the tradeoffs in realizing multi-source sessions over single-source multicast remain poorly understood. The focal point of this paper is the realization of a multisource distance learning conferencing platform (ET&L) over a novel singlesource IP multicast protocol (SLIM). We have formulated the design space for managing trees rooted at multiple senders in a conferencing session, using both previously proposed schemes as well as new methods exploiting the application semantics of synchronous distance learning. We have prototyped each of these methods to prove their respective viability and conducted experimentation within our laboratories and over the Internet without changes or cooperation from ISPs or network administrators. The principal outcome of this work is a study of the various alternatives for implementing multi-source sessions over single-source multicast. In general, our work shows that it is feasible and efficient to use single-source multicast as a building block for implementing multisource group communication applications.