An Architecture for Multicast Telepresentations

Abstract

We have developed a scalable reliable multicast architecture for delivering one-to-many telepresentations. Whereas the transport for interactive real-time audio and video is concerned with timely delivery, other media, such as slides, images and animations require reliability. We propose to support reliability by combining multicast with forward error correction (FEC), as well as additional techniques depending on the nature of the data. Two related but distinct protocols are used for dynamic and persistent session data. For dynamic session data, we use erasure-correcting scalable reliable multicast (ECSRM), an enhanced version of SRM by Floyd et al. that is based on NACK suppression, but improves scalability and rate control. Session-persistent data is delivered using Feast, a protocol that combines FEC and data carouseling with no back-channel from receiver to sender. Our approach is scalable to large heterogeneous receiver sets, and supports late-joining receivers. We have implemented our approach in a layered, multicast version of PowerPoint, a graphical slide presentation tool.