Reliable dissemination protocol for interactive collaborative applications

The widespread availability of networked multimedia workstations and PCs has caused a significant interest in the use of collaborative multimedia applications. Examples of such applications include distributed shared whiteboards, group editors, and distributed games or simulations. Such applications often involve many participants and typically require a specific form of multicast communication called dissemination in which a single sender must reliably transmit data to multiple receivers in a timely fashion. This paper describes the design and implementation of a reliable multicast transport protocol called TMTP (Tree-based Multicast Transport Protocol). TMTP exploits the efficient best-effort delivery mechanism of IP multicast for packet routing and delivery. However, for the purpose of scalable flow and error control, it dynamically organizes the participants into a hierarchical control tree. The control tree hierarchy employs restricted nacks with suppression and an expanding ring search to distribute the functions of state management and error recovery among many members, thereby allowing scalability to large numbers of receivers. An Mbone-based implementation of TMTP spanning the United States and Europe has been tested and experimental results are presented.