Supporting Video-mediated Communication over the Internet

The tremendous success of the Internet in providing a global communication infrastructure for a wide variety of applications has inspired the invention of packet video systems for synchronous interpersonal communication. The potential benefits of video-mediated communication are numerous, ranging from improved social interactions between individuals to more efficient distributed collaborative work. <p />However, since the Internet was originally designed as a data communication network, primarily supporting asynchronous applications like file transfer and electronic mail, the realization of Internet-based packet video systems presents considerable technological challenges. Specifically, the best-effort service model of the Internet, that does not guarantee timely delivery of packets, implies that video applications must be resilient to packet loss and adaptive to variations in bandwidth and delay. <p />Two fundamental issues are how to make the systems scalable to large numbers of widely distributed users, and how to support video-mediated communication in highly heterogeneous environments. Since the Internet is built upon network connections of widely different capacities and since the computers connected to the network have vastly different characteristics, video applications must be adaptive to diverse and dynamic conditions. Furthermore, video-mediated communication systems must take various application-specific requirements and usability concerns into consideration. <p />This thesis contributes to the realization of a flexible framework for videomediated communication over the Internet by presenting scalable and adaptive algorithms for multicast flow control, layered video coding, and robust transport of video. Enrichments of video-mediated communication, in the shape of stereoscopic video transmission mechanisms and mobility support, are proposed along with design and implementation guidelines. Furthermore, the scope of Internet video is broadened through the introduction of a novel video gateway technology interconnecting multicast videoconferences with the World Wide Web. <p />In addition to the contributions on core technology, the thesis also deals with applications of video-mediated communication. Specifically, the use of video for distributed collaborative teamwork is explored through experiments with prototype implementations