Yima : A Second Generation of Continuous Media Servers

We report on the design, implementation and evaluation of a scalable real-time streaming architecture, termed Yima, that enable applications such as video-on-demand and distance learning on a large scale. While Yima incorporates lessons learned from first generation research prototypes, it also complies with industry standards in content format (MP4) and communication protocol (RTP/RTSP). Meanwhile, it distinguishes itself from both research prototypes and commercial products because it incorporates our recent research and it pushes the industry envelope by supporting HDTV and multi-channel panoramic clients. This article describes the principles of existing approaches (both research and commercial) and how Yima improves upon them through our research. We also included some detailed information on how we tweaked available hardware and software to achieve certain objectives (e.g., playback of HDTV streams on an HDTV monitor). We describe three major contributions of Yima. First, we show how we have reduced inter-nodal data exchange and hence improved the scalability of Yima using a bipartite design. We report our comparison results of two such designs, both implemented in a realworld experimental setup. Second, we explain two alternative approaches to handling variable-bit-rate (VBR) video. Finally, in order to recover from RTP’s potential packet-loss, we report on our observations in integrating a selective retransmission protocol into Yima’s RTP server. Since packet-loss can mainly be observed in a WAN environment, we experimented with streaming MPEG-4 data over the Internet. Yima is operational and supports a variety of display bandwidths from MPEG-4 at 800 Kb/s to five synchronized channels of MPEG-2 at a total of 20 Mb/s.