The New Architecture of Realcourse

摘要

Realcourse by Zhang Jinyu and Li Xiaoming (2004) is a distributed digital content (including video) publishing and delivering platform deployed on Internet, with over 20 servers across cities in China. It is supported by the ChinaGrid. For the past two years, Realcourse has proven itself a great success for having accumulated over 3000 hours of university lecture videos and servicing about ten thousand video streams a day. Nevertheless, we realize two design limitations that will impair the scalability while the system grows to its next level. In this paper, after a brief introduction of the limitations, a new architecture and operational mechanism are described in details together with an elaboration of the design philosophy behind it. One key point is emphasized that the straightforward application positioning at non-critical video publishing and delivering greatly reduces the strictness of consistency requirement of Realcourse, which leads to a different architecture from some traditional distributed file systems such as Sprite , NFS and AFS . In this architecture, the "proximity rule" is the fundamental design goal which requires that in most cases the video is delivered to the user from the "closest" sever and of better performance