Dynamic scheduling techniques for interactive hypermedia servers

Future multimedia-on-demand systems will bring interactive applications in education, entertainment, advertisement, and visualisation to a large number of users at homes, offices, classrooms and laboratories. A class of multimedia data, called hypermedia, is represented by graph structures whose branches represent different video and audio segments and whose nodes represent user interactions. To provide satisfactory service in an interactive hypermedia system, disruptions and delays in the concurrent delivery of continuous media data streams from storage devices cannot be tolerated. Slow response to new requests generated by on-line users is also highly undesirable. The frequent arrivals and completions of user requests can seriously degrade the throughput of typical servers that are designed to maintain performance at the steady state. To address these issues, we propose a dynamic approach to the retrieval of continuous media and sporadic data in an interactive hypermedia server. The throughput and efficiency of our server are improved by observing runtime information to skip or reorder service sequences, as well as maximising disk reads. Through pipelining the admission of new streams with the departure of ongoing streams, the performance is also immune to the presence of transients. User response times under identical loads are reduced significantly with respect to other existing approaches. Furthermore, our scheduler can efficiently redirect disk bandwidth to service sporadic requests when the demand on real-time services decreases. We evaluate our technique by comparing its performance with static techniques via thorough experiments under different buffer capacities, stream lengths and request arrival rates. Results of experiments show that our approach can significantly improve continuous media data throughput, user response time, as well as sporadic data throughput, and is thus a plausible approach for more interactive multimedia applications such as hypermedia.