In this paper, we propose and study a dynamic approach to schedule real-time requests in a video-on-demand (VOD) server. Providing quality of service in such servers requires uninterrupted and on-time retrieval of motion video data. VOD services and multimedia applications further require access to the storage devices to be shared among multiple concurrent streams. Most of the previous VOD scheduling approaches use limited run-time,0 information and thus cannot exploit the potential capacity of the system fully. Our approach improves throughput by making use of run-time information to relax admission control. It maintains excellent quality of service under varying playout rates by observing deadlines and by reallocating resources to guarantee continuous service. It also reduces start-up latency by beginning service as soon as it is detected that deadlines of all real-time requests will be met. We establish safe conditions for greedy admission, dynamic control of disk read sizes, fast initial service, and sporadic services. We conduct thorough simulations over a wide range of buffer capacities, load settings, and over varying playout rates to demonstrate the significant improvements in quality of service, throughput and start-up latency of our approach relative to a static approach.
No abstract
Disruptions and delays in the retrieval of continuous motion video data streams from storage devices are unacceptable for Video-On-Demand (VOD) service. Concurrent VOD services require careful scheduling of accesses to the storage device in real-time. In this paper, we propose a dynamic approach to schedule the retrieval of motion video data in interactive VOD servers. Most of the previous VOD scheduling approaches use fixed disk read sizes and pre-determined reading orders. Run-time information is seldom used to filly exploit the potential capacity of the system. To maximize throughput, our approach relaxes admission control by observing run-time information. To improve performance under heavy transients, we introduce mechanisms to dynamically control the read sizes of disk accesses, to pipeline admission of new streams with departure of ongoing streams, and to safely deviate from seekreducing service sequence to provide early initial service. Most important of all, our scheduler is designed to reduce start-up delay significantly. When the demand on real-time services decreases, our scheduler is also highly efficient in redirecting disk bandwidth to service sporadic requests. We evaluate our technique by comparing its perfonnance with two static seek-reducing techniques via thorough experiments under different buffer capacities and load settings. Results of experiments show our technique's significant improvements in real-time service throughput, initial response time, and sporadic service throughput.
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