TR-IIS-01-008    pdffile

A Feedback-Controlled EDF Scheduling Algorithm for Real-time Multimedia Transmission

Wang, Chia-Hui, Jan-Ming Ho, Ray-I Chang, and Shun-Chin Hsu

Institute of Information Science, Academia Sinica, Nankang, Taipei, Taiwan

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Real-time communication is important for time-critical multimedia applications. However, conventional real-time schedulers such as EDF (Earliest Deadline First) and RM (Rate Monotonic) are designed for task sets with sophisticated characteristics. They can perform well in the idea network with precise workloads. But, in a realistic network with shared bandwidth and unpredictable workloads, their performances may be poor. In this paper, a control-theoretical approach of EDF called BC-EDF (Buffer-Controlled EDF) is proposed to resolve the real-time scheduling problem in multimedia communications. Based on the feedback control ideas (that have been used successfully in systems with unpredictable workloads), BC-EDF utilizes the feedback of buffer-occupancy to prevent packet loss from buffer's overflow/underflow (whether its occupancy is prevented to run above/below the watermark). It can tolerate diverse system behaviors to provide reliable multimedia communications and playback quality. Experiments show that BC-EDF outperforms other schedule mechanisms that don't reflect on the changes of buffer-occupancy.

Keywords: feedback control, buffer-occupancy, EDF, real-time, multimedia communications.