Abstracts - 1997 ANNUAL TECHNICAL CONFERENCE
Overcoming Workstation Scheduling Problems in a Real-Time Audio Tool
Isidor Kouvelas and Vicky Hardman
Department of Computer Science
University College London
The recent interest in multimedia conferencing is a result of the
incorporation of cheap audio and video hardware in today's workstations, and
also as a result of the development of a global infrastructure capable of
supporting multimedia traffic - the Mbone.
Audio quality is impaired by packet loss and variable delay in the network,
and by lack of support for real-time applications in today's general purpose
A considerable amount of research effort has focused on solving the network
side of the problem by providing packet loss robustness techniques, and
network conscious adaptive applications.
Effort to solve the operating system induced problems has concentrated on
This paper presents an architecture for a real-time audio media agent that
copes with the problems presented by the UNIX operating system at the
The mechanism produces a continuous audio signal, despite the variable
allocation of processing time a real-time application is given under UNIX.
Continuity of audio is ensured during scheduling hiccups by using the
buffering capabilities of workstation audio devices drivers.
Our solution also tries to restrict the amount of audio stored in the device
buffers to a minimum, to reduce the perceived end-to-end delay of the
audio signal. A comparison between the method presented here (adaptive
cushion algorithm), and that used by all other audio tools shows substantial
reductions in both the average end-to-end delay, and the audio sample loss
caused by the operating system.