Table Of ContentINTERACTIVE
VIDEO-ON-DEMAND
SYSTEMS
Resource Management and
Scheduling Strategies
THE KLUWER INTERNATIONAL SERIES
IN ENGINEERING AND COMPUTER SCIENCE
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INTERACTIVE
VIDEO-ON-DEMAND
SYSTEMS
Resource Management and
Scheduling Strategies
by
T. P. Jimmy To
The Hong Kong Polytechnic University
Babak Hamidzadeh
University ofB ritish Columbia
SPRINGER SCIENCE+BUSINESS MEDIA, LLC
Library of Congress Cataloging-in-Publication Data
A C.I.P. Catalogue record for this book is available
from the Library of Congress.
ISBN 978-1-4613-7578-4 ISBN 978-1-4615-5635-0 (eBook)
DOI 10.1007/978-1-4615-5635-0
Copyright © 1998 by Springer Science+Business Media New York
Originally published by Kluwer Academic Publishers in 1998
Softcover reprint ofthe hardcover lst edition 1998
AII rights reserved. No part of this publication may be reproduced, stored in a
retrieval system or transmitted in any form or by any means, mechanical, photo-
copying, recording, or otherwise, without the prior written permission of the
publisher, Springer Science+Business Media, LLC
Printed on acid-free paper.
TABLE OF CONTENTS
PREFACE vii
1 INTRODUCTION
1.1 Video-On-Demand service 2
1.2 VOD system model 2
1.3 Disk scheduling policies 5
1.4 Data placement schemes 5
1.5 Buffer management options 6
1.6 Organization of the book 8
2 PERFORMANCE ISSUES IN INTERACTIVE VOD SERVICE
2.1 Steady-state stream throughput 9
2.2 Effect of transients on stream throughput 10
2.3 Admission ratio and queuing time 12
2.4 Start-up latency 12
2.5 Sporadic service throughput 13
2.6 Quality-of-Service 13
2.7 Summary 14
3 RELATED WORK
3.1 Work on disk scheduling 17
3.2 Work focusing on specific issues 20
4 A DYNAMIC APPROACH TO VOD SCHEDULING
4.1 Introduction 23
v
VI TABLE OF CONTENTS
4.2 Closely related work 24
4.3 Greedy-but-Safe, Earliest-Deadline-First scheduling 24
4.4 Experimental evaluation 42
4.5 Summary 52
5 ON IMPROVING THE TRANSIENT PERFORMANCE OF
CSCANSCHEDULERS
5.1 Introduction 55
5.2 Closely related work 56
5.3 Greedy-but-Safe, Seek-Reducing scheduling (GSSR) 56
5.4 Experimental evaluation 68
5.5 Summary 77
6 PRIORITIZED ADMISSION STRATEGIES TO IMPROVE
USER-PERCEIVED PERFORMANCE
6.1 Introduction 79
6.2 Model and problem 80
6.3 Prioritized admission strategies 82
6.4 Experimental evaluation 88
6.5 Summary 101
7 RUN-TIME OPTIMIZATION OF READSIZE
7.1 Introduction 103
7.2 Modeling CM data access 105
7.3 Readsize bounds 108
7.4 Readsize control strategies 110
7.5 Experimental evaluation 113
7.6 Summary 124
8 CONCLUSIONS
8.1 General conclusions 127
8.2 Future extension 129
REFERENCES 131
INDEX 135
PREFACE
This book addresses issues in scheduling and management of resources in an
interactive continuous-media (e.g., audio and video) server. A main emphasis of the
book is on dynamic and run-time strategies for resource scheduling and
management. Such strategies provide effective tools for supporting interactivity
with on-line users who require the system to be responsive in serving their requests,
and whose needs and actions vary frequently over time.
The dynamic techniques discussed in the book recognize the need for adjusting
strategies based on the demand on the system, or the current system status,
information about which becomes available as the system is operating. This is in
contrast to static techniques that execute and provide scheduling solutions prior to
system start-up.
Part of the scheduling and resource management problem in media servers has to
do with designing admission tests that guarantee quality of service to new requests
and their on-going services before admitting such new requests. To guarantee
quality of service, these tests tend to be conservative. They over-allocate system
resources by assuming a request's worst-case resource requirements. The dynamic
techniques discussed in the book aim at monitoring actual resource requirements to
reclaim over-allocated resources, in order to provide additional and early service to
other requests.
We believe that this book will be of interest to researchers, practitioners, and
educators in the field of multimedia systems. Post-graduate and upper-division
undergraduate students in computer science and computer engineering would also
benefit from this book in learning advanced issues in the design of large-scale
VB
Vlll INTERACTIVE VIDEO-aN-DEMAND SYSTEMS
multimedia systems. Therefore, the book can be used as a text, supplemental
reading, or reference in a multimedia systems or advanced operating systems course.
The book is organized as the set of following chapters. Chapter 1 provides an
introduction to the topic. It introduces basic concepts, a model of the system
architecture, and an overview of the alternative resource management and
scheduling policies.
Chapter 2 discusses issues such as steady-state and transient-state operation of
an interactive continuous-media server. The chapter also introduces performance
factors specific to interactive continuous-media servers.
Chapter 3 provides an overview of the related work on continuous-media
servers.
Chapter 4 introduces a dynamic, real-time scheduling strategy for an interactive
continuous-media server. This chapter discusses mechanisms for exploiting run-
time information to improve the system performance.
Chapter 5 introduces another dynamic scheduling strategy, for an interactive
continuous-media server, that emphasizes the reduction of disk seek latencies in
improving performance. The chapter also discusses how this dynamic strategy takes
advantage ofrun-time information to expedite service to new streams.
Chapter 6 introduces a set of strategies that sequence the admission of pending
multimedia requests. In this chapter it is shown how prior-to-admission scheduling
strategies can be utilized to improve performance significantly.
Chapter 7 introduces dynamic techniques for improving the efficiency of disk
reads at run time. It is shown, in the chapter, how disk read sizes can be optimized
and how disk rotational latencies can be reduced.
Chapter 8 concludes the book by summarizing the main results of the research,
and by discussing the directions for future work.
Jimmy To & Babak Hamidzadeh.
Chapter 1
INTRODUCTION
Advances in technologies such as high-speed networks, image and data
compression algorithms, optical storage and magnetic storage have accelerated the
onset of the multimedia era. Recent improvements in the capacity of networks and
storage technologies have made VOD service more cost effective. Destined to
compete with existing broadcast cable services and video stores, various techniques
have thus been proposed to design large VOD servers (more specifically, Movie-On-
Demand servers) with the steady-state throughput or the maximum number of
simultaneous viewers as the main performance objective. Therefore, most of the
existing work on scheduling in VOD servers has mainly concentrated on
maximizing the steady-state throughput.
In a broader view, VOD service need not be limited to lengthy programs.
Short-length video clips can be more prevalent in Interactive Video-On-Demand
(IVOD) applications. These include digital libraries, programs for education,
entertainment, advertisement, information, guidance and visualization. In contrast
to movies, IVOD programmes are seldom linear. IVOD programmes usually consist
of short video branches separated by user interactions. Unlike VOD users
requesting delivery of movies, IVOD users will not be satisfied with long latency for
start-up and restart of video branches. Apart from maximizing the number of
admitted requests, reducing startup and queuing delays become important user-
perceived performance objectives in IVOD service. With these additional
performance objectives in mind, resource management and scheduling in IVOD
servers is a more complex problem than it is in other video servers. In this thesis,
we shall address issues pertinent to the performance of IVOD servers. As IVOD
applications continue to proliferate, the insights and techniques provided in this
thesis can be fundamental to IVOD service.
In this chapter, we shall first give an overview on the fundamental concepts
underlying typical VOD services, before we study performance requirements
specific to IVOD service in Chapter 2.
T. P. J. To et al., Interactive Video-On-Demand Systems
© Kluwer Academic Publishers 1998
2 Chapter 1
1.1 Video-On-Demand service
A major feature of a multimedia system is the presentation of motion video
accompanied by audio. Since video and audio programmes consist of continuous
sequences of samples to convey information, they are referred to as continuous
media (CM). Due to advancements in magnetic storage technologies offering short
seek latency, large cylinder capacities and high data bandwidth, a considerable
number of concurrent requests for CM data streams from the same disk can feasibly
be supported by a file server. However, failures in the timely delivery of successive
CM data samples can cause annoying effects in the presentation, such as audio
'pops' and video 'hiccups'.
Conventional file servers cannot guarantee real-time delivery of data, so they
cannot be simply used to service concurrent CM data retrievals. Thus, a special
class of storage servers known as eM servers is designed to provide real-time
retrieval and delivery of CM data streams. A CM server designed to provide video
retrieval service is referred to as a Video-On-Demand server (VOD server). In a
CMNOD server, four kinds of resources, namely the disk(s), memory buffers,
processor time and network bandwidth, are involved in CM data retrievals. These
multiple resources need to be collectively scheduled in order to provide timely
retrieval of CM data. Traditional resource scheduling techniques are not directly
applicable mainly because they are designed only for a single resource, or they are
not designed to meet real-time constraints. The pressing need for novel scheduling
techniques in CM servers is, thus, receiving increased attention from the research
community [16,9,15].
1.2 VOD system model
A typical VOD system consists of clients and servers on a network, as shown in
Figure 1.1. The resources in each CM server consist of one or more magnetic disk
drives, a pool of memory buffers and at least one CPU to execute the scheduler.
Each client may generate real-time requests for CM data, or occasional single-shot
sporadic requests for CM or non-CM data. The client requests are sent to the CM
server via network connections which also serve as the transmission medium for
data. The existence of buffers in each client is used to provide some tolerance on
variations in network delay as well as data consumption rates. We do not exclude
the possibility of having both a client and a server coexist on the same physical
workstation, as long as the cumulative resource requirements are satisfied. In a
server, the scheduler controls the sequence and sizes of disk accesses, manages the
memory buffers, and invokes periodic functions to transmit data via the network to
the clients' buffers.
Upon arrival of a real-time request, the CM scheduler performs an admission
test to ensure that nonstarvation guarantees to the ongoing services can be extended,
before service to the new request can be committed. The admission test also
determines the readsize (amount needed to be read) in servicing each stream. Once
