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`AMAZON-1010
`7,532,808
`
`

`

`Digital Video Communications
`
`

`

`
`
`Digital Video Communications
`
`t
`
`|
`
`|
`
`MartynJ. Riley
`Iain E. G. Richardson
`
`Artech House
`Boston ® London
`
`

`

`Library of Congress Cataloging-in-Publication Data
`Riley, Martyn J,
`Digital video communications / Martyn J. Riley, Iain E. G. Richardson.
`.
`em.
`Includesbibliographical references and index.
`ISBN 0-89006-890-9
`1. Digital television.
`TK6678.R55
`1996
`621.388—dc21
`
`I. Richardson, lainE.G.
`
`ILTitle.
`
`96-37127
`CIP
`
`British Library Cataloguing in Publication Data
`Riley, MartynJ.
`Digital video communications
`1. Digital communications 2. Digital video 3. Image transmission 4. Image
`processing—Digital technique
`I. Title 1. Richardson,Iain E. G.
`621.387
`
`ISBN 0-89006-890-9
`
`Cover design by Jennifer Makower
`
`© 1997 ARTECH HOUSE,INC.
`685 Canton Street
`Norwood, MA 02062
`
`All rights reserved. Printed and bound in the United States of America, No part ofthis
`book may be reproduced or utilized in any form or by any means, electronic or me-
`chanical, including photocopying, recording, or by any information storage and re-
`trieval system, without permission in writing from the publisher.
`All terms mentioned in this book that are known to be trademarks or service marks
`have been appropriately capitalized. Artech House cannotattest to the accuracyofthis
`information. Use of a term in this book should not be regarded as affecting the validity
`of any trademark or service mark.
`
`International Standard Book Number: 0-89006-890-9
`Library of Congress Catalog Card Number: 96-37127
`
`10987654321
`
`‘
`
`

`

`
`
`To Laura and Phyllis
`and in memory of Jim Riley
`
`

`

`Contents
`
`SOCOANNNOFWe
`
`Introduction
`Chapter 1
`Digital Video Communications
`1.1.
`The Market
`1.2
`Key Issues
`1.3.
`Structure of This Book
`1.4
`Reference
`
`Chapter 2 Applications for Digital Video Communications
`2.1
`Introduction
`2.2
`Entertainment Broadcasting
`2.3.
`Video on Demand
`2.4
`Conferencing
`2.4.1
`Telemedicine
`2.4.2 Videoconferencing and Education
`Summary
`2.5
`References
`
`3.2
`
`Chapter 3 Video Compression Techniques and Standards
`Introduction
`3.1
`Digital Video
`3.2.1 Representation of Video Information
`3.2.2
`CCIR 601 Standard
`3.2.3
`The Need for Compression
`Coding of Still Images
`3.3.1
`Predictive Coding
`3.3.2 Discrete Cosine Transform Coding
`3.3.3 Other Image Coding Techniques
`Coding of Moving Images
`3.4.1
`“Generic” DCT/DPCM CODEC
`3.4.2 Bidirectional Prediction
`
`3.3
`
`3.4
`
`
`vil
`
`

`

`
`
`viii Digital Video Communications
`
`3.5
`
`JPEG:Still Image Coding
`3.5.1
`The Baseline CODEC
`3.5.2 Other Features and Modes
`H.261: Motion Video Coding for Videoconferencing
`3.6
`H.263: Low Bit Rate Video Coding
`3.7
`3.8 MPEG: Motion Video Coding for Entertainment and
`Broadcast
`3.8.1 MPEG1 for CD Storage
`3.8.2 MPEG2for Broadcasting
`3.8.3 MPEG4for Integrated Visual Communications
`Digital Audio Visual Council (DAVIC)
`3.9
`3.10 Future Developments and Research Areas
`3.10.1 Optimization and Application of Existing
`Standards
`3.11 Summary
`References
`
`4.3.
`
`Chapter 4 The Internet
`4.1
`Introduction
`4.2.
`The Internet Architecture
`4.2.1 Gateways or Routers
`4.2.2
`Internet Addresses
`4.2.3
`The Domain Name System
`Internet Protocols
`4.3.1.
`Internetworking Protocol (IP)
`4.3.2 Mapping Internet Addresses to Physical
`Addresses
`TCP and UDP
`4.3.3
`Congestion in the Internet
`The Internet and Real-Time Traffic
`4.5,1 M-BONE (IP Multicast)
`4.5.2
`RSVP
`Summary
`4.6
`References
`
`4.4
`4.5
`
`Chapter 5 B-ISDN and Asynchronous Transfer Mode Networks
`5.1
`Introduction
`5.2
`Principles of the Asynchronous Transfer Mode
`5.2.1 Virtual Circuit Operation
`5.2.2
`Statistical Multiplexing
`ATM Protocol Architecture
`5.3.1
`Physical Layer
`5.3.2 ATM Layer
`5.3.3. ATM Adaptation Layer (AAL)
`
`5.3
`
`
`
`
`

`

`EES?——
`
`:
`
`ATM Switching Technology
`5.4
`Congestion Control
`5.5
`ATM Signaling
`5.6
`UPC Functions
`5.7
`LAN Emulation
`5.8
`Video Over ATM
`5.9
`5.10 Example ATM Networks
`5.11 Summary
`References
`
`6.3
`
`Chapter 6 Quality of Service for Video Communications
`6.1
`Introduction
`6.2
`Video Quality Requirements
`6.2.1
`Image Quality
`6.2.2 Visible Errors
`6.2.3 Delay
`Quality of Service Requirements for a Video
`Transport System
`Quality of Service for Coded Video
`6.4.1 Data Transmission Rate
`6.4.2
`Errors and Losses
`6.4.3 Delay
`6.5 Multiplexing and Demultiplexing Traffic Streams
`6.5.1 MPEG2 Systems Layer
`6.5.2
`Transmission of MPEG2 Transport Packets
`Over ATM
`Summary
`6.6
`References
`
`6.4
`
`Contents
`
`ix
`
`82
`84
`86
`86
`87
`87
`89
`89
`90
`
`91
`91
`93
`93
`93
`94
`
`94
`95
`95
`97
`98
`100
`100
`
`104
`105
`105
`
`107
`107
`108
`108
`108
`109
`109
`115
`123
`123
`124
`125
`
`7.1
`7.2
`
`7.3
`
`Chapter 7 The Effect of Bit Errors and Packet Loss on
`Compressed Video
`Introduction
`Sources of Errors
`7.2.1
`Bit Errors
`7.2.2
`Packet Loss
`Effect of Errors on Coded Video
`7.3.1
`Error Effects and Error Propagation
`7.3.2
`Error Effects: Experimental Results
`Coding Techniques to Reduce the Effect of Errors
`7.4.1
`Error Correction
`7.4.2
`Error Concealment
`7.4.3
`Encoding Parameters
`
`7.4
`
`

`

`
`
`x Digital Video Communications
`
`7.4.4 Case Study: Varying Slice Size to Improve Error
`Tolerance of MPEG Video
`Summary
`7.5
`References
`
`Chapter 8 Forward Error Correction
`8.1
`Introduction
`8.2.
`Some Definitions
`8.3.
`Finite (or Galois) Fields
`8.4
`Linear Block Coding
`8.4.1 Hamming Codes
`8.4.2
`Bose, Chaudhuri Hocquenghem (BCH) Codes
`8.4.3 Reed-Solomon Codes
`8.4.4
`Fast Implementation Techniques for Fourier
`Transforms in Galois Fields
`Convolutional Coding
`Interleaving
`Applications of FEC
`8.7.1 Broadcasting
`8.7.2
`Packet Loss Recovery
`Summary
`8.8
`References
`
`8.5
`8.6
`8.7.
`
`Chapter 9 Layered Video Coding
`9.1
`Introduction
`9.2
`Layered Coding in International Standards
`9.2.1.
`SNR Scalability
`9.2.2
`Spatial Scalability
`9.2.3
`Temporal Scalability
`9.2.4
`Frequency Scalability
`Research Issues
`9.3.1
`Filtering in the Compressed Domain
`9.3.2
`Case Study: Prioritizing MPEG Picture Classes
`Summary
`9.4
`References
`
`9.3.
`
`Chapter 10 Rate Control
`10.1
`Introduction
`Rate Control Requirements
`10.2
`10.2.1 Constant Bit Rate Transmission/Storage
`10.2.2 Variable Bit Rate Transmission
`Effect of Encoding Parameters on Coded Bit Rate
`10.3.1 Spatial and Temporal Resolution
`10.3.2 Quantization Step Size
`
`10.3
`
`126
`
`128
`
`128
`
`131
`
`131
`
`132
`
`134
`
`136
`
`138
`139
`
`141
`
`148
`
`148
`
`1541
`
`152
`
`152
`
`153
`
`154
`
`155
`
`157
`
`157
`
`160
`
`160
`
`162
`
`164
`
`166
`169
`
`169
`
`171
`
`172
`
`172
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`175
`
`175
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`178
`
`178
`
`179
`
`181
`
`182
`
`182
`
`=oeolOese
`
`

`

`10.3.3 Group of Pictures Structure (MPEG)
`10.3.4 Slice Size (MPEG)
`10.4 Rate Control Techniques
`10.4.1 Constant Bit Rate
`10.4.2 Variable Bit Rate
`10.5 Summary
`References
`
`Chapter 11 Conclusions
`11.1 Applications and Requirements
`11.2 Meeting Video Quality of Service Requirements
`11.2.1 Encoding
`11.2.2 Protocol Processing
`11.2.3 Transmission
`11.2.4 Decoding
`11.3 Future Developments
`Glossary
`About the Authors
`
`Index
`
`Contents xi
`
`184
`
`185
`
`185
`
`186
`
`192
`
`195
`
`195
`
`197
`
`197
`
`198
`
`198
`
`198
`
`199
`
`200
`
`200
`
`203
`
`207
`
`209
`
`

`

`
`
`Introduction
`
`1.1 DIGITAL VIDEO COMMUNICATIONS
`
`Digital video has emergedin the last few years as a technology that can provide
`anew “dimension” to electronic communications, Digital video is video infor-
`mation represented in digital form. Digital representation has a numberof key
`advantages over “traditional” analog video andtelevision. All information can
`be represented in digital form, so the same techniques and systems can be used
`to store, process, and transmit a wide rangeof different types of data (multiple
`media or ‘“‘multimedia’’). The rapid growth in digital processing power means
`that complex processing and coding operations can becarried out on digital
`video data in real time. Digital video can be integrated into computer applica-
`tions and systems. This in turn makesit possible to create interactive applica-
`tions, where the user is no longer a “‘passive’’ observer but has the opportunity
`to interact with the video information.
`Advances in computing and processing capabilities have been matched
`by advancesin data networking technology.In a short space of time, the number
`of computers and systems connected by networks such as the Internet has
`grown exponentially. As well as becoming more widespread, networks can
`handle higher volumesof data and higher transmission rates. The current net-
`working structure is loosely defined and ‘“‘heterogeneous”’ (consisting of a range
`of interconnected networks with different technologies and capabilities). Broad-
`band networks based on the asynchronoustransfer mode, in whichall data is
`processed and transmitted as small, fixed-length cells, can support efficient
`transmission of high data rates, and these networks are beginning to replace
`older, less efficient technologies.
`As weshall describe in Chapter 3, digital video has an inherently high
`bandwidth (i.e., a digitized video signal requires a very high data rate for
`transmission). In order to store and transmit this information effectively, it has
`been necessary to develop techniques for compressing the video data[i.-e.,
`
`

`

`
`
`2 Digital Video Communications
`
`encoding it into a smaller number of bits). The emergence of international
`standards for encoding video data has enabled a wide range of applications
`that make use of digital video transmission and storage. Image coding provides
`a means of compressing digitized photographic images by around 10 to 20
`times. Current video coding techniques enable video data to be compressed by
`between 20 and 50 times. By using these techniques, it has becomepractical
`to store, transmit, and manipulate digital image and video information using
`currently available storage systems and data networks. The range of applications
`for digital video continues to grow andincludesthe following:
`
`* Video conferencing and videotelephony. Two way, real-time video and
`audio communications. Video and audio information is transmitted via
`data networks such as integrated services digital network (ISDN) and the
`Internet (IP-based network). Implementations range from one-to-one video-
`telephony to studio-based group conferencing.
`¢ Home entertainmentdigital video. The video compactdisc (based on the
`CD-ROM format) provides a digital alternative to analog home video. Com-
`pact disc digital video brings many of the advantages of audio compact
`discs (e.g., durability and random access) to video entertainment, together
`with further features such as user interaction and interactive video games,
`¢ Broadcast digital television. Digital television channels are beginning to
`replace analog transmissions overcable, satellite, and terrestrial broadcast
`media. This should provide (arguably) greater choice and picture quality
`to the viewer together with further advantages and features associated with
`digital transmission.
`* Video databases and video on demand. These applications involve the
`storage of digital video information in large databases. The user can access
`the stored information and play back the video data. Application areas
`include homeselection and viewingof centrally stored films and programs
`(“video on demand”) as well as archival and accessof educational learning
`video material.
`¢ Medical applications. Many of the above techniques can be integrated
`into the healthcare system. Experimental trials to date have made use of
`videoconferencing between medical practitioners as well as medical image
`communication and storage using electronic media.
`
`These applications are all in use at the time of writing. The continual
`improvements in processing power and network capacities should lead to a
`wider penetration of digital video into the marketplace. Digital video communi-
`cation has the capability to change dramatically the way we communicate and
`do business.
`
`

`

`
`
`introduction 3
`
`Many morepotential applications have been identified that make use of
`digital video techniques. These include high definition digital
`television
`(HDTV), which provides higher spatial and temporal resolutions than existing
`analog (or digital) television, applications that involve much moreinteraction
`from the user (for example, where the video information is manipulated as
`individual components or objects within a scene) and stereoscopic (three-
`dimensional) or multiple viewpoint video. Advanced encoding techniques may
`offer very high compression of video information that could enable high-quality
`video at low bit rates and should lead to further availability of digital video
`applications.
`
`1.2 THE MARKET
`
`The rapidly expanding digital video market has been studied in a numberof
`marketing reports. It is widely predicted that in many of the application areas,
`growth will be extremely rapid over the next few years.
`For example, videoconferencing has been identified as one of the major
`application areas. This can be divided into systemsbased in specially equipped
`rooms(referred to as suites) and desktop conferencing. Desktop videoconferenc-
`ing is carried out from a user’s desktop with a specially equipped personal
`computer (PC). With regard to suites, it has been stated [1] that
`
`Research commissioned by GPT (and others) estimates that global
`sales of small and large group [videoconferencing] systems reached
`14,000 units and generated a revenue of [US]$621m in 1994. This
`year [1995] those figures are expected to rise to 20,000 units and
`[US]$819m and in 1998 it will be 40,000 units and [US]$1.345 Bn.
`
`The situation for desktop systems is considered [1]
`promising:
`
`to be even more
`
`This steady growth contrasts with the data provided for PC-based
`desktop systems where 1994 figures suggest sales of 12,500 units and
`revenue of [US|$31m and 1995 is expected to generate sales of 86,000
`units and [US]$120m in revenue. Then, according to the research,
`the market will soar with 987,000 units likely to be shipped and
`revenue leaping to [US]$789m.
`
`According to [1], this explosion in revenue will lead to a 1998 market of
`5.225m units and revenue of over (U.S.)$2 billion.
`This growth is likely to create turmoil in a number of industries since
`digital video technology involves a combination of telecommunications, televi-
`
`rrrgytm
`
` L
`
`

`

`
`
`4 Digital Video Communications
`
`sion, and computer engineering. Companies are being required to develop
`expertise in new areas and form strategic partnerships to exploit the rapidly
`developing market. In this book, we aim to provide an introduction to a range
`of the relevant technologies and then consider someofthe key technicalissues.
`
`1.3 KEY ISSUES
`
`Manyof the applications for digital video that are currently in use have been
`designedfor fixed network topologies and systems. For example, videoconfer-
`encing over ISDNscan rely on a fixed transmission bit rate and a well-defined
`transmission delay anderror rate. If these parameters can be accurately pre-
`dicted, then a video coding system can be designed that provides acceptable
`performance in this configuration. However, the ever-changing networking
`infrastructure is made up of an increasingly heterogeneous mix of networks
`and technologies. The transmission characteristics provided to a particular
`connection (the quality of service) can vary from connection to connection and
`even during a connection, depending on the path taken thrpugh the network
`and on the othertraffic currently in transit through the network.
`A communication networkoffers a particular quality of service (QoS) to
`traffic transmitted through the network. Important QoS parameters include data
`rate (mean data rate and rate variation), delay characteristics (transmission
`delay, delay variation), and error or loss probability (bit errorrate, cell or packet
`loss probability, error patterns).
`All of these parameters can affect the quality and reliability of digital
`video communications. The available data rate has a significant effect on the
`quality and resolution of coded video information that can be transmitted
`through the network. Different coding techniques are appropriate for different
`data rates. Transmission delay and delay variation are very important since
`real-time video applications are sensitive to changes in transmission delay.
`Decoded video frames must be presented to the viewer at a constant rate, and
`if a particular frame is delayed too long then it cannot be displayed and is
`“lost.” Errors and losses have a particularly severe effect on the quality of
`decodedvideo. Video coding schemes achieve compression by removing redun-
`dant information from the video data, which meansthatall of the coded data
`is significant and hence a transmission error is likely to have a significant
`impact on video quality.
`Some of these problems are addressed by the video coding standards
`themselves. However, many of the implementation details are left to be
`addressed by the developerof a particular application. The video coding stan-
`dards have intentionally been kept as broad asis practical. There is therefore
`considerable scope for optimization of video coding techniques in order to
`address these problems and providereliable video communications.
`
`
`
`

`

`
`
`Introduction 5
`
`Ideally, a video communication system should provide the user with a
`service that offers video at an acceptable quality. The networking environment
`is not likely to “‘stabilize’”’ in the foreseeable future and so a practical video
`communication system should be adaptable, reliable, and robust in order to
`cope with varying QoS from the network.A further useful feature is scalability:
`a flexible video communication system should be able to scale the quality of
`the video depending on the capabilities of the network and ofthe display.
`
`1.4 STRUCTURE OF THIS BOOK
`
`This book aims to introduce the concepts and systems required to support
`digital video communications and to discuss someof the issues that need to
`be addressed to providereliable,flexible video communications in the changing
`networking environment. The intended audiencefor the book includes:
`
`¢ Practicing engineers and technical staff who have an involvementin the
`video, television, computing, and communications industries;
`¢ Academics and researchers in electronic engineering, computer science,
`andrelated fields who havea research or teaching interest in digital video
`communications;
`¢ Final year undergraduate and postgraduate students in electronic engi-
`neering, computer science, and related fields who require an introduction
`to the concepts and issues involved in digital video communications.
`
`In the early chapters, we describe the applications for digital video and
`introduce some of the key technologies that are required to support digital
`video communications.
`Chapter 2 describes application areas in which digital video is used,
`including those areas mentioned in Section 1.1.
`Chapter 3 introduces the techniques for encoding (compressing) and
`decoding digital video data. In this chapter, we concentrate in particular on
`the international standards for video encoding.
`Chapters 4 and 5 provide an introduction to key network technologies
`that are being used for digital video transmission. In Chapter 4 we describe
`the structure and protocols of the Internet and in Chapter 5 we introduce
`asynchronous transfer mode (ATM) networks and broadband ISDN,
`Chapter6 is a pivotal chapter. Here, we discuss the QoS issues related to
`the transmission of coded digital video through networks. These QoSrequire-
`ments must be met in order to provide flexible, reliable, and robust video
`transmission.
`
`

`

`
`
`6 Digital Video Communications
`
`The later chapters concentrate on a series of issues related to supporting
`the QoS required for digital video communications and are based on research
`work by the authors and others.
`Chapter 7 analyzes the effect of transmission errors on coded video data.
`Anypractical transmission system or network will introduce errors and losses
`into transmitted data. We discuss the problems that this can cause for video
`quality and look at ways of improving quality in the presence oferrors.
`Chapter 8 deals with forward error correction coding and its application
`to error control for digital video communications. Forwarderror correction is
`particularly suited to real-time information such as digital video and weintro-
`duce the fundamental techniques and someofthe applications for video com-
`munications.
`In Chapter 9 we discuss scalable or layered video coding. We describe
`some of the main layered coding techniques and how they might be applied
`to improve the QoSavailable to coded video data.
`Chapter 10 introducesthe topic of rate control for coded video. Practical
`networks placerestrictions on the rate of data that can be transmitted and for
`this reason rate control is a key part of any video coding system.
`Digital video communications offer considerable scope to change the way
`we communicate. Providing practical and robust digital video communications
`systems requires an understanding of coding and transmission techniquesas
`well as an appreciation of how video QoS requirements may be supported. We
`hope that this book goes some way towards meeting these needs.
`
`[1] “Bringing Video Conferencing into Line,” Audio-Visual Communications for Business Maga-
`zine, May 1995.
`
`Reference
`
`

`

`
`
`
`
`Applications for Digital
`
`Video Communications
`
`2.1 INTRODUCTION
`
`Analog video communications technology hassignificantly affected the lives of
`millions of people worldwide. The vast majority of householdsin the developed
`world own at least one television set, which provides a major sourceof entertain-
`ment to the home.
`Digital video offers many advantagesover analog videofor the vast majority
`of applications. Therefore, as digital video technology becomes more mature
`we would expect to see a gradual shift from analog to digital technology. The
`ease with which digital video can be integrated with computers, together with
`the introduction of global communication networksthat support the integration
`of video with audio and conventional computer data make a whole range of
`new applications possible.
`Many people are now familiar with personal computers (PCs) both at
`home and in their working environment. These PCs are now being produced
`with support for multimedia, including audio and video. The costs of this
`multimedia support are dropping rapidly. The increasing power of the micro-
`processors in these PCs makes more and moreprocessing possible in software,
`thereby reducing the need for specialist hardware. Multimedia PCs represent
`a powerful platform and motivating factor in the developmentof digital video
`technology.
`In this chapter, we provide a discussion of some of the applications of
`digital video communications and concentrate on twocase studies: one relating
`to the use of digital video to support telemedicine and the other to support
`education and distance learning.
`
`2.2 ENTERTAINMENT BROADCASTING
`
`It is expected that analog television technology will gradually be replaced with
`digital technology. Entertainment television may be delivered to the homeusing
`
`
`
`

`

`8 Digital Video Communications
`
`terrestrial broadcasting, fixed cable networks, and/or satellite broadcasting,
`Standards [1-3] have been defined for digital television broadcasting. Digital
`television offers a number of advantages over analog television. Many fixed
`cable networksare already digital and provide a whole rangeof digital commu-
`nication services such as Internet access, home banking, and interactive shop-
`ping in addition to entertainment television. Digital compression techniques
`combined with advanced modulation allow very efficient utilization of band-
`width for broadcasting. This is extremely important whenthe radio spectrum
`is very congested. Four to five digital channels of comparable quality can be
`broadcast with the same bandwidth as one analog channel. Digital television
`facilitates the integration of television with the home computer system, thereby
`providing the user with muchgreater flexibility. Digital video can be stored on
`computer disks at a wide range of quality levels and can be used as an integral
`part of a computer software application.
`The replacementof analog with digital technologyis likely to be an evolu-
`tionary one wherein thefirst instance analog and digital systems coexist. The
`first users of digital television technology will buy a set-top box, which will
`demodulate and decodethe digital video signal. This will be converted to the
`equivalent analog signal and fed into a standard analogtelevision. Eventually
`this technology will be integrated into a single consumerproduct, possibly also
`including the home computer.
`
`2.3 VIDEO ON DEMAND
`
`Video on demandallows a user to request the video that they want to watch
`and have the requested program supplied to them. In somesenses, the video
`rental shop provides a very slow video on demandservice. Fixed cable networks
`provide the communications infrastructure to allow a user to select a video of
`interest electronically and have that video transmitted to them. Video on
`demand can be implemented in many different ways. The Internet does not
`yet reliably support real-time video traffic. In Chapter 4, we discuss how the
`Internet is evolving to become a suitable communications infrastructure for
`providing video on demand. Manycable television companies have communi-
`cation infrastructures capable of two-way communication and therefore are
`suitable for supporting video on demand. A video server consisting of a high-
`speed disk subsystem would be usedfor storing the video material. In Chapter
`5, we describe an example of a video on demand system that is being developed
`to deliver video-based computer-assisted learning material across a metropoli-
`tan area ATM network (ABMAN).
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`Applications for Digital Video Communications 9
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`2.4 CONFERENCING
`
`Conferencing applications are concerned with real-time two-way communica-
`tion and are designedto replace face to face communication.In order to provide
`effective interactive communicationit is necessary to limit the end-to-end delay.
`For delays greater than about 300 ms, interaction between people becomes
`difficult. Traditionally, videoconferencing has been performed using videocon-
`ferencing suites. These are rooms specially equipped with videoconferencing
`equipment. Traditionally, this videoconferencing equipment has been expen-
`sive and only available to large multinational organizations.
`Low-cost desktop videoconferencing systems are now emerging. These
`systems are usually integrated with a PC and consist of a small video camera
`and hardware- or software-based video compression/decompression adapters
`(CODECs). Conference participants are viewed in one or more small video
`windowson the PC screen. In addition, these systems usually support audio
`communication and data interchange. Increases in PC processing power are
`enabling high-performance video CODECsto be implementedin software, caus-
`ing the cost of the systemsto fall rapidly.
`Videoconferencing can be usedeffectively in a numberofdifferent applica-
`tion areas, usually with the aim of avoiding the inconvenience and/or cost of
`traveling. In the following sections we consider how videoconferencingis useful
`in the fields of telemedicine and distance learning.
`
`2.4.1 Telemedicine
`
`Telemedicine can be defined as medicine practiced whenthepatient is at a
`site that is at some distance from the doctor or medical expert. The practice of
`telemedicine makes use of telecommunications and information technology,
`includingdigital video communications, to providethis healthcareat a distance.
`In many areas of the world, major hospitals are a considerable distance
`apart. Healthcare is providedin the local community by a local health provider,
`which may be a smaller community-based health center or general practice
`hospital. Although these local centers can provide effective healthcare for many
`medical problems, there is frequently a need for patients with more specialized
`problemsto be referred to a major hospital. The costs required for this patient
`transfer can be considerable and may involvetransporting the patient by ambu-
`lance, helicopter, or airplane and at least an overnightstay at the major hospital.
`In manycases, this patient transfer could be avoidedif sufficient details of the
`patient’s conditions could be communicated to the consultants at the major
`hospital. Following a remote consultation with the general practitioners at the
`local center, it may be possible to decide on a course of treatment that can
`be administered locally. To make this procedureeffective, it is necessary to
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`10 Digital Video Communications
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`communicate sufficient patient details. Following this communication of
`patient details, it is also necessary to provide high-quality communication
`between the consultant at the major hospital and the local health expert.
`Patient information may include medical records stored on a computer
`database, digital images from patient scans or x-ray images, vital signs such as
`electrocardiograms, and either recorded or live video images of the patient.
`Live video images of the patient may provide the consultant with the ability
`to carry out a remote examination of the patient with the aid of the local health
`expert. This techniqueis referred to as telepresence.
`In order to make such a system work well, it is necessary to effectively
`integrate many separate pieces of equipment together and communicate the
`data from this equipment across the wide area. This requires that multimedia
`data is communicated over a communication network that supports the trans-
`mission of integrated services. In many situations the most challenging part of
`implementing this communicationsis the support of real-time two-way video-
`conferencing. The video requires large bandwidths even when compressed,
`which maystill be significantly higher than manyof the other data types. Two-
`way conferencingalso requires that end-to-end delays are minimized to provide
`effective interaction across the communication link. It is only in recent years
`that the communication systems capable of supporting this integration of ser-
`vices and the necessary digital video compression techniques have become
`available at practical costs.
`An example of a project concerned with implementing a telemedicine
`application is the Study of Video ImageTransfer: Orthopedics Up to Rehabilita-
`tion (SAVIOUR)project [4] that commenced in 1993. The project is funded as
`part of the European Union (EU) Advanced Informatics in Medicine (AIM)
`program. The SAVIOURproject is directed by the research unit of RGIT Ltd.
`(based in Aberdeen, Scotland) and the other project partners are The Robert
`Gordon University, Aberdeen Royal Hospitals Trust, and ABB-NERA Ltd.
`One of the purposesofthis project is to establish the practice of telemedi-
`cine between a local general practice hospital in Peterhead, whichis situated
`40 miles north of Aberdeen, and the Accident and Emergency Department
`of Aberdeen Royal Hospitals Trust. The project aims to largely use existing
`technologyto perform a clinicaltrial and in particular to investigate the interface
`between the telemedicine equipment and the clinicians rather than develop
`new technology. Two alternative communication systemsare available for use
`during the project. These are a basic rate Integrated Services Digital Network
`(ISDN) connection providing 128 Kbps anda satellite connection providing
`64 Kbps. In addition, the clinicians can communicate over the public switched
`telephone network (PSTN}. ISDN connections are widely available in the North
`of Scotland, but there are many other locations wherethis is not the case and
`the purpose ofthe satellite connection is to allow evaluation of the system for
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`Applications for Digital Video Communications 11
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`subsequent possible use in these situations. For example, the Health Division
`of RGIT Ltd. specializes in providing healthcare to remote and inhospitable
`locations, including a medical service to the British Antarctic Survey and to
`the British sector of the North Seaoil fields. In such situations, remote healthcare
`may be extremely beneficial since patient evacuation is very costly or even
`impossible.
`A block diagram of the SAVIOURsystem is shown in Figure 2.1. British
`Telecom VC-7000 videotelephone units are located at both of the sites to provide
`a videoconferencing capability. This provides the ability for ‘‘face to face”’
`consulting. The videophones implement the ITU-TS H.261 videoconferencing
`standard, which compresses the video to a data rate of either 64 Kbps or
`128 Kbps. Wediscuss this and other video compression techniques in Ghapter
`3. The quality of the video is acceptable, but significantly lower than (for
`example) standard VHS entertainment quality video. Another British Telecom
`product referred to