• Providing Video Films on Demand
• Local News and Weather Forecasting
• Games, Music and Leisure
• Education and Remote Learning Facilities
• Home Shopping and Other Consumer Services
• Banking

Fig : An interactive user 云南博客!]4~0[I'X]8?
interface under development by BT

2 : Video on Demand : a Brief Look

Formats...
7Qe*go+C&FW4K7{0Prerecorded videos be digitally stored in a video server. These videos are then transmitted in a coded, compressed format. After the videos are ordered (either via interactive voice response or two-way remote control), they are decoded and decompressed by set-top converters in individual homes. In preliminary demonstrations, picture quality has been equal to standard VHS.

Functionality...
6T1Wyt;C`]0The customer can call on a range of services. While watching movies, performing operations such as video selection, pause, rewinding etc. can be selected as if it were a video player. These are processed by the set-top-box and sent to the local server. The local server processes the request if possible, otherwise it relays the request to a video archive server, much as a hierarchy system.

Network..云南博客RggRM
Video-on-Demand currently runs over cabled networks, the most widespread being the standard telephone line. The difficulty in this, though, is the relatively low transmission speed of the telephone line.

To overcome this shortfall, there are several viable networking standards, developed for multimedia transmission over the Internet as explained later.

We will now examine the roles of the set-top-box, video server storage, Media compression standards and Transmission protocols. Following that, we shall see how these relate to VoD.

3 : Into the Details..

3.1 : Set-Top Box

3.2 : Video Server

• Capacity to hold hundreds of Mbytes (or perhaps order of Terabytes) of digital information
• Provide simultaneous access to several hundreds (or thousands) of subscribers on real-time, giving each one an appropriate bandwidth (usually in the order of 1.5-6 Mbps)
• Make economical use of resources by dynamically allocating programmes into different media such as Magnetic tape, optical W/R disks, hard disks, by considering the relative usage and level of interactivity supported.

As the table 1 highlights, solid-state storage as RAM is prohibitively expensive. On the other hand, cheap alternatives such as tapes limits the sessions per device and also impose difficulties in virtual VCR functioning.

There are several important considerations in designing a feasible video server:

1. Hierarchical storage scheme
2. Scalable Architecture
3. Storage Subsystem
4. Expanded Storage

Fig : A loosely coupled implementation of a Video storage system
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2. Scalable Architecture : 云南博客r'AR F!c$Y$k
The server system should be expandable both in terms of the number of titles held and the number of subscribers. This can be achieved by incoorporating set of parallel data servers and a name server to store the location and access control information of the programmes, as shown in the figure. Thus any user request is served by first accessing the Name Server to locate the appropriate Data Server.

3. Storage Subsystem :
2oP5g|xqT t#?0The storage subsystem consists of control units, disk/tape storage and access mechanism.

There are several techniques to increase the performance by interleaving digital data of a programme on multiple disks:

• Striping involves interleaving portions of disk blocks on multiple disks. The aim here is to reduce the latency for block access by parallel reading of the complete block.

• Declustering, on the other hand, distributes blocks of files on several disks, thus allowing parallel block access from the same file and increasing the rate of the video stream.

• The overall performance can also be enhanced by replicating files among the servers by considering the demand for a programme, relative dispersion of subscribers and the access patterns (eg: time/day of peak access, average number of simultaneous viewers..)

4. Expanded Storage (ES) (ie. solid-state memory) containing RAM modules would be the best for storing programmes with the highest demands, as in theory, ES has infinite bandwidth; and in practice the transfer rate is only limited by the system bus speed.

3.3 : Audio/Video Standards

Apple Quicktime

Apple Quicktime is a motion picture compression standard which is currently used for video conferencing. Quicktime provides constant play speed, but when transmission rates slow down, picture quality is compromised: the images blur, frame. skipping occurs, causing jerkiness.

Quick-Time is being used for media-compression by several firms including BT, MGM and Bell Atlantic (US). Apple is working with a number of partners on the development of an interactive television set-top box, based on the PowerPC processor. Apple is also developing a proprietry set-top-box based on PowerPC processor for Quick-Time compatibility.

Motion Picture Experts Group (MPEG)

MPEG is a group of people that meet under ISO (the International Standards Organization). They generate standards for digital video (sequences of images in time) and audio compression. MPEG works closely with many international standards bodies:

• jointly with the ITU-TS for ATM Video Coding.
• collaborates with representatives from EBU, ITU-RS, SMPTE, and the North American High Definition TV community.

MPEG video has a compression ratio of about 26:1 while that for audio goes up to 7:1.

Real time MPEG encoding (and decoding, of course) hardware exist, costing from US$10,000. There are several MPEG decoding chips available since 1993, such as;

• SGS-Thompson STi-3500 - The first MPEG-2 chip on market
• LSI Logic L64112 successor - capable of 15Mbit throughput
• IBM Single-chip decoder (http://www.crs4.it/~luigi/MPEG/ibmchip.html)

MPEG is currently being adapted to many applications:

• MPEG-2 video and audio will be soon used in DSB (Direct Satellite Broadcast) with Thomson's STi-3500 architecture in DirecTV in N. America.

• The Cable Industry has more or less settled down for MPEG-2, but with conflicting options for audio standards. (Eg: Generl Instruments, US's lagrest cable TV set-top box manufacturer, has announced the Dolby AC-3 as thier future audio standard.)

• The US Grand Aliance, a consortium for US terrestrial HDTV standard, has already agreed to use MPEG-2 Video and System Syntax.

Comparison of Quicktime and MPEG compressions

Click here for Quick-Time G_'R:Uz0video clips from Speechless云南博客"\`}R m6~)rz-M2{ and Tankgirl.		Click for an MPEG encoded云南博客-Um2V]4EZs L movie clip from Under Siege

Caution : The movies are over 1 Mbyte in length. This may云南博客6S Xb0Z|
take a considerable time in heavy traffic periods.

3.4 : Transmission Protocols

ISDN (Integrated Services Digital Network)

ISDN is a set of communications standards allowing a single wire or optical fiber to carry voice, digital network services and video. ISDN is intended to replace POTS (Plain Old Telephone System) and differs in the telephone company central switches, software and other equipment. Its bandwidth standards range from 64 kps up to 2.0 Mbps. ISDN is the current affordable alternative to POTS and is avaliable readily in Australia, France, Japan and Singapore, with the UK somewhat behind and availability in the USA rather spotty.

ADSL (Asymmetric Digital Subscriber Loop)

ADSL has the advantage that it runs over the current twisted pair copper (POTS) phone lines addressing the problem with changing to coax/fiber: For example, in New Jersey, Telcos phone company installs new cabling up to 7% of their installed access line base per year, itself growing at about 3% annually. Hence, the net upgrade to overhaul the network at 4% annual would take 25 years, after Telcos reach top speed. ADSL presents the solution using POTS.

ATM (Asynchronous Transfer Mode)

ATM is a current research hot topic. It is a method for dynamic allocation of bandwidth using a fixed 53 byte packet (cell), known also as "fast packet".

1. Scalable technology; potential for extremely high speeds.
2. Cell switching, a compromise between delay-sensitive and conventional data transmissions.
3. Flexible implementation on many media (copper, coax, fibre).

4 : Summary

Video/audio compression & standards

MPEG-2 becomes the Standard

Transmission protocols

ATM is ideal for its high bitrate. A shortfall for linking ATM all the way to the home is the enormous cost of the equipment and the sheer size (currently the size of a medium TV). This makes ATM an unfeasible solution for the time being.

5 : The Future : Developments, Concerns and Fears

Fig: An HDTV with 3D displaying developed by NHK, the telecomm giant in Japan. Such products have a great potential to make fully operational IMMSs a reality in the near future.

© NHK, Japan

Customer drift
(FR3?J:Pdw0As the total subscriber population is almost constant, the revenues for VoD services largely depends upon whether it is implemented jointly with CATV or as a rival alternative; In the latter case, the drift of viewers from conventional media to interactive services would cause less revenue for both.

Role of Advertising 云南博客UMX/}B|3|LM D
Broadcasting companies get the bulk of income from advertisers. No doubt that the VoD system coming will still contain advertisement of some kind, possibly interactive. Highlights of advertisements may be screened on regular media as they are currently.

Issues on Copyright
-R+j#f\&N `[0 Copyrights and piracy may prove to be something difficult to enforce once VoD is born. There is little doubt that people will record movies using home VCRs and lend them to friend or neighbours. Illegal video shops could flourish when it becomes much easier for them to obtain movies, and sell these to residents not willing to pay for overheads of installing VoD.

"Do the viewes want to be libetared to be interactive ?"
(sG!\(o,]] Hv9{0 An ordinary viewer sticks to an average of 7 channels, regardless of the sheer availability of 50-plus alternatives in CATV. Viewers also show strong habits of watching a "strip" of programs and flipping through channels. Consequently, VoD applications need well structured indexes and user friendly menus for quick browsing.

6 : Conclusion

Video on Demand is an important aspect of this interactive media technology that is currently conquering the information systems worldwide. VoD systems will definitely add a new meaning to the home entertainment, and also will change many aspects of public media such as programme making and advertising.

Looking at current research and trials, VoD is likely to be initially implemented over ADSL technology until ATM becomes available. MPEG has conquered huge grounds as far as standards go and make great efforts to ensure that they remain as international standards for moving picture coding.

Video-on-Demand is set to become the future home entertainment system, though it isn't about to happen 'by storm' before ATM is realized. Much work is ongoing, and we should expect to see results within the next two years!

APPENDIX A : CASE STUDIES

Q$y.FHw2y?;x5a l0This type of an Interactive Multi-Media Interface would be a commonplace in future homes..

The figure shown here is an Algebraic Video Systems Browser
/\;q"ilwq8z0facility for digital video presentations.
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Although not fully compatible with True-VoD, there are several operational VoD-related services available, mainly in US and also in some other countries.

PACIFIC BELL : The California First Plan

In 1994, Pacific Bell, a regional subsidiery of Bell Operating Companies, US, announced the plans to build an interactive video platform. throughout California at a cost of $16 billion. With partnership with AT&T, Pac-Bell was expected to provide a full range of interactive services, including movies on-demand, time-shifted TV, interactive news, tele-education, home shopping, video games, and electronic citizenship. The company might also develop "an interactive home improvement channel" and "access to community experts on a wide range of issues." The initial implementation was carried out in San Francisco, Los Angeles, Orange County, and San Diego.

Essentially, the upgrade will add ATM capabilities to its existing fiber-coaxial trunk, and transport broadband services to powerful 750 MHz digital nodes serving 500 homes apiece. It will also replace the copper wire that leads to most residences with coaxial cable.

More than two million homes and one million businesses will be served after the first phase of construction, in 1996. More than 5.5 million homes-or roughly 50 percent of Pac Bell's customers will ultimately be served, by the end of this decade.
q1T p?6Pu*R+?)O`0[source : Interactive Television Testbeds, Working Paper #7, Benton Foundation. ]

Interactive Movies : Making of World's First Interactive TV Series

With the aid of one of their own budding CD-i technology, Philips Interactive Media Inc., made another revolution in games industry: Creating a hybrid movie-game version of Hulk Hogan's Thunder in Paradise on CD, making in the first ever interactive movie.

Directed by two people, one for the TV series and the other for the "interactive" version, Thunder would really involve the player into the sequel, by giving him the opportunity to determine the subesequent events in the game /movie.

With picture quality better than VHS, Philips hopes to sell around 500,000 copies of Thunder worldwide: "At least one per every CD-i unit" David McElhatten, president of Philips Media Games says, "We have further plans for 3 other major interactive movies with Paramount Pictures, including a version of Star Trek... We explore a whole new technology here, and as far as I can see, the sky's the limit...!"

The boys will go where none has ventured before...
FwA P-{:S?.NC0But better still, you will be able to determine 云南博客N,On S.u3G
their destiny with Philips' Interactive Movie..

CellMaster : ATM-ADSL Interconnections

Cell-Master is one such product and is installed in the local exchange. It can accept an ATM input (e.g. at 155 Mbit/s) and to regenerate forty E1 data-streams from this single ATM connection. With two CELL-MASTERs you could thus regenerate eighty 2 Mbit/s data-streams. These steams are connected to lots of ADSL modems in the exchange, then linked to individual homes via telephone wires. There, an ADSL modem receives the signal, which is passed on to the set-top-box, regenerating the video images.

"Quality is a matter of opinion. E1 rate MPEG-2 is OK but nowhere near BBC broadcast quality."
m] s)tpw_$H0- Kim Booth, Cellware.

APPENDIX B :

Acronyms

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• ADSL : Asymetric Digital Subscriber Loop
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• AES : Audio Engineering Society 云南博客3isf'N e8Cv,T h1N
  
• ATM : Asynchronous Transfer Mode
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• CATV : Community Antenna (Cable) TV 云南博客M%t8ToYI
  
• SCSI : Small Computer System Interface 云南博客s)s"y)| txb0vm
  
• DSB : Direct Satellite Broadcast 云南博客5x0c MQ1V/H\
  
• EBU : European Broadcast Union 云南博客 O,~HM$S
  
• HDSL : High speed Digital Subsriber Loop 云南博客 \$Q2b6n#E-T,]gG][
  
• HDTV : High Definiion TV 云南博客z1?C{EgB&x#W!c`
  
• ITU-T : International Telecommunications Union, Telecommunication standardisation sector 云南博客8I ?NM)Fg2QU
  
• IMMS : Interactive Multi-Media Systems
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• ISDN : Integrated Services Digital Network 云南博客Ne"l7u0L6b#\*H/BA
  
• ISO : International Organization for Standardization 云南博客B~'RS]i
  
• MPEG : Moving Pictures Expert Group 云南博客1f1ta+m,~O+Q[L
  
• NTSC : National Television Systems Committe 云南博客pjgD z~
  
• POTS : Plain Old Telephone System 云南博客oj;\!^xOo&h
  
• SMPTE : Society of Motion Pictures and Television Engineers 云南博客4D$I&pwFY H L*r+z
  
• S-VHS : Super Video Home System 云南博客mwos]G$k
  
• VHS : Video Home System
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• VoD : Video-on-Demand

APPENDIX C

References :

1. 1993-94 Annual Review of Communications:
   1. Prospects of Video on Demand, August E. Grant, Univ. of Texas
   2. A Hewlett-Packard Video Server, Daniel Pitt & Manu Thapar, HP Labs.
   3. 21st century TV: Cable TV and the Information Age, Roger Pience, NCTA Science & Technology

2. Computer Weekly, April 27, 1995
3. First Interactive Movie, CD-ROM Magazine, August 1994.
4. IEEE Multimedia, Fall 1994
5. Making a Cost-Effective Video Server, Y. Doganata & A.Tantawi, IEEE Multimedia, Winter 1994.
6. I nteractive Television Testbeds, Working Paper 7, by Peter Krasilovsky,Benton Foundation. (http://www.cdinet.com/benton/Catalog/Working7/working7.html)
7. IBM Introduces MPEG-2 Decompression Device, FISHKILL, N.Y., July 26, 1994 (http://www.crs4.it/~luigi/MPEG/ibmchip.html)
8. CellWare Information Service, Germany. (http://www.cellware.de/systems/vod.html)
9. ADSL Forum, Jason Dominguez, On-Line Publishing Specialist (http://www.sbexpos.com/sbexpos/associations/adsl/home.htm)
10. ISDN (http://www.combinet.com/ISDN1.html)
11. ATM applications, Allen Robel, Senior Network Engineer, Indiana University (http://www.telematrix.com/vendor/igi/publications/atm1294.html)
12. Quicktime Conferencing, Apple Computer, Inc. (http://quicktime.apple.com/qtconf.html)
13. MPEG Standards, Cho Han Wook, Scientific Visualization Group, CRS4. (http://vod.isl.goldstar.co.kr/doc/mpeg/mpeg.html)

Comments and suggestions to
G6hqL'DfH0 DP Quek
S3tKv@n0 SH Rajapakshe