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`Library of Congress Cataloging-in-Publicatton Date
`
`O'Driscoll, Gerard.
`
`The essential guide to digital set—top boxes and interactive TV / Gerard O’Dnscoll.
`p.
`cm. -—- (Essentiai guide series)
`Includes bibliographical references and index.
`ISBN 0—13-017360—6
`
`l. Interactive telev1310n. 2. Interactive television—Equipment and supplies. 3.
`Gateways (Computer networks} 4. Internetworking (Telecommunication) I. Title. 11.
`Essential guide series (Prentice-Hall, Inc.)
`
`TK6679.3 037
`621 .388—dc21
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`99-05-1468
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`Overview of Digital TV
`
`in this chapter...
`
`- Terminology
`
`2
`
`What is Digital Television?
`
`3
`
`international Standard Bodies and Agreements
`
`5
`
`Building Blocks of a Digital TV System
`
`11
`
`Summary
`
`23
`
`
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`The tremendous potential of digital television is attracting interest from telecom-
`munications providers, computer manufacturers, network providers. consumer elec-
`tronic companies, and broadcasters around the world. Pay Per \fiew. high speed
`Internet access. video on demand, cable telephony, and e-commerce represent a por-
`tion of the new money Spinning ventures in which industry firms are investing increas-
`ing amounts of dollars and resources. This chapter acts as a foundation block for the
`technology discussions that follow in later chapters. Here. we introduce the basic con;
`cepts and benefits of digital television. Then we introduce the venous international
`standard bodies that are involved in establishing sets of technical specifications for
`implementing digital TV systems throughout the world. Finally. this chapter provides
`you with some detailed information abour how the components of the digital broad-
`casting environment work together.
`
`TERMINOLOGY.............................
`
`Before entering a detailed discussion about digital television systems. it is important
`that you understand a number of industry-specific terms. Here's a short list of the most
`important ones.
`
`Head-end ' An industry term that is used to describe a TV operator‘s main oper—
`ations center.
`
`Set-top box - A set-top box may be defined as a consumer electronics device
`used to decode and tune digital signals and convert them to a format that is understood
`by your television.
`
`MHz - MHz is an abbreviation for megahertz. One Ml—iz represents a million
`cycles per second. The speed of a processor in a digital set—top box (defined below) is
`measured in MHz.
`
`Bandwidth I If you have ever waited for a page to download into your PC on a
`Saturday evening. then you're already familiar with the concept of bandwidth. Think
`of bandwidth as a pipe that carries information. The less bandwidth you have, the
`longer the time it will take to download a Web page onto your PC.
`
`Return path ' Many of the digital TV services on offer require some form of
`interaction between the subscriber and either the program provider or the network
`operator. This interaction may consist of transmitting a couple of user commands but
`can be as extensive as the conununications required by a telecommunications link to
`the Internet. The term “return path” is used to describe the physical channel that facil-
`itates this two-way interaction.
`
`Protocol - A protocol is a formal description of the. messages that need to be
`exchanged and the rules that need to be followed for two or more systems to exchange
`information.
`
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`Network service provider - Many of the cable, microwave multipoint distribu-
`tion services (MMDS), terrestrial, satellite, and broadcasting companies are beginning
`to move into the telecommunications sector to offer a variety of services that have not
`been associated with their traditional TV—based offerings. Consequently, in this book
`we sometimes refer to this group of companies as service providers or network service
`providers. A network service provider will not only manage the network infrastruc—
`ture, but will also control the various services that run over its high-Speed networks.
`
`WHAT IS DIGITAL TELEVISION?
`
`.
`
`.
`
`.
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`.
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`.
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`.
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`.
`
`.
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`.
`
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`.
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`Digital television, commonly known as digital TV, is a completely new way of broad-
`casting and is the future of television. it is a medium that requires new thinking and
`new revenue-generating business models. Digital TV is the successor to analog TV
`and eventually all broadcasting will be done in this way.
`
`Around the globe, cable, satellite, and wireless operators are moving to a digital
`environment. Affiliates of the four major networks in the United States—ABC, NBC,
`CBS. and Fox were slated to begin digital broadcasts by November [999. By 2006, the
`Federal Communications Commission (FCC) in the U.S. has mandated that no more
`
`analog television signals be broadcast. In Europe, the digital TV train is also rolling out
`of the station, with broadcasters in France, Ireland, Spain, Germany, Holland, and the
`U.K. planned to launch digital technologies in 1999. Most industry analysts are pre-
`dicting that the transition to digital TV will be an evolution rather than a revolution.
`changing the way of life for hundreds of millions of families around the world.
`
`Companies are acknowledging that the convergence between personal comput-
`ers, TV sets, and the Internet has already begun and are positioning themselves to
`maximize revenue from this new computing paradigm.
`
`For consumers, the digital age will improve their viewing experience through
`cinema—quality pictures, CD-quality sound, hundreds of new channels, the power to
`switch camera angles, and improved access to a range of exciting new entertainment
`services. Digital TV also gives subscribers the opportunity to enjoy more program—
`ming through cinema-style wide screen TVs. Gone are the days of choosing between
`a small range of channels. Television will become more fun and powerful to use, yet
`at the same time simpler and friendlier.
`
`For the broadcaster, a move to a digital environment decreases the bandwidth
`utilization per channel, facilitates the offering of Internet applications to their sub-
`scribers, and opens a new era of business opportunities.
`
`The new digital technologies will allow cable companies, satellite providers, and
`wireless broadcasters to offer a variety of powerful revenue-generating services,
`
`including:
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`U Internet access at blazing speeds;
`
`rnulti-user network games:
`
`video on demand;
`
`streaming video and audio;
`
`home banking services;
`
`e-commerce applications:
`
`PC software upgrades;
`
`I Broadcasting rich multimedia content; and
`
`0 electronic newspapers.
`
`Digital television also opens up a new world of opportunities for companies who
`want to develop content and applications for the new paradigm. This includes the cre-
`ative communities within the television and film industry, Internet content providers.
`and software development houses, as well as new companies that will be created
`
`around this new industry.
`
`To fully understand digital TV. we need to look at its origin and how various
`compression and transmission technologies were used to revolutionize the television
`experience. For the past 50 years. broadcasters have been using analog signals as a
`means of transmitting TV to the mass market. During this period, we experienced the
`transition from the black-and—white sets to color TV sets. The migration required
`viewers to purchase new TV sets and broadcasters had to acquire new transmitters.
`posts and production equipment.
`
`The switch from black~and—white to color had palpable benefits for everyone.
`Today. the industry is going through a profound and amazing transition: migrating
`from conventional TV to a new era of digital technology. Television operators are
`upgrading their existing networks and deploying advanced digital platforms to open a
`new world of opportunities for consumers, content providers, and entrepreneurs.
`
`First, digital TV offers high speed data transfer rates. which make the delivery
`of rich multimedia content a reality. Second. many cable, terrestrial, and satellite com-
`panies are establishing themselves as Internet service providers, which will enable TV
`viewers to browse the Internet on their TV sets.
`
`Finally, the new medium will allow viewers from the comfort of their homes to
`use a simple remote control to electronically purchase goods and services offered by
`various content providers. Digital TV uses the same language as computers—a long
`stream of binary digits. each of which is either 0 or 1. With digital television. the sig-
`nal is compressed and only the updated data is transmitted. As a result. it is possible
`to squeeze six or eight channels into a frequency range that was previously occupied
`by only one analog TV channel.
`
`The digital TV cycle begins by recording a particular event or program with dig-
`ital equipment and is relayed to a redistribution center. In most cases. the redistribu-
`
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`tion center will be a cable, satellite, MMDS, or terrestrial operator. From here, the
`operators use specific transmission techniques to broadcast the new digital signal to
`subscribers on their network.
`
`INTERNATIONAL STANDARD BODIES AND
`
`AGREEMENTS
`
`Making digital television a reality requires the cooperation of a variety of industries
`and companies. along with the development of many new standards. A wide variety of
`international organizations have contributed to the standardization of digital TV over
`the past couple of years. Most standards organizations create formal standards by
`using specific processes: organizing ideas, discussing the approach, developing draft
`standards, voting on all or certain aspects of the standards, and then formally releas-
`ing the completed standard to the general public. Some of the best-known interna-
`tional organizations that contribute to standardizing of digital television include:
`
`I the European Telecommunications Standards Institute (ETSI);
`
`I Digital Video Broadcasting (DVB);
`
`I the Advanced Television Systems Committee (ATSC);
`
`I the Digital Audio Visual Council (DAVlC);
`
`I the European Cable Communications Association (ECCA);
`
`I CableLabs;
`
`I the W3 consortium; and
`
`I the Federal Communications Commission (FCC).
`
`Their contribution to the standardization process is explained and detailed in the
`following sections.
`
`Euro ean Telecommunications Standards
`Instl ute (ETSI)
`
`ETSI is a nonprofit organization whose mission is to determine and produce a wide
`range of telecommunication standards. It is an open forum that unites approximately
`647 members from countries all over the globe, representing administrations, service
`providers, manufacturers, and end-users. Any European organization proving an inter-
`est in promoting European telecommunications standards has the right to represent
`that interest in ETSI and thus to directly influence the standards-making process. ETSI
`consists of a General Assembly, a Board. a Technical Organization, and a Secretariat.
`The Technical Organization produces and approves technical standards. It encom-
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`passes ETSI projects, technical committees, and special committees. More than 3,500
`experts are at present working for ETSI in over 200 groups. (Additional information
`about ETSl is available from their web site at http://wwwetsio‘rg/l.
`
`Digital Video Broadcasting (DVB)
`
`The DVB project was conceived in 1991 and was formally inaugurated in 1993 with
`approximately 80 members. Today, the DVB project has made huge advancements and
`boasts a membership of over 230 organizations in more than 30 countries worldwide.
`
`Members of the group include electronic manufacturers, network operators,
`broadcasters, software companies, and various regulatory bodies.
`
`The DVB project has been a big success and has generated various standards for
`delivering digital TV to people throughout Europe. Asia, Australia, and North America.
`
`The work of the DVB project has resulted in a comprehensive list of technical
`and nontechnical documents that describe solutions for implementing digital televi-
`sion in a variety of different environments.
`
`The international standards and solutions developed by DVB over the past few
`years can be classified and summarized as follows:
`
`1. DVB-S—An international standard for transmitting digital
`
`television
`
`using satellites.
`
`2. DVB-C—An international standard for transmitting digital
`using digital cable systems.
`
`television
`
`3. DVB -T-—An international standard for transmitting digital television in a
`terrestrial environment.
`
`4. DVB-MC/S—An international standard for transmitting digital television
`using microwave multipoint video distribution systems.
`
`5. DVB-Sl—An international standard that defines the data structures that
`
`accompany a digital television signal.
`
`6. DVB—CA—An international standard that defines digital television secu—
`rity standards.
`
`7. DVB-CI—An international standard that defines a common interface to
`
`the digital TV security system.
`
`8. DVB-I—An international standard for deploying interactive TV.
`
`9. DVB-Data—An international standard designed to allow operators to
`deliver software downloads and high speed data services to their customers.
`
`10. Interfaces—An international standard that defines digital TV interfaces to
`high speed backbone networks.
`
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`
`The Standard for the
`
`Digital World
`
`Figure 1 .l
`DVB Logo
`
`Copies of these standards are available for download on ETSI‘s web site.
`
`DVB-compliant digital equipment is widely available and is easily identified by
`the DVB logo illustrated in Figure 1.1. The DVB has had its greatest success in
`Europe, however the standard has implementations in North and South America,
`Africa, Asia, and Australia. For additional information about DVB, visit their web site
`
`at http://www.dvb.org/.
`
`Advanced Television Systems Committee
`(ATSC)
`
`The ATSC committee was formed to establish a set of technical standards for broad-
`
`casting standard and High Definition TelevisiOn (HDTV). Pictures based on this stan-
`dard can have 3 to 5 times the sharpness of today’s analog broadcasts.
`
`The committee is composed of 136 member organizations, standard bodies, IT
`corporations, educational institutions. and electronic manufacturers. It has been for-
`mally adopted in the United States. where an aggressive implementation of digital TV
`has already begun.
`In addition to the U.S., Canada, South Korea, Taiwan, and
`
`Argentina have also adopted the ATSC digital TV standard for terrestrial broadcasts.
`A sample of the ATSC standards are outlined in Table 1.1.
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`Table 1.!
`
`ATSC Standard Documents
`
`Document Standard Description Brief Overview
`Number
`
`Web Address of
`Detailed Document
`
`N52
`
`ATS? Digital Audio
`Compression
`
`Specifies coded represen-
`union of audio inlormation
`
`mtit.atsc.orgl’StandardsKAS33'
`
`and the decoding process.
`as well as information on
`
`the encoding process
`
`A/53
`
`ATSC Digital
`Television Standard
`
`Specifications and charac- www.atsc,orgl’Standards/Afiill
`teristics for an advanced
`
`TV (ATV) system
`
`AIS-l
`
`ATSC‘ Guide
`
`Description of ATV system www.misc.orngtandnrdsfx—XS-l.’
`
`N64
`
`Transmission measure- Description of measure-
`
`wwwatsc.org/Standardsl’Adéil‘
`
`merit and compliance
`for digital television
`
`ment and ATSC compli-
`ance system
`
`This table only displays a snapshot of the ATSC standards. To review the com-
`plete listings of ATSC standards, we recommend you visit the ATSC Web page at
`http:f/www.atsc.org/Standardslstan_rps.html for a more detailed listing.
`
`For the latest information and updates about ATSC, visit their web site at
`httpzflwwwatseorgl.
`
`Digital Audio Visual Council (DAVIC)
`
`The organization was formed in 1994 with the aim of defining standards for the end-
`to-end transfer of digital audio. video, and Internet-based content.
`
`DAVIC is a nonprofit standards organization currently located in Switzerland. The
`organization currently has a membership of over 180 companies from 25 countries around
`the globe, representing companies and individuals from all sectors of the audio—visual
`industry. DAVIC members meet on a regular basis to define specifications and use their
`web site (wwwdavicorg) to collaborate and implement various international projects.
`
`European Cable Communications
`Assocmtion (ECCA)
`
`ECCA is the European Association of cable operators. The main goal of the
`Association is to foster cooperation between operators. and to promote their interests
`
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`at a European level. ECCA gathers European cable operators, consisting of more than
`40 million subscribers. The first informal cooperation between European cable opera-
`tors started in 1949. As these informal meetings became more frequent, a formal struc-
`ture for European cooperation was required and on September 2, 1955, the Alliance
`
`Internationale de la Distribution par cable (AID) was set up by representatives of
`Switzerland, Belgium, and The Netherlands. In 1993, AID was renamed the European
`Cable Communications Association.
`thus stressing the communication role of its
`members as well as its European goals.
`
`ECCA now has 29 members in 17 countries. It also has 5 associate members in
`
`central and eastern Europe. ECCA has considerably contributed to European policies
`related to cable on the regulatory as well as on the technical standards field.
`
`On the regulatory, ECCA has done a lot of work on areas such as digital TV,
`copyright, must-carry, and open—access issues. In addition to these projects. ECCA
`members have also compiled the following technical specifications.
`
`E urobox
`
`On initiative of the ECCA organization, a common specification for cable set-top
`boxes following DVB standards was agreed upon by a large number of cable opera-
`tors in Europe (the Eurobox platform).
`
`The Eurobox platform was set up in 1997, and has more than 5.5 million sub—
`scribers. A more detailed description of the Eurobox is available in Chapter 5 of this
`book.
`
`Euromodem
`
`A collective resolution to develop a global standard for high speed cable modems was
`signed at the ECCA Cable Forum in November 1998. The standard fully complies
`with European standards and with several DVB specifications. The ECCA group has
`considered two different types of modems: class A and class B. Class A modems are
`capable of transmitting data at very high speeds in a downstream direction (maximum
`of 50.8 Mbits/sec) and 3 Mbits/sec in the upstream direction. They are capable of
`accessing the Internet at high speeds and support a number of security technologies.
`Class B is the second type of modem considered by the group. It extends the func-
`tionality of class A devices through the support of time critical services such as video
`conferencing and telephony. At the time of going to press, a number of electronic man-
`ufacturing companies were invited to submit plans to manufacture modems compliant
`with the Euromodern standard.
`
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`Cable telephony
`
`On the basis of the full liberalization of the telecommunications sector in Europe,
`cable companies, satellite providers, and terrestrial broadcasters in different countries
`are planning to become competitors to the local telephony companies. Therefore, their
`networks are being or have been upgraded to broadband telecommunications net-
`works. which are able to provide all kinds of services from telephony and local
`Internet access to high speed broadband connections. ECCA is also actively working
`in this area. For additional
`information about ECCA. visit
`their web site at
`
`http:lfwww.ecca.bel.
`
`CableLabs
`
`Cable Television Laboratories, Incorporated (CableLabs), was originally established
`in May 1988 as a research and develoPment consortium of cable television system
`operators. To qualify as a member of CableLabs. a company needs to be a cable tele-
`vision system operator. CabieLabs currently represents more than 85. percent of the
`cable subscribers in the United States. 70 percent of the subscribers in Canada. and 10
`percent of the subscribers in Mexico. CableLabs plans, funds. and implements a num-
`ber of research and projects that help cable companies take advantage of future Oppor-
`tunities in the areas of digital TV, telephony. and high speed lntemet. For additional
`information about CableLabs. visit their web site at http:l/wwwcablelabscomf.
`
`W3 Consortium (W3C)
`
`The W3 Consortium (W3C) was originally founded in 1994 to lead the World Wide
`Web to its full potential by developing common protocols that promote its evolution
`and ensure its interoperability. The organization is an international consortium, joint-
`ly hosted by the Massachusetts Institute of Technology in the U.S; an organization in
`EurOpe called the Institut National de Recherche en Informatique et en Automatique,
`and Keio University in Japan.
`
`The consortium provides a range of services. including: a repository of infor-
`
`mation about the World Wide Web for developers and users; reference code imple-
`mentations to embody and promote standards; and various prototype and sample
`applications to demonstrate use of new technology. For detailed information about the
`W3C, visit their web site at http://www.w3c.org/.
`
`Federal Communications Commission (FCC)
`
`The Federal Communications Commission (FCC) is an independent United States gov—
`ernment agency. directly responsible to Congress. The FCC was established by the
`
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`30
`
`BASICCONCEPTS
`
`When you think of a set-top box. you generally picture a TV set and a black box con-
`nected to the set with lots of wires. The true picture of a digital set-top is one of a com-
`plex electronics device comprised of many hardware and software components.
`
`It is usually connected to your TV set and the cable connection on the wall. Your
`local cable. terrestrial, or satellite operator normally installs these devices. This may
`change soon when set-top boxes enter retail stores across the globe. Set-top boxes can
`also be descfibed as types of computers that translate digital signals into a format.
`which can be viewed on a television screen.
`
`The main features of a set-top box may be classified as folloyvs;
`
`O decodes the incoming digital signal:
`
`verifies access rights and security levels;
`
`displays cinema-quality pictures on your TV set:
`
`0 outputs digital surround sound: and
`
`I processes and renders lnternet and interactive TV services.
`
`HOWASET-TOPWORKS......................
`
`Basically. the tuner in the box receives a digital signal from a cable. satellite. or ter-
`restrial network and isolates a particular channel. The signal is then forwarded to a sil—
`icon chip called a demodulator and convened to binary format. Once in binary format.
`the demodulator will check for errors and forward the binary signal to another chip
`called a denrulriplexer. This chip will then extract the audio. video. and data from the
`binary stream and send the data to the appropriate decoder chips. This demultiplexer
`chip may also work with the security subsystem to determine your access rights to var-
`ious Internet and digital TV services.
`
`the three decoders will
`Once the demultiplexer has finished with the signal,
`transform the digital bits into a format suitable for viewing on your television.
`
`UNDERTHEHOOD..........................
`
`At the moment. every network operator has unique set—top box requirementsTherefore,
`manufacturers are forced to have a distinct design for each operator. Hence. the archi—
`tecture we describe in this chapter is for a pretty advanced set-top box and is not spe-
`cific to any network operator or set-top box manufacturer.
`
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`The physical components may be roughly divided into the following categories.
`
`31
`
`system board.
`
`tuner(s),
`
`modulator and demodulator,
`
`demultiplcxcr and decryptor,
`
`decoders.
`
`graphics processor,
`
`I CPU and memory,
`
`I storage devices,
`
`0 physical interfaces, and
`
`I physical characteristics.
`
`If we look more closely at the architecture of a digital set-top in Figure 2.3, you will
`notice that the hardware architecture is very similar to a standard desktop multimedia
`computer. This figure shows an expanded and simplified view of a set-top box capable of
`supporting broadcast analog, broadcast digital, and interactive digital transmission.
`
`System Board
`
`If you were to open up your digital set-top and look inside, you would see a large
`printed circuit board: the system board. All the main hardware components of the set-
`top are connected to the system board. The digital TV information is carried between
`set-top hardware components using buses. The system board is made of a fiberglass
`sheet that has miniature electronic circuitry embedded in it.
`
`This digital information is in the form of bits and bytes. A bit is the smallest unit of
`information that can be processed by a set—top. A single bit can hold only one of two
`values: zero or one. A byte contains more meaningful information and is obtained by
`combining 8 consecutive bits. A byte represents one American Standard Code for
`Information Interchange (ASCII) character inside the digital set—top. ASCII is a code
`used to represent English characters as numbers. For example, if a subscriber uses a
`wireless keyboard to type A on the TV screen, this character is processed within the
`set-tori as 01000001. You can think of a bus as a type of highway or pathway in which
`data travels within a digital set-top box.
`
`The width of this bus determines how much data can be sent between internal set-top
`box components. For example, an 8-bit bus is capable of transmitting 8 bits of data.
`whereas a 16-bit bus is capable of transmitting double the amount of information.
`
`In addition to bus width. set—top designers also measure the clock speed of a bus to
`determine how fast interactive TV applications can run within the box. All buses on
`the system board consist of two parts: an address bus and a data bus. As the name sug—
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`Apple 1010
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`Electrically Erasable Programmable Read Only Memory (EEPROM)
`
`EEPROM is a special type of memory used in set-top boxes to store controls and
`boot up information. The data is permanently stored on the chip. even when the sub—
`scriber powers off the set-top box.
`
`To remove this control information you need to expose the EEPROM chip to
`ultraviolet light and electrical charges. A set-top box will contain a small amount of
`EEPROM ( usually kilobytes) and has slower access rates than RAM.
`
`FLASH Memory
`
`A Flash memory chip is very similar in functionality to an EEPROM. The only
`difference between the two is that a Flash memory chip can be erased and repro-
`grammed in blocks of data bytes instead of one byte at a time. This feature allows
`operators to update the seHop's operating system and resident software applications
`over the network without physically visiting the subscriber’s home place.
`
`This update can be done in either the foreground or the background. A fore-
`ground set-top software update is very intrusive to the viewing experience. A message
`normally appears on the TV screen notifying the viewer that a code update is avail-
`able. If the subscriber chooses to proceed with the update, the set-top box is taken off
`line while the software update occurs.
`
`Foreground updates can take as little as two minutes or as long as a half an hour.
`depending on the write performance of the Flash memory and the amount of code that
`needs to be downloaded. Set-tops designed for foreground updates require less Flash
`memory and often rely on a single flash component. By contrast, a background update
`does not interrupt the viewing experience. The viewer is not even aware an update is
`taking place. In this case. the set-top contains two Flash memory devices. The first
`device stores the existing code while the second is used for updates. The system switch-
`es to the flash device with the new code when the power is recycled. An onscreen dis-
`play will notify the subscriber of the new features that have been installed. While this
`method of downloading software is more elegant.
`it is obviously more expensive.
`Besides using Flash memory to store software code. it can also be used to store sub-
`scriber-specific infomiation. Every time a customer makes a purchase or visits a site on
`the Internet, details of this action are stored in the flash for marketing purposes.
`
`Unlike a hard disk, Flash memory is a solid-state device. It has no mechanical
`
`parts and therefore provides subscribers with instant performance without suffering
`from long seek times.
`
`The recommended minimum memory configuration for a digital set—top box is 8
`MB of RAM, 2 KB of EEPROM, and 8 MB of Flash memory.
`
`If you decide to add additional memory. it is important that you purchase mem-
`ory that matches the speed requirements of your set-top.
`
`Digital set-top boxes were released in 1999 with the following memory configu-
`rations.
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` Memory Type
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`Quantity
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`RAM
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`Flash Memory
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`EEPROM
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`24 MB
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`16 MB
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`400 KB
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`Storage Devices
`
`The ability to locally store and retrieve information is expected to become the most
`important commodity for customers of digital TV services. While the storage space on
`the first generation of set-tops was limited to Flash memory, today we are beginning to
`see designers adding interfaces to the motherboard that will allow subscribers to inte-
`grate high capacity hard drives into their set-top boxes. The capacity of a hard drive is
`measured in gigabytes (GB) and may be used by subscribers to store personal docu-
`ments, favorite Internet sites, and e—mail. The basic architecture is comprised of mag-
`netic-coated circles of material that contain stored information. These circles are called
`
`platters and are stacked on top of each other to increase the storage capacity of the drive.
`Information is read from or stored to the hard disk using read and write heads.
`
`Hard disks can be integrated within the set-top or else connected as an external
`device through high-speed data port interfaces. There are two disk interface technolo-
`gies that are currently competing for a slice of the set-top market: Small Computer
`Systems Interface (SCSI; pronounced “scuzzy") and Integrated Drive Electronics
`(IDE). Drives with an IDE interface are capable of transferring data within a set-top
`at speeds ranging from 3.3 Mbps to 16.6 Mbps. SCSI hard drives offer subscribers
`faster access and retrieval times, but they are more expensive than IDE-based drives.
`Disk drives are capable of retrieving data at high-speeds. In the early days of hard disk
`manufacturing, drives were only capable of storing around 10 or 20 MB of data. Now,
`drive capacities have increased dramatically and costs of manufacturing hard disks
`have plummeted downward. Today, a standard PC will come with a 9-GB drive for
`storing program and data files. By adding high capacity drives to set-top boxes, digi-
`tal TV subscribers will be able to download and store digital movies. At the time of
`this writing. a 17.2-GB drive could be purchased for around $120. This gives cus-
`tomers the ability to store four m