Microsoft
`Broadcast Technologies White Paper
`
`
`
`Introduction to Broadcast Architecture
`
`This paper provides an overview of what broadcast-enabled computers are, how they work, and what
`opportunities they offer.
`
`Contents
`Overview of Broadcast-Enabled Computers ............................................................................................................ 3
`A Brief Look at the New Technology ...................................................................................................................... 7
`Implications and Applications of the New Technology ......................................................................................... 11
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`© 1997 Microsoft Corporation. All rights reserved.
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`SAMSUNG 1021
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` Introduction to Broadcast Architecture — 2
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`This document is for informational purposes only. MICROSOFT MAKES NO WARRANTIES, EXPRESS OR
`IMPLIED, IN THIS DOCUMENT.
`Microsoft Corporation may have patents or pending patent applications, trademarks, copyrights, or other
`intellectual property rights covering subject matter in this document. The furnishing of this document does not
`give you any license to the patents, trademarks, copyrights, or other intellectual property rights except as
`expressly provided in any written license agreement from Microsoft Corporation.
`Microsoft does not make any representation or warranty regarding specifications in this document or any product
`or item developed based on these specifications. Microsoft disclaims all express and implied warranties,
`including but not limited to the implied warranties or merchantability, fitness for a particular purpose and
`freedom from infringement. Without limiting the generality of the foregoing, Microsoft does not make any
`warranty of any kind that any item developed based on these specifications, or any portion of a specification, will
`not infringe any copyright, patent, trade secret or other intellectual property right of any person or entity in any
`country. It is your responsibility to seek licenses for such intellectual property rights where appropriate.
`Microsoft shall not be liable for any damages arising out of or in connection with the use of these specifications,
`including liability for lost profit, business interruption, or any other damages whatsoever. Some states do not
`allow the exclusion or limitation of liability or consequential or incidental damages; the above limitation may not
`apply to you.
`ActiveMovie, ActiveX, BackOffice, Developer Studio, Direct3D, DirectDraw, DirectInput, DirectPlay,
`DirectSound, DirectVideo, DirectX, Microsoft, NetMeeting, NetShow, Visual Basic, Win32, Windows, and
`Windows NT are trademarks or registered trademarks of Microsoft Corporation in the United States and/or other
`countries. Other product and company names mentioned herein may be the trademarks of their respective owners.
`© 1997 Microsoft Corporation. All rights reserved.
`
`© 1997 Microsoft Corporation. All rights reserved.
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` Introduction to Broadcast Architecture — 3
`
`Overview of Broadcast-Enabled Computers
`A broadcast-enabled computer is a versatile next-generation computer that blends television with
`exciting new forms of information and entertainment. It blurs the line between television, web pages,
`and computer content. Software running under Windows® 95 together with receiver cards allows
`broadcast-enabled computers to provide five new capabilities:
` Computer-driven versatility and power in choosing shows and planning television consumption.
`Broadcast-enabled computers display program guide information of many different sorts in a
`single form, where shows can easily be previewed, scheduled, and if appropriate paid for. Parents
`will particularly appreciate the flexibility with which they can place restrictions on what their
`children may watch.
` Digital display of digital television signals. Broadcast-enabled computers complete the path for
`delivering full-resolution digital picture and audio rather than converting digital signals to analog.
`Broadcast-enabled computers thus offer an incremental, flexible, and affordable migration path to
`higher resolution television.
` Television transformed into a multimedia experience. The combination of television with
`broadcast digital data offers a new world of entertainment possibilities.
` Marketing and delivery of digital goods and services to viewers by way of digital data broadcasts.
`Broadcast-enabled computers are designed to filter high-bandwidth broadcast data streams so as
`to extract and save whatever the viewer may have subscribed to, requested, or purchased. In
`combination with the broadcast-enabled computer’s system security, this capacity provides a
`reliable and economical channel for selling digital goods and services. Such broadcast data
`channels today can deliver more than 10 gigabytes of data per day, and within a year they are
`projected to deliver more than 60 gigabytes per day.
` Potential for immediate viewer response. A low-cost, low-bandwidth modem back channel — the
`segment of a two-way communications system that flows from the consumer back to the service
`provider — permits viewers to react immediately to television program content and
`advertisements. Given the excellent security of broadcast-enabled computer systems, viewers can
`easily purchase goods and services from their living rooms.
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`These capabilities are achieved through a combination of hardware and software components that
`allows personal computers to serve as clients of broadband digital and analog broadcast networks.
`Following a standard client/server computing model, broadcast-enhanced computers in the home are
`equipped to act as “clients.” In other words, they serve as data tuners that receive and process
`broadcast streams provided to them by powerful “servers,” which are transmitters of all sorts.
`A broadcast-enabled computer can easily be equipped with appropriate receiver cards and supporting
`software to receive broadcasts in virtually any format from almost any source. Whether the
`transmission is from a satellite, by cable, or by conventional terrestrial antenna, whether the signal is
`digital or analog, whether it is a video, audio, or binary data stream, broadcast-enabled computers are
`designed to accommodate it in a standard way using Windows 95. In fact, the same broadcast-enabled
`computer can receive almost any combination of sources and data types.
`Almost all the technology and infrastructure needed to create broadcast-enabled computers is
`currently in place. In particular, broadcast-enabled computers rely on broadcast networks and a
`phone-line back channel that are inexpensively and reliably available in virtually every home today.
`Broadcast-enabled computers are the most flexible and cost-effective path to television of the future.
`Not only do they have a lot to offer immediately, but also they support low-cost incremental steps to
`higher resolutions, growing back-channel bandwidth, increasing interactivity, and new multimedia
`forms of television. For viewers and content producers alike, broadcast-enabled computers provide
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`© 1997 Microsoft Corporation. All rights reserved.
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` Introduction to Broadcast Architecture — 4
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`painless interim solutions at every stage of the path. Rather than becoming obsolete when new
`technology becomes available, they are designed to incorporate technological advances smoothly.
`Broadcast-enabled computer software has been designed so that some simple, impressive
`combinations of television and information content can immediately be delivered in the form of web
`pages. Broadcasters can thus take advantage of standard web design tools, scripts built in the Visual
`Basic® programming system, and skills they already have to create multimedia television rapidly and
`easily. In the cases where web functionality is insufficient, programmers can readily take advantage of
`the power of the system software provided for the broadcast-enabled computer to write special-
`purpose applications.
`The Broadcast Architecture presented in this kit enables existing broadcast networks, such as satellite
`or analog cable, to serve as carriers for video, audio, and data bound for broadcast enabled computers.
`The following sections review the components of the Broadcast Architecture:
` Broadcast Head End
` Client Hardware in the Home
` Broadcast Content
` Client Software
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`Broadcast Head End
`Before any broadcast-enabled computer can receive television signals and data, the content must
`originate from one or more broadcast sources. Whether the data originates from a satellite transmitting
`information to receiver dishes or a cable office sending information over the cable network, content
`bound for the broadcast-enabled computer begins its journey from a head end.
`In conventional television broadcasts, the analog signal received by the television set is broadcast
`from studios by powerful antennas. Individual television sets can receive the broadcast content at any
`time simply by being turned on and tuned to the appropriate frequency. With the Broadcast
`Architecture described in this kit, broadcast transmitters send many different kinds of content (video,
`audio, and arbitrary data), both analog and digital, through different types of broadcast networks
`(satellite, cable, and so on). People can then tune individual broadcast-enabled computers to receive
`the content in those broadcasts.
`The components at the head end consist of various content server applications that obtain the data to
`be broadcast, schedule broadcast times, and pass the data to other components that manage data
`transmission. The Broadcast Architecture provides special data services to facilitate movement of
`content from the content server application to the point of broadcast. Bridge software handles sending
`the data to the broadcast hardware.
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`Client Hardware in the Home
`Like any multimedia computer, a broadcast-enabled computer has a fast processor and bus, plenty of
`memory and hard drive capacity, a CD-ROM or DVD drive, a modem, a keyboard, a pointing device,
`and high-quality sound components. With advanced power-saving features, it is always on, silently
`monitoring broadcast channels 24 hours a day, ready to respond instantly at the touch of a button. Its
`operating system is Windows 95. It is usually connected to a large video monitor.
`The broadcast-enabled computer has its own remote control that includes its pointing device. In
`addition, its keyboard is generally wireless and also includes television control keys. In both remote
`control and keyboard, the television keys are implemented using standard Windows 95 key codes.
`Inside the broadcast-enabled computer’s case are specialized cards necessary to receive, tune, decode,
`and display the large data streams received at speeds up to 30 megabits per second. These cards
`offload so much of the video and audio processing that playing full-screen television requires only a
`small portion of the CPU’s capacity.
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`© 1997 Microsoft Corporation. All rights reserved.
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` Introduction to Broadcast Architecture — 5
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`A modem attachment to the home telephone line can provide a secure and inexpensive back channel
`to head-end servers. Connected to a merchant server, the modem can let viewers make immediate
`purchases from advertisers and broadcasters.
`Note, however, that a back channel is not necessary for viewers to interact with multimedia television
`shows. The computer by itself provides ample capacity for complex interaction. The back channel is
`necessary for communication and commerce, but not for viewers’ active participation in the
`multimedia television experience.
`
`Broadcast Content
`Broadcasting data is a very efficient way to distribute information and applications. Analog and
`digital broadcast transmissions already reach over 90 million households in the United States — there
`were 95.9 million television households in the United States in 1995, according to Digital Household
`Report of August 31, 1996, the number projected to grow to 96.9 million by the end of 1996.
`Broadcasts will also reach more households overseas as international direct-broadcast satellite
`networks continue to proliferate.
`Although television will occupy the bulk of broadcasts for the near-term future, many other goods and
`services can be delivered using existing digital channels, including the vertical blanking interval
`(VBI) within analog television signals. For example, the Broadcast Architecture on the client
`computer can automatically receive and display electronic program guide data such as that provided
`by StarSight and other companies.
`In addition, viewers will be able to subscribe to a wide variety of digital broadcast services that
`incorporate news, stock quotes, software and games for sale or rent, and so on. A broadcast-enabled
`computer can continuously monitor data streams arriving over the broadcast channels 24 hours a day;
`it can automatically store the latest stock quotes, sports scores, local news and weather forecasts,
`software upgrades, and whatever other information the viewer subscribes to, without using a modem
`or Internet connection. Strong encryption makes such data streams suitable for delivering high-priced
`or confidential products.
`Currently, broadcast digital data streams have capacities in the neighborhood of 1.2 gigabits per
`second, which translates into the transfer of more than 10 gigabytes every 24 hours. As these streams
`grow to around 6 gigabits per second in the relatively near future, they will be able to deliver over 64
`gigabytes of information per day.
`Broadcasts can also occur over less traditional channels. Broadcasting over a computer network to
`many different recipients at once is termed multicasting, in contrast to the usual practice of
`unicasting, which involves sending a separate copy of the message to each recipient. In a corporate
`context, multicasting can greatly reduce network traffic over intranets when compared to unicasting
`the same data to the same recipients. The broadcast-enabled computer is a perfect client for such
`multicasts both because of its high-bandwidth capabilities and because internally it handles all
`broadcast data as standard Internet Protocol (IP) multicasts.
`Even without a back channel, television and digital data broadcasts can be synchronized and
`combined to deliver multimedia television, allowing viewers to interact on-screen with shows so as to
`play games, obtain supplementary information, express opinions, test their knowledge or skills, and so
`on. Content providers can use common tools for web site design to create enhancements for their
`shows, delivered as Hypertext Markup Language (HTML) pages.
`With the addition of a back channel, viewers can interact not only with the computer but also more
`directly with broadcasters, advertisers, and other viewers. A secure back channel also offers an
`unprecedented opportunity to sell directly into people’s homes, letting them purchase from the
`comfort of their couches.
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`Client Software
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`© 1997 Microsoft Corporation. All rights reserved.
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` Introduction to Broadcast Architecture — 6
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`The software needed to make a broadcast-enabled computer work can be divided into three
`categories:
` System software. Broadcast Architecture system software is based on industry standards to ensure
`its reliability and ongoing development.
` The container for Broadcast Architecture applications. Broadcast Architecture applications all run
`within a standard container, which allows new applications downloaded by data broadcasters to
`take full advantage of all the broadcast-enabled computer’s capabilities just as if the programs
`were integral parts of the system.
` Broadcast Architecture applications. These applications can be controls running in the container,
`web pages with associated scripts, any other Internet application supported by Microsoft Internet
`Explorer, or even ordinary Windows-based programs running outside the broadcast-enabled
`computer container. Among the most important Broadcast Architecture applications is the
`Electronic Program Guide (EPG) control that lets viewers search, sort, filter, select, and schedule
`television shows and other content of all kinds.
`
`These general categories of software are described in more detail following.
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`System Software Built on Standards
`The system software of the Broadcast Architecture is intentionally based on industry standards,
`including the Transmission Control Protocol/Internet Protocol (TCP/IP) for Internet networking,
`Internet HTML, the current Motion Pictures Experts Group video and audio compression format
`(MPEG-2), ActiveX™ object technology, and the Windows 95 operating system. These standards
`guarantee developers, manufacturers, and viewers a stable, well-supported platform that will
`gracefully evolve to support new technologies as they appear.
`In some areas, extensions to these standard technologies have been required to accommodate the very
`large bandwidth occupied by high-quality digital audio and video streams, and to provide for flexible
`control over broadcast streams. In such cases, Microsoft has provided and documented interfaces to
`these extensions, so that programmers can easily take advantage of the services the extensions deliver.
`
`An Open Container Architecture for Broadcast Application Software
`The software that a viewer sees on a broadcast-enabled computer consists of ActiveX controls
`running in a standard ActiveX container called TV Explorer. Among the controls running in TV
`Explorer is one that can display web pages, which broadcasters can use to easily place their own
`digital content on-screen. Standard web authoring tools are widely available for creating such
`supplementary material.
`In addition, as documented in this kit, broadcasters have the option of writing their own special-
`purpose applications in the form of ActiveX controls to accompany their television content. Such
`controls fit smoothly into the Broadcast Architecture container’s user interface and have full access to
`Broadcast Architecture system services. Although special-purpose programs are seldom necessary, the
`Broadcast Architecture design can use such programs to extend its capabilities with complete
`flexibility.
`Similarly, independent software vendors (ISVs) can use ActiveX controls to write new kinds of
`applications for broadcast-enabled computers or to give existing programs broadcast awareness.
`While the Broadcast Architecture software is designed to be open to developers, great care has been
`taken to ensure that system security can be maintained, so that broadcast-enabled computers can
`provide a secure platform for commercial transactions.
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`Applications Defining the Broadcast Architecture User Interface
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`© 1997 Microsoft Corporation. All rights reserved.
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` Introduction to Broadcast Architecture — 7
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`Various applications in the form of ActiveX controls create the screens that viewers see. Because one
`of these controls uses Microsoft Internet Explorer technology to interpret and display web page
`material, applications can also take the form of web pages interpreted by this control.
`Of the applications included with a broadcast-enabled computer, probably the most visible one is the
`EPG control. This control gives a user access to the EPG database, which can be continuously
`updated with program guide information from various providers. In clear graphical form, the EPG
`control displays all the programming available to the person using it over various time periods; the
`EPG control makes it easy to select shows for watching or recording. With all the power of the
`computer at your command, you can search for your favorite shows, keep track of episodes, set up
`reminders, and watch previews.
`Also, using the EPG control, a parent can easily restrict children’s access to certain shows, to certain
`types of show, to shows that exceed a specified rating, or even to individual episodes of a certain
`show. A parent can limit the weekly watching time or aggregate expense of shows selected by each
`child. Achieving this kind of complex control over children’s television habits is a high priority for
`many families.
`
`A Brief Look at the New Technology
`Subsequent papers describe the hardware and software technologies that underlie broadcast-enabled
`computers. The goal of this section is to provide a brief overview of what makes broadcast-enabled
`computers work.
`
`Client Hardware Technology
`To achieve their purposes, broadcast-enabled computers require hardware components of the
`following sort:
` A digital-ready display. Broadcast-enabled computers are intended for home display of television.
`To achieve this goal requires a progressive-scan SVGA monitor with a resolution of at least 800 x
`600 pixels, a refresh rate of 60 or 120 hertz, and phosphors with matching persistence so as to
`minimize flicker while matching the luminance of television picture tubes. Suitable monitors for
`various locations vary in size from smaller than 17" to larger than 35".
` A network receiver card. The receiver card, installed on a PCI or other high-bandwidth bus,
`provides functionality such as data tuning, decryption, demultiplexing, and other capabilities that
`permit it to receive signals from specific broadcast sources such as the DIRECTV Digital Satellite
`System (DSS).
` An MPEG-2–capable video card. A video card with MPEG-1 and MPEG-2audio and video
`decoding capabilities, also installed on a PCI or other high-bandwidth bus, must provide
`functionality such as SVGA video display, MPEG decoding, and National Television System
`Committee (NTSC) or PAL signal demodulation and encoding. This functionality is needed for
`DVD optical disks as well as for videotape input/output and ordinary television broadcasts.
` Broadcast access hardware. Broadcasters who provide pay-per-view programming require
`hardware and software to provide security access control for decryption and billing purposes.
`This hardware and software might include a smart card, a smart card reader, and a decryption
`module (as is required, for example, to work with existing DSS access control systems).
` A standard modem. Customers require a back channel to purchase pay-per-view movies and other
`premium data services and to interact with advertisers and broadcasters. A 14.4–kilobit-per-
`second or faster telephone modem provides a low-bandwidth back channel that is more than
`adequate for these needs. As Integrated Services Digital Network (ISDN), ADSL, and cable
`modems become widely available, faster back channels become practical. As they do, more
`dynamic forms of interactive entertainment will evolve.
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`© 1997 Microsoft Corporation. All rights reserved.
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` Introduction to Broadcast Architecture — 8
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` A keyboard, pointing device, and remote control. Viewers must be able to control a broadcast-
`enabled computer, together with other consumer electronic devices such as a VCR or stereo
`system, comfortably and conveniently from a sofa some distance from the screen. The
`keyboard/pointer/remote control device or devices that meet this need will preferably be wireless
`and designed for easy use on the lap.
` Custom hardware device drivers. Vendors of special-purpose cards to be part of the system need
`to provide standard device drivers for their hardware based on the Network Driver Interface
`Specification (NDIS).
`
`While detailed minimum and recommended hardware configurations are specified later in this kit,
`alternate configurations are encouraged within the scope of providing good television reception for
`digital broadcasts.
`
`Broadcast Technology
`Even without new broadcast programming, broadcast-enabled computers provide an appealing
`integration of excellent digital picture and sound quality with a state-of-the-art multimedia computer
`and gaming platform. The computer gives viewers a great deal of flexibility in planning television
`programming, and it displays Electronic Program Guide information very conveniently and clearly.
`Using a modem connection to the Internet, data services of all kinds are available today.
`
`Existing Products and Services
`A broadcast-enabled computer provides an excellent client for the following currently available data
`streams:
` Digital television broadcasts. The broadcast client can handle digital MPEG-2 video, audio, and
`control streams coming from systems such as DIRECTV DSS satellite broadcasts.
` Electronic Program Guide (EPG) data. Program guide information from broadcast or network
`sources can be loaded into the broadcast-enabled computer’s database. Customers can then
`search, filter, sort, and select programs for viewing now or in the future.
`Internet content. Viewers can obtain digital information from the Internet, downloaded either by
`modem or from a satellite broadcast.
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`New Products and Services
`Very quickly, however, new types of broadcast streams will appear that greatly extend the utility of
`the broadcast client. These include:
` Broadcast digital data. Broadcast channels provide a fast and inexpensive way of distributing
`information. The broadcast-enabled computer can monitor digital data streams 24 hours a day to
`keep caches of subscribed information up-to-date without picking up the phone.
`Digital broadcasts are ideal for delivering such time-sensitive data as stock prices, local news and
`weather, product catalogs, software updates, and many other subscription services. For example,
`frequently visited Internet sites can easily be broadcast in this fashion and cached on the hard
`drive so as to be instantly available in an up-to-date form when a viewer wants them, perhaps in
`conjunction with an associated show or advertisement.
` Multimedia television. The combination of digital data broadcasts synchronized to television
`shows allows all kinds of annotation and extension of existing television and advertising content,
`using HTML, Visual Basic scripts, and ActiveX controls.
`If a back channel is available, advertisers can actually solicit real-time responses from viewers.
`Viewers can, for example, play games in which they expressed product preferences, or they can
`inquire about products of interest or even make immediate purchases.
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`© 1997 Microsoft Corporation. All rights reserved.
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` Introduction to Broadcast Architecture — 9
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` Software and Internet content enhancements. Background images, video, and music downloaded
`over high-bandwidth broadcast channels can be used to make software more attractive and fun to
`use, particularly entertainment software and educational programs. Regularly updating games or
`courseware with new scenarios, information, backgrounds, and so forth provides users a
`constantly changing landscape of interactivity.
`Broadcasting and caching popular Internet content can make visiting useful pages much less
`frustrating, while also reducing server loads so that other interactions, such as purchases, can
`proceed without delay.
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`Tools for Creating New Kinds of Broadcast Content
`Microsoft has developed tools and documentation to make it easier for content providers of all sorts to
`take advantage of new digital data broadcast opportunities. In particular, the following components
`serve this purpose:
` Microsoft Broadcast Data Network (MSBDN). Microsoft has designed a national broadcast
`network for digital data, MSBDN, that is based on TCP/IP networking standards and that can use
`strong Data Encryption Standard (DES) encryption to secure valuable goods and services so that
`only paying subscribers have access to them. This high level of security makes MSBDN a
`suitable channel for delivery of software and other expensive digital goods and services that
`would otherwise be vulnerable to theft.
`Information on how to create multimedia television. Documentation, an expansion of the material
`found on this compact disc, will be created that is devoted to content providers. This
`documentation will contain overviews and real-world examples that show how to go about
`preparing and delivering enhancements for advertising and television using HTML and other
`solutions.
` webcasting. The webcast client and server software shipped with the Broadcast Architecture
`facilitates the gathering and broadcast of Internet content over one-way digital data channels. It
`includes the ability to test the resulting data streams before broadcasting them live, through
`simulated broadcasts over high-speed networks using IP multicast technology.
` Network bridge router. At a low level, Microsoft is also providing basic bridge technology to
`connect data networks so as to move content to consumers.
`
`
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`Client Software Technology
`Broadcast-enabled computers must be able to handle a wide variety of very high-bandwidth streams
`requiring different kinds of special-purpose hardware for reception and processing. The software that
`makes this demanding environment work is characterized by three design objectives:
` To use industry-standard technology wherever possible.
` To expose and document extensions specific to the Broadcast Architecture.
` To maintain adequate security to protect all parties using the Broadcast Architecture.
`
`Using Industry Standards
`Wherever possible, Broadcast Architecture software relies on standard solutions that are widely
`accepted, understood, and supported in the industry. These standards include:
` The TCP/IP networking protocol. This protocol is the one used by the Internet. By using it as
`their primary networking protocol, broadcast-enabled computers make a standard way available
`to communicate with virtually any network in the world.
` MPEG-2 compression. This format is becoming the most widely accepted standard for delivering
`compressed video and audio and related data.
`
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`© 1997 Microsoft Corporation. All rights reserved.
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` Introduction to Broadcast Architecture — 10
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`
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` The Windows 95 operating system. In addition to being the most widely used and understood 32-
`bit operating system, Windows 95 includes a number of components that are becoming or have
`become standards themselves:
` Windows Sockets version 2.0. This application programming interface (API) provides a
`network abstraction layer that allows application software to receive and send network data
`without needing any information about the network involved. Sockets also provides access to
`the TCP/IP protocol that is the Internet standard.
` NDIS version 4.0 ports. The standard Network Driver Interface Specification allows hardware
`device drivers to be written independently of the target operating system.
` CryptoAPI. This API provides an abstraction layer for encryption and decryption services, so
`that applications can use different encryption methods without requiring any information
`about the hardware or software involved. This API also provides a way of protecting sensitive
`key data.
`Internet Explorer. By incorporating Microsoft Internet Explorer technology, the broadcast-
`enabled computer can take advantage of all the latest Internet and web enhancements.
` Component Object Model (COM). Microsoft has opened this technology and passed control of
`it to a public standards group in an effort to ensure that it continues to meet users’ needs.
`COM allows different software modules, written without information about each other, to
`work together as if they were part of the same program.
` ActiveMovie™. This recent ActiveX addition provides an extremely flexible and capable
`architecture for managing and playing related multimedia streams, which the broadcast-
`enabled computer particularly relies on. The key concept of ActiveMovie is to connect many
`independent “filter” programs together. Each filter handles a part of the process of receiving,
`decoding, transforming, scheduling, and displaying interdependent video, audio, and data
`streams.
` Key codes for television remote control. Remote control buttons included on keyboards and
`other devices communicate with broadcast-enabled computers using standard Windows 95 key
`codes, making integration of these functions very simple for hardware manufacturers.
`
`ActiveMovie technology is sufficiently important for broadcast-enabled computers that its flexibility
`should be stressed. ActiveMovie filters are modular software components that work together to
`process a data stream. When one feature of the stream changes, only the filt