Kilroy Hughes, Dave Marsh, Tom McMahon and Skip Pizzi Microsoft Corporation Redmond, WA, USA

Getting the Picture: how will enhanced, high-resolution TV services be

displayed in the home?
Introduction
 
This paper presents an architectural analysis of the interfaces between modern, consumer-friendly interconnection systems to be used with Advanced Set Top Boxes (ASTBs), Integrated Digital Television receivers (IDTVs) and high-resolution display devices (such as HDTV projection systems, plasma panels and CRTs).
 
Recent decisions in the US DTV environment have identified IEEE 1394 as a primary or sole interface required to feed digital content to display devices. This movement is based on the belief that use of 1394-based interconnects will remove all remaining obstacles to consumer acceptance of DTV. Such a premise is substantially flawed, as the arguments below will indicate. Alternative, superior solutions to these interface issues will also be presented.
 
As a fundamental starting point, it must be recognized that the requirements for advanced digital television products and services will be diverse. Any interconnection schemes for such devices must therefore accommodate a broad scope of applications. Recommendations for interconnection and labeling must consider the services, software applications, consumer receiver architectures and content types that will run across these interfaces.
 
Even in cases where the 1394 interface may provide an adequate solution, it is by no means the only such interface available. For example, new versions of the Universal Serial Bus (USB) interface will soon meet or exceed the capacity of the 1394 interface (“NEC, In-System to Develop USB 2.0 Chip, ”Electronic News Online, September 1, 2000")
 
To assure a rich, cost-effective and competitive DTV marketplace, flexibility in these interfaces will be required. This implies that interconnection options other than 1394 must be provided for future interactive DTV services.
 
Specifically, those options must include a type of interconnection that allows high-resolution digital video to be sent directly to HDTV display devices in uncompressed, protected form.
 
Definition of Terms: What is a “Digital Television Appliance”?
 
ASTBs [Advanced Set Top Boxes] and IDTVs [Integrated Digital Television receivers] are examples of digital television appliances. They contrast with analog NTSC television devices in their ability to receive television signals in digital form via terrestrial transmission, cable or satellite. Attributes common to all digital television appliances include:
 
1) the reception of program streams in a compressed digital form and
2) the processing and intelligence required to navigate and decode the digital stream. (In this context, the term intelligence refers to computational hardware, applications and algorithms.
 
Additional intelligence may be required for interactive services such as shopping, personal video recording (PVR) functionality, gaming, chat, e-mail and web access.
 
The type of digital television appliance(s) that a consumer acquires will depend on many factors, including the target location in the home and the consumer’s disposable income level.
 
In place of the traditional integrated NTSC television – or analog set top box attached to an NTSC display – in the living room, examples of consumer configurations likely to evolve include:
 
• A large-screen HDTV system for the living/media room that is able to deliver a wide range of entertainment.
• A PC in the den/office that can receive TV in a small window while performing productivity and communications tasks.
• A small-screen DTV for the bedroom(s) with gaming and other applications.
• A flat-screen DTV in the kitchen with recipe, calendar and messaging capabilities.
 
Many other possibilities arise, particularly when the choice of display screen (the “glass”) is independent of the device that provides it with the video signal and navigation or control capabilities (the “intelligence”).
 
When considering digital television appliances, it therefore may be useful to apply the so-called RIG model, as shown in Figure 1. It illustrates that a consumer digital television system consists of three potentially independent functional parts: Receiver, Intelligence and Glass.
 
The Receiver module tunes the desired frequency (channel), demodulates the signal, handles any Conditional Access/Rights Management, and outputs an MPEG-2 video stream, compressed digital audio stream(s) and related data stream(s). There may be more than one type of receiver module in the home. The receiver can either be integrated with the Intelligence module (see below) or it can be separate.
 
The receiver can also authorize a connection between the digital content provider and the home. It contains everything that is necessary for user-identification and signal-decryption. In the context of cable, this interface module has traditionally been provided and controlled by the cable company to which the consumer subscribes. (With the recent emergence of OpenCable-compliant ASTBs and removable Point-of-Deployment [POD] modules, consumers will be able to make their own choice of ASTB and connect it to the cable system themselves. The network-specific POD module will continue to be controlled by the respective cable operator.)
 
Receiver modules (sometimes referred to as Residential Gateway Modules) will connect to Intelligence components via standardized consumer interconnects. When integrated into a single box, this interconnect can be a PCI or other computer bus.
 
Many receiver modules will be separate set top boxes, however, and it is likely that they will connect using 1394 or USB. There may be multiple receiver modules (i.e., multiple tuners) fitted to a system in order to provide multiple video windows (e.g., for picture-in-picture), or multiple video providers (e.g., cable, satellite and terrestrial). An example is a satellite receiver that is also capable of terrestrial DTV reception (The RCA DTC-100 is an example of this type of device. See: http://www.rca.com/product/viewdetail/0,,PI640,00.html
 
When interactive services are provided, the connection between receiver and intelligence should support bi-directional communications. This is because the user interface and local rendering of interactive elements will be generated by the intelligence component, while return transmissions of interactive commands from the user to the service provider (the so-called back-channel) will likely be handled by the receiver module.
 
IEEE 1394, USB and IP networks are well-suited for this type of interconnect.
 
At a minimum, the Intelligence component handles MPEG video and AC3TM audio decoding
 
On more advanced devices, this section also serves as the platform for generation and rendering of graphics for the system’s user interface (UI), Electronic Program Guide (EPG) and other value-added and interactive services.
 
This could include a platform for any downloadable applications and the management of any local content-storage capability. Such functionality could take the form of an OpenCable or ATSC-DASE STB, a DTV-PC, an advanced DTV home theatre console system with integrated PVR [personal video recording], any of a number of proprietary STB [Set Top Boxes] platforms or just a simple 8-bit processor and MPEG decoder in an integrated DTV receiver.
 
It is important to provide very fast pixel rates for the decoded video when linking the Intelligence to the Glass. Note that 1394 and “VSB over coax” interfaces are not contenders for viable Intelligence-to-Glass interfaces because the MPEG stream has already been decoded (i.e., uncompressed) in the intelligence section. Neither of these interfaces can handle the required resolution and speeds without significant additions to the cost and complexity of the Intelligence module. (This issue is described further below.)
 
This is especially true of 5C-protected 1394 links, because the required encryption overhead may reduce the net payload of the basic 1394 transport even further, given the typical cost constraints of consumer electronics equipment.
 
There is usually no need for bi-directional communication between the Intelligence and Glass. However, if it is provided, it can enable features such as adaptive remote setup and calibration of the display. The Glass provides the image display for the user. The RIG model [Receiver, Intelligence and Glass] assumes that an audio reproduction system is also at the “Glass end” of the diagram. This component can take the form of an (H)DTV projection system, a CRT, a plasma flat panel, an LCD or even an NTSC analog TV.
 
Note that with an installed base of some 250+ million NTSC televisions in the U.S., it will be quite common to see consumers connecting their “intelligent” DTV appliances (especially cable and satellite ASTBs) to their NTSC television sets for many years to come. Subsequently, it is expected that these consumers will replace their NTSC displays with EDTV/HDTV displays fed by existing DTV set-top boxes.
 
There is no intrinsic grouping of these three functional parts or prescribed method for their integration. CEA has issued definitions that allow many different configurations. Substantial latitude exists for product differentiation and added value to the consumer in this respect. With the amount of flux that exists in today’s DTV environment, most vendors find it sensible to implement DTV systems in at least two separate boxes. This accommodates the independent paths along which display and receiver/decoder technologies are currently evolving.
 
Moreover, consumers may want to purchase different parts at different times. The choice of display is often dictated by aesthetic or physical constraints of the viewing space. The display can also be quite costly and typically has a long life expectancy, thus it is less frequently updated or replaced. This implies that the consumer transition to DTV usage may occur faster if low-cost set top boxes are available, allowing the cost of expensive new displays to be deferred.
 
In addition, the proliferation of inexpensive ASTBs and their associated services will eventually accelerate consumer demand for new displays, thereby providing earlier cost reductions for all of these products due to economies of scale (This trend has already been demonstrated by the early adoption of “HDTV ready” displays driven by reasonably priced and widely available digital video sources such as DVD and high-definition satellite services, even in the current absence digital terrestrial receivers. It can only be expected to expand if other DTV sources (i.e., terrestrial and cable DTV) come to market at similar price points and availabilities. This approach will speed the transition to DTV among U.S. consumers.
 
Start with the “Glass” and work backwards
 
As the era of digital television dawns, much of the enthusiasm among consumers is generated by the large-screen, high-resolution displays currently coming to market. The larger screen is a key enabler for HDTV because its quality is only fully appreciated at such display size.
 
Current products targeting early adopters place little or no inherent intelligence in these display devices. This implies that all of the intelligent receiver and decoder functions noted in the RIG [Receiver, Intelligence and Glass] model above are upstream of the display. The type of interconnection between display systems and upstream intelligence is therefore non-trivial and critical to the deployment of existing and future products.
 
In today’s consumer environment, such interconnections are well established, with a large base of NTSC, composite video and S-Video equipment currently in use. These interconnect types are generally unsuitable for DTV because they will not accommodate its higher-resolution video formats. Without an industry-standardized video interface that can sustain EDTV and HDTV signals, mainstream consumer acceptance of large screen DTV displays will face an insurmountable obstacle.
 
Because such large screen, HDTV-ready display products typically have no intrinsic signal-decoding capabilities, they are incapable of dealing with a compressed video stream. This implies that the new industry display interconnect – whatever form it may take – must be capable of handling HDTV streams in high speed uncompressed form. Such uncompressed HDTV signals may be transported in either analog or digital form. Both are examined below.
 
Analog Consumer Interconnects
 
Options for analog interconnect schemes, of which S-Video is a common example in today’s consumer space, become quite limited if they are required to accommodate HDTV signals. Few, if any, of the existing standards are suitable in their current form. S-Video is incapable of supporting the resolution required and there is simply no HDTV equivalent for composite analog video.
 
Component analog video is a contender, for which VGA stands as an example in today’s consumer environment. But because an analog signal is easily diverted, split and copied, the issue of copy protection immediately arises. This is particularly critical in the case of an HDTV signal’s high resolution, which can deliver near-theatrical quality program content. Use of HDTV component analog interconnects is a stumbling block because there are no existing industry standards for copy protection of these signals.
 
While some CE manufacturers have nevertheless produced designs with unprotected HDTV component-analog outputs, this does not meet the needs of the content industry, and could prevent the broadcast of high-resolution premium content, such as movies. Although HDTV component analog signals are not recordable with any of today’s standard consumer electronics products, they are quite easily recordable with professional and industrial equipment.
 
Premium HDTV programming shipped “in the clear” over component analog interconnects can therefore be easily pirated. Even if a copy protection scheme existed (such as an HDTV version of Macrovision), encrypted component analog signals would be easily decoded by anyone with moderately sophisticated skills.
 
Subsequent evolution and deployment of new encryption standards in this area would likely render the current generation of consumer HDTV products obsolete and incapable of displaying an image.
 
Analog interconnects also impose certain quality constraints and may severely limit the length of the cables that consumers could reliably use. Potential signal distortion and noise pickup could greatly reduce the quality of the HDTV viewing experience.
 
Finally, as the industry moves toward display technologies such as DLPTM, GLVTM, LCD and other inherently digital HDTV display systems, the disadvantages of using an analog interconnect will become increasingly obvious.
 
For reasons of quality, convenience, content security and cost, a standardized digital interconnect between the DTV appliance and the display is therefore required – and expected – by the industry.
 
Digital Consumer Interconnects
 
Common HDTV image formats such as 1920 by 1080 pixels at 30 frames per second interlaced (commonly referred to as “1080i”), or 1280 by 720 pixels at 60 frames per second progressive (commonly referred to as “720p”) have data rates on the order of 1.4 gigabits per second (Gb/s) in their uncompressed component form. As a point of reference, this is almost 25,000 times faster than a common dial-up computer modem connection.
 
More importantly, these HDTV speeds are approximately seven times faster than the maximum speed of today’s IEEE 1394 implementations for consumer electronics equipment (sometimes called FireWire or i.LINKTM in these products).
 
While future versions of 1394 may eventually reach speeds in the 1.4 Gb/s range, it is important to note that the 1394 interface was not designed to carry sustained HDTV data rates without interruption, as is required by continuous television viewing.
 
Regarding such eventual development, industry insiders and observers generally agree that use of 1394 for contentprotected, baseband uncompressed DTV video will likely not be feasible in the consumer environment for quite some time. Further, the 5C content protection proposed for use with 1394 is also not currently extensible to such speeds.
 
The application of 1394 for the task of a standardized DTV display interface format is therefore a poor match. On the other hand, 1394 is an excellent consumer interconnection scheme for compressed DTV signals. An example of this would be its use for transport of a 19.39 Mb/s ATSC stream. Even the slowest (200Mb/s) version of 1394 is easily capable of transporting such compressed signals.
 
But with no intelligence at the glass, the display is not capable of rendering a picture from such a compressed signal. ATSC and other compressed stream types must be decoded into viewable signals by DTV appliances upstream of the display. Therefore, given the requirements of today’s television content and consumer electronics components, HDTV-capable display devices [CEA Expands Definitions for Digital Television Products” (Press Release), Consumer Electronics Association, Arlington, VA, August 31, 2000] are simply not compatible with the use of 1394 as an interconnect technology.
 
One solution for this is to use 1394 as the sole interface to the display, and incorporate all required DTV decoding technology inside each display
 
Given the variety and volatility of the DTV format environment, plus the inherently high cost of displays, this approach would likely be unattractive to many consumers. A modular solution, in which plug-in decoder components could be housed in the display device, implies that at some point an uncompressed transport bus would still be required in the receiver (at the output of the decoder module).
 
Some standard form of protected, high-bandwidth interface will be required for this bus, so the issue under discussion is simply moved inside the display, but at an easily accessible point.
 
Moreover, with such an approach, any content locally rendered in the intelligence device (e.g., EPGs, user interfaces/displays, interactive applications, gaming environments, etc.) would have to be MPEG/AC3-encoded simply to pass through the 1394 interface from the intelligence component to the display. This would add substantial cost and likely reduce display quality.
 
A better solution involves the addition of a high-bitrate, protected digital video display interface to all DTV displays. Such an interconnection standard has been proposed for use with consumer DTV displays. It is called the Digital Visual Interface (DVI) and includes an extension known as High-bandwidth Digital Copy Protection (HDCP),  See White Paper, Silicon Image, Sunnyvale, CA. February 2000.
 
DVI technology already has been widely deployed in high-resolution computer displays and adapted for consumer applications with HDCP for protection of digital video content. Its features and advantages have stimulated a rapid growth in its popularity for interconnecting DTV appliances with their respective display systems. A substantial and growing number of computer and consumer electronics companies have announced their intent to deploy products that support this interconnect standard.
 
Key features of DVI are its low cost, resolution independence and potential for supporting advanced copy protection suitable for feature film content. It is capable of handling the bit-rates associated with all existing and proposed EDTV and HDTV formats.
 
Note also that while 1394 is a bi-directional link, suitable for connecting communicating devices such as cameras or recorders to STBs, DVI is optimized for one-way, high-speed connections to display devices [IEEE 1394 is a different interface designed for different applications.
 
It's for a two-way communication link, perfect for connecting a VCR or a camera to a set-top. DVI is designed for a one-way connection for uncompressed signals. Both interface standards will coexist." Rich Nelson, Director of Marketing, Broadcom, quoted in EE Times, “Broadcom Makes Pivotal Bid for DVI, Bluetooth Technologies,” May 25, 2000]. High bandwidth Digital Copy Protection (HDCP) on the DVI link Security for premium content is of vital importance.
 
If uncontrolled digital copying of premium content such as early-release-window movies were allowed to occur, the revenue structure of the film industry could be threatened. For this reason it is critical that every link in the DTV chain be secure.
 
There is no point in protecting some of the links if others are left open to attack. Each stage in the chain needs to verify that it is passing premium content to a downstream stage that can be trusted as secure.
 
A copy-protection scheme known as DTCP (Digital Transmission Content Protection), typically referred to as “5C” [The 5C specification of DTCP was developed by Hitachi, Intel, Matsushita, Sony and Toshiba. The name “5C” was coined in recognition of these five companies.], can be used on any one of a number of interconnection types (1394, IP transport, etc.) to determine that the link from the “Receiver” to the “Intelligence” is secure, or else the “Receiver” will not pass on the content.
 
Likewise the link from the “Intelligence” to the “Glass” needs to be secure, or the “Intelligence” device will not pass on the content to the display.
 
The HDCP system was designed by many of the same engineers who developed the 5C system. The high data rate of DVI exceeds the capability of the 5C system, so 5C cannot be directly applied to DVI. Thus HDCP was developed to accommodate the requisite faster scrambling scheme for DVI. The authentication process of [High-bandwidth Digital Copy Protection] HDCP (which happens before the content data starts flowing and determines if the downstream device is a trusted receiver) retains much in common with the 5C scheme.
 
This authentication process is a critical step. It is important that it not be possible for a device to report that it is a display when it is actually a recording device. To prevent this possibility, display manufacturers must obtain certificates from the [High-bandwidth Digital Copy Protection] HDCP licensing authority for their displays.
 
These securely encrypted electronic certificates are stored within the display devices. During the authentication process, the certificate is read by the upstream “Intelligence” to verify that the display is a valid device (i.e., “trusted Glass”).
 
As part of the process, the “Intelligence” component checks the certificate against an up-to-date revocation list to verify that no security breaches have been reported for that display model. HDCP uses a 56-bit key, with individual keys distributed to authorized vendors. A violated key can be tracked down and revoked, and this revocation can be distributed to consumers’ “Intelligence” devices via a TV broadcast network, for example.
 
DVI with HDCP is an ideal solution for the consumer electronics industry to protect the link from an ASTB to any display device. It is also an ideal technology for DTV receivers to use as an alternative to low-resolution analog S-Video or composite video inputs, and in addition to 1394 ports.
 
Developers of HDCP have reported strong positive reactions from the content community [“We are enabling the industry transition to new high-definition digital content. This latest demonstration reflects our ability to successfully execute on our DVI innovation strategy, lead the market we are pioneering and receive endorsement of this vital new technology from members of the Motion Picture Association (MPA).” Steve Tirado, Executive Vice President of Marketing, Silicon Image, quoted in Silicon Image press release, ibid], and several major Hollywood studios have endorsed the technology [“Warner Bros. has a library of movies and television productions that look great in the new high-definition digital formats. We are pleased to see the work done by Silicon Image to develop the HDCP chip set and welcome the deployment of such technology. It is important for consumers to understand that systems which lack an effective technology to limit unauthorized copying of our most valuable and highest quality content will not be able to receive it.” Wendy Aylsworth, Vice President, Technology, Warner Bros., quoted in Silicon Image press release, March 14, 2000] and [“Secure interconnections such as HDCP are important elements of an overall content delivery system, addressing a key need in the development of new channels for high quality digital content delivery.” Phil Lelyveld, director of Digital Industry Relations, The Walt Disney Company, quoted in Silicon Image press release, ibid.]
 
Worldwide adoption of DVI with HDCP by multiple industries will have a positive impact on the DTV industry, because content producers such as Hollywood studios will be able to release new, high-definition digital content with high confidence in its security. [“HDCP also answers a plea from the entertainment industry, particularly from the studios that provide much of today's premium content.” Electronic Design, June 12, 2000]
 
A comparison of digital interconnection proposals
 
Table 1 and Figure 2 summarize the considerations made above. They compare the requirements of various uncompressed video signal resolutions and the capacities of various digital interconnection systems. The values shown are derived from currently published specifications
 
UDTV refers to 1920 x 1080 x 60Hz progressively scanned displays (1080p).
 
Per DVI 1.0 spec with 165 MHz maximum pixel clock rate and 24 bits per pixel. Dual-link version extends this value to 7920 Mb/s. Format/Interface Bit-rate requirements/capacity
 
SDTV Tuner/Monitor 248 Mb/s
EDTV Tuner/Monitor 498 Mb/s
HDTV Tuner/Monitor 1,327-1,493 Mb/s
UDTV23 Tuner/Monitor 2,986 Mb/s
IEEE 1394 (with 5C) 200-400 Mb/s
DVI/HDCP (single link)24 3,960 Mb/s
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 2 clearly indicates the inadequacy of the 1394 interface for transport of most uncompressed video formats, and the capability of the DVI interface to handle current applications and beyond.
 
 
 
What DTV equipment will consumers buy?
 
Keeping in mind the RIG model [Receiver, Intelligence and Glass], consider the following permutations for DTV equipment options in the consumer’s home:
 
1. Integrated digital television: includes all “RIG” components in a single device. No inter-component interfaces are required, unless external STBs are used for additional services.
 
2. External receiver: STB receiver serves as a tuner [See High Definition Television (HDTV) Tuner, Enhanced Definition Television (EDTV) Tuner, CEA press release, ibid.] (R) and sends a demodulated but not decoded signal (i.e., a compressed bit stream) across an interface to an integrated decoder/display (I+G, or “intelligent glass”).
 
3. External receiver/decoder: STB demodulates and decodes all signals (R+I), and sends audio and video across appropriate interface(s) to display devices (G) [See High Definition Television (HDTV) Monitor, Enhanced Definition Television (EDTV) Monitor, CEA press release, ibid.].
 
Next, consider that interactivity will be added to this environment, so any Receiver-Intelligence interfaces that are used must support bi-directional communication, for reasons explained earlier.
 
Finally, consider that an ideal technical and regulatory environment will allow all of these options to coexist and interoperate, thus stimulating competition and maximizing flexibility. This in turn (See High Definition Television (HDTV), Enhanced Definition Television (EDTV). “CEA Expands Definitions for Digital Television Products” (Press Release), Consumer Electronics Association, Arlington, VA, August 31, 2000) will optimize user choices and satisfy the widest range of consumer budgets. Now consider the needs of the interfaces between the components listed above.
 
Option 1 essentially requires no device interfaces, but it is the least likely to be deployed. This type of integrated DTV product is virtually nonexistent in today’s environment, and does not seem to be high on either consumers’ or manufacturers’ priority lists for new product development.
 
This is partially due to the current uncertainty in formats and requirement for easy hardware upgrades. In addition, the prevalence of incompatible cable and satellite TV systems in the US dictates separate and perhaps multiple set top boxes in the consumer’s home, the functionality and network-specific security features of which will typically not be integrated with the digital television set.
 
There is little harmony across digital cable, digital satellite and ATSC platform standards, dimming hope for integration of all interactive services into all receivers for the foreseeable future. While this situation may eventually change, it remains likely that the integrated DTV receiver model will apply primarily to the evolution of non-interactive, lowerend integrated DTV sets (i.e., non-HDTV), for use as secondary units in the home. Therefore Option 1 is not a critical factor in this discussion.
 
Option 2 above presents a fairly simple technical interface, given that compressed incoming signals could be passed through a moderate-bandwidth interface (such as 1394, USB or HomePNA) to the decoder/display.
 
But this implies that a standard signal format to the decoder exists, which is certainly not the case. Over-the-air terrestrial, digital cable and satellite television systems all use different formats, and this is unlikely to change, as established above. In particular, the interactive applications proposed for these systems are widely divergent, largely ruling out the possibility of any comprehensive solution in this case.
 
Option 3 is the most likely to be accepted by consumers for home theater and interactive systems, based on current trends and future product plans. It would allow a variety of services to coexist and interoperate with a given display. It would improve competition in the less expensive and more volatile receiver/decoder market segment, while protecting consumers’ investments in the more expensive display components.
 
This allows consumers to upgrade or change services with relative ease and low cost, and without replacing expensive screens. It also keeps down the cost of display devices, by reducing their requirements for additional signal-processing circuitry.
 
Finally, it allows any number of competing interactive TV formats (either standard or proprietary) to interoperate with the consumer’s choice of display. The consumer simply selects or purchases the appropriate STB for the service, and connects it to the service and to the display.
 
Clearly this is a technically sound and simplified regulatory environment that benefits the consumer.
 
To allow Option 3 to work, a wide-bandwidth interface to the display is required. It must have the capability of carrying a base-band digital video signal – approximately 1.5 Gb/s. To satisfy the content community, this high-quality signal interface must also incorporate copy protection. An example of such an interface is the Digital Visual Interface (DVI) with High-bandwidth Digital Content Protection (HDCP) described above. (Although variations of the 1394 interface have been proposed for Option 3-type display interconnect applications, they remain inadequate for EDTV and HDTV display applications at present.)
 
The model provided in Option 3 also allows the value-added services of DTV service providers – such as electronic program guides (EPGs), branded graphical user interfaces (GUIs) and picture-in-picture (PIP) – to be locally rendered in the STB with high quality and passed through to the display without difficulty, along with received video content. The same local rendering requirement applies for some interactive TV content, DVD, and game displays.
 
Again, this is only possible with a wideband interface between the STB and the display
 
Otherwise, the locally rendered content could only be delivered with the video on an analog S-Video or NTSC interface, or it would have to be compressed along with the video in real-time after rendering. In either case, image quality could be substantially reduced.  Any additional compression and decompression circuitry required would also add cost to both the STB and the display.
 
The Option 3 architecture model also maximizes the flexibility and functionality of a local storage device (PVR) [Personal Video Recording], which is likely to become a popular component of interactive DTV systems. For best results, this local storage should be integrated with the receiver and decoder components of the system.
 
Finally, the migration to home networking should also be considered in this assessment. Limitations of space preclude thorough coverage of this topic here, but suffice it to say that a similar application of the RIG model applies for home networks. It is desirable that signals remain in the compressed domain through the home network, with distributed intelligence/user-interface components feeding each display individually via the same wideband interface (DVI/HDCP) described above for standalone systems.
 
Conclusions
 
The above discussion points out the critical role that signal interfaces will play in the success or failure of the DTV environment. If properly managed, these interfaces will foster simplicity that ultimately benefits consumers by providing flexibility, compatibility and a broadly competitive marketplace. Without appropriate interfaces, however, the DTV experience will become complex, cumbersome and frustrating to the consumer, and likely fail to achieve its potential economic maturity and cultural impact.
 
To maximize interoperability, the best approach toward interface specifications involves flexibility. This implies that multiple interfaces may be required, but that in all cases, displays and the devices feeding them should include a protected interface capable of handling uncompressed digital video, such as DVI with HDCP.
 
The industry is at a pivotal point in determining the course of future DTV technology and practice. Good decisions made today will pay dividends well into the future. Conversely, inappropriate choices or non-decisions today may haunt the industry for decades to come.

(c) Copyright 2001 National Association of Broadcasters

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