Projection screen in a home theater, displaying a high-definition television image.

High-definition television (HDTV) is a digital television broadcasting system with higher resolution than traditional television systems (standard-definition TV, or SDTV). HDTV is digitally broadcast because digital television (DTV) requires less bandwidth if sufficient video compression is used.

History of high-definition television

The term high definition once described a series of television systems from the 1930s and 1940s, starting with the British 240 line and 405 line black-and-white systems introduced in 1936, and including the American 525-line NTSC system established in 1941. However, these systems were only "high definition" when compared to earlier systems.

The British high definition TV service started trials in August 1936 and a regular service in November 1936 using both the Baird 240 line and Marconi-EMI 405 line systems. The Baird system was discontinued in February 1937.

A brief itemized history of early analog HD systems follows; these would be considered standard definition television systems today.

All used interlacing and a 4:3 aspect ratio except the 405 line system which started as 5:4 and later changed to 4:3.

The post–WWII French 819-line black-and-white system was high definition in the contemporary sense, but was discontinued in 1986, a year after the final British 405-line broadcast. Experimental 405 line colour transmissions were made in the 1950s using a modified NTSC system.

Since the formal adoption of DVB's widescreen HDTV transmission modes in the early 2000s the 525-line NTSC (and PAL-M) systems as well as the European 625-line PAL and SECAM systems are now regarded as standard definition television systems. In Australia, the 625-line digital progressive system (with 576 active lines) is officially recognized as high definition.^[1]

Color

In Mexico, Guillermo González Camarena (1917–1965), invented an early color television transmission system. He received patents for colour television systems in 1942 (U.S. Patent 2,296,019), 1960 and 1962. The 1942 patent (filed in Mexico on August 19, 1940) was for a synchronized colour filter wheel adapter for monochrome television, similar to the field sequential colour receiver demonstrated by Baird in England in July 1939[53] and by CBS in the United States in August 1940. _|_

On August 31, 1946 González Camarena sent his first colour transmission from his lab in the offices of The Mexican League of Radio Experiments at Lucerna St. #1, in Mexico City. The video signal was transmitted at a frequency of 115 MHz. and the audio in the 40 meter band. He made the first publicly announced colour broadcast in Mexico, on February 8, 1963, of the programme Paraíso Infantil on Mexico City's XHGC-TV.

In 1958, the U.S.S.R. created ?ransformator (Russian: ?????????????, "Transformer"), the first high-resolution (definition) television system capable of producing an image composed of 1,125 lines of resolution for the purpose of television conferences among military commands; as it was a military product, it was not commercialized.^[2]

Modern systems

In 1969, the Japanese state broadcaster NHK first developed consumer high-definition television with a 5:3 aspect ratio, a slightly wider screen format than the usual 4:3 standard.^[3] However, the system was not launched publicly until late in the 1990s.

In 1981, the first HDTV demonstration in the United States was held. It had the same 5:3 aspect ratio as the Japanese system.^[4] Upon visiting a demonstration of the Japanese Multiple sub-nyquist sampling Encoding system (MUSE) HDTV system in Washington, US President Ronald Reagan was most impressed and officially declared it "a matter of national interest" to introduce HDTV to the USA. Several systems were proposed as the new standard for the USA, including the Japanese MUSE system, but all were rejected by the FCC because of their higher bandwidth requirement.

A new standard had to be radically efficient, needing less bandwidth for HDTV than the existing NTSC standard for SDTV. It was commonly understood only a digital system could possibly bring desired results, however nothing such had yet been developed. Pattern-recognition research for cruise missile development at the NASA Jet Propulsion Laboratory provided the basis for developing the MPEG set of compression standards.

The rise of digital compression

As soon as the MPEG-1 standard provided the foundation for digital TV, development of modern TV standards started worldwide. After finalization of MPEG-2 in mid 1993, the DVB organisation within the International Telecommunication Union's radio telecommunications sector (ITU-R) developed the ETSI standard 300-327 by the end of December 1993.

It became known as DVB-T for digital terrestrial TV. DVB-S and DVB-C standards soon followed for terrestrial, satellite and cable transmission of SDTV and HDTV. In the USA the Grand Alliance proposed ATSC as the new standard for SDTV and HDTV. Both ATSC and DVB were based on the MPEG-2 standard. The DVB-S2 standard is based on the newer and more efficient H.264/MPEG-4 AVC compression standards. Common for all DVB standards is the use of highly efficient modulation techniques for further reducing bandwidth, and foremost for reducing receiver-hardware and antenna requirement.

In 1983, the International Telecommunication Union's radio telecommunications sector (ITU-R) set up a working party (IWP11/6) with the aim of setting a single international HDTV standard. One of the thornier issues concerned a suitable frame/field refresh rate, with the world already strongly demarcated into two camps, 25/50Hz and 30/60Hz, related by reasons of picture stability to the frequency of their mains electrical supplies.

The WP considered many views and through the 1980s served to encourage development in a number of video digital processing areas, not least conversion between the two main frame/field rates using motion vectors, which led to further developments in other areas. While a comprehensive HDTV standard was not in the end established, agreement on the aspect ratio was achieved.

Initially the existing 5:3 aspect ratio had been the main candidate, but due to the influence of widescreen cinema, the aspect ratio 16:9 (1.78) eventually emerged as being a reasonable compromise between 5:3 (1.67) and the common 1.85 widescreen cinema format. (It has been suggested that the 16:9 ratio was chosen as being the geometric mean of 4:3, Academy Ratio, and 2.35:1, the widest cinema format in common use, in order to minimise wasted screen space when displaying content with a variety of aspect ratios.)

An aspect ratio of 16:9 was duly agreed at the first meeting of the WP at the BBC's R & D establishment in Kingswood Warren. The resulting ITU-R Recommendation ITU-R BT.709-2 ("Rec. 709") includes the 16:9 aspect ratio, a specified colorimetry, and the scan modes 1080i (1,080 actively-interlaced lines of resolution) and 1080p (1,080 progressively-scanned lines).

It also includes the alternative 1440 x 1152 HDMAC scan format. (According to some reports, a mooted 720p format (720 progressively-scanned lines) was viewed by some at the ITU as an "enhanced" television format rather than a true HDTV format,^[5] and so was not included, although 1920x1080 and 1280x720p systems for a range of frame and field rates were defined by several US SMPTE standards.)

The demise of analog HD systems

However, even that limited standardization of HDTV did not lead to its adoption, principally for technical and economic reasons. Early HDTV commercial experiments such as NHK's MUSE required over four times the bandwidth of a standard-definition (SDTV) broadcast, and despite efforts made to shrink the required bandwidth down to about 2 times that of SDTV, it was still only distributable by satellite. In addition, recording and reproducing a HDTV signal was a significant technical challenge in the early years of HDTV. Japan remained the only country with successful public broadcast analog HDTV, known as "Hi-vision", featuring a 5:3 aspect ratio screen with 1,125 interlaced lines (1,035 active lines) at the rate of 60 fields per second. The single satellite transponder MUSE service was turned off on January 1, 2007.

In Europe, analog 1,125-line HD-MAC test broadcasts were performed in the early 1990s, but did not lead to any established public broadcast service.

Inaugural Digital HDTV Public broadcast

HDTV technology was introduced in the United States in the 1990s by the Digital HDTV Grand Alliance, a group of television companies and MIT.^[6][7] On April 6, 1997, CBS went on the air with WCBS-HD from the top of the Empire State Building, New York, doing demos and evaluations.^[8] Astronaut John Glenn's return to space, on board the Space Shuttle Discovery wasn't the only thing launched on October 29, 1998. The American Advanced Television Systems Committee (ATSC) HDTV system had its public launch during the live coverage of the lift-off.^[9] The signal was transmitted coast-to-coast, and was seen by the public in science centers, and other public theaters specially equipped to receive and display the broadcast.^[9] The broadcast was made possible by the Harris Corporation, which sponsored the equipment necessary for transmitting and receiving the broadcast.^[9] The broadcast was hosted by former CBS News anchor, Walter Cronkite, former Gemini/Apollo era astronaut Pete Conrad and former NBC News anchor Mary Alice Williams.^[10]

Modern digital compression and standardization

Digital compression methods such as MPEG-2 and H.264/MPEG-4 AVC allow the bandwidth of a single analog TV channel (6 MHz in the US) to carry up to 5 standard-definition or up to 2 high-definition digital TV channels instead.

Most developed nations have plans in place for a transition to digital television, but not necessarily (or exclusively) to HDTV.

For example, on February 17, 2009, the US will terminate all full-power terrestrial analog broadcasting (although some smaller local stations have later deadlines), with both standard definition TV (SDTV) and HDTV being allowed.

Current HDTV broadcast standards include ATSC (North America, parts of Central America and South Korea), DVB (Europe, Australia, parts of Asia, South America and Africa) and ISDB-T (Japan, Brazil).

HDTV sources

The rise in popularity of large screens and projectors has made the limitations of conventional Standard Definition TV (SDTV) increasingly evident. An HDTV compatible television set will not improve the quality of SDTV channels. It will make it even worse because of scaling artifacts. To display a superior picture, high definition televisions require a High Definition (HD) signal. Typical sources of HD signals are as follows:

Over the air with an antenna. Most cities in the US with major network affiliates broadcast over the air in HD. To receive this signal an HD tuner is required. Most newer high definition televisions have an HD tuner built in. For HDTV televisions without a built in HD tuner, a separate set-top HD tuner box can be rented from a cable or satellite company or purchased.

Cable television companies often offer HDTV broadcasts as part of their digital broadcast service. This is usually done with a set-top box or CableCARD issued by the cable company. Alternatively one can usually get the network HDTV channels for free with basic cable by using a QAM tuner built into their HDTV or set-top box. Some cable carriers also offer HDTV on-demand playback of movies and commonly viewed shows.

Satellite-based TV companies, such as Astra (in the Netherlands), Premiere (in Germany), DirecTV and Dish Network (both in North America), Sky Digital and freesat (in the UK and Ireland), Bell TV and Star Choice (both in Canada) and NTV Plus (in Russia), offer HDTV to customers as an upgrade. New satellite receiver boxes and a new satellite dish are often required to receive HD content.

Video game systems, such as the PlayStation 3 and Xbox 360, and digital set-top boxes that rely on an Internet connection, such as the Apple TV, can output an HD signal. The Xbox Live Marketplace, iTunes Music Store, and PlayStation Network services offer HD movies, TV shows, movie trailers, and clips for download, but generally at lower bitrates than a Blu-ray Disc.

Most newer computer graphics cards have either HDMI or DVI interfaces, which can be used to output images or video to an HDTV.

The optical disc standard Blu-ray Disc (25GB-50GB) can provide enough digital storage to store up to 10 hours of HD video content, depending on encoder settings.^[12]

A DVD-R disc (~4.7GB-9GB) can also provide storage for up to 3 hours of HD video content, readable by a Blu-ray player, PlayStation 3 video game console or Blu-ray drives installed on PC towers, depending on encoder settings.

Notation

HDTV broadcast systems are identified with three major parameters:

Frame size in pixels is defined as number of horizontal pixels x number of vertical pixels, for example 1280 x 720 or 1920 x 1080. Often number of horizontal pixels is implied from context and is omitted.

Scanning system is identified with the letter p for progressive scanning or i for interlaced scanning.

Frame rate is identified as number of video frames per second. For interlaced systems an alternative form of specifying number of fields per second is often used. Recently the uniform notation of specifying number of frames per second both for progressive and interlaced video became increasingly popular.^[14]

If all three parameters are used, they are specified in form frame size  scanning system  frame rate. Often, one parameter can be dropped if its value is implied from context. In this case the remaining numeric parameter is specified first, followed by the scanning system.

For example, 1920x1080p25 identifies progressive scanning format with 25 frames per second, each frame being 1920 pixels wide and 1080 pixels high. The 1080i25 or 1080i50 notation identifies interlaced scanning format with 50 fields(25 frames) per second, each frame being 1920 pixels wide and 1080 pixels high. The 1080i30 or 1080i60 notation identifies interlaced scanning format with 60 fields (30 frames) per second, each frame being 1920 pixels wide and 1080 pixels high. The 720p60 notation identifies progressive scanning format with 60 frames per second, each frame being 720 pixels high, 1280 pixels horizontally are implied.

While 50Hz systems have only three scanning rates: 25i, 25p and 50p, 60Hz systems operate with much wider set of frame rates: 23.98p, 24p, 29.97i/59.94i, 29.97p, 30p, 59.94p and 60p. In the days of standard definition television, the fractional rates were often rounded up to whole numbers, like 23.98p was often called 24p, or 59.94i was often called 60i. High definition television allows using both fractional and whole rates, therefore strict usage of notation is required. Nevertheless, 29.97i/59.94i is almost universally called 60i, likewise 23.98p is called 24p.

For commercial naming of a product, the frame rate is often dropped and is implied from context, e.g. a "1080i television set". A frame rate can also be specified without a resolution. For example 24p means 24 progressive scan frames per second, and 50i means 25 interlaced frames per second. Most HDTV systems support resolutions and frame rates defined either in the ATSC table 3, or in EBU specification. The most common are noted below.

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8VSB is the 8-level vestigial sideband modulation method adopted for terrestrial broadcast of the ATSC digital television standard in the United States, Canada, and other countries. 8VSB is capable of transmitting three bits (2³=8) at a time.

Throughput

In the 6 MHz (megahertz) channel used for broadcast ATSC, 8VSB carries a symbol rate of 10.76 Mbaud, a gross bit rate of 32 Mbit/s, and a net bit rate of 19.39 Mbit/s of usable data. The net bit rate is lower due to the addition of forward error correction codes. The eight signal levels are selected with the use of a trellis encoder. There are also the similar modulations 2VSB, 4VSB, and 16VSB. 16VSB was notably intended to be used for ATSC digital cable, but quadrature amplitude modulation (QAM) has become the de facto industry standard instead.

Power saving advantages

A significant advantage of 8VSB for broadcasters is that it requires much less power to cover an area comparable to that of the earlier NTSC system, and it is reportedly better at this than the most common alternative system, COFDM. Some stations can cover the same area while transmitting at an effective radiated power of approximately 25% of analog broadcast power. While NTSC and most other analog television systems also use a vestigial sideband technique, the unwanted sideband is filtered much more effectively in ATSC 8VSB transmissions. 8VSB uses a Nyquist filter to achieve this. Reed-Solomon error correction is the primary system used to retain data integrity.

In summer of 2005, the ATSC published standards for Enhanced VSB, or E-VSB [1]. Using forward error correction, the E-VSB standard will allow DTV reception on low power handheld receivers with smaller antennas in much the same way DVB-H does in Europe, but still using 8VSB transmission.

Disputes over ATSC's use

For some period of time, there had been a continuing lobby for changing the modulation for ATSC to COFDM, the way DVB-T is transmitted in Europe, and ISDB-T in Japan. However, the FCC has always held that 8VSB is the better modulation for use in U.S. digital television broadcasting. In a 1999 report, the Commission found that 8VSB has better threshold or carrier-to-noise (C/N) performance, has a higher data rate capability, requires less transmitter power for equivalent coverage, and is more robust to impulse and phase noise.^[1] As a result, it denied in 2000 a petition for rulemaking from Sinclair Broadcast Group requesting that broadcasters be allowed to choose between 8VSB or COFDM as is most appropriate for their area of coverage.^[2] The FCC report also acknowledged that COFDM is "generally be expected to perform better in situations where there is dynamic multipath," such as mobile operation or in the presence of trees that are moving in high winds. Since the original FCC report, further improvements to VSB reception technologies as well as the introduction of E-VSB option to ATSC have reduced this challenge somewhat. Because of continued adoption of the 8VSB-based ATSC standard in the U.S., and a large growing ATSC receiver population, a switch to COFDM is now essentially impossible. Congress passed a law mandating that all analog terrestrial transmissions in the US will be turned off in February 2009, and 8VSB tuners are increasingly widespread in new TVs due to FCC tuner mandates, further complicating a future transition to COFDM.

Yet, a Centris study released in February 2008 revealed "serious 'gaps' in digital TV signal coverage across the country "when taking into account 'outdoor receiving antenna sensitivity and multipath interference.'" As a result, the Centris study states, "certain households - for example: those that are not elevated; are surrounded by trees; or have set-top antennas instead of roof-top antennas; among other factors - are at higher risk of having limited or no signal coverage. Centris surveys reveal that 75% or more of over-the-air households have only set-top antennas."^[3]

8VSB vs COFDM

The previously cited FCC Report also found that COFDM has better performance in dynamic and high level static multipath situations, and offers advantages for single frequency networks and mobile reception. Nonetheless, in 2001, a technical report compiled by the COFDM Technical Group concluded that COFDM did not offer any significant advantages over 8VSB. The report recommended in conclusion that receivers be linked to outdoor antennas raised to roughly 30 feet (9 m) in height. Neither 8VSB nor COFDM performed acceptably in most indoor test installations. ^[4]

However, there were questions whether the COFDM receiver selected for these tests - a transmitter monitor[2] lacking normal front end filtering - colored these results. Retests that were performed using the same COFDM receivers with the addition of a front end band pass filter gave much improved results for the DVB-T receiver, but further testing was not pursued.

The debate over 8VSB versus COFDM modulation is still ongoing. Proponents of COFDM argue that it resists multipath far better than 8VSB. Early 8VSB DTV (digital television) receivers often had difficulty receiving a signal in urban environments. Newer 8VSB receivers, however, are better at dealing with multipath. Moreover, 8VSB modulation requires less power to transmit a signal the same distance. In less populated areas, 8VSB may outperform COFDM because of this. However, in some urban areas, as well as for mobile use, COFDM may offer better reception than 8VSB. In order to broaden the application of VSB, several "enhanced" VSB systems are now in development, most notably E-VSB, A-VSB, and MPH.

Bifurcation of digital transmission systems

The United States is also notable for creating a separate transmission system for digital radio. An in-band on-channel (IBOC) system developed by iBiquity will be used instead of the Eureka 147 Digital Audio Broadcasting system that has been selected in Europe. This is partially because the L band normally used for that technology is unavailable in the U.S. However, the American IBOC system uses COFDM, as does Eureka 147 and another standard known as Digital Radio Mondiale.

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Digital television (DTV) is the sending and receiving of moving images and sound by discrete (digital) signals, in contrast to the analog signals used by analog TV. Introduced in the late 1990s , this technology appealed to the television broadcasting business and consumer electronics industries because it offers new financial opportunities.

Digital television is more flexible and efficient than analog television. When properly used by broadcasters, digital television can allow higher-quality images, sound, and more programming choices than analog does. However, a digital signal does not inherently produce higher-quality video and audio than an analog signal.

The first country to make a wholesale switch to Digital Over-the-Air (terrestrial) broadcasting was the Netherlands, in 2006. This was followed by Finland in 2007. ^[1] After February 17, 2009, full-power television stations in the USA will broadcast in digital only. In Canada, this is scheduled to happen Aug. 31, 2011. China is scheduled to switch in 2015.

While the majority of the viewers of over-the-air broadcasting in the USA watch full-power stations (which number about 1800), there are three other categories of TV stations in the USA: “low-power” stations, “Class A” stations, and “TV translator” stations. There is presently no deadline for these stations, about 7100 in number, to convert to digital broadcasting.

Technical information

Formats and bandwidth

Digital television supports many different picture formats defined by the combination of size, aspect ratio (height to width ratio) and interlacing. With terrestrial broadcasting in the USA the range of formats can be coarsely divided into two categories: HDTV and SDTV. It should be noted that these alone are not very precise, and many subtle intermediate cases exist.

High-definition television (HDTV), which is usually used over DTV, uses one of two formats: 1280 × 720 pixels in progressive scan mode (abbreviated 720p) or 1920 × 1080 pixels in interlace mode (1080i). Each of these utilizes a 16:9 aspect ratio. (Some televisions are capable of receiving an HD resolution of 1920 × 1080 at a 60 Hz progressive scan frame rate — known as 1080p60 — but this format is not standard and no broadcaster is able to transmit these signals over the air at acceptable quality yet.)

Standard definition TV (SDTV), by comparison, may use one of several different formats taking the form of various aspect ratios depending on the technology used in the country of broadcast. For 4:3 aspect-ratio broadcasts, the 640 × 480 format is used in NTSC countries, while 720 × 576 (rescaled to 768 × 576) is used in PAL countries. For 16:9 broadcasts, the 704 × 480 (rescaled to 848 × 480) format is used in NTSC countries, while 720 × 576 (rescaled to 1024 × 576) is used in PAL countries. However, broadcasters may choose to reduce these resolutions to save bandwidth (e.g., many DVB-T channels in the United Kingdom use a horizontal resolution of 544 or 704 pixels per line).^[2] The perceived quality of such programming is surprisingly acceptable because of interlacing—the effective vertical resolution is halved to 288 lines.

Each commercial terrestrial DTV channel in North America is permitted to be broadcast at a data rate up to 19 megabits per second, or 2.375 megabytes per second. However, the broadcaster does not need to use this entire bandwidth for just one broadcast channel. Instead the broadcast can be subdivided across several video subchannels of varying quality and compression rates, including non-video datacasting services that allow one-way high-bandwidth streaming of data to computers.

A broadcaster may opt to use a standard-definition digital signal instead of an HDTV signal, because current convention allows the bandwidth of a DTV channel (or "multiplex") to be subdivided into multiple subchannels (similar to what most FM stations offer with HD Radio), providing multiple feeds of entirely different programming on the same channel. This ability to provide either a single HDTV feed or multiple lower-resolution feeds are often referred to as distributing one's "bit budget" or multicasting. This can sometimes be arranged automatically, using a statistical multiplexer (or "stat-mux"). With some implementations, image resolution may be less directly limited by bandwidth; for example in DVB-T, broadcasters can choose from several different modulation schemes, giving them the option to reduce the transmission bitrate and make reception easier for more distant or mobile viewers.

Reception

There are a number of different ways to receive digital television. One of the oldest means of receiving DTV (and TV in general) is using an antenna (known as an aerial in some countries). This way is known as Digital Terrestrial Television (DTT). With DTT, viewers are limited to whatever channels the antenna picks up. Signal quality will also vary.

Other ways have been devised to receive digital television. Among the most familiar to people are digital cable and digital satellite. In some countries where transmissions of TV signals are normally achieved by microwaves, digital MMDS is used. Other standards, such as DMB and DVB-H, have been devised to allow handheld devices such as mobile phones to receive TV signals. Another way is IPTV, that is receiving TV via Internet Protocol, relying on DSL or optical cable line. Finally, an alternative way is to receive digital TV signals via the open Internet. For example, there is a lot of P2P Internet Television software that can be used to watch TV on your computer.

Some signals carry encryption and specify use conditions (such as "may not be recorded" or "may not be viewed on displays larger than 1 m in diagonal measure") backed up with the force of law under the WIPO Copyright Treaty and national legislation implementing it, such as the U.S. Digital Millennium Copyright Act. Access to encrypted channels can be controlled by a removable smart card, for example via the Common Interface (DVB-CI) standard for Europe and via Point Of Deployment (POD) for IS or named differently CableCard.

Protection parameters for terrestrial DTV broadcasting

In order for digital television to be broadcast, it must initially interoperate with analog television. When analog television ceases to exist, digital television signals must not interfere with each other. Propagation research carried out by several important digital television regulators has derived a table of acceptable parameters for tolerable interference margins. This table below provides all the important acceptable interference margins.

Interaction

Interaction happens between the TV watcher and the DTV system. It can be understood in different ways, depending on which part of the DTV system is concerned. It can also be an interaction with the STB only (to tune to another TV channel or to browse the EPG).

Modern DTV systems are able to provide interaction between the end-user and the broadcaster through the use of a return path. With the exceptions of coaxial and fiber optic cable, which can be bidirectional, a dialup modem, Internet connection, or other method is typically used for the return path with unidirectional networks such as satellite or antenna broadcast.

In addition to not needing a separate return path, cable also has the advantage of a communication channel localized to a neighborhood rather than a city (terrestrial) or an even larger area (satellite). This provides enough customizable bandwidth to allow true video on demand.

Advantages to conversion

DTV has several advantages over analog TV, the most significant being that digital channels take up less bandwidth (and the bandwidth needs are continuously variable, at a corresponding cost in image quality depending on the level of compression). This means that digital broadcasters can provide more digital channels in the same space, provide high-definition television service, or provide other non-television services such as multimedia or interactivity. DTV also permits special services such as multiplexing (more than one program on the same channel), electronic program guides and additional languages, spoken or subtitled. The sale of non-television services may provide an additional revenue source. In many cases, viewers perceive DTV to have superior picture quality, improved audio quality, and easier reception than analog.

Disadvantages to conversion

Impact on existing analog technology

The analog switch-off ruling, which so far has met with little opposition from consumers or manufacturers, would render all non-digital televisions obsolete on the switch-off date unless connected to an external off-the-air tuner, analog or digital cable, or a satellite system. An external converter box can be added to non-digital televisions to lengthen their useful lifespan. Several of these devices have already been shown and, while few were initially available, they are becoming more available by the day. In the United States, a government-sponsored coupon is available to offset the cost of an external converter box. Once connected to the converter unit, operation of non-digital units is achievable and, in most cases, rich in new features (in comparison to previous analog reception operation). At present, analog switchoff is scheduled for February 17, 2009 in the United States and August 31, 2011 in Canada.

Some existing analog equipment will be less functional with the use of a converter box. For example, television remote controls will no longer be effective at changing channels, because that function will instead be handled by the converter box. Similarly, video recorders for analog signals (including both tape-based VCRs and hard-drive-based DVRs) will not be able to select channels, limiting their ability to automatically record programs via a timer or based on downloaded program information. ATSC-capable VCRs are likely to be far less common than their NTSC counterparts, with most current offerings being VCR/DVD combo units. Also, older handheld televisions, which rely primarily on over-the-air signals and battery operation, will be rendered impractical since the proposed converter boxes are not portable nor powered with batteries, except one: The Artec T3A.

Portable radios that are able to listen to television audio on VHF channels 2-13 would also lose this ability, while television stations which formerly broadcast on Channel 6 (with analog FM audio on 87.75 MHz) would no longer be heard on standard FM broadcast band radios. These stations would lose the ability for commuters to listen to their broadcasts.

If any new TVs contained only an ATSC tuner, this could prevent older devices such as VCRs and video game consoles with only an analog RF output from connecting to the TV. Connection would require an analog to digital converter box, which is the opposite of what is currently being sold. Such a box would also likely introduce additional delay into the video signal. Fortunately, analog inputs suitable for connection to VCRs have remained available on all current digital-capable TV's.

Compression artifacts and allocated bandwidth

DTV images have some picture defects that are not present on analog television or motion picture cinema, because of present-day limitations of bandwidth and compression algorithms such as MPEG-2.

When a compressed digital image is compared with the original program source, some hard-to-compress image sequences may have digital distortion or degradation.

Broadcasters attempt to balance their needs to show high quality pictures and to generate revenue by using a fixed bandwidth allocation for more services.

Buffering and preload delay

Unlike analog televisions, digital televisions have a significant delay when changing channels, making "channel surfing" more difficult.

Different devices need different amounts of preload time to begin showing the broadcast stream, resulting in an audio echo effect when two televisions in adjacent rooms of a house are tuned to the same channel.

Effects of poor reception

Changes in signal reception from factors such as degrading antenna connections or worsening weather conditions may gradually reduce the quality of analog TV. The nature of digital TV results in a perfect picture initially, until the receiving equipment starts picking up noise or losing signal. Some equipment will show a picture even with significant damage, while other devices may go directly from perfect to no picture at all (and thus not show even a slightly damaged picture). This latter effect is known as the digital cliff or cliff effect.

For remote locations, distant analog channels that were previously acceptable in a snowy and degraded state may be anything from perfect to completely unavailable. In areas where transmitting antennas are located on mountains, viewers who are too close to the transmitter may find reception difficult or impossible because the strongest part of the broadcast signals pass above them. The use of higher frequencies will add to these problems, especially in cases where a clear line-of-sight from the receiving antenna to the transmitter is not available. Many intermittent signal fading conditions, such as the rapid-fade effect caused by reflections of UHF television signals from passing aircraft, will not produce intermittently-snowy video, but potential intermittent loss of the entire signal.

Multi-path interference is a much more significant problem for DTV than for analog TV and affects reception, particularly when using simple antennas such as rabbit ears. This is perceived as "ghosting" in the analog domain, but this same problem manifests itself in a much more insidious way with DTV. Unlike the problems of the preceding paragraph, multi path can in fact be worse for DTV under high signal conditions. It is perceived by the viewer as a spotty loss of audio or picture freezing and pixelation as people move about in the vicnity of the antenna and is often worse in wet weather due to increased reflection re-polarization of the DTV signal arriving from multiple paths. In extreme cases the signal is lost completely. The cure is to employ a directional antenna outdoors, aligned with the transmitting location.

Limitations

The greatest DTV detail level currently available is 1080i, which is a 1920x1080 interlaced widescreen format. Interlacing is done to reduce the image bandwidth to one-half of full-frame quality, which gives better frame update speed for quick-changing scenes such as sports, but at the same time reduces the overall image quality and introduces image flickering and "crawling scanlines" because of the alternating field refresh.

Full-frame progressive-scan 1920x1080 (1080p) is not part of the ATSC specification^[6]. High frame-rate 1080p may become an option in the near future, as a result of recent technology advances such as H.264/MPEG-4 AVC video coding, allowing more detail to be sent via the same channel bandwidth allocations that are used now.

The limitations of interlacing can be partially overcome through the use of advanced image processors in the consumer display device, such as the use of Faroudja DCDi and using internal frame buffers to eliminate scanline crawling.

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A Nokia Mediamaster 260 S digital satellite-television set-top box

A set-top box (STB) or set-top unit (STU) is a device that connects to a television and an external source of signal, turning the signal into content which is then displayed on the television screen.

History

Before the All-Channel Receiver Act of 1962 required US television receivers to be able to tune the entire VHF and UHF range (which in North America was NTSC-M channels 2 through 83 on 54 to 890 MHz), a set-top box known as a UHF converter would be installed at the receiver to shift a portion of the UHF-TV spectrum onto low-VHF channels for viewing. As some 1960s-era twelve-channel TV sets remained in use for many years, and Canada and Mexico were slower than the US to require UHF tuners to be factory-installed in new TV's, a market for these converters continued to exist for much of the 1970s.

Cable television represented a possible alternative to deployment of UHF converters as broadcasts could be frequency-shifted to VHF channels at the cable head-end instead of the final viewing location. Unfortunately, cable brought a new problem; most cable systems could not accommodate the full 54-890 MHz VHF/UHF frequency range and the twelve channels of VHF space were quickly exhausted on most systems. Adding any additional channels therefore needed to be done by inserting the extra signals into cable systems on non-standard frequencies, typically either below VHF channel 7 (midband) or directly above VHF channel 13 (superband).

These frequencies corresponded to non-television services (such as two-way radio) over-the-air and were therefore not on standard TV receivers. Before cable-ready TV sets became common in the late 1980s, a set-top box known as a cable converter box was needed to receive the additional analog cable TV channels and convert them to frequencies that could be seen on a regular TV. These boxes often provided a wired or wireless remote control which could be used to shift one selected channel to a low-VHF frequency (most often channels 3 or 4) for viewing. Block conversion of the entire affected frequency band onto UHF, while less common, was used by some models to provide full VCR compatibility and the ability to drive multiple TV sets, albeit with a somewhat non-standard channel numbering scheme.

Newer television receivers greatly reduced the need for external set-top boxes, although cable converter boxes continue to be used to descramble premium cable channels and to receive digital cable channels, along with using interactive services like video on demand, pay per view, and home shopping through television. Satellite and microwave-based services also require specific external receiver hardware, so the use of set-top boxes of various formats never completely disappeared.

Digital television

A consumer Palcom DSL-350 satellite-receiver, the IF demodulation tuner is on the bottom left, and a Fujitsu MPEG decoder CPU in the center of the board. Power supply on the right.

Special digital set-top boxes are available for receiving digital television broadcasts on TV sets that do not have a built in digital tuner. In the case of direct broadcast satellite (mini-dish) systems such as SES Astra, Dish Network, or DirecTV, the set-top box is an integrated receiver/decoder (or IRD).

In the United Kingdom, digital set-top boxes (often referred to as digiboxes, after Sky Digital's trademark for their unit) are usually for digital terrestrial television through services such as Freeview, a service operated by the Freeview Consortium, or through digital satellite with BSkyB and also with digital cable. They are used to access television as well as audio and interactive services through the "Red Button" promoted by broadcasters such as the BBC with BBCi or Sky with Sky Active. Current Freeview set-top boxes and digital televisions are not capable of decoding the protocol DVB-T2 that terrestrial High-definition will use in 2009, so viewers will need to purchase an HD receiver when the time comes.

In Australia set-top boxes are the principal means of receiving digital terrestrial broadcasts as comparably few television sets have in-built digital tuners. The Foxtel set-top boxes (including the Foxtel iQ unit) are also used to receive subscription television from Foxtel. For HDTV receiving they are using Beyonwiz manufactured media centers which came to market at March 2007.

In the United States, deployment of a very basic coupon-eligible converter box is supported through a $40 federal subsidy to encourage viewers of over-the-air television to adopt ATSC standards before the shutdown of full-power analog broadcasts planned for February 17, 2009. These boxes are not readily available in Canada and Mexico, where broadcasters are not yet required to transition to digital television, although ATSC-capable tuners are appearing in some new TV's and television-related products such as computer video capture cards, satellite receivers and DVD recorders.

Globally, some boxes also have a built-in digital video recorder (or DVR) which often utilises the electronic programme guide scheduling data and records content to an internal hard drive.

Many TV signal sources

The signal source might be an ethernet cable , a satellite dish, a coaxial cable (see cable television), a telephone line (including DSL connections), Broadband over Power Line, or even an ordinary VHF or UHF antenna. Content, in this context, could mean any or all of video, audio, Internet webpages, interactive games, or other possibilities.

 IPTV

In IPTV networks, the set-top box is a small computer providing two-way communications on an IP network, and decoding the video streaming media. IP set-top boxes have a built in home network interface which can be Ethernet or one of the existing wire home networking technologies such as HomePNA.

In the US and France, IPTV is being used by telephone companies (often on ADSL or optical fibre networks) as a means to compete with traditional local cable television monopolies.

Most of the set top boxes in France are distributed by the Internet providers and allow the consumer to have access to IPTV, VoIP, Internet and media centre functionalities.

Ambiguities in the definition

With the advent of flat panel televisions set-top boxes are now deeper in profile than the tops of most modern TV sets. Because of this set-top boxes are often placed beneath televisions and the term set-top box has become something of a misnomer.

A set-top box does not necessarily contain a tuner of its own. A box connected to a television (or VCR) set's SCART connector is fed with the baseband television signal from the set's tuner, and can ask the television to display the returned processed signal instead.

This SCART feature had been used for connection to analogue decoding equipment by Pay TV operators in Europe, and in the past was used for connection to teletext equipment before the decoders became built-in. The outgoing signal could be of the same nature as the incoming signal, or RGB component video, or even an "insert" over the original signal, thanks to the "fast switching" feature of SCART.

In case of analogue pay-TV, this approach avoided the need for a second remote control. The use of digital television signals in more modern pay-TV schemes requires that decoding take place before the digital-to-analogue conversion step, rendering the video outputs of an analogue SCART connector no longer suitable for interconnection to decryption hardware. Standards such as DVB's Common Interface and ATSC's CableCARD therefore use a PCMCIA-like card inserted as part of the digital signal path as their alternative to a tuner-equipped set-top box.

The distinction between external tuner or demodulator boxes (traditionally considered to be "set-top boxes") and storage devices (such as VCR, DVD or disc-based PVR units) is also blurred by the increasing deployment of satellite and cable tuner boxes with hard discs, network or USB interfaces built-in.

Devices with computer terminal-like capabilities, such as the WebTV thin-client, also fall into a grey area.

Software quality

As complexity of the set-top box increases, the software quality practices of the industry become obvious and many systems have bugs;^[1] this is a particularly troublesome issue with digital television apparatus being rushed to market before the government-mandated shutdown of full-power analogue television broadcasts. See Comparison of CECB units for details on individual units.

However, users of computer-based solutions such as Linux MCE and MythTV have a very flexible list of possible features ranging from basic DVR-like functionality to features such as DVD copying, home automation, and house-wide music/video file playing. They also can fix any software bugs just by joining the development team.A

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Switched Video, also called Switched Digital Video or SDV, is a telecommunications industry term for a network scheme for distributing digital video via a cable. Switched video sends the digital video in a more efficient manner so that additional uses may be made of the freed up bandwidth. The scheme applies to digital video distribution both on typical cable TV systems using QAM channels, or on IPTV systems. Users of analog video transmitted on the cable are unaffected. See diagram below for an illustration of how Switched Video saves bandwidth on a cable company's cables in the last mile where channels are transmitted via coaxial cable.

In current Hybrid fibre-coaxial systems, a fiber optic network extending from the operator's central office carries all video channels out to a fiber optic node which services any number of homes ranging from 1 to 2000 homes. From this point, all channels are sent via coaxial cable to each of the homes. Note that only a percentage of these homes are actively watching channels at a given time. Rarely are all channels being accessed by the homes in the service group.

In a Switched Video system, the unwatched channels do not need to be sent.

In cable TV systems in the United States, equipment in the home sends a channel request signal back to the distribution hub. If a channel is not currently being transmitted on the coaxial line, the distribution hub allocates a new QAM channel and transmits the new channel to the coaxial cable via the fiber optic node. For this to work, the equipment in the home must have two-way communication ability. Switched video uses the same mechanisms as Video on Demand and may be viewed as a non-ending video on demand show that any number of users may share.

Two-way communication is handled differently between cable and IPTV schemes. IPTV use communication protocols used on the Internet but requires entirely new video distribution infrastructure. Cable companies in the United States elected the less costly approach of upgrading existing infrastructure, and European operators may well take the same approach. In the upgrade approach, various proprietary schemes use specific frequencies for passing messages back to the distribution hub. In the United States, there is a recent standard for two-way communications from consumer electronics devices using CableCARDs, such as digital video recorders, high-definition televisions and home theater computers known as OpenCable which require three things to work: hardware that implements these three standards which allow the cable receiver to communicate with the cable head end: SCTE 55-1 which is the ALOHA protocol-based standard used by General Instrument and Motorola equipment, SCTE 55-2 a.k.a. DAVIC which is a slotted ALOHA-based standard used by Scientific Atlanta and Cisco cable boxes, and DOCSIS Set-top Gateway, an extension to the DOCSIS cable modem standard to make it degrade gracefully under adverse conditions and still provide as much functionality as possible; a CableCARD that decrypts the channel for the cable receiver; and a Java-based OpenCable Application Platform (abbreviated as OCAP) stack that allows the cable company to download an application written in OCAP to run on any cable receiver which contains an OCAP stack. This application programs the cable receiver on how to communicate with the switched video server, and does other tasks like running an interactive program guide and programming the receiver on how to perform video on demand. The cable company could choose whichever two-way communication standard it wants out of the three. It could choose the standard that its pre-OCAP hardware used in order to preserve its investment in legacy hardware, or could deploy DOCSIS Set-top Gateway in order to provide much more capacity and efficiency than either of the other two protocols.

For a switched video system to work on cable systems, all digital television users in a subscription group must have devices capable of communicating to the distribution hub in a compatible manner. Unlike other features dependent on two-way communication such as Video on Demand, the requirement to upgrade all digital set-top boxes within a group makes conversion to switched video extremely expensive. CableLabs proposed in the CableCARD 2.0 specification that two-way communication be supported with a scheme which required more powerful hardware capable of running Java programs. Many cable companies have indicated they will build lower cost devices that do not require this OCAP programing environment, so that upgrading to a switched video system would not be as costly. Consumer electronics companies also prefer a more light weight solution for two-way communication, and so absent a standard for two-way communication, the conversion to switched video may require many years to complete.

Switched video is sometimes abbreviated as SDV for switched digital video, or SVB, for switched video broadcast.A

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Digital television radio (or DTR) is an informal term which describes the music channels that are provided with a digital television service. In terms of price and musical variety, DTR falls somewhere between regular AM or FM radio, and satellite radio. However, because it is delivered through a digital signal, the actual sound quality is, in theory, equal to satellite radio.

DTR cannot be purchased as a service on its own. To obtain it, one must subscribe to a digital television service, typically satellite television or digital cable. DTR music channels are usually provided as part of the "basic" television subscription service or package.

Number of channels

The number of music channels offered varies with each service provider. In the United States, DirecTV offers up to 72 channels of XM Satellite Radio, and Dish Network offers 95 channels, 65 provided by Sirius Satellite Radio, and a few offerings from Muzak for residential subscribers.

In Canada, Bell TV and Vidéotron offer 45 channels provided by Galaxie, while Star Choice, Shaw Digital Cable and Rogers Digital Cable each offer 40 music channels: 20 provided by Max Trax, the other 20 provided by Galaxie. In many markets, Rogers Cable also provides digital cable feeds of most local AM and FM radio stations; Rogers no longer offers the older model of cable FM service. Persona offers 39 channels from Galaxie and Maxtrax.

In the United Kingdom, digital television radio from satellite is received mainly by Sky Television customers, as part of their satellite television service, however other equipment is available to receive many of the non subscription radio and TV channels free. As of June 2004, there were approximately 90 radio stations on the Sky Digital service. Around 15 channels are available on the digital terrestrial television service, free of charge.

In Australia, Federal Government funded television stations ABC and SBS broadcast multiple music channels alongside their digital TV services. These stations are non-commercial, each featuring specific types of music such as Jazz, Blues or Classical, with the SBS channels featuring foreign and ethnic programming, which are not normally played on commercial radio.

Some cable and satellite television providers also simulcast AM and FM radio stations along with their DTR bundles.

Listening to DTR

One can listen to a DTR channel simply by entering the channel on one's television. However, this requires leaving the television on, and uses television speakers which are fairly limited in sound quality. Therefore, the recommended set-up is to connect the audio outputs of the television set-top box directly to a stereo system. Set-top boxes typically have an extra set of audio outputs to facilitate this. Also, as a song is playing, additional information such as the song title, artist and album typically appear on the television screen.

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Cable modem terminations system.

A cable modem termination system or CMTS is equipment typically found in a cable company's headend, or at cable company hubsite and is used to provide high speed data services, such as cable internet or Voice over IP, to cable subscribers.

In order to provide these high speed data services, a cable company will connect its headend to the Internet via very high capacity data links to a network service provider. On the subscriber side of the headend, the CMTS enables the communication with subscribers' cable modems. Different CMTSs are capable of serving different cable modem population sizes - ranging from 4,000 cable modems to 150,000 or more, depending in part on traffic. A given headend may have between half a dozen to a dozen or more CMTSs to service the cable modem population served by that headend or HFC hub.

One way to think of a CMTS is to imagine a router with Ethernet interfaces (connections) on one side and coax RF interfaces on the other side. The RF/coax interfaces carry RF signals to and from the subscriber's cable modem.

In fact, most CMTSs have both Ethernet interfaces (or other more traditional high-speed data interfaces) as well as RF interfaces. In this way, traffic that is coming from the Internet can be routed (or bridged) through the Ethernet interface, through the CMTS and then onto the RF interfaces that are connected to the cable company's hybrid fiber coax (HFC). The traffic winds its way through the HFC to end up at the cable modem in the subscriber's home. Traffic going from a subscriber's home systems go through the cable modem and out to the Internet in the opposite direction.

CMTSs typically carry only IP traffic. Traffic destined for the cable modem from the Internet, known as downstream traffic, is carried in IP packets encapsulated in MPEG transport stream packets. These MPEG packets are carried on data streams that are typically modulated onto a TV channel using Quadrature Amplitude Modulation.

Upstream data (data from cable modems to the headend or Internet) is carried in Ethernet frames modulated with QPSK, 16-QAM, 32-QAM, 64-QAM, or S-CDMA. This is done at the "subband" portion of the cable TV spectrum (also known as the "T" channels), a much lower part of the frequency spectrum than the downstream signal.

A typical CMTS allows a subscriber's computer to obtain an IP address by forwarding DHCP requests to the relevant servers. This DHCP server returns, for the most part, what looks like a typical response including an assigned IP address for the computer, gateway/router addresses to use, DNS servers, etc.

The CMTS may also implement some basic filtering to protect against unauthorized users and various attacks. Traffic shaping is sometimes performed to prioritize application traffic, perhaps based upon subscribed plan or download usage. However, the function of traffic shaping is more likely done by a Policy Traffic Switch. A CMTS may also act as a bridge or router.

A customer's cable modem cannot communicate directly with other modems on the line. In general, cable modem traffic is routed to other cable modems or to the Internet through a series of CMTSs and traditional routers. A route could conceivably pass through a single CMTS.

A CMTS provides many of the same functions provided by the DSLAM in a DSL system.

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Digital cable is a type of cable television distribution using digital video compression. The technology was developed by Motorola.

Uses

Cable distributors use digital video compression to transfer more channels through cable networks already in place. Digital technology also gives two-way communication capability to the cable box, so users can purchase pay-per-view programming without use of a telephone line, in addition to video on demand services and a secure signal. Some providers also display caller ID information to users which have that provider's cable telephone service.

Channels

The addition of this capability complicates the notion of a "channel" in digital cable (as well as in over-the-air ATSC digital broadcasts). The formal names for these three numbers are the "major channel" number, "minor channel" number, and "physical channel".

The major number is also known as a virtual channel number. This is a number that the broadcaster chooses that can display on your television (if their cable box doesn't reassign it) that masks the actual "physical channel."

The minor channel is a logical channel of data within the major/physical channel. Technically there can be up to 1024 minor channels in a major channel, though in practice only a few are used (since the bandwidth must be divided among the minor channels).

The physical channel is a number corresponding to a specific frequency range. See: North American cable television frequencies.

There are two ways providers try to make this easier for consumers. The first is PSIP, in which program and channel information is broadcast along with the video, allowing the consumer's decoder (set-top box or display) to automatically identify the many channels and subchannels.

Second, in an effort to hide subchannels entirely, many cable companies map virtual channel numbers to underlying major and minor channels. For example, a cable company might call channel 5-1 "channel 732" and channel 5-2 "channel 733". This also allows the cable company to change the frequency of a channel without changing what the customer sees as a channel number. In such arrangements, the major/minor channel number are called the "QAM channel", and the alternative channel designation is called the "mapped channel", "virtual channel", or simply "channel".

In theory, a set-top box can decode the PSIP information from every channel it receives and use that information to build the mapping between QAM channel and virtual channel. However, cable companies do not always reliably transmit PSIP information. Alternatively, CableCards receive the channel mapping and can communicate that to the set-top box.

Technical information

The standard for HDTV signal transmission over digital cable television systems in the United States is now fixed as both 64-QAM and 256-QAM (Quadrature Amplitude Modulation), which is specified in SCTE 07, and is part of the DVB standard (but not ATSC). This method carries 38.4 Mbit/s using 256-QAM on a 6 MHz channel, which can carry nearly two full ATSC 19.39 Mbit/s transport streams. Each 6-MHz channel is typically used to carry 7–12 digital SDTV channels (256-QAM, MPEG2 MP/ML streams of 3–5 Mbit/s). On many boxes with QAM tuners (most notably the DVR boxes), High Definition versions of local channels and some cable channels are available, and can be picked up even on the older analog TVs, however, the signal is converted to an analog signal.

Digital Cable allows for the broadcast of EDTV (480p) as well as HDTV (720p, 1080i, and eventually 1080p). By contrast, analog cable transmits programs solely in the 480i format (the lowest television definition in use today).

The ATSC standards include a provision for 16-VSB transmission over cable at 38.4 Mbit/s, but the encoding has not yet gained wide acceptance. Some MATV systems may carry 8-VSB and QAM signals, mostly in apartment buildings and similar facilities that use a combination of terrestrial antennas and cable distribution sources (such as HITS or "Headend In The Sky", a unit of Comcast that delivers digital channels by satellite to small cable systems).

Digital cable channels typically are allocated above 552 MHz, the upper frequency of cable channel 78. (Cable channels above channel 13 are at lower frequencies than UHF broadcast channels with the same number, as seen in North American cable television frequencies.) Between 552 and 750 MHz, there is space for 33 6-MHz channels (231–396 SDTV channels); when going all the way to 864 MHz, there is space for 52 6-MHz channels (364–624 SDTV channels).

In the U.S., digital cable systems with 750 MHz or greater activated channel capacity are required to comply with a set of SCTE and CEA standards, and to provide CableCARDs to customers that request them.

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Downloadable Conditional Access System or DCAS is a proposal advanced by CableLabs for secure software download of a specific Conditional Access client (computer program) which controls Digital Rights Management (DRM) into a OCAP-compliant host consumer media device. The National Cable & Telecommunications Association (NCTA) proposes that DCAS be used as a substitute for physical CableCARDs, a standard also created by CableLabs for which products began appearing in August 2004 as part of industry compliance to the FCC mandate, which in turn is pursuant to the Telecommunications Act of 1996. DCAS is a controversial proposal for a variety of reasons: it currently does not exist, has no set deadlines for support on all cable systems, the specification even in draft form is not currently public, may not satisfy FCC requirements that security modules be separable, and requires an operating system (OCAP) that a majority of consumer electronics (CE) manufacturers do not wish to implement.

DCAS System Diagram

DCAS, as currently envisioned, removes the need for physical set-top boxes or CableCARDs currently required to protect encrypted digital content. It is proposed that instead of a card with removable circuitry, a custom ASIC chip be soldered onto the circuitboard of any digital cable-ready device. DCAS software would run on this custom chip. Additional circuitry needed to run the OCAP operating system would be required. OCAP programs then would be used as the sole method of interacting with DCAS since it will enable cable companies to force the download of new security software.

The basic purpose of DCAS is to implement DRM protection in software, supported by future OCAP-compliant consumer devices such as digital televisions, DVRs, and set-top boxes (still required to support legacy non-OCAP-compliant devices). This secures the information transmitted in the link between the cable company and the consumer device. Besides decryption, the DCAS software controls how the content is used—whether it must be deleted immediately after viewing, or after a set period of time, which devices it may be transferred to and if transfer or recording is permitted. The scheme may be used more broadly and is being advanced by Rupert Murdoch's company NDS as a DRM method useful also for portable media players and other devices not attached to cable networks. A working DCAS prototype was created by Samsung and NDS for the cable industry and was demonstrated to the FCC in November 2005.^[1]

It is asserted by proponents that DCAS provides greater security for the cable industry because it allows them to change their entire security structure by downloading new software into host devices. If a particular encryption algorithm is cracked, it can be replaced by another one. Detractors note that if the physical circuitry is compromised, it may not be replaced as is the case with CableCARDs. Some DCAS scenarios do use removable cards: OCAP-based devices may incorporate internal support for a kind of "smart card" (similar to the current SIM chip in a GSM cell-phone) to identify the subscriber and provide further protection. Proponents assert that DCAS is more supportable since DCAS devices would not require a qualified technician to install the card. Detractors assert that the final version of DCAS may require a physical card insertion, and that technicians are not required to insert CableCARDs anyway, since they are merely the same kind of cards that consumers routinely insert in their laptops. It is asserted that if cable companies are finally forced to agree on a standard for two-way communication that Cablecards will be able to be remotely configured as would be the case with DCAS devices.

The appearance of DCAS as a possible future technology has been used as a reason that the FCC should release cable companies from obligations regarding CableCards. Verizon FiOS wishes to be released from having to support cablecards at all on its network. Cable companies point to DCAS as a reason that they should be released from their obligation to use Cablecards in their devices, as the FCC directed in 1998. The Consumer Electronics Association representing major Consumer electronics manufacturers disagrees with these applications for waivers pointing to the insubstantiality of the proposal and that cable companies are notoriously late and half-hearted in their support of their own standards, as evidenced by their behavior with their earlier CableCARD proposal. Detractors of DCAS point out that the proposal is being used to sow fear, uncertainty, and doubt in the minds of consumers, CE companies, and the FCC. Consumers are motivated to hold off buying Cablecard devices, CE companies are wondering whether their cablecard technology investments will soon be obsolete, and it causes doubt amongst FCC regulators whether they should enforce deadlines and restrictions placed on cable companies regarding CableCARDs. Detractors point to this as the latest in a decade-long set of delaying tactics that the cable company has used to avoid compliance with the Telecommunications Act of 1996. Cable companies counter that CableCARD devices have failed in the marketplace and that it would be foolish for them to be forced to use CableCARDs when the superior technology of DCAS will soon be available.

FCC mandate

The FCC has ruled that starting July 1, 2007, cable customers are to be able to purchase DVRs and other third-party devices to legally view digital cable without having to rent hardware from the cable company.

Diskless PC Card

Wyse Winterm 3125SE

ISO8583 Payment Gateway

SyNET USB Pack

intel wireless solution

kick start hub

hardware of dslam

high density module

led driver module

Drop Wire Module

Pals LCD Module

Electronic Tuner Module

computer netzwerk router

optical fingerprint module

Digital Measuring Module

copy apple iphone

Fortinet Fortigate 200A

Audio Interface Module

Switch For Networking

Spectrum Analyzer Module

Infrared Imaging Module

Client For Network

Cable Connection Cabinet

wired networking products

aqua usb hub

light sensing module

line side module

digital carmera module

high power network

used/refurb cisco products

CableCARD is a plug-in card approximately the size of a credit card that allows consumers in the United States to view and record digital cable television channels on digital video recorders, personal computers and televisions without the use of other equipment such as a set top box (STB) provided by a cable television company. The card, provided by the local company for a nominal monthly fee, is a PCMCIA card and looks exactly like those used with laptops. In technical contexts, "CableCARD" refers more broadly to a set of technologies created by the United States cable television industry in response to requirements by federal government's Telecommunications Act of 1996 that cable companies allow non cable company provided devices to access their networks. Use of the term CableCARD can be confusing, because some technologies refer not to the physical card, but to a device ("Host") that uses the card. Some CableCARD technologies can be used with devices that have no physical CableCARDs.

A CableCARD is a special-use PCMCIA (PC) card