Virtual channel

In most telecommunications organizations, a virtual channel is a method of remapping the program number as used in H.222 Program Association Tables and Program Mapping Tables to a channel number that can be entered via digits on a receiver's remote control. A "virtual channel" was first used for DigiCipher 2 in North America and then later used and referred to as a logical channel number (LCN) for private European Digital Video Broadcasting extensions widely used by the NDS Group and NorDig in other markets.

Pay television operators were the first to use either of these systems as a method of channel reassignment or rearrangement that suited their need to group multiple channels by their content or origin as well as to a lesser extent to localize advertising to a particular market.

Free-to-air ATSC uses the DigiCipher 2 method to maintain the same television frequency channel allocation that the NTSC channel was using when both were simulcasting so the same number could bring up either service.

Free-to-air DVB network operators such as DTV Services Ltd. (d.b.a. Freeview) and Freeview New Zealand Ltd. use the NorDig method and follow the same practice as pay TV operators. The exception is Freeview Australia Ltd., which also use the NorDig method and partially follow the ATSC practice of using the same VHF radio frequency channel allocation that the PAL channel is simulcasting on from the metropolitan station's main transmission point (i2, 7, 9 and 10) with the major and minor format emulated by multiplying by ten.

Implementation

The DigiCipher 2 method uses a privately defined virtual channel table (VCT) to set the channel's major and minor numbers that appear on-screen separated by a decimal point. The major number for ATSC represents the original analog or non-simulcast channel frequency while the minor is a sequentially assigned number for the selected channel with zero reserved for the analog channel. The channel may also be marked as hidden from the viewer.

The DVB extensions use privately defined descriptors within the Bouquet Association Table for DVB-S or the Network Information Table for DVB-T. The NorDig version allows for marking a channel as hidden, while the NDS Group version simply omits the channel entry.

The DVB system neither promotes nor mentions either system due to the simple fact that the already defined H.222 Program number and Transport Stream ID can achieve the same purpose and also hide a channel by simply omitting it from the Program Association table.

All these methods share the same principle of not allowing any kind of viewer reordering as could be achieved under analog and generic digital systems. This locked-down ordering is one of the main criticisms of using either method.

Digital television multiple channels

Because DTV can carry any number of streams referred to as multiplexing, program numbers can be used to group them into more than one channel which can then be reassigned by virtual or logical channel numbers.

North America

An example of the ATSC major and minor numbers used for a station in the United States or Canada would be to typically have its main programming airing on say channel 8 (the "major channel") with analog on 8.0 and digital on 8.1 (the first two "minor channels") with other entertainment channels being below 8.99 on channels 8.2, 8.3, and up and any additional informational data channels ranging from 8.100 to 8.999. The channels can also be displayed using a hyphen (such as 8-1) or a space; however, on a common seven-segment display, a decimal point would not waste a whole character. The decimal point is more familiar to FM radio listeners who tune by frequency rather than channel, and avoids confusion with ranges of values (for example, 2-4 may be misinterpreted as the range 2 to 4 instead of the fourth sub-channel of channel 2).

Most stations in the United States follow the ATSC numbering guidelines; however, there are some exceptions for low-power stations such as New York City's WNYZ-LP, which was temporarily broadcasting on VHF channel 6 in digital, but used the virtual channel 1.1, instead of 6. This operation lasted for approximately one year beginning in November 2008, after which WNYZ-LP reverted to low-power analog.

The assignment of virtual channels in the United States is defined within the stream via terrestrial or cable versions of a "Virtual Channel Table" as outlined by ATSC document "A/65", Annex B.[1][2] Rules for assignment of major channel numbers are as follows:

  • Existing analog stations were assigned a major channel number matching their existing analog number
  • New digital stations assigned to a channel whose matching major channel number is not in use must use that number
  • New digital stations assigned to a channel whose matching major channel number is in use (by a former analog station) must reciprocate, using the major channel number that matches the actual channel of the station in question.

These rules generally ensure that no overlapping will occur, although in the case of stations where large numbers of stations in adjacent markets are in close proximity to each other, it is possible that such overlap can occasionally happen (see, for example, the case of WJLP). Additionally, stations may apply for a license to broadcast some of their subchannels under a secondary major channel in the 70–99 range; these numbers are certain to be unused, as 69 was the highest assigned channel prior to the conversion to digital broadcasting. The document does not address the use of certain other major channel numbers:

  • Numbers below 70 that were never used in NTSC (0, 1 and 37)
  • The real numbers of stations that are using virtual channels from 52 to 69 (these stations are not covered by the reciprocity rule, as real station numbers are not assigned above 51)
  • Numbers in the range of 52–69 that are not being used by a former analog station

Additionally, broadcasters owning more than one station that overlap in coverage area may set all of the channels to use the major channel of just one of the stations, so long as different minor channel numbers are used to avoid overlap.

When the United States began buying back licenses in a broadcast spectrum auction in 2017, it also allowed companies that had a duopoly in a market to sell one of the licenses but continue to use the virtual channel of the sold channel on a subchannel of the other. For example, Sunbeam Television sold WLVI in the auction, but in turn was allowed to use its virtual channel 56 on WHDH, which uses virtual channel 7 for its main channel; thus, the WHDH license uses both virtual channels, 7 and 56, on the same license.

The range for pay TV free-to-air local stations is from 2 to 29. All other channels are based on the service provider's preference.

Usage examples

The order for cable provider Charter:

  1. Reserved for subscriber on-demand services
  • Basic subscriber channels are from 30 to 120
  • Extra subscriber channels are from 121 to 199
  • Informational subscriber channels are from 200 to 244
  • Sporting subscriber channels are from 245 to 279
  • Movie subscriber channels are from 280 to 299
  • Latin American targeted subscriber channels from 300 to 399 and 800 to 899
  • Extra HD subscriber channels are from 400 to 499
  • Extra movie subscriber channels are from 500 to 599
  • Extra foreign subscriber channels are from 600 to 699
  • Extra season pass NBA/NHL/MLB subscriber channels from 700 to 769
  • Premium adult subscriber channels from 770 to 799
  • Extra audio only music subscriber channels from 900 to 999

The order for cable provider Comcast:

  1. Reserved for subscriber on-demand services
  • Basic subscriber channels are from 30 to 99 and 170 to 200
  • Extra subscriber channels are from 100 to 170 and 201 to 299
  • Extra foreign subscriber channels are from 300 to 399
  • Extra sporting subscriber channels are from 400 to 469
  • Extra Christian subscriber channels are from 470 to 499
  • Extra movie subscriber channels are from 500 to 599
  • Latin American targeted subscriber channels from 600 to 699
  • Extra HD subscriber channels are from 700 to 899
  • Extra audio-only music subscriber channels from 800 to 999

The order for satellite provider DirecTV:

  1. Reserved for DirecTV subscriber information (as well as 201)
  • Local free-to-air stations are from 2 to 69
  • Shopping subscriber channels are from 70 to 99
  • Extra movie subscriber channels are from 100 to 200
  • Basic (and extra HD) subscriber channels are from 202 to 389
  • NY east and CA west coast FTA network subscriber channels from 390 to 400
  • Latin American targeted subscriber channels from 401 to 499
  • Premium subscriber channels from 500 to 573
  • Premium adult subscriber channels from 575 to 599
  • Extra regional sporting subscriber channels from 600 to 699
  • Extra season pass NFL/NBA/NHL subscriber channels from 700 to 799
  • Extra audio only music subscriber channels from 800 to 999
  • Extra non-North/Latin American subscriber channels from 2000 to 2199
  • DirecTV system/hidden interactive channels from 9000 to 9539 and 9950
  • DirecTV system/hidden HD channels from 9540 to 9559
  • DirecTV system/hidden instrumental channels from 9560 to 9599

Mexico

Upon the introduction of digital television in Mexico, most stations used virtual channels that matched their former analog channel positions, with a select number of stations branding as their physical channel (such as XHMNU-TDT in Monterrey, which eschewed virtual channel 53 for 35). However, Mexican television is considerably more centralized than in other ATSC countries, with three of the four national commercial networks branding with their Mexico City channel numbers. There was also the potential that new entrants, which would almost universally be on UHF, would be disadvantaged by higher virtual channels than existing stations that began on VHF—a particular concern given the recent award of a national television network to Grupo Imagen.

In December 2015, the Federal Telecommunications Institute opened a public comment period on public guidelines for the assignment of virtual channels, and on June 17, 2016, the IFT officially released the final version of the guidelines.[3] The plan called for standardization of virtual channels according to network, not former analog position, with automatic assignment based on the programming information on file with the IFT; it also set a date of October 27 for a coordinated switch of all virtual channels. In early September, a full list of virtual channel assignments was released.[4]

The plan eliminated much of the local variance for national and regional networks. Prior to standardization, Canal 5, a national network, was seen on 25 different virtual channel numbers in different Mexican cities; the plan standardized it as channel 5 nationwide.

In all, the IFT accredited nine national television networks and awarded them national rights to a virtual channel. Five were commercial: Azteca Trece (channel 1, changed from 13 at the request of TV Azteca); Las Estrellas (channel 2), Imagen (channel 3), Canal 5 (channel 5), and Azteca 7 (channel 7)). Additionally, the national public broadcasters received channels: Canal Once (channel 11), Una Voz con Todos (channel 14, later renamed Canal Catorce as a result), TV UNAM (channel 20), and Canal 22 (channel 22). The IFT also awarded common numbers to 14 regional networks (primarily operated by state governments) and virtual channels to nearly 100 local stations across the country.[5] Local stations were mostly assigned to channels 4, 8, 10, 12, and less commonly 9, as well as other numbers. Some retained existing channel numbers, particularly if they broadcast on UHF in analog. Initially, channel 6 was reserved, in the event that a 2017 auction of local TV stations produced a national network (which was not the case).

The largest exception to standardization is on the US-Mexico border, where due to the presence of US stations on desired virtual channels and objections from the US Federal Communications Commission, 11 Mexican stations operate on virtual channels other than would be expected. In Tijuana, only one Mexican station was able to change its virtual channel.

Australia

In Australia, allocation of logical channel numbers is governed by guidelines set by the commercial broadcasters' association, Free TV Australia.[6]

These are defined within the terrestrial broadcast stream using the NorDig descriptor format within the DVB "Network Information Table."

LCNs in Australia may have one, two or three digits. Each network is allocated LCNs starting with a certain prefix - for instance, all metropolitan Nine Network services use LCNs beginning with the digit '9'. Generally, but not always, the single-digit LCN is allocated to the primary SD service (Network Ten's sub-channel One being the main exception). LCNs need not be contiguous, and a channel may be identified by more than one LCN. For instance, ABC Television's primary ABC service is allocated LCNs 2 and 21; the latter allows it to be easily accessed amongst other ABC services which lie in the 21–24 range.

Regional affiliates of the three metropolitan networks are provided with a different LCN prefix. For instance, channels owned by affiliates of the Nine Network (in this case NBN Television) are prefixed with the digit '8' rather than '9'. This allows areas that are part of both a metropolitan market and a regional market, such as the Gold Coast, Sunshine Coast and Central Coast, to receive all local commercial services. The ABC and SBS use the same prefix in all areas.

Prefixes for remote-area services are intended to be overlaid over this model. When digital transmission starts in these areas, services licensed for the Remote Central and Eastern Australia licence area (Imparja and Southern Cross Central) have been reserved the "metropolitan" prefixes corresponding to their affiliation; those in Remote Western Australia (GWN and WIN WA) the "regional" prefixes.

A number of LCNs are reserved for various reasons:

  • LCN 4 was originally intended for a free-to-air video program guide. In practice, the LCN 4 prefix has for most of its life been largely unused, except in Sydney (where it was used by the Digital Forty Four trial datacasting service from 2004 to 2010). Since 2010, capital city community television stations (or "Channel 31" stations, after their typical analogue channel position) use LCN 44.
  • The LCN range 350-399 is intended to be allocated by receivers to channels which either duplicate a stronger signal's LCN, or are transmitted without an LCN. For instance, if two broadcasts of LCN 2 were found, one signal (generally the stronger) will be allocated to LCN 2, and the weaker should be allocated to, say, LCN 350.
  • The LCN range 450-499 is intended for use by trial services by non-broadcasters.

Usage examples

The order for Freeview (aka FreeTV) is defined by broadcaster transport:[7]

  1. Ten network metropolitan HD channel is on channel 1
  2. ABC primary SD channel is on channel 2
  3. SBS primary SD channel is on channel 3
  4. VAST regional news guide
  5. 9 regional primary SD channel is on channel 5
  6. 7 regional primary SD channel is on channel 6
  7. 7 network metropolitan primary SD channel is on channel 7
  8. Ten regional and 9 Network Northern NSW primary SD channel is on channel 8
  9. 9 network metropolitan primary SD channel is on channel 9
  10. Ten network metropolitan primary SD channel is on channel 10
    • Ten network metropolitan other TV channels are from 11 to 19
  11. ABC HD channel is on channel 20
    • ABC other TV channels are from 21 to 29
  12. SBS HD channel is on channel 30
    • SBS other channels are from 31 to 39
    • local public service is 44
    • Miscellaneous/Government-owned channels are from 40 to 43 and 45 to 49
  13. 9 Network HD channel is on channel 50
    • 9 regional other TV channels are from 51 to 59
  14. 7 Network regional HD channel is on channel 60
    • 7 regional other TV channels are from 61 to 69
  15. 7 network metropolitan HD channel is on channel 70
    • 7 network metropolitan other TV channels are from 71 to 79
  16. Ten regional and 9 Network Northern NSW HD channel is on channel 80
    • Ten regional and 9 Network Northern NSW other TV channels are from 81 to 89
  17. 9 network metropolitan HD channel is on channel 90
    • 9 network metropolitan other TV channels are from 91 to 99
  • Ten Network extended other TV channels are from 100 to 199
  • ABC Audio Only channels are from 200 to 219
  • ABC out of region/extended channels are from 220 to 299
  • SBS out of region/extended channels are from 300 to 349
  • Any out of region channels are from 350 to 399
  • Regional VAST news channels are from 400 to 499
  • VAST community channels are from 600 to 699
  • 7 network extended other TV channels are from 700 to 799
  • VAST informational channels are from 800 to 899
  • 9 network extended other TV channels are from 900 to 999

The order for Foxtel (who wholesale to Austar and Optus) is largely based on the channel's content:

  • System Services from 1 to 99 and above 989
  • General Entertainment from 100 to 149
  • Time-shifted from 150 to 169
  • Specialist from 170 to 179
  • Community from 180 to 199
  • High Definition from 200 to 299
  • Interactive/Miscellaneous from 300 to 399
  • Movies from 400 to 499
  • Sport from 500 to 599
  • News/Informational from 600 to 699
  • Young Children from 700 to 799
  • Music from 800 to 829
  • Music Audio Only from 830 to 849
  • Free to Air Audio Only from 850 to 899
  • Pay Per View from 900 to 939
  • European from 940 to 959
  • Adult Pay Per View from 960 to 989
  • Help on 999

Europe, Africa and the Middle East

In Europe, Africa and the Middle East, there is no special numbering system for subchannels; two related "channels" (that is, programme streams) may have completely unrelated numbers (for example, in the United Kingdom, ITV is channel 3 and its digital sister channel ITV2 is channel 6 on Freeview).

In the United Kingdom and Ireland, Freeview channel numbers are defined within the terrestrial broadcast stream using the NorDig descriptor format within the DVB "Network Information Table".

Usage examples

The order for Freeview/Sky hybrid bundling is largely based on the channel's content:

  • General Entertainment from 1 to 99
  • High Definition from 100 to 119
  • Young Children from 201 to 219
  • News/Public Service from 230 to 239
  • MHEG-5 non-broadcast Internet streaming are from 260 to 299
  • Reserved for YouView from 300 - 599
  • MHEG-5 Interactive from 600 to 609
  • Adult Pay Per View from 670 to 695
  • Audio Only from 700 to 777
  • ITV3 HD on 778
  • Tests and old channels from 790 to 799
  • D RATED Channels (on first day) (Samsung only) 800-850

The order for the Republic of Ireland's Saorview is based on the priority of the channel to that of the state owned broadcaster:

  1. State owned RTÉ primary HD TV channel
  2. State owned RTÉ secondary HD TV channel
  • other TV channels from 3 to 5
  • other state owned RTÉ TV channels from 6 to 8
  • state owned RTÉ Audio Only channels from 200 to 209

In continental and eastern Europe, virtual channels are not used, since television sets and receivers there allow users to freely assign arbitrary "programme numbers" or "programme letters" to channels.

Stations still market themselves as "first", "second", or "third" channel (and so on), or "channel A", "channel B" or "channel C", etc., but this reflects the programme number at which the channel should be stored, not the RF channel used for transmitting the signals.

Virtual channels are also used on direct broadcast satellites, such as Dish Network, DirecTV, and Astra. Rather than a few dozen channels with a few subchannels each, these services map to a range of hundreds of individually numbered channels. This is true of digital cable and satellite radio services, as well.

Japan

In Japan, digital terrestrial TV broadcasters in each region are allocated a "remote control key ID" (or, "remocon key ID"), currently numbered from 1 to 12.[8] Remote control ID allocations for broadcasters outside the Kanto region generally follow their Tokyo-based network flagships; however, some stations in some prefectures deviate from this. Current technical standards allow for expansion to a maximum of 16 broadcasters per region.

Each underlying channel is then assigned a three-digit number, which is based on their assigned remote control ID, followed by the sub-channel number. For example, NHK Educational TV is assigned remote control ID 2 (nationwide). Their primary channel is therefore assigned virtual channel 021. If the broadcaster multichannels (of which the ISDB-T standard allows up to three standard definition streams), the additional streams would be assigned virtual channels 022 and 023, respectively. Current standards allow for a maximum of eight virtual channels per broadcaster (in this example 021-028).

Additional datacasting services use virtual channels in the 200–799 range – in this example, the network could use the 22x, 42x and 62x ranges.

New Zealand

The allocation of logical channel numbers is governed by Freeview and inserted into the transport stream by mostly Kordia maintained equipment with the encoding done by TVNZ who also do the encoding for all other non critical DVB metadata such as the EPG and channel naming.

SKY Network Television also define their own channel numbering which uses a similar NDS encoded format. They wholesale their channels to the only other NZ Pay TV operator Vodafone and to the short lived Telecom First Media.

The Freeview LCNs are encoded within a terrestrial broadcast stream using the NorDig descriptor format within the DVB "Network Information Table." And within the two satellite broadcast streams also using the NorDig descriptor format, but is instead within the DVB "Bouquet Association Table." The BAT is used on satellite so channel region-ization can be done on certified receivers (i.e., channel order locked receivers).

Usage examples

The order for Freeview is based on how a channel pays[9] for broadcast services:

  • nationwide high viewership TV channels are below 20
  • nationwide lower viewership TV channels are from 20 to 29
  • locally inserted TV channels are from 30 to 40
  • local non-Kordia operators are from 41 to 49
  • nationwide high priority audio only channels are from 50 to 69
  • nationwide low priority audio only channels are from 70 to 79
  • TVNZ Provided MHEG-5 Interactive (currently unused) are from 80 to 99
  • Broadcast Test channels (no longer used) are from 100 to 199
  • TVNZ Provided MHEG-5 non-broadcast Internet streaming are from 200 to 299
  • TVNZ Provided System Services (currently unused) from 300 to 399
  • TVNZ Provided MHEG-5 Interactive informational channels are from 500 to 599
  • TVNZ Provided MHEG-5 Interactive test channels are from 600 to 699
  • TVNZ Provided Receiver Downloads are from 700 to 799

The order for Sky is largely based on the channel's content:[10]

  • General Entertainment below thirty (before April 2013 was below twenty)
  • Movies from 30 to 39 (before April 2013 was 20 to 29)
  • Sport from 50 to 69 and 333 (before April 2013 was 30 to 39 and 333)
  • Pre-Teenage from 100 to 109 (before April 2013 was 40 to 49)
  • Informational from 70 to 79
  • Public Service from 80 to 84 (before April 2013 was from 85 to 89)
  • News from 85 to 99 (before April 2013 was from 90 to 99)
  • Music from 110 to 119 (before April 2013 was 60 to 69)
  • Movie Pay Per View from 120 to 139 (before April 2013 was 200 to 219)
  • Adult Pay Per View from 140 to 139 (before April 2013 was 200 to 219)
  • Religious/State Funded from 200 to 299 (before April 2013 was 110 to 119)
  • Asian Language from 300 to 309
  • Asian Audio Only from 311 to 314
  • Non-Asian Eastern Language from 315 to 319
  • Music Audio Only from 400 to 419
  • Free to Air Audio Only from 420 to 429 (before April 2013 was 500 to 599)
  • Timeshift from 500 to 599 (before April 2013 was 80 to 84)
  • System Services from 800 to 999
  • Interactive/Miscellaneous (before April 2013 was 50 to 59)
  • European (before April 2013 was 100 to 109)

The order for Sky/TVNZ/Kordia Freeview hybrid bundling called Igloo is as follows:

  • Primary Freeview national channels from 1 to 5
  • Sky Pay TV channels from 6 to 19
  • Secondary Freeview national channels from 30 to 39
  • Sports related Freeview channels from 40 to 44
  • Infomercial Freeview channels from 45 to 49
  • News related Freeview channels from 50 to 54
  • Religious Freeview channels from 55 to 59
  • Secondary language Freeview channels from 60 to 64
  • non-English Freeview channels from 65 to 69
  • locally inserted English Freeview channels from 80 to 89
  • Local non-Freeview channels from 100 to 109
  • Freeview audio only channels from 110 to 119

Philippines

As the Philippines started its transition to digital terrestrial television back in 2008, virtual channels have been tentatively assigned to TV networks who are now in operation. In June 2010, the National Telecommunications Commission finally adopted ISDB-T as the sole digital terrestrial television standard in the country.

LCN used in ISDB-T in the Philippines was pre-assigned to the currently operating networks in digital TV. Small-player GEM HD on DZCE-TV was the first ever Philippine TV network to go ISDB-T, being assigned to LCN 2.11 which is using the analog channel 49. Government-owned People's Television Network or PTV was assigned to 1.1 using its analog channel 48 because of its status as government-owned. High definition channels are being assigned with the decimal with "11", while a multiple-SD channel uses decimal with "1, 2, 3... and so on" as its subchannel.

In the first quarter of 2011, the NTC convened to form the TWG-IRR that will draft the implementing rules and regulations on digital TV. Aside from that, it will cover the frequency planning for the upcoming TV networks that will go digital.

Digital radio

Digital radio also uses channels and subchannels in the DAB format. iBiquity's HD Radio uses HD1, HD2, ..., HD7 channels. HD1-3 are available in FM hybrid mode, while all seven HD channels are available in the pure digital mode.

IBOC system (Digital Radio Mondiale) stations do not currently use any virtual channels because of the limited bandwidth available in analog sidebands.

References

  1. ^ "ATSC Standard: Program and System Information Protocol for Terrestrial Broadcast and Cable(PSIP)" (PDF). 23 December 1997. Archived from the original (PDF) on 18 September 2010. Retrieved 29 November 2010.
  2. ^ Eyer, Mark; Mark C. Whitaker (2002). PSIP: program and system information protocol; naming, numbering, and navigation for digital television. pp. 105–107.
  3. ^ IFT Press Release, June 17, 2016
  4. ^ IFT Press Release, September 2, 2016
  5. ^ "IFT List of Virtual Channels - September 2, 2016" (PDF). Archived from the original (PDF) on September 15, 2016. Retrieved September 10, 2016.
  6. ^ Free TV Australia (July 2005). Free TV Australia Operational Practice OP-41: Logical Channel Descriptor (Issue 3). Retrieved on 2009-09-01.
  7. ^ ‘Driving Digital’ A Review of the Duration of the Analogue/Digital Television Simulcast Period (PDF). Broadcast Australia. Department of Broadband, Communications and the Digital Economy. November 2005. p. 31. Archived from the original (PDF) on 23 July 2008. Retrieved 26 October 2008.
  8. ^ Association of Radio Industries and Businesses (2006). ARIB Technical Report TR-B14 version 2.8: Operational Guidelines for Digital Terrestrial Television Broadcasting (official English translation, Fascicle 3). Volume 7: Provisions for Carrier Operations. Accessed on 2009-09-01.
  9. ^ "Archived copy" (PDF). Archived from the original (PDF) on 2013-05-08. Retrieved 2012-12-05.CS1 maint: Archived copy as title (link)
  10. ^ http://www.skytv.co.nz/Default.aspx?tabid=202&art_id=44011
Asynchronous transfer mode

Asynchronous Transfer Mode (ATM) is, according to the ATM Forum, "a telecommunications concept defined by ANSI and ITU (formerly CCITT) standards for carriage of a complete range of user traffic, including voice, data, and video signals". ATM was developed to meet the needs of the Broadband Integrated Services Digital Network, as defined in the late 1980s, and designed to integrate telecommunication networks. Additionally, It was designed for networks that must handle both traditional high-throughput data traffic (e.g., file transfers), and real-time, low-latency content such as voice and video. The reference model for ATM approximately maps to the three lowest layers of the ISO-OSI reference model: network layer, data link layer, and physical layer. ATM is a core protocol used over the SONET/SDH backbone of the public switched telephone network (PSTN) and Integrated Services Digital Network (ISDN), but its use is declining in favour of all IP.

ATM provides functionality that is similar to both circuit switching and packet switching networks: ATM uses asynchronous time-division multiplexing, and encodes data into small, fixed-sized packets (ISO-OSI frames) called cells. This differs from approaches such as the Internet Protocol or Ethernet that use variable sized packets and frames. ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the actual data exchange begins. These virtual circuits may be “permanent”, i.e. dedicated connections that are usually preconfigured by the service provider, or “switched”, i.e. set up on a per-call basis using signaling and disconnected when the call is terminated.

Use of ATM technology was eventually largely superseded by Internet Protocol (IP)-only technology. Wireless and mobile ATM never established a significant foothold.

Channel 21 virtual TV stations in the United States

The following television stations operate on virtual channel 21 in the United States:This table is sorted ascending by call sign; click on any of the arrows to change how the table is sorted.

The following station, which is no longer licensed, formerly operated on virtual channel 21:

K41MM-D in Pateros, Washington

KDUG-LD in Hemet, California

Channel 52 virtual TV stations in the United States

The following television stations operate on virtual channel 52 in the United States:

K15HQ-D in Sayre, Oklahoma

K23IY-D in Weatherford, Oklahoma

K25LQ-D in Elk City, Oklahoma

K27IG-D in Cortez, etc., Colorado

K27JO-D in Strong City, Oklahoma

K30MI-D in Redding, California

K31JW-D in Elk City, Oklahoma

K35LF-D in Eureka, California

KDTS-LD in San Francisco, California

KFWD in Fort Worth, Texas

KSBI in Oklahoma City, Oklahoma

KVEA in Corona, California

W23DM-D in Falmouth, Kentucky

W49BE-D in Hackettstown, New Jersey

WGGN-TV in Sandusky, Ohio

WGVK in Kalamazoo, Michigan

WHLV-TV in Cocoa, Florida

WKON in Owenton, Kentucky

WNJT in Trenton, New Jersey

WNYI in Ithaca, New York

WRFB in Carolina, Puerto Rico

WWRS-TV in Mayville, WisconsinThe following stations, which are no longer licensed, formerly operated on virtual channel 52 in the U.S.:

WBTD-LD in Suffolk, Virginia

WMSY-TV in Marion, Virginia

Channel 57 virtual TV stations in the United States

The following television stations operate on virtual channel 57 in the United States:

K09DM-D in Cortez, Colorado

K21KB-D in Brookings, Oregon

KFUL-LD in San Luis Obispo, California

KJLA in Ventura, California

KUBE-TV in Baytown, Texas

KWOG in Springdale, Arkansas

KXTU-LD in Colorado Springs, Colorado

W25AT-D in Tupper Lake, New York

W25BT-D in Monkton, Vermont

WACH in Columbia, South Carolina

WATC-DT in Atlanta, Georgia

WBND-LD in South Bend, Indiana

WBWP-LD in West Palm Beach, Florida

WCFE-TV in Plattsburgh, New York

WCVW in Richmond, Virginia

WDCI-LD in Chicago, Illinois

WFXU in Live Oak, Florida

WGBY-TV in Springfield, Massachusetts

WIFS in Janesville, Wisconsin

WMLD-LD in Brownsville, Florida

WPSG in Philadelphia, Pennsylvania

WYMT-TV in Hazard, KentuckyThe following stations, which are no longer licensed, formerly operated on virtual channel 57:

W46IT-D in Port Henry, New York

Channel 59 virtual TV stations in the United States

The following television stations operate on virtual channel 59 in the United States:

KFRE-TV in Sanger, California

KPXC-TV in Denver, Colorado

W30DN-D in Manteo, North Carolina

WAOE in Peoria, Illinois

WCTX in New Haven, Connecticut

WDNM-LD in Memphis, Tennessee

WJEB-TV in Jacksonville, Florida

WJMB-CD in Butler, Pennsylvania

WKHU-CD in Kittanning, Pennsylvania

WMVH-CD in Charleroi, Pennsylvania

WVNS-TV in Lewisburg, West Virginia

WWKH-CD in Uniontown, Pennsylvania

WWLM-CD in Washington, Pennsylvania

WXIN in Indianapolis, IndianaThe following stations, which are no longer licensed, formerly operated on virtual channel 59 in the United States:

WEMW-CD in Greensburg, Pennsylvania

WEPA-CD in Pittsburgh, Pennsylvania

WJPW-CD in Weirton, West Virginia

WPCP-CD in New Castle, Pennsylvania

Channel 62 virtual TV stations in the United States

The following television stations operate on virtual channel 62 in the United States:

KAKW-DT in Killeen, Texas

KOPX-TV in Oklahoma City, Oklahoma

KRCA in Riverside, California

KSMO-TV in Kansas City, Missouri

KZOD-LP in Odessa, Texas

WDMI-LD in Minneapolis, Minnesota

WFPT in Frederick, Maryland

WFPX-TV in Fayetteville, North Carolina

WFTT-TV in Venice, Florida

WJYS in Hammond, Indiana

WMFP in Lawrence, Massachusetts

WWJ-TV in Detroit, Michigan

WWSI in Atlantic City, New Jersey

WYCW in Asheville, North Carolina

Channel 63 virtual TV stations in the United States

The following television stations operate on virtual channel 63 in the United States:

KBEH in Oxnard, California

WBEC-TV in Boca Raton, Florida

WHSG-TV in Monroe, Georgia

WIPX-TV in Bloomington, Indiana

WKTC in Sumter, South Carolina

WMBC-TV in Newton, New Jersey

WYTU-LD in Milwaukee, Wisconsin

Channel 64 virtual TV stations in the United States

The following television stations operate on virtual channel 64 in the United States:

K14AT-D in Ridgecrest, California

K20LH-D in Ridgecrest, California

KILM in Barstow, California

KTFK-DT in Stockton, California

KZTE-LD in Fulton, Arkansas

WAXN-TV in Kannapolis, North Carolina

WDPB in Seaford, Delaware

WECN in Naranjito, Puerto Rico

WLLA in Kalamazoo, Michigan

WNAC-TV in Providence, Rhode Island

WQPX-TV in Scranton, Pennsylvania

WSTR-TV in Cincinnati, OhioThe following stations, which are no longer licensed, formerly operated on virtual channel 64 in the United States:

WBOA-CD in Kittanning, Pennsylvania

Channel 66 virtual TV stations in the United States

The following television stations operate on virtual channel 66 in the United States:

KFSF-DT in Vallejo, California

KPXO-TV in Kaneohe, Hawaii

WFXP in Erie, Pennsylvania

WGBO-DT in Joliet, Illinois

WLGA in Opelika, Alabama

WPXW-TV in Manassas, Virginia

WSMH in Flint, Michigan

WUNI in Marlborough, Massachusetts

WWIW-LD in Raleigh, North Carolina

WXPX-TV in Brandenton, FloridaThe following stations, which are no longer licensed, formerly operated on virtual channel 66:

WNNB-CD in Beaver, Pennsylvania

WNYJ-TV in West Milford, New Jersey

Channel 67 virtual TV stations in the United States

The following television stations operate on virtual channel 67 in the United States:

K48NY-D in Gainesville, Texas

KFTH-DT in Alvin, Texas

KFXV-LD in McAllen, Texas

KSMS-TV in Monterey, California

KXFX-CD in Brownsville, Texas

WBBZ-TV in Springville, New York

WFTY-DT in Smithtown, New York

WHVD-LD in Huntsville, Alabama

WMPB in Baltimore, Maryland

WPXP-TV in Lake Worth, Florida

WUPX-TV in Morehead, Kentucky

Channel 68 virtual TV stations in the United States

The following television stations operate on virtual channel 68 in the United States:

KPXD-TV in Arlington, Texas

KTLN-TV in Novato, California

W16AX-D in Ithaca, New York

WABM in Birmingham, Alabama

WBPX-TV in Boston, Massachusetts

WDTJ-LD in Toledo, Ohio

WEFS in Cocoa, Florida

WFUT-DT in Newark, New Jersey

WIWN in Fond du Lac, Wisconsin

WJAL in Hagerstown, Maryland

WKMJ-TV in Louisville, Kentucky

WLFG in Grundy, Virginia

WMFD-TV in Mansfield, Ohio

WSYT in Syracuse, New York

WVSN in Humacao, Puerto RicoThe following stations, which are no longer licensed, formerly operated on virtual channel 68 in the United States:

W38FI-D in Laurel, Mississippi

KASN

KASN, virtual channel 38 (UHF digital channel 34), is a CW-affiliated television station serving Little Rock, Arkansas, United States that is licensed to Pine Bluff. The station is owned by Mission Broadcasting, as part of a duopoly with Little Rock-licensed Fox affiliate KLRT-TV (channel 16); Nexstar Media Group, which owns NBC affiliate KARK-TV (channel 4) and MyNetworkTV affiliate KARZ-TV (channel 42), operates KLRT and KASN under joint sales and shared services agreements. The four stations share studios in the Victory Building on West Capitol Avenue in Downtown Little Rock, one block east of the Arkansas State Capitol; KASN's transmitter is located near Redfield.

Even though KASN broadcasts a full-power signal, it is barely viewable in the northern portions of the market. Therefore, in order to reach the entire market, it is simulcast in high definition on KLRT's third digital subchannel (UHF channel 30.3 or virtual channel 16.3 via PSIP) from a transmitter on Shinall Mountain near the Chenal Valley section of Little Rock.

On cable, KASN is available on Comcast Xfinity channel 7 (ABC affiliate KATV, which broadcasts over the air on virtual channel 7, is carried on cable channel 8).

KBFX-CD

KBFX-CD, virtual channel 58 (UHF digital channel 29), is a low-powered, Class A Fox-affiliated television station licensed to Bakersfield, California, United States. Owned by the Sinclair Broadcast Group, it is a sister station to CBS affiliate KBAK-TV (channel 29). The two stations share studios on Westwind Drive west of downtown Bakersfield; KBFX's transmitter is located atop Breckenridge Mountain.

In addition to its own digital signal, KBFX is simulcast in high definition on KBAK's second digital subchannel (virtual channel 58.2, UHF channel 33.2) from the same transmitter site.

KCRP-CD

KCRP-CD, virtual channel 41 (UHF digital channel 17), is a low-power, Class A UniMás-affiliated television station licensed to Corpus Christi, Texas, United States. Owned by Entravision Communications, it is a sister station to Univision affiliate KORO (channel 28). The two stations share studios on North Mesquite Street in Downtown Corpus Christi; KCRP-CD's transmitter is located on Navigation Boulevard in western Corpus Christi.

Due to KCRP-CD's low-power status, the station is simulcast in standard definition on KORO's second digital subchannel to expand its broadcasting radius. This signal can be seen on UHF channel 27.2 (or virtual channel 28.2 via PSIP) from a transmitter between Petronila and Robstown.

KCWT-CD

KCWT-CD, virtual channel 21, is a low-power CW affiliate in McAllen, Texas, owned by Entravision Communications.

Previously, KCWT was a low-powered translator of KXFX-CA and KTFV-CA.

Until 2014, KCWT broadcast on analog channel 30. KCWT launched a digital feed on RF channel 23 that March; however, through the use of Program and System Information Protocol, the station maps to virtual channel 21, as nearby Mexican station XHAB-TV in Matamoros, Tamaulipas, whose digital broadcasts use RF channel 30, also maps to virtual channel 30 rather than its analog channel 7 due to Mexico not fully following the PSIP standard. (Channel 23 is itself unavailable to KCWT as a virtual channel, as it is used in the Rio Grande Valley by KVEO-TV.) Even before then, KCWT, as had previous CW affiliate KSFE-LD (channel 67, now KFXV-LD), has long branded as "CW 21" in reflection of its channel 21 slot on area cable systems.

KFTU-DT

KFTU-DT, virtual channel 3 (UHF digital channel 36), is a UniMás owned-and-operated television station serving Tucson, Arizona, United States that is licensed to Douglas. The station is owned by the Univision Local Media subsidiary of Univision Communications, as part of a duopoly with Green Valley-licensed Univision owned-and-operated station KUVE-DT (channel 46). The two stations share studios on Forbes Boulevard in Tucson; KFTU's transmitter is located on Juniper Flats Road northwest of Bisbee.

KFTU-CD, virtual channel 34 (UHF digital channel 18), is a low-power Class A television station licensed to Tucson that rebroadcasts KFTU-DT to the city, as KFTU's coverage area falls well short of Tucson proper. KFTU-DT is also rebroadcast on KUVE's second digital subchannel in order to reach the entire market; this signal can be seen on UHF channel 34.2 (or virtual channel 46.2 via PSIP) from a transmitter atop Mount Bigelow. Likewise, KUVE is rebroadcast on KFTU's second digital subchannel. Master control and most internal operations for KFTU and KUVE are based at the studios of sister station KTVW-DT on 30th Street in southern Phoenix.

Similar to sister station KFPH-DT in Flagstaff, KFTU brands itself as UniMás 34, using the over-the-air channel of its Class A repeater in Tucson. On cable, the station is available on Cox Communications channel 60.

WAXN-TV

WAXN-TV, virtual channel 64 (UHF digital channel 50), is an independent television station serving Charlotte, North Carolina, United States that is licensed to Kannapolis. The station is owned by the Cox Media Group subsidiary of Atlanta-based Cox Enterprises, as part of a duopoly with Charlotte-licensed ABC affiliate WSOC-TV (channel 9). The two stations share studios on North Tryon Street (U.S. 29/NC 49) north of uptown Charlotte; WAXN's transmitter is located near Reedy Creek Park in the Newell section of Charlotte.

The station's programming is simulcast on fill-in digital repeaters operating on UHF channel 36 (virtual channel 64.7) in China Grove, channel 30 (virtual channel 64.5) from Crowders Mountain, W42DR-D (UHF channel 42, virtual channel 6.2) in Marion (from a transmitter southwest of Connelly Springs), and in Statesville on channel 46 (virtual channel 64.9) from Cool Springs.

On cable, WAXN-TV is carried in standard definition on Charter Spectrum channel 10 in the immediate Charlotte area (channel 2 in Kannapolis and Concord, channel 4 on legacy Charter systems), Comporium Communications channel 110 and AT&T U-verse channel 64, and in high definition on Spectrum channel 1230 (channel 703 on legacy Charter systems), Comporium channel 1110 and U-verse channel 1064.

WBQM-LD

WBQM-LD is a low-power Spanish independent television station licensed to New York City. It broadcasts on UHF channel 50 and it is owned by Aquiles Jiménez Fernández. From January 2012 to November 2013, WBQM used virtual channel 3.1. The station formerly broadcast on VHF channel 3 and was previously owned by Renard Communications Corp. As of November 2013, they now use virtual channel 51. WBQM can't use its real channel of 50 as its virtual channel because of nearby New Jersey PBS station WNJN which broadcasts on Channel 51 and uses its old analog channel 50 as its virtual channel.

WZDC-CD

WZDC-CD, virtual channel 44 (UHF digital channel 48), is a Class A Telemundo owned-and-operated television station licensed to the American capital city of Washington, District of Columbia. Owned by the NBC Owned Television Stations subsidiary of NBCUniversal (itself a subsidiary of Comcast), it is sister to NBC owned-and-operated station WRC-TV (channel 4) and regional sports network NBC Sports Washington. WZDC-CD and WRC-TV share studios and transmitter facilities on Nebraska Avenue in the Tenleytown neighborhood of northwest Washington.

Digital television in North America
Terrestrial
Cable
Satellite TV
IPTV
Technical issues

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