This article may be too technical for most readers to understand.(March 2015)
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.
Often, "virtual channels" are implemented in digital television, helping users to find a desired channel easily, or easing the transition from analogue to digital broadcasting in general. The practice of assigning virtual channels is most common in those parts of the world where TV stations were colloquially named after the RF channel they were transmitting on ("channel 6 Springfield"), as it was common in North America during the analogue TV era. In other parts of the world, such as Europe, virtual channels are rarely used or needed, as TV stations there identify themselves by name, not by RF channel or callsign.
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.
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 or dash. 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.
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.
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. Rules for assignment of major channel numbers are as follows:
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 broadcast some of their subchannels under major channel(s) in the 70-99 range, so long as multiple stations do not attempt to use the same major channel(s). 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:
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.
The order for cable provider Charter:
The order for cable provider Comcast:
The order for satellite provider DirecTV:
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. 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.
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. 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; this did not come to pass, and Multimedios Televisión stations now use channel 6.
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.
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:
The order for Freeview (aka FreeTV) is defined by broadcaster transport:
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".
The order for Freeview is largely based on the channel's content:
The order for the Republic of Ireland's Saorview is based on the priority of the channel to that of the state owned broadcaster:
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 historic or colloquial usage, or is purely done for marketing purposes. For example, in Germany the term "third programme" refers to the local public station, which was usually the third TV station to go on air in most areas[circular reference][circular reference]. There is no connection between these terms and the transmitting RF channel. Referencing above's example, the third programmes in Germany never transmitted on a RF channel below 21.
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.
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. 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.
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).
The order for Freeview is based on how a channel pays for broadcast services:
The order for Sky is largely based on the channel's content:
The order for Sky/TVNZ/Kordia Freeview hybrid bundling called Igloo is as follows:
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.[needs update]
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.