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 and/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 radio 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 Freeview in the UK and New Zealand use the NorDig method and follow the same practice as pay TV operators. The exception is FreeTV Australia, 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 channels 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 doesn't promote nor mention 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 LED, 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 broadcasts on VHF channel 6 in digital, but uses the virtual channel 1.1, instead of 6.
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 guarantee that no overlapping will occur. 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.
The range for pay TV free-to-air local stations are from 2 to 29. All other channels are based on the service providers preference.
Usage examples
The order for cable provider TimeWarner:
- 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:
- 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:
- Reserved for DirecTV subscriber information (as well as 201)
- Local free-to-air stations are from 30 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 549
- Premium adult subscriber channels from 550 to 599
- Extra regional sporting subscriber channels from 600 to 699
- Extra season pass 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
Australia
In Australia, allocation of logical channel numbers is governed by guidelines set by the commercial broadcasters' association, Free TV Australia.[3]
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 HD 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 ABC1 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, WIN Television and 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). As of 2010, capital city community television stations (or "Channel 31" stations, after their typical analogue channel position) have begun to air in digital using LCN 44; one of which (West TV in Perth) airs exclusively via digital transmission.
- 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:[4]
- Ten network metropolitan HD channel
- ABC primary SD channel
- SBS primary SD channel
- VAST regional news guide
- Ten regional primary SD channel
- 7 regional primary SD channel
- 7 network metropolitan primary SD channel
- 9 regional primary SD channel
- 9 network metropolitan primary SD channel
- Ten network metropolitan other TV channels are from 10 to 19
- ABC other TV channels are from 20 to 29
- SBS other channels are from 30 to 39
- local public service is 44
- Miscellaneous/Government channels are from 40 to 43 and 45 to 49
- Ten regional other TV channels are from 50 to 59
- 7 regional other TV channels are from 60 to 69
- 7 network metropolitan other TV channels are from 70 to 79
- 9 regional other TV channels are from 80 to 89
- 9 network metropolitan other TV channels are from 90 to 99
- ABC Audio Only channels are from 200 to 219
- ABC out of region channels are from 220 to 299
- SBS out of region 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
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 109
- Young Children from 120 to 129
- News/Public Service from 130 to 139
- Adult Pay Per View from 170 to 199
- MHEG-5 Interactive from 200 to 219
- MHEG-5 non-broadcast Internet streaming are from 220 to 299
- Reserved for YouView from 300 - 599
- System Services from 600 to 609
- Audio Only from 700 to 789
- Tests and old channels from 790 to 799
The order for the Republic of Ireland's Saorview is based on the priority of the channel to that of the state owned broadcaster:
- State owned RTÉ primary HD TV channel
- 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.[5] Remote control ID allocations for broadcasters outside the Kanto region generally follow their Tokyo-based network flagships; however, stations in some regions 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[6] 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:[7]
- 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
- ↑ "ATSC Standard: Program and System Information Protocol for Terrestrial Broadcast and Cable(PSIP)" (PDF). 23 December 1997. Retrieved 29 November 2010.
- ↑ Eyer, Mark; Mark C. Whitaker (2002). PSIP: program and system information protocol; naming, numbering, and navigation for digital television. pp. 105–107.
- ↑ Free TV Australia (July 2005). Free TV Australia Operational Practice OP-41: Logical Channel Descriptor (Issue 3). Retrieved on 2009-09-01.
- ↑ ‘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. Retrieved 26 October 2008.
- ↑ 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.
- ↑ http://www.freeviewnz.tv/media/3500/freeview_service_provider_code_of_practice_september11.pdf
- ↑ http://www.skytv.co.nz/Default.aspx?tabid=202&art_id=44011
External links
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