Virtual channel

For the SDRAM technology, see VC-RAM. For the computer networking term, see virtual circuit.

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:

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:

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:

  1. Reserved for subscriber on-demand services

The order for cable provider Comcast:

  1. Reserved for subscriber on-demand services

The order for satellite provider DirecTV:

  1. Reserved for DirecTV subscriber information (as well as 201)

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:

Usage examples

The order for Freeview (aka FreeTV) is defined by broadcaster transport:[4]

  1. Ten network metropolitan HD channel
  2. ABC primary SD channel
  3. SBS primary SD channel
  4. VAST regional news guide
  5. Ten regional primary SD channel
  6. 7 regional primary SD channel
  7. 7 network metropolitan primary SD channel
  8. 9 regional primary SD channel
  9. 9 network metropolitan primary SD channel

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

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:

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

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:

The order for Sky is largely based on the channel's content:[7]

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

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. 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. ↑ Free TV Australia (July 2005). Free TV Australia Operational Practice OP-41: Logical Channel Descriptor (Issue 3). Retrieved on 2009-09-01.
  4. ↑ ‘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.
  5. ↑ 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.
  6. ↑ http://www.freeviewnz.tv/media/3500/freeview_service_provider_code_of_practice_september11.pdf
  7. ↑ http://www.skytv.co.nz/Default.aspx?tabid=202&art_id=44011

External links

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