Digital cable is a all-encompassing appellation for any blazon of cable television administration application agenda video compression or distribution. The technology was originally developed by Motorola.1
Monday 26 March 2012
Background
In 1989, General Instrument (which was after acquired by Motorola) approved that it was accessible to catechumen an analog cable arresting to agenda and address it in a accepted 6-MHz television channel. In the 1990s cable providers began to advance heavily in new agenda based administration systems. Increased antagonism and programming choices from Direct-broadcast agenda casework such as DirecTV, Dish Network, and PrimeStar acquired cable providers to seek new means to accommodate added programming. Barter were added absorbed in added channels, pay-per-view programming, agenda music services, and top acceleration internet services. By 2000, a lot of cable providers in the US were alms some anatomy of agenda casework to their customers.
Digital cable technology has accustomed cable providers to abbreviate video channels so that they yield up beneath abundance amplitude and to action assorted two-way advice capabilities. This has enabled agenda cable providers to action added channels, video on appeal casework (without use of a blast line), blast services, top acceleration internet services, and alternate television services. In addition, agenda cable technology allows for absurdity alteration to ensure the superior of the accustomed arresting and uses a defended agenda administration arrangement (i.e. a defended encrypted arresting to anticipate eavesdropping and annexation of service)
Most agenda cable providers use QAM for video casework and DOCSIS standards for abstracts services. Some providers accept aswell amorphous to cycle out video casework application IPTV or Switched video.
Digital cable technology has accustomed cable providers to abbreviate video channels so that they yield up beneath abundance amplitude and to action assorted two-way advice capabilities. This has enabled agenda cable providers to action added channels, video on appeal casework (without use of a blast line), blast services, top acceleration internet services, and alternate television services. In addition, agenda cable technology allows for absurdity alteration to ensure the superior of the accustomed arresting and uses a defended agenda administration arrangement (i.e. a defended encrypted arresting to anticipate eavesdropping and annexation of service)
Most agenda cable providers use QAM for video casework and DOCSIS standards for abstracts services. Some providers accept aswell amorphous to cycle out video casework application IPTV or Switched video.
Channels
Digital cable technology can acquiesce abounding TV channels to absorb the abundance amplitude that would commonly be active by a individual analog cable TV channel. The amount of channels placed on a individual analog abundance depends on the compression used. Abounding cable providers are able to fit about 10 agenda SD channels or 2 agenda HD channels on a individual analog approach frequency. Some providers are able to clasp added channels assimilate a individual abundance with college compression, but generally this can could cause the video superior of the approach to degrade.
The accession of this adequacy complicates the angle of a "channel" in agenda cable (as able-bodied as in over-the-air ATSC agenda broadcasts). The academic names for the two numbers that now analyze a approach are the concrete approach and the subchannel.
The concrete approach is a amount agnate to a specific 6 MHz abundance range. See: North American cable television frequencies.
The subchannel is a analytic approach of abstracts aural the concrete channel. Technically there can be up to 1024 subchannels in a concrete channel, admitting in convenance alone a few are acclimated (since the bandwidth have to be disconnected a part of all the subchannels).
There are two means providers try to accomplish this easier for consumers. The first, able through PSIP, is area affairs and approach advice is advertisement forth with the video, acceptance the consumer's decoder (set-top box or display) to automatically analyze the abounding channels and subchannels.
The additional (also able through PSIP) is where, in an accomplishment to adumbrate subchannels entirely, abounding cable companies map basic approach numbers to basal concrete and sub-channels. For example, a cable aggregation ability alarm approach 5-1 "channel 732" and approach 5-2 "channel 733". This aswell allows the cable aggregation to change the abundance of a approach after alteration what the chump sees as a approach number. In such arrangements, the physical/sub-channel numbers are alleged the "QAM channel", and the another approach appellation is alleged the "mapped channel", "virtual channel", or artlessly "channel".
In theory, a set-top box can break the PSIP advice from every approach it receives and use that advice to body the mapping amid QAM approach and basic channel. However, cable companies do not consistently anxiously address PSIP information. Alternatively, CableCards accept the approach mapping and can acquaint that to the set-top box.
The accession of this adequacy complicates the angle of a "channel" in agenda cable (as able-bodied as in over-the-air ATSC agenda broadcasts). The academic names for the two numbers that now analyze a approach are the concrete approach and the subchannel.
The concrete approach is a amount agnate to a specific 6 MHz abundance range. See: North American cable television frequencies.
The subchannel is a analytic approach of abstracts aural the concrete channel. Technically there can be up to 1024 subchannels in a concrete channel, admitting in convenance alone a few are acclimated (since the bandwidth have to be disconnected a part of all the subchannels).
There are two means providers try to accomplish this easier for consumers. The first, able through PSIP, is area affairs and approach advice is advertisement forth with the video, acceptance the consumer's decoder (set-top box or display) to automatically analyze the abounding channels and subchannels.
The additional (also able through PSIP) is where, in an accomplishment to adumbrate subchannels entirely, abounding cable companies map basic approach numbers to basal concrete and sub-channels. For example, a cable aggregation ability alarm approach 5-1 "channel 732" and approach 5-2 "channel 733". This aswell allows the cable aggregation to change the abundance of a approach after alteration what the chump sees as a approach number. In such arrangements, the physical/sub-channel numbers are alleged the "QAM channel", and the another approach appellation is alleged the "mapped channel", "virtual channel", or artlessly "channel".
In theory, a set-top box can break the PSIP advice from every approach it receives and use that advice to body the mapping amid QAM approach and basic channel. However, cable companies do not consistently anxiously address PSIP information. Alternatively, CableCards accept the approach mapping and can acquaint that to the set-top box.
Preserving bandwidth
Digital cable has accustomed for out of bazaar television stations to be removed from the basal cable calendar from Channels 2 through 13. They would be confused over to agenda cable channels 100 and aloft for bandwidth preservation. Currently, Comcast Cable outlets in New Jersey and Virginia are adapting this in decidedly beheld counties that are adjoining adjacent television markets.
Technical information
The accepted for arresting manual over agenda cable television systems in the United States is now anchored as both 64-QAM and 256-QAM (Quadrature Amplitude Modulation), which is defined in SCTE 07, and is allotment of the DVB accepted (but not ATSC). This adjustment carries 38.47 Mbit/s application 256-QAM on a 6 MHz channel, which can backpack about two abounding ATSC 19.39 Mbit/s carriage streams. Each 6-MHz approach is about acclimated to backpack 7–12 agenda SDTV channels (256-QAM, MPEG2 MP/ML streams of 3–5 Mbit/s). On abounding boxes with QAM tuners (most conspicuously the DVR boxes), High Analogue versions of bounded channels and some cable channels are available.
Digital Cable allows for the advertisement of EDTV (480p) as able-bodied as HDTV (720p, 1080i, and eventually 1080p). By contrast, analog cable transmits programs alone in the 480i architecture (the everyman television analogue in use today).
The ATSC standards cover a accouterment for 16-VSB manual over cable at 38.4 Mbit/s, but the encoding has not yet acquired advanced acceptance. Some MATV systems may backpack 8-VSB and QAM signals, mostly in accommodation barrio and agnate accessories that use a aggregate of earthbound antennas and cable administration sources (such as HITS or "Headend in the Sky", a assemblage of Comcast that delivers agenda channels by agenda to baby cable systems).
Digital cable channels about are allocated aloft 552 MHz, the high abundance of cable approach 78. (Cable channels aloft approach 13 are at lower frequencies than UHF advertisement channels with the aforementioned number, as apparent in North American cable television frequencies.) Between 552 and 750 MHz, there is amplitude for 33 6-MHz channels (231–396 SDTV channels); if traveling all the way to 864 MHz, there is amplitude for 52 6-MHz channels (364–624 SDTV channels).
In the U.S., agenda cable systems with 750 MHz or greater activated approach accommodation are appropriate to accede with a set of SCTE and CEA standards, and to accommodate CableCARDs to barter that appeal them.
Digital Cable allows for the advertisement of EDTV (480p) as able-bodied as HDTV (720p, 1080i, and eventually 1080p). By contrast, analog cable transmits programs alone in the 480i architecture (the everyman television analogue in use today).
The ATSC standards cover a accouterment for 16-VSB manual over cable at 38.4 Mbit/s, but the encoding has not yet acquired advanced acceptance. Some MATV systems may backpack 8-VSB and QAM signals, mostly in accommodation barrio and agnate accessories that use a aggregate of earthbound antennas and cable administration sources (such as HITS or "Headend in the Sky", a assemblage of Comcast that delivers agenda channels by agenda to baby cable systems).
Digital cable channels about are allocated aloft 552 MHz, the high abundance of cable approach 78. (Cable channels aloft approach 13 are at lower frequencies than UHF advertisement channels with the aforementioned number, as apparent in North American cable television frequencies.) Between 552 and 750 MHz, there is amplitude for 33 6-MHz channels (231–396 SDTV channels); if traveling all the way to 864 MHz, there is amplitude for 52 6-MHz channels (364–624 SDTV channels).
In the U.S., agenda cable systems with 750 MHz or greater activated approach accommodation are appropriate to accede with a set of SCTE and CEA standards, and to accommodate CableCARDs to barter that appeal them.
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