Datacasting (data broadcasting) is the broadcasting of data over a wide area via radio waves. It most often refers to supplemental
information sent by television stations along
with digital television, but may also be applied to digital signals on analog TV or radio. It generally does not apply to data which is
inherent to the medium, such as PSIP data which defines
virtual channels for DTV or direct
broadcast satellite systems; or to things like cable modem or satellite modem, which use a completely separate channel for data.
Datacasting often provides news, weather, traffic, stock market, and other information which may or may not relate to the program[s] it is carried with. It may also be
interactive, such as gaming, shopping, or education. An electronic program guide is usually included, although this stretches the definition somewhat,
as this is often considered inherent to the digital broadcast standard.
The ATSC, DVB and ISDB
standards allow for broadband datacasting via DTV, though they do not necessarily define how.
The overscan and VBI are used for analog
TV, for moderate and low bandwidths (including closed captioning in the VBI)
respectively. DirectBand and RDS/RBDS are medium and narrow subcarriers used for analog FM radio.
The EUREKA 147 and HD Radio standards both
allow for datacasting on digital radio, defining a few basics but also allowing for later
expansion.
The term IP Datacasting (IPDC) is used in DVB-H for the
technical elements required to send IP packets over DVB-H broadband downstream channel
combined with a return channel over a mobile communications network such as GPRS or UMTS. The set
of specifications for IP Datacast (phase1) was approved by DVB in October 2005.
Datacasting Services around the World
Australia
- See also: Digital television in
Australia
Australian broadcast infrastructure company Broadcast Australia are undertaking a three year
trial in Sydney of a datacasting service using the DVB-T system for use in Australia.
The trial consists of a number of services on one standard 7MHz multiplex,
collectively known as Digital Forty Four.
The collection includes:
- A combined program guide for the free-to-air broadcasters (Channel 4)
- ABC news, sport, and weather items (Channel 41)
- Channel NSW (link) Government and Public Information, including real time traffic information and life surf webcam images (Channel
45)
- Australian Christian Channel (Channel 46)
- Expo Home Shopping (Channel 49) and
- Federal parliamentary audio broadcasts.
More recently a near-Australia wide broadcast of a datacasting channel called MyTalk has
begun. Broadcasting as part of the multiplex on Southern Cross and
Southern Cross Ten stations, it provides news, weather and other information,
available free to anyone able to tune in. The stream consists of text applicable to the viewer's location and a 4:3 video window
of broadcast TV from the relevant Southern Cross/Southern Cross Ten station.
Malaysia
Malaysian multi-channel pay-TV operator, MiTV Corporation Sdn Bhd has launched its IP over UHF
service in September 2005. The full digital broadcast capacity is being used to deliver IP services which such as multicast
streaming and datacasting.
South Africa
Mindset Network has developed an IP satellite datacast platform for the distribution
of educatinal and health content to sites around South Africa and increasingly throughout the rest of Africa as well. The model
is a forward and store model allowing users of the platform to view content in an on-demand fashion. Content distributed in this
way includes video content, print-based content (in the form of PDF files), as
well as interactive computer-based multimedia content.
Significantly, the model also includes access to a GPRS network that allows the receiving sites to communicate back to the
Mindset central server. Communications include statistics about the physical health of the machine (e.g. power status, disk drive
usage) as well as usage statistics indicating what content has been viewed.
The model also includes a distributed deployment of the Moodle LMS, allowing users to take
assessments and then have the results transmitted via GPRS to the Mindset server for accreditation.
See also
External links
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