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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 terrestrial 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 DTT 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 programs 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 DTT, 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 the DVB project in October 2005.
Datacasting services around the world
Ambient Information Network
Ambient Information Network, a datacasting network owned by Ambient Devices presently hosted by U.S.A. Mobility, a U.S. paging service and focuses on information of interest to the local (or larger) area, such as weather and stock indices, and with a paid subscription Ambient will provide a particular device with more personalized information.
A slight variation of the European Radio Data System, RBDS is carried on a 57kHz subcarrier on FM radio stations. While originally intended for program-associated data, it can also be used for datacasting purposes including paging and dGPS.
DirectBand, owned by Microsoft, uses the 67.65 kHz subcarrier leased from FM radio stations. This subcarrier delivers about 12 kbit/s (net after error correction) of data per station, for over 100 MB per day per city. Data includes traffic, sports, weather, stocks, news, movie times, calendar appointments, and local time.
The now-defunct MovieBeam service used dNTSC technology by Dotcast to transmit 720p HDTV movies in the lower vestigial sideband of NTSC analog TV. The set-top box stored the movies to be viewed on demand for a fee. This was distributed through PBS's National Datacast.
TV Guide On Screen
TV Guide On Screen is an advertising-supported datacast sent by one local station in each media market. It supplements or replaces the limited electronic program guide sent by each TV station, which is already mandated by the U.S. Federal Communications Commission (FCC).
ATSC-M/H is yet another mobile TV standard, although it is transmitted and controlled by the broadcasters instead of a third party, and is therefore mostly free-to-air (although it can also be subscription-based). From a technical standpoint, it is an IP-encapsulated datacast of MPEG-4 streaming video, alongside the ATSC MPEG transport stream used for terrestrial television broadcasting. Heavy error correction, separate from that native to ATSC, compensates for ATSC's poor mobile (and often fixed) reception.
The collection included:
- 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 commenced on April 13, 2007. Broadcasting as part of the multiplex on Southern Cross and Southern Cross Ten stations, it provided news, weather and other information, available free to anyone able to tune in. The stream consisted of text applicable to the viewer's location and a 4:3 video window of terrestrial TV from the relevant Southern Cross/Southern Cross Ten station.
On February 25, 2008, MyTalk ceased broadcasting. Digital Forty Four was shut down at exactly midnight on the night of April 30, 2010.
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.
Mindset Network has developed an IP satellite datacast platform for the distribution of educational and health content to sites around South Africa and increasingly throughout the rest of Africa as well. he 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.
Teletext was used extensively on analogue channels; a type of datacasting using the overscan on analogue transmissions. Teletext Limited and Ceefax were the main providers. Within digital terrestrial television, the Digital Teletext name is used extensively although the technology used to provide this service is unrelated and uses the MHEG-5 UK profile.
Outernet's goal is to provide free access to content from the web through geostationary and Low Earth Orbit satellites, made available effectively to all parts of the world. The project uses datacasting and User Datagram Protocol through both small satellites, such as CubeSats, and larger, more conventional geostationary communications satellites in a satellite constellation network. Wi-Fi enabled devices would communicate with the satellite hotspots, which receive data broadcasts from satellites.
Advantages over Internet transmission
Datacasting has a number of significant advantages over using the Internet, specifically when it comes to privacy and censorship resistance.
Both satellite and terrestrial broadcast channels can carry multicast IP data which can be forwarded onto a LAN with a suitable receiver, which can be as simple as a low-cost set-top-box running custom firmware. The software to transmit web pages over multicast is fairly easy to implement and some of the technology has been already developed.
Because the data stream is receive only, nobody can tell what you are receiving. Thus the government cannot round up citizens for reading forbidden material in oppressive regimes. In extreme cases the receiver can be physically disconnected from the Internet to ensure maximum security, thus providing a system much more secure than Internet based anonymity networks such as Tor.
It is much more difficult, on a technical and political level to jam a satellite signal compared to blocking a web site. Data streams can be transmitted alongside television channels. An attempt to jam the data stream will end up jamming the TV stations as well.
Despite the very high cost of satellite bandwidth, broadcasting to hundreds of thousands or millions of receivers may well be cheaper than using the Internet.
- Interactive television
- Multimedia home platform
- MPEG Multiprotocol encapsulation
- MPEG Unidirectional Lightweight Encapsulation
- "Datacasting | Homeland Security". www.dhs.gov.