Vertical Blanking Interval (VBI),
Teletext & MINITEL
understand Teletext, it’s helpful to understand television's Vertical Blanking Interval (VBI).
VBI - (Vertical Blanking
Interval) - The Vertical Blanking Interval (VBI), also known as
the vertical interval or VBLANK, is the time between the last line of a
frame, or field and the beginning of the next frame, or field. It's
present in analog television, VGA, and DVI signals. During this
very short time, the data transmitted is not displayed on the screen (Wikipedia). Typically the
VBI is expressed as the number of horizontal lines scanned. The VBI
signal however must be too weak to adversely affect the electron beams
carrying the main picture signal. (Analog TV signals need to cause
0-beam intensity during the VBI to ensure that the picture is not
affected.) Fortunately it's possible for circuitry in the TV to detect
and interpret the weak VBI signals.
The analog TV format for North and Central America, as well as
Japan, is set by the National Television Standards Committee
(NTSC.) They specified that 525 horizontal lines be scanned on
the TV picture (though only 486 are visible.) They also specified
that the 'frame refresh rate' be 60 Hz. For the VBI they
specified that 40 horizontal lines (which are part of the 525 just
mentioned,) be VBI lines.
The VBI can carry data such as closed captioning or
Teletext. (See Teletext definition further below.) ATVEF
standards allow the VBI to be used for enhanced/interactive TV
content. However, the limited bandwidth available in the VBI severely
restricts the amount of data that can be transmitted.
Work done to develop closed
captioning was essential to the discovery of how to use the VBI.
The VBI was an unused portion of the analog television signal for
years. The VBI broadcasts closed captioning and other data, including
that which is HTML-based, to television sets, set-top boxes
(connected to TVs,) as well as computers with TV
tuner cards, DVR cards etc. Also with the right hardware and
software, including an appropriate video capture card, you can send the
VBI signal from your computer to your TV.
Originally, the VBI was used for
hardly anything, then in
cooperation with ABC (the network) the National Bureau of Standards
funded early experiments to send the time out over the television
signal. Their experiments failed to provide the desired results
so ABC suggested text captions instead. This, and other experiments
throughout the 70's on programs like the "Mod Squad", led to
engineering partnerships with the Public Broadcasting Service (PBS).
With PBS, ABC developed early decoders (a function of a set-top box or
the like) to interpret the VBI signal and display captioning on the
screen. But, it wasn't until the public television station WETA encoded
and broadcasted data successfully on line 21 of the VBI, that closed
captioning became possible on a mass scale.
After the government deregulated the VBI signal, two-way
enhanced platforms like Microsoft's WebTV
for Windows, Intel's Intercast, Wink and WorldGate were developed
to provide graphical and informational enhancements to their viewers.
Europe's VBI Teletext can offer a great many pages and is accessible
using a remote control. Teletext and Digital Teletext are the best
examples of the commercial use of the VBI. Europe embraced VBI
interactivity a lot more than America and that's one reason the
Internet initially didn't grow as fast in Western Europe as in the
States. Literally Teletext had already given many the interactivity of
the Internet, unlike in the States. In fact in France alone, over 20
million users had access to over 25,000 online services (early 2001
statistic.) In the UK, around 60% of televisions in use, or being
sold, have VBI viewing capacity (early 2001 statistic). (That includes
those that view the VBI through decoders connected to TVs, and those
that have TVs with the decoder built into it).
The limited amount of information that can be carried in the VBI
means that a page of standard teletext might take several seconds to
load. The low resolution of existing TVs means that information
displayed is often not readable when in small text sizes (below about
Teletext is most popular in Europe and originated in Great Britain.
Teletext is information and data made available via the unused VBI
the PAL & SECAM broadcasts. The display can also be altered (made
smaller) so that viewing of this information is clearer. (Teletext is
primarily used in Europe but teletext is available in various parts of
the States.) Teletext can be interactive and was the most popular form
of early interactive television. It's been stated that every line of
the television can carry Teletext.
Teletext and Digital Teletext consists of information, such as news and
sports, viewed on a compatible television set, or via a set-top box
attached to a standard TV set. Its roots lie in the 70s, when the BBC
and Oracle started the first test services. A new and improved version
of Teletext was released in 1997. Some Teletext set-top boxes/built-ins
have the ability to cache multiple pages of Teletext at a time for
faster access times. (One such system is known as FasText. Fastext is a
shortcut key that allows quick, one-button access to a particular
page.) Microsoft incorporated Teletext capacity into it's update of
Windows 98, the "Windows Millennium Edition".
As well as news and sports information, Teletext contains financial
information, such as the latest stock prices, also recipes,
entertainment listings, advertisements, movie schedules and reviews,
music and TV program reviews, additional information on various TV
programs, and more. Teletext also broadcasts subtitles (closed
captions) for various programs, and news bulletins that are overlaid on
top of the TV picture. The incorporation of Digital TVs by consumers
will not end Teletext use we're told but instead will enhance it. The MHEG-5
hypermedia standard has been picked as the standard authoring language
for Teletext services using the digital terrestrial platform in the
U.K. Also see MINITEL further below.
The teletext system was
initially devised in the early 1970's by engineers from the BBC and the
Independent Broadcasting Authority (IBA). The BBC version of teletext
was originally called "Teledata" but later it was changed to "Ceefax".
It was based on a Teletext page containing 24 rows of 32 characters per
row while the IBA version, called ORACLE (Optional Reception of
Announcements by Coded Line Electronics,) allowed 22 rows of 40
characters per row. The Teletext system became operational in 1976. (Reference.)
Like Teletext, Viewdata (sometimes
referred to as Videotex) provided a public information system, but
there are significant differences between it and Teletext. This
interactive videotex system was developed in the late 1970s by the
telecommunications department of the Post Office. It became operational
in 1979. Later the name was changed to Prestel. (Reference.)
Superteletext – A digital teletext browser core.
TVs - Televisions with
the built-in ability to be teletext compatible.
(This was written in
- A largely French interactive
television/telephone collection of networks & service providers.
MINITEL is a form of "Teletext". MINITEL is composed of 25,000+
service providers. There are 20 million plus French users, along
with many, many thousands outside France.
You can book ferry rides,
check tolls and road conditions, book ski accommodations, check your
bank accounts, pay holiday homes' gas/electricity bills, book trains,
tele-shopping with your credit card and much, much more.
In the early 1980s, the
Government stated its desire to start two experimental VIDEOTEX
one was in Paris, and the other was in Ille et Villaine, situated in
between Cotes du Nord, and Mayenne. The idea was to use a low cost
terminal in conjunction with a computerized French Phone Directory. At
the end of 1982, the Télétel network had been introduced
and there was
a launch of the first service to go live - the 11 or Onze.
In France you pay to look at
services by paying for it on your phone bill.
Internet Appliance type
often used to access the MINITEL system as well as Kiosks. Its
existence is one reason why Europeans were slower to jump on the
Internet bandwagon than Americans. Many Europeans already had
Internet type capacities that Americans only discovered with the
is Internet Protocol over
the Vertical Blanking Interval?
(Internet Protocol over the
Vertical Blanking Interval) – The transmission of data (including video
& audio) over the VBI bands of
is an Internet Appliance?
Appliance - (a.k.a. Information
Appliance, Intelligent Appliance, Net Appliance, Net Device) –
These include intelligent kitchen appliances, intelligent
media devices, PDAs, home networked computers and
other devices connected to
the Internet so people can access and operate home equipment from a
distance. Teletext systems, (particularly MINITEL) often