Vertical Blanking Interval (VBI), Teletext & MINITEL

To 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 14 point.)

Digital Teletext


  Teletext is most popular in Europe and originated in Great Britain. Teletext is information and data made available via the unused VBI lines of 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.
    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.)


Digital Teletext

Superteletext –  A digital teletext browser core.

Teletext TVs -
Televisions with the built-in ability to be teletext compatible.

More Definitions of Vertical Blanking Interval and/or Teletext:
  5. (PDF File)
  6. (Videotex)

What is MINITEL?

(This was written in 2001)

MINITEL - 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 French Government stated its desire to start two experimental VIDEOTEX sites, 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 these services by paying for it on your phone bill.
   Internet Appliance type devices are 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 Internet.

Minitel (France)


What is Internet Protocol over the Vertical Blanking Interval?

IPVBI - (Internet Protocol over the Vertical Blanking Interval) – The transmission of data (including video & audio) over the VBI bands of television.


What is an Internet Appliance?

Internet Appliance - (a.k.a. Information Appliance, Intelligent Appliance, Net Appliance, Net Device) – These include intelligent kitchen appliances, intelligent phones, portable 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 use Internet Appliances