Videotex - Standards

Standards

Work to establish an international standard for videotex began in 1978 in CCITT. But the national delegations showed little interest in compromise, each hoping that their system would come to define what was perceived to be going to be an enormous new mass-market. In 1980 CCITT therefore issued recommendation S.100 (later T.100), noting the points of similarity but the essential incompatibility of the systems, and declaring all four to be recognised options.

Trying to kick-start the market, AT&T Corporation entered the fray, and in May 1981 announced its own Presentation Layer Protocol (PLP). This was closely based on the Canadian Telidon system, but added to it some further graphics primitives and a syntax for defining macros, algorithms to define cleaner pixel spacing for the (arbitrarily sizeable) text, and also dynamically redefinable characters and a mosaic block graphic character set, so that it could reproduce content from the French Antiope. After some further revisions this was adopted in 1983 as ANSI standard X3.110, more commonly called NAPLPS, the North American Presentation Layer Protocol Syntax. It was also adopted in 1988 as the presentation-layer syntax for NABTS, the North American Broadcast Teletext Specification.

Meanwhile, the European national Postal Telephone and Telegraph (PTT) agencies were also increasingly interested in videotex, and had convened discussions in European Conference of Postal and Telecommunications Administrations (CEPT) to co-ordinate developments, which had been diverging along national lines. As well as the British and French standards, the Swedes had proposed extending the British Prestel standard with a new set of smoother mosaic graphics characters; while the specification for the proposed German Bildschirmtext (BTX) system, developed under contract by IBM Germany for Deutsche Bundespost, was growing increasingly baroque. Originally conceived to follow the UK Prestel system, it had accreted elements from all the other European standards and more. This became the basis for setting out the CEPT recommendation T/CD 06-01, also proposed in May 1981. However, due to national pressure, CEPT stopped short of fixing a single standard, and instead recognised four "profiles": CEPT1, corresponding to the German BTX; CEPT 2, the French Minitel; CEPT 3, the British Prestel; and CEPT 4, the Swedish Prestel Plus. National videotex services were encouraged to follow one of the existing four basic profiles; or if they extended them, to do so in ways compatible with a "harmonised enhanced" specification. There was talk of upgrading Prestel to the full CEPT standard "within a couple of years". But in the event, it never happened. The German BTX eventually established CEPT1; the French Minitel continued with CEPT2, which was ready to roll out; and the British stayed with CEPT3, by now too established to break compatibility. The other countries of Europe adopted a patchwork of the different profiles.

In later years CEPT fixed a number of standards for extension levels to the basic service: for photographic images (based on JPEG; T/TE 06-01, later revisions), for alpha-geometric graphics, similar to NAPLPS/Telidon (T/TE 06-02), for transferring larger data files and software (T/TE 06-03), for active terminal-side capabilities and scripting (T/TE 06-04), and for discovery of terminal capabilities (T/TE 06-05). But interest in them was limited.

CCITT T.101