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ITU-T T.100

INTERNATIONAL INFORMATION EXCHANGE FOR INTERACTIVE VIDEOTEX

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Organization: ITU-T
Publication Date: 1 November 1988
Status: active
Page Count: 47
scope:

This Recommendation describes the characteristics of coded information that is exchanged between countries participating in the international interactive Videotex service (as described in Recommendation F.300) and defines the display features corresponding to its various elements.

Videotex systems are text communication systems having in addition the capability of a given level of pictorial representation and a repertoire of display attributes. The text and the pictures obtained are intended to be displayed using the current television (TV) raster standards of the different countries.

Different options are offered as a choice for the Administrations to implement their national services. Substantial degrees of compatibility exist between these options, but some transcoding may be necessary to facilitate interworking.

For the international service, four different options for representing pictorial information have been recognized:

a) mosaic character sets;

b) geometric system;

c) dynamically redefinable character sets;

d) photographic representation.

These options are not mutually exclusive and it is possible that systems may develop using two or more options.

For international interworking, two categories of TV systems have to be considered:

a) systems having a vertical resolution of 525 lines per TV frame at 30 TV frames per second;

b) systems having a vertical resolution of 625 lines per TV frame at 25 TV frames per second.

Interworking problems at the pictorial level between countries having different recognized pictorial systems and/or television standards require further study.

This Recommendation is structured as follows:

§§ 1, 2 and 3 deal with the features common to all the options;

§ 4 deals with the coding of characters of the Videotex alphanumeric repertoire defined in Annex B;

§ 5 deals with the alphamosaic option;

§ 6 deals with the alphageometric option;

§ 7 deals with the dynamically redefinable character sets (DRCS) option;

§ 8 deals with the alphaphotographic option;

§ 9 deals with future enhancements and identifies features requiring further study such as: audio, downloaded software, motion, etc.;

§ 10 deals with line and end-to-end protocols;

§ 11 deals with interworking with other services.

Some of these parts have not been completed, and therefore contain guidelines towards future extensions rather than a complete technical specification.

Purpose

The purpose of this Recommendation is:

a) to facilitate an orderly introduction of early Videotex services (including the continuation of existing services, with a clear identification of potential enhancements) that need to be considered in future developments;

b) to identify parameters needed to design Videotex terminals; and

c) to provide technical recommendations desirable for potential interworking of other services with Videotex services.

Document History

ITU-T T.100
November 1, 1988
INTERNATIONAL INFORMATION EXCHANGE FOR INTERACTIVE VIDEOTEX
This Recommendation describes the characteristics of coded information that is exchanged between countries participating in the international interactive Videotex service (as described in...

References

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