scope:

This European Telecommunication Standard (ETS) defines the application of CCIR Teletext System B to CCIR 625 Line 50 field Television Systems B, D, G, H, I, K and L. The System is optimised for broadcast media using cable, terrestrial and satellite transmission and the associated service and product environment. Reliable reception of data is ensured, since there is a good match between the service area defined for vision and sound reception and that provided for Teletext data broadcasting.

The data is organized in a manner optimum for broadcast media by using the rigid timing framework of the television signal. When multiplexed with a video waveform, this permits a fixed relationship to be provided between the data bytes on a television signal data line and locations in the decoder memory. Using this relationship, error identification and correction are available, matched to the statistical occurrence of bit errors. Critical control data and addressing information are protected by Hamming coding. Basic data is protected by using parity checks.

Teletext data packets are normally grouped together to form "pages" of information, although some have a "stand-alone" function. The range of presentation and application features are arranged to be downward compatible. This permits initial services to be defined and existing services to be upgraded, without rendering obsolete equipment already in the field.

Four presentation Levels are defined:

Level 1: - Alphamosaic characters

- spacing attributes

- fixed colour palette

- 24 rows of 40 columns

Level 1.5: - Extends the character repertoire

Level 2.5: - Extends the language repertoire

- increases the colour palette with re-definable colours

- introduces non-spacing attributes

- allows a number of simple re-definable characters

- provides side panels for additional text or graphics

Level 3.5: - Extends the number of re-definable characters and their complexity

- introduces different font styles and proportional spacing

Levels 2.5 and 3.5 are intended to replace Levels 2 and 3 respectively as defined in earlier specifications. The new Levels offer more display features and can be transmitted more efficiently. Level 1.5 has evolved in the field due to the language requirements in certain countries and is documented here for the first time.

The facility to invoke the presentation of characters of any writing system or language, or a mixture of such systems is included. This ETS includes the coding for Arabic, Cyrillic, Greek, Hebrew and Latin alphabets. Where appropriate the character repertoires and coding structures of the ISO are used.

In addition to the basic text and graphics display presentation, a wide range of other applications can be supported. Protocols for user-friendly navigation techniques also exist. These topics are covered in the reference documents and the other documents listed in annex P.