scope:

Videotex is a public access information system which allows for the connection of a variety of terminal equipment to databases of information (servers) or to other terminals over widely available public telecommunications facilities. Initially, terminals were connected to information servers over the conventional Public Switched Telephone Network (PSTN). This was accomplished using low cost modems: typically at 1 200/75 or 1 200/1 200 bit/s. With the introduction of the Integrated Services Digital Network (ISDN) and improved modem facilities, a number of other optional configurations are becoming viable for the connection of Videotex terminals to server systems. These include higher speed conventional modems at 2 400 or 4 800 bit/s, much higher speed modems such as 9 600 bit/s (CCITT Recommendation V.29 [18], CCITT Recommendation V.32 [19]) or 14 400 bit/s (CCITT Recommendation V.17 [17]) and ISDN connections using packet mode on a B or D channel and circuit switched mode.

A number of Videotex communications configurations are possible using these new communications facilities. This ETS describes the method by which these facilities will be used in Videotex.

This ETS describes the application layer and lower layer protocols which are to be used for terminal to host Videotex systems operating over various types of networks. This includes:

- ISDN 64 kbit/s circuit mode;

- ISDN 64 kbit/s packet mode;

- ISDN D channel packet mode;

- PSTN packet mode operation using CCITT V. series modems.

In addition, the existing PSTN based Videotex services are identified. These services make use of relatively low speed modems operating in asynchronous circuit switched mode over the PSTN or equivalent networks.

This ETS also identifies the data syntax profiles to be used in the various configurations within the various countries, together with the common data syntaxes for audio and photographic information. The relationships between the various CCITT Recommendations applicable to Videotex are defined.