Interactive Picture Information Systems

Two types of picture information systems, TELETEXT and VIDEOTEX, have come into existence¹ within the past decade. Both were originally aimed at displaying still frames of information from a remote data base on a home TV set. The TV is augmented by special terminal memory and logic.

In TELETEXT, a broadcast television channel with data signals describing pictures embedded in lines in the vertical interval is used to send a magazine of frames (see Fig. below) The frames are repetitively broadcast. A typical magazine might have 100 frames, and 20 seconds are required to cycle through them. A customer of the service uses a small number pad to indicate the frame he desires to see, and the next time that frame is broadcast, its description is stored in memory in the terminal, and the frame is refreshed on the customer's TV. At least one of the frames of the magazine is an index to the remaining frames, so a customer will have knowledge of what can be selected. Provision is also made² for mixing data display with the normal TV picture to give subtitles or news flashes.

In VIDEOTEX (originally called VIEWDATA), the transmission medium is the switched telephone network. A customer calls up a database computer and requests a frame of information to be sent to his terminal for storage and display (see Fig. 13). Table of contents frames tell a customer the numbers of frames that he can select, including more specialized table of contents frames.

public switched telephone network

modem

modem

videotex computer

decoder and storage

data base

data base

home TV

data base

The principal difference between Teletext and Videotex is that videotex service uses the public switched telephone network to transmit the coded textual information. Because of this two-way communications can be used, rather than³ the one-way broadcasting of teletext. This means that a dialogue can be set up between the user and the videotex center so that sophisticated service requirements of the user may be satisfied. Another feature of the interactive type of service is that it may be used for data gathering (for which the term "ingathering" has been coined) as well as data distribution. There are many exciting new possibilities for ingathering like electronic shopping for goods and tickets and some others.

The digitally coded frames of videotex are transmitted along the telephone line in the form of modulated tone that is contained within the audio band passed by long distance telephone lines. This means that it is possible to use videotex systems in offshore vessels⁴ over a radio telephone channel which has, in fact, about the same bandwidth capability as a long distance telephone line. Thus, mariners would be able to receive any of the services of a videotex base, for example, weather forecasts.

Notes

1. have come into existence – появились

2. provision is also made – предусматривается также

3. rather than – а не

4. in offshore vessels – на кораблях, находящихся в открытом море

III. Find in the text answers to the following questions:

1. What types of picture information systems have come into existence? 2. What were they aimed at? 3. What is Teletext? 4. What is the transmission medium in Videotex? 5. Can Teletext and Videotex be used for electronic shopping of goods and tickets? 6. Where else can interactive picture information systems be used?

IV. Speak about the difference between Teletext and Videotex. Find the information in the text.