Top teletext - new projects of the teletext decoder: the fastext (flof) project and its disadvantages

An improvement of this service is offered by the FLOF (Full Level One Feature) procedure proposed by Philips/Valvo. This procedure is known today under the commercial name of "FASTEXT". Besides the traditional selection of pages by way of their three figured numbers, the possibility to use a particular "search tree" operating 5 separate keys on the remote control, is also available, thanks to a special teletext decoder . Four of these 5 keys, in sequence red, green, yellow and light blue, allow the user to enter into a lower level of the structure of this "tree", while the 5 th key always leads directly back to the higher index. The 4 possibilities to move downwards are indicated in entries, that act as a guide to the user, with the normal teletext page, at line 24, unused up to now.

In fact, in a teletext page, only lines 0 to 23 are used. The colours of the single entries and the corresponding keys are ordered on the screen in the same sequence. Technically, this possibility is offered by the broadcasters through the description of line 27 with concatenation orders. Such orders and line 24 are analyzed in the software of the FASTEXT decoder. Moreover, 4 page memories are provided, that automatically memorize as quickly as possible the 4 pages indicated in line 24. Until the user selects the following page, in the case it has not been cancelled from the cycle, the successive pages are already memorized and ready for call-back. When the search tree is used, there is a reduction of the overall access time.

However, the introduction of the FASTEXT procedure involves remarkable consequences for the broadcasters. Besides the remarkable costs for adapting the teletext computer, of its equipment and of the combinatory system available, the editorial staff must permanently change the supplementary data necessary to FASTEXT (lines 24 and 27) and to take care of the search tree. For example, when a page is erased from a cycle, the editorial staff must change the data of lines 24 and 27 in all pages that contain the call-back data of the pages to erase.

Moreover, for every new page introduced to the cycle, the editorial staff must establish from which of the other pages the new ones must directly be selected and to which of these new pages it must be possible to jump directly. The maintenance costs of the search tree are substantial and cause an increase of the staff costs. If, on one hand, the flexibility offered by the FASTEXT call-back system is preferable, on the other, it hides the danger of a "chaotic organization of pages".

This technique is comparable to the jump command of the well known "GO TO." listing in the various languages of software programming. Also, in this case, unclear structures can be created.

Another inconvenience is represented by the lengthening of the cycle time by approximately 10%, due to the additional transmission of lines 24 and 27. Consequently, with the FASTEXT it is not possible to execute some programme methods, as used by several TV broadcasters. Some examples are useful to better understand this inconvenience:

The programming methods, used for example by ARD/ZDF (1 st and 2 nd German tv channel), with a limited number of pages in the morning and in the afternoon and a full program in the late afternoon, mean a remarkable employment of editing time, due to the fact that two search trees must be considered . At the moment of the commutation from the partial program to the integral program and vice versa, the data of lines 24 and 27 must be corrected, for example, in 100 pages.

The programming methods, that are based on the acquisition, in the cycle of pages deriving from other transmission sources, through a combiner, come up against significant difficulties, because the pages inserted by the combiner contain erroneous call-back data. The elaboration of this call-back data calls for new generation combiners. It is practically impossible to re-code the numbers of the pages, as currently occurs in the transfer of the teletext pages of ARD/ZDF.

During the daily movement of page blocks of the television programs organized by days (VPV pages, Videotext Programmed Videorecorder), the editorial staff must correct the call-back data of the lines 24 and 27 in all pages.

Therefore, for all the reasons mentioned, it cannot reasonably be considered that this procedure constitutes an optimal solution in order for it to be employed by television broadcasters.