The Story of PLP

The development of information systems during the 1970's was primarily directed to the needs of commercial businesses and manufacturers. Now, with the advances in communications technology and the significant increase in microprocessor capabilities, the informational needs of the entire consumer market can be satisfied. However, to minimize the variables in developing products for the mass market that includes businesses as well as residences, the systerns that are required to provide the informational vehicle must reach a high level of standardization. Since 1978, the international arena has attempted to standardize the character sets and coding of a class of information systems referred to as Videotex. The first agreement reached was in November 1980 by the International Telegraph and Telephone Consultative Committee (CCITT), in Geneva. This CCITT recommendation was referred to as "International Information Exchange for Interactive Videotex, Recommendation S.100," and included three incompatible coding schemes. In May 1981, a Presentation Level Protocol (PLP) was announced by AT&T which combined all of the functions of the three incompatible coding schemes of S.100, with more complete graphical and color capabilities, into a unified coding syntax. This article covers the rationale for PLP prior to May 1981 and recent progress toward a North American standard for videotex.