The present invention permits a teletext system operator to adjust subscriber access to service levels individually by adjusting a code at the head end station. A head-end station transmits a tier description page and a tier authorization page. The tier description page divides the data base into a group...http://www.google.de/patents/US4600921?utm_source=gb-gplus-sharePatent US4600921 - Full-field teletext system with dynamic addressability
