초록 ▼

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

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 of tiers each comprising a defined range of pages. The authorization page lists authorization codes for all subscribers, one code per subscriber. Each subscriber station includes a permanent location code. When access is requested by the subscriber, the subscriber station uses the location code to acquire the authorization code transmitted by the head-end station. The authorization code indicates which tiers the subscriber station may decode. To change the service, the system operator may change the authorization codes at the head-end station or change the range definitions for the service level tiers.

대표청구항 ▼

In a teletext system having a head-end station, a group of subscriber stations, a data base comprising a multiplicity of data pages transmitted from the head-end station to the subscriber stations on a video channel, each data page comprising a group of data, said data base arranged into program ser

In a teletext system having a head-end station, a group of subscriber stations, a data base comprising a multiplicity of data pages transmitted from the head-end station to the subscriber stations on a video channel, each data page comprising a group of data, said data base arranged into program service levels each comprising a respective set of pages in the data base, the data base and service levels being individually accessible to particular subscribers on a selective basis in response to subscriber requests for access to the teletext system, the improvement for controlling and adjusting subscriber access to particular service levels comprising: means at the head-end station for transmitting to each of the subscriber stations a service level description page comprising data defining each of said service levels and a subscriber service level authorization code page comprising a group of subscriber service level authorization codes for plural subscribers, each of said authorization codes specifying the service levels to which a corresponding subscriber is entitled to have access; and a respective logic circuit located at each subscriber station responsive to said description page and said authorization page for controlling access at its subscriber station to service levels on the basis of the authorization code corresponding to such subscriber station and the service level corresponding to the request by the subscriber.