Communications format for a subscription television system permitting transmission of individual text messages to subscribers
US4890321A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 30, 1988 |
| Grant date | Dec 26, 1989 |
| Priority date | — |
| Expiry date | Sep 30, 2008 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N21/4882
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A subscription television system in which individual decoders are enabled to receive individually addressed messages is disclosed. The composite signal, including video and teletext, also comprises addressed packets which are detected by decoders and which indicate that a message addressed to a particular subscriber is forthcoming, and system control data. In a preferred embodiment, both addressed packets and teletext are encrypted. The addressed packet is decrypted using a decoder-specific code and a transmitted code, while the teletext message is decrypted using a decryption key contained in the system control data. The teletext message cannot be received until the addressed packet has been decrypted. Therefore, redundant levels of security are provided to the system. Messages for display to the user can be selected in response to user initiated commands, in response to decoder initiation, or in response to the transmitter.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.