Abstract: A method for transmitting information over a communication network between a population of remote terminals and a central location having a capacity of simultaneously communicating with a predetermined number of remote terminals in the population. A first time period is fixed during which every remote terminal may initiate one attempt to communicate with the central location over the communication network. Respective times within the first time period are established at which each of the remote terminals will initiate its attempt to communicate with the central location. A number of the remote terminals which successfully communicate with the central location to transmit information therebetween is monitored. The first time period is then decreased to a second time period if the number of remote terminals which successfully communicate with the central location is less than the capacity of the central location.

Abstract: A subscription television system for distributing program material protected by copyright to subscribers comprises a transmitter including a data insertion circuit for inserting a control bit in a transmitted signal comprising other control data and the protected program material. A receiver of the system includes a memory for storing a pre-assigned subscriber identification. Upon receipt and identification of the control bit at the receiver, the receiver inserts the subscriber identification into the program material so that any unauthorized copy made of the program material may be found to include the subscriber identification.

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.

Abstract: A communication system enabling transmission of individual subscriber teletext messages, audio and video to individual subscribers and permitting group communications of audio, video, teletext and data information from a single central subscriber location, such as a corporate head office to a plurality of satellite offices, such as field or sales offices of the corporation, is disclosed. A composite signal including the information to be transmitted as well as system wide, individual decoder and group decoder control signals is transmitted. The system-wide control signals include data germane to operation of each of the decoders of this system, including key information needed to decode the composite signal. The system-wide control data is transmitted at a first relatively high frequency. The group decoder information includes information permitting individual groups of decoders to receive information portion of the composite signal being transmitted at a given time.

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. The decoder detects an addressed packet addressed to itself, whereby it is enabled to select the appropriate teletext message and to display the same. In a preferred embodiment, both address packets and teletext are encrypted. The addressed packet is decrypted using a decoder-specific code and a system key transmitted as part of the system control data, while the teletext packet is decrypted using the system key, but cannot be received until the addressed packet has been decrypted. Therefore, redundant levels of security are provided to the system.