ISDN multimedia communications system

A multimedia communications system comprising a plurality of terminal stations interconnected by an integrated services digital network to which a database is also connected, each of said terminal stations being operable as a data terminal for exchanging computer-generated data with a distant station or accessing said database during a data communication mode and operable as a video terminal for exchanging digital video signals with said distant station during a video communication mode, each of said terminal stations comprising:

• a source for generating a video-to-data mode switching command signal and a data-to-video mode switching command signal;
• a central processing unit responsive to said video-to-data mode switching command signal for generating an outgoing data mode identifier indicating that a signal to be transmitted to a distant station is computer-generated data and an outgoing video-to-data mode switching signal, indicating the distant station to switch to a data mode of reception, and responsive to said data-to-video mode switching command signal for generating an outgoing video mode identifier indicating that a signal to be transmitted to the distant station is a video signal and an outgoing data-to-video mode switching signal indicating the distant station to switch to a video mode of reception, said outgoing video-to-data mode switching signal and said outgoing data-to-video mode switching signal being further generated respectively in response to receipt of an incoming data mode identifier and an incoming video mode identifier from said distant station, respectively indicating the terminal station to switch to data and video modes of reception;
• LAPB (link access procedure balanced) control means for exchanging signals with said central processing unit;
• video coder/decoder means for generating an outgoing digital video signal and decoding an incoming digital video signal;
• multiplexer means for synchronously multiplexing said outgoing digital video signal from the video coder/decoder means with said outgoing data mode identifier to generate an outgoing composite video signal;
• demultiplexer means for synchronously demultiplexing an incoming composite video signal from said distant station into said incoming data mode identifier and a digital video signal, and supplying the demultiplexed video signal to said video coder/decoder means;
• an ISDN (integrated services digital network) interface for interfacing the terminal station with said integrated services digital signal network to which said distant station is also terminated;
• voice coder/decoder means connected to said ISDN interface for decoding an incoming voice digital signal from said distant station via said interface and transmitting an outgoing voice digital signal to said distant station via said interface, said interface multiplexing said outgoing voice digital signal with said outgoing composite video signal for transmission to said distant station and demultiplexing signals from said distant stations into said incoming voice digital signal and said incoming composite video signal;
• and
• switching means responsive to said outgoing video-to-data mode switching signal for coupling said LAPB control means to said ISDN interface for allowing said central processing unit to exchange said computer-generated data and said incoming and outgoing video mode identifiers with said distant station and to access said database, and responsive to said outgoing data-to-video mode switching signal for coupling said LAPB control means to said interface via said multiplexer and demultiplexer means for allowing said video coder/decoder means to exchange said outgoing and incoming composite video signals with said distant station, allowing said demultiplexer means to supply said incoming data mode identifier to said central processing unit via said LAPB control means and allowing said central processing unit to supply said outgoing data mode identifier to said multiplexer means via said LAPB control means.