Abstract: A single medium (audio) voice grade call initiated by an ISDN video phone and directed to another ISDN video phone is converted into a multimedia (audio and video) ISDN call by a) maintaining the connection for the voice grade call while the ISDN audio and video connection is being established over a bearer channel of the ISDN subscriber loop different from the bearer channel being used by the voice grade connection, b) switching the audio signals from the voice grade call to the ISDN audio and video connection, once the ISDN audio and video connection is established, and c) tearing down the initial voice grade call.

Abstract: In a video telephony system, a coaxial cable network, which is preferably a part of an existing cable television system, provides a local link for the transmission of the video telephone signals between each originating and destination location and a respective "head end" located on the cable company premises. Each of the head ends is connected to a "point of presence" of a telephone interexchange carrier so that a connection between pairs of head ends, and thus between a pair of video telephone locations, can be made via a switched digital network maintained by the carrier. Certain of originating and destination locations comprise a standard television set, serving as the audio/video display, and a consumer-type camera or camcorder, serving as the audio/video source. Others of the originating and destination locations comprise ISDN video telephones which are connected to the various points of presence of the interexchange carrier via local exchange carrier telephone networks.

Abstract: In a video telephony system, a coaxial cable network, which is preferably a part of an existing cable television system, provides a local link for the transmission of the video telephone signals between each originating and destination location and a respective "head end" located on the cable company premises. Each of the head ends is connected to a "point of presence" of a telephone interexchange carrier so that a connection between pairs of head ends, and thus between a pair of video telephone locations, can be made via a switched digital network maintained by the carrier. Certain of originating and destination locations comprise a standard television set, serving as the audio/video display, and a consumer-type camera or camcorder, serving as the audio/video source. Others of the originating and destination locations comprise ISDN video telephones which are connected to the various points of presence of the interexchange carrier via local exchange carrier telephone networks.