Television – Two-way video and voice communication – User positioning
Patent
1994-07-19
1997-07-01
Woo, Stella
Television
Two-way video and voice communication
User positioning
379 9317, H04N 714
Patent
active
056443552
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates generally to the technical field of electronic storage and transmission of video data and, more particularly, to a subscriber system for receiving and/or transmitting video data in a compressed digital format over a comparatively narrow bandwidth communication channel such as that provided by an Integrated Services Digital Network ("ISDN") twisted pair communication channel, and for presenting images and/or sounds represented by received, compressed video data.
BACKGROUND ART
To deal rationally with the complexity of present communication systems and with the need to make different systems mutually compatible, the International Standards Organization ("ISO") developed a model for specifying such systems. Using this model, called the Open Systems Interconnect ("OSI") model, a communication system can be broken down into a hierarchial structure that permits standards to be defined at each level in the structure. The OSI model provides a hierarchy of seven different layers that can occur in a communication system. Each layer in the OSI model covers a different function performed by the communication system.
The lowest layer in the OSI model, called the physical layer, specifies the physical structure of interfaces in a particular communication system or network. Thus, a standard for the physical layer of a communication system specifies such things as the number of wires, their electrical characteristics, the characteristics of signals transmitted over the wires, connectors used for joining two sets of wires into a single longer set of wires, etc.
The next higher layer in the OSI model, called the data link layer, specifies how data is transmitted error free through the communication system. Thus, a standard for the second layer in the OSI model specifies how to detect errors in transmissions passing over the physical layer, and how to correct any errors that may occur during transmission.
The next higher layer in the OSI model, called the network layer, specifies the manner in which connections are formed between various places in the communication system for transmitting data between them. The standard for the third layer in the OSI model, therefore, specifies the signals transmitted over the data link layer that cause the communication system to transfer data between two places on the network.
A standard defined by an International Telegraph and Telephone Consultative Committee ("CCITT") for the ISDN communication channel specifies these three lowest levels in the OSI model. Under the CCITT standard, a basic ISDN access consists of two full-duplex 64 kilobits per second ("kbps") digital data channels, called channel B1 and channel B2, plus another full-duplex 16-kbps digital channel, called a D channel. Under the CCITT standard, using time division multiplexing, all three of these digital data channels may be transmitted over a single pair of twisted wires, or over two pairs of twisted wires. ISDN basic access, as specified by CCITT, was originally intended to provide a basic digital data transmission capability suitable for use by individuals such as in their homes or small businesses.
When ISDN basic access was initially specified, each of the B channels was intended to carry either:
1. digital data, such as that from a personal computer or from a computer terminal;
2. Pulse Code Modulation ("PCM") encoded digital voice communication; or
3. a mixture of lower data rate communications including digital data and digitized voice that were each encoded at a fraction of each B channel's full 64-kbps capacity. D channel carries signaling information that controls the transmission of data over the two B channels. In addition, when the D channel is not carrying signaling information, it may be used to transmit packet-switching or low-speed telemetry. The combined data rate at which digital data may be transmitted over twisted pairs of wires in accordance with the ISDN standard for basic access is 144-kbps, i.e. 128-kbps for the combined B1 and B2 channels plus 16
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"A Store-and-Forward Archictecture for Video-on-Demand Service"; A.D. Gelman, H. Kobrinski, L.S. Smoot, S.B. Weinstein; c. 1991; pp. 27.3.1-27.3.5; from the International Conference on Communications 1991.
Hata Masato
Koz Mark Christopher
Intelligent Instruments Corporation
Schreiber Donald E.
Woo Stella
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