Abstract: A method and system for compressing bitmap data in a system for sharing an application running on a host computer with a remote computer, wherein the shared application's screen output is simultaneously displayed on both computers. Simultaneous display of screen output is achieved by efficiently transmitting display data between the host computer and the remote computer. When a font used by the host computer for displaying text is not available on the remote computer, the host computer sends a bitmap representation of the text for display, rather than the text itself. Bitmap representations are cached by the remote computer, so that the same bitmap representation need not be repeatedly transmitted from the host computer to the remote computer. Bitmap representations are compressed by the host computer prior to transmission, transmitted, then decompressed by the remote computer.

Abstract: A transmitting terminal transmits the data to a server and the server transmits the data to a receiving terminal. The server detects transmission errors in the data. If the server detects a transmission error, the server sends a request to the transmitting terminal for data correcting the effects of the detected transmission error on data affected by the detected transmission error. The server also sends the affected data to the receiving terminal prior to receiving the correction data. In other words, the server does not wait to receive the correction data before sending the affected data to the receiving terminal. Additionally, the server modifies the data received from the transmitting terminal to conceal the detected error from the receiving terminal.

Abstract: A method and system for compressing bitmap data in a system for sharing an application running on a host computer with a remote computer, wherein the shared application's screen output is simultaneously displayed on both computers. Simultaneous display of screen output is achieved by efficiently transmitting display data between the host computer and the remote computer. When a font used by the host computer for displaying text is not available on the remote computer, the host computer sends a bitmap representation of the text for display, rather than the text itself. Bitmap representations are cached by the remote computer, so that the same bitmap representation need not be repeatedly transmitted from the host computer to the remote computer. Bitmap representations are compressed by the host computer prior to transmission, transmitted, then decompressed by the remote computer.

Abstract: A multipoint control unit (MCU) includes a plurality of segment processors arranged to extract segment data from a corresponding plurality of input video streams and a plurality of data queues, each one of the data queues being coupled to a corresponding one of the plurality of segment processors for storing segment data provided from the segment processors. The (MCU) also includes a data combiner coupled to the data queues for combining output data from the data queues and a controller coupled to the combiner for selectively providing data to the combiner in accordance with the amount of the data in the data queues. Several different approaches for determining what queues to obtain data from are described to reduce insertion delay Asymmetric picture rates are also used to reduce the video mixing delay.

Abstract: A system and method communicate a single stream of data using an arbitrary and time-varying number of channels of arbitrary, differing, and time-varying bit-rates. A transmitter and a receiver both including finite state machines capable of synchronizing the pattern by which data is sent onto and read from the channels. The finite state machines are capable of dynamically adjusting for changes in the number and data rate of the channels.

Abstract: A method and apparatus for distributing audio signals from one of a plurality of audio sources to an output connect compressed audio signals from each one of the plurality of audio sources to an audio processor. Uncompressed audio signals are derived from the compressed audio signals. The compressed audio signal from one of the plurality of audio sources is selectively coupled to the output based upon the uncompressed audio signals. In a preferred embodiment, the compressed audio signal from one of the plurality of audio sources is coupled to the output selectively in accordance with speech information detected in the uncompressed audio signals from the plurality of audio sources.

Abstract: A method and system for controlling flow of output data between computers sharing an application program. The application program is executed on a host computer and shared with shadow computers. Each computer has a sharing system for coordinating the sharing of the application program. The sharing system of the host computer requests a flow control system of the host computer for permission to transmit output data. The flow control system of the host computer, upon receiving the request for permission, determines whether the amount of output data currently in transit from the host computer to the shadow computers exceeds the amount that can be in transit. When the amount is not exceeded, the flow control system grants permission to the sharing system of the host computer; and when the amount is exceeded, the flow control system denies permission to the sharing system of the host computer.

Abstract: A public-key method of cryptographic key exchange using modular exponentiation in which memory, for storing pre-computed results, can be flexibly traded off against the computational complexity of key-exchange. In a typical embodiment, the invention performs key exchange by the method of Diffie-Hellman but with exponents having a constrained form such that by use of a small table of pre-computed powers of a user's public key, any possible shared secret key within the allowed set can be computed with many fewer modular multiplications than the number of bits of effective key-length thereby obtained. The table of pre-computed powers is transmitted as part of the key exchange protocol. The party in receipt of the table uses the pre-computed powers of the sender's public key to replace calculations that would otherwise need to be done at key-exchange time. The method allows a flexible trade-off between computation and table size.

Abstract: A method and apparatus for distributing audio signals from one of a plurality of audio sources to an output connect compressed audio signals from each one of the plurality of audio sources to an audio processor. Uncompressed audio signals are derived from the compressed audio signals. The compressed audio signal from one of the plurality of audio sources is selectively coupled to the output based upon the uncompressed audio signals. In a preferred embodiment, the compressed audio signal from one of the plurality of audio sources is coupled to the output selectively in accordance with speech information detected in the uncompressed audio signals from the plurality of audio sources.

Abstract: In a finite state machine having a plurality of registers, a stream of pseudo-random numbers is generated by a method having characteristic non-zero integral value N. Repeatedly, over a series of time steps, a set of N combined values is calculated by applying N non-linear combining functions to N input sets of values and registering each combined value in one of N registers. At any time step after N time steps each input set consists of combined values, except that one input set may include as one value the result of combining a combined value with a value from an input stream, and at least two input sets comprise only registered values from distinct registers.

Abstract: A finite state machine for producing a stream of pseudo-random numbers, having characteristic positive integral values S and T. The finite state machine has a w-bit non-linear combiner having an input and an output, a plurality of w-bit registers including at least a chained series of S registers and a chained series of T registers. The non-linear combiner receives as the input data from the last of the chained series of S registers and from the last of the chained series of T registers. The first of the chained series of T registers receives input from the last of the chained series of S registers. The first of the chained series of S registers receives input from the output of the non-linear combiner.

Abstract: Samples of an audio signal are converted into grouped frames of transformed transform coefficients, each frame having a plurality of regions (subbands). The power in each region is determined, quantized and encoded. A predetermined number of categorizations are applied to the transform coefficients in the plurality of regions. Each categorization assigns to each one of the regions a selected one of a plurality of different scalar nonuniform quantization step sizes. The step size is selected in accordance with the quantized power in the region and the quantized powers in all the regions. The quantized power encoded transform coefficients and an identification of the selected categorization are variable-length encoded and transmitted to a decoder. During decoding, the power of the transform coefficients in each of the regions is reconstructed from the quantized and encoded power. The selected one the categorizations used by the encoder is determined from the transmitted identification thereof.

Abstract: A method in a computer system for displaying data generated by a shared application on a host computer system on both a host display of the host computer system and a shadow display of a shadow computer systems The host computer system has a window manager for managing windows displayed on the host display. The shadow computer system has a window manager for managing windows displayed on the shadow display. Under control of the host computer system, a Share System executes the shared application. Then, the Share System registers a host window with the windowing system of the host computer system. Upon registration of the host window, the Share System sends a notification of registration of the host window to the shadow computer system. At the shadow computer system, the Share System receives the sent notification of registration of the host window.

Abstract: A method and apparatus for providing a flexible and scalable videoconferencing system for use in connection with a network provides for scalably encoding an image sequence for transmission onto the network. The encoding enables the encoded image sequence to be decoded at any one of at least two spatial resolutions and any one of at least two frame rates. The decoder, depending upon the computing platform, its resources, speed, and efficiencies, can select to decode the received image at any of the available spatial resolutions and at any of the available frame rates. A lower spatial resolution and/or a lower frame rate require less computing resources. Multiple received image sequences can be decoded simultaneously, at, for example, a lowest resolution. The decoded images can be displayed for viewing on the computer monitor at the desired spatial resolution level and frame rate.

Abstract: A method and apparatus for encoding a sampled signal using a nonscalar vector quantizer. A lapping window operator is applied to blocks of signal samples of length greater than N to produce length-N transform vectors which are then encoded by a nonscalar vector quantizer. The method and apparatus may use or have a window operator that is identical to that of the modulated lapped transform, that is a 2N.times.N matrix operator, that is identical to that of the modulated lapped transform with asymmetrical, orthogonal butterflies, or that has butterfly transmittances given by h?n!=sin?(2n+1).pi./4N!. The method and apparatus may use or have a vector quantizer is an unconstrained mean-square optimized vector quantizer having codewords of length N.

Abstract: A microphone system for use in an environment where an acoustic source emits energy from diverse and varying locations within the environment. The microphone system has at least two directional microphones, mixing circuitry, and control circuitry. The microphones are held each directed out from a center point. The mixing circuitry combines the electrical signals from the microphones in varying proportions to form a composite signal, the composite signal including contributions from at least two of the microphones. The control circuitry analyzes the electrical signals to determine an angular orientation of the acoustic signal relative to the central point, and substantially continuously adjusts the proportions in response to the determined orientation and provides the adjusted proportions to the mixing circuitry.

Abstract: An acoustic signal processing method and system using a pair of spatially separated microphones to obtain the direction or location of speech or other acoustic signals from a common sound source is disclosed. The invention includes a method and apparatus for processing the acoustic signals by determining whether signals acquired during a particular time frame represent the onset or beginning of a sequence of acoustic signals from the sound source, identifying acoustic received signals representative of the sequence of signals, and determining the direction of the source based upon the acoustic received signals. The invention has applications to videoconferencing where it may be desirable to automatically adjust a video camera, such as by aiming the camera in the direction of a person who has begun to speak.

Abstract: A video conferencing system wherein a director controller is adapted for disposition on a lecture podium. The controller includes an interconnected control section and a video display section for controlling the distribution of generated audio and video information signals among a local and remote sites selectively in accordance with command signals fed to the controller by a podium speaker. The system is adapted to operate in one of two operating modes: a "Main-screen" mode and a "Mark-up" mode. In the "Main-screen" mode, the video display section is made up of two display areas; a "presentation" display area, and a "preview" display area. The "presentation" display area displays the video information which typically is currently being viewed by the audience/participants at the remote and local sites. The "preview" video display area is privately viewable by the podium speaker, displays video information signals from a second podium speaker selected one of the video sources.