At&t Bell Laboratories

American Telephone and Telegraph, Co.

Dominick Scordo

John R Colton

David M Simmons

Lawrence Baranyai

A memory matrix for storing control words for controlling a common control time division multiplexed (TDM) switch is formed by employing a plurality of shift registers connected in recirculating configuration. Synchronization of control word time slots in the memory matrix to system timing is realized by storing a timing marker which is advanced in identical manner as the control word time slots. If synchronization between the system timing and control word time slots is interrupted, it is restored by controllably inhibiting advancing of the control word time slots and the stored timing marker.

Control memory using recirculating shift registers for a TDM switching

Synchronization of a local timing signal with an incoming reference timing signal is realized by employing a frequency estimator and frequency synthesizer in conjunction with a local fixed oscillator. The frequency estimator includes a first phase-locked loop including an integrator for generating a frequency estimate which is the difference between the frequency of the incoming reference timing signal and the frequency of the fixed oscillator signal. The phase value of the frequency estimate obtained by integrating the frequency estimate is supplied to a second phase-locked loop which includes a digitally controlled oscillator to generate the local timing signal. If the incoming reference timing signal is lost or if there is too large a variation in a phase error signal in the first phase-locked loop, the value of the frequency estimate is held constant. Consequently, the second phase-locked loop never free runs and the local timing signal remains in synchronization with the reference timing signal.

Clock circuit synchronizer using a frequency synthesizer controlled by a

Decryption of a plurality of simultaneously received, randomly phased signals is realized by employing a single data encryption standard module in a time shared manner. A plurality of process state counters, each of which is associated with a received signal, are employed to direct operations of the decryptor on a time shared basis. These operations include the generation on a time shared basis of so-called plain text data for each received signal, generation of corresponding encryption requests, and generation of cipher text data for each received signal which is used to decrypt associated received signal samples.

Common control audio decryptor

Clock recovery pulse signals for use in recovering transmitted data are generated by employing a digitally variable phase oscillator. The variable phase oscillator includes an oscillator having a substantially fixed frequency output signal, a phase encoder and a comparator. Coded phase values of the oscillator output signal are periodically generated by the phase encoder. These coded phase values are compared to a prescribed phase value to generate periodically clock recovery pulse signals. The prescribed phase value is obtained in one embodiment by storing the coded phase value being generated upon the occurrence of an incoming data transition and adding a predetermined phase value to it to center the clock recovery pulse signals substantially in the center of the incoming data eye pattern.

Data clock recovery circuit

In a multilocation conference terminal for transmitting audio and video information to a plurality of remote locations, rapid video and non-disrupted audio switching are obtained by employing a plurality of single composite digital signals each including all the video information from an associated location and all of the audio mixes for all of the locations in a conference. Then, the composite signals are switched prior to conversion for transmission to one or more of the locations. Since each composite signal includes all the audio mixes for all of the locations, when video from anyone of the locations is selected for transmission to any of the locations, the audio mixes for those locations are also switched.

Multilocation video conference terminal including rapid video switching

Audio mixes for a plurality of conference locations are controllably obtained by using a matrix multiplication arrangement. The audio mixes for the individual conference locations are obtained by multiplying a dynamically determined gain matrix by an audio input matrix. Coefficient values in the gain matrix are dependent on whether incoming and outgoing transmission paths are assigned to a location and on whether an audio sample is being received or not.

Programmable audio mixer

In a multilocation video conference system, contention for the video to be transmitted to the locations is resolved by employing so-called talker and graphics contention resolution processes. Both the talker and graphics contention processes may be overridden by manual selection of the video to be viewed at each location. In the talker contention process, the video to be transmitted is not switched until one and only one talker location is detected during a predetermined talker timing interval. In the graphics contention process, all requests for graphics transmission are rejected until one and only one graphics transmission request is detected during a predetermined graphics request timing interval. Once transmission of graphics has been assigned to a location, all other locations in the conference are transmitted the graphics video information until the location displaying graphics releases from the graphics transmission mode or there is a manual override. The location transmitting graphics information is transmitted the video from the last of the other locations selected for talker video transmission.

Multilocation video conference terminal including video switching

In a Multilocation Conference Terminal (MLCT), disruptions in the video being viewed which are caused by switching from one conference location to another are minimized by delaying switching of the video signal until a so-called get ready control signal is received from the conference location to be viewed. The conference location transmits the get ready control signal a predetermined interval prior to transmitting a so-called fast video picture update in response to a request from a Multilocation Conference Terminal (MLCT). Additional possible disruptions in the video are eliminated by minimizing the number of fast video picture updates that are used to serve a multiplicity of requests from other conference locations. When multiple MLCTs are employed in a conference, the MLCTs communicate to each other the video select modes of all the conference locations in the conference, i.e., a manual select mode or an automatic select mode. Then, the video select mode information is used to minimize the number of fast video picture updates needed to serve conference locations in the automatic select mode.

Multilocation video conference terminal including an arrangement to

In a multilocation video conference system, conference locations are dynamically added to or deleted from an ongoing conference without disrupting it. This is realized by controllably enabling or disabling communications ports assigned to the conference locations in a Multilocation Conference Terminal (MLCT). Both audio information and control channel information transmitted from a conference location assigned to a port are monitored to determine if the audio information is satisfactory and if the control channel communication is 'good'. If the audio information is unsatisfactory, it is muted and selection of the video from that location as a one-and-only-one talker is inhibited. If the control channel communication is not good the video signal from the conference location is excluded from the conference.

Growing community of inventors

Middletown, NJ, United States of America

Dominick Scordo