Abstract: An apparatus includes a wavelength-selective optical switch able to route light between a first optical port and a plurality of second optical ports. The wavelength-selective optical switch includes a bank of optical wavelength-converters. Each wavelength converter of the bank is able to selectively optically couple an optical data stream on a wavelength-channel between the first optical port and individual ones of the second optical ports.

Abstract: An apparatus includes a wavelength-selective optical switch able to route light between a first optical port and a plurality of second optical ports. The wavelength-selective optical switch includes a bank of optical wavelength-converters. Each wavelength converter of the bank is able to selectively optically couple an optical data stream on a wavelength-channel between the first optical port and individual ones of the second optical ports.

Abstract: Synchronizing local timing units to a central timing unit to determine the difference in timing between external links and the local timing units so as to synchronize the centralized timing unit to the external links. This difference in timing is then transmitted to the central timing unit, which utilizes this information to adjust the timing of the central timing unit. The adjustment to the central timing unit brings it into synchronization with the selected external link. The local timing units are synchronized to the central timing unit via multiple timing paths set up through switching units within the network. Each switching unit switches one bit of data for each group of data being received on each of the external links. In addition, information received by each of the external links designating the accuracy of the external link is transmitted to the central timing unit so that the central timing unit can select the external link having the highest accuracy.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: A smooth pulse sequence (SSM) which is a rational fraction (M/N) of an available uniform sequence (SIN) is generated by employing an address generator (10) and a read only memory (ROM 15). Signal representations are stored in the ROM (15) which define the smooth sequence pulse transitions. The address generator (10) is driven by the reference signal and, in turn, generates a sequence of address signals which, when applied to the ROM (15) cause the smooth pulse sequence (SSM) to be read out. The smooth pulse sequence (SSM) is filtered (16) and shaped (17) to obtain a desired uniform pulse sequence (SOUT) which is in synchronism with the reference signal (SIN).