Abstract: In a Digital Data System (DDS) a method and apparatus for providing multipoint multiport service. Differences in time delays through the network are compensated by an alignment training wherein the delays from each remote station are measured at a Central station. The Central station determines how much delay to insert at each remote station and then instructs the remote stations to insert the delays. This allows all inbound data to be aligned in time so that when the data are combined within the network by the Multipoint Junction Units (MJU) data errors are not produced. Aligned frames are combined in the MJU operating in data mode in a logical AND operation so that marks transmitted by inactive ports are combined with data from active ports to produce a composite signal which is passed to the Central DSU.

Abstract: An Expert System 10 for providing diagnostics to a data communications network 5. Alarms from a Network Manager 24 are received and queued by an Event Manager 117 and then filtered by an Alarm Filter 118 to remove redundant alarms. Alarms which are ready for processing are then posted to a queue referred to as a Bulletin Board 120. A Controller 112 determines which one of the posted goals has the highest priority by considering a priority number associated with the goal plus a time of arrival of the goal. An Inference Engine 122 uses information from an Expert Information Structure 111 to solve the highest priority goal by a process called instantiation. The process of solving the goal may be interrupted by a pause or suspension in order to perform tests under the direction of a Network Test Manager 124 or retrieve other information during which time other goals may be processed.

Abstract: Disclosed is a divide-by-m counter for generating an ouptut clock signal having a fifty percent duty cycle from a higher frequency source clock signal having m cycles for each single cycle of the output clock signal and wherein m may be an odd or even integer number, the divide-by-m counter including a modulo binary counter for counting up to a predetermined number, circuitry for presetting the modulo binary counter by another predetermined number, counter clock selector for providing a counter clock signal to the modulo binary counter which, when m is odd, will be either an non-inverted source clock or an inverted source clock based upon the occurrence of either the HIGH or LOW intervals of the output clock, and interval defining circuitry for defining the beginning of such HIGH and LOW intervals of the output clock based upon the occurrence of a ripple carry pulse from the modulo binary counter.

Abstract: A method and apparatus for disabling an echo canceller in a digital telephone network. An originating DSU transmits a sequence of synchronization codes which are shifted by the various delays in the network. The answering DSU receives the shifted codes and determines how much adjustment is required by the originating modem in order to have byte boundaries aligned with those of the network. The answering DSU then transmits this information back to the originating DSU so that the originating DSU can adjust its transmit time to align with the byte boundaries of the network. The originating DSU then transmits byte aligned 2100 Hz tone samples in order to disable the network's echo canceller.

Abstract: The present invention is directed toward a method and apparatus in a communications device for mapping a selected group of data bits into a predetermined number of two-dimensional symbols selected from a minimized alphabet of M two-dimensional symbols forming a symbol constellation, with one of the two-dimensional symbols being transmitter during each symbol (i.e., baud) interval. A plurality of symbol mappers in an adaptive communications device use a superframe of bits per baud. Each superframe includes at least two groups of frames, a low bit frame and a high bit frame. The superframe has A) one of these two types of frames uses whole bits per baud and the other uses fractional bits per baud or B) both of these two types of frames will use fractional bits per baud.

Abstract: A data communication network management system allows a user to establish rules which are pattern matched to attributes of incoming events, such as alarms, from network objects. When a match is found, the network management system retrieves a user prepared command SCRIPT file and substitutes attributes from the event into the command SCRIPT. The command SCRIPT is then invoked to allow the user to program the system to automatically take predetermined actions upon the occurrence of network generated events specified by the user.

Abstract: A soft start circuit for hot installation of modules into an active bus. A very low R.sub.ds MOSFET provides bias through its drain to source path from a bus supply. This path is activated by a gate bias network which charges a capacitor from a supply located on the bus. Further control of the module supply is obtained by circuitry which permits addressing of the module to turn it off or on, temperature sensing to provide thermal protection and current sensing to provide short circuit protection.

Abstract: In a packet based communication network 10, a key management center 20 is used to distribute cryptographic keys for either a switched virtual circuit or a permanent virtual circuit. The disclosed methods allow the key management center 20 to communicate directly with the data encryption/decryption devices (DE's) 14 even though they operate in a transparent mode (rather than a store and forward mode). This is accomplished by balancing link counters with calls to fictitious addresses and/or use of interrupt packets transferred between the DTE 12 and the DE 14. In permanent virtual circuits, the MAC of the last packet transmitted under the old cryptographic key is exchanged to synchronize the key change.

Abstract: A method for estimating an amount of phase roll on a transmission channel. A signal of known frequency is transmitted over the channel by a near end modem. An average noise autocorrelation matrix is subtracted from an average signal plus noise autocorrelation matrix, both as received by a near end modem. The eigenvector of the resulting matrix is computed. The complex root of a quadratic with coefficients equal to the eigenvector elements is computed to solve for a difference between the frequency of the transmitted signal and the echoed receive signal to determine the phase roll.

Abstract: A method and apparatus for providing communication among N modules connected to a common communication bus uses a bus structure with a reserve line for signaling the occurrence of a reservation time slot during which time each of the N modules which have information to transmit may reserve a time for transmission over the bus. A plurality of at least N data lines are used for transmission of data words over the bus. Each of the N modules are also assigned use of one of the plurality of data lines for signaling during the reservation time slot that the module has information to transmit over the bus. The reserve line is also used for signaling, that a word of data being transmitted over the plurality of data lines is a last word in a current transmission to be transmitted by the module currently transmitting.

Abstract: A device for providing teleconference capabilities in an ISDN includes a first receiver for receiving a first signal representing a first message over a first ISDN B-channel. A second receiver receives a second signal representing a second message over a second ISDN B-channel. A receive mixer mixes the first signal with the second signal to produce a receive mixed signal. A local receiver receives a local signal representing a local message to be transmitted over the first and second ISDN B-channel. A first transmit mixer mixes the first signal with the local signal to produce a first transmit mixed signal. A first transmitter transmits the first transmit mixed signal over the second ISDN B-channel. A second transmit mixer mixes the second signal with the local signal to produce a second transmit mixed signal. A second transmitter transmits the second transmit mixed signal over the first ISDN B-channel.

Abstract: A modem side diagnostic loopback apparatus for a two wire communication circuit includes a transformer having a mechanism for connecting to a two wire transmission line on a transmission line side and for coupling to a modem on a modem side. A modem transmitter generates modem transmitter signals and a modem receiver receives signals from the transmission line. A subtracting circuit subtracts the modem transmitter signal from a signal containing both the modem transmitter signal and the received signals. The subtracting circuit may be selectively unbalanced so that the transmitter signals are supplied to the modem receiver and the received signals are inhibited from being received by the modem receiver to effect a loopback.

Abstract: In a packet based communication network 10, a key management center 20 is used to distribute cryptographic keys for either a switched virtual circuit or a permanent virtual circuit. The disclosed methods allow the key management center 20 to communicate directly with the data encryption/decryption devices (DE's) 14 even though they operate in a transparent mode (rather than a store and forward mode). This is accomplished by balancing link counters with calls to fictitious addresses and/or use of interrupt packets transferred between the DTE 12 and the DE 14. In permanent virtual circuits, the MAC of the last packet transmitted under the cold cryptographic key is exchanged to synchronize the key change.

Abstract: An architecture for a switching node of a communication network includes a dedicated hardware Layer 1 processing portion and a Layer 2 and 3 processing portion based on multiple programmed general purpose processors. An array of such processors are used with an arbitration scheme for selecting which of the processors is to be used for any given Layer 2 or Layer 3 process. The architecture allows the node's capacity to be expanded by simply adding more processors to handle increased traffic.

Abstract: A data modem includes a data compression circuit which compresses incoming data prior to transmission. The compression ratio obtained from the compression process is used to select a constellation for transmission of the data. When higher compression rates are achieved, fewer constellation points (symbols) representing fewer bits per point are transmitted. In this manner, incoming data rate can be held constant while utilizing a more robust constellation which has greater immunity to transmission line impairments. This reduces errors and retransmissions which can ultimately lead to reduction in effective throughput in conventional systems.

Abstract: A modem is disclosed having a data transmission protocol involving lower-speed, full-duplex operation during the connect sequence with a remote modem and an automatic switch to higher-speed, half-duplex operation for data transfer. Further, the modem data transmission involves transparently changing between lower-speed, interactive operation and higher-speed operation based upon data transmission demands. The operation is controlled by a processor monitoring the contents of a transmit data buffer and providing a mode control command to the modem transmitter. The modem also adapts its speed to the quality of the telephone line by fallback or fallforward to a different speed based upon predetermined data frame retransmission criteria.

Abstract: A method of assuring consistency of constants in a multilanguage software system, includes generating a first set of code written in a first language using a plurality of symbolic constants to represent a corresponding plurality of actual constants. A second set of code is written in a second language using the plurality of symbolic constants to represent the corresponding plurality of actual constants. A common header file is generated which contains information which relates the plurality of symbolic constants to the corresponding plurality of actual constants. The header is included within the first and second sets of code. The symbolic constants in the first and second sets of code are replaced with their corresponding actual constants during a preprocessing step. Any constructs which are not a part of the first language are stripped from the second set of code including the header file.

Abstract: Disclosed is an arrangement having a main card cage, a plurality of remote card cages, and a data transport system for transmitting synchronous information, the data transport system having at least one bust electrically coupling the card cages to define a plurality of data lines between the main card cage and each of the remote card cages, a master clock generator at the main card cage for generating a single master clock, and a clock resynchronizer at the main card cage for resynchronizing with the master clock data messages received from the remote card cages which have the same frequency, but are shifted in phase from the master clock.

Abstract: An apparatus for controlling access to a time division multiplexed (TDM) bus includes a frame address register having a plurality of storage registers for storing a plurality of frame addresses designated for use in communicating over said TDM bus. A frame address latch stores a current frame address. A frame comparator, coupled to the frame address register and the frame address latch, compares the designated frame addresses with the current frame address and produces a first signal indicative of the storage register containing a frame address matching the current frame address. A time slot register has a plurality of storage registers for storing a time slot number designated for use in communicating over said TDM bus. A time slot generator generates a current time slot number.

Abstract: A multi-port (multiplexed) modem for implementing automatic reconfiguration of the ports so that transmission bandwidth can be optimized. The modem utilizes a sequence of communications and acknowledgments transmitted over the donor port donating the bandwidth and the recipient port receiving the bandwidth. This allows reconfiguration of the modem ports without need for interruption of the unaffected ports and requires no secondary channel to implement. Only the port going idle and the port receiving the bandwidth are affected so that communication channel throughput is maximized and unaffected ports are not interrupted.

Abstract: An Expert System for providing diagnostics to a data communications network. Expert information is entered using a user friendly User Interface which reduces need for the participation of a Knowledge Engineer. The User Interface including a template for entering a plurality of attributes for a hypothesis tree node. Among the attributes are an identifier for identifying a second node connected to the hypothesis tree node by a branch of a hypothesis tree. If the second node has not been defined, it is added to and displayed in a list of undefined nodes. Once all attributes for a template are completed, an identifier for the hypothesis tree node is added to and displayed in a list of defined nodes.