Abstract: A method and system for robust delimiting of transmitted messages in switched-carrier operation in which a preamble precedes each communication message with the preamble comprising symbols transmitted at a rate lower than that of the following data. The lower rate symbols of the preamble significantly increase the probability that the decoder will decode the preamble symbols error free. Communication line control information can be included in the robust preamble, thereby ensuring that line control information is reliably transferred over the communication channel. The first symbol of the preamble can be transmitted at the lower symbol rate and at an increased power level, thereby clearly and reliably delimiting the beginning of a transmission. The end of the communication message can be reliably delimited by sending the first symbol containing only bits from a next cell of information at a lower symbol rate and including an extra bit in that symbol.

Abstract: A non-symmetrical half-duplex data communications apparatus and method provides for transmitting and receiving non-symmetrical half-duplex signals over a communications link. The non-symmetrical half-duplex data communications apparatus includes interface circuitry that is connectable to the communications link and modulation circuitry to transmit and receive the non-symmetrical half-duplex signals over the communications link. The modulation circuitry of the non-symmetrical half-duplex data communications apparatus includes the ability to transmit data signals with a transmission time that is different than the transmission time of receive signals. The modulation circuitry of the non-symmetrical half-duplex data communications apparatus also includes the ability to transmit data signals with a transmission data rate different than the transmission data rate of receive signals.

Abstract: A system and method are disclosed for using tolerances obtained from a user together with historical information about a communication network to analyze the network's performance and to calculate and recommend a specific change to the committed information rate (CIR) over a given frame relay permanent virtual circuit (PVC). The historical information, which is collected by a network management system connected to at least two communication devices in a communication network, relates to various performance parameters, which may include the total data transmitted, received and dropped above and within the original CIR, and the burstiness of the data. The historical information is automatically analyzed in view of the user's designated tolerances to determine the network's data transmission performance, and a forward-looking recommendation of an optimum CIR is made, based on the analysis. The results of the analysis and the recommended change to the CIR are displayed to the user in a graphical format.

Abstract: The power budgeter controls the rate of data flow in a transceiver. The power budgeter monitors transceiver activity (data flow) during a predefined period, and limits transceiver data transmit and receive rates during times when the aggregate transceiver activity would otherwise exceed a predefined threshold. If total data flow during the monitored time period exceeds the threshold, data flow through the transceiver during the next (second) time period is limited. Data flow rates are limited in a transceiver by shutting off the transceiver (receiver and/or transmitter) for a specified portion of the second time period. In other types of transceivers, the transmitter and/or receiver may be forced into a low-power idle state or similar operating condition for a specified portion of the second predefined time period.

Abstract: The invention enables a communication device to efficiently communicate large circular signal constellations by embedding a square signal constellation in each of the circular signal constellation points. By embedding a square signal constellation in the error free slicing region associated with each circular constellation signal point, the beneficial shape of the circular constellation is retained while significantly increasing the amount of information that can be transmitted in each constellation. The invention allows the communication of high bit-per-symbol signal constellations (on the order of 15 or more bits-per-symbol) without the added cost of external memory for large look-up tables or the cost and power consumption of line drivers required to communicate high peak factor square signal constellations.

Abstract: A method for testing subscriber loop conditions includes receiving test signal data from a test signal provider, receiving a request for transmitting a test signal described by the test signal data, and transmitting the test signal over a subscriber loop. The test signal may correspond to a pre-qualification test signal, a qualification test signal, or an in-service test signal. Test results may be transmitted to the test signal provider or to some other designated.

Abstract: In a communications environment wherein data terminal equipment (DTE) transmits a data signal to data communication equipment (DCE) synchronously with a clocking signal provided by the DCE to the DTE, a circuit and method are configured to automatically detect a condition in which the data signal is sampled near a transition in the data signal, which may result in system clocking errors. Upon detecting this condition, the clocking signal used to sample the data signal is automatically inverted relative to the data signal to ensure that that the data signal is sampled near the midpoint between transitions in the data signal. In this manner, data clocking errors may be significantly reduced.

Abstract: The power budgeter controls the rate of data flow in one or more transceivers among a plurality of transceivers. The power budgeter monitors aggregate transceiver activity (data flow) during a predefined period, and limits transceiver data transmit and receive rates during times when the aggregate transceiver activity would otherwise exceed a predefined threshold. If total data flow during the monitored time period exceeds the threshold, data flow through the active transceiver during the next (second) time period is limited. Data flow rates are limited in a transceiver by shutting off transceivers (receiver and/or transmitter) for a specified portion of the second time period. In other types of transceivers, the transmitter and/or receiver may be forced into a low-power idle state or similar operating condition for a specified portion of the second predefined time period.

Abstract: A symbol timing derivation system derives receiver timing from received symbols which avoids the need for a pilot tone, thereby reducing power consumption and expanding usable bandwidth. The system is implemented by using a calculation that finds the timing phase error. The timing phase error is then averaged and controls a phase locked loop (PLL). This PLL in turn controls a voltage-controlled oscillator, which handles the modem receiver timing. A centroid calculation can be included to bias the voltage-controlled oscillator to push the equalizer coefficients back to the ideal position. The system can be implemented in either a point-to-point modem environment or a multi-point environment, for example, but not limited to, MVL or DMT. The voltage-controlled oscillator may also be implemented to control transmitter timing, so that the central office modem and the remote modem will operate more-or-less synchronously, reducing the need for large equalizer corrections at either end.

Abstract: A plain old telephone system (POTS) device, for example but not limited to, a telephone, facsimile machine, analog modem, caller identification (ID) system, speaker phone, cordless phone, etc., employs an on-board transistor-based linear polarity guard to enable decoupling of a POTS channel from one or more xDSL channels on a telephone connection (subscriber loop associated with a public service telephone network), while reducing undesirable interference, such as intermodulation distortion imposed upon the POTS and xDSL channels. Transistors associated with the polarity guard are operated in the ohmic region, or in a nonsaturated linear mode, to achieve a substantially linear transfer function through the transistors and through the overall linear polarity guard. Current that is input to the polarity guard and the voltage drop across the transistors that conduct the current in the polarity guard exhibit a substantially linear relationship, or linear VI transfer function.

Abstract: A network congestion control system and method facilitate the transmission of information on a communication network by monitoring the data streams coming out of the communication network for congestion notifications, and actively rate controlling the end user application sessions based on such congestion notifications to alleviate the network congestion. This provides congestion control for the network and can be used to avoid congestion reaching the point where the network has to discard data. The end user sessions can be divided into mission critical sessions and non-mission critical sessions. These session types can be prioritized so that non-mission critical sessions are rate controlled during periods of congestion, while mission critical sessions remain unaffected. Mission critical sessions are effectively reserved a specific amount of bandwidth with the rest of the available bandwidth (up to the congestion point) being allocated dynamically to the non-mission critical sessions.

Abstract: A plain old telephone system (POTS) device, for example but not limited to, a telephone, facsimile machine, analog modem, caller identification (ID) system, speaker phone, cordless phone, etc., employs an on-board POTS filter to enable reliable and efficient decoupling of a POTS channel from one or more xDSL channels on a telephone connection, while permitting and not interfering with the xDSL channels. The POTS device, which connects to a subscriber loop associated with the public service telephone system, includes a subscriber loop connection switch (for example, a hook switch), a POTS transmitter, receiver, or transceiver, and a low pass filter interconnecting the subscriber loop connection switch with the transmitter, receiver, or transceiver. The switch effectively isolates the POTS filter from the telephone line when the POTS device is disconnected, or is on hook, and interfaces the telephone line through the POTS filter to the POTS transceiver when the POTS device is connected, or is off hook.

Abstract: A discrete multi-tone (DMT) digital subscriber line (DSL) communication device employs a linear block interleaver for mathematically combining multiple tones into n-tone combinations in order to efficiently suppress or eliminate correlated noise or impulse noise generated in the communication channel. In architecture, the linear block interleaver includes logic configured to combine multiple signaling constellations into n-tone combinations. The multiple constellations are mathematically combined such that noise energy present in at least one of the n-tone combinations is spread among each of the multiple tones, thus reducing the energy of the noise on each of the multiple tones.

Abstract: A system and method for the measurement of communication network performance over a secondary communication channel sends an inquiry signal containing information pertaining to network performance from a near end communication device to a far end communication device. From the inquiry signal the far end communication device can determine the number of packets of information lost through the network. Once received the inquiry signal is modified by the far end communication device with additional information and sent as a reply signal to the near end communication device. The near end communication device receives the reply signal and can determine therefrom the network latency.

Abstract: A system for providing a backup network is disclosed that includes a glare detection circuit, an arbitration circuit, and a line control circuit. The glare detection circuit receives a dial signal associated with the call control circuit and a cause value from a backup circuit, and asserts a glare present signal responsive to the dial signal and the cause value being asserted. The arbitration circuit receives the glare present signal and produces an arbitration signal responsive to an arbitration procedure. The line control circuit receives the arbitration signal and determines whether the call control circuit will discontinue an outgoing call on the backup circuit and wait a specified period of time for an incoming call on the backup circuit or wait for the outgoing call on the backup circuit to be answered. Methods and other systems are also provided.

Abstract: A subscriber line driver (SLD) is provided for the continuous and automatic transformation of the characteristics of a communication system signal so that the signal conforms to a power spectral distribution (PSD) standard. The signal is transformed by the SLD which may increase (amplify) portions of the signal to a predefined specification, decrease (attenuate) portions of the signal to a predefined specification, and/or frequency modulate or filter the transmit signal frequencies to fit within the communication channel frequency bandwidth as defined by a predefined frequency band. After modification by the SLD, the transformed communication signal is injected (transmitted) into a communication transmission line. An SLD device can be employed in a variety of communication systems such as a public telephony system, a private branch exchange (PBX), a coaxial cable system, a fiber optic system, a microwave system, a radio communication system or the like.

Abstract: The eavesdropping prevention system and method of the present invention provides a mask signal generator which generates a mask signal superimposed over a leakage signal. The mask signal prevents meaningful detection and amplification of the leakage signal. The amplitude of the mask signal is low enough so as not to interfere with the transmission of analog POTS signals over the communication line on which the mask signal is superimposed. In the preferred embodiment, the amplitude of the mask signal exceeds the amplitude of any anticipated leakage signals which may be manifested on the communication line. Alternative embodiments of a mask signal are described.

Abstract: The eavesdropping prevention system and method of the present invention provides a controllable line selection unit which couples a receiver and a transmitter to a selected one of a plurality of subscriber loops according to the current channel of a time-multiplexed communication signal. The controllable line selection unit prevents meaningful detection and amplification of the leakage signal by physically isolating communication connections from each other. In the preferred embodiment, the controllable line selection unit actuates a plurality of switches coupled to a plurality of communication connections. Alternative embodiments of a controllable line selection unit are described.

Abstract: A central office (CO) filter system connects between a CO telephone switch and a telephone connection (subscriber loop) that can communicate voice and digital data channels. The CO filter system suppresses transients and harmonics on the connection caused by a telephone ring signal (typically, 90 to 150 Vrms at 15 to 68 Hz) generated by the switch in order to minimize adverse effects on the digital data channel on the connection. Architecturally, the CO filter system includes a first filter designed to implement a first low pass filter function to attenuate frequencies higher than a ring signal so that transients and harmonics produced from the ring signal are suppressed, a second filter designed to implement a second low pass filter function to attenuate frequencies higher than a voice channel, and a current detector designed to detect when a telephone is off-hook.

Abstract: A filter system (and associated filtering method) is disclosed, the filter system being connected between a large-amplitude, high-frequency noise source and a frequency-division multiplexed communications channel. The large-amplitude, high-frequency noise commonly being a POTS (plain old telephone service) ring signal generated by a CO (central office) telephone switch. The frequency-division multiplexed communications channel generally used to carry digital signals at frequencies above the POTS baseband in order to implement a digital subscriber line (DSL). Large-amplitude, high-frequency signal components from the POTS ring signal impair the performance of frequency-division multiplexed channels on a transmission line such as a subscriber loop. The filter system of the present invention utilizes amplitude and also may utilize frequency to selectively suppress the transients and harmonics on the transmission line caused by a telephone ring signal.