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.

Abstract: The preferred embodiments of the present invention generally provide improved communications over a subscriber loop that is loaded with at least one and potentially a plurality of load coils. The preferred embodiments of the present invention will support digital subscriber line service over loaded subscriber loops that also support a native POTS interface and offer various techniques for advantageously arbitrating use of the 0-4 KHz baseband between POTS and DSL. Furthermore, the rapid start and stop DSL modulation techniques as well as various mechanisms such as protocol spoofing allow DSL service to appear to be always-on for many end user applications even though DSL communication may cease for POTS signaling messages and completed POTS telephone calls.

Abstract: A method and apparatus for automatically adjusting the transmit power level of a data communication equipment (DCE) device being used in an environment in which one or more telephones and one or more DCEs may be connected to the same twisted wire pair. When a telephone goes off-hook, the receiver of the DCE notifies the processor of the DCE that the telephone has gone off-hook. The receiver comprises an equalizer which generates a tap signature based on the off-hook condition of the telephone and deliver the tap signature to the processor. The processor compares the tap signature with tap signatures stored in a memory device until a match has occurred. The processor then reads the transmit power level associated with the matching tap signature out of the memory device and sets the transmit power level of the transmitter of the DCE to the transmit power level read out of the memory device.

Abstract: The present invention provides a method and apparatus for eliminating or reducing local area and broad area interference in a twisted pair transmission system. The apparatus of the present invention includes a detection device, such as an antenna, for example, for detecting electromagnetic interference coupled into a twisted pair line, a sampling/scaling device which samples and scales the detected signal, and a combiner device which combines a signal correction component with the signal received over the twisted pair by a differential receiver. The sampling/scaling device preferably includes an analog-to-digital converter (ADC) which converts the detected analog signal into a digital signal and a digital signal processor, which receives the digital signal from the ADC and processes the signal to generate a correction signal. The correction signal is then subtracted from the signal received by the differential receiver. The sampling/scaling device may be fixed or adaptive.

Abstract: A frequency dependent synthetic termination system varies a simulated impedance of a communications device as a function of signals received by the communications device. A feedback mechanism receives signals from a transmission line and attenuates the signals when the signals have a frequency within a predefined frequency range. The feedback mechanism then transmits the signals to a current source which drives the transmission line, thus simulating a termination impedance of the communications device based on the signals transmitted from the feedback mechanism. By varying the impedance of the communications device, the communications device can be designed to support communications of various frequencies over the transmission line.

Abstract: An improvement to a half duplex multipoint communication environment wherein a pilot tone enables a control modem to maintain synchronization with a plurality of remote modems. By employing a VCXO in a remote modem, a low jitter timing pulse is generated thus allowing a control modem to maintain synchronization with a plurality of remote modems.

Abstract: The present invention provides a method and apparatus for eliminating or reducing local area and broad area interference in a twisted pair transmission system. The apparatus of the present invention comprises a detection device, such as an antenna, for example, for detecting electromagnetic interference coupled into a twisted pair line, a sampling/scaling device which samples and scales the detected signal, and a combiner device which combines a signal correction component with the signal received over the twisted pair by a differential receiver. The sampling/scaling device preferably comprises an analog-to-digital converter (ADC) which converts the detected analog signal into a digital signal and a digital signal processor which receives the digital signal from the ADC and processes the signal to generate a correction signal. The correction signal is then subtracted from the signal received by the differential receiver. The sampling/scaling device may be fixed or adaptive.

Abstract: A transceiver capable of transmitting and receiving current-driven communication signals is implemented within a communication system, for example a subscriber loop associated with the public-switched-telephone-network (PSTN). By utilizing current drivers having high source impedance the load across a communication connection servicing the transceiver is significantly reduced such that additional transceivers may be bridged to the communication connection without substantially affecting the quality of the communication signals.

Abstract: A plurality of distributed POTS filters (DPF) are associated with a respective plurality of POTS communications devices and decouple a POTS channel from a telephone connection, while permitting and not interfering with a second communications channel (e.g., DSL, ADSL, SDSL, RADSL, VADSL, etc.) on the telephone connection that is utilized by a modem, and permit the passage of additional signals, such as caller ID signals, to the plurality POTS communications devices. In architecture, the DPF system includes a plurality of POTS communications devices, such as telephones, and a plurality of the DPFs corresponding respectively with and connecting each of the POTS communications devices to the telephone connection. Each of the DPFs comprise an automatic control mechanism, which includes circuitry configured to allow the passage of additional signals, such as caller ID signals, to the plurality of POTS communications devices and a POTS filter.

Abstract: Apparatus and method are provided for qualifying POTS devices for optimum operation that involve measurements and analysis of the POTS device's impedance over the modem spectrum, noise emanations, and non-linear distortion. The apparatus includes a test port that analyzes the POTS device measurements that could impact the data communication device performance over the POTS line into the user premises. Testing for line monitoring of the entire premises while the data communication device is in an operating state is also possible. Operating state testing measures the minimum and maximum data rate achievable by the data communication device while each POTS device is in an on-hook or off-hook state. The data communications device is configured to provide notice if a less than desirable data rate occurs. This notice indicates that there is a device connected within the user premises that is limiting the overall data rate and that testing of each individual POTS device is needed.

Abstract: An adaptive voice and data bandwidth management system is implemented in a subscriber loop to permit higher data rates and adaptive allocation of this increased capacity between multiple applications. The management system communicates digital data across multiple-lines when these lines are not in use by other communication equipment. However, when a request for use of a line by another device is detected, a modem clears down a subscriber line and connects the subscriber line to the appropriate communication device. As a result, simultaneous use of a modem and other communication devices is allowed. Once the other communication device ends its communication session, the system adapts to once again communicate digital data over multiple lines in order to increase the speed and efficiency of the data communication.

Abstract: A plurality of passive distributed POTS filters (DPF) are associated with a respective plurality of POTS communications devices and decouple a POTS channel from a telephone connection, while permitting and not interfering with a second communications channel (e.g., DSL, ADSL, SDSL, RADSL, VADSL, etc.) on the telephone connection that is utilized by a modem. In architecture, the DPF system includes a plurality of POTS communications devices, such as telephones, and a plurality of the DPFs corresponding respectively with and connecting each of the POTS communications devices to the telephone connection. Each of the DPFs comprise an automatic control mechanism and a POTS filter. The automatic control mechanism is configured to isolate the POTS filter when a respective POTS communications device is on-hook. Each DPF is configured to permit POTS communications over a POTS channel on the telephone connection with the respective POTS communications device when the POTS communications device is off-hook.

Abstract: A multiple line modem and method enable a user to automatically usurp a plurality of telephone lines for data transfer when the telephone is not in use and the ability to switch from multiple line data operation to one (or more) line data and one (or more) line telephone operation automatically when the telephone handset is lifted or an incoming call is detected signaling a request for voice service. The multiple line modem will automatically reestablish the data connection on the line(s) that was used for voice service when the voice service terminates. The multiple line modem allows end to end service that is transparent to the central office. When all lines are operating in data transfer mode, the aggregate data transfer rate is multiplied by the number of lines available for data transport. When one line(s) is operating in voice service mode, the other line(s) maintains data transfer operation at a reduced rate.

Abstract: A modem is disclosed which is separated into two parts, a first modem circuit consisting of digital circuits, and a second modem circuit consisting of a CODEC and analog circuits. The two modem circuits are separately powered by a first and second power source, respectively, and connected by an isolation circuit. The second power source derives all of its power from the telephone line to which the modem is connected. The portions of the isolation circuit which transfer data and control signals between the first and second modem circuits are constructed using coupling capacitors and latch circuits, and a similar capacitor is connected between the reference grounds of the first and second power sources. Each latch circuit uses a nand gate having two inputs, one of which is connected to momentarily receive a potential equivalent to logical zero, thereby providing a reset when the modem is first energized.

Abstract: An integrated loop current detector for a public switched telephone network modem. The present invention solves the loop current detect problem in general, and is especially useful in modems employing echo cancellation techniques due the linearity afforded by the invention. In one advantageous embodiment of the present invention, the current detector includes a solid-state loop hold circuit coupled to terminals of the PSTN. A current mirror circuit is coupled in parallel with the loop holding circuit, wherein the current mirror circuit includes a transistor having a control terminal coupled to the DC operating point of the loop holding circuit. The transistor is operable to detect interruptions in loop current. An opto-coupler device having an input coupled to the switching device has an output coupled to a current detect input line of said modem thereby providing an isolated output for quick and reliable indication of current interruptions in said loop hold circuit.