Abstract: The present invention synthesizes a prescribed impedance. The impedance is synthesized by generating a current having a value substantially equal to a voltage divided by a prescribed impedance. Sensing the line voltage and converting that sensed line voltage to its digital equivalent accomplish this first step. The digital line voltage is processed by a factor related to the prescribed impedance to produce an output voltage that has a value substantially equal to the sensed voltage divided by the prescribed impedance. The output voltage controls a voltage to current converter that generates the appropriate current across the points or terminals where the line voltage was measured. Thus, the prescribed impedance is generated across these points or terminals because the line voltage divided by the generated current is substantially equal to the prescribed impedance.

Abstract: In the course of a reflectometry-based qualification procedure of a local loop, which connects customer premises to a central office of a telecommunication network, and in the event of being unable to identify the loop termination associated with the customer premises, a second reflectometry measurement of the local loop is carried out with a different impedance load at the customer premises. Next, the two reflectograms are compared with each other in the time domain in order to delineate among all the reflections those at the customer premises and to determine therefrom the position of the customer premises in the local loop.

Abstract: Single ended line probing techniques for determining if a telephone line qualifies for digital subscriber line service are disclosed.

Abstract: A system and method of troubleshooting a communication connection for a remotely located security system is disclosed. A communication line test unit is incorporated into the remote security system and its communication unit. A central control unit can then contact the remote security system communication unit, enable the communication line test unit and perform tests on various operational parameters of the communication unit located in the remote unit and the communication connection of the local unit. The tests conducted can include loop current, tip to ring voltage, ring to ground current, circuit loss, circuit noise, power influence as well as other tests. Based on the results of these tests a determination can be made if the problem is an extraneous influence, such as a poor local telephone line connection, or some problem with the security system communication unit itself.

Abstract: Circuits for testing POTS service on a shared POTS/xDSL carrier include microfilters for selective coupling to the subscriber loop side of an xDSL filter associated with a subscriber line interface circuit. Such configurations facilitate testing of the POTS service using an insertion point that is between the xDSL filter and the subscriber loop in a manner that is transparent to subscribers.

Abstract: Methods and systems for proactively maintaining a telephone system local loop. One embodiment includes communicating with a communications network and acquiring status information associated with telephone lines. Proactive maintenance is predicted using upon the status information. Work orders describing the predicted proactive maintenance may be generated and dispatched. Another embodiment includes communicating with a communications network and acquiring at least one customer information associated with copper line pairs, service information associated with copper line pairs, and status information associated with telephone lines. The acquired information is stored in a database. The database is updated with the status information associated with telephone lines. Proactive maintenance is predicted using the stored information.

Abstract: A loop loss measurement and reporting mechanism for a digital data services unit obviates interaction with a test unit at a far end of the loop, by relying upon a priori knowledge of the signal power and spectral content of a data port at the far end of the loop to conduct threshold detection and power level measurements. A received signal is amplified by amplifier circuitry, the gain of which is controllably adjusted by the microcontroller based upon the outputs of threshold detectors and power level measurement circuitry that monitor the amplified received signal. A front panel display is controlled by the microcontroller to display loop loss parameter information. To measure and report loop loss, the digital data services unit turns off its transmitter for a prescribed period of time and monitors an in-band signal of known power and spectral content sourced from the far end of the loop.

Abstract: A method and apparatus for testing telephone equipment for longitudinal balance. A signal generating circuit places a test signal at a certain frequency on the tip and ring wires of a telephone line. The telephone line is monitored and the signals on the tip and ring wires are measured and compared against each other. The frequency is gradually increased in set increments until the test frequency is in the megahertz range.

Abstract: The current invention provides a method and apparatus for determining insertion loss in wireline communication systems. The method may be implemented with any modulation protocol but is particularly suited for multi-carrier modulation protocols such as discrete multi-tone (DMT). The method for calculation of the insertion loss uses a received signal and a discrete subset of frequency ranges, e.g. DMT tones, within that signal. For each of the subset of frequency ranges the average received power on each of the selected set of tones is determined. Next the average power on each received subset of tones is converted to log2 using a simple log2 estimation circuit that avoids the complexity associated with log tables and other prior art methods of computing logarithms. Then the sum of the log2 of the average power received in each of the selected subset of tone bins is determined.

Abstract: A periodic waveform-based wireline measurement circuit derives a voltage that is very precisely proportional to the differential voltage across a wireline pair, and uses this voltage to modulate the width of a periodic waveform, such as one derived from a ringing signal. This periodic waveform can be interfaced in an asynchronous manner with digital processing components, such as a DSP codec, to provide for automatic compensation for the resistance of the phone line.

Abstract: An alarm filter circuit used in telecommunication systems for interconnecting between incoming telephone lines and alarm unit located at a subscriber's premises so as to block DSL data signals to and from the alarm unit for preventing interference is provided. In one preferred embodiment, the alarm filter circuit includes a second-order low-pass filter section for blocking the DSL data signals to and from the alarm unit, a first-order high-pass filter section for bypassing the DSL data signals on the incoming telephone lines to the house wiring, and a first-order low-pass filter section for blocking high-frequency signals between the house wiring and the alarm unit. In a second embodiment, a fourth-order elliptical low-pass filter section replaces the second-order low-pass filter section. In a third embodiment, a third-order high-pass filter section replaces also the first-order high-pass filter section.

Abstract: A characteristic of a local loop is used to estimate the loop's data carrying capacity. The characteristic is measured and applied to a table previously stored in memory which contains values relating the characteristic to downstream data rates. Using interpolation when required, an estimate of the data carrying capacity of the local loop is estimated based on the measured characteristic. The measured characteristic may be, for example, the input impedance or the DC resistance of the local loop.

Abstract: A method and system for determining the high speed data service capability of a subscriber line includes sending an embedded test signal to a subscriber line. A reflected signal received in response to the test signal is analyzed for determining transmission characteristics of the subscriber line. Based on the reflected signal, a determination about the high speed data service capabilities of the subscriber line is made and stored for future reference.

Abstract: Method for measuring a load impedance (ZL) of a load circuit which is connected to an SLIC circuit (6) of an analog terminal connection of a terminal device, having the following steps: specifically a digital toll signal (x1) is generated by means of a Codec circuit (13) connected to the SLIC circuit (6), said toll signal (x1) being converted into an analog toll signal; the analog toll signal is output by the SLIC circuit (6) to the load circuit; an analog voltage which is brought about at the terminal connection (4,5) of the terminal device of the SLIC circuit (6) via the analog toll signal is sensed; the digital toll signal (x1) is filtered by means of an adaptive filter (39) which is provided in the Codec circuit (13) and has adjustable filter coefficients (g1, g2) for generating a filtered digital comparison signal (yv) which is converted into an analog comparison voltage (Uv); the filter coefficients (g1, g2) of the adaptive filter (39) are adjusted until the analog comparison voltage (Uv) and the analog

Abstract: In a subscriber loop interface circuit, a novel method and apparatus for measuring loop impedance. Measurement of loop impedance including charging and discharging a capacitor using current derived from loop current and loop voltage. The discharge time interval of the capacitor may provide information on loop impedance. A look-up table in a subscriber loop interface circuit may include previously calculated impedance values corresponding to discharge time.

Abstract: A telephonic apparatus comprises terminals for connecting it to respective electric cables, telephonic circuitry, and a switch between the terminals and the circuitry. It also includes a sensor for detecting a DC voltage above a first level between said terminals. It the sensor detects a DC voltage between said terminals above the first level, it prevents the switch from connecting the circuitry between the terminals.

Abstract: An alarm filter circuit used in telecommunication systems for interconnecting between incoming telephone lines and alarm unit located at a subscriber=s premises so as to block DSL data signals to and from the alarm unit for preventing interference is provided. In one preferred embodiment, the alarm filter circuit includes a first inductor, a second inductor and a third capacitor functioning as a second-order low-pass filter section so as to block the DSL data signals to and from the alarm unit. Second and third capacitors functioning as a first-order high-pass filter section is provided so as to bypass the DSL data signals on the incoming telephone lines to the house wiring. A third inductor and a fourth inductor functioning as a first-order low-pass filter is provided so as to block high-frequency signals between the house wiring and the alarm unit. In a second embodiment, a fourth-order elliptical low-pass filter section replaces the second-order low-pass filter section.

Abstract: A computer-executable method for diagnosing trouble causes in telephone cable segments when trouble data are available only for entire cables is presented. This method diagnoses problems in the components of processes when the component location of process problems is not known. It gives a statistical relationship between component attributes and process problem rates, to facilitate assessment and improvement of policies about the process. This method may be used for diagnosing systematic problems in segments of telephone cable connections of given central offices.

Abstract: Telephone line service type identification is provided to a telephone technician in the field by the placement of one or more tuned circuit(s) across the telephone line. In one embodiment, an inexpensive tuned circuit such as a ceramic resonator forms a telecom service resonator ID device which is placed across a telephone line, either at the central office or at the customer premises. Injection of a test current at a predetermined frequency, and a suitable amplitude of the same indicates to the technician aspects of telecom service to that particular telephone line (e.g., the existence of POTS, ISDN, and/or xDSL) and or use of the telephone line by a home network such as HPNA. In another embodiment, a telecom service transponder ID device is formed to provide line service identification to an interrogating line technician. The telecom service transponder ID device is activated when the test signal including an appropriate frequency is present to cause excitation in the telecom service transponder ID device.

Abstract: A method detects a fault in a subscriber line having two wires with separate input impedances. The method includes driving the subscriber line from one end with an alternating voltage, making one-ended electrical measurements on the driven liner and determining from the measurements a quantity proportional to the phase difference of the two input impedances. The method also includes identifying a fault in response to the phase difference having a signature associated with presence of a fault in the line.

Abstract: A method and automatic test system for determining qualification of a twisted pair transmission line to propagate data signals. The method includes measuring phase imbalance in the twisted pair transmission line. The phase imbalance is determined by resistance imbalance in the twisted pair transmission line. The resistance imbalance is determined by applying a common mode voltage to the twisted pair transmission line; and, determining phase imbalance in the twisted pair in response to the applied common mode voltage. The method includes applying a common mode voltage to the twisted pair transmission line; determining phase imbalance if the twisted pair in response to the applied common mode voltage; detecting a peak in the determined phase imbalance; determining a frequency of the detected peak; determining line qualification in accordance with the determined frequency.

Abstract: Through the use of a least squares minimization concept, the loop length, the number of bridged taps and length of the bridged taps on a transmission line can be determined from readily available modem data. In particular, the loop length, the number of bridge taps and the length of bridged taps can be estimated by comparing a measured frequency domain channel impulse response of the transmission line to a model of a loop that is comprised of multiple sections and multiple bridge taps.

Abstract: The present invention is generally directed to a telephone handset for testing the transmission quality of a local loop. In accordance with one aspect of the invention, the telephone handset includes a connector configured to connect to the local loop at, for example, a junction box. The invention also includes a low-pass filter circuit electrically interposed between the connector and operational circuitry of the telephone handset. In operation, the low-pass filter is designed to pass (substantially undisturbed) electrical signals within the POTS frequency band from the connector to the operational circuitry. In the same way, the low-pass filter is designed to substantially block the passage of electrical signals above the POTS frequency range. In this way, the low-pass filter blocks the introduction of high frequency signals, which may otherwise generate intermodulation products within the audible range, from reaching the operational circuitry of the testing handset.

Abstract: The present invention is generally directed to a telephone handset for testing the transmission quality of a local loop. In accordance with one aspect of the invention, the telephone handset includes a connector configured to connect to the local loop at, for example, a junction box. The invention also includes a low-pass filter circuit electrically interposed between the connector and operational circuitry of the telephone handset. In operation, the low-pass filter is designed to pass (substantially undisturbed) electrical signals within the POTS frequency band from the connector to the operational circuitry. In the same way, the low-pass filter is designed to substantially block the passage of electrical signals above the POTS frequency range. In this way, the low-pass filter blocks the introduction of high frequency signals, which may otherwise generate intermodulation products within the audible range, from reaching the operational circuitry of the testing handset.

Abstract: The invention presented herein is directed to a battery injection and loop supervision (BILS) system and method that can be used in the DSL environment. The BILS of the present invention provides battery injection, loop supervision, and butt set operation mode detection in the DSL environment. A voltage source, detector and comparator in the BILS unit can be used to supervise the copper loop status from the central office. In addition, using the present invention, a field technician using a conventional butt set can detect battery voltage and receive an audible tone from the cooper loops in the DSL environment. Furthermore, the BILS can be implemented in accordance with two preferred embodiments, voltage sensing and current sensing. The BILS includes circuitry, working in conjunction with a shared common resource card and a conventional butt set, for testing, maintaining, and installing copper loops in the DSL environment.

Abstract: A telephone test system (2) includes a controller (4), a programmable gate array (PGA) (24) and a digital signal processor (DSP) (26) connected by a common bus (20). The PGA (24) includes an output connected to an input of a digital-to-analog converter (DAC) (36) and input connected to an output of an analog-to-digital converter (ADC) (32). A driver circuit (46) is connected between the DAC (36) and a telephone circuit (60) and between the ADC (32) and the telephone circuit (60). Under the control of the DSP (26), the driver circuit (46) generates voltages to the telephone circuit (60) and samples the response of the telephone circuit (60) to such generated voltages. The driver circuit (46) includes control inputs for receiving from the PGA (24) an impedance adjust signal (D) and a resistance adjust signal (R). An output impedance (124) of the driver circuit (46) connected to the telephone circuit (60) is adjustable as a function of the impedance adjust signal (D) and/or the resistance adjust signal (R).

Abstract: A method and apparatus for single-ended qualification of subscriber loops for xDSL services is described. The method involves first screening a subscriber loop database record for disqualifying devices or services on the subscriber loop. If none are found, a set of predetermined electrical characteristics of the subscriber loop are derived from information in the database, or directly measured using test equipment at a central office end of the subscriber loop. The electrical characteristics are used to compute an available bandwidth on the subscriber loop for xDSL services. The advantage is the rapid and inexpensive qualification of subscriber loops which reduces response time to potential customer queries and facilitates deployment of xDSL services.

Abstract: An apparatus and method for characterizing a loading pattern of a twisted pair telecommunications transmission line includes a variable frequency signal generator and a measurement receiver connected to the twisted pair line. The signal generator applies a variable frequency signal to the twisted pair line and the measurement receiver acquires magnitude values representative of the impedance of the twisted pair line. A controller, operating under program control, models a plurality of baseline transmission line and twisted pair lines to generate magnitude values representative of the models. Error values are generated between the acquired magnitude values and the modeled magnitude values. The error values are compared to each other to determine the model with the minimum error value which is used as the model for charactering the twisted pair transmission line.

Abstract: The performance of digital subscriber loops is tested through transmission, reception and analysis of a multi-tone power ratio (MTPR) waveform, containing plural discrete tones having equal spectral spacings and notches periodically distributed among the tones. The noise floor at a missing sub-carrier spectral location is integrated and compared to signal power of an adjacent sub-carrier within the test vector waveform. From these two values, MTPR is determined for various carrier locations, so that maximum theoretical loop payload can be calculated. To generated a figure of merit (FOM) under test, a data modem is placed at each end of the loop. The FOM obtained from MTPR analysis is channel based, not equipment based, and is independent of receiver implementation. Before placing a new customer in service, the MTPR FOMs for a number of loops are compared to bit rate information in a database, which correlates MTPR with a bit rate for a specific modem.

Abstract: A loop loss measurement and reporting mechanism for a digital data services unit obviates interaction with a test unit at a far end of the loop, by relying upon a priori knowledge of the signal power and spectral content of a data port at the far end of the loop to conduct threshold detection and power level measurements. A received signal is amplified by amplifier circuitry, the gain of which is controllably adjusted by the microcontroller based upon the outputs of threshold detectors and power level measurement circuitry that monitor the amplified received signal. A front panel display is controlled by the microcontroller to display loop loss parameter information. To measure and report loop loss, the digital data services unit turns off its transmitter for a prescribed period of time and monitors an in-band signal of known power and spectral content sourced from the far end of the loop.

Abstract: A Digital Subscriber Line (DSL) modem determines the proper transnit power level in a splitterless environment by transmitting a probe signal at different power levels to a telephone set and measuring the distortion signal reflected from the telephone set for each power level. The proper transmit power level is determined by detecting the “comer point” of the reflected distortion signal.

Abstract: A method and apparatus is provided for regulating transmission power of a signal on a line. The method includes determining characteristics of the line, determining the transmission power needed to transmit the signal in response to the characteristics of the line, and transmitting the signal on the line in response to determining the transmission power.

Abstract: An impedance blocking filter circuit is provided for use in telecommunication systems for interconnecting between incoming telephone lines and customer's terminal equipment so as to unconditionally block impedances above 20 KHz due to the customer's terminal equipment from an ADSL network unit and/or home networking interface unit. The filter circuit includes first, second, and third inductors connected in series between a first input terminal and a first common point. A first resistor has its one end connected also to the first common point and its other end connected to a first output terminal. Fourth, fifth and sixth inductors are connected in series between a second input terminal and a second common point. A second resistor has its one end also connected to the second common point and its other end connected to a second output terminal. A capacitor has its ends connected across the first and second common points.

Abstract: The present invention is generally directed to an xDSL modem that is capable of transmitting at multiple data rates. Specifically, the xDSL modem is configured to generally transmit at a high data rate (typically the highest data rate supported by the line), but will reduce its data transmission rate in response to one or more sensed conditions. In this regard, it has been found that transmitting at a data rate that is low enough to avoid significant corruption, and thus retransmission, achieves a higher overall data transmission rate than that which is achieved if re-transmissions are required. Further, various conditions may be sensed that will prompt the xDSL modem to alter its transmission rate, including detecting an unfiltered POTS device going Off-Hook. In accordance with one aspect of the present invention, at modem startup, the Off-Hook condition and other line problems are detected by direct measurement of the line impedance.

Abstract: An impedance blocking filter circuit is provided for use in telecommunication systems for interconnecting between incoming telephone lines and customer's terminal equipment so as to unconditionally block impedances above 20 KHz due to the customer's terminal equipment from an ADSL network unit and/or home networking interface unit. The filter circuit includes first, second, and third inductors connected in series between a first input terminal and a first common point. A first resistor has its one end connected also to the first common point and its other end connected to a first output terminal. Fourth, fifth and sixth inductors are connected in series between a second input terminal and a second common point. A second resistor has its one end also connected to the second common point and its other end connected to a second output terminal. A capacitor has its ends connected across the first and second common points.

Abstract: In a 2-wire connection from a telephone exchange to a subscriber, the connection is made via a subscriber line interface circuit (SLIC) and a termination box, the termination box having a capacitor and a resistor connected in series between the two wires of the connection and between the SLIC and the subscriber. The SLIC includes means to reverse the polarity between the two wires of the connection and there is measuring means whereby the current required to change the capacitor to the opposite polarity may be measured enabling determination of the impedance between the two wires of the connection.

Abstract: A line pair testing and fault diagnostic apparatus implementing three-terminal measurement techniques using a multiple frequency source waveform transmission to propagate a reflected waveform. The apparatus implements a microcomputer circuit executing a program. The program has frequency domain analysis algorithms to process the reflected waveform to provide a craftsperson with the electrical characteristic data of a line pair to inform the craftsperson the existence of a line pair fault and the location of the fault in the line pair. The apparatus implements relays for switching between several diagnostics circuits within the apparatus for providing the craftsperson with numerous methods and techniques for troubleshooting a line pair.

Abstract: A system and method for testing a telephone connection using an interactive telephone response module (ITRM). In one embodiment, the ITRM is connected between the handset and station set of a telephone terminating one end of the connection to be tested. In another embodiment, the ITRM is connected between the telephone connection and the station set of a telephone terminating one end of the connection to be tested. By operating switches on the ITRM, a user can impose predetermined conditions on the connection. A test coordinator located at a test point or other termination in the telephone network then tests the connection under the predetermined conditions.

Abstract: A telephone wire pair is qualified for digital signal transmission by central office testing. The tip-to-ring capacitance of the wire pair is measured while applying an test signal in the 20-30 Hz range to the wire pair. The tip-to-ring capacitance is used to compute a first length, and the first length is compared to a pre-determined length. If the first length exceeds the pre-determined length, then the wire pair is qualified based upon another comparison of the measured capacitance to a pre-determined capacitance. On the other hand, the first length is less than the pre-determined length, the tip-to-ring capacitance is measured at a frequency of, preferably, 600 Hz. The test signal at this frequency minimizes errors due to resistive and inductive components of the primary constants of the wire pair and/or a ringing device connected to the wire pair.

Abstract: A test terminal includes a circuit for opening a loop switch to prevent setting up of calls from the terminal via a telephone line when a signal received from the telephone line via a first high-impedance connection exceeds a predetermined threshold indicating that the telephone line is busy. An alarm circuit indicates that any call from the terminal is prohibited. Operation of the terminal in discreet monitoring mode is also prohibited if the line is busy.

Abstract: A system and method for providing software-implemented, programmable testing of telephone subscriber line power conditions. The system detects subscriber line faults including resistive faults and foreign voltages on a telephone subscriber line. A user interface is provided to enter user-programmable threshold values corresponding to subscriber line fault conditions. A fault threshold memory is coupled to the user interface to store the generated threshold values. A processing unit is configured and arranged to compare signal attributes on the telephone subscriber line to the generated threshold values stored in the fault threshold memory, and is further configured and arranged to identify an occurrence of a fault corresponding to a predetermined condition introduced onto the telephone subscriber line in response thereto.

Abstract: The performance of digital subscriber loops is tested through transmission, reception and analysis of a multi-tone power ratio (MTPR) waveform, containing plural discrete tones having equal spectral spacings and notches periodically distributed among the tones. The noise floor at a missing sub-carrier spectral location is integrated and compared to signal power of an adjacent sub-carrier within the test vector waveform. From these two values, MTPR is determined for various carrier locations, so that maximum theoretical loop payload can be calculated. To generated a figure of merit (FOM) under test, a data modem is placed at each end of the loop. The FOM obtained from MTPR analysis is channel based, not equipment based, and is independent of receiver implementation. Before placing a new customer in service, the MTPR FOMs for a number of loops are compared to bit rate information in a database, which correlates MTPR with a bit rate for a specific modem.

Abstract: The invention provides radio communications with an up-down signal link. In accordance with the purpose of the invention, as embodied and broadly described herein, the invention is directed to a method, system and computer readable medium with program instructions (hereafter collectively referred to as "the invention"). The invention includes receiving a downstream signal in a receiver portion of an outdoor unit, producing in the receiver portion of the outdoor unit an intermediate frequency (IF) signal from the downstream signal, and processing the IF signal in the receiver portion of the outdoor unit to produce a clean line code signal.

Abstract: A telephone wire pair is qualified for digital signal transmission by central office testing. The tip-to-ring capacitance of the wire pair is measured while applying to the wire pair an AC test signal at 600 Hz. The test signal at this frequency minimizes errors due to line inductance and/or a ringing device connected to the wire pair. Reliable measurement of the length of the wire pair is achieved. Flaws in cable sheathing can also be detected based on measurement of tip-to-ground capacitance and/or ring-to-ground capacitance.

Abstract: A system and method for performing diagnostic leakage impedance testing at the subscriber line interface utilizing portions of existing circuitry designated for driving current on the telephone line during normal operation is provided. The diagnostic apparatus is used with a telephone line drive system having a tip-line current-mode amplifier for driving current on the tip line and a ring-line current-mode amplifier for driving current on the ring line during normal operation. A control signal generator generates voltage control signals corresponding to desired subscriber loop voltage characteristics. A voltage sense circuit compares the voltage control signals to actual subscriber loop voltage characteristics resulting from driving the current on the subscriber loop. The current driven onto the subscriber loop is adjusted accordingly.

Abstract: In a telephone system wherein a number of distant terminals are each connected to a remote terminal and in which a number of remote terminals are each connected to a central office, a distant terminal includes a drop testing circuit for making sequential measurements on a plurality of customer telephones. The drop test circuit is included in a measurement system for providing condition responsive signals describing parameters of the telephone system, The drop test circuit includes circuitry such as scaling resistors, voltage sources, switching elements, and a multiplexed analog to digital voltage-sensing converter for providing digital data for transmission to the remote terminal or other more central location. The remote terminal comprises a computer based analyzer for interpreting, processing, and storing the data transmitted to it.

Abstract: A line interface circuit (120) receives an audio signal from a signal generator (132). A reflected signal is produced at the output port (216) of a SLIC (210). The reflected signal is combined with the received audio signal to produce a combined audio signal. The combined audio signal is measured to determine if a fault exists in the subscriber loop (130).

Abstract: A subscriber station provides the wireless connection of user telecommunications equipment to a remote central station of a wireless telecommunications system. The subscriber station includes a transmitter/receiver for wireless communication with a central station and for processing signals for transmission and/or received signals, at least one telephone line for connection to subscriber telecommunications equipment, and a high impedance test circuit connected across a telephone line under test. The use of a high impedance test circuit means that the test circuit can effectively be connected permanently across a telephone line under test.

Abstract: Method and apparatus for detecting whether load coils are attached to a telephone line. A stimulus waveform having multiple frequency components is applied to the line. The current and voltage at the near end of the line are coherently sampled and transformed to the frequency domain. The frequency spectra are used to compute auto and cross power spectra of the current and voltage. These power spectra are then used to compute the impedance on the line as well as a coherence function that indicates the extent to which the computed impedance was influenced by noise. If the coherence values indicate that the computed impedance is sufficiently reliable, load coils are detected by finding peaks in the magnitude of the impedance function or sign changes in the phase of the impedance function. Calibration, offset adjustments and ensemble smoothing are used to increase the accuracy of the results. The computation is fast because computing the spectra avoids the need for individual measurements at multiple frequencies.

Abstract: A line test system for diagnosing and segmenting faults in a switched telephone network. The system includes a remote measurement unit installed at a switch and a test system controller. The test system controller stores data about operating parameters of each of the subscriber lines when they are believed to be free of faults. When a fault is reported, the parameters are measured again. By comparison of the measured parameters with the stored parameters, the fault can be segmented between the premise and the network. Segmentation is performed using knowledge based analysis techniques. The actual source of the fault once it is repaired is also stored by the test system controller. This historical information is used to improve the accuracy of the knowledge based analysis techniques used for segmentation. The line test system is capable of detecting the presence of high impedance ringers.