Abstract: A method is provided for introducing analog loss to an information-bearing signal being transmitted to or from end-user terminal equipment over a communication system such as a cable network The method begins by establishing a communication path to the terminal equipment over the communication system and then introducing a level of loss into the communication path to reduce echo. The level of loss that is introduced is based on the information content of the information-bearing signal.

Abstract: A housing having a shell, a first compartment, and a second compartment within the first compartment is provided. A first cover is pivotally attached to the shell for selectively opening and closing the first compartment. The first cover has a resilient latch biased for grasping the shell and a lead-out for wires. A second cover is pivotally attached to the shell for selectively opening and closing the second compartment. A plurality of pivot connectors is located in the first compartment. Each of the plurality of pivot connectors is oriented to receive a wire in a direction parallel to a plane of the lead-out for wires. A plurality of jacks is also located in the first compartment. Each of the plurality of jacks has at least one resilient conductor. Each of the plurality of jacks is oriented so that the resilient conductor lies in a plane perpendicular to the plane of the lead-out for wires.

Abstract: A line powered codec which adaptively allows operation with power supplied from a telephone line in many countries as conditions warrant. A startup procedure uses country-specific register settings, which are powered and maintained from a low voltage side other than the telephone line. Thus, during low line power conditions a programmed state of the line powered codec can be maintained even after a power loss in the telephone line. In another aspect, a current and voltage detection module in the line powered codec is always powered from the telephone line. If sufficient power is not present, the line powered codec does not power up. In yet another aspect, a plurality of power rails may be provided.

Abstract: Apparatuses and methods for selectively coupling the signals of multiple communications service providers operating in different frequency bands onto one or more station wire segments of a customer premises wiring plant are disclosed herein. The apparatus can include various filtering networks and switching modules to enable each station wire segment of the premises wiring to be concurrently and independently connected to differing service providers.

Abstract: To secure an ADSL connection between a first ADSL transceiver (4) in a central office and a second ADSL transceiver (5) on a subscriber's premises on a telephone line (1) between a SLIC (2) in the central office and a telephone (3), a request to the SLIC (2) to apply a ringing signal to the telephone line (1) is detected. In response to such detection, the first ADSL transceiver (4) switches from a normal bit rate to a lower bit rate for the ADSL connection, and orders the second ADSL transceiver (5) to do the same before the ringing signal is applied. In response to an off-hook condition, the lower bit rate is maintained for the ADSL connection. In response to an on-hook condition after the off-hook condition as well as in response to a disappearance of the ringing request without an off-hook condition, the first ADSL transceiver (4) switches back to the normal bit rate and orders the second ADSL transceiver (5) to do the same.

Abstract: A method for controlling a line-powered network element in an access network is provided. The method includes provisioning at least one instance of a line power controller at the line-powered network element, provisioning at least one conductive medium associated with the at least one instance of the line power controller, receiving at least one primitive for use by the line power controller for managing the line-powered network element, monitoring at least one of the at least one primitive, and selectively taking action through the at least one line power controller based on the monitored ones of the at least one primitive in response to power conditions for the line-powered network element.

Abstract: The present disclosure relates to a DSX device including a jack body with three ports including a monitor port, a switching mechanism within the jack body for making and breaking an electrical connection between the other two ports when a plug is withdrawn or inserted and a monitor network including a dielectric substrate electrically connecting the monitor port and one of the other ports. The present disclosure also relates to DSX modules incorporating DSX devices.

Abstract: A directional coupler for a modem has a high common mode noise rejection characteristic with low transmit signal leakage, and reduced distortion of components mixed with a received signal. A primary filter network is connected to a communications circuit. The primary filter network has an output connected to an input of an amplifier. A feedback network is connected between the input and output of the amplifier. The primary filter network, the amplifier and the feedback network are arranged to provide a virtual ground at the input of the amplifier, and a filter characteristic which attenuates frequencies in the transmit signal band. The advantage is reduced component count while providing excellent transmit signal rejection and reducing received signal distortion.

Abstract: The invention relates to a monolithically integrated telephone circuit for driving wide-band telephone lines and transmitting digital data at a very high frequency. The telephone circuit is powered from a battery DC supply providing a pair of voltage references. The telephone circuit includes an output circuit portion including a pair of differential output stages, each having a pair of inputs and being connected with its output to a respective lead of a two-wire telephone line. The telephone circuit also includes a device for deriving a reference voltage from the supply voltage, and includes a low-voltage supply network which is input a DC signal and produces a voltage reference to be added to the reference voltage for delivery to one input of each output stage. The other input of each stage receives an AC signal in order to present at the circuit output a suitable AC+DC differential voltage for driving the telephone line.

Abstract: The present invention uses a wiring scheme for data transmission. The wiring scheme includes designating N−1 telecommunication wires and a common wire to each carry N−1 signals. The wiring scheme further includes designating one telecommunication wire, other than the N−1 telecommunication wires, as a common wire for each of the N−1 wires. In addition, the DC voltage polarities of at least one of the N−1 telecommunication wires may be reversed to reduce the likelihood of overloading the common wire. The wiring scheme may be utilized in the context of many data transmission systems including: POTS, PSTN, DSL, data modems, facsimile modems, and ISDN. The wiring scheme of the present invention may achieve higher data rates for data transmission.

Abstract: In an apparatus for supplying a tip and ring telephone line with voice band and broadband signals, a first pair of drivers supply at least DC signals to the respective tip and ring line components, and a second pair of drivers supply broadband signals to the tip and ring line components. Feed components combine the outputs of said respective drivers for the respective tip and ring components of the telephone line.

Abstract: The present invention provides a digital pre-distortion filter in arrangement with a data access arrangement (DAA) on the component side (e.g., in a modem chipset). This arrangement of the pre-distortion filter outside of the DAA allows digital processes such as digital emulation of the central office impedance to remain unaffected by the pre-distortion in the transmitted signal, allowing the dynamic range of the transmitted signal to be flattened to minimize return loss without complicating the transfer function of the digital emulation of the central office complex load. In the case of a digital emulation filter, placement of a digital pre-distortion filter outside of an analog-to-digital (A/D) digital-to-analog (D/A) loop also minimizes the noise otherwise associated with the use of a pre-distortion filter. Thus, benefits of a pre-distortion filter can be gained without interfering with emulation of impedance, and without causing a significant amount of noise in the transmitted signal.

Abstract: A telephone set of a telephone system is provided with an infrared interface. This infrared interface is able to communicate with an infrared port on a local computer. The computer is configured to send data to the infrared port, and receive data from the infrared port, in the same manner as if the computer was sending and receiving data over a telephone system. The telephone circuitry in the telephone system receives the infrared data and converts the infrared data into a format for transmitting across the telephone system.

Abstract: A line driver apparatus includes a peak detector operable to receive a data signal and output a first logic signal when the data signal is below a threshold value and output one of a plurality of alternate logic signals when the data signal exceeds the threshold value. The peak detector includes a signal magnitude calculator operable to calculate an amount by which the data signal exceeds the threshold value. The line driver apparatus also includes an amplifier operable to receive a filtered analog data signal and one of a time-delayed first logic signal and one of a time-delayed alternate logic signal, wherein the amplifier operates at a first voltage level upon receiving the time-delayed first logic signal, and the amplifier operates at a voltage level that is increasing toward one of an alternate voltage level upon receiving the time-delayed second logic signal.

Abstract: A protective cable cover separates cable routing from patchcords and cross-connect wire in a wiring trough, and includes a printed wiring board that provides a means for mounting electronic circuitry and components. The cable cover is placed over the cable conductors on a wiring block cable organizer. A circuit designation strip and row marking pads are provided to designate rows and circuit connections. A strike engages a latch on a patchcord plug to releasably retain the plug in engagement with the wiring block. Mounting holes are formed integral with the cable cover to engage latches on the cable organizer for releasably mounting the cable cover on the cable organizer.

Abstract: A method and apparatus is provided for adjusting DC feed control of a connection. The method includes receiving a signal from the connection and determining if the change in the signal is greater than a first preselected value. The method further includes adjusting the DC feed in response to determining that the change in the signal is greater than the first preselected value.

Abstract: A fixed wireless terminal such as a wireless local loop terminal comprising: memory (210) storing characteristics for at least one network, means (214, 220) for accepting network information particular to a subscriber and processing means (208) for reading the subscriber network information and, on the basis of the subscriber network information, selecting appropriate network characteristics for subsequent use by the terminal. Preferably the processing means (208) is arranged to configure a subscriber line interface circuit (212) in accordance with the selected appropriate network characteristics, such as ringing tone, dialling tone, busy tone etc.

Abstract: A comparator-based switchmode power converter monitors the most negative of the tip and ring line voltages, to control the supply voltage to a SLIC. The voltage applied to the SLIC's power terminals is slightly higher than the sensed voltage for different loop signaling conditions, including loop start, ground start balanced ringing. The switchmode converter includes a comparator coupled to a DC-DC output node downstream of a MOSFET switch installed in a DC supply rail of a source of DC supply voltage, and coupled to a power supply terminal of the SLIC. The comparator is also coupled to a set point node, which is coupled through a voltage offset path to each of tip and ring portions of the telephone line.

Abstract: A communication system being made up of a two-wire/four-wire hybrid circuit, an echo canceller, and a control device and having functions of forming a plurality of communication paths and changing communication paths is provided which is capable of ensuring high speech quality by suppressing and canceling an echo occurring in telephone speech after establishment of path connection. The communication system also includes a training signal source to feed a training signal to the echo canceller, a switching circuit to do switching of a signal to be fed to the echo canceller between an ordinary signal and the training signal, and a control device to exert control on path connection and path changing and to feed the training signal to the switching circuit to make a training signal be fed from the training signal source to the echo canceller and to have the echo canceller converge its training operation.

Abstract: A subscriber loop interface circuit and method for externally programming the on-hook, off-hook, and transition states of the subscriber loop interface circuit. The circuit having an off-hook overhead sufficient for long loop applications and having a continuous loop current to loop voltage relationship. The circuit may have plural means for generating reference currents for comparison with loop currents.

Abstract: A line driver for connection to a transmission line having a characteristic impedance. The line driver can be arranged in a voltage-mode or a current-mode configuration. In the voltage-mode configuration, the line driver comprises an amplifier, a transformer, a reference resistor and a feedback circuit. The first winding of the transformer has a first end connected to the output of the amplifier and the second winding is connectable to the transmission line. The reference resistor has an end connected to the second end of the first winding at a junction point and the feedback circuit is connected to the input and output of the amplifier and also to the junction point. The reference resistor has a resistance equal to {fraction (1/k)} times the characteristic impedance of the transmission line. The feedback circuit is arranged to produce a voltage at the output of the amplifier substantially equal to −(K−1) times the voltage at the junction point, for a predetermined value of K.

Abstract: A relay-less telephone line interface circuit is disclosed which incorporates a low-voltage transistor to suppress high-voltage, short-term voltage surges. Specifically, a low-voltage transistor such as a Central Semiconductor C2TA44, a Motorola MPSA42, or similar such transistors actually can withstand a high-voltage spike exceeding the manufacturers specified parameters. The present circuit exploits this undocumented feature by employing such a transistor in combination with a metal oxide varistor in order to provide adequate voltage surge protection for the interface circuit. Thus, a zenor diode is not necessary (avoiding on-hook problems) and the relay-less circuit still passes the FCC Part 68 test.

Abstract: A telephone loop monitoring and isolation device which can be connected to a wireless telephone subscriber unit providing an interface between an analog or digital central station network and the internal telephone wiring of a subscribers premises. The device is also operable with a cable telephone subscriber unit. The device provides passive real time loop status information as well as loop isolation if the voltage across the loop falls below a predetermined level. When normal loop impedance conditions are restored, the subscriber loop is automatically reconnected to the subscriber telephone unit. The device is effective for examining open circuit and abnormal impedance conditions and provides loop status information to the telephone subscriber.

Abstract: A circuit configuration is provided for supplying a telephone subscriber loop with a supply voltage, for transmitting a transmitted signal into the telephone subscriber loop, and for receiving a received signal from the telephone subscriber loop. The telephone subscriber loop has a first line and a second line. The circuit configuration has a supply voltage source with a first terminal and a second terminal between which a supply voltage drops; a first circuit connected with the first line and having first and second supply voltage connections; and a second circuit connected with the second line and having third and fourth supply voltage connections. The first supply voltage connection is connected with the first terminal and the fourth supply voltage connection is connected with the second terminal. A network-side terminal of a telephone subscriber loop and a chip set are also provided.

Abstract: A line card for interfacing with a plurality of subscriber lines includes a plurality of data processors and a tone detector. Each of the data processors is associated with one of the subscriber lines. The tone detector is adapted to detect one of a plurality of activation tones on a selected subscriber line. The plurality of activation tones include a first activation tone having an active portion and a silent portion. The active and silent portions repeat periodically at a first frequency having a first period. A second activation tone has a phase reversal portion repeating at a second frequency and having a second period. The tone detector is further adapted to sequence between the subscriber lines at a predetermined interval. The predetermined interval is based on the first and second periods. The tone detector is adapted to signal the data processor associated with the selected subscriber line in response to detecting one of the activation tones.

Abstract: A circuit and supplemental power source connection scheme for a telecommunications modem transmission link are described. The supplemental power source is connectable at any point along a telecommunications wire, including the terminals of repeaters and remote terminals. The combiner circuit includes a diode bridge for ensuring the proper connection of externally connected high voltage power to internal circuitry of the power combiner. The combiner also includes a line polarity matching circuit that automatically configures to signally connect internal positive and negative voltage signals to corresponding positive and negative external signal lines on a telecommunications modem transmission link.

Abstract: A WLL system having personal stations, either mobile stations or telephone sets with an NIU, a base station and a switching center. For faster connectivity, a method in accordance with the present invention includes the steps of (1) if the personal station is in an off hook state, the personal station transmits an origination message to the base station and assigns a traffic channel between the personal station and the base station, (2) the personal station transmits a destination telephone number to the base station, and (3) the switching center connected to the base station connecting a call to a destination personal station according to the destination telephone number, thereby reducing a delay time in setting up a call, and thereby providing a fast communication service.

Abstract: A line terminal circuit comprises a buffer section (A, D) for connection to a transmission line (TL) and for performing at least one of the functions receiving signals from said transmission line and transmitting signals via said transmission line; a controllable current source section (S1, S2) connected to inject or withdraw a current (Iu, Id) into or from a node (ND1, ND2) between said buffer section and said transmission line in accordance with a current control signal (CS); and a common mode voltage control section (CT) for detecting a common mode voltage component on the transmission line (TL) connected to the buffer section (A, D) and for generating said current control signal (CS) in response to said detected common mode voltage component and outputting said current control signal to said current source section (S1, S2); said common mode voltage control section (CT) being adapted to output said current control signal (CS) such that said common mode voltage component is within the limits of a predetermi

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 telecommunications pair gain system for use when all lines served by the pair gain system are within a limited distance of the pair gain system remote terminal. The distance is such that a lower voltage output from the remote terminal can be used for powering the POTS telephones. Advantageously, a single remote terminal can be used for controlling, for example, 8 POTS lines, at significantly lower expense than would be incurred using standard subscriber loop carrier technology. Advantageously, the loops no longer required for serving all of the 8 POTS lines directly, can be utilized to provide services such as Digital Subscriber Line (DSL) service to other customers without requiring the installation of additional loops between the central office and the remote terminal.

Abstract: A universal line driver interface which enables a digital telephone computer/telephony interface to configure itself automatically or on the fly to accommodate different PBXs. The interface is connected to a PBX and to a digital telephone. The interface also is connected to network interface logic. A microcontroller, which is part of the computer in the computer telephony system, is connected in controlling relation to the interface and to the interface logic. The microcontroller under program control changes operational parameters in the interface as a function of electrical characteristics of the particular type of PBX to which the interface is connected. The changes in operation parameters of the interface, in turn, are used to configure the interface logic depending upon the type of PBX. The universal nature of the interface is achieved by adaptability to different transmission and receiver voltage, levels and an ability to match a range of telephone line impedances.

Abstract: An integrated plain old telephone service (POTS) and metallic loop testing (MLT) card provides lifeline telephone service with multiple channel data service. The integrated card can be piggybacked with an ADSL card to provide a single package of POTS, MLT, and ADSL services.

Abstract: A system for determining the transmit power of a communication device operating on a twisted pair subscriber line includes a communication server coupled to a first subscriber line and a second subscriber line. The communication server comprises a communication device that communicates a signal using the first subscriber line. A memory coupled to the communication server stores noise information and cross-channel-coupling information for the first subscriber line and the second subscriber line. A processor coupled to the memory determines the transmit power of the communication device based upon the noise information and the cross-channel-coupling information.

Abstract: As part of a system and method for transmitting a signaling tone over a packet switched data (or other communication) network, an audio encoder may have a speech encoding unit and a tone distorter. The tone distorter may distort one or more components of a signaling tone within an audio signal and the speech encoding unit may encode speech and the distorted signaling tone within the audio signal. A control signal may be sent to a tone generator to reproduce the distorted tone.

Abstract: A telephony device such as a digital telephone or personal computer attaches to phone lines and automatically determines both the type of switch to which is connected, and the type of line card in the switch providing that connection. In addition, device functions and data types supported by the switch and line card are automatically determined, providing a fully automatically configurable device. Programming in the device monitors polling messages provided by the switch and line card having different formats to make the determination. The devices switch between two different flow control types supported by the different line cards, while listening for the polling messages. If a message is not received while using a first flow control type, the second is used. The capability of channel, voice or data, is also automatically determined once the switch type is known.

Abstract: A telephone system capable of judging kinds of various signals (line input signals) obtained through a line is disclosed, that enables reduction of the number of parts, detection with high accuracy, reduction of a mounting area, and reduction in costs. The telephone system includes an A/D converter for making A/D conversion of the line input signal such as a CPC signal, a bell signal, and a usage state signal indicating a telephone line usage state to output a digital line input signal, and a frequency analyzing unit for making frequency analysis of the digital signal converted by the A/D converter, and the central processing unit judges the kind of the line input signal based on a result of the frequency analyzing unit.

Abstract: A regulated power supply interface has a current feedback and voltage level shift circuit that monitors power supply output (load) current and controllably diverts current to a current reference node. A differential amplifier-based, voltage feedback and voltage level shift circuit monitors the load voltage and controllably diverts output current to the current reference node. A current mode setpoint circuit has multiple voltage dropping current paths, through one or more of which a summation of the diverted load currents are programmably directed, to generate a control voltage for controlling the operation of a pulse width modulator unit of the regulated power supply.

Abstract: To secure an ADSL connection to an ADSL transceiver connected to a telephone line to be used also by an associated telephone, the telephone is normally kept disconnected from the telephone line and a predetermined number of bits is allocated to the ADSL connection. Upon an off-hook condition of the telephone in connection with an outgoing call, and upon a presence of a ringing signal on the telephone line or an off-hook condition of the telephone in connection with an incoming call, a predetermined lower number of bits is allocated to the ADSL connection before the telephone is connected to the telephone line.

Abstract: An AC impedance matching architecture which provides programmable AC impedance matching in a given range using a digital filter to filter a signal fed back from the impedance matched line to generate an AC impedance emulation control signal. The AC impedance emulation control signal is combined with a transmit signal (if desired) and drives a voltage controlled current source, which is in parallel with a reference impedance. A voltage is developed across the reference impedance to drive, e.g., the telephone line. The reference impedance is chosen based on a desired maximum AC impedance. The gain of the digital filter, a first order sigma delta filter in the disclosed embodiment, is chosen based on the desired value of the AC impedance. The transfer function of the digital filter is derived based on a desired AC impedance.

Abstract: A computer telephony integration adapter for a telephone system includes a network interface to transmit data to, and receive data from, a network. A network controller is provided to transmit data to, and receive data from, the network interface. The network controller is adapted to package data being transmitted to the network and to unpackage data being transmitted to the telephone system. A telephony interface is also provided to transmit data to, and receive data from, the telephone system. The computer telephony integration adapter also includes a traffic steering device to sort data received from the telephone system, the network, and a computer interface, and to transmit data appropriately to the telephone system, the network, and the computer interface. A signaling device is provided to transmit signaling data to, and receive signaling data from, the telephone system, and to transmit signaling data to, and receive signaling data from, the network.

Abstract: A circuit provides a modulation signal to an input terminal of a line modulator which places a line current modulated in accordance with the modulation signal on a telephone line. An amplifier of the circuit amplifies an analog input signal to provide the modulation signal at an output terminal. A first resistor and a first capacitor are coupled in series between a first input terminal of the amplifier and the line, and a second resistor and a second capacitor are coupled in series between a second input terminal of the amplifier and the line. First and second precharge amplifiers are used to precharge the first and second capacitors, respectively, to reduce DC setup time.

Abstract: A modem generally comprising an analog front end circuit, a hybrid circuit, and a variable impedance element. The hybrid circuit may be configured to couple the analog front end circuit to a transmission line. The variable impedance may be disposed within the analog front end circuit and connected to the hybrid circuit to trim an echo cancelling function of the hybrid circuit.

Abstract: A voltage regulator circuit arrangement limits the DC voltage applied to a tip and ring amplifiers of a subscriber line interface circuit (SLIC), each of which has a first polarity input coupled to a first current flow path to which a DC input (battery) voltage is coupled. A first current source supplies a first current derived via a low pass filter path from that flowing through the first current flow path to a second polarity input node of the tip amplifier, while a second current source supplies a similarly low pass filter path-derived second current to a second polarity input node of the ring amplifier. A voltage regulator is coupled with the first current flow path and is operative to regulate the voltage at the first polarity inputs of the tip and ring amplifiers to a regulated voltage value Vreg, so that the magnitudes of the first and second currents are based upon the regulated voltage value Vreg.

Abstract: An tie line adapter for use with a first communication system and a second communication system, the first communication system having a tie line with a first characteristic and the second communication system having a tie line with a second characteristic. The tie line adapter having a first controller for controlling the first characteristic, a second controller for controlling the second characteristic, wherein the first characteristic and the second characteristic are adjusted to match each other to allow communication between the first communication system and the second communication system.

Abstract: Driver circuit for at least one subscriber terminal, comprising a first driver (14) for amplifying the power of a direct-voltage signal applied for supplying power to the subscriber terminal, the first driver (14) being supplied by a first supply voltage (V1), and comprising a second driver (37; 37a, 37b), following the first driver, for modulating high-frequency signal currents onto the power-amplified direct-voltage signal.

Abstract: A digital subscriber line (DSL) compatible plain old telephone service (POTS) line card that interface a telecommunications switching system to a subscriber over a two-wire subscriber line, wherein the subscriber line card detects whether a DSL line card is connected to the subscriber line. A digital signal processor on the POTS line card is configured to process voice-band signals with a first set of parameters if a DSL line card is connected to the subscriber line and to process voice-band signals with a second set of parameters if the DSL line card is not connected to the subscriber line. Detecting the presence of a DSL line card may be performed by sending a voice band tone on the subscriber line and the return loss measured. Additionally, a tone above voice band may be sent on the subscriber line and a return loss measured.

Abstract: Broadband driver circuit for driving voice and data signals, having a current dividing circuit (37), which divides a current generated by a current source (38), in a manner dependent on a voice and data signal present at a signal input (21), into two base currents (Ib1, Ib2) for driving a first driver transistor (39) and a second driver transistor (40), the two driver transistors (39, 40) being constructed identically.

Abstract: A method and apparatus for coupling a voiceband modem circuit to a common phoneline connector, the common phoneline connection having a ring line connection and a tip line connection which couples a ring/tip line pair to a subscriber loop circuit, the voiceband modem circuit operating in a voiceband modem operating frequency band and having a voiceband modem interface ring line and a voiceband modem interface tip line. The voiceband modem interface ring line is coupled to the ring line and the voiceband modem interface tip line is coupled to the tip line connection by inserting, between the ring line connection and the voiceband modem interface ring line and between the tip line connection and the voiceband modem interface tip line, a series pair of inductors. A first inductor of the series pair has a low inductance and a high self-resonant frequency and a second inductor of the series pair has a high inductance and low self-resonant frequency.

Abstract: A signal detector for detecting a signal having a first nominal frequency, F1 and a second nominal frequency F2, the signal intermixed with an interfering signal to form a composite signal, the signal detector including a first and a second band pass filter centered at F1 and F2 for filtering the composite signal to provide an F1 and F2 signal; a parameter estimator for determining an F1 and F2 period for the F1 and F2 signal for a sequence of frames and an average period shift (APS) for a current frame and a plurality of earlier frames; a metric calculator for calculating a metric that corresponds to the F1 and F2 period and the APS; and a decision processor for deciding whether the signal has been detected based in part on a comparison of the metric and a threshold.

Abstract: A subscriber circuit is capable of realizing a CLIP service in an old-fashioned switching system. The subscriber circuit has a ringer transmitting circuit, which is connected to line A and line B, and which transmits a ringer signal in accordance with a ringer transmission request signal from a host system; a battery feed circuit, which supplies speech current to line A and line B; and a timer, which detects, in accordance with a change in the level of a ringer transmission request signal from the above-mentioned host system, the end of transmission of a ringer signal transmitted by the ringer transmitting circuit, starts timer operation, and ends this timer operation after a predetermined time has elapsed. The battery feed circuit supplies speech current to line A and line B from the above-mentioned battery feed circuit during the operation period of the timer.