Abstract: This device is designed so that although voice of the opposite party will be amplified when telephone 1 on the side of the device is first placed on-hook during a telephone conversation, amplification will not occur if the opposite party places his or her phone on-hook first during a telephone conversation or if the user places telephone 1 on-hook before the opposite party picks up the telephone. The structure, which is shown in FIG. 1 such that during a telephone conversation between telephone 1 and telephone 12, when telephone 1 is placed on-hook first, the on-hook status is detected by means of the photocouplers PC-1 or PC-2, and the voice of the opposite party at telephone 12 is amplified by means of contacts y1-1 and y1-2, which are in the make position, line transformer 2, amplifier 3 and speaker 4.

Abstract: An automatic telephone calling system that characterizes the responses from telephone subscribers' telephone stations to placed calls from the system. The system comprises communication lines which enable the system to place a call to a subscriber's station, to receive the response thereto, and exchange information therebetween. Operator stations enable operators of the calling system to communicate, via a respective communication line, with a subscriber's station upon an operable connection of the line to the subscriber's station and to the operator station. A call processor places calls to subscribers' stations and operably connects and disconnects each communication line to a respective subscriber's station and to a respective operator station. A trunk processor characterizes the response from a respective subscriber's station to a placed call and determines whether a response characterized as a voice signal is delivered by an answering machine.

Abstract: Method and apparatus for detecting make-break clicks on a telephone line, i.e., clicks produced by going on-hook or off-hook. A click is detected by analyzing time slices of a telephone signal to detect a sharp positive transition in signal energy followed by a diminishing envelope of short duration. Three signal measures are utilized to determine whether a click has occurred: (a) a magnitude transition, i.e., a change of the magnitude of the amplitude of the signal over a short period of time; (b) a peak magnitude, i.e., a magnitude of the amplitude of the signal corresponding to the first acceptably large magnitude transition (the beginning of the click); and (c) a duration of the signal envelope. In accordance with the present invention: (a) the minimum allowable peak magnitude of a valid click is scaled to the maximum magnitude encountered as the telephone signal is analyzed, i.e.

Abstract: In a ringing signal control circuit for controlling supply of a ringing signal from a ringing signal generator to a subscriber's line in response to a call signal destined thereto, a switching element is repeatedly switched to connect the ringing signal generator to the subscriber's line under control of a switching signal from a switch controller. In order to suppress a surge voltage due to connection and disconnection of the subscriber's line for the ringing signal generator, a memory stores a time data signal representative of a transition time from a reference voltage level to an optimum voltage level for the subscriber's line. The optimum voltage level is the level at which the connection and disconnection can be carried out without generation of the surge voltage. A voltage comparator compares the ringing signal with the reference voltage to produce a coincident signal.

Abstract: A secondary communications device, such as a modem, a facsimile machine, an automatic meter reader or an answering machine, shares a telephone line with a subscriber's telephone and must grant the telephone primary access to the line. The present invention prevents the secondary device from seizing the line when the telephone is already off-hook and will terminate a line seizure by the secondary device if the subscriber picks up the telephone handset during use of the line by the secondary device. An average interval for charging a capacitor to a threshold voltage in response to an on-hook voltage appearing across the telephone line is determined. When the secondary communications device is ready to use the line, circuitry measures an interval for charging the capacitor in response to the current voltage appearing across the telephone line. The secondary communication device seizes the line only if the measured interval does not exceed the average interval by more than a predetermined amount.

Abstract: An automatic loss compensation for use in a two to four wire hybrid converter in a telephone system. Many hybrid converters provide a substantially fixed gain for receive signals that are provided to the customer loop telephone line and for transmit signals that are provided to the digital carrier transmission line. The compensation circuit includes a measurement circuit, controller, and receive and transmit amplifier. The measurement circuit determines the length of the customer loop telephone line and provides a length signal. The controller receives the length signal and categorizes the length as being within one of a plurality of segments. The controller appropriately varies the amplification and phase of the receive signal, which is then combined with an inverted transmit signal, in order to substantially reduce reflected signals from the transmission line and transmission line termination.

Abstract: A substantially-universal detector (FIG. 2) of far-end call disconnect-indicative tones detects the foreseeable forms of tone-based signalling of remote-end call disconnect that are likely to be employed anywhere in the world, without reconfiguration or reprogramming for different tones or countries. Implemented in the digital signal processor (DSP 30) of port circuits (14, 20) of switching systems (11) or adjunct processors (12), the detector determines parameters (204) of signals carried by the call to the near end and uses them, along with already-present linear predictive coding (LPC) predictor coefficients (202) and indications of energy (203) in the signals, in a multivariate classification (230) of call progress tones from other tones. When presence of any call progress tones is thus detected substantially without interruption for a predetermined minimum time in the received signals, the call is considered (240) to have been disconnected at the far end.

Abstract: A communication unit connectable in parallel with other communication equipment to a two-wire telephone line communicates through the telephone line and a detector detects a voltage across the two-wire telephone line. A command unit commands communication by the communication unit and a controller controls the communication by the communication unit according to the detection by the detector and the command by the command unit.

Abstract: A ring trip deciding method in a ring trip circuit detects voltage change in the on-hook state and the on-hook state of a terminal when the terminal such as telephone set connected to the telephone line is called.

Abstract: A parallel phone detection circuit is described, the function of which is to enable a phone call to be transferred from a first telephone set to a second telephone set. The detection circuit maintains the first telephone set connected to the telephone line until the handset of the second telephone set has been taken off-hook, and then disconnects the first telephone set. The circuit operates by detecting the line current from the telephone line and produces the reference value for comparison purposes related to that line current.

Abstract: A telephone communication enable state maintaining circuit is disclosed, and the circuit includes a communication circuit 10, a communication operating circuit 20 and an operation maintaining circuit 30. The communication circuit 10 includes contacts 3,4,5, and a condenser C.sub.1. The communication operating circuit 20 includes a resistor r.sub.1, a condenser C.sub.2, a transistor 6 and contacts R.sub.3 a, R.sub.3 b, R.sub.1 a, R.sub.1 b. The operation maintaining circuit 30 includes contacts R.sub.1 c, R.sub.3 c, a resistor r.sub.2, a condenser C.sub.3, and a transistor 7. According to the present invention, telephone calls from the outside can be received, even if the telephone receiver is placed in an abnormal manner.

Abstract: An automatic protection and recovery method for a telephone line interface circuit is described. The interface circuit monitors current on the line, and in the event of a fault producing an excessive current a protection relay interrupts a connection of the interface circuit to the line, and the interface circuit monitors common mode voltage on the line. The interface circuit is reconnected in response to the monitored voltage being below a relatively high threshold. If a second interruption results, the interface circuit is then reconnected in response to the monitored voltage being below a lower threshold. If a further interruption results, the interface circuit enters a ground fault recovery process. The method facilitates protection and rapid recovery from arbitrary fault conditions on the telephone line.

Abstract: Dual tone multifrequency (DTMF) signals are automatically generated by a telecommunications device after a telephone number is called. The signals generated to call the telephone number are determined by a manually operated switch indicating pulse code signal generation or dual tone multifrequency signal generation. It is determined that the telephone number has been dialed by detecting a ring-back signal, voice frequency signals, DTMF signals, or data stream signals. Alternatively, if a predetermined period of time, such as ten seconds, passes without the user pressing a number on the keypad, it may be assumed that the telephone number has been dialed. Upon detecting one of these signals or the passage of time, the telecommunications device is controlled to generate only dual tone multifrequency signals for communication with automated services, such as voicemail, telephone banking, reservation systems, etc.

Abstract: The invention relates to remotely powered circuitry, and in particular to telephones. The circuit of the invention uses a counter to measure or compare the duration of power supply interruptions on the remote power supplying line to cause the remotely powered circuitry to be initialized whenever the duration of such an interruption becomes greater than or less than a specified duration. Advantageously, comparators are used so as to be able to take a plurality of durations into consideration. Thus, each time the power supply on the remote power line is interrupted, if the interruption is not of an acceptable duration, then the remotely powered circuitry is initialized.

Abstract: A headset telephone having an in-use indicator for notifying passers-by when the wearer of the headset is carrying on a telephone conversation. In one embodiment of the invention, an in-use indicator comprising a light-emitting diode is disposed on the end of the headset's voice boom, and is illuminated in response to activation of the headset. In another embodiment of the invention, activation of the headset causes a transmitter to transmit a signal to a remote in-use indicator not physically connected to the remainder of the telephone system.

Abstract: A circuit for indicating the status of a telephone line at the CPE end, where the status is either on-hook, ringing, or off-hook is disclosed. The telephone line is the normal two-wire telephone line. First, a transconductance amplifier converts a floating voltage difference between the two-wire telephone line into a current. The current is proportional to the voltage difference. Next, a current to voltage converter converts the current from the transconductance amplifier to a single ended ground referenced voltage. The single ended voltage is proportional to the current from the transconductance amplifier, thus the single ended voltage is proportional to the voltage difference across the two-wire telephone line. A voltage controlled switch is turned ON when the single ended voltage is greater than a predefined value indicating the on-hook status. When the single ended voltage is below the predefined value, the voltage switch is turned OFF indicating the off-hook status.

Abstract: To supervise a telephone subscriber line (v'2, v'1,) and provide it with adjustable AC and DC termination impedances from the exchange (v1, v2), these are supplied by an impedance synthesis multiple loop split into separate DC and AC loop parts by filters at the output of a sense amplifier in the common loop part and fed (e) through a Herter bridge. The amplifier AC output has however to be limited to avoid saturation by a larger DC signal. It now includes a Miller effect integrator output stage (A2) with a low pass frequency response supplying the DC loop and also feeding back an input stage (A1) so that the latter exhibits a high pass frequency response with a DC free output to drive the AC loop and the consequent ability to supply a larger AC output. Further circuits improve dial pulse detection (LP), reduce external capacitances (C1) and limit power consumption (PG5 and PG6).

Abstract: An integrated PCM-CODEC circuit including a plurality of PCM subscriber lines consisting of a SLIC for interfacing a telephone line with a switching system, an impedance conformer and a PCM-CODEC, a common bus for transferring a telephone signal into or from a subscriber according to the time division rule for the timing of telephone line use, a telemetering signal source and a (synchronization signal for controlling portion of the telephone call called by the n'th subscriber. The PCM-CODEC circuit includes a buffer, a signal selector, an applied gain controller, an anti-aliasing filter, a telemetering signal filter, a BPF, a coder, a decoder, a LPF, a received-gain controller, a smoothing filter, an operational amplifier and a telemetering gate.

Abstract: A correction circuit for use with a subscriber line interface circuit (SLIC) to control the level of a DC voltage supplied to the tip and ring wires of a telephone circuit includes a current sink with a differential operational amplifier. The amplifier output terminal is connected through an output resistor to a control input of the SLIC which influences the DC voltage level. The non-inverting input terminal of the amplifier is connected to the tip or ring wire, or both, and the inverting input terminal is connected to the output resistor and a DC reference circuit. The level of the voltage supplied by the SLIC is a function of the current supplied by the correction circuit.

Abstract: A ring trip detection circuit detects an OFF-hooked state of a telephone receiver during ringing of a telephone set by detecting a change in a voltage across two terminals of a transmission resistor through which a ringing signal is supplied to the telephone set from a ringing signal source.

Abstract: According to the invention, an interface circuit for quickly establishing a DC loop current in response to off-hook detection is provided by a circuit which uses a transistor, where its collector electrode is connected to the first one of the telephone lines; an emitter resistor connected between an emitter electrode of the transistor and the second one of the telephone lines; a bias resistor having a first terminal connected to the collector electrode; a Zener diode connected between a second terminal of the bias resistor and the second line; a first capacitor connected in parallel to the constant-voltage means; switching means connected between the second terminal of the bias resistor and a base electrode of the transistor for the switching means to be conductive in response to an off-hook signal; and charging means, typically formed of a series connection of a capacitor, a resistor and a Zener diode, connected in parallel to the bias resistor so as to allow a current to flow through the series connection t

Abstract: A circuit for interfacing a host telephone system having a trunk line pair with a central office line pair and an additional circuit line pair includes a loop current monitor circuit for monitoring the host telephone system trunk line pair which is normally connected to the central office line pair. The loop current monitor provides a status signal output indicating the presence or absence of loop current. A relay controller receives the status signal and provides a relay control signal and a hold signal. A relay selectively connects the host telephone system trunk line pair to the additional circuit line pair in response to the relay control signal when loop current is detected after the host telephone goes off-hook. A hold termination circuit receives the hold signal and traps any loop current signals which may be detectable over the central office line pair.

Abstract: A sensor circuit for telephone line includes a detection coil (52) inserted in a telephone line (22). The coil generates a magnetic flux according to a line current which flows in the telephone line. A magnetic sensor (54) such as a Hall element generates a voltage signal in response to the magnetic flux. An output of the magnetic sensor is applied to a comparing circuit (58) and a tone deriving circuit (60) via an amplifier (56). The comparing circuit includes two comparators one of which compares the voltage signal from the magnetic sensor with a first reference voltage (V1) and the other of which compares the output signal with a second reference voltage (V2), so that a line current supervisory signal is outputted from the comparing circuit. The tone deriving circuit includes a band-pass filter and derives a tone signal from the voltage signal of the magnetic sensor.

Abstract: A method of processing a signal having characteristics and received from a telephone line is presented. The method includes defining a frame by measuring a plurality of samples from the signal over a predetermined period. Additionally, linear prediction coding coefficients of a selected group from the plurality of samples are determined. Further, the variance of the linear prediction coding coefficients are determined and the variances compared to a reference variance. A heuristic rule is applied to a selected characteristic of the signal to determine if the signal comprises a voice signal.

Abstract: A detector for On-Hook/Off-Hook state of a telephone line includes a capacitor connected to the telephone line in series with a resistance large enough to be allowed as load on an On-Hook telephone line. A low impedance voltage sensing means in series with a normally open switch is connected across the capacitor, and the switch is closed in response to a polling signal to determine if the line is in On-Hook state. The capacitor transforms a very low charging current lasting seconds into a large discharge current lasting only milliseconds. This makes it possible to use an inexpensive low impedance voltage sensing device, such as an opto-coupler in series with a zener diode. Such components provide high-voltage galvanic insulation at low cost, and a very compact apparatus can be made. The invention also provides for inexpensive ring detector circuits and for overload protection for the equipment connected to the telephone line.

Abstract: In an on-hook transmission circuit provided in a subscriber circuit connected between a subscriber terminal and an exchange, a constant-current source unit causes a constant current to flow in first and second wires during a period in which a control signal indicating that on-hook transmission should be turned ON is being received. A loop supervisory unit detects establishment of a loop including the first and second wires and a subscriber terminal connected thereto, and generates a scan signal used for causing the constant-current source means to stop the constant current flowing in the first and second wires after detecting the establishment of the loop.

Abstract: A called party response detecting apparatus of a terminal equipment includes a plurality of filter units, a determining unit, and an analyzing unit. The filter units are commonly connected to an input side and detects specific frequency components included in a plurality of signal tones coming from a telephone line. The determining unit checks the presence/absence of each output from the filter units for each fundamental period to determine a signal type on the basis of a predetermined output pattern. The analyzing unit analyzes various signal tones and a called party response on the basis of occurrences of signal type outputs during a predetermined time period of the determining unit.

Abstract: Changes in a telephone subscriber line voltage are detected in a telephone set by supplying a voltage dependent upon the subscriber line voltage to a potential divider having first, second, and third tapping points, the second tapping point being between the first and third tapping points, and comparing the voltages at the first and third tapping points with a smoothed version of the voltage at the second tapping point to produce pulses at respective terminals when the line voltage is falling or rising. An algorithm is described for responding to the pulses to distinguish changes in hook state of another telephone connected to the same subscriber line from interfering signals. The arrangement facilitates remote release from hold and privacy indication functions for the telephone set.

Abstract: A digital line card for interfacing a remotely located digital telephone to a central office system by a two-wire connection is disclosed. The digital line card consists of a line interface connected to the two-wire connection. The line interface provides a full duplex transmission link with the remotely located digital telephone over the two-wire connection. A buffer is connected between the line interface and the central office system. The buffer converts data between the line interface and the central office system. The line card further comprising a protocol controller connected to the line interface. The protocol controller performs a packet protocol for communications with the remotely located telephone.

Abstract: A line unit, used in a line shelf having a line shelf processor and common logic, is provided with an EEPROM device for storing information relative to the line unit. The stored information includes line unit type identification codes, auto provisioning data, gain and equalization adjustment data and signaling translation tables. The data contained within the EEPROM may be utilized by the line shelf processor to provide automatic initialization and provisioning of the line unit when first inserted into the line shelf, and automatic signaling translation so that line unit signaling becomes compatible with a transmission facility connected to the line shelf. The need for factory preset resistors installed in the line unit may be eliminated by storing within the EEPROM a required gain setting.

Abstract: On-hook VF transmission through a channel unit to a subscriber telephone instrument is provided by a control unit which generates control signals for the channel unit. The control unit responds to receipt of an "idle" code by creating commands which establish a VF path through the channel unit regardless of whether the subscriber instrument is on-hook or off-hook.

Abstract: To detect tones for call progress monitoring, hysteresis apparatus is provided whereby the output of a typical tone detector such as a comparator operating in conjunction with a selective filter is monitored by a counter. The counter is incremented and decremented according to whether the input is indicative of the presence or absence of a tone. If the counter reaches a predetermined count within a given period of time, then an indication is made that the tone exists. If the counter does not reach this predetermined count or threshold within the applicable time, then it is an indication that the tone does not exist. The thresholds of the counters plus the amount by which a counter may be incremented or decremented for each input signal is variable for each tone.

Abstract: The no balance duplex signalling circuit eliminates the need for setting balance resistors and capacitors to match or be proportional to cable resistance and capacitance as was required of previous duplex signalling circuit designs. A microcomputer is also used to evaluate the output of a simple loop current and voltage sensing circuit to dynamically determine the signalling state of the far end of the trunk conductors. The microcomputer stores a plurality of data which indicate signalling thresholds for all possible duplex signalling states. The microcomputer can then compare the measured voltage and current on the trunk conductors to automatically make a determination of the signalling state based on the stored data indicative of permissible signalling states.

Abstract: A ringing signal control circuit used in a Subscriber Line Interface Circuit (SLIC) for connecting a ringing signal bus to a subscriber loop. The ringing signal bus transmits ringing signals along the subscriber loop to a subscriber instrument. The SLIC includes a High Voltage Line Interface (HVLI) circuit connected to the subscriber loop and the ringing signal bus is connected to a ringing generator that provides a source of ringing signals. The ringing signal control circuit comprises a logic interface circuit connected via an address/data bus to a central controller that is arranged to receive ringing connection signals from the central controller and to generate a ringing activation signal. A ring timing circuit receives the ringing activation signal and generates a first and second output signals. The second output signal is transmitted from the ring timing circuit at a specific time interval subsequent to the first output signal.

Abstract: A low-frequency alternating current signal detector for recognizing tone signals in a central office line interface circuit connecting a private telephone installation to an analog telephone network subscriber line. The low-frequency alternating current signal detector includes an amplifier (1) connected to the input of a bandpass filter (2) and to the input of a first rectifier-filter (3), a second rectifier-filter (4) and a threshold presence detector (5) connected to the output of the bandpass filter (2). The output of the threshold presence detector (5) selectively enables comparison by a comparator (6) of the bandpass filter input and output signals and signalling of the presence of an alternating current signal.

Abstract: A telephone headset on-line indicator uses a light emitting diode located on a boom of a headset to indicate that the user is on-line with another telephone. Circuits are described for use with use with conventional telephones, electronic telephones and PBX telephone base units.

Abstract: A plurality of consoles (111-113) share use of a single landline (101) with minimal requirements for internal maintenance data signalling. As two or more consoles both share use of the link, a telephone interface (103) assigns one of the consoles to be responsible for maintenance signalling. If and when the assigned console concludes its communication needs or otherwise becomes unable to continue the maintenance signalling, the telephone interface will assign a new interested console to provide the maintenance signalling. This continues until no consoles remain having an interest in maintaining the communication link. In one embodiment, when the link is used by only a single console, a hold function can be accommodated. When two or more consoles are serviced, however, the hold function is not applied. Also, when the link has been placed on hold, any console can remove the hold condition.

Abstract: A telephone line card circuit includes an operational amplifier circuit having first and second inputs and an output. A field-effect transistor circuit has first, second and control electrodes, the control electrode is coupled to the output of the operational amplifier circuit, the first electrode is coupled to the TIP/RING terminal, and the second electrode is coupled to the second input of the operational amplifier circuit. A first resistor is coupled between the TIP/RING terminal and the first input of the operational amplifier circuit. A second resistor is coupled between the first input of the operational amplifier circuit and a terminal of the circuit whereby the terminal of the circuit is typically coupled to a supply voltage terminal.

Abstract: An over-current verifier circuit used in a Subscriber Line Interface Circuit (SLIC) for validating an over-current condition on a subscriber loop comprising a first counter connected to the SLIC disposed to receive an oversense signal from the SLIC. The first counter begins counting when the oversense signal is received and produces an output signal when the oversense signal is still active after the counter finishes, denoting a dc over-current in the subscriber loop. A timer circuit connected to the SLIC also receives the oversense signal. The timer is arranged to begin counting when the oversense signal is received. A second counter further receives the oversense signal and is advanced by one count on the high to low transition of the oversense signal. The second counter produces an output signal when three counter advances are produced before the timer times out, denoting an ac over-current condition.

Abstract: A control circuit for an electrical telephone accessory detects if the telephone receiver is on the cradle, the telephone ringer is actuated, or if the telephone receiver is lifted from the cradle. The control circuit connects the electrical telephone accessory to a power supply source when the telephone ringer is actuated or when the telephone receiver is lifted from the cradle.

Abstract: A telephone set is provided enabling seizure for originating and terminating calls of a telephone line connected thereto to be performed as well as release thereof, as the result both of a first command produced by a first switching entity actuated from the handset of the telephone set as well as via a second command produced by a second switching entity that is able to be actuated independently of the handset, switching entities producing the commands via individual communication establishment elements which are inserted in parallel in a loop which links, via the controlled power feeding arrangement, the output terminals of a first diode bridge, the input terminals of which are connected to the two line wires via a protection circuit, together with a second diode rectifying bridge, performing actual rectification, linked via capacitors to the output of the protection device, in parallel with the first diode bridge, and adapted to power a microprocessor and relevant circuits of telephone set circuitry, via a

Abstract: A line state detector for a telephone line tests a voltage derived from the telephone line by closing a switch in series with a voltage sensing circuit in response to a polling signal. A modem testing the line state go Off-Hook immediately after it finds that the line was in On-Hook state, so it can use a low impedance voltage sensor directly on the telephone line. Monitoring equipment will need a line state detector with high impedance, which can be achieved by a high impedance in series with a capacitor. The capacitor voltage can then be tested by a low impedance sensing circuit.

Abstract: A telephone line bridging sensor circuit is provided which provides a variable output frequency signal to a microprocessor for measuring and storing the frequency count on a periodic basis. The circuit includes an isolation transformer to isolate the audio component of the telephone line from the sensing circuit. The loop current present in the telephone line is rectified through a full wave diode rectifier and the output of the rectifier is filtered and regulated to provide an input voltage to an astable, voltage controlled oscillator. As the current on the telephone line varies, the input voltage to the oscillator also varies a proportionate amount causing the output frequency of the oscillator to change accordingly.

Abstract: An apparatus and method for detecting telephony signaling states, comprises an analog to digital converter and a microcomputer with associated firmware for controlling the operation of the microcomputer. The analog to digital converter digitizes incoming analog voltages containing telephony signaling state information and presents the digitized data samples for operation by the microcomputer. The microcomputer performs various digital filtering and analysis of the digital data samples in order to determine the signaling states represented by such digital data samples, and upon detection of the signaling states, outputs information indicative of such detected states. The present invention also incorporates use of such a detection circuit within line cards used to interface telephone subscriber lines with the central office terminal. The present invention further encompasses the methodology of performing such digital data sampling and analysis so as to determine telephony signaling states.

Abstract: An arrangement that enables an adjunct processor to determine the service status of switching system communication ports to which the adjunct processor is connected, without reliance on switch-to-adjunct status-conveying messages. In-service and idle ones of the ports participate in calls on a rotating basis. Following receipt of N calls, where N is the number of in-service ports connected to the adjunct processor, the arrangement determines whether each port that is presently designated as being in-service and idle has participated in one communication before a port has participated in a second communication. The arrangement then treats as out-of-service any port presently designated as being in-service that has been so determined a predetermined number of sequential times. It also selectively designates as in-service ports that have participated in communications since the last determination had been made.

Abstract: An analog communication signal such as the signal transmitted over a telephone line is converted to digital form for storage in the memory of a computer. Segments of the digital representation of the signal are analyzed to determine whether or not the signal has uniform frequency components repeating at regular intervals. Detection of such regularly repeating uniform frequency components is useful in an automated telephone system to determine whether a telephone signal consists of voice or a call progress signal.

Abstract: There is disclosed a tone type recognition method capable of recognizing a call progress state of a central office line switching system by using a tone detector. The method enables the system to correctly recognize the type of call progress tone, regardless of its frequency, by conducting periodic detection of characteristics of cadence classified by tone-type.

Abstract: A system for transmitting data via a telephone line by means of a data communications device (4) connected to the telephone line, at least one other communications device being connected to the telephone line and each device being switchable between an inactive state, in which the device is not in use and presents a high impedance to the telephone line, and an active state, in which the device reduces the telephone line voltage and signals can be transferred between the device and the telephone line, the system including a telephone line state detection unit (10) associated with the data communications device (4) and connected to the telephone line for electrically monitoring the telephone line to provide an indication of the state of another communications device connected to the telephone line.

Abstract: A telephone line loop current regulator combines the functions of current regulation, current detection, loop disconnect signalling and speech switching. It comprises a gyrator circuit formed by resistor (R1), capacitor (C1), transistor (T1) and resistor (R3). Loop current is regulated by transistor (T1) and resistor (R3) while loop current detection is achieved by monitoring the voltage across resistor (R3) by an opto-diode which forms part of an opto-electronic coupler (OP2). Speech switching is performed by transistor (T3) which also monitors the voltage across resistor (R3) so that speech is switched onto the line via transformer (TR1) when d.c. loop current is present. Line seizure and loop disconnect signalling are carried out by switching the opto-coupler (OP1) to turn the transistor (T1) on and off.

Abstract: An apparatus for use with a telephone including, in one embodiment, a detector for detecting when the telephone is in an off-hook condition and disconnect circuit for eliminating the off-hook condition when the off-hook condition is caused by the telephone so that phone calls may be received by the line. An alarm responsive to the detector produces a warning of the off-hook condition if another phone on the line is off hook.