Abstract: Protection circuitry for use with a modem is provided that detects excessive voltage between the tip and ring lines of a telephone subscriber loop when the modem is off-hook. When the over-voltage condition is detected, a switch is active, creating a circuit path that directs current away from the DC-holding circuit of the modem, thereby protecting the modem. The protection circuit of the present invention may be implemented using a minimal number of simple and inexpensive components.

Abstract: A telephone line protection module having a printed circuit board base with conductive paths connected to pins of the module. Overvoltage sensitive semiconductor devices are soldered to the ends of a conductive bridge, and the bridge is spring-biased between a module cover and the conductive bridge. The semiconductor devices are thus forced into electrical contact with the printed circuit paths. In addition, in the event the semiconductor devices are thermally destroyed, the conductive bridge is forced by the spring into direct contact with the printed circuit paths.

Abstract: A network interface device includes a base, a cover and a circuit board secured in the base. The circuit board includes terminations for input and output communication lines. Each pair of input and output communication lines corresponds to a single standard telephone line, a high speed data line or other type of line. The communication line terminations may be implemented as insulation displacement connectors, and the cover may include projections on its inner surface such that closing the cover also closes the insulation displacement connectors on the circuit board. For each communication line, the circuit board may include a subscriber bridge which establishes a breakable connection between the input and output line terminations via traces in the circuit board. In fixed wireless, fiber-to-the-home (FTTH) and other similar applications, the circuit board may also include terminations for input and output power lines, and the base and cover may be extended to accommodate an uninterruptible power supply.

Abstract: A current-limiting circuit (110) of a battery-feed circuit (FIG. 1) for a digital telecommunications line (T,R) provides a low start-up current limit (I3) when power is initially applied to the digital line. It automatically and gradually changes (40) to a high current limit (I1) as the load on the line is charged. When the load is fully charged, the circuit provides a low impedance to the line. Upon occurrence of a fault, the circuit switches back to the initial low current-limit state. The circuit comprises a feed transistor (Q1, Q11), a control transistor (Q2, Q12), and a high-impedance resistive circuit (R1-R4, R15). The feed transistor limits (403) current flowing to the R lead of the line to the high limit when the voltage across the feed transistor is low (0-V2) and the feed transistor is saturated.

Abstract: An improved surge protection circuit for withstanding surges is provided. A first node is provided for coupling to a tip lead, and second node is provided for coupling to a ring lead. The surge protection circuit has a first current path for turning on a first transistor, and a second current path for redirecting current from the remaining excess surge energy from one lead to the other lead. The first current path further includes a first sub-path to direct the initial voltage surge to the base electrode of the first transistor to cause the first transistor to turn on hard. The second sub-path redirects current from the initial excess surge energy from the voltage surge to a capacitor prior to the time before the first transistor is fully turned on, so as to protect the base-emitter junction of a second transistor from being reverse biased.

Abstract: A network interface device (NID) including a plurality of cavities beneath the base surface of the NID. Each cavity extends downwardly between the base surface of the NID and the bottom of the NID defined by bosses and extensions extending downwardly from the base surface. Each cavity provides sufficient space for additional electronics, such as a test circuit, to be housed in the NID. The test circuit is housed within the cavity and is electrically connected between the incoming telephone company line and the jack of a line module. The line module is mounted above the test circuit by mating connecting means on the bottom of the line module to cooperative connection means on the base surface.

Abstract: Connector including a housing including a resilient portion provided with a cavity, connectors mounted in the cavity, the resilient portion deformable to increase access to the cavity to facilitate insertion and mounting of the connectors in the cavity, the connectors for mechanically and electrically engaging a first pair of terminals to which an incoming telephone line is connected and a second pair of terminals to which a telephone subscriber line is connected to mount the connector to the pairs of terminals and to electrically interconnect the incoming telephone line with the telephone subscriber line, a telephone circuit is provided in the connector which is connected to the connectors for connection to one of the lines or to both of the lines; alternate connector includes test terminal assemblies for the external testing of the incoming telephone company line and telephone subscriber line and a telephone circuit mounted internally of the connector without dismounting the connector from a connector block

Abstract: Terminal equipment for telecommunications and information processing with improved electromagnetic compatibility (EMC). The equipment has a human-machine interface (HMI), a metallic telecommunications interface (TCI), and optionally a power line interface (PLI). First common-mode rejection filters consisting of common-mode choke coils and shunt capacitors are placed at the HMI interface of the equipment, while second common-mode rejection filters consisting of the same components are placed at the TCI and PLI interfaces. High-frequency junction points of the first and second common-mode rejection filters are interconnected with a bypass circuit. Being isolated from the signal ground and frame ground of the equipment, the bypass circuit is an independent non-grounded circuit. Such internal structure makes it possible to reject noise signals induced by an external noise source and also to suppress spurious radiation from an internal noise source.

Abstract: The invention relates to a communication system comprising a station (2) for charge metering of a connection point. This station comprises a monitoring circuit (7) for detecting a request for a connection set-up from the connection point (3), either for establishing the absence of a message after a given period of time, or for evaluating the contents of a message that has arrived from the connection point (3) after the request for a connection set-up has arrived, and for rejecting the request for a connection set-up if invalid parameters of the connection point (3) are established.

Abstract: A telephone and data communications line protection apparatus is provided for protecting at least one telephone line pair. The telephone and data communications line protection apparatus includes a housing containing protection circuitry for protecting at least one telephone line pair. The housing includes a cavity for receiving a terminal portion of an electrical grounding, earthing spring clip member. The protection circuitry includes an electrical grounding contact extending into a housing cavity for electrical and mechanical contact engagement with the terminal portion of the electrical grounding, earthing spring clip member. The electrical grounding, earthing spring clip member has a predetermined profile corresponding to the housing. The electrical grounding, earthing spring clip member includes an aperture to receive a grounding wire.

Abstract: An isolating circuit for isolating a telephone set from an exchange passes a D.C. feed current but prevents A.C. currents over the range of operating frequencies of the equipment, typically about 300 Hz to 4 KHz. The circuit comprises a T-filter having two resistive branches arranged between the source and the load, and a capacitive branch arranged between the resistive branches and earth. The resistive branches each include a resistive element having an amplifier (A.sub.1, A.sub.2) in parallel with a resistor (R.sub.1, R.sub.4). The effective resistance of the resistive branches is dependent on the gain of the amplifier, which is isolated from D.C. by capacitors (C.sub.1, C.sub.2, C.sub.3, C.sub.4). The impedance of the capacitive branch is chosen so as to be lower than that of the resistive branches over the frequency range of interest thus isolating the two resistive branches from one another at those frequencies.

Abstract: An isolation system is provided that is suitable for use in telephony, medical instrumentation, industrial process control and other applications. Preferred embodiments of the invention comprise a capacitive isolation barrier across which a digital signal is communicated. The system provides a means of communication across the isolation barrier that is highly immune to amplitude and phase noise interference. Clock recovery circuitry may be employed on one side of the isolation barrier to extract timing information from the digital signal communicated across the barrier, and to filter the effects of phase noise introduced at the barrier. Delta-sigma converters may be disposed on both sides of the isolation barrier to convert signals between analog and digital domains. An isolated power supply may also be provided on the isolated side of the barrier, whereby direct current is generated in response to the digital data received across the isolation barrier.

Abstract: A line interface circuit (LIC) used in telecommunications networks operates in either a high frequency mode or a low frequency mode, depending upon the status of its associated customer premises equipment. A LIC main controller detects a change in state of customer premises equipment via a battery feed circuit. If the customer premises equipment is off-hook, a switch associated with a resistor-capacitor (RC) circuit is activated to lower the resistance value of the RC circuit, and thereby, increase the operating frequency of the LIC. During on-hook intervals, the main controller deactivates the switch, and the LIC operates at a lower, default frequency.

Abstract: A power cross circuit detects a ring trip condition in order to switch a pair of switch relays to a protection circuit and to appropriate line driver circuitry to enable a talking condition for a telephone. The power cross circuit detects a rise in a DC current across a feed resistor connected to a ring bus and a ring line. The power cross circuit determines a difference in current passing across a first and second sense amplifier connected to respective ends of the feed resistor. The current difference is then converted to a voltage difference, and utilized by the power cross circuit to output a power cross condition when the current difference exceeds a predetermined value.

Abstract: A customer bridge module for connecting telephone company wiring and subscriber telephone wiring in a telephone network interface apparatus, the customer bridge module having a plug-actuated switchable socket and an overcurrent protection circuit, a half-ringer, a maintenance termination unit or a radio frequency interference (RFI) filter.

Abstract: A telephone interface protection circuit and modem incorporating the telephone interface protection circuit. The circuit includes a sensing circuit and a determining circuit. The interface protection circuit checks for an active telephone line and checks the line for over-current conditions caused when a modem designed for the public switched telephone network is plugged into a private digital telephone network. The circuit functions when the modem is operating to provide continuous monitoring. It can be built as a stand-alone device or incorporated into a modem. The circuit notifies the user of the line condition either with LEDs or with a status message sent to the user via the host computer interface.

Abstract: The telephone line coupler circuit has a single transmit opto-coupler whose output includes a DC bias component connected to a gate of a line seize switch for connecting a DC line seize load across the ring and tip contacts of the telephone line. The line seize switch is saturated by the transmit opto-coupler bias output and the AC component of the transmit opto-coupler output is sent over the telephone lines. The receive opto-coupler is used both for receiving communications signal and for detecting the ring signal. The band pass filter connected to the output of the receive opto-coupler may be switched to pass a ring signal frequency band or a communications frequency band. The circuit operates using two opto-coupler devices while conventional circuits require four opto-coupler devices.

Abstract: The balancing bridge circuit is provided between a four-wire circuit and a two-wire circuit, to provide a thin-type balancing bridge circuit having satisfactory transmission characteristics and a MODEM and an exchange and a repeater of a telephone circuit having this balancing bridge circuit built therein. The transmitting terminals of the four-wire circuit and the connection points of the balancing bridge circuit are connected together through the photo-coupler. The receiving terminals of the four-wire circuit and the connection points of the balancing bridge circuit are connected together through the photo-coupler. The terminals of the two-wire circuit are connected to the connection points of the balancing bridge circuit. By the presence of the compact photo-couplers, it is possible to ground the transmitting terminal and the receiving terminal together. Common-mode noise reaching the terminals is not transmitted to the receiving terminals.

Abstract: Network interface apparatus for being mounted on a connector block and for interconnecting at least one incoming telephone company line to at least one telephone subscriber line and for providing a response to signals carried by the incoming telephone company line such as a response to test signals carried by the incoming telephone line to locate a fault as being on the telephone central office side of the apparatus or on the telephone subscriber side of the apparatus.

Abstract: Disclosed is a maintenance termination unit which is protected against lightening strikes and excessive currents. Resistors are placed in series with the tip and ring switches of the unit. Voltage breakdown devices, such as gas tube protectors, are coupled in a parallel with the resistors and switches.

Abstract: Module for being mounted to telephone network interface apparatus and for interconnecting and disconnecting a subscriber premises line to and from an incoming telephone company line and for providing a demarcation point between the lines for facilitating the determination of whether a fault exists on the subscriber premises line side of the module or on the incoming telephone company line side of the module, the module includes a base provided with a first latch, a jack provided on the base for being connected to the incoming telephone company line, subscriber terminals provided on the base for being connected to the subscriber premises line, a cover mounted pivotally to the base and provided with a second latch which is resilient and for releasably engaging the first latch to releasably latch the cover to the base upon the cover being pivoted toward said base sufficiently to engage the first and second latching means.

Abstract: A digital access arrangement, coupled between a data terminal equipment having a transmit line and a receive line and tip and ring lines of a network, having a circuit that provides polarity check, hook/switch control, and data modulation functionality. The circuit includes a controller and six controllable switches, each having a conducting state and a blocking state.

Abstract: Methods and apparatus are provided for enabling an operator to provide pre-recorded information to a customer in an interactive manner. The methods and apparatus utilize an audio storage medium which contains one or more audio information segments that can be accessed and played by an audio device without playing any of the other audio information segments. The audio device is coupled directly to the telephone network via interface circuitry which, among other things, matches the impedance of the audio output of the device to the impedance of the telephone network. Once a telephone call has been established between the operator and the customer, if the customer desires more information, the operator utilizes the audio device to select the appropriate audio information segment from the audio storage medium. It is important to note that when the operator plays the selected segment, both the operator and the customer remain listening.

Abstract: Disclosed is a device for providing an interface between a customer and a combined telecommunications and cable TV network. The device includes a bottom portion including cable TV interdiction equipment which is connected through the top portion by a coaxial jumper cable. The top and bottom portions are mounted so as to prevent access to the interdiction equipment by the customer.

Abstract: A line conditioner system is provided for use with an in-line wire terminating base for terminating a plurality of telephone line pairs. The line conditioner system includes an electrical grounding, earthing bar and an integral module for conditioning a single telephone line pair. The electrical grounding, earthing bar extends along the length of the in-line wire terminating base and includes a pair of electrical grounding terminals received in electrical and mechanical contact engagement with an electrical grounding member of the in-line wire terminating base. The electrical grounding, earthing bar includes an elongated straight plate portion extending between the pair of electrical grounding terminals. The electrical grounding earthing bar is configured for easy assemble, manufacture and cleanability. The integral module includes a printed wiring board carrying protection circuitry for conditioning the single telephone line pair.

Abstract: An overvoltage protection apparatus is used with a pair of telephone or communications TIP/A and RING/B lines including voltage clamping circuitry for clamping voltage signals on the lines at a predetermined voltage potential. The voltage clamping circuitry includes a pair of voltage clamping devices connected in series between the TIP/A and RING/B lines and a third voltage clamping device connected between a junction connection of the pair of the voltage clamping devices and a ground potential connection and current limiting devices for limiting current flow in the lines. The predetermined voltage potential exceeds a primary alternating current (AC) power line peak value by a set tolerance value.

Abstract: An apparatus interfaces with a subscriber line interface circuit (1) and protects the interface circuit (1) against overvoltages exceeding a supply voltage source supplied to the subscriber line interface circuit. The apparatus includes first and second diodes (DA1, DB1) having respective anodes connected to first and second input wires (A, B). The cathodes of the first and second diodes are connected to a positive terminal of the supply voltage source. The apparatus further includes third and fourth diodes (DA2, DB2) having cathodes connected the first and second input wires (A, B). The anodes of the third and fourth diodes are connected to a cathode of a thyristor (TAB). The anode of the thyristor, in turn, is connected to the positive terminal of the supply voltage source, and the gate the thyristor is connected to a negative terminal of the supply voltage source.

Abstract: An adaptive signal processing device employed in a hand-portable telephone configured to adaptively estimate signal transfer characteristics in a transmission system and process signals based upon such estimation includes a power calculating unit, a filter coefficient updating unit, an arithmetic-logical unit and an echo removing unit. The power calculating unit calculates the power of a first input signal x(n) entering the device via a transmission system. The filter coefficient updating unit calculates a filter coefficient h(n+1)(i) updated at time n+1 based upon the first input signal x(n), a signal e(n) corresponding to a second input signal d(n) to be transmitted over the transmission system less a pseudo-echo component, a signal 2.sup.Pe outputted by the power calculating unit, a control constant a and a filter coefficient h(n)(i) at time n, in accordance with an equationh.sub.(n+1) (i)=h.sub.(n) (i)+.alpha.(e(n).times.(n-i))2.sup.

Abstract: A method and circuit for loopback testing a telephone subscriber line interface circuit (SLIC) includes current sources connected to each of tip and ring circuits from which switch-hook is detected in the SLIC. A loopback test of the SLIC is conducted when the telephone is on-hook and is successful when the current from the current sources simulates a switch-hook detection, The current sources may also be used during on-hook transmission. A ground key detect circuit in the SLIC may be used to verify a successful loopback test by using current from the current sources in the ground key detect circuit to check for a grounded ring circuit in the SLIC.

Abstract: Resistive circuits are provided at the tip and ring of the battery feed circuit as a method of alleviating the need for bulky DC transformers or complex integrated circuitry. The voltage is monitored through a set of comparators eliminating the expense of maintaining fused resistors. The voltages for voice or data transmission is amplified prior to being transmitted. Received signals are AC coupled, with proper biasing, onto the tip and ring lines. Any AC noise on the tip and ring line is shifted 180 degrees out of phase and re-inserted on the line to cancel the noise. As an enhancement to the battery feed circuit, another voltage comparator is added to check the line for DC current signifying an off hook condition.

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

Abstract: A system and method of remotely recording a telephone message at a selected recording device connected to a telephone receiver by an RF link may include a base station having an RF transmitter connected to a telephone receiver, and plural paging/recording devices, each with an RF receiver and a message recorder. The paging/recording devices may be contained within suitable children's toys. A caller calls the telephone receiver and when the telephone connection has been made provides a first code signal to the telephone receiver to gain access to the RF transmitter, and then provides a second code signal to identify a particular paging/recording device that is to receive and record the message.

Abstract: Method and apparatus for interfacing a peripheral to a local area network with an interactive network board connected to the peripheral via a bi-directional peripheral interface and connectable to the local area network via a local area network interface. The interactive network board executes an access management program such as a socket server to monitor the local area network for communications from a network client directed to a proprietary socket. In response to communications detected by the access management program, the access management program establishes direct communication between the network client and itself and executes commands requested by the network client, such as commands to obtain or to alter the status of the network peripheral, or commands to obtain or to alter the status of the interactive network board itself. The interactive network board may also execute a peripheral server program such as a print server in a multitasking environment with the access management program.

Abstract: An electromagnetic interference by-pass filtering mechanism suppresses RF noise currents conducted over the tip and ring leads of a telephone line-powered telephone instrument. Such RF noise currents may result from amplitude modulated radio broadcast signals emanating in the vicinity of the telephone instrument. The filtering mechanism comprises a conductive material coated on the interior surface of the housing of the telephone instrument, so as to surround the printed circuit board containing the telephone circuitry of the instrument. The conductive material is coupled to earth. First and second capacitors are coupled between the tip and ring leads and the conductive material, and first and second inductors are coupled in series with the tip and ring conductors and connections of the tip and ring conductors to the printed circuit board containing the telephone circuitry.

Abstract: A power cross detection circuit that detects a power cross condition on the ring and tip lines of a telephone system. The power cross detection circuit senses a loop current flowing across a ring feed resistor, as well as a loop voltage at a first node and a second node at opposite ends of the ring feed resistor. Based on these sensed values, a threshold voltage for detecting a power cross condition can be adjusted to detect the power cross condition at a lower voltage value.

Abstract: A power-cross detection circuit includes a zero crossing detection circuit for detecting a first zero crossing of the current from a first positive half-cycle to a first negative half-cycle, a second zero crossing of the current from a second positive half-cycle to a second negative half-cycle, and a third zero crossing of the current from a third positive half-cycle to a third negative half-cycle and a circuit for detecting a voltage level and outputting a first signal when the voltage level exceeds a predetermined voltage level, between the first zero crossing and the second zero crossing and between the second zero crossing and the third zero crossing. The zero crossing detection circuit outputs a second signal based on the first, second and third zero crossings.

Abstract: An apparatus for determining a power cross condition during a ringing state of a telephone. The apparatus also is capable of distinguishing a true power cross condition from a short loop ringing condition, by including a first path for receiving a signal indicative of a voltage across a ring feed resistor exceeding a predetermined value, and determining if that voltage is in an active state for a predetermined amount of time (i.e., 14 milliseconds). The apparatus also includes a second path for receiving a first and second current that flow respectively across a first and second sense resistor connected to opposite ends of the ring feed resistor. On the second path, the first and second currents are subtracted, converted to a digital value, filtered, and compared to a threshold value to determine if a ring trip has occurred. If so, the potential ring trip is sent to a persistence timer circuit, for checking if it is in an active state for a predetermined amount of time (i.e., 104 milliseconds).

Abstract: A telephone line power strip-off circuit includes a low loss polarity guard sub-circuit, a low loss line seize sub-circuit, a low loss speech transformer sub-circuit and a high efficiency switched mode power supply which has an output voltage less than the input voltage, arranged to recover 80% approximately of the power presented to the terminals of the phone.

Abstract: Combination telephone network interface apparatus for interconnecting an incoming telephone lines to a telephone subscriber premises line and cable television module mounted to the telephone network interface apparatus and for connecting incoming cable television signals to a television set or sets of the telephone company subscriber(s). Cable television module embodiments, per se, for being mounted to telephone network interface apparatus and for connecting incoming cable television signals to the aforementioned television sets.

Abstract: A telephone answering device with a direct telephone line connection eliminates the need for a transformer, optoisolators and relays that are normally used in telephone answering devices to isolate the telephone answering device system from the central office circuit. Isolation is instead achieved directly at the exposed metal points of the system by physical isolation, switched isolation, resistive isolation and dielectric isolation.

Abstract: Combination apparatus for connecting one or more incoming telephone company lines to one or more telephone subscriber premises lines and for connecting incoming coaxial cable signals such as incoming cable television signals to a receiver of such signals such as a television set, and a coaxial cable module which may be embodied as a cable television module for being mounted to telephone network interface apparatus and for connecting incoming cable television signals to a television set.

Abstract: Device for limiting the working voltage for mechanical switches in telephony includes terminals for connection to a telephone line, a connection and power supply branch for a control circuit extending from a first terminal, the branch having a first switch, the cathode terminal of a first Zener diode and the source terminal of a first MOSFET transistor being connected to the output terminal of the first switch, the gate terminal of the first MOSFET transistor being connected, through the anode terminal of the Zener diode, to the first terminal. The current absorbed by the device may be adjusted.

Abstract: Cable television module and combination cable television module and telephone network interface apparatus including a pair of coaxial cable connectors at least one of which disposed angularly with respect to each other to facilitate connection with coaxial cables entering the telephone network interface apparatus and connected to one or more television sets of a telephone subscriber whose subscriber line is connected to an incoming telephone line through the telephone network interface apparatus.

Abstract: A subscriber module (40) for a network interface device (10) having a jack (100) defining a plug-receiving cavity (102) thereinto, and having a plug (50) insertable into the jack. The plug includes a plurality of interconnecting contacts (56) disposed at a mating end (58) thereof, and the jack includes first and second contacts (106,112) secured within the plug-receiving cavity in spaced-apart disconnected pairs. Insertion of plug (50) into jack (100) moves interconnecting contacts (56) between associated ones of first and second contacts (106,112) to electrically interconnect them, completing otherwise unconnected circuits between the distribution cable and the subscriber premise wiring. Preferably plug (50) includes a sealing member (74) therearound to seal the mating interface when plug (50) is inserted into jack (100).

Abstract: Combination apparatus for connecting one or more incoming telephone company lines to one or more telephone subscriber premises lines and for connecting incoming cable television signals to a television set.

Abstract: Combination apparatus for connecting one or more incoming telephone company lines to one or more telephone subscriber premises lines and for connecting incoming coaxial cable signals such as incoming cable television signals to a receiver of such signals such as a television set, and a coaxial cable module which may be embodied as a cable television module for being mounted to telephone network interface apparatus and for connecting incoming cable television signals to a television set.

Abstract: A CPE such as an ISDN telephone subset or multimedia equipment includes an interface recognition unit that connects to the network interface and adapts itself to allow the CPE to be used with standard ISDN interfaces and an analog interface. The interface recognition unit includes an interface recognition switch (IRS) that performs two functions. First, the IRS protects the CPE from damage in those instances where a non-standard network interface is connected to the CPE. Second, for standard interfaces, it identifies the type of network interface and routes the incoming signals appropriately. Specifically, if the IRS detects a T interface, the incoming signals are switched directly to a T interface circuit for controlling and powering the higher functions of the CPE. If the IRS detects a U interface, incoming signals are automatically switched to a U interface circuit for controlling and powering the CPE.

Abstract: An improved isolation circuit for protecting data communication equipment from high voltages on a transmission line has two mixers. The first dual balanced mixer (DBMX) translates a data signal on the transmission line to a high frequency and is coupled with an isolation circuit to the second DBMX. The second DBMX then translates the output of the first DBMX to an isolated data signal with the same frequency content as the original data signal.

Abstract: The invention relates to a switching device comprising at least one feeding circuit provided for DC power supply to at least one subscriber's terminal unit. The feeding circuit is especially provided for digital subscribers' terminal units. The invention furthermore relates to the feeding circuit used. There is proposed to provide a first and a second limiting circuit. The first limiting circuit comprises a first series combination of a first supply transistor arrangement and a first supply resistor arrangement to limit a supply current flowing through the first series combination. The second limiting circuit comprises a second series combination of a second supply transistor arrangement and a second supply resistor arrangement to limit a supply current (Is) flowing through the second series combination. A potential (V0) present on the control input of the second supply transistor arrangement depends on the voltage (Ur) present on the first series combination.

Abstract: Disclosed is a network interface unit which comprises a multilayer modular design. The upper layer includes an array of customer bridges. The lower layer includes a splice chamber and a protector panel. The splice chamber includes openings which permit a plurality of units to be stacked. The upper layer is removably mounted to the lower layer so it can be used with existing building entrance protectors which have no interface section.