FR2913165A1 - Low frequency signals reinjecting device for wired local loop framework, has low pass filter connected to transmission line, and protection circuit connected to filter and foreign exchange subscriber port of modem - Google Patents

Abstract

The device (DR) has a low pass filter (FPB) connected to a transmission line (LT) and passing low frequency signals, where the device is connected to a personal digital subscriber port and a foreign exchange subscriber port of a modem for high and low frequency signals, respectively. An electrical protection circuit (P3) is connected to the filter and the foreign exchange subscriber port. The circuit includes a loop detector connected between the filter and an electrical insulation unit for detecting closing and opening of current loop in the transmission line.

Description

Device for reinjecting signals at low frequencies between a modem

  The present invention relates to a device for reinjecting signals at low frequencies between a user's modem and a private telephone installation of the user. The invention is in the context of a wired local loop that does not support low-frequency signal switched telephone service. This local loop is designated by the terms telecommunications line. This telecommunications line is connected to the internet via a telecommunications network. Thus, this telecommunications line carries only high frequency signals of the DSL ("Digital Subscriber Fine") type between the modem and the telecommunications network. The modem receives and transmits packets via the high frequency signals. In addition to data packets intended for a personal computer of the user, packets are particularly related to voice over IP (VoIP: "Voice over Internet Protocol" in English) and correspond to the signaling and voice of the user. incoming and outgoing calls between a telephone terminal of the private telephone installation of the user and a terminal of a remote user. The packets received by the modem are decompressed and converted into analog low frequency signals transmitted to the user's terminal. Conversely, analog low frequency signals from the user's terminal are digitized and packaged by the modem and transmitted by the

  telecommunications and telecommunications network to the terminal of the remote user.

  As shown in FIG. 1, the modem offers the user a PDSL port for the high frequency signals supporting packets, a PFXS (FXS: "Foreign eXchange Subscriber") port for low frequency signals enabling access the Voice over IP service and Universal Serial Bus (USB) serial bus port for connection to the PC. The PDSL port is directly connected to a female T-phone wall socket PT a so as to receive and transmit the high frequency signals through the telecommunications line LT. The PFXS port is connected to the telephone wall socket PTa via a low-pass filter FBa so as to exchange the low-frequency signaling and voice signals with TT telephone terminals of the ITP private telephone system. . Each TT telephone terminal in the private telephone system is connected through a low-pass filter FB to a telephone wall jack PT connected to the telecommunications line LT. Low pass filters are used to prevent high frequency signals from degrading the quality of service at the telephone terminals. In practice, the PDSL and PFXS ports are connected to the low-pass filter FBa and the telephone jack PTa through a two-pair CRa telephone wire reinjection cable. Such a modem connection allows the user to receive VoIP over any TT terminal in his installation.

  However, this connection of the modem has major disadvantages in terms of electrical safety of the user.

  By connecting the CRa feedback cable to the PTa telephone wall jack on the one hand, and the PDSL and PFXS ports of the MD modem on the other hand, the PFXS port for low frequency signals is connected not only to the entire installation. telephone of the user, but also to the telecommunications network. However, the telecommunications network, like all metallic wired networks, is subject to electrical and / or electromagnetic disturbances carried by the LT line conductors that may originate from a fault in the electrical network or from overvoltages induced by the stormy activity. The PDSL port for high frequency signals, which is connected to the telecommunications network, is designed to withstand these electrical and / or electromagnetic disturbances while guaranteeing relative electrical safety for users and electronic equipment such as a personal computer PC connected to the MD modem. The PDSL port is TRT-3 type for Telecommunications Network Circuits capable of withstanding overvoltages up to a peak value of approximately 1500 volts. On the other hand, the modem's PFXS port is of the TRT-2 type for Telecommunications Network Circuits and is not designed to withstand the electrical and / or electromagnetic disturbances mentioned above. Thus, the PFXS port does not guarantee the electrical safety of the user and the protection of the electronic equipment connected to the modem. In

  Especially in the modem, no galvanic isolation is provided between the PFXS port and the USB port. In case of electrical and / or electromagnetic disturbances, electrical continuity is created between these two ports. For example, when an electrical and / or electromagnetic disturbance occurs, an overvoltage in the telecommunications network propagates through the modem and into the patch cord of electronic equipment, such as the personal computer PC, connected to the port USB and held by the hand of the user. If the user is connected by his other hand to the earth of his premises for example through the metal housing of the computer, a water pipe or a heating pipe, he incurs serious risks of electrification or even electrocution since the electrical disturbance will seek to flow to the earth through its body. In addition, electronic components in the modem will be damaged or destroyed.

  To overcome these drawbacks, the invention proposes a device for reinjecting signals at low frequencies from a modem into a private telephone installation of a user connected to a telecommunications line supporting signals at high frequencies, said device being able to be connected to a first port of the modem for the high frequency signals and a second port of the modem for the low frequency signals and comprising a filter adapted to be connected to the telecommunications line and passing the signals at low frequencies. The device is characterized in that it comprises a first means

  electrical protection connected to the filter and able to be connected to the second port of the modem. In the reinjection device according to the invention, the first electrical protection means is external to the modem and provides both the reinjection of signals at low frequencies relating to the signaling and the voice to benefit from the service of voice over IP ( VoIP), while guaranteeing against electric and / or electromagnetic disturbances the electrical protection of the modem and the equipment connected to it as well as the electrical safety of the user when he is in contact with the modem or one of the equipment. The filter connected to the telecommunication line separates the low frequency signals from the high frequency signals by passing the low frequency signals to the modem through the first electrical protection means.

  The reinjection device according to the invention is provided so as not to disturb the transmission of signals at low frequencies from telephone terminals of the private telephone installation of the user to the second port of the modem, and conversely the transmission of signals at low frequencies. frequencies from the second port of the modem to the telephone terminals. In particular, the first electrical protection means passes the various signaling signals during the establishment of an incoming or outgoing call, while ensuring the electrical protection of the second port of the modem. In this regard, the first electrical protection means may comprise an electrical isolation means, a loop detector connected between the filter and the electrical insulation means for

  detecting closure and current loop opening in the telecommunication line, a generator controlled by the loop detector through the electrical isolation means for generating and removing a DC current in the second port of the modem in response respectively to the closing and opening current loop, a signaling detector for detecting low frequency signaling signals transmitted by the second port of the modem, and a signaling generator connected between the electrical isolation means and the filter and controlled by the signaling detector for generating low frequency signaling signals in the telecommunications line to the private telephone system of the user. Depending on the degree of electrical insulation desired and the cost of the device, the electrical isolation means may comprise at least one electrical transformer, and / or an optocoupler, and / or an optical fiber. As will be seen in the following description, the reinjection device of the invention may comprise a second electrical protection means to be interconnected between an electrical network and an electrical outlet of the modem to electrically protect the modem and the device from the electrical network, and third electrical protection means to be interconnected to the first port of the modem and to the telecommunications line. These last two protection means improve the protection of the modem when electrical and / or electromagnetic disturbances propagate in the electrical network to which the device is connected.

  the invention for powering the modem, or in the telecommunications line through the first port for high frequency signals. The reinjection device may advantageously be in the form of a compact housing. The housing may have faces supporting complementary electrical outlets connected to the second electrical protection means and to connect to the electrical network and the modem.

  In order to facilitate the connections of the device, the box has ports to connect to the telecommunications line and the first and second ports of the modem and accessible on a housing edge.

  Other features and advantages of the present invention will appear more clearly on reading the following description of several embodiments of the invention given as non-limiting examples, with reference to the corresponding appended drawings in which: FIG. a schematic block diagram of a modem with a reinjection cable in a telephone system according to the prior art already commented; FIG. 2 is a schematic block diagram of a signal re-injection device at low frequencies interconnected to a telephone installation and to a modem according to the invention; FIG. 3 is a block diagram of a protection circuit for signals at low frequencies in the feedback device.

  Referring to FIG. 2, a reinjection device DR according to the invention is interconnected between a user telecommunications line LT and

  an MD modem of the ITP private telephone system in the premises of a user. The telephone installation comprises, for example, four female T-jacks of which a PTd is connected to a LIN port of the feedback device by a 2-wire CDSL cable. For example, two PT telephone jacks are connected to TT telephone terminals through low-pass filters FB. The telecommunications line LT conventionally comprises a pair of wires for transmitting high frequency signals of the DSL type, in particular ADSL signals ("Asymmetric Digital Subscriber Fine") in the context of a wired local loop that does not support switched telephone service with low frequency signals. The high frequency signals support packets exchanged between the MD modem and a digital subscriber line access multiplexer (DSLAM) connected to the Internet in a telephone exchange connected to the line LT. Typically, the band of high frequency signals is between at least ten kilohertz and at least one megahertz and is separated from the band of low-frequency signals below about 4 kHz.

  The reinjection device DR is in the form of a small housing made of insulating material, such as plastic material, comprising three LIN, LOU 'and LFXS ports for pairs of telecommunication line wires and a two-hole F1 female electrical socket. and a ground pin and a two-pin M2 male electrical outlet and a grounding hole. The ports LOU 'and LFXS are respectively connected to a PDSL port of the modem for signals to

  high frequencies supporting packets and a PFXS port of the modem for low frequency signals including voice support through a 4-wire CR reinjection cable.

  For example, the housing comprises two half-shells hinged by a plastic hinge and contains all the electrical protection circuits P1, P2, P3 and other electrical and electronic components of the device DR. Rear faces FR and front FV of the housing respectively support the female complementary electrical outlets F1 and M2 male which are superimposed coaxially on either side of the electrical protection circuit P1. Each electrical socket F1, M2 is molded with a respective half-shell of the housing. The LIN, LOU 'and LFXS ports are female RJ-type jacks made in an upper edge CS of the case for plugging in respectively a male plug of the RJ type of the CDSL cable and two male plugs of the RJ type of the CR feedback cable.

  The F1 female electrical outlet is connected to an M1 male electrical outlet at the end of an MD Modem AC power cord. The male electrical plug M2 is connected to a female electrical socket of the electrical network RE in the premises of the user. The F1 and M2 electrical outlets have the earth which makes the flow of electrical and electromagnetic disturbances through the modem more efficient.

  The feedback device DR comprises three protection circuits P1, P2 and P3 and a low-pass filter FPB.

  The protection circuit P1 is interconnected to the electrical female F1 and male M2. It electrically protects the MD modem and the user and the other circuits included in the DR re-injection device against electrical and / or electromagnetic disturbances from the electrical network RE. For example, the protection circuit P1 comprises in a single component three surge protectors, such as varistors or surge arresters, two of which between the phase and the earth and between the neutral and earth provide a common mode of protection and one between the phase and the neutral provides protection in differential mode. The protection circuit P2 is connected between the LIN line port and the LOU 'port of the feedback device. The LOU 'port is plugged into an RJ-type plug at the end of the two wires in the CR cable connected to the PDSL port of the MD modem to bi-directionally pass the high-frequency signals carrying the packets. The PDSL port is TRT-3 type for Telecommunications Network Circuits capable of withstanding overvoltages up to a peak value of approximately 1500 volts. The P2 circuit completes the electrical protection of the modem's PDSL port by protecting the user and the modem against electrical and / or electromagnetic disturbances propagating in one or both wires of the telecommunications line LT and likely to penetrate the cable. modem. For example, the circuit P2 comprises a three-pole surge arrester comprising three elementary surge arresters, or varistors or clipping diodes, two of which are connected between the line wires and the earth and provide protection in common mode and another is connected between the

  line wires and provides protection in differential mode.

  The protection circuit P3 is connected through the low-pass filter FPB to the LIN port connected to the CDSL cable and to the second pair of low-frequency signal wires in the CR feedback cable between the LFXS and PFXS ports. The low-pass filter FPB is identical to the low-pass filters FB in the telephone system and bi-directionally passes the signals at low frequencies of telephone signaling and voice. The modem's PFXS port is of the TRT-2 type for Telecommunications Network Circuits and is not able to withstand surges due to electrical and / or electromagnetic disturbances from the LT telecommunication line, unlike the PDSL port. The protection circuit P3 guarantees the safety of the user and the modem against these overvoltages in particular and more generally against electrical and / or electromagnetic disturbances propagating along the telecommunications line LT.

  As shown in FIG. 3, the protection circuit P3 comprises on the telecommunications line side LT a current loop closure and opening detector DBO and a call signal generator GSA, on the modem side a generator of GCL line current and a DSA call signal detector, an electrical isolation circuit IE between its circuit pairs, and a DC voltage source STC. The BOD detector and the GSA generator form a set of interconnected circuits at the FPB low-pass filter and the isolation circuit

  Electric IE. The GCL generator and the DSA call signal detector form a set of interconnected circuits to the IE electrical isolation circuit and the modem's PFXS port through the CR cable.

  The electrical isolation circuit IE ensures the safety of the user and the protection of the modem when electrical and / or electromagnetic disturbances propagate in the telecommunication line LT especially while signals at low signaling frequencies and relative voices an incoming or outgoing call is carried between one of the TT terminals and the modem MD, the latter exchanging packets corresponding to the call with a terminal of another remote user via the port of high frequency signals PDSL and the LT line. The IE circuit has a bandwidth greater than the voice frequency band and may include one or more electrical transformers, and / or one or more optocouplers, and / or one or more optical fibers. The DC voltage source STC is connected to the electrical network RE through the protection circuit P1 to permanently supply a DC voltage, for example 48 volts, to the DBO and GSA circuits and therefore to the installation example, the source LT telecommunications line and ITP private telephone line. By continuous voltage includes a rectifier. BOD detects a transformer loop closure and the current detector in the line when taking the handset of a telecommunication terminal LT line by TT telephone stall in the ITP installation and a current loop opening in the line during the release of the line by hanging up the terminal handset

  telephone. For example, during an outgoing call, the closing and opening of the current loop activates and deactivates a relay in the detector BOD so as to transmit without galvanic contact through the isolation circuit IE a control signal controlling a contact in the GCL line generator which generates a DC current in the two wires between the LFXS and PFXS ports in response to the current loop closure and suppresses the DC current in response to the current loop opening. Between a closure and a current loop opening, the BOD detector and the GCL generator allow bidirectional transmission of signaling signals and voice signals at low frequencies during the outgoing call. The signaling signals include a dial-up signal, DTMF (Dual Tone Multiple Frequency) and a ringback signal. The IE circuit ensures the electrical insulation of the modem and the user with respect to any electrical and / or electromagnetic disturbances originating from the telecommunications line during the outgoing call.

  The detector DSA detects signaling signals at low frequencies such as a timed call signal transmitted by the modem's PFXS port which has interpreted packets transmitted by the telecommunications line LT through the PDSL port at the beginning of an incoming call requested by a remote terminal. For example, a relay in the detector DSA is activated in response to the clocked call signal so as to transmit without galvanic contact a control signal to the generator GSA through the isolation circuit IE. The GSA generator generates

  then a timed call signal, also called ringing signal, in the telecommunications line LT through the low-pass filter FPB to the private telephone system ITP to ring TT telephone terminals and therefore any terminal phone of the ITP installation. The clocked call signal is for example an alternating signal whose frequency of 50 or 60 Hz is established from that of the electrical network RE through the voltage source STC. The circuit IE ensures the electrical insulation of the modem and the user with respect to any electrical and / or electromagnetic disturbances coming from the telecommunications line during the incoming call.

  Likewise, the DSA detector and the GSA generator return the call return signal to the ITP installation through the isolation circuit IE during the phase of establishing an outgoing call.

Claims (9)

  1 - Device (DR) for reinjecting signals at low frequencies from a modem (MD) in a private telephone system (ITP) of a user connected to a telecommunications line (LT) supporting high frequency signals, said device being capable of being connected to a first port (PDSL) of the modem for high frequency signals and a second port (PFXS) of the modem for signals at low frequencies and comprising a filter (FPB) adapted to be connected to the telecommunications line and passing the signals at low frequencies, characterized in that it comprises a first electrical protection means (P3) connected to the filter (FPB) and adapted to be connected to the second port (PFXS) of the modem.   2 - Device according to claim 1, wherein the first electrical protection means (P3) comprises an electrical insulation means (IE), a loop detector (DBO) connected between the filter (FPB) and the means of electrical insulation for detecting a current loop closure and opening in the telecommunication line (LT), a generator (GCL) controlled by the loop detector through the electrical isolation means for generating and suppressing a DC current in the second port (PFXS) of the modem in response to closing and opening of current loop respectively, a signaling detector (DSA) for detecting low frequency signaling signals transmitted by the second port (PFXS) of the modem, and a signaling generator (GSA) connected between the electrical isolation means and the filter (FPB) and controlled by the signaling detector to generate signaling signals at low frequencies equations in the telecommunications line (LT) to the telephone installation (ITP).   3 - Device according to claim 2, wherein the electrical insulation means (IE) comprises an electrical transformer, and / or an optocoupler, and / or an optical fiber.   4 - Device according to any one of claims 1 to 3, comprising a second electrical protection means (P1) to be interconnected between an electrical network (RE) and an electrical outlet (M1) of the modem (MD) to electrically protect the modem (MD) and the device (DR) in relation to the power grid.   5 - Device according to claim 2 or 3 and claim 4, comprising a means (STC) adapted to be connected to the electrical network (RE) through the second electrical protection means (P1) to provide a DC voltage to the detector loop (BOD) and the signaling generator (GSA) and the telecommunications line (LT).   6 - Device according to claim 4 or 5, comprising a housing having faces (FR, FV) supporting complementary electrical outlets (F1, M2) connected to the second electrical protection means (P1) and to connect to the electrical network (RE ) and the modem (MD).   7 - Device according to claim 6, wherein the housing has a edge (CS) for ports (LIN, LOUT, LFXS) to connect to the telecommunications line (LT) and the first and second ports (PDSL, PFXS) the modem (MD).   8 - Device according to any one of claims 1 to 7, comprising a third electrical protection means (P2) to be interconnected to the first port (PDSL) of the modem and to the telecommunications line (LT).   9 - Device according to claim 8, wherein the second electrical protection means (P2) comprises a tripolar arrester.