WO2002049333A1

WO2002049333A1 - Isolator device for adsl line

Info

Publication number: WO2002049333A1
Application number: PCT/FR2001/003866
Authority: WO
Inventors: Alain Rahyer; Alain Bencivengo; Vincent Durel
Original assignee: France Telecom
Priority date: 2000-12-14
Filing date: 2001-12-07
Publication date: 2002-06-20
Also published as: FR2818477B1; AU2002217202A1; FR2818477A1

Abstract

The invention concerns an isolator device for an ADSL transparent to the line, that is the voice band and the broadband services are not affected by its insertion. Said device comprises isolating means (IS), ADSL filtering means (LPF, HPF) arranged on the telephone exchange side (AC) and means for controlling (P) said isolating means (IS) to connect or disconnect the line filtering means in accordance respectively with a first operating mode which corresponds to normal operating conditions of the line, that is digital and analog transmission of signals or a second operating mode of the line which corresponds to test measurements.

Description

ISOLATOR DEVICE FOR ADSL LINE.

The invention relates to an isolating device for ADSL line and more generally xDSL (from the acronym Digital Subscriber Line). The invention applies to analog links comprising equipment to provide, in addition to narrowband services (analog or digital telephony), broadband services based on xDSL technologies.

Broadband service means any service transmitted in a spectral band located above narrowband services (ie telephony or ISDN) or in practice at frequencies above 10 KHZ. Typically these are the services delivered by the xDSL network.

Broadband is generally referred to as broadband services grouping together all the technological families such as SDSL, ADSL, ADSL-lite.

In the following, we will speak of ADSL services for simplicity, it being understood that the invention applies to all the services mentioned above. In general, a telephone operator uses measurement robots in its exchanges for needs related to the supervision of its lines, when a fault is observed on the line. A robot uses two types of measures to allow location, these measures are as follows:

The so-called “open” measurement which allows a frank location and which is based on the calculation of the effective capacity of the line: effective •

“Insulation and loop” fault measurements. to perform these, the robot performs insulation and R loop resistance measurements.

Fault location measurements by ultrasound. Thereafter, two operating modes are considered: 1. transmission mode: the robot is unused and the filtering means are connected, the line is in normal situation and allows the transmission of analog and digital signals. 2. Measurement mode: the robot performs one or more measurements on the line in question. In this case, it will be seen that according to the invention, the filtering means are disconnected. Remember that the deployment of technology

ADSL involves the implementation of band splitter filters (also known as “splitter”) on the telephone center side and at the user's site in order to multiplex and separate so-called “analog” signals from those linked to broadband services (ADSL ). These “Splitters” generally include a low-pass filter referenced

LPF in the following, and a “Y” structure as shown in FIG. 1. A high-pass filter referenced HPF is generally positioned directly on the electronic card enabling ADSL services to be provided.

In the current state of knowledge, the ADSL filters placed on the central side and available on the market are not transparent to the test measurement tools used to date.

On the other hand, even if they were transparent to these signals, the presence of the high-pass filter positioned in the ATU-C, ADSL card of the exchange would disturb the value of the measurements made and consequently their interpretation would be incorrect.

The development of ADSL technology has the consequence of making impossible on the lines concerned, any subsequent maintenance procedures or localization of faults as they are implemented by current test robots.

The invention relates to a device which makes compatible the implementation of ADSL or XDSL filters on the central side and the use of current measurement robots. This solution allows in particular when the measurement mode is activated for a line considered for testing purposes, not to have to modify the current testing tools to make them compatible with ADSL filters. The device developed by the depositor allows the filters to be completely transparent to these tools, that is to say on the one hand transparent to the signals transmitted and on the other hand not modifying the measured values. With this device, the interpretation of the measurements therefore remains similar, whether the line is equipped with a ADSL filter (placed on the terminal side) or not. The only exception, the measurement of loop resistances requires that the line is terminated by a non-zero resistance. The result of the measurement must therefore take into account its value.

The invention relates more particularly to an ADSL line isolator device transparent to the line, that is to say that the voice band as well as the broadband services are not affected by its insertion; this device comprises isolation means, ADSL filtering means arranged on the telephone exchange side and means for controlling said isolation means for connecting or disconnecting the line filtering means according respectively to a first or a second operating mode of the line.

According to another characteristic of the invention, the control means comprise: two output terminals respectively connected to the wires of the line upstream of the filtering means, means for detecting the first and second operating mode of the line and, means for controlling the connection or disconnection of filters, activated by these detection means.

According to another characteristic of the invention, the operating mode detection means comprise a circuit for charging and discharging a capacitor from the supply voltage of the line, said circuit being intended to supply a control voltage isolation means; the device consuming only during the second operating mode of the line, that is to say during the test measurements (charging and discharging of the capacitor). According to a preferred embodiment, the charging and discharging circuit of a capacitor comprises said capacitor connected in series with at least one relay and a first and second transistor to supply said control voltage. The charging and discharging circuit of the capacitor further comprises respective bias circuits for the first and the second transistor.

According to another characteristic of the invention, the isolation means comprise a plurality of contacts placed on the line wires to connect or disconnect the filters while ensuring the continuity of said line.

The first and second transistors are connected so as to allow, depending on their on or blocked state, to open and close the contacts placed on the line.

According to a preferred embodiment, the connection means, disconnection of the ADSL filtering means comprise a diode bridge making it possible to polarize said means to make them independent of the polarization of the line.

According to one embodiment, the ADSL filtering means comprise at least one low-pass filter and at least one high-pass filter connected to the wires of the line. According to the invention, the device is connected on the telephone exchange side, upstream of a test robot, the first operating mode corresponds to the normal operation of the line so as to ensure analog and digital transmission, the second operating mode is a mode corresponding to test measurements made on the line by the robot; the device disconnecting the filtering means from the line and thus making them transparent to the test robot, that is to say on the one hand transparent to the signals emitted by the robot and on the other hand not modifying the measured values.

Other features and advantages of the invention will appear on reading the description given below and with reference to the appended drawings in which: FIG. 1 represents the block diagram of an ADSL filtering system placed on an ADSL line on the side telephone center ; - Figure 2 shows the diagram of the isolation device according to the invention;

FIG. 3 represents the detailed diagram of the device according to the invention; FIGS. 4A and 4B represent the functional diagram of charging and discharging of the capacity

Cr. The device according to the invention makes it possible, according to the operating mode of an ADSL line, to isolate the ADSL filters while ensuring the continuity of the line. The device allows, when the test robot is activated, to control the insulation of the LPF / HPF filters.

As can be seen in FIG. 2, the device for this includes: - an IS isolator LPF / HPF circuit: this circuit completely isolates the two filters so that the subscriber line regains its original characteristics. a piloting circuit P which makes it possible to control the LPF / HPF isolator during the measurements carried out by the test robot while being entirely transparent with respect to the latter. The device according to the invention has the following advantages: Total transparency to the tests and to the subscriber line. The voice band and broadband services are not affected by the insertion of the device.

In addition, the device consumes only when it is put into service to carry out test measurements.

The IS circuit isolating filters LPF / HPF includes, as will be seen below, several work / rest contacts actuated by a relay. These allow, during measurements of the test robot exclusively, to completely isolate the LPF and HPF filters while ensuring the continuity of the line.

The HPF filter being isolated, it is assumed that the ADSL transmission is momentarily interrupted during the measurements for a duration of approximately a few tens of seconds (typically 25 s). It is note that the test measurements disturb the ADSL system to the point of desynchronizing the modems.

The P circuit ensuring the piloting function controls the relay whose work / rest contacts constitute the LPF / HPF isolator. It includes a number of components and is fully transparent during activation of the RT robot.

The energy necessary to carry out this operation is obtained from the discharge of a so-called “reservoir” capacity, which is charged when the line is connected to the automatic switch (53V) or to the measurement robot. Indeed, before the execution of the measurements, the latter delivers a DC voltage of approximately 48V between two series of tests. When an insulation fault on a wire or between wires (loop test) is present on the line, the robot performs measurements of echometry, loop current and capacity from the central.

As has been said on an ADSL link, the presence of LPF low-pass filters and HPF high-pass filters on the central AC side does not allow certain tests to be performed (fault location and capacity measurements).

The proposed device therefore makes it possible to circumvent this problem. The principle of the device, located on the central side, is to isolate the low-pass and high-pass filters from work / rest contacts whose relays are activated only when the test robot performs measurements. For information and in general, client-side equipment (telephone, modem, filters ...) are likely to modify the intrinsic parameters of the line (line only), but do not in any way call into question the validity of the line supervision tools (test robot). On a subscriber line that does not have ADSL equipment, we find ourselves in a little the same situation insofar as the value of the capacity depends either on the connected terminal or on the RC module

(20 Ω // 2.2μF). In this configuration, the robot detects the presence of a terminal.

We will now explain in more detail the operation of the device DI by referring to the detailed diagram of FIG. 3 and of FIGS. 4A and 4B. In the proposed embodiment, the values of the components are mentioned for information. Optimizations and adjustments remain of course possible without calling into question the principle of the invention described. Charging and discharging times are also given for information.

The IS circuit isolating the LPF / HPF filters disconnects or reconnects the filters of the line as follows: - When the test robot is activated, that is to say during the execution of the measurements, the rest contacts relι ₂ , rel _2i and rel ₂₂ open and thus allow the disconnection of the low pass and high pass filters. At the same time, the working contacts rel ₂₃ and rel ₂₄ (bypass at points AB and CD) close and thereby ensure total transparency of the line.

In the absence of test measures, the line has the characteristics of an ADSL link on the local network; i.e. maintaining voice band services (ringing, Class services, etc.) and broadband services

The control circuit P detects the change in the operating mode of the line. This circuit P controls the relays Reli and Rel ₂ , the supply of these relies on the principle of a charge / discharge through the capacity Cr called "reservoir capacity".

This operation is carried out in 2 phases: - a charging phase of the "tank capacity C _r " (Figure 4A):

This phase is carried out when the line is connected to the central AC or to the RT test robot (before execution of the measurements). The capacitor C _r then charges under a voltage V _a ii _m (typically 41V) via the transistor Ti, the resistor R ₄ and the resistors of the coils Reli and Rel ₂ ; the transistor T ₂ being blocked with respect to the line remote supply (53V at open output), the voltage drop observed (12V in this arrangement) is due to the voltage V _gs of the field effect transistor Ti. The charging time of the device is approximately lmnl5s, which gives approximately a charging time constant for the assembly τ _c te τ _ps carge = 13s. - a phase of discharging the “tank capacity C _r ” (FIG. 4B):

As soon as the measurements of the test robot are executed, the DC voltage drops to 0V (absence of supply voltage) and the transistor T ₂ then turns on, Ti then being blocked. The capacity C _r is then discharged through Reli and Rel ₂ relays connected in series (the device discharge time is approximately 19s, which gives approximately a discharge time constant of the assembly τ _cte tps cha _r ge = 8.2s).

During the execution of the measurements (about 10s), the robot also sends DC voltages of 48v. The rest contact relll by opening the supply loop of the 2 transistors Ti and T ₂ (V _gs = 0) in order to avoid a new charge / discharge of the capacity C _r . It also guarantees the line insulation resistance (R _{A / B} ) •

In the embodiment described by way of example, the duration of the discharge time of the capacitor C _r is twice greater than the duration necessary to carry out the test measurements. It is possible to consider other values for the components: Reli and Rel ₂ relays (coil resistances); capacitor C _{r in} order to increase or reduce the discharge time.

We will now detail the role of the different components, specifying the values of the preferred example given. - The zener diodes: The zener diodes DZi and DZ ₂ (V _seu ii = 12V) are used to fix the gate-source voltages V _gs of the 2 field effect transistors Ti and T ₂ (reference chosen by way of example BS 250 and 2N 4191) . - Resistances Ri to R3:

They constitute the polarization bridge of the zener diodes O ^~ χ and DZ ₂ . They also have a high resistance value (> 1 MΩ). therefore, the current consumption is almost zero. - Capacities C _x and C ₂ (InF):

They play a filtering role with respect to ringing trains.

Resistor R: It is used to limit the ringing current. The value of this resistance must be between a minimum value and a maximum value (value of the assembly, R ₄ = 4.7 kΩ) because a rather high value of this resistance would increase too much the charging time of the capacitor C _r . - Reli and Rel ₂ relays:

As has been described in the operation of the device, it is they which insulate the filters of the various work / rest contacts. The selected relays (TX2 telecom series) have a nominal voltage of 24V and also have a high coil resistance (4.2 kΩ). This makes it possible to increase the discharge time of the capacity C _r .

The diode bridge at input Di to D ₄ : It is used to bias the entire control circuit P circuit ensuring the isolation of the filters during the mode operative test measurements on the line. Thus, it is not necessary to know the polarities of the line to connect it.

The device which has just been described makes it possible to keep the existing tools and measuring robots used by the operators in the same state.

The measurements and their interpretation remain intact for the qualification of subscriber lines. The device consumes only during testing of test measurements.

Reference may be made to the appended table which illustrates various measurement results carried out by a test robot in the various configurations mentioned: cases 1 to 8.

• Cases 1, 2 and 3 are given for information only and may serve as a reference. The first two correspond to an analog line without ADSL equipment and connected either to a terminal or to an RC beacon (2.2 μF in series with 22 kΩ). 3 ^rd case is that of an analog line to an ADSL modem (ATU-R + card filter) only user side for comparison (not shown). The differences observed mainly concern the capacity measurements between Ca / b // wires (C a / T + C b / T).

• Case 4 constitutes an open line reference in the absence of ADSL equipment. In this configuration, a fault is effectively noted and located by the test robot. • Case 5 shows that in the absence of the device, the test measurements are completely distorted: in particular the echometry and the capacity measurements. The robot locates a fault at 1 m (this actually corresponds to the robot / filter distance) and does not see a terminal installation.

• Case 6 demonstrates the value of the device. We find the same measurements as those corresponding to case 3 (no ATU-C).

• Case 7, device in the absence of ATU-C simply confirms its transparency with respect to the filter on the central side.

• Case 8 also makes it possible to verify that the device does not alter the detection of the open output fault measured in case 4.

B.A.E (good at tests)

Claims

1. Isolating device for ADSL line transparent to the line, ie the voice band and broadband services are not affected by its insertion; this device comprises isolation means (IS), ADSL filtering means (LPF, HPF) arranged on the telephone exchange side (AC) and control means (P) of said isolation means (IS) for connecting or disconnecting the line filtering means according to respectively a first or a second operating mode of the line.

2. An isolating device according to claim 1, characterized in that it is connected on the telephone exchange side (AC) upstream of a test robot (RT), the first operating mode corresponding to the normal operation of the line so as to ensure analog and digital transmission, the second operating mode being a test measurement mode carried out on the line by the robot, the device (DI) disconnecting the filtering means from the line and thus making them transparent to the test robot. to say on the one hand transparent to the signals emitted by the robot and on the other hand not modifying the measured values.

3. An isolating device according to claim 1 or 2, characterized in that the control means (P) comprise: two output terminals (a, b) respectively connected to the wires of the line upstream of the filtering means, detection means (Cr, Reli, Rel ₂ ) of the first and second operating mode of the line and, control means (T1, T2) for connecting or disconnecting the filters, activated by these detection means.

4. An isolating device according to claim 3, characterized in that the means for detecting the operating mode (C _r , Reli, Rel ₂ ) comprise a circuit for charging and discharging a capacitor from the supply voltage of the line, supplying a control voltage to the isolation means (IS); the device consuming only during the second operating mode, that is to say during the test measurements

(charge and discharge of capacitor C _r ).

5. An isolating device according to claim 4, characterized in that the charging and discharging circuit of a capacitor comprises said capacitor connected in series with at least one relay and a first and second transistor to supply said control voltage.

6. An isolating device according to claim 4 or 5, characterized in that the charging and discharging circuit of the capacitor comprises circuits for respective polarization for the first and the second transistor.

7. An isolating device according to any one of the preceding claims, characterized in that the isolation means comprise a plurality of contacts placed on the line wires to connect or disconnect the filters while ensuring the continuity of said line.

8. An isolating device according to claims 5 and 7, characterized in that the first and second transistors allow according to their state to open and close the contacts placed on the line.

9. An isolating device according to any one of the preceding claims, characterized in that the connection means, disconnection of the ADSL filtering means comprise a diode bridge making it possible to polarize said means to make them independent of the polarization of the line.

10. An isolating device according to any one of the preceding claims, characterized in that the ADSL filtering means comprise at least one low-pass filter and at least one high-pass filter connected to the wires of the line.