TESTING A COMMUNICATION INTERFACE CONNECTED TO AN ANALOGUE TELEPHONE LINE

Description

FIELD OF INVENTION

[0001] This disclosure relates in particular to a test method for a communication interface connected to an analog telephone line. STATE OF THE ART

[0002] A component used as a communication interface between an analog telephone network and a digital network providing access, for example, to a Voice over IP (Voice Over Internet Protocol) service is the FXS (Foreign exchange subscriber) port.

[0003] An FXS port can take both states: a state called "off-hook" when the FXS port believes it is connected via an analog telephone line to an off-hook telephone device (in other words, when the FXS port believes the analog telephone line is busy), and a state called "on-hook" when the FXS port believes it is not connected to any off-hook telephone device (in other words, when the FXS port believes the analog telephone line is not busy).

[0004] The FXS port can report itself as off-hook for various reasons: due to a malfunction of the FXS port, due to a problem connecting the FXS port to the analog telephone network, or because the analog telephone line is genuinely busy, either with a call in progress or because a user has voluntarily taken their phone off the hook to avoid being disturbed.

[0005] To discriminate between these different cases, it is known to command the FXS port to implement tests on the telephone line which are defined in the standard known to the person skilled in the art as GR-909 (the name of the specification describing the content of this standard is "GR909-CORE: Generic Criteria for Fiber in the Loop Systems").

[0006] However, these tests are not always accurate.

[0007] Other tests were proposed in documents US2009 / 034690A1 and US6438212B1, but these have the disadvantage of requiring external equipment as well as user intervention. DESCRIPTION OF THE INVENTION

[0008] One aim of the invention is to test a precise communication interface with an analog telephone network that does not require external equipment.

[0009] To this end, a test procedure for a communication interface connected to an analog telephone line comprising two electrical wires is proposed, according to a first aspect, the procedure comprising the following steps: detection of a change of state of the communication interface between an off-hook state and an on-hook state; if it is detected that the change of state is from the on-hook state to the off-hook state, collection of measurements acquired by the communication interface, the measurements relating to at least one of the following physical quantities: ∘ a voltage supplied by a converter of the communication interface, ∘ a voltage between the two electrical wires, ∘ an intensity of a loop current flowing in one of the two electrical wires, ∘ an intensity of a leakage current from one of the two electrical wires to a ground of the communication interface; verification of correspondence of the measurements with respective nominal values; if the verification reveals that all the measurements have nominal values, implementation of a process comprising the following steps: ∘ detection of a maintenance of the state of the communication interface for a predefined duration;• If it is detected that the communication interface remains in the off-hook state for the predefined duration, a supplementary test on the telephone line is ordered by the communication interface, in order to collect diagnostic data in addition to the measurements; • If the supplementary diagnostic data reveals a fault in the analog telephone network, an alarm is issued; • If the supplementary diagnostic data does not reveal a fault on the analog telephone line, the process is repeated.

[0010] The process may also include the following optional features, taken alone or in combination with each other whenever technically possible.

[0011] Optionally, the procedure includes the following steps: if verification of measurements reveals that at least one measurement among the voltage between the two electrical wires, the loop current intensity and the leakage current intensity is not nominal, ordering of the additional test on the telephone line by the communication interface, so as to obtain diagnostic data complementary to the measurements, and issuing of the alarm if the diagnostic data reveal a fault in the analog telephone network.

[0012] Optionally, the process includes the following steps: If the verification of the measurements reveals that the supplied voltage does not have a nominal value, a restart command is issued for the communication interface converter; if the verification of the supplied voltage has a nominal value, a verification of correspondence with the respective nominal values ​​of at least one measurement relating to at least one of the following physical quantities is performed: ∘ the voltage between the two electrical wires, ∘ the intensity of the loop current, ∘ the intensity of the leakage current.

[0013] Optionally, the process includes the following steps implemented if it is detected that the change of state is from the off-hook state to the on-hook state, or if the communication interface remains in the on-hook state. Collection of a voltage between the two electrical wires acquired by the communication interface; verification of the collected voltage, so as to determine if the collected voltage has a nominal value; if the voltage has a nominal value, implementation of the processing; if the voltage does not have a nominal value, access to information stored by the communication interface, the information indicating whether the communication interface has received a power supply command from the analog telephone line or not; if the information indicates that the communication interface has not received a power supply command, then command of the communication interface so that the communication interface supplies power to the analog telephone line; if the information indicates that the communication interface has received a power supply command, command to restart the converter.

[0014] Optionally, the process further includes the following steps implemented after the communication interface is ordered so that the communication interface feeds the analog telephone line: collection of new measurements acquired by the communication interface, the new measurements relating to at least one of the physical quantities; verification of correspondence of the new measurements with the respective nominal values; if the verification of correspondence of the new measurements reveals that all the new measurements have nominal values, implementation of the processing; the verification of correspondence of the new measurements reveals that at least one of the new measurements does not have a nominal value, command to restart the converter.

[0015] Optionally, the process also includes the following steps implemented after the converter restart command: repeat the steps of collecting and verifying new measurements; if the repetition of the steps of collecting and verifying new measurements reveals that all new measurements have nominal values, implement the processing; if the repetition reveals that a new measurement does not have a nominal value, command to reset the communication interface hardware.

[0016] Optionally, the procedure also includes the following steps implemented after the hardware reset command for the communication interface: second repetition of the steps of collecting and verifying new measurements; if the second repetition reveals that all new measurements have nominal values, implementation of the processing; if the second repetition reveals that a new measurement does not have a nominal value, issuance of an alarm.

[0017] Optionally, the supplementary test includes at least one test defined by the GR-909 standard.

[0018] A second aspect of this disclosure is a computer program product comprising program code instructions for executing the steps of the above process, when that program is executed by a processor.

[0019] A third aspect of this disclosure is a device, for example an internet access gateway, comprising: a communication interface suitable for connection to an analog telephone line comprising two electrical wires; a processor configured to test the communication interface using the method described above. DESCRIPTION OF THE FIGURES

[0020] Other features, purposes and advantages of the invention will become apparent from the following description, which is purely illustrative and not limiting, and which should be read in conjunction with the accompanying drawings on which: There figure 1 illustrates schematically a device 1 according to a first embodiment of the invention. figure 2 shows voltage values ​​expected to be used by an FXS port in an off-hook and on-hook state. figure 3 , there figure 4 and the figure 5 are flowcharts of steps in a process according to a method of implementation.

[0021] Across all figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION

[0022] With reference to the figure 1 ,a device 1, such as an internet gateway, includes a first communication interface 2 with an analog telephone network A, a processor 4, and a second communication interface 6 with a digital network B, for example a WAN (Wide Area Network).

[0023] In the continuation of this disclosure, we will consider a non-limiting embodiment in which the first communication interface 2 with the analog telephone network is, or includes, an FXS (Foreign exchange subscriber) port.

[0024] The FXS port is designed to be connected to an analog telephone via an analog communication line comprising two electrical wires conventionally called TIP and RING.

[0025] One function provided by the FXS port is to ensure the proper functioning of the connected analog telephone, to transmit and receive the signaling necessary for the realization of an analog communication (voltage and current supply of the telephone line, ringing signal during an incoming call, loop status).

[0026] The electrical communication line may therefore include a cable designed to be removably connected to device 1 and the analog telephone. This cable may include, for example, an RJ11 connector.

[0027] The FXS port includes a line 20 interface, or LIF, comprising two electrical contacts suitable for being electrically connected respectively to the first and second electrical wires of the analog telephone line.

[0028] The FXS port also includes a Subscriber Line Interface Circuit (SLIC). The SLIC is configured to perform certain processing tasks, such as audio conversion between an analog signal from the analog telephone and the digital network connected to the gateway. Other processing tasks (gain adjustments, transcoding, echo cancellation) can also be performed by the SLIC or by processor 4.

[0029] The FXS port also includes a converter 24 configured to power the other FXS port components (SLIC, LIF) as well as the analog communication line and any connected analog telephone. Converter 24 is a DC-DC converter, meaning it provides the analog communication line with a direct current output from a direct current input of a different intensity. The input current comes from an external power source.

[0030] The 24V converter is capable of generating different voltages depending on the operating mode of the FXS port. These voltages are, for example, higher than the gateway's general power supply voltage provided by the external source (12 Volts in France).

[0031] As is well known, an analog telephone is likely to be in an off-hook state or an on-hook state. These state names refer to the fact that an analog telephone can consist of a base and a handset including a speaker and a microphone, the handset being able to be either lifted off the base or hung up on it.

[0032] When an analog telephone is off-hook, it establishes a connection exclusively with the FXS port. The telephone receives electrical current through one of the two wires of the telephone line and retransmits this current through the other wire, thus forming a current loop. The telephone line is then conventionally said to be "busy" with the analog telephone. A dial tone indicates that the phone is off-hook. The user can then dial a phone number to establish a telephone connection with a recipient.

[0033] When the analog telephone is in the on-hook state, no communication is established with the FXS port. No current flows through the two electrical wires of the analog telephone line.

[0034] We have represented on the figure 2The voltage values ​​intended for use in the off-hook and on-hook states. These voltages are negative with respect to the FXS port ground. These voltages are as follows: GND: ground reference, Vbat: voltage supplied by the converter, Vring: voltage between the RING wire and ground, Vtip: voltage between the TIP wire and ground, Vloop: voltage between the two TIP and RING wires, VOV_GND and VOV_BAT: predefined offset voltages allowing the transmission of audio signals, Vcm: arbitrary reference voltage, equal to (Vtip+Vring) / 2.

[0035] The FXS port includes a memory configured to store various measurements related to the analog telephone line. This memory is, for example, included in the SLIC 22 circuit. These measurements include the aforementioned voltages and are shown on the figure 2 Thus, the intensity of the following currents: Iloop: intensity of the current flowing in the TIP and RING electrical wires in two opposite directions, and we will call this "loop current" in this disclosure, Ilong: intensity of a leakage current from the TIP or RING electrical wire to ground.

[0036] The FXS port includes an internal measuring device suitable for measuring the aforementioned voltages and currents, and for regularly updating the information stored in memory, for example periodically, so that the measurements stored in these registers at any given time strive to reflect the state of the analog telephone line at that given time.

[0037] The memory includes, for example, 32-bit registers, each register storing one of the aforementioned measurements.

[0038] For example, the least significant bit of a memory register for voltage is 931.323 - 9 Volts. For example, the least significant bit of a memory register for current is 1.676 - 9 Amperes.

[0039] The memory is also configured to store a boolean value estimating whether the FXS port is in a disconnected or connected state (the value of this boolean is automatically adjusted by the SLIC circuit). This information indicates that: The FXS port is in the off-hook state when the FXS port believes it is connected via the analog telephone line to an off-hook telephone device (in other words, when the FXS port believes the analog telephone line is busy), and the FXS port is in the on-hook state when the FXS port believes it is not connected to any off-hook telephone device (in other words, when the FXS port believes the analog telephone line is not busy).

[0040] In practice, this boolean can be coded on a single bit.

[0041] Processor 4 is configured to run a computer program that performs various functions, including controlling the operation of the FXS port. To achieve this, the program includes, or is combined with, a dedicated FXS port driver, which comprises various code functions.

[0042] Certain driver code functions pass commands to the FXS port requesting that the FXS port perform tests on the analog telephone line, such as tests defined in the GR-909 standard cited in the introduction to this disclosure. These tests are described in sections 12.4.6 (Interface to Embedded Loop Testing Systems) and 12.4.7 (Generic Testing Interface) of the GR-909 standard specification.

[0043] Other driver code functions allow read access to information stored in the FXS port memory.

[0044] The computer program itself is stored in a memory 8 of device 1, external to the FXS port.

[0045] We will now describe a test procedure for the FXS port implemented by processor 4, when this processor 4 executes the aforementioned computer program.

[0046] With reference to the figure 3 , processor 4 detects in step 100 a change in the state of the FXS port. There are two possible state changes: a dropout (the FXS port goes from the on-hook state to the off-hook state) or a dropout (the FXS port goes from the off-hook state to the on-hook state).

[0047] This detection step 100 can be performed, for example, by repeatedly reading from the FXS port's memory register that stores the boolean value indicating its state, for example, periodically. A reading of a zero followed by a 1 or a 1 followed by a zero reflects a change of state.

[0048] If processor 4 detects a stall, then processor 4 collects measurements acquired by the FXS port by reading from the corresponding registers in the FXS port's memory. The measurements relate to at least one of the following physical quantities: the voltage Vbat supplied by the converter, the voltage Vloop between the two electrical wires, the intensity Iloop of the loop current flowing in the first electrical wire or in the second electrical wire, the intensity Ilong of the leakage current.

[0049] For each measurement of a physical quantity collected, processor 4 checks for a correspondence between the collected measurement and a nominal value of the physical quantity. A nominal value is an expected value for the physical quantity in question, reflecting normal operation.

[0050] Processor 4 can verify this correspondence by comparing the measurement with the nominal value, which has been previously stored by device 1. If the difference between the measurement and the stored nominal value is found to be less than a threshold (the threshold can be zero or a value other than zero to reflect a tolerance margin), then the measurement is considered to correspond to a nominal value. If the difference is found to be greater than the threshold, then the measurement is considered not to correspond to a nominal value.

[0051] Alternatively, processor 4 can verify such a match by comparing the measurement with an abnormal value previously stored by device 1 (this value is called abnormal because it represents an abnormal situation). If the difference between a measurement and the stored abnormal value is found to be less than a threshold (the threshold can be zero or a value other than zero to reflect a tolerance margin), then the measurement is considered not to correspond to a nominal value. If the difference is found to be greater than the threshold, the measurement is considered to correspond to a nominal value.

[0052] If the verification of the measurements reveals that all measurements correspond to nominal values, then the situation is considered normal, and processor 4 implements a cyclic test process which is represented on the figure 3 by block A. This cyclic test treatment will be detailed later.

[0053] Preferably, the measurements are verified in two successive verification steps 102 and 104.

[0054] In the first verification step 102, the processor 4 checks whether the measured voltage Vbat corresponds to a non-zero nominal voltage value stored by the device 1. The processor 4 can, for example, use a tolerance margin, for example of 5%.

[0055] If the measured voltage Vbat does not correspond to the nominal value (i.e. the difference between Vbat and the nominal value is greater than the tolerance margin), then the process moves to block B. Block B is representative of an error case which triggers the implementation of certain steps of the process which will be described later.

[0056] If on the contrary the measured voltage Vbat corresponds to the nominal value, then processor 4 moves to the second verification step 104, during which processor 4 checks whether the other collected measurements (Vloop, Iloop, Ilong) correspond to nominal values.

[0057] An abnormal value for the Vloop voltage is zero. Indeed, such a zero value would indicate a short circuit between the first and second wires. Under these conditions, processor 4 considers the measured Vloop voltage to be nominal if and only if the absolute value of the Vloop voltage is greater than a threshold constituting the chosen tolerance margin (equal to zero or close to zero).

[0058] A nominal value for the loop current intensity Iloop is a predefined non-zero value Iref stored by device 1. Under these conditions, processor 4 considers the measured Iloop intensity to be nominal if and only if the difference between Iloop and this predefined non-zero value is less than a threshold constituting the chosen tolerance margin (equal to zero or close to zero). Otherwise, a resistance fault likely occurs.

[0059] The nominal value for the leakage current intensity Ilong is zero. A non-zero value would reflect current leakage from the analog telephone line to ground. Therefore, processor 4 considers the measured intensity Iloop to be nominal if and only if its absolute value is below a threshold constituting the chosen tolerance margin (equal to or close to zero).

[0060] Ultimately, the Vloop, Iloop and Ilong measurements correspond to nominal values ​​if the following relationships are all respected, within a margin of tolerance: Vloop = 0 Iloop ≠ Iref Ilong ≠ 0

[0061] As previously stated, the process moves to block A if all these relationships are respected.

[0062] If on the contrary at least one of the following relationships is not respected, otherwise if at least one of the measurements Vloop, Iloop and Ilong does not correspond to a nominal value, then the processor 4 commands, in a step 106, the implementation by the FXS port of a supplementary test of the telephone line, so as to collect diagnostic data supplementary to the measurements.

[0063] The supplementary test includes at least one of the following tests, as defined by the GR-909 standard. Test name GR-909 translated into French Name of the test in original language (English) Additional data collected #1 Hazardous potential and foreign electrical motive force test Hazardous Potential and Foreign Electrical Motive Force test Residual voltage measured between the TIP and RING wires Residual voltage measured between the TIP wire and ground Residual voltage measured between the RING wire and ground #2 Resistive fault testing Resistive Faults Test Impedance measured between the TIP and RING wires Impedance measured between the TIP wire and ground Impedance measured between the RING wire and ground #3 Receiver dropout test Receiver Off Hook test Specific impedance test: a disconnected radio exhibits a variable impedance depending on the voltage between the TIP and RING wires

[0064] For example, the follow-up test might initially include tests #1 and #2, and only include test #3 if tests #1 and #2 do not reveal any faults. Test #3 is actually an impedance coherence test used to verify the presence of an off-hook analog telephone. This test can differentiate between an off-hook telephone and one with a similar impedance value.

[0065] Tests #1, #2, and #3 can be performed in any order. For example, the supplementary test could include test #3 first, followed by tests #1 and #2.

[0066] Once this additional data has been collected, processor 4 issues an alarm (step 108).

[0067] This alarm can be communicated to a user of device 1, for example, as a message displayed on a screen of device 1. Alternatively, or in addition, the alarm is transmitted to a maintenance server via the first communication interface. In this way, the user and / or the maintenance organization of device 1 is informed of a malfunction in the analog telephone network. The additional data collected characterizes and quantifies this malfunction. This additional data can indicate the location of the malfunction (at the FXS port, at the analog telephone, or at the analog telephone line) and / or quantify the malfunction (for example, via impedance measurements).

[0068] So far, we have described steps performed by processor 4 when a stall is detected.

[0069] When processor 4 detects a hang-up (change of the FXS port state from the off-hook state to the on-hook state), processor 4 implements the following steps.

[0070] In step 110, processor 4 collects the Vloop voltage measured by the FXS port and checks if this Vloop voltage is nominal (according to the rule described previously). If so, the situation is normal, and the process proceeds to block A. Otherwise, the process executes step 112.

[0071] In step 112, processor 4 accesses information stored in the FXS port memory, indicating whether the communication interface has received a power command from the analog telephone line. If so, the process proceeds to block B. Otherwise, the process proceeds to block C.

[0072] Unlike block A, which reflects a normal situation, blocks B and C reflect two abnormal situations to varying degrees.

[0073] We will now detail the cyclic test processing materialized by block A on the figure 3 This cyclic test treatment includes the following steps, shown in the diagram. figure 4 .

[0074] In step 200, processor 4 detects that the FXS port state (on-hook or off-hook) remains unchanged for a predefined duration. This predefined duration can be greater than one hour, six hours, twelve hours, or even twenty-four hours. In all cases, the predefined duration is significantly longer than the reading period of the boolean value indicating this state.

[0075] If processor 4 detects that the FXS port remains in the off-hook state for the predefined duration, then processor 4 proceeds to step 202.

[0076] In step 202, processor 4 commands a supplementary test on the analog telephone line, so as to collect additional diagnostic data, in accordance with step 106 described above.

[0077] In step 202, processor 4 also checks whether this additional diagnostic data reveals a fault in the analog telephone network. Such a fault can occur at the FXS port, at the analog telephone itself, or in the analog telephone line between the two.

[0078] If diagnostic data reveals a fault in the analog telephone network, processor 4 implements an alarm emitting step 204, which may be identical to step 108.

[0079] If the diagnostic data does not reveal a fault in the analog telephone network, then processor 4 returns to block A. The steps described above can then be implemented again upon detection of a state maintenance for the predefined duration.

[0080] If processor 4 detects at step 200 that the FXS port remains in the on-hook state for the predefined duration, then processor 4 implements steps 210 and 212, identical to steps 110 and 112, following the same logic and with the same consequences as in the previously described on-hook detection case. The implementation of steps 210 and 212 can thus result in block A, B, or C, depending on the situation.

[0081] We will now detail the steps implemented by processor 4 when the process is in block B with reference to the figure 5(remember that this situation occurs if processor 4 concludes that the FXS port has not received a power command to supply the analog telephone line).

[0082] In this situation, processor 4 controls the FXS port so that the FXS port supplies power to the analog telephone line (step 300). To this end, the processor sends an appropriate power command to the FXS port.

[0083] Next, in step 302, processor 4 collects new measurements for the physical quantities discussed previously, and then verifies that each new measurement corresponds to a nominal value. Thus, step 302 corresponds to steps 102 and 104 shown in figure 1 .

[0084] If the verification performed in step 302 reveals that all the new measurements have nominal values, then the process proceeds to block A (normal situation). If the verification reveals that at least one of the new measurements does not have a nominal value, then the process proceeds to step 304.

[0085] At step 304, processor 4 commands a restart of the FXS port converter, using an appropriate command.

[0086] Next, in step 306, processor 4 collects new measurements for the physical quantities discussed previously, and then verifies that each new measurement corresponds to a nominal value. This step is identical to step 302.

[0087] If the verification reveals that all the new measurements have nominal values, then the process proceeds to block A (normal situation). If the verification reveals that at least one of the new measurements does not have a nominal value, then the process proceeds to step 308.

[0088] At step 308, processor 4 commands a hard reset of the FXS port. Processor 4 can also restart the program it is running, or at least a module of the program using the FXS port, for example, a communication management module between the telephone network and a VoIP service accessible via the digital network.

[0089] Next, in step 310, processor 4 collects new measurements for the physical quantities discussed previously, and then verifies that each new measurement corresponds to a nominal value. This step is identical to step 302.

[0090] If the verification reveals that all the new measurements have nominal values, then the process proceeds to block A (normal situation). If the verification reveals that at least one of the new measurements does not have a nominal value, then processor 4 issues an alarm in step 312 (which may be identical to step 108).

[0091] We will now detail the steps implemented by processor 4 when the process is at block C (recall that this situation occurs if processor 4 concludes that the FXS port has received a power command to supply the analog telephone line).

[0092] In this case, the process goes directly to the step of restarting converter 304, and then implements the steps subsequent to the step of restarting the converter described in case B.

[0093] We will now detail an example of the implementation of the process with nominal values ​​that find application, for example, in France.

[0094] The FXS is configured to provide a quiescent voltage of 47 Volts and a dropout current of 36 mA. The VOV_GND and VOV_BAT offsets are set to 5.25 Volts.

[0095] Upon detection of a stall, processor 4 collects the following measurements: Vbat = 26.83 Volts, Vtip = 5.47 Volts, Vring = 22.46 Volts.

[0096] Here, Vbat seems correct since Vbat > Vtip, but we notice that we do not have the relationship Vbat = Vtip+ VOV_BAT.

[0097] Processor 4 then checks the other measurements. It notes that: Vloop = Vtip - Vring = 19.99 Volts (which is different from 0 Volts). Iloop = 35.46 mA; with a 5% tolerance, we have the predefined loop current (36 mA). Ilong = 0.31 mA; with a margin of error, this value can be considered zero.

[0098] We are thus in a situation where all the collected measurements have nominal values; the process therefore proceeds to cyclic processing (block A). After waiting the predefined time, processor 4 observes that the FXS port has remained in the off-hook state. Processor 4 then performs the additional test. In particular, test #3, "Receiver Off-Hook," indicates that the off-hook state perceived by the FXS port is not caused by an analog telephone. Under these conditions, processor 4 performs test #2, thus collecting the following impedances: Impedance between TIP wire and ground: 2000000 ohms Impedance between RING wire and ground: 2000000 ohms Impedance between TIP and RING wires: 220 ohms.

[0099] These values ​​indicate a fault, as the impedance measured between the TIP and RING wires is lower than that of a normal, functioning unit (impedance between 400 and 600 ohms). The alarm is therefore triggered.

[0100] The processor 4 is capable of executing instructions loaded into memory 8 from a Read-Only Memory (ROM), external memory (such as a Secure Digital (SD) card), storage media (such as a hard drive), or a communication network. When device 1 is powered on, the processor 4 can read instructions from memory 8 and execute them. These instructions form a computer program that causes the processor 4 to implement all or part of the behaviors, processes, algorithms, and steps described herein.

[0101] Thus, all or part of the algorithms, processes, and steps described here can be implemented in software form by executing a set of instructions by a programmable machine, such as a DSP (Digital Signal Processor), a microcontroller, or a processor. All or part of the algorithms, processes, and steps described here can also be implemented in hardware form, or as a combination of hardware and software, by a machine or component (a "chip"), such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specific Integrated Circuit). Therefore, Device 1 includes electronic circuitry adapted and configured to implement the behaviors, processes, algorithms, and steps described here.

Claims

1. A method for testing a communication interface connected to an analog telephone line comprising two electrical wires, the method comprising the following steps: • detecting (100) a change of state of the communication interface between an off-hook state and an on-hook state; • if it is detected that the change of state switches from the on-hook state to the off-hook state, collecting measurements acquired by the communication interface, the measurements relating to at least one of the following physical quantities: • a voltage provided (Vbat) by a converter of the communication interface, • a voltage (Vloop) between the two electrical wires, • an intensity of a loop current (Iloop) flowing in one of the two electrical wires, • an intensity of a leakage current (Ilong) from one of the two electrical wires to a ground of the communication interface; • verifying (102, 104) matching of the measurements to respective nominal values; • if verifying the matching reveals that all the measurements have nominal values, implementing a processing operation comprising the following steps: • detecting (200) a maintenance of the state of the communication interface for a predefined duration; • if it is detected that the communication interface is maintained in the off-hook state for the predefined duration, ordering (202) a complementary test on the telephone line by the communication interface, so as to collect diagnostic data complementary to the measurements; • if the complementary diagnostic data reveal a fault in the analog telephone network, issuing (204) an alarm; • if the complementary diagnostic data do not reveal a fault on the analog telephone line, repeating the processing operation.

2. The method according to the preceding claim, further comprising the following steps: • if verifying the matching reveals that at least one measurement among the voltage (Vloop) between the two electrical wires, the intensity of the loop current (Iloop) and the intensity of the leakage current (Ilong) does not have a nominal value, ordering (202) the complementary test on the telephone line by the communication interface, so as to obtain the diagnostic data complementary to the measurements, and issuing the alarm if the diagnostic data reveal a fault in the analog telephone network.

3. The method according to any one of the preceding claims, comprising the following steps implemented if it is detected that the change of state switches from the off-hook state to the on-hook state or if the communication interface is maintained in the on-hook state, • collecting a voltage (Vloop) between the two electrical wires acquired by the communication interface; • verifying (110, 210) the voltage (Vloop) between the two electrical wires, so as to determine whether the collected voltage has a nominal value; • if the voltage (Vloop) between the two electrical wires has a nominal value, implementing the processing operation; • if the voltage (Vloop) between the two electrical wires does not have a nominal value, accessing (112) a piece of information stored by the communication interface, the piece of information indicating whether or not the communication interface has received a power supply order for the analog telephone line; • if the piece of information indicates that the communication interface has not received a power supply order, then ordering (300) the communication interface so that the communication interface supplies the analog telephone line; • if the piece of information indicates that the communication interface has received a power supply order, ordering (304) the restart of the converter.

4. The method according to the preceding claim, further comprising the following steps implemented after the order of the communication interface so that the communication interface supplies the analog telephone line: • collecting new measurements acquired by the communication interface, the new measurements relating to at least one of the physical quantities; • verifying (302) the matching of the new measurements with the respective nominal values; • if the verification of the matching of the new measurements reveals that all the new measurements have nominal values, implementing the processing operation; • if the verification of the matching of the new measurements reveals that at least one of the new measurements does not have a nominal value, ordering (304) the restart of the converter.

5. The method according to any one of claims 3 and 4, further comprising the following steps implemented after the converter restart order (304): • repeating (306) the steps of collecting and verifying new measurements; • if the repetition (306) of the steps of collecting and verifying new measurements reveals that all the new measurements have nominal values, implementing the processing operation; • if the repetition (306) reveals that a new measurement does not have a nominal value, ordering (308) a hard reset of the communication interface.

6. The method according to the preceding claim, further comprising the following steps implemented after ordering the hard reset of the communication interface: • repeating (308) a second time the steps of collecting and verifying new measurements; • if the second repetition (308) reveals that all the new measurements have nominal values, implementing the processing operation; • if the second repetition (306) reveals that a new measurement does not have a nominal value, issuing (312) an alarm.

7. A method according to any one of the preceding claims, wherein the complementary test comprises at least one test defined by standard GR-909.

8. A computer program product comprising program code instructions for the execution of the steps of the method according to any one of the preceding claims, when this program is executed by a processor (4).

9. A device (1), for example an internet access gateway, comprising: • a communication interface (2) suitable to be connected to an analog telephone line comprising two electrical wires (TIP, RING); • a processor (4) configured to test the communication interface (2) using the method according to any one of claims 1 to 7.