DE4323781A1 - Apparatus and method for testing a telephone subscriber loop - Google Patents

Description

The invention relates to a device for testing a Telephone subscriber loop and a method for testing the loop.

In a typical telephone system, a large number, usually a few thousand, participants with a central office or a central office each over an electrical Pair of conductors commonly connected as a subscriber loop referred to as. To maintain the quality of services It is necessary to have any facilities to check for any subscriber loop to errors determine and identify. For that purpose that is Central office with one or more test heads, which are used for Measurement of the electrical properties of subscriber loops are trained to diagnose errors in this way. These test heads are relatively expensive equipment parts, but are, because each test head serves a large number of participants can, the cost per line low.

Now systems are introduced in which a small Number, for example 100, participants over relatively short Subscriber loops with a local multiplexer Demultiplexer road unit and then over one Optical fiber path or a feeder line with a remote central office are connected. At a such system has no direct electrical connection between the central office and the participant, causing the Use of a test head arranged at the central office is excluded. Installing such systems Organizations are reluctant for understandable reasons the overhead of using a test head in each Road unit in purchase. In addition, the requires Installation of a test head in a road unit the  Reservation of a considerable channel capacity on the Fiber optic path to the Central Office, making the for the Subscriber traffic limited bandwidth available becomes. The use of a test head still requires the Install complicated switches that act as test access cards are known, which allow the probe to a certain channel is switched on.

Customer reported line faults therefore require the Presence of an engineer using a portable tester equipped. This procedure is much less than ideal. If the error is actually in the terminal of the Participant is, so this can not be within the Responsibility of the network operator, and the ride of the engineer thus represents lost time and lost Expenses dar. Furthermore, the nature of the error can be such that he is outside the competence of a test engineer and requires the attention of a maintenance engineer. This too again puts an unnecessary effort and a delay in the error repair process.

The invention is based on the object, a tester and to provide a test method that these disadvantages as far as possibly reduced or eliminated.

According to one aspect of the invention, a device for Checking a telephone subscriber loop created a electrically conductive signaling path between a Telephone device and an optical fiber path includes, via the loop with a remote central office is connected, wherein the device is characterized in that Means for applying an electrical pulse along the Branches of the loop are provided, and that facilities for Measurement of the pattern of a transition voltage signal provided that is the answer to the impulse to get to this Way to determine the electrical state of the loop.

According to another aspect of the invention is a Method for checking a telephone subscriber loop created, which has an electrically conductive signaling path  between a telephone set and an optical fiber path covers over which the loop with a remotely located Central office is connected, whereby the procedure thereby is characterized in that it is the application of an electrical Pulse along the branches of the loop includes, wherein the Pulse the occurrence of a transient voltage signal along the Branches of the loop causes, and that the electrical state the loop from the pattern of the transient voltage signal is determined.

In a preferred embodiment, the electrical Pulse applied to the loop by the polarity of the Power supply to this loop is reversed. The The nature of the transient voltage signal is determined by a small Number of discrete voltage measurements. These Measurements can be the maximum voltage, the voltage at one fixed time after the pulse, for example, the voltage after 1.2 ms, the time it takes for the voltage to go to one value and the "infinity" - Including the state of tension, which Voltage decay limit represents. Other voltage / Current measurements can also be used to characterize the Transition signal to be performed.

The loop test can either be done as a routine or at Existence of a bug report from a participant be performed.

An embodiment of the invention will be described below explained in more detail in the drawings.

In the drawing show:

Fig. 1 shows a telecommunication system in which a central office with the subscribers via a light waveguide path and a locally arranged road unit is coupled,

FIG. 2 is a schematic diagram of a loop tester coupled to a subscriber loop of the system of FIG. 1; FIG.

FIG. 3 shows a typical transient voltage signal obtained at a subscriber loop, and FIG

Fig. 4 shows an embodiment of a decision table to determine the type of error.

According to FIG. 1, the telecommunication system includes a central office or central office 11 , which is coupled to an interface unit 12 via electrical conductor pairs. The interface unit forms multiplexer / demultiplexer means and further forms an interface between the central office 11 and a number of fiber optic paths or tributaries 13 . Each optical fiber path 13 serves a number of subscribers and is terminated in a local road unit 14 which includes a local multiplexer / demultiplexer. The connection between the road unit and each subscriber terminal 15 takes place via a pair of conductors or a subscriber loop 16 . Each subscriber loop is coupled to a corresponding line card 17 in the road unit 14 . In addition to forwarding telephone traffic, the system may continue to carry, for example, cable television signals.

It will be appreciated that there is no direct electrical connection between the central office 11 and the subscriber loops 16 in the system of FIG .

In Fig. 2, the subscriber loop is schematically represented by the resistors R11, R12 and R13, the capacitors C11 and C12 and the inductors L11 and L12. At the subscriber end, the branches of the loop are connected along the subscriber line socket, which is represented by the capacitor C21 and the resistor R21. The terminal of the subscriber is shown in the form of a resistor R31 and an inductor L31, which are connected to the resistor R21 of the junction box.

An interface between the road unit and the Subscriber loop is formed by the line card. In addition to coupling speech signals to the loop the line card continues to supply a power supply,  typically 48 volts along the loop to the Operate subscriber terminal. To her normal function a line card includes a switch, with its help, the polarity of the supply voltage to the Line can be reversed. This is a technical one Demand. The effect of reversed polarity on a in-state line is that the Lead a voltage jump with twice the supply voltage is suspended, d. H. a jump of 96 volts for the usual Supply voltage in the UK.

The subscriber loop is over with the line card Output resistors R41 and R42 connected, wherein along a (R41) of these resistors the inputs of a differential amplifier AMP are turned on. Optionally, a switch SW1 provided to couple the amplifier AMP along the To enable branches of the loop. The output of the amplifier is connected to an analog / digital converter A / D whose digital output signal to the central office over the Fiber optic path is transmitted, for example, to a Monitoring channel. Preferably, the amplifier AMP and the Analog / digital converter A / D arranged on the line card.

If a subscriber loop is to be checked, then a Signal delivered by the Central Office to the appropriate card, this signal causes the polarity of the Power supply to the subscriber loop is reversed. This gives an electrical impulse to the loop that goes to a corresponding transient current leads, the nature of a Function of the electrical state of the loop is. A this one Transient current corresponding voltage signal appears longitudinal of the resistor R41, creating a corresponding output signal is generated by the amplifier AMP. This output signal is in the analog / digital converter in a corresponding Digital signal is converted, and this signal is sent to the Returned to central office, for example via a Monitoring channel. The switch SW1 allows the implementation a similar measurement along the branches of the loop.

An analysis of the transition signal gives an indication of the electrical condition of the subscriber loop and possibly gives an error information. This is shown in Figure 3, which shows a typical transient waveform for a subscriber loop.

An analysis of the transient mode is done with the help of a relatively small number of measurements of the characteristic Characteristics of the waveform performed, the current is preferably limited to a certain value. suitable Characterizing parameters are in the following table 1, but it should be understood that these Parameter are given only in the form of an example and should in no way be construed as limiting.

Characteristic parameters symbol parameter V _max75 Maximum voltage measured along the supply resistor with a current limit set to 75 mA V _{∞ 35} Long-term open-circuit voltage measured along the supply resistor with current limit set to 35 mA V _{∞ 75} Long-term open-circuit voltage measured along the supply resistor with current limit set to 75 mA V _1,2 The voltage measured along the supply resistor 1.2 ms after applying the voltage jump t₇₅ Time required for the voltage across the feed resistor to drop to 37% of V _1.2 V₂ Voltage measured along the line terminals before applying the voltage jump

If the subscriber line is initially installed, so these parameters are measured and, for example, at Network Manager saved. Typical values of these parameters are in the following Table 2 for both modern and older telephone devices listed:

Table 2

Initial line identification

A periodic check of the loop can be performed to detect major changes in these parameters, the may indicate an error condition. Alternatively, the Loop in the presence of a request from the subscriber being checked. Typical error conditions and the associated Parameters are listed in the following Table 3:  

Table 3

error conditions

The results of this measurement may provide an indication of an error condition at the central office. Using a suitable decision table ( Figure 4), it is possible to determine from a few simple measurements whether there is an error in the subscriber loop, in the socket or in the terminal of the subscriber.

It can be seen that the cost of the line card arranged equipment is relatively low. It is therefore economically useful, the above-described Provide test device for each subscriber loop.

Claims (7)

An apparatus for testing a telephone subscriber loop comprising an electrically conductive signaling path between a telephone set and an optical fiber path through which the loop is connected to a remotely located central office, characterized in that means for applying an electrical pulse along the branches of the loop are provided, and that means are provided for measuring the pattern of a transient voltage signal which is a response to the pulse, whereby the electrical condition of the line is determined. 2. Testing device according to claim 1, characterized in that the means for applying a electrical impulse means for reversing the polarity a power supply to the subscriber loop. 3. Testing device according to claim 1 or 2, characterized in that the measuring means a Differential amplifier include whose inputs along a Resistors are connected in series with the loop. 4. Testing device according to claim 1, 2 or 3, characterized in that the device is placed in a subscriber Line card is inserted. 5. A method for checking a telephone subscriber loop, the an electrically conductive signaling path between a Telephone device and an optical fiber path includes, over the the loop with a remote central office connected is, characterized in that the method comprises the installation of a electrical impulse along the branches of the loop, that the pulse is the occurrence of a transient voltage signal  along the branches of the loop causes, and that the electrical state of the loop from the pattern of Transient voltage signal is determined. 6. The method according to claim 5, characterized in that the pulse by reversing the Polarity of a power supply coupled to the loop is created. 7. The method according to claim 5 or 6, characterized in that the transition voltage by measuring their maximum voltage, the time it takes for the voltage to to a given function of the maximum voltage decay, and characterizes the limit to which the Tension subsides.