WO2002033941A1 - Procede et dispositif permettant de tester des lignes telephoniques et de donnees dans un systeme de telecommunications - Google Patents

Procede et dispositif permettant de tester des lignes telephoniques et de donnees dans un systeme de telecommunications Download PDF

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Publication number
WO2002033941A1
WO2002033941A1 PCT/US2001/029138 US0129138W WO0233941A1 WO 2002033941 A1 WO2002033941 A1 WO 2002033941A1 US 0129138 W US0129138 W US 0129138W WO 0233941 A1 WO0233941 A1 WO 0233941A1
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WO
WIPO (PCT)
Prior art keywords
telephone line
fault
discontinuity
transfer function
calculating
Prior art date
Application number
PCT/US2001/029138
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English (en)
Inventor
John Kelvin Fidler
Jiliang Yu
Original Assignee
Porta Systems Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Porta Systems Corporation filed Critical Porta Systems Corporation
Priority to AU2001294583A priority Critical patent/AU2001294583A1/en
Publication of WO2002033941A1 publication Critical patent/WO2002033941A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/46—Monitoring; Testing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M3/00—Automatic or semi-automatic exchanges
    • H04M3/22—Arrangements for supervision, monitoring or testing
    • H04M3/26—Arrangements for supervision, monitoring or testing with means for applying test signals or for measuring
    • H04M3/28—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor
    • H04M3/30—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor for subscriber's lines, for the local loop
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/11—Locating faults in cables, transmission lines, or networks using pulse reflection methods
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M3/00—Automatic or semi-automatic exchanges
    • H04M3/08—Indicating faults in circuits or apparatus
    • H04M3/085—Fault locating arrangements

Definitions

  • This invention relates generally to telecommunication networks, and more particularly to the accurate testing and determination of the location of faults on and the propagation speed of telephone lines commonly used in such networks.
  • Telecommunication systems are generally complex electrical systems that are subject to failure from a variety of fault modes.
  • the rapid and accurate classification and isolation of a fault within a telecommunication system is highly desirable to minimize dispatch and repair costs associated with such faults. Therefore, it is a long-standing objective within the telecommunication industry to provide a system that can use measured data to automatically diagnose one of several failure modes.
  • LTS automated line testing system
  • a remote test unit (RTU) 10 is employed at each local exchange (EX) 12 within the telecommunication system.
  • the RTU 10 is a hardware device, which generates test signals. These test signals are introduced into the system through the EX 12.
  • the test signals propagate through a main distribution frame (MDF) 14 and into telephone lines 16.
  • MDF main distribution frame
  • DP distributing points
  • the signals reach various customer apparatus (CA) 22 such as a modem, facsimile machine, telephone handset, and the like,
  • the telecommunication system when operating normally, exhibits characteristic parameters in response to the RTU 10 test signal. These parameters include voltage, current, resistance, capacitance, and the like.
  • the RTU 10 samples and evaluates these parameters tlirough the use of software. During a fault condition, these parameters change in response to a given fault.
  • Diagnostic software 24 implements a simple heuristic algorithm.
  • the algorithm includes decision rules, which compare one or more measurements with threshold values to determine whether a fault exists. As an example, the algorithm may compare measured resistance values between a pair of lines against a set of expected threshold values, which are stored in the program to decide whether a fault exists in either the exchange 12 or customer apparatus 22.
  • the algorithm uses linear decision rules to perform these functions.
  • the LTS is also capable of recording the measured parameters in a database 26 for future reference. Additionally, the LTS has the capability of accepting manually entered data 28 regarding each fault from an operator via a keyboard. This information may include customer fault reports and service personnel codes, which indicate the actual location of a fault. In this way, a large amount of data is assembled regarding fault history and parameter values associated with various fault locations. However, the LTS is unable to use this data to improve its own operation. If desired, the data stored in the database 26 may be evaluated periodically, and the decision thresholds employed by the algorithm may be manually updated. This is an extremely labor intensive, and therefore expensive, operation. Therefore, it is a long-standing objective in the field of telecommunication diagnostics to develop a system that can overcome this limitation.
  • Local networks play an important role in telecommunication networks since they directly connect customers to exchanges and failures in the local network will directly affect services provided to the customer. Unlike other parts of the telecommunication network, twisted-pair copper wires have dominated local networks since the birth of telephony and promise to do so for the foreseeable future. While the rest of the telecommunication network has undergone substantial improvements and modernization, the local network is rapidly becoming the weak link in terms of reliability and transmission performance. For example, the local network accounts for about 90% of all faults in the telecommunication network.
  • LTS techniques can typically only locate a fault to the exchange, local network, cable, or customer's premises. This technique is not accurate enough to enable an engineer repairing the fault to proceed directly to the fault without further testing.
  • portable equipment must be connected at various points along the cable to accurately locate the fault. The use of such portable equipment is time-consuming and often creates additional faults since it involves significant mechanical interference with the network, such as splicing the telephone line. Thus, equipment that can accurately and non-invasively determine the location of faults from the exchange would be invaluable in maintaining the local network.
  • the time domain reflectrometry (TDR) technique although widely used with conventional portable equipment, is also not ideal for an exchange-based test system.
  • the TDR technique essentially involves applying an impulse or spike to a telephone line and recording the delay until the reflection of the impulse is received.
  • the relatively high attenuation and limited frequency band of local network cable seriously attenuates and distorts the narrow impulse typically used in the TDR technique. If a spike of greater amplitude is used, the function and reliability of components, such as switches, in the telecommunication network are likely to be compromised.
  • the TDR technique inherently requires a wide assortment of pulse widths to accurately characterize the line. This significantly increases the length of time required to locate the fault.
  • TDR time domain reflectrometry
  • LTS automatic line testing systems
  • LTS line testing systems
  • a method of determining the location of a fault on a telephone line includes the steps of calculating a first transfer function of the telephone line without the fault, and calculating a first inverse Fourier transform of the first transfer function.
  • the telephone line includes at least one discontinuity and an end.
  • the discontinuity is a distance M from the end, and is associated with a first time component T in the first inverse Fourier transform.
  • a second echo transfer function of the telephone line with the fault is calculated, from which a second inverse Fourier transform is calculated.
  • a second time component x, which is associated with the fault, is determined from the second inverse Fourier transform, and a distance m to the fault is then calculated using the following equation:
  • the method may also be performed from a second end of the telephone line.
  • a mean, median, or average may then be calculated from the distance to the fault from the first end and the distance to the fault from the second end to further enhance accuracy.
  • the method may be utilized between various components of a telecommunication network, even while it is in use, and may be integrated with conventional line testing systems.
  • a method of determining the location of a fault on a telephone line in which the first and second time components are calculated from the same echo transfer function and inverse Fourier transform.
  • a method of determining a propagation velocity of a telephone line includes the steps of calculating a first transfer function of the telephone line, calculating a first inverse Fourier transform of the transfer function, and calculating the propagation velocity ⁇ of the telephone line using the following equation:
  • the telephone line includes an end and at least one discontinuity, which is a distance M from the end.
  • the discontinuity is associated with a first time component T in the first inverse Fourier transform.
  • the method may also be performed from a second end of the telephone line.
  • a mean, median, or average may then be calculated from the propagation velocity ⁇ calculated from the first end and the propagation velocity ⁇ calculated from the second end to further enhance accuracy.
  • the method may be utilized between various components of a telecommunication network, even while it is in use, and may be integrated with conventional line testing systems.
  • FIG 1 is a block diagram of a conventional line testing system (LTS).
  • LTS line testing system
  • Figure 2 is a model of a conventional telephone line.
  • Figure 3 is a Dirac distribution of the inverse Fourier transform of a normalized echo transfer function of the telephone line shown in Figure 1.
  • Figure 4 is a Dirac distribution of the inverse Fourier transform of a normalized transfer function of a telephone line having multiple discontinuities.
  • Figure 5 is a Dirac distribution of the inverse Fourier transform of a normalized transfer function obtained over a narrower frequency range than that shown in Figure 5.
  • Figure 6 is a block diagram showing preferred testing schemes using the methods in accordance with the present invention.
  • the subject invention enables faults, which occur in the so-called "final mile", to be accurately located.
  • the final mile describes the twisted-pair copper wires in a telecommunication network that run from a public switch to a customer ' s premises. As more and more homes become data dependent there is a concomitant need to more accurately identify the electrical characteristics of this link to the customer. Such information is extremely useful in determining the precise location of a failure or fault in the telecommunication network.
  • the present invention essentially uses the time component of signals associated with discontinuities in a telephone line, which are located at a known distance from the source of an excitation signal applied to the line, to determine the distance from the source to unknown faults on the same telephone line.
  • the time components are obtained from an inverse Fourier transform of a transfer function of the telephone line stimulated by the excitation signal.
  • the excitation signal preferably includes a wide variety of frequency components to ensure that the transfer function accurately represents the telephone line.
  • the transfer function is preferably calculated from measurements obtained at the exchange end of the telephone line.
  • the frequency range of the signals used to calculate the transfer function should typically be from about 100 Hz to about 500kHz for a telephone line having a length of about 3000m.
  • the frequency range may be smaller for shorter lines, but the number of signal frequencies is preferably greater than 100 within the frequency range to ensure the accuracy of the echo transfer function and the resulting Fourier analysis.
  • the measurements required to obtain the transfer function may be done in many different ways depending upon the system being used. For instance, a signal generator may be used to sweep the frequency range or generate a complex signal containing a wide variety of frequency components. The echo response of the telephone line is then processed using digital signal processing techniques or time domain analysis to obtain the transfer function.
  • an adaptive filter may be used on the telephone line to measure the transfer function over a broad frequency range. Such a technique may even be used while the line is in use, and is similar to a method used by echo cancellation circuits in devices, such as modems and speaker phones, to measure the transfer function.
  • Figure 2 shows a model of a telephone line having a finite length L, terminated in a load impedance ZL 30, and stimulated by an alternating current (ac) source 30.
  • the ac source 32 includes an internal impedance Z ( 34.
  • the value of a reflected voltage VA at point A is provided by the following equation:
  • Vi is the voltage of the ac source 32
  • 1 is the distance from the ac source 32 to a discontinuity
  • ⁇ is the frequency in radians per second
  • p is a reflection coefficient of the load Z L 30.
  • ⁇ is a phase angle of the reflected waveform
  • Z 0 is the characteristic impedance of the telephone line
  • ⁇ is the propagation factor of the telephone line given by the following equation:
  • ⁇ ( ⁇ ) a( ⁇ ) + j ⁇ ( ⁇ ) , (4)
  • phase shift of the reflection coefficient p is substantially independent of frequency for a resistive load. It is then possible to write
  • ⁇ represents the delta function, which is used to generate a Dirac distribution
  • ⁇ is the time component of elements in the Dirac distribution
  • FIG 3 shows a Dirac distribution of the inverse Fourier transform of the normalized echo transfer function represented by equation (8).
  • the Dirac distribution in this example includes a spike 36 having a time component of about 50 ⁇ s, which is associated with the discontinuity in the telephone line.
  • the time component will be directly proportional to the distance 1 from an end of the telephone line to the fault for a given propagation velocity.
  • the echo transfer function of the telephone line is as follows:
  • the attenuation factor ⁇ ( ⁇ ) is roughly proportional to -J ⁇ .
  • Figure 4 is a Dirac distribution of the inverse Fourier transform of the echo transfer function of the telephone line with multiple discontinuities. From equation (14), it becomes apparent that for a line with n discontinuities, the inverse Fourier transform of the reflection transfer function includes n components shifted in time corresponding to the distances of the discontinuities from the source of the excitation signal. This is shown in Figure 4 by a spike 40 at 53.030 ⁇ s. a spike 42 at 79.545 ⁇ s, and a spike 44 at 92.803 ⁇ s. Therefore, by analyzing the distribution shown in Figure 4, it becomes readily feasible to accurately locate any discontinuity along the telephone line.
  • Equation (14) also provides a method for calculating the propagation velocity of the telephone line within the measurement frequency range.
  • the propagation speed is conventionally approximated by the following equation:
  • Equation (14) the propagation velocity can be calculated more accurately. For instance, suppose there is a known discontinuity at a distance M from the source of the excitation signal, and that the time corresponding to this discontinuity is T. From equation (14), it follows that the propagation speed of the telephone line is given by the following equation:
  • Figure 4 shows the Dirac distribution of the Fourier transform of the normalized transfer function of a 3.5km screened telephone cable.
  • the telephone cable has a discontinuity at 2 km, which corresponds to the spike 40 at 53.030 ⁇ s; a fault, which corresponds to the spike 42 at 79.545 ⁇ s; and a mismatched load at the end of the cable, which corresponds to the spike 44 at 92.803 ⁇ s.
  • the measurements were simulated using PSpiceTM on a personal computer.
  • the calculation of the normalized transfer function and the Fourier transform was performed by ProbeTM, a graphical tool, which is included with the PSpiceTM software package.
  • the distance to the unknown fault is 3000m.
  • the distance to the fault may also be calculated by using the parameters of the line L and C in accordance with equations (7) and (19), which results in the following equation:
  • LTS line testing systems
  • Such systems generally have digital signal processing capabilities, which may be used to calculate the Fourier transform used in the method of the present invention.
  • the LTS system may be used to quickly test and locate the fault to the exchange, cable, or customer's premises. If the LTS system determines the fault to be in the cable, then the method of the present invention may be utilized to further pinpoint the location of the fault.
  • the method of the present invention may be used in conjunction with or to augment a telecommunication database containing Fourier distributions of telephone lines with only the normally occurring discontinuities.
  • a fault is reported along a particular line
  • the echo transfer function of the line is measured and processed to obtain the corresponding Fourier distribution.
  • the Fourier distribution of the line with only the expected discontinuities is then retrieved from the database and compared to the Fourier distribution with the fault to accurately locate the fault.
  • a simulation of the method in accordance with the present invention using PSpice yields only a 30cm error in the location of a fault on a 3000m line.
  • conventional portable equipment which relies on audio signals, tones, or heat to detect faults, may essentially be eliminated.
  • the time required to complete the method in accordance with the present invention may significantly be decreased by using adaptive filtering techniques to obtain the transfer function.
  • the time to perform the method may be further reduced by taking measurements while the line is in use. In either case, the method of the present invention is significantly faster than the conventional application of portable equipment to the line at various locations, which may take several hours.
  • the line may be stimulated, the Fourier transform of the transfer function may be calculated, and the resulting information may be analyzed independently or applied to the LTS. Once in the LTS, this information is preferably used with other records concerning the telecommunication network to more accurately locate and identify faults.
  • FIG. 6 is a block diagram showing four preferred implementations (A) - (D) of the method of the present invention to a telecommunication network.
  • the implementations outline various schemes in which single and dual-end testing is preferably used or combined to enhance line-testing capabilities.
  • the path for each of the implementations is indicated between circled reference designations corresponding to the specific implementation.
  • implementation A is shown between a modem 50 and a public switch 52.
  • implementation B is shown between the modem 50 and a remote test unit (RTU) 54
  • implementation C is shown between the modem 50 and a digital service line access module (DSLA * M) 56
  • implementation D is shown between the modem 50 and a remote access server (RAS) 58.
  • the term "communication module” is used to refer to at least one of the customer's modem, the public switch, the remote test unit, the digital subscriber line access module (DSLAM). and the remote access server (RAS).
  • Implementation A enables the telephone line from the customer's modem 50 to the public switch or exchange 52 to be tested. This implementation is preferably initiated by the user's modem 50 using specialized hardware and/or software designed to apply the method of the present invention to the telephone line and determine the condition of the line and its ability to carry voice and data.
  • Implementation B enables the telephone line from the customer's modem 50 to the RTU 54 to be tested.
  • This implementation may be initiated by the user's modem 50, which provides single-ended information concerning the telephone line.
  • the RTU 54 includes an intelligent modem, either the user's modem 50 or the RTU 54 may initiate the test, either sequentially or concurrently, which provides double-ended information regarding the telephone line. Double-ended information significantly increases the accuracy in determining the location of the fault by, for instance, calculating a mean or average of the distance to the fault calculated from the ends of the line.
  • the resulting test information is preferably collated at the RTU 54 and made available to a line test system (LTS) 60.
  • LTS line test system
  • Implementation C enables a high frequency path from the customer's modem 50 to the DSLAM 56 to be tested.
  • the increased bandwidth of the high frequency path significantly increases the accuracy of fault location while enabling the test to be automated from a remote location.
  • This implementation may be initiated by the user's modem 50, which provides single- ended information concerning the telephone line.
  • the DSLAM 56 commonly incorporates an intelligent modem, either the user's modem 50 or the DSLAM 56 may sequentially or concurrently initiate the test, which would provide double-ended information regarding the telephone line.
  • Implementation D enables the telephone line from the customer's modem 50 to the RAS 58 to be tested. This implementation may be initiated by the user's modem 50. which provides single-ended information concerning the telephone line, or the RAS 58, either sequentially or concurrently, which would provide double-ended information. Since the RAS 58 is preferably coupled to the public switch 52 by a digital path, the RAS 58 can act as a virtual modem on the telephone line to initiate and monitor testing of the line.
  • the RAS 58 may alternatively be controlled by a digital line test system 62, which is preferably accessible to the customer via the Internet 64.
  • the digital line test system 62 preferably provides information concerning the results of the test to the line test system to further enhance the accuracy of fault location.
  • the method and apparatus in accordance with the present invention locates faults in a telephone line more quickly and accurately at any end of the line, even while the line is being used, than conventional techniques, such as time domain reflectrometry (TDR), and currently available portable equipment, such as automatic line testing systems (LTS). Further, it will be appreciated that the method and apparatus in accordance with the present invention can readily be integrated as an enhancement to conventional line testing systems (LTS), or can be used as a standalone system without physical interference with the telephone line.
  • TDR time domain reflectrometry
  • LTS automatic line testing systems
  • the method and apparatus in accordance with the present invention determines the propagation speed of a telephone line more quickly and accurately at any end of the line than conventional techniques, even while the line is in use. Further, it will be appreciated that the method and apparatus in accordance with the present invention does not require physical interference with the telephone line.

Abstract

L'invention concerne un procédé permettant de déterminer avec précision l'emplacement d'une panne sur une ligne téléphonique. Ce procédé consiste à établir une fonction de transfert de la ligne et à soumettre cette fonction à une transformée de Fourier, laquelle comprend une pointe à composante temporelle représentative d'une discontinuité située à une distance connue d'une extrémité de la ligne. La composante temporelle et la distance associées à la discontinuité connue et la composante temporelle associée à la panne permettent ensuite de calculer la distance entre l'extrémité de la ligne et la panne. On peut aussi utiliser la composante temporelle et la distance associées à la discontinuité connue pour calculer une vitesse de propagation propre à la ligne. Il est possible de choisir une mise en oeuvre sur la base d'une extrémité ou de deux extrémités, entre différents éléments d'un réseau de télécommunications, du type modem d'utilisateur (50), commutateur public (52), unité d'essai à distance (54), module d'accès à une ligne d'abonné numérique (56), et serveur d'accès à distance (58).
PCT/US2001/029138 2000-10-16 2001-09-19 Procede et dispositif permettant de tester des lignes telephoniques et de donnees dans un systeme de telecommunications WO2002033941A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001294583A AU2001294583A1 (en) 2000-10-16 2001-09-19 Method and apparatus for testing voice and data lines in a telecommunication system

Applications Claiming Priority (2)

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GB0025316.1 2000-10-16
GB0025316A GB2367971A (en) 2000-10-16 2000-10-16 Locating the position of a fault on a telephone line

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WO2002033941A1 true WO2002033941A1 (fr) 2002-04-25

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GB (1) GB2367971A (fr)
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Publication number Priority date Publication date Assignee Title
GB2493684A (en) * 2011-05-17 2013-02-13 British Telecomm Measurement method
EP2525502A1 (fr) 2011-05-17 2012-11-21 British Telecommunications Public Limited Company Procédé de mesure
WO2018178388A1 (fr) 2017-03-30 2018-10-04 British Telecommunications Public Limited Company Procédé de mesure

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US6058162A (en) * 1997-12-05 2000-05-02 Harris Corporation Testing of digital subscriber loops using multi-tone power ratio (MTPR) waveform
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US6215855B1 (en) * 1999-01-21 2001-04-10 Bell Atlantic Network Services, Inc. Loop certification and measurement for ADSL

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US5446387A (en) * 1992-10-20 1995-08-29 Asea Brown Boveri Ab Method and a device for determining a fault on a transmission line
US5844235A (en) * 1995-02-02 1998-12-01 Yokogawa Electric Corporation Optical frequency domain reflectometer for use as an optical fiber testing device
US6144721A (en) * 1996-01-05 2000-11-07 Communications Technology Corporation Apparatus and method for line pair testing and fault diagnostics
US5994905A (en) * 1997-12-02 1999-11-30 Wavetek Corporation Frequency domain reflectometer and method of suppressing harmonics
US6058162A (en) * 1997-12-05 2000-05-02 Harris Corporation Testing of digital subscriber loops using multi-tone power ratio (MTPR) waveform
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AU2001294583A1 (en) 2002-04-29
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