DETECTING A SINGLE WIRE INTERRUPTION

Abstract

It is suggested to detect a single wire interruption (SWI) of a line comprising two wires, wherein such line is part of a vectoring group, comprising (i) determining a capacitance between the single wires of the line; and (ii) determining whether a single wire interruption is present based on the determined capacitance.

Claims

1. A method for detecting a single wire interruption of a line comprising two wires, wherein such line is part of a vectoring group, comprising: determining a capacitance between the single wires of the line; determining whether a single wire interruption is present based on the determined capacitance.

2. The method according to claim 1, wherein the vectoring group is utilized by a vectoring system.

3. The method according to claim 2, wherein the vectoring system utilizes a G.fast service.

4. The method according to any of claim 2, wherein vectoring system utilizes a start frequency of at least 1 MHz, in particular 2.2 MHz.

5. The method according to claim 1, wherein determining the capacitance between the single wires of the line comprises: determining an overall capacitance; determining a line capacitance; determining a terminal capacitance.

6. The method according to claim 5, wherein the overall capacitance is determined via metallic line testing (MELT).

7. The method according to claim 5, wherein the line capacitance is determined based on an attenuation of a signal and/or based on a signal propagation delay.

8. The method according to claim 5, wherein the presence of the single wire interruption is determined based on the overall capacitance, the line capacitance and the terminal capacitance.

9. The method according to claim 8, wherein the presence of the single wire interruption is determined based on a difference between the overall capacitance and the line capacitance, which difference is compared with the terminal capacitance and/or another threshold.

10. The method according to claim 9, wherein the presence of the single wire interruption is determined in case the following condition is met:
C.sub.meas−C.sub.line>th, wherein C.sub.meas indicates the overall capacitance, C.sub.line indicates the line capacitance, and th is a threshold, preferably amounting to C.sub.CPE/2 or selected from a range around C.sub.CPE/2, wherein C.sub.CPE is the CPE capacitance.

11. The method according to claim 5, wherein the line capacitance is determined based on at least one of the following: a k10 method; a ToD method; a Tg method.

12. The method according to any of the preceding claims, which is run on a central unit, in particular a distribution point unit (DPU), a digital subscriber line access multiplexer (DSLAM), a multi service access node (MSAN) or a media converter.

13. The method according to claim 1, wherein a predetermined action is triggered in case of at least one of the following: a single wire interruption is detected; a single wire interruption is not detected; a single wire interruption is no longer detected.

14. The method according to claim 13, wherein the predetermined action comprises at least one of the following: issuing a notification, in particular an alarm notification; using a reduced frequency range after the single wire interruption has been detected; deactivating the line for which the single wire interruption has been detected; using a reduced transmit power; using a reduced power spectral density level.

15. A central communication device comprising a processing unit that is arranged to conduct the following steps: determining a capacitance between two single wires of a line, wherein such line is part of a vectoring group; determining whether a single wire interruption is present based on the determined capacitance.

16. The device according to claim 15, wherein the device is a distribution point unit (DPU), a digital subscriber line access multiplexer (DSLAM), a multi service access node (MSAN) or a media converter.

17. A non-transitory computer readable medium storing code portions that cause a digital processing device to perform operations comprising: determining a capacitance between two single wires of a line, wherein such line is part of a vectoring group; determining whether a single wire interruption is present based on the determined capacitance.

18. The non-transitory computer readable medium of claim 17, wherein the presence of the single wire interruption is determined based on the overall capacitance, the line capacitance and the terminal capacitance.

19. The non-transitory computer readable medium of claim 18, wherein the presence of the single wire interruption is determined based on a difference between the overall capacitance and the line capacitance, which difference is compared with the terminal capacitance and/or another threshold.

20. The non-transitory computer readable medium of claim 19, wherein the presence of the single wire interruption is determined in case the following condition is met:
C.sub.meas−C.sub.line>th, wherein C.sub.meas indicates the overall capacitance, C.sub.line indicates the line capacitance, and th is a threshold, preferably amounting to C.sub.CPE/2 or selected from a range around C.sub.CPE/2, wherein C.sub.CPE is the CPE capacitance.

Description

[0071] FIG. 2 shows a DPU with an FTU-O, which is connected via two wires to a CPE, wherein one of the wires is interrupted (SWI);

[0072] FIG. 3 shows a diagram visualizing a line length in view of a capacitance;

[0073] FIG. 4 shows a diagram visualizing the line length in view of the capacitance with line length compensation;

[0074] FIG. 5 shows an alternative diagram visualizing the line length in view of the capacitance with line length compensation in case the attenuation per loop length or capacitance values is/are not exactly known;

[0075] FIG. 6 an exemplary flow chart comprising steps to detect a single wire interruption (SWI);

[0076] FIG. 7 shows a circuit diagram comprising capacitance values C.sub.tr, C.sub.rg and C.sub.tg that can be measured using MELT.

[0077] Examples described herein are directed to a detection of an interrupted wire of a line. When the affected line with an SWI loses its showtime state, the line may re-initialize and a transmission across the line may still be possible when the signal's strength is adjusted to the higher line attenuation based on the capacitive coupling explained above with regard to FIG. 1.

[0078] The capacitive coupling can be detected using standard-compliant G.fast test parameters. There are two basic effects that can be detected in case of a SWI:

[0079] (1) The attenuation of the line is higher, predominately in the lower frequency range.

[0080] (2) The capacitance between the two wires of the line measured by the DPU using MELT is reduced.

[0081] There may be a particular capacitance between the two connections of the CPE's G.fast interface. This capacitance is in series with one coil of a transformer and has a minimum value in order to allow for transmission of ITU G.994.1 handshake tones. This capacitance may be in the order of, e.g., 10 nF. It is also referred to as CPE capacitance C.sub.CPE (see also capacitance 201 in FIG. 2 below).

[0082] FIG. 2 shows the DPU 101 with the single FTU-O 103, which is connected via two wires to the CPE 106, wherein one of the wires is interrupted (SWI). The remaining FTU-Os and CPEs of FIG. 1 are not shown, but they may be present as well. The FTU-R of the CPE 106 shows a capacitance 201 that can be measured by the FTU-O 103 using MELT.

[0083] Without the SWI, the capacitance measured at the DPU by MELT is the sum of the line capacitance C.sub.line and the CPE capacitance C.sub.CPE. With the SWI, only the line capacitance C.sub.line from DPU to the interruption is measured. The capacitance between the two interrupted ends of the wire may be negligible. Hence, if the measured capacitance for reasonably short loop length is smaller than the known CPE capacitance C.sub.CPE, the presence of the SWI is obvious. This may be summarized by the following table:

TABLE-US-00001 Measured capacitance Result >=C.sub.CPE no SWI if capacitance of the uninterrupted line C.sub.line is smaller than C.sub.CPE <C.sub.CPE SWI detected

[0084] The capacitance of a wire pair may amount to 50 pF/m if its characteristic impedance in the G.fast frequency range is 100 Ohm, which is an exemplary impedance of transmission lines used for DSL or G.fast.

[0085] If the known CPE capacitance amounts to 10 nF, it is possible to use the SWI detection with lines up to 200 m. At a length of the line amounting to 200 m, the line capacitance reaches

[00001]$200m.Math.\frac{50\mathrm{pF}}{m}=10\mathrm{nF},$

[0086] which is in the order of the CPE capacitance C.sub.CPE.

[0087] FIG. 3 shows a diagram visualizing the line length in view of the capacitance.

[0088] A line length is regarded as the full line length between the DPU 101 and the CPE 106.

[0089] A curve 301 is the CPE capacitance that is present if it is measured by MELT with a line length of 0 meters. The CPE capacitance C.sub.CPE in this examples amounts to 10 nF.

[0090] A curve 302 depicts the lowest possible measured capacitance value when an SWI is present assuming that the interruption is close to DPU. In this example, the capacitance measured amounts to (substantially) 0 F.

[0091] A curve 303 shows the highest possible measured capacitance value when an SWI is present assuming that the interruption is close to the CPE 106. Hence, the capacitance measured merely shows the line capacitance C.sub.line without the CPE capacitance C.sub.CPE.

[0092] A curve 304 shows the measured capacitance when no SWI is present. Hence, the capacitance measured shows both, the line capacitance C.sub.line and the CPE capacitance C.sub.CPE.

[0093] Hence, with an SWI (curves 302 and 303) the measured capacitance is somewhere above curve 302 and below curve 303 depending on the actual location of the interruption. At a line length amounting to 200 m, the curve 303 reaches (intersects with) the curve 301. Therefore, it is not possible to reliably detect the absence of the CPE capacitance C.sub.CPE above a line length amounting to (ca.) 200 m.

[0094] If the line length is larger than 200 m or in case the CPE capacitance C.sub.CPE is smaller than 10 nF, it is advantageous to know the capacitance of the line C.sub.line to be able to subtract it from the measured capacitance.

[0095] For estimation of the line capacitance C.sub.line several approaches may be used.

[0096] The k10 method

[0097] The k10 method results in a k10 value, also referred to as k10 parameter. For estimating the line length, the k10 parameter (from UPBOKLE, UPBOKLE-R, HLOGpsds or HLOGpsus as described in ITU G.997.2) can be used. The line length in meters and line attenuation in dB may in particular be strictly proportional to each other. The k10 value is measured during the initialization of the G.fast link. It is the so-called electrical length of the line and is the theoretical attenuation at 1 MHz derived from the attenuation of different subcarriers of the G.fast signal.

[0098] Unfortunately, there can be many different cable types that have different k10 values for the same length. That means that it is not possible to precisely determine the cable length and thus the cable capacitance. However, the approach may suffice for some (distinct) cable types.

[0099] An average cable has a length amounting to 30 m per 1 dB attenuation if the attenuation is measured as k10 value(s). This ratio may vary from 20 m/dB to 40 m/dB depending on the type of cable used. The line capacitance per length may be in the order of 50 pF/m. Hence, the average cable capacitance may amount to 1.5 nF per 1 dB attenuation if the attenuation is measured as k10 value(s). This ratio may respectively vary from 1 nF/dB to 2 nF/dB depending on the type of cable used.

[0100] In case an average cable is used and in case of a CPE capacitance C.sub.CPE amounting to 10 nF, a line length compensation may work for any line length.

[0101] FIG. 4 shows a diagram visualizing the line length in view of the capacitance with line length compensation.

[0102] A curve 401 shows a threshold.

[0103] A curve 402 depicts the lowest possible measured capacitance value when an SWI is present assuming that the interruption is close to DPU. In this example, the capacitance measured amounts to (substantially) 0 F.

[0104] A curve 403 shows the highest possible measured capacitance value when an SWI is present assuming that the interruption is close to the CPE 106. Hence, the capacitance measured merely shows the line capacitance C.sub.line without the CPE capacitance C.sub.CPE.

[0105] A curve 404 shows the measured capacitance when no SWI is present. Hence, the capacitance measured shows both, the line capacitance C.sub.line and the CPE capacitance C.sub.CPE.

[0106] The SWI is considered present if the measured capacitance value is at or below the threshold 401. There is no SWI if the measured capacitance is above the threshold 401. The SWI detection may be robust against measurement errors in case the threshold 401 is placed around the middle between curve 403 and 404 (in this example starting at a capacitance amounting to 5 nF at a line length of 0 m).

[0107] However, the maximum cable length for SWI detection may be limited by the value of the CPE capacitance C.sub.CPE and the ratio between the highest and lowest capacitance per k10 values.

[0108] FIG. 5 shows an alternative diagram visualizing the line length in view of the capacitance with line length compensation in case the attenuation per loop length or capacitance values is/are not exactly known.

[0109] A curve 501 shows a threshold.

[0110] A curve 502 depicts the lowest possible measured capacitance value when an SWI is present assuming that the interruption is close to DPU. In this example, the capacitance measured amounts to (substantially) 0 F.

[0111] A curve 503 shows the highest possible measured capacitance value when an SWI is present assuming that the interruption is close to the CPE 106. Hence, the capacitance measured merely shows the line capacitance C.sub.line without the CPE capacitance C.sub.CPE.

[0112] A curve 504 shows the lowest possible measured capacitance when no SWI is present. Hence, the capacitance measured shows both, the line capacitance C.sub.line and the CPE capacitance C.sub.CPE.

[0113] In contrast to FIG. 4, the curves in FIG. 5 depict what happens if the values are unknown and the line capacitance per electrical length may vary from 1 nF/dB to 2 nF/dB. This could be considered as a worst case regarding the k10 value based line length compensation.

[0114] The curve 504 is based on 1 nF/dB instead of 1.5 nF/dB line capacitance and the curve 503 increases from 1.5 nF/dB to 2 nF/dB. Both curves 503 and 504 intersect at a line length amounting to 300 m.

[0115] That means that in this example an SWI detection beyond a line length of 300 m may not be possible. Also, the detection becomes less robust against measurement errors the closer the line length gets to 300 m.

[0116] On the other hand, a line length of 300 m may be much longer than what is actually necessary for targeted G.fast deployments.

[0117] It is noted that k10 may be affected by the SWI. For example, k10 measured during the SWI will be higher compared to k10 measured without the SWI being present. This may lead to an overestimation of the loop length and may thus result in a higher estimated line capacitance and therefore makes the SWI detection more reliable.

[0118] The detection of an SWI as described may utilize MELT. This may be time consuming, also MELT resources are limited. If an actual k10 value does not differ much (e.g., by less than 0.3 dB) from a previous k10 value, it may be likely that there is no change concerning SWI. In this case it may not be necessary to initiate another MELT.

[0119] For example, the k10 value can be determined by the DPU and/or the CPE. The CPE's k10 value is transmitted to the DPU. The DPU may thus decide which k10 to select. For further details, reference is made to ITU G.9701.

[0120] MELT may be conducted according to ITU G.996.2.

[0121] Creating a short circuit on the line also causes k10 to change but the subsequent MELT may not produce a valid capacitance result. Hence, if MELT may indicate an invalid capacitance, this may be regarded as “no SWI”.

[0122] Alternative line capacitance estimation methods

[0123] Instead of estimating the line length and the line capacitance value using the line attenuation, the line length and associated capacitance value may be estimated from its propagation delay.

[0124] Two length estimation methods (ToD and Tg methods) using standard compliant test and reporting parameters are described in US 2019/0036800 A1. Methods using the propagation delay to estimate the loop length may be more accurate than attenuation based techniques.

[0125] The ToD method

[0126] The most accurate technique involves the utilization of the ToD messages exchanged between the DPU and the CPE (ITU-Recommendation G.9701, clause 8.5). It is an option to implement the ToD method in only a selection (and not all) of the DPUs and/or CPEs.

[0127] Most cables have a propagation speed of about 0.7 times the speed of light. Hence, the capacitance per delay is about

[00002]$\frac{50\mathrm{pF}}{m}.Math.3.Math.{10}^8\frac{m}{s}.Math.0.7.$

[0128] The Tg method

[0129] This method also measures the line propagation delay and is based on a gap timing in the TDD frame. The Tg processing (ITU-Recommendation G.9701, clause 10.5) is partially vendor specific. That is why it may be necessary to check the DPU's and the CPE's inventory information to adjust the delay results accordingly. The capacitance per delay is also in the order of

[00003]$\frac{50\mathrm{pF}}{m}.Math.3.Math.{10}^8\frac{m}{s}.Math.0.7.$

[0130] SWI detection procedure

[0131] Depending on the expected environment and the detection method, the DPU containing the detection algorithm may in particular utilize at least two parameters. These parameters can be either fixed in the detection algorithm or they can be configurable by an operator.

[0132] The line capacitance C.sub.line can be determined based on parameters that are derived from either the k10 method (resulting in a parameter Cm) or the ToD or Tg method (resulting in a parameter C.sub.delay).

[0133] These parameters C.sub.k10 and C.sub.delay may be configured by an operator to meet the demands of the network. Also, these parameters C.sub.k10 and C.sub.delay may be fixed pursuant to an initial estimation. Also, both approaches may be combined.

[0134] After each line has been initialized, the line capacitance C.sub.line may be determined as follows, depending on the method used: [0135] C.sub.line=C.sub.k10.Math.k10 in case the k10 method is used, or [0136] C.sub.line=C.sub.delay.Math.delay in case the ToD or the Tg method is used.

[0137] FIG. 7 shows a circuit diagram comprising capacitance values C.sub.tr, C.sub.rg and C.sub.tg that can be measured using MELT. Nodes tip and ring visualize the two wires of the line.

[0138] The capacitance C.sub.tg is arranged between the node tip and ground, the capacitance C.sub.rg is arranged between the node ring and ground and the capacitance C.sub.tr is located between the nodes tip and ring.

[0139] For line length estimation purposes, an overall capacitance C.sub.meas is determined between the two wires indicated by the nodes tip and ring. This capacitance C.sub.meas can be calculated based on the three values determined by MELT as follows:

[00004]$C_{\mathrm{meas}}=C_{\mathrm{tr}}+\frac{1}{\frac{1}{C_{\mathrm{rg}}}+\frac{1}{C_{\mathrm{tg}}}}.$

[0140] The SWI may be considered to be present, if the MELT capacitance measurement is indicated as valid and if

[00005]$C_{\mathrm{meas}}-C_{\mathrm{line}}<\frac{C_{\mathrm{CPE}}}{2}.$

[0141] Otherwise SWI is considered as not present.

[0142] Instead of the exemplary threshold C.sub.CPE/2, any value between C.sub.CPE and 0 may be used.

[0143] Alternatively, if only short loops are used (i.e. C.sub.line<C.sub.CPE), the line capacitance may be negligible. In such case, a length compensation is not necessary and the SWI is considered to be present, if the MELT capacitance measurement is indicated as valid and if C.sub.tr<C.sub.CPE-ε, otherwise SWI is considered as not present. ε may indicate a tolerance that stems from measurement discrepancy and/or from a variance of the CPE's capacitance.

[0144] FIG. 6 shows an exemplary flow chart comprising steps to detect a single wire interruption (SWI).

[0145] In a step 601, the overall capacitance C.sub.meas is determined, which is expected to be the sum of the CPE capacitance C.sub.CPE (in case there is no SWI) and the line capacitance C.sub.line.

[0146] This step 601 may be triggered by the DPU or by a DSLAM or by any central entity. The overall capacitance C.sub.meas is determined for a line comprising two wires. The line may be connected to a CPE or any terminal device. Reference is made to the examples shown in FIG. 1 and FIG. 2.

[0147] In a step 602 the line length is determined, which can be done based on an attenuation or based on a signal propagation delay. Both are exemplarily described above.

[0148] Utilizing a predetermined line capacity of, e.g., 50 pF/m, the line capacity C.sub.line can be determined applying the previously determined line length.

[0149] In a step 603, a capacitance difference C.sub.diff is determined based on the overall capacitance C.sub.meas and the line capacitance C.sub.line as follows:

C.sub.diff=C.sub.meas−C.sub.line.

[0150] In a step 604, the capacitance difference C.sub.diff is compared with the capacitance C.sub.CPE. If the capacitance difference C.sub.diff is larger than the capacitance C.sub.CPE/2, no SWI is detected (see step 605). If the capacitance difference C.sub.diff is smaller or equal than the capacitance C.sub.CPE/2, the SWI is detected (see step 606).

[0151] After step 605, the whole detection may be reiterated, e.g., after a predetermined delay or immediately.

[0152] After step 606, a predefined action may be triggered. This is described in the next section.

[0153] Actions after Detecting the SWI

[0154] After detection of the SWI, the power spectral density (PSD) transmitted over the line can be automatically modified to reduce the line's impact on the vectoring system. That may imply deactivating the line completely or limiting the utilized frequency range.

[0155] Returning to the normal PSD can happen manually by the operator or automatically after a predetermined (e.g., fixed or configurable) amount of time has elapsed without still detecting the SWI.

[0156] Additionally, a DPU management system may be informed of the SWI being detected (and/or no longer being detected). The DPU may hence notify the operator, e.g., via an alarm or any other notification.

[0157] Although various exemplary embodiments of the invention have been disclosed, it will be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the spirit and scope of the invention. It will be obvious to those reasonably skilled in the art that other components performing the same functions may be suitably substituted. It should be mentioned that features explained with reference to a specific figure may be combined with features of other figures, even in those cases in which this has not explicitly been mentioned. Further, the methods of the invention may be achieved in either all software implementations, using the appropriate processor instructions, or in hybrid implementations that utilize a combination of hardware logic and software logic to achieve the same results. Such modifications to the inventive concept are intended to be covered by the appended claims.

LIST OF ABBREVIATIONS

[0158] AN Access Node [0159] CPE customer premises equipment (terminal) [0160] DPU distribution point unit [0161] DSL Digital Subscriber Line [0162] DSLAM DSL Access Multiplexer [0163] FAST Fast Access To Subscriber Terminals [0164] FEXT far-end-crosstalk [0165] FTTB fiber to the building [0166] FTU-O FAST Transceiver Unit at the optical network unit [0167] FTU-R FAST Transceiver Unit at the remote site (i.e., subscriber end of the [0168] loop) [0169] MELT Metallic Line Testing [0170] MSAN Multi Service Access Node [0171] PSD power spectral density [0172] RFI Radio Frequency Interference [0173] TDD Time Division Duplex