1、 International Telecommunication Union ITU-T G.996.2TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 2(04/2012) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital sections and digital line system Access networks Single-ended line testing for digital subscriber li
2、nes (DSL) Amendment 2 Recommendation ITU-T G.996.2 (2009) Amendment 2 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.
3、200G.299 INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE
4、TELEPHONY G.450G.499 TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 General G.900G.909 Parameters for optical fibre cable systems G.910G.919 Digital sections at h
5、ierarchical bit rates based on a bit rate of 2048 kbit/s G.920G.929 Digital line transmission systems on cable at non-hierarchical bit rates G.930G.939 Digital line systems provided by FDM transmission bearers G.940G.949 Digital line systems G.950G.959 Digital section and digital transmission system
6、s for customer access to ISDN G.960G.969 Optical fibre submarine cable systems G.970G.979 Optical line systems for local and access networks G.980G.989 Access networks G.990G.999MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERIS
7、TICS G.6000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999 ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T G.996.2 (2009)/Amd.2 (04/2012) i Recommendation ITU-T G.996.2 Single-ended lin
8、e testing for digital subscriber lines (DSL) Amendment 2 Summary Amendment 2 to Recommendation ITU-T G.996.2 (2009) provides updates to Annexes E and F, defining revised new measurement parameters for a MELT-PMD and a MELT-P. History Edition Recommendation Approval Study Group 1.0 ITU-T G.996.2 2009
9、-05-22 15 1.1 ITU-T G.996.2 (2009) Amd. 1 2009-10-09 15 1.2 ITU-T G.996.2 (2009) Amd. 2 2012-04-06 15 ii Rec. ITU-T G.996.2 (2009)/Amd.2 (04/2012) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and com
10、munication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
11、The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolutio
12、n 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and
13、a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met
14、. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibi
15、lity that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Rec
16、ommendation development process. As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information a
17、nd are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2012 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T G.996.2 (2009)/Amd.2 (04/2012) 1 Recommend
18、ation ITU-T G.996.2 Single-ended line testing for digital subscriber lines (DSL) 1) References Add the following reference to clause 2: ITU-T G.991.2 Recommendation ITU-T G.991.2 (2003), Single-pair high-speed digital subscriber line (SHDSL) transceivers. 2) Updates to Annex E Specific requirements
19、for a MELT-PMD Update Annex E as follows: Annex E Specific requirements for a MELT-PMD (This annex forms an integral part of this Recommendation.) E.1 MELT-PMD functions MELT-PMD functions are applicable at the C reference point only. Various implementations of the MELT-PMD feature are possible, inc
20、luding the use of a common functional block shared among multiple lines and capable of executing the procedures described herein on the basis of one line at a time. It is assumed that the MELT-PMD measurements are performed when there is no transmission in the frequency band up to 4 kHz on the loop
21、under test. The method of ensuring this is beyond the scope of this Recommendation. E.1.1 MELT-PMD measurement functions The maximum allowed time for single or combined measurement (see clause E.2.1.1), excluding the processing time in the MELT-P, shall not exceed 20 seconds for a test sequence made
22、 of foreign DC and AC voltage, 4-element resistance with a controlled metallic voltage, and 3-element capacitance with a controlled metallic voltage. E.1.1.1 Measurement of the 4-element DC resistance with a controlled metallic voltage E.1.1.1.1 4-element DC resistance This parameter defines a measu
23、rement, or a series of measurements, to measure the relevant resistance values from an equivalent DC resistance network located between tip, ring, and GND as shown in Figure E.1. 2 Rec. ITU-T G.996.2 (2009)/Amd.2 (04/2012) G.996.2(09)-Amd.2(12)_FE.1RTGTIPR or RTR RTRINGRRGFigure E.1 DC resistance be
24、tween tip, ring, and GND Four resistance values RXYshall be reported: 1) RTR DC resistance between tip and ring 2) RRT DC resistance between ring and tip 3) RTG DC resistance between tip and GND 4) RRG DC resistance between ring and GND. RTRis measured with a voltage applied between tip and ring suc
25、h that tip is positive with respect to ring. A reversed voltage is applied between the tip and ring leads for the measurement of RRT. In the case where the metallic branch elements, RTRor RRT, may be in parallel with a signature network containing a non-linear element such as a zener diode, it will
26、be required to limit the metallic test voltage such as to remain below the conduction threshold when measuring the cable leakage resistances. To this effect, the metallic voltage used by this procedure shall be lower than the minimum far-end signature conduction voltage configuration parameter (see
27、clause E.2.1.6). The accuracy of this parameter is for further study. The accuracy numbers apply to a measurement performed with only one resistance component at a time connected to one of tip and ring, ring and tip, tip and GND, or ring and GND. The accuracy for each element of this parameter is de
28、fined in Table E.1. Table E.1 4-element DC resistor accuracy RXYRange Accuracy 0 250 10 250 1 k 4 % 1 k 100 k 4 % 100 k 1 M 8 % 1 M 5 M 15 % 5 M 10 M 25 % Rec. ITU-T G.996.2 (2009)/Amd.2 (04/2012) 3 E.1.1.1.2 Test voltages for the measurement of the 4-element DC resistance with a controlled metallic
29、 voltage This parameter reports the voltages present on the tip and ring wires while executing the measurement with a controlled metallic voltage and which are used to calculate the resistance results. Four values are reported in relation with the tip-to-ground, ring-to-ground, tip-to-ring, and ring
30、-to-tip branches. If a branch is measured by comparing the load current at two different source voltages, the voltage delta is reported instead of each individual voltage. NOTE The voltage values can be based on a calculation, using the source voltage, the load current and the output impedance, or c
31、an be a direct measurement. Four voltage values VDCXYshall be reported: 1) VDCTR DC voltage between tip and ring 2) VDCRT DC voltage between ring and tip 3) VDCTG DC voltage between tip and GND 4) VDCRG DC voltage between ring and GND. The accuracy for each element of this parameter is for further s
32、tudy. E.1.1.1.3 Test currents for the 4-element DC resistance with a controlled metallic voltage This parameter reports the DC currents measured during the test execution. Those currents are useful to identify the possible presence of a foreign voltage source. To this effect, the current contributio
33、n resulting from the application of the test voltage to the measured external resistance shall be removed from the reported currents. Four current values IDCXYshall be reported: 1) IDCTR DC current between tip and ring 2) IDCRT DC current between ring and tip 3) IDCTG DC current between tip and GND
34、4) IDCRG DC current between ring and GND. The accuracy for each element of this parameter is for further study. NOTE Removing the current contribution resulting from the application of the test voltage only leaves the current due to a foreign potential, if any is present. To this effect, the IDCTRan
35、d IDCRTresults are equivalent to the results that would be obtained when connecting a current meter between tip and ring. Similarly, the IDCTGand IDCRGresults are equivalent to the results that would be obtained when connecting two current meters, one between tip and ground and one between ring and
36、ground. E.1.1.2 Measurement of the 3-element capacitance with a controlled metallic voltage This parameter defines a measurement, or a series of measurements, to measure the capacitance of the cable plus line equipment, if present, from an equivalent AC network located between tip, ring, and GND as
37、shown in Figure E.2. 4 Rec. ITU-T G.996.2 (2009)/Amd.2 (04/2012) G.996.2(09)-Amd.2(12)_FE.2CTGTIPCTRRINGCRGFigure E.2 Capacitance between tip, ring, and GND The capacitance CXYis defined as the measured capacitance between nodes X and Y. The measuring method for CXYis vendor discretionary. Three cap
38、acitance values CXYshall be reported: 1) CTR Capacitance between tip and ring 2) CTG Capacitance between tip and GND 3) CRG Capacitance between ring and GND. In the case where the metallic branch element, CTR, may be in parallel with a signature network containing a non-linear element such as a zene
39、r diode, it will be required to limit the metallic test voltage such as to remain below the conduction threshold when measuring the cable capacitances. To this effect, the metallic voltage used by this procedure shall be lower than the minimum far-end signature conduction voltage configuration param
40、eter (see clause E.2.1.6). The accuracy of this parameter is for further study. The accuracy of each element of this parameter is defined in Tables E.2 and E.3. The accuracy of each element of this parameter in cases of MELT measurements on SHDSL equipment according to ITU-T G.991.2 is defined in Ta
41、bles E.4 and E.5. The accuracy numbers apply to a measurement performed with only one capacitance component at a time connected to one of tip and ring, tip and GND, or ring and GND. NOTE In cases of MELT measurements on loops connected to SHDSL equipment according to ITU-T G.991.2, the accuracy requ
42、irements have to be relaxed. This accounts for the typically high input capacitance of SHDSL equipment ports. Table E.2 Capacitance accuracy CTRCapacitance range Accuracy 0 nF - 60 nF 3 nF 60 nF - 1 F 5 % 1 F - 5 F 10 % Rec. ITU-T G.996.2 (2009)/Amd.2 (04/2012) 5 Table E.3 Capacitance accuracy CTG,
43、CRGCapacitance range Accuracy 0 nF - 20 nF 1 nF 20 nF - 1 F 5 % 1 F - 5 F 10 % Table E.4 Capacitance accuracy CTRfor MELT-measurements on SHDSL equipment according to ITU-T G.991.2Capacitance range Accuracy 0 nF - 1 F 50 nF 1 F - 5 F 10 % Table E.5 Capacitance accuracy CTG, CRG for MELT-measurements
44、 on SHDSL equipment according to ITU-T G.991.2 Capacitance range Accuracy 0 nF - 100 nF 5 nF 100 nF - 1 F 5 % 1 F - 5 F 10 % E.1.1.3 Measurement of foreign voltages Foreign voltages may occur differentially between tip and ring, in common mode between tip/ring and GND, or be single-ended, between ti
45、p and GND or between ring and GND. Therefore, three types of VXYmeasurements are defined: 1) VTR Foreign voltage between tip and ring 2) VTG Foreign voltage between tip and GND 3) VRG Foreign voltage between ring and GND. The measurement parameter foreign voltage (see clause E.2.3.53) shall be repor
46、ted for each of the three types, including the following information: Foreign DC voltage level (VXY,DC) Foreign AC rms voltage level (VXY,AC) Foreign AC voltage frequency (fFXY,AC) estimated on the basis that the foreign AC voltage is sine-shaped with a constant frequency. When measuring the foreign
47、 voltages, the input impedance of the measuring instrument can affect the measurement and should be reported in addition to the results. The accuracy of this parameter is for further study. The accuracies for each of these parameters are defined in Tables E.6 to E.8. The accuracy requirements apply
48、when only one foreign voltage source at a time is connected to one of tip and ring, ring and tip, tip and GND, or ring and GND. The frequency accuracy numbers only apply to foreign AC voltages VXYhigher than 5 Vrms. NOTE Typically the maximum capacitance connected between tip and ring does not excee
49、d 5 F. The maximum foreign DC voltages error due to the residual charge at this maximum capacitance is not expected not be higher than 1 V. 6 Rec. ITU-T G.996.2 (2009)/Amd.2 (04/2012) Table E.6 Foreign DC voltages accuracy Foreign DC voltages VXYrange Accuracy 0 V - 20 V 1 V 20 V - 250 V 5 % Table E.7 Foreign AC voltages accuracy Foreign AC voltages VXY range Accuracy 0 V - 20 Vrms 1 V rms 20 V - 250 Vrms 5 % Tabl
