1、 International Telecommunication Union ITU-T G.996.2TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (05/2009) 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 lines (DSL) R
2、ecommendation ITU-T G.996.2 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.200G.299 INDIVIDUAL CHARACTERISTICS OF INT
3、ERNATIONAL 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 TELEPHONY G.450G.499 TRANSMISSION MEDIA AN
4、D 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 hierarchical bit rates based on a bit rate
5、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 systems for customer access to ISDN G.960G.969 O
6、ptical fibre submarine cable systems G.970G.979 Optical line systems for local and access networks G.980G.989 Access networks G.990G.999 MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DATA OVER TRANSPORT GEN
7、ERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T G.996.2 (05/2009) i Recommendation ITU-T G.996.2 Single-ended line testing for digital subscriber lines (DSL) Summary Re
8、commendation ITU-T G.996.2 specifies line testing for xDSL transceivers in the form of single-ended line testing (SELT), dual-ended line testing (DELT) and metallic line testing (MELT). Source Recommendation ITU-T G.996.2 was approved on 22 May 2009 by ITU-T Study Group 15 (2009-2012) under Recommen
9、dation ITU-T A.8 procedures. ii Rec. ITU-T G.996.2 (05/2009) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-
10、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. The World Telecommunication Standardization Assembly (WTSA), which meets every four ye
11、ars, 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 Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the nec
12、essary 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 a recognized operating agency. Compliance with this Recommendation is voluntary. Howev
13、er, 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. The words “shall“ or some other obligatory language such as “must“ and the negative eq
14、uivalents 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 possibility that the practice or implementation of this Recommendation may involve the use of a
15、 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 Recommendation development process. As of the date of approval of this Recommendation, ITU
16、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 and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/
17、ITU-T/ipr/. ITU 2009 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 (05/2009) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 1 4 Abbreviations 1 5 Overview 2 5.1 Line test referen
18、ce model . 2 5.2 Test measurements . 3 6 Test management and communications 4 Annex A Specific requirements of a SELT-PMD 5 A.1 SELT-PMD functions. 5 A.2 SELT-PMD management entity. 7 A.3 Test management and communications 10 Annex B Specific requirements of a SELT-P . 11 B.1 SELT-P functions . 11 B
19、.2 SELT-P management entity . 13 B.3 Test management and communications 17 Annex C Specific requirements for a DELT-PMD. 18 Annex D Specific requirements for a DELT-P. 19 Annex E Specific requirements for a MELT-PMD 20 E.1 MELT-PMD functions . 20 E.2 MELT-PMD management entity 23 E.3 Test management
20、 27 Annex F Specific requirements for a MELT-P. 28 F.1 MELT-P functions 28 F.2 MELT-P management entity 30 F.3 Test management 34 Appendix I SELT application models. 35 I.1 CO SELT application models. 35 Bibliography. 37 Rec. ITU-T G.996.2 (05/2009) 1 Recommendation ITU-T G.996.2 Single-ended line t
21、esting for digital subscriber lines (DSL) 1 Scope This Recommendation specifies line testing for use on xDSL lines. This Recommendation contains annexes that describe specifications for single-ended line testing (SELT), dual-ended line testing (DELT) and metallic line testing (MELT). Separate annexe
22、s describe physical medium dependent (PMD) and processing functions for SELT, DELT and MELT. An informative appendix is also included describing SELT application models. In this Recommendation, one or more of the line testing (LT) functional blocks may, but are not required to, be the same as the xD
23、SL transceiver unit (xTU) functional block. 2 References This Recommendation does not contain any references to external documents. 3 Definitions None. 4 Abbreviations This Recommendation uses the following abbreviations: ACS Automatic Configuration System ADC Analogue-to-Digital Conversion AFE Anal
24、ogue Front End AGC Automatic Gain Control CO Central Office CPE Customer Premises Equipment DELT Dual-Ended Line Test DSLAM DSL Access Multiplexer DSP-FE Digital Signal Processor Front End HPF High-Pass Filter LPF Low-Pass Filter LT Line Test ME Management Entity MELT Metallic Line Test MIB Manageme
25、nt Information Base NSC Number of SubCarriers OSS Operations Support System PGA Programmable Gain Amplifier PMD Physical Medium Dependent 2 Rec. ITU-T G.996.2 (05/2009) POTS Plain Old Telephone Service PSD Power Spectral Density QLN Quiet Line Noise Rx Receive SELT Single-Ended Line Testing Tx Trans
26、mit UER Uncalibrated Echo Response xDSL Any DSL xTU-C xDSL Transceiver Unit at the Central side xTU-R xDSL Transceiver Unit at the Remote side (e.g., subscriber at the end of the loop) 5 Overview Line testing involves the measurement of electrical signals on a line, with or without a stimulus applie
27、d to the near end or the far end of the loop. These measurements are used to determine measurement parameters which are the basic parameters that characterize the loop and its noise environment. Derived parameters are derived from the measurement parameters and provide specific features of the loop
28、and the noise environment. 5.1 Line test reference model In order to produce the parameters to be delivered to the management system from observations of the loop connected at one termination side to the U-C interface and at the other side to the U-R interface, a number of distinctive functions can
29、be identified. Each of these functions is represented by a functional block (rectangle) in the functional reference model. Reference points are introduced into the model. Some reference points correspond to functional interfaces. Figure 5-1 depicts the functional reference model. Line Under Test Q i
30、nterface LT - ME - PMD - C MIB LT - ME - P - C MIB C ref point C ref point C ref point LT - PMD - C LT - P - C OSS U-CG interfaceLT - ME - PMD - R MIB LT - ME - P - R MIB Rref point R ref pointRref pointLT-PMD - RLT-P - RT interfaceACS U-RNOTE Arrows show flow of data elements only; flow of control
31、elements are bidirectional (not shown) Figure 5-1 Functional reference model There are four functional blocks at each end of a line. The following general descriptions of the functionality of each block apply at both ends of the line but the detail of their functionality may be different at each end
32、. Rec. ITU-T G.996.2 (05/2009) 3 The first functional block is called the LT-PMD (line test Physical medium dependent). The LT-PMD function performs measurements on the physical medium to which the line test device is connected. The result of a measurement is a quantity represented as a parameter (o
33、ne or more dimensional, discrete or continuous). From these parameters, measurement parameters are derived, usually through multiple measurements. The fact that the functional block is connected to the physical medium motivates calling it “PMD“. The prefix LT indicates that this functional block is
34、specific to line testing. However, in some instantiations, this may be the same as, or nearly the same as, instantiations of an xTU-PMD functional block. The second functional block is called the LT-P (LT Processing). The LT-P function transforms the measurement parameters into derived parameters. T
35、hese derived parameters directly reflect the characteristics of the loop under test. The third functional block is denoted LT-ME-P (LT Management entity P) and has the following functionalities: a) Data plane: to provide an interface point to the OSS, ACS or user for access to both derived and measu
36、rement parameters across the Q, G or T interfaces, respectively; to access the measurement parameters in the LT-ME-PMD across the reference point. b) Management plane: to manage the LT-P-MIB; to control the functionality of the LT-P across the reference point; to communicate with the far end LT-ME-P
37、 across the U interface to coordinate testing and exchange derived and measurement parameters. The fourth functional block is denoted LT-ME-PMD (LT Management entity PMD) and has the following functionalities: a) Data-plane: to provide to the LT-ME-P access to measurement parameters. b) Management p
38、lane: to manage the LT-PMD-MIB; to control the measurements performed by the LT-PMD across the reference point. The term “LT“ in the line test reference model refers to all forms of line test (i.e., SELT, DELT and MELT). In Annexes A and B, which contain SELT requirements, the term “SELT“ is used in
39、 place of the term “LT“. In Annexes C and D, which contain DELT requirements, the term “DELT“ is used in place of the term “LT“. In Annexes E and F, which contain MELT requirements, the term “MELT“ is used in place of the term “LT“. 5.2 Test measurements The test measurements are fundamental electri
40、cal measurements. Three types of measurements can be distinguished: 1) Measurements at the near end that are associated with an excitation of the physical medium from the PMD block at the near end. 2) Measurements at the near end that are associated with an excitation of the physical medium from the
41、 PMD block at the far end. 3) Measurements that do not require any excitation. 4 Rec. ITU-T G.996.2 (05/2009) A sequence of measurements of the first two measurement types is defined as the measurements associated with a sequence of corresponding excitations. For the third measurement type, the PMD
42、blocks at either end shall not inject any signal on to the line. 6 Test management and communications Test management and communications are for further study. Rec. ITU-T G.996.2 (05/2009) 5 Annex A Specific requirements of a SELT-PMD (This annex forms an integral part of this Recommendation) A.1 SE
43、LT-PMD functions A.1.1 SELT-PMD measurement functions A.1.1.1 Measurement of uncalibrated echo response The uncalibrated echo response function UER(f) is defined as the estimated mean value of the voltage ratio V(f)/E(f) measured inside the SELT-PMD. =)()()( with)(_)(fEfVfXfXMeanEstimatedfUER where
44、E(f) is the excitation signal and V(f) the measured signal at frequency f. E(f) is the voltage of a 0 ohm voltage source applied to the SELT-PMD transmitter front end, which transmits a voltage waveform V1+ on the SELT-PMD U-interface. The U-interface is connected to the one-port network (line) unde
45、r test, that will generate a reflected voltage wave V1. A linear combination of the voltage waveform V1+ and the reflected voltage wave V1 is transformed by the SELT-PMD receiver front end into a voltage V(f) measured with a high impedance voltage measurement unit. The schematic representation of th
46、e SELT-PMD unit is shown in Figure A.1. One-port network U-interface V SELT PMD unitE SELT-PMD Transmitter use of Trellis coding; target margin equal to CAP-TARSNRM (see clause B.2.1.4); transmit signal PSD at the U-interface of the xTU-transmitter equal to CAP-SIGNALPSD (see clause B.2.1.2); noise
47、PSD at the U-interface of the xTU-receiver equal to CAP-NOISEPSD (see clause B.2.1.3); support of bit loading from 1 to 15 bits included, in steps of 1 bit increments. As the capacity is a best-effort estimate, accuracy for this parameter is vendor proprietary. The parameter in the downstream direct
48、ion is CAPACITYds, and the parameter in the upstream direction is CAPACITYus. B.2 SELT-P management entity B.2.1 SELT-P configuration parameters B.2.1.1 Capacity estimate calculation enabling (CECE) This parameter specifies if the SELT-P function shall perform the “downstream capacity“ and “upstream
49、 capacity“ estimations, if supported. This parameter is expressed as a binary flag and takes the value 0 if xDSL performance estimation is not required, 1 otherwise. 14 Rec. ITU-T G.996.2 (05/2009) B.2.1.2 Capacity estimate signal PSD (CAP-SIGNALPSD) This configuration parameter defines the PSD template of the transmit signal to be used in capacity estimate evaluation. The PSD template CAP-SIGNALPSD shall be specified through a set of breakpoin
