1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T G.712TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/2001) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital terminal equipments Coding of analogue signals by pulse code modulation Transmission performance characteristics
2、of pulse code modulation channels ITU-T Recommendation G.712 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
3、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 TELEPHONY
4、 G.450G.499 TESTING EQUIPMENTS G.500G.599 TRANSMISSION MEDIA CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 General G.700G.709 Coding of analogue signals by pulse code modulation G.710G.719 Coding of analogue signals by methods other than PCM G.720G.729 Principal characteristics o
5、f primary multiplex equipment G.730G.739 Principal characteristics of second order multiplex equipment G.740G.749 Principal characteristics of higher order multiplex equipment G.750G.759 Principal characteristics of transcoder and digital multiplication equipment G.760G.769 Operations, administratio
6、n and maintenance features of transmission equipment G.770G.779 Principal characteristics of multiplexing equipment for the synchronous digital hierarchy G.780G.789 Other terminal equipment G.790G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 For further details
7、, please refer to the list of ITU-T Recommendations. ITU-T Rec. G.712 (11/2001) i ITU-T Recommendation G.712 Transmission performance characteristics of pulse code modulation channels Summary This Recommendation deals with the transmission performance characteristics of PCM channels of digital trans
8、mission equipment. Requirements to be met between 4-wire and 2-wire analogue ports are given as well as requirements for analogue-to-digital and digital-to-analogue connections. The parameters and values specified in this Recommendation apply to the use of PCM equipment connected to analogue trunks
9、or to analogue and digital exchanges. Source ITU-T Recommendation G.712 was prepared by ITU-T Study Group 15 (2001-2004) and approved under the WTSA Resolution 1 procedure on 29 November 2001. ii ITU-T Rec. G.712 (11/2001) FOREWORD The International Telecommunication Union (ITU) is the United Nation
10、s specialized agency in the field of telecommunications. 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 telecommunicatio
11、ns on a worldwide basis. 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 la
12、id down in WTSA Resolution 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 telecommunic
13、ation administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility 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
14、 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 had not received notice of intellectual property, protected by patents, which may be required
15、 to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2002 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any
16、 means, electronic or mechanical, including photocopying and microfilm, without permission in writing from ITU. ITU-T Rec. G.712 (11/2001) iii CONTENTS Page 0 Scope 1 1 General . 1 1.1 Measurement considerations 1 1.2 Port definitions . 2 1.3 Abbreviations . 3 2 Relative levels at analogue ports 3 2
17、.1 Relative levels at 4-wire ports (E4) 3 2.2 Relative levels at 2-wire ports (E2) 4 3 Adjustment of actual relative levels . 4 3.1 Adjustment of the decoding side (Tinto Eout). 4 3.2 Adjustment of the encoding side (Einto Tout). 4 3.3 Load capacity (overload point) 4 4 Short- and long-term variatio
18、n of loss with time . 4 5 Nominal impedance and return loss of analogue ports 5 5.1 Nominal impedance 5 5.2 Return loss 5 6 Impedance unbalance about earth 6 6.1 Longitudinal conversion loss . 6 6.2 Longitudinal conversion transfer loss 7 7 Attenuation/frequency distortion 7 8 Group delay 10 8.1 Abs
19、olute group delay . 10 8.2 Group delay distortion with frequency. 10 9 Idle channel noise. 12 9.1 Weighted noise. 12 9.2 Single frequency interference. 13 10 Discrimination against out-of-band signals 13 10.1 Input signals above 4600 Hz at analogue ports E4 and E2 13 10.2 Input signals below 300 Hz
20、at analogue ports E4 and E2 13 10.3 Overall requirement (4-wire only) . 13 11 Spurious signals at the channel output port 14 11.1 Spurious out-of-band signals at the channel output port 14 11.1.1 In-band input signal 14 iv ITU-T Rec. G.712 (11/2001) Page 11.1.2 Overall requirement 14 11.2 Spurious i
21、n-band signals at the channel output port 14 12 Total distortion, including quantizing distortion 15 13 Variation of gain with input level. 16 14 Crosstalk. 17 14.1 General . 17 14.2 Interchannel crosstalk, channels between analogue ports 17 14.2.1 Far-end crosstalk 17 14.2.2 Go-to-return crosstalk
22、for channels between 4-wire analogue ports 17 14.3 Interchannel crosstalk, channels between analogue and digital ports 18 14.3.1 Far-end and near-end crosstalk measured with analogue test signal . 18 14.3.2 Go-to-return crosstalk measured with analogue test signal . 20 14.3.3 Far-end and near-end cr
23、osstalk measured with digital test signal 20 14.3.4 Go-to-return crosstalk measured with digital test signal 21 15 Interference from signalling . 22 15.1 Channels between 4-wire analogue ports. 22 15.2 Channels between 2-wire analogue ports. 22 15.3 Channels between 4-wire analogue and digital ports
24、. 22 15.4 Channels between 2-wire analogue and digital ports. 23 16 Echo and stability at 2-wire ports, E2 23 16.1 Terminal Balance Return Loss (TBRL). 23 16.2 Stability Loss (SL) . 24 Appendix I Alternative measurement methods using band limited noise signals 25 I.1 Variation of gain with input lev
25、el 25 I.2 Total distortion, including quantizing distortion 26 Appendix II Method of derivation of the signal-to-total distortion ratio for the A-law . 29 ITU-T Rec. G.712 (11/2001) 1 ITU-T Recommendation G.7121Transmission performance characteristics of pulse code modulation channels 0 Scope This R
26、ecommendation deals with the transmission performance characteristics of PCM channels transmitted via digital transmission equipment. Requirements to be met between 4-wire and 2-wire analogue ports are given as well as requirements for analogue-to-digital and digital-to-analogue connections. 1 Gener
27、al Performance characteristics which follow should be met between voice-frequency ports or between the voice-frequency and digital ports of PCM channels coded in accordance with ITU-T Rec. G.711. Equipment which meets the analogue-to-analogue requirements, but not the analogue-to-digital requirement
28、s, may only be used as permanently connected pairs of equipment. The parameters and values specified in this Recommendation apply to the use of PCM equipment connected to analogue trunks or to analogue and digital exchanges. When PCM equipment is connected directly to analogue subscriber lines, diff
29、erent values for some of the parameters may be required. ITU-T Rec. Q.552 contains those values. The requirements in this Recommendation may also be applied if the PCM equipment is directly connected to an analogue local exchange that is virtually transparent with regard to the impedances connected
30、to its ports and the subscriber lines are short (e.g. less than 500 metres). Line current is not normally to be expected at the ports of the PCM equipment. If “line current“ is nevertheless present, as is the case when signalling takes place on the two wires, any noise it contributes should meet req
31、uirements at the appropriate interface as described in the Q.550-series of Recommendations. The limits should be met when any signalling function is in the normal speaking condition, but excluding any dynamic signalling conditions, e.g. metering. 1.1 Measurement considerations When a nominal referen
32、ce frequency of 1020 Hz is indicated (e.g. measurement of attenuation/frequency distortion and adjustment of relative levels), the actual frequency should be 1020 Hz, +2 Hz, 7 Hz in accordance with ITU-T Rec. O.6. In the following subclauses, the concepts of a “standard digital generator“ and “a sta
33、ndard digital analyser“ should be assumed and these are defined as follows. A standard digital generator is a hypothetical device which is absolutely ideal, i.e. a perfect analogue-to-digital converter preceded by an ideal low pass filter (assumed to have no attenuation/frequency distortion and no g
34、roup delay distortion), and which may be simulated by a digital processor. A standard digital analyser is a hypothetical device which is absolutely ideal, i.e. a perfect digital-to-analogue converter followed by an ideal low pass filter (assumed to have no attenuation/frequency distortion and no gro
35、up delay distortion), and which may be simulated by a digital processor. _ 1This Recommendation replaces ITU-T Recs. G.712, G.713, G.714 and G.715 of the CCITT Blue Book Volume III, Fascicle III.4. 2 ITU-T Rec. G.712 (11/2001) ITU-T Rec. O.133 contains information about test equipment based on these
36、 concepts. Account should be taken of the measurement accuracy provided by test equipment designed in accordance with that Recommendation. A PCM quiet signal is defined to be an idle character signal corresponding to decoder output value number 0 for -law or decoder output value number 1 for A-law w
37、ith the sign bit in a fixed state. The following specifications are based on ideal measuring equipment. Therefore, they do not include any margin for measurement errors. 1.2 Port definitions The term “port“ in this Recommendation is defined as a functional unit (e.g. a connector) of the PCM equipmen
38、t through which signals can enter or leave the unit under test. The measurements are made at the equipment, and the requirements do not include an allowance for wiring to a distribution frame. Figure 1 shows two elements of PCM equipment connected via a digital cross-connect (DXC) system. Each eleme
39、nt of PCM equipment is shown to have a 4-wire analogue voice-frequency port, E4, and a 2-wire analogue voice-frequency port, E2. Each of the PCM elements is connected to the DXC by digital ports A or B (ports A and B are defined in 1.1/Q.551), which consists of transparent 64 kbit/s PCM channels wit
40、hin a higher order digital signal conforming to applicable Recommendations. The DXC implements transparent 64 kbit/s cross connections between its own A or B ports, or to the digital test point, T. The T point consists of a 64 kbit/s channel within a digital signal suitable for connection to the sta
41、ndard digital generator and analyser. Since the connections provided by the DXC are 64 kbit/s transparent, the paths within the DXC are assumed not to affect the recommended transmission performance characteristics except for absolute delay. The test points T are defined for specification purposes.
42、They may not physically exist in a DXC but may be accessed via the DXC network. Unless stated otherwise, measurements between two-wire ports (E21into E22outconnections) should be made with the 4-wire loop opened in such a way that the impedances presented to the 4-wire port of the 2-wire/4-wire term
43、inating unit are representative of those that will occur in normal operation. This condition may be achieved by interrupting the digital signal in the opposite direction to the direction of measurement and injecting a PCM quiet signal into the appropriate channel. It should be noted that the opening
44、 of the 4-wire loop is considered necessary to determine the intrinsic performance of the equipment. In normal operation, where the loop is not opened, the impact on overall performance of the terminating impedances connected to the 2-wire ports needs to be taken into account. Figure 1 is similar to
45、 Figure 1/Q.551, which identifies interfaces, transmission levels designations and test points at a digital exchange. The performance characteristics between ports were previously specified in CCITT Blue Book, Volume III, Fascicle III.4, as shown in the Table 1. ITU-T Rec. G.712 (11/2001) 3 T1507320
46、-02LiLoLiLoLiLiLoLo0 dBr 0 dBr0 dBr0 dBrMultiplexer 1Digitalcross-connectsystemAnalogue portsTinToutAnalogue pathDigital path Analogue padA/D conversionMultiplexer 2Analogue portsDigitalport, A or B Digitalport, A or B Digital test point, TE41inE41outE42outE42inE22out, in NOTE Numbers 1 or 2 in the
47、subscript indicate multiplexers 1 or 2.E21in,outFigure 1/G.712 PCM equipment and test ports Table 1/G.712 Equivalence between previous ITU-T Recommendations and channels specified in this Recommendation Channel Previous ITU-T Recommendation 4-wire analogue to 4-wire analogue (E41to E42channels) G.71
48、2 2-wire analogue to 2-wire analogue (E21to E22channels) G.713 4-wire analogue-to-digital (E4 to A or B for a primary multiplexer) G.714 2-wire analogue-to-digital (E2 to A or B for a primary multiplexer) G.715 1.3 Abbreviations This Recommendation uses the following abbreviations: DXC Digital Cross
49、-Connect FDM Frequency Division Multiplex FEXT Far-End crosstalk NEXT Near-End crosstalk PCM Pulse Code Modulation SL Stability Loss TBRL Terminal Balance Return Loss 2 Relative levels at analogue ports 2.1 Relative levels at 4-wire ports (E4) When attenuation pads are set to zero loss, Loat E42outand Liat E41inmust have one of the following two series of nominal values: Maximum Lo= +4 dBr and minimum Li= 14 dBr; or maximum Lo = +7 dBr and minimum Li= 16 dBr. See 11/G.232. 4 ITU-T Rec. G.712 (11/2001) 2.2 Relative levels at
