1、INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU G.992.2 (06199) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital transmission systems - Digital sections and digital line system - Access networks Splitterless asymmetric digital
2、 subscriber line (ADSL) transceivers ITU-T Recommendation G.992.2 (Previously CClTT Recommendation) STD=ITU-T RECMN G=992=2-ENGL 1999 m 118b2591 Obb8137 0117 m ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS
3、 INTERNATIONAL ANALOGUE CARRIER SYSTEM GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER- TRANSMISSION SYSTEMS INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE WITH METALLIC LINES COORDINATION OF R
4、ADIOTELEPHONY AND LINE TELEPHONY TESTING EQUIPMENTS TRANSMISSION MEDIA CHARACTERISTICS DIGITAL TRANSMISSION SYSTEMS TERMINAL EQUIPMENTS DIGITAL NETWORKS DIGITAL SECTIONS AND DIGITAL LINE SYSTEM SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION General Parameters for optical fibre cable s
5、ystems Digital sections at hierarchical bit rates based on a bit rate of 2048 kbitls Digital line transmission systems on cable at non-hierarchical bit rates Digital line systems provided by FDM transmission bearers Digital line systems Digital section and digital transmission systems for customer a
6、ccess to ISDN Optical fibre submarine cable systems Optical line systems for local and access networks G.100-G.199 G.200-G.299 G.3004.399 G.4004.449 G.450-G.499 G.700-G.799 G.800-G.899 G.900-G.999 G.900-G.909 G.910-G.919 G.920-G.929 G.930-G.939 G.940-G.949 G.950-G.959 G.960-G.969 G.970-G.979 G.980-G
7、.989 For jtrther details, please reJm to ITU-T List of Recommendations. ITU-T RECOMMENDATION G.992.2 SPLITTERLESS ASYMMETRIC DIGITAL SUBSCRIBER LINE (ADSL) TRANSCEIVERS Summary This Recommendation describes the interface between the telecommunications network and the customer installation in terms o
8、f their interaction and electrical characteristics. This Recommendation allows the transmission of POTS and V-series data services simultaneously with a digital channel over a single mixed gauge twisted metallic pair. Annex C defines the procedures to operate in a TCM-ISDN noise environment. Operati
9、on in the frequency band over BRA-ISDN is for further study. This Recommendation includes procedures to allow provisioning without the need for “splitters“, typically installed at the ingress to the customer premises. Additionally, power management procedures and link states are specified to achieve
10、 power savings at the central office and customer premises. Source ITU-T Recommendation G.992.2 was prepared by ITU-T Study Group 15 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on 22 June 1999. Recommendation G.992.2 (06199) i FOREWORD ITU (International Telecommunication
11、Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a vie
12、w to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which,.in their turn, produce Recommendations on these topics. The approval of Recommend
13、ations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1, In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation, the expression “Ad
14、ministration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectua
15、l Property Right. The 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, the ITU had not rece
16、ived notice of intellectual property, protected by patents, which may be required 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. o ITU 2000 All rights reserv
17、ed. No part of this publication may be reproduced or utilized in any fm or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. ii Recommendation G.992.2 (06/99) 1 2 3 3.1 3.2 4 4.1 4.2 5 6 6.1 6.2 7 7.1 7.2 7.3 7.4 7.6 7.7 7.8 7.9
18、 . . . . STD.ITU-T RECMN G.992-2-ENCL 1999 m q8b2591 Obb8LqO by1 m CONTENTS Page Scope 1 References . 1 Definitions and abbreviations . 2 Definitions . 2 Abbreviations 3 Reference models . 6 System reference model . 6 ATU reference model 7 Transport capacity 8 ATU interfaces 9 ATU interface for ATM
19、transport 9 ATU PMD to TC logical interface . 9 ATU fnctional characteristics . 10 ATM transport protocol specific fnctionalities 10 7 . 1 . 1 . Payload transfer delay . 10 7.1.2 ATM cell specific fnctionality 10 7.1.3 Framing structure for ATM transport 12 Network Timing Reference 12 7.2.1 Optional
20、 NTR capability . 12 7.2.2 Transport ofthe NTR . 12 Framing . 13 7.3.1 Relationship to G.992.1 fiaming 13 7.3.2 Bit ordering 13 7.3.3 Data fiaming and reference points . 13 Scrambler 17 7.5 Reed-Solomon Forward Error Correction . 17 7.5.1 Reed-Solomon coding 18 7.5.2 Reed-Solomon Forward Error Corre
21、ction superframe synchronization 18 Interleaver . 18 Tone ordering 19 Constellation encoder 19 7.8.1 Bit extraction 19 7.8.2 Constellation encoder 19 Gain scaling . 22 7.1 O Modulation 22 . Recommendation G.992.2 (06199) 111 7.1 1 7.12 8 8.1 8.2 8.3 8.4 8.5 9 9.1 9.2 iv 7.10.1 Subcarriers 7.10.2 Mod
22、ulation by the inverse discrete Fourier transform (IDFT) 7.10.3 Synchronization symbol 7.10.4 Upstream data pattern . 7.10.5 Downstream data pattern Cyclic prefix Transmitter dynamic range . 7.12.1 Maximum chppmg rate 7.12.2 NoiseDistortion floor . 7.12.3 Transmitter spectral masks Embedded Operatio
23、ns Channel (eoc) . eoc introduction . 8 . 1 . 1 eoc messages overview . 8.1.2 eoc protocol overview ; . eoc message encoding 8.2.1 ADDRESS field (# 1) . 8.2.2 DATA or OPCODE field (# 2) 8.2.3 BYTE PARITY field (# 3) . i 8.2.4 AUTONOMOUS MESSAGE field (# 4) . 8.2.5 INFORMATION field (# 5) eoc message
24、 descnptlon . 8.3.1 Latching bidirectional eoc messages 8.3.2 End of Data message (EOD) . 8.3.3 Dying Gasp message (DGASP) . 8.3.4 Autonomous messages 8.3.5 Data registers in the ATU-R eoc protocol 8.4.1 Outstanding eoc messages . 8.4.2 eoc state transltlons Clear eoc . ADSL overhead channel . The A
25、DSL Overhead Control (aoc) channel introduction . 9 . 1 . 1 Bit swap channel . 9.1.2 Supe all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently val
26、id ITU-T Recommendations is regularly published. ITU-T Recommendation 1.361 (1999), B-ISDNATM layer spec$cation. ITU-T Recommendations 1.432 x-series, B-ISDN user-network interface - Physical layer spedjcation . ITU-T Recommendation G.703 (1 998), Physical/electrical characteristics of hierarchical
27、digital interfaces. ITU-T Recommendation G.707 (1996), Network node interface for the synchronous digital hierarchy (SDH). ITU-T Recommendation G.961 (1993), Digital transmission system on metallic local lines for ISDN basic rate access. ITU-T Recommendation G.994.1 (1999), Handshake procedures for
28、digital subscriber line (OSL) transceivers. ITU-T Recommendation G.992.1 (1999), Asymmetric digital subscriber Zine (ADSL) transceivers. ITU-T Recommendation G.996.1 (1999), Test procedures for digital subscriber line PSL) transceivers. ITU-T Recommendation G.997.1 (1999), Physical layer management
29、for digital subscriber line (DSL) transceivers. Recommendation G.992.2 (06199) 1 101 CCITT Recommendation T.35 (1991), Procedure for the allocation of CCITT defined codes 1 11 ITU-T Recommendation 0.41 (1994), Psophorneter for use on telephone-type circuits. for non-standard facilities. 3 Definition
30、s and abbreviations 3.1 Definitions This Recommendation defines the following terms: 3.1.1 data frame: A fiame of bytes that compose part of the superfkame. 3.1.2 downstream: The transport of data in the ATU-C to ATU-R direction. 3.1.3 DMT symbol: A collection of analog samples that constitute a mod
31、ulated Data Frame. 3.1.4 mux data frame: A data entity consisting of ASOLSO and the Sync Byte (SB). 3.1.5 ASO: The data channel fiom the ATU-C to the ATU-R. 3.1.6 superframe: A data entity consisting of 68 Data Frames and one Sync Frame. 3.1.7 LSO: The data channel fiom the ATU-R to the ATU-C. 3.1.8
32、 sync byte: A byte of data in the Mux Data Frame that contains either aoc, eoc or IB bits. 3.1.9 sync symbol: A DMT symbol modulated with a constant data pattern. 3.1.10 sync frame: A fiame of bytes that compose part of the superfiame. 3.1.11 FEC output frame: A fiame of data presented to the conste
33、llation encoder after Reed- Solomon encoding. 3.1.12 upstream: The transport of data in the ATU-R to ATU-C direction. 3.1.13 indicator bits: Bits used for OAM purposes. 3.1.14 subcarrier: A particular complex valued input, Zi, to the IDFT. 3.1.15 splitter: A filter that separates the high kequency s
34、ignals (ADSL) fiom the voiceband signals (fiequently called POTS splitter). 3.1.16 voiceband: The frequency band ?om O to 4 kHz. 3.1.17 voiceband services: POTS and all data services that use the voiceband or part of it. 3.1.18 network timing reference: An 8 kHz timing marker used to support the dis
35、tribution of a timing reference over the network. Power Cutback definitions 3.1.19 absolute downstream fast retrain power cutback The addition of Fast Retrain Politeness Power Cutback and Relative Downstream Fast Retrain Power Cutback. 3.1.20 absolute upstream fast retrain power cutback A power cutb
36、ack at the ATU-R transmitter relative to ATU-R Nominal Level. Transmitted to the ATU-C in R-MSG-FR1. 3.1.21 fast retrain politeness power cutback: A power cutback relative to the Nominal Level at the ATU-C as applied to the previous C-REVERB-FR1 signal. Transmitted in C-MSG-FR1. 3.1.22 initializatio
37、n politeness power cutback A power cutback at the ATU-C transmitter as a result of measurement of the average upstream loop attenuation during R-REVERB l. 3.1.23 nominal level: Nominal transmit level at the ATU-R shall be -38 dBm/Hz. Nominal transmit level at the ATU-C shall be -40 dBm/Hz. 2 Recomme
38、ndation G.992.2 (06/99) 3.1.24 relative downstream fast retrain power cutback An additional power cutback to the ATU-C transmit power that is requested by the ATU-R. This power cutback shall be relative to: (ATU-C Nominal Level - the ATU-C Fast Retrain Politeness Power Cutback). Transmitted to the A
39、TU-C in R-MSG-FR.1. 3.2 Abbreviations This Recommendation uses the following abbreviations: ADSL AFE AGC ANSI aoc ASO ATM ATN ATU ATU-C ATU-R BER C-B - or multiple bit error detection. Error detection shall be implemented as defined in Recommendation 1.432 with the exception that any HEC error shall
40、 be considered as a multiple bit error, and therefore, HEC error correction shall not be performed. Recommendation G.992.2 (06199) 11 7.1.3 Framing structure for ATM transport The ATU-C transmitter shall preserve V-C and T-R interfce byte boundaries (explicitly present or implied by ATM cell boundar
41、ies) at the U-C interface. 7.2 Network Timing Reference 7.2.1 Optional NTR capability To support the distribution of a timing reference over the network, an ATU-C may optionally transport an 8 kHz timing marker as NTR. The 8 kHz timing marker is input to the ATU-C as part of the interface at the V-C
42、 reference point. 7.2.2 Transport of the NTR If included, an ATU-C shall transport the NTR as follows: The ATU-C shall generate an 8 kHz local timing reference (LTR) by dividing its sampling clock by the appropriate integer. It shall transmit the change in phase offset between the input NTR and LTR
43、(measured in cycles of a 1.104 MHz clock in units of approximately 905 m) fiom the previous superframe to the present one. The phase offset shall be encoded into four bits ntr3-ntr0 (with ntr3 the MSB), representing a signed integer in the -8 to +7 range in twos-complement notation. The bits ntr3-nt
44、r0 shall be carried in the indicator bits 23 (ntr3) to 20 (ntr0); see Table 4. NOTE 1 -A positive value of the change of phase offset, A*$, shall indicate that the LTR is higher in frequency than the NTR. NOTE 2 - The NTR has a maximum frequency variation of +32 ppm. The LTR, as specified in 7.2.2,
45、has a maximum frequency variation of +50 ppm. The maximum mismatch is therefore +82 ppm. This would result in an average change of phase offset in one 17 ms superframe of approximately f1.75 clock cycles, which can be mapped into four overhead bits. NOTE 3 - One method that the ATU-C may use to meas
46、ure this change of phase offset is shown in Figure 7. NOTE 4 - Alternatively, the ATU-C may choose to lock its downstream sampling clock (l. 1 O4 MHz) to 138 times the NTR frequency; in that case it shall encode A t$ to zero. 2 9 9 9 I I I *+Il NTR register I register 9 d I _. - count 1.104 MHz - MC
47、 mod 136 MC , mod 138 count register b T153338099 (MC is maxcount indication before foldover to O) Figure 7/6.992.2 - Example implementation of the A24 measurement 7.3 Framing 7.3.1 Relationship to G.992.1 framing The fiaming is equivalent to the “reduced overhead mode with merged fast and sync byte
48、s“ as defined in Recommendation 7.4.4.2/G.992.1 using only the “interleave buffer“ definition. Only a single duplex channel is supported, consisting of a simplex ASO downstream channel and a simplex LSO upstream channel. 7.3.2 Bit ordering External to the ASOLSO serial interfaces data bytes are tran
49、smitted MSB first in accordance with Recommendations G.703, G.709, 1.361 and 1.432. All serial processing in the superfiame (e.g. crc, scrambling, etc.) shall, however, be performed LSB first, with the outside world MSB considered as the LSB. As a result, the first incoming bit (outside world MSB) will be the first bit processed by the ATU (ATU LSB). 7.3.3 Data framing and reference points Figure 2 shows a hctional block diagram of the ATU transmitter with reference points for data framing. A cyclic redundancy check (crc), scrambling, forward error correction (FEC)
