INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU G.991. 0/001) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital sections and digital line system Access networks Single-pair high-speed digital subscriber line SHDSL) transceivers ITU-T Recommendation G.991.
ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS 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 SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY TESTING EQUIPMENTS TRANSMISSION MEDIA CHARACTERISTICS DIGITAL TERMINAL EQUIPMENTS DIGITAL NETWORKS DIGITAL SECTIONS AND DIGITAL LINE SYSTEM General Parameters or optical ibre cable systems Digital sections at hierarchical bit rates based on a bit rate o 048 kbit/s 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 or customer access to ISDN Optical ibre submarine cable systems Optical line systems or local and access networks Access networks G.100 G.199 G.00 G.99 G.300 G.399 G.400 G.449 G.450 G.499 G.500 G.599 G.600 G.699 G.700 G.799 G.800 G.899 G.900 G.999 G.900 G.909 G.910 G.919 G.90 G.99 G.930 G.939 G.940 G.949 G.950 G.959 G.960 G.969 G.970 G.979 G.980 G.989 G.990 G.999 For urther details, please reer to the list o ITU-T Recommendations.
ITU-T Recommendation G.991. Single-pair high-speed digital subscriber line SHDSL) transceivers Summary This Recommendation describes a transmission method or data transport in telecommunications access networks. SHDSL transceivers are designed primarily or duplex operation over mixed gauge two-wire twisted metallic pairs. Optional our-wire operation is supported or extended reach applications. Optional signal regenerators or both single-pair and two-pair operation are speciied, as well. SHDSL transceivers are capable o supporting selected symmetric user data rates in the range o 19 kbit/s to 31 kbit/s using a Trellis Coded Pulse Amplitude Modulation TCPAM) line code. They are designed to be spectrally compatible with other transmission technologies deployed in the access network, including other DSL technologies. SHDSL transceivers do not support the use o analogue splitting technology or coexistence with either POTS or ISDN. Regional requirements, including both operational dierences and perormance requirements, are speciied in Annexes A, B and C. Requirements or signal regenerators are speciied in Annex D. Annex E describes application-speciic raming modes that may be supported by SHDSL transceivers. See G.99.1, Annex H [1] or speciications o transceivers or use in networks with existing TCM-ISDN service as speciied in ITU-T G.961, see Appendix IV [B1]). Source ITU-T Recommendation G.991. was prepared by ITU-T Study Group 15 001-004) and approved under the WTSA Resolution 1 procedure on 9 February 001. ITU-T Rec. G.991. 0/001) i
FOREWORD The International Telecommunication Union ITU) is the United Nations specialized agency in the ield o telecommunications. The ITU Telecommunication Standardization Sector ITU-T) is a permanent organ o ITU. ITU-T is responsible or studying technical, operating and tari 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 our years, establishes the topics or study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval o ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas o inormation technology which all within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression "Administration" is used or conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation o this Recommendation may involve the use o a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability o claimed Intellectual Property Rights, whether asserted by ITU members or others outside o the Recommendation development process. As o the date o approval o this Recommendation, ITU had received notice o intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest inormation and are thereore strongly urged to consult the TSB patent database. ITU 00 All rights reserved. No part o this publication may be reproduced or utilized in any orm or by any means, electronic or mechanical, including photocopying and microilm, without permission in writing rom ITU. ii ITU-T Rec. G.991. 0/001)
CONTENTS Page 1 Scope... 1 Reerences... 1 3 Deinitions and abbreviations... 3.1 Deinitions... 3. Abbreviations... 4 Reerence models... 5 4.1 STU-x unctional model... 5 4. User plane protocol reerence model... 7 4.3 Application models... 7 5 Transport capacity... 8 6 PMD layer unctional characteristics... 8 6.1 Data mode operation... 8 6.1.1 STU data mode PMD reerence model... 8 6.1. TCM encoder... 8 6.1.3 Channel precoder... 10 6.1.4 Spectral shaper... 11 6.1.5 Power backo... 11 6. PMD activation sequence... 1 6..1 PMD activation reerence model... 1 6.. PMD activation sequence description... 13 6..3 Framer and scrambler... 16 6..4 Mapper... 16 6..5 Spectral shaper... 16 6..6 Timeouts... 16 6.3 PMD pre-activation sequence... 17 6.3.1 PMD pre-activation reerence model... 17 6.3. PMD pre-activation sequence description... 18 6.3.3 Scrambler... 19 6.3.4 Mapper... 0 6.3.5 Spectral shaper... 0 6.3.6 PMMS target margin... 0 6.4 G.994.1 pre-activation sequence... 0 6.4.1 G.994.1 code point deinitions... 1 6.4. G.994.1 tone support... 6.4.3 G.994.1 transactions... 6.4.4 Operation with signal regenerators... ITU-T Rec. G.991. 0/001) iii
Page 7 PMS-TC layer unctional characteristics... 7.1 Data mode operation... 7.1.1 Frame structure... 7.1. Frame bit deinitions... 4 7.1.3 CRC generation crc1 crc6)... 6 7.1.4 Frame synchronization... 7 7.1.5 Scrambler... 7 7.1.6 Dierential delay buer... 8 7. PMS-TC activation... 8 7..1 Activation rame... 8 7.. Activation scrambler... 30 8 TPS-TC layer unctional characteristics... 30 8.1 Payload block data structure... 30 8. Data interleaving in our-wire mode... 31 9 Management... 3 9.1 Management reerence model... 3 9. SHDSL perormance primitives... 3 9..1 Cyclical redundancy check anomaly CRC anomaly)... 3 9.. Segment anomaly SEGA)... 3 9..3 Loss o sync deect LOSW deect)... 33 9..4 Segment deect SEGD)... 33 9..5 Loop attenuation deect... 33 9..6 SNR margin deect... 33 9..7 Loss o sync word ailure LOSW ailure)... 33 9.3 SHDSL line related perormance parameters... 33 9.3.1 Code violation CV)... 33 9.3. Errored second ES)... 33 9.3.3 Severely errored second SES)... 34 9.3.4 LOSW second LOSWS)... 34 9.3.5 Unavailable second UAS)... 34 9.3.6 Inhibiting rules... 34 9.4 Perormance data storage... 34 9.5 Embedded operations channel... 34 9.5.1 Management reerence model... 34 9.5. EOC overview and reerence model... 35 9.5.3 EOC startup... 36 9.5.4 Remote management access... 38 9.5.5 EOC transport... 38 iv ITU-T Rec. G.991. 0/001)
Page 9.5.6 Examples o virtual terminal control unctions... 54 10 Clock architecture... 54 10.1 Reerence clock architecture... 54 10. Clock accuracy... 55 10.3 Deinitions o clock sources... 55 10.4 Synchronization to clock sources... 56 11 Electrical characteristics... 56 11.1 Longitudinal balance... 56 11. Longitudinal output voltage... 57 11.3 Return loss... 58 11.4 Transmit power testing... 60 11.4.1 Test circuit... 61 11.4. Test circuit calibration... 61 11.4.3 Total transmit power requirement... 61 11.5 Signal transer delay... 61 1 Conormance testing... 6 1.1 Micro-interruptions... 6 Annex A Regional requirements Region 1... 63 A.1 Scope... 63 A. Test loops... 63 A.3 Perormance tests... 64 A.3.1 Crosstalk margin tests... 65 A.3. Impulse noise tests... 70 A.3.3 Power spectral density o crosstalk disturbers... 7 A.4 masks... 78 A.4.1 Symmetric masks... 78 A.4. Asymmetric 1.536 or 1.544 mask... 80 A.4.3 Asymmetric masks or 768 or 776 kbit/s data rates... 83 A.5 Region-speciic unctional characteristics... 85 A.5.1 Data rate... 85 A.5. Return loss... 85 A.5.3 Span powering... 86 A.5.4 Longitudinal balance... 9 A.5.5 Longitudinal output voltage... 93 A.5.6 PMMS target margin... 93 Annex B Regional requirements Region... 93 ITU-T Rec. G.991. 0/001) v
Page B.1 Scope... 93 B. Test loops... 93 B..1 Functional description... 93 B.. Test loop topology... 94 B..3 Test loop length... 95 B.3 Perormance testing... 96 B.3.1 Test procedure... 96 B.3. Test set-up deinition... 96 B.3.3 Signal and noise level deinitions... 99 B.3.4 Perormance test procedure... 100 B.3.5 Impairment generator... 101 B.4 masks... 111 B.4.1 Symmetric masks... 111 B.4. Asymmetric.048 Mbit/s and.304 Mbit/s masks... 114 B.5 Region-speciic unctional characteristics... 116 B.5.1 Data rate... 116 B.5. Return loss... 117 B.5.3 Span powering... 117 B.5.4 Longitudinal balance... 118 B.5.5 Longitudinal output voltage... 118 B.5.6 PMMS target margin... 118 Annex C Regional requirements Region 3... 118 Annex D Signal regenerator operation... 119 D.1 Reerence diagram... 119 D. Start-up procedures... 119 D..1 SRU-C... 119 D.. SRU-R... 1 D..3 STU-C... 14 D..4 STU-R... 14 D..5 Segment ailures and retrains... 14 D.3 Symbol rates... 14 D.4 masks... 14 Annex E Application-speciic TPS-TC raming... 14 E.1 TPS-TC or clear channel data... 14 E. TPS-TC or clear channel byte-oriented data... 15 E.3 TPS-TC or unaligned DS1 transport... 16 vi ITU-T Rec. G.991. 0/001)
Page E.4 TPS-TC or aligned DS1/ractional DS1 transport... 17 E.5 TPS-TC or European 048 kbit/s digital unstructured leased line D048U)... 18 E.6 TPS-TC or unaligned European 048 kbit/s digital structured leased line D048S)... 18 E.7 TPS-TC or aligned European 048 kbit/s digital structured leased line D048S) and ractional... 19 E.8 TPS-TC or synchronous ISDN BRA... 130 E.8.1 ISDN BRA over SHDSL rames... 130 E.8. Mapping o ISDN B- and D-channels on SHDSL payload channels... 131 E.8.3 Multi-ISDN BRAs... 13 E.8.4 ISDN BRA or lieline service... 133 E.8.5 Time slot positions o ISDN B- and D 16 -channels EOC signalling)... 133 E.8.6 Time slot positions o ISDN B- and D 16 -channels and the optional ast signalling channel... 135 E.8.7 Signalling over the SHDSL EOC or the ast signalling channel... 138 E.8.8 S-Bus control... 141 E.8.9 BRA termination reset... 14 E.8.10 Transport o ISDN EOC messages over SHDSL EOC... 14 E.9 TPS-TC or ATM transport... 143 E.9.1 Abbreviations... 143 E.9. Reerence model or ATM transport... 143 E.9.3 Transport capacity and low control... 146 E.9.4 Operations and maintenance... 147 E.10 Dual bearer TPS-TC mode... 149 E.10.1 Dual bearer clock synchronization... 151 E.10. Dual bearer mode types... 151 Appendix I Test circuit examples... 153 I.1 Example crosstalk injection test circuit... 153 I. Example coupling circuits or longitudinal balance and longitudinal output voltage 153 I.3 Return loss test circuit... 154 I.4 Transmit /total power measurement test circuit... 154 Appendix II Typical characteristics o cables... 155 II.1 Typical characteristics o cables or Annex B... 155 Appendix III Signal regenerator start-up description... 156 III.1 STU-R initiated start-up... 157 III. STU-C initiated start-up... 158 III.3 SRU initiated start-up... 159 III.4 Collisions and retrains... 160 ITU-T Rec. G.991. 0/001) vii
Page III.5 Diagnostic mode activation... 160 Appendix IV Bibliography... 160 viii ITU-T Rec. G.991. 0/001)
Introduction This Recommendation describes a transmission method or data transport in telecommunications access networks. SHDSL transceivers are designed primarily or duplex operation over mixed gauge two-wire twisted metallic pairs. Optional our-wire operation is supported or extended reach applications. Optional signal regenerators or both single-pair and two-pair operation are speciied, as well. SHDSL transceivers are capable o supporting selected symmetric user data rates in the range o 19 kbit/s to 31 kbit/s using a Trellis Coded Pulse Amplitude Modulation TCPAM) line code. They are designed to be spectrally compatible with other transmission technologies deployed in the access network, including other DSL technologies. SHDSL transceivers do not support the use o analogue splitting technology or coexistence with either POTS or ISDN. Regional requirements, including both operational dierences and perormance requirements, are speciied in Annexes A, B and C. Requirements or signal regenerators are speciied in Annex D. Annex E describes application-speciic raming modes that may be supported by SHDSL transceivers. ITU-T Rec. G.991. 0/001) ix
ITU-T Recommendation G.991. Single-pair high-speed digital subscriber line SHDSL) transceivers 1 Scope This Recommendation describes a transmission method or providing Single-pair High-speed Digital Subscriber Line SHDSL) service as a means or data transport in telecommunications access networks. This Recommendation does not speciy all the requirements or the implementation o SHDSL transceivers. Rather, it serves only to describe the unctionality needed to assure interoperability o equipment rom various manuacturers. The deinitions o physical user interaces and other implementation-speciic characteristics are beyond the scope o this Recommendation. For interrelationships o this Recommendation with other G.99x-series ITU-T Recommendations, see ITU-T G.995.1 [B] in Appendix IV. The principal characteristics o this Recommendation are as ollows: provisions or duplex operation over mixed gauge two-wire or optional our-wire twisted metallic pairs; speciication o the physical layer unctionality, e.g. line codes and orward error correction; speciication o the data link layer unctionality, e.g. rame synchronization and raming o application, as well as Operations, Administration and Maintenance OAM) data; provisions or optional use o repeaters or extended reach; provisions or spectral compatibility with other transmission technologies deployed in the access network; provisions or regional requirements, including unctional dierences and perormance requirements. Reerences The ollowing ITU-T Recommendations and other reerences contain provisions which, through reerence in this text, constitute provisions o this Recommendation. At the time o publication, the editions indicated were valid. All Recommendations and other reerences are subject to revision; users o this Recommendation are thereore encouraged to investigate the possibility o applying the most recent edition o the Recommendations and other reerences listed below. A list o the currently valid ITU-T Recommendations is regularly published. [1] ITU-T G.99.1 1999), Asymmetric digital subscriber line ADSL) transceivers. [] ITU-T G.994.1 001), Handshake procedures or digital subscriber line DSL) transceivers. [3] ITU-T G.997.1 1999), Physical layer management or digital subscriber line DSL) transceivers. [4] IETF RFC 166 1994), PPP in HDLC-like Framing. [5] ISO 8601:000, Data elements and interchange ormats Inormation interchange Representation o dates and times. [6] ITU-T G.996.1 001), Test procedures or digital subscriber line DSL) transceivers. [7] IEC 60950 1999), Saety o inormation technology equipment. ITU-T Rec. G.991. 0/001) 1
[8] ITU-T I.43.1 1999), B-ISDN user-network interace Physical layer speciication: General characteristics. 3 Deinitions and abbreviations 3.1 Deinitions This Recommendation deines the ollowing terms: 3.1.1 bit-error ratio: The ratio o the number o bits in error to the number o bits sent over a period o time. 3.1. downstream: STU-C to STU-R direction central oice to remote terminal). 3.1.3 loopback: A reversal in the direction o the payload i.e. the user data) at a speciied SHDSL network element. 3.1.4 mapper: A device or associating a grouping o bits with a transmission symbol. 3.1.5 micro-interruption: A temporary line interruption. 3.1.6 modulo: A device having limited value outputs not the same as the mathematical modulo operation). 3.1.7 payload block: One o the sections o a rame containing user data. 3.1.8 plesiochronous: A clocking scheme in which the SHDSL rame is based on the input transmit clock but the symbol clock is based on another independent clock source. 3.1.9 precoder: A device in the transmitter or equalizing some o the channel impairments. 3.1.10 precoder coeicients: Coeicients o the ilter in the precoder that are generated in the receiver and transerred to the transmitter. 3.1.11 remote terminal: A terminal located downstream rom a central oice switching system. 3.1.1 scrambler: A device to randomize a data stream. 3.1.13 segment: The portion o a span between two terminations either STUs or SRUs). 3.1.14 SHDSL network element: An STU-R, STU-C or SRU. 3.1.15 span: The link between STU-C and STU-R, including regenerators. 3.1.16 spectral shaper: A device that reshapes the requency characteristics o a signal. 3.1.17 stu bits: Bits added to synchronize independent data streams. 3.1.18 synchronous: A clocking scheme in which the SHDSL rame and symbol clocks are based on the STU-C input transmit clock or a related network timing source. 3.1.19 upstream: STU-R to STU-C direction remote terminal to central oice). 3. Abbreviations This Recommendation uses the ollowing abbreviations: α The interace between the PMS-TC and TPS-TC layers in an STU-C β The interace between the PMS-TC and TPS-TC layers in an STU-R γ C The interace between the TPS-TC layer and the application speciic section in an STU-C ITU-T Rec. G.991. 0/001)
γ R a k AFE AGC b k BER bit/s C k CMRR CO CPE CRC CRC-6 crcx) DAC dbm DC DLL DS DSL DUT EOC ES s sym FCS FEC FEXT FSW gx) HDLC HW I/F kbit/s LB The interace between the TPS-TC layer and the application speciic section in an STU-R Convolutional Encoder Coeicients Analogue Front End Automatic Gain Control Convolutional Encoder Coeicients Bit Error Ratio Bits per second The kth Precoder Coeicient Common Mode Rejection Ratio Central Oice Customer Premises Equipment Cyclic Redundancy Check CRC o Order 6 used in SHDSL rame) CRC Check Polynomial Digital-to-Analogue Converter db reerence to 1 mw, i.e. 0 dbm = 1 mw Direct Current Digital Local Line Downstream Digital Subscriber Line Device Under Test Embedded Operations Channel Errored Second Sampling rate Symbol rate Frame Check Sequence Forward Error Correction Far-End CrossTalk Frame Synchronization Word Generating Polynomial or CRC High-level Data Link Control Hardware Interace kilobits per second Longitudinal Balance ITU-T Rec. G.991. 0/001) 3
LCL losd LOSW LSB LT mx) Mbit/s MSB MTU NEXT NT OAM OH PAM -PAM PBO PL-OAM PMD PMMS PMS-TC ppm PPP ps PTD REG rms RSP Rx S/T sb sbid sega segd SES SHDSL SNR Longitudinal Conversion Loss Bit indicating Loss o signal at the application interace Loss O Sync Word ailure Least Signiicant Bit Line Termination Message Polynomial or CRC Megabits per second Most Signiicant Bit Maintenance Termination Unit Near-End CrossTalk Network Termination Operations, Administration and Maintenance Overhead Pulse Amplitude Modulation PAM having two levels used at startup) Power BackO Physical Layer OAM Physical Media Dependent Power Measurement Modulation Session Line Probe) Physical Media-Speciic TC Layer Parts Per Million Point-to-Point Protocol Power status bit Power Spectral Density Path Terminating Device CO side terminating equipment) Signal Regenerator Root mean square Regenerator Silent Period bit Receiver Logical interace between the STU-R and attached user terminal equipment stu bit stu bit identiied indicator bit segment anomaly indicator bit segment deect indicator bit Severely Errored Second Single-Pair High Speed Digital Subscriber Line Signal-to-Noise Ratio 4 ITU-T Rec. G.991. 0/001)
TPS-TC TPS-TC SRU SHDSL Regenerator Unit STU SHDSL Transceiver Unit STU-C STU at the Central Oice STU-R STU at the Remote End TBD To Be Determined TC Transmission Convergence layer TCM Trellis Coded Modulation TCM-ISDN Time-Compression Multiplexed ISDN speciied in ITU-T G.961, see Appendix IV [B1]) TCPAM Trellis Coded PAM used in data mode) TPS-TC Transmission Protocol-Speciic TC Layer Tx Transmitter U-C Loop Interace Central Oice end U-R Loop Interace Remote Terminal end UAS Unavailable Second US Upstream UTC Unable to Comply V Logical interace between STU-C and a digital network element such as one or more switching systems xdsl a collective term reerring to any o the various types o DSL technologies 4 Reerence models 4.1 STU-x unctional model STU-R β γ R STU-C α γ C Customer Interaces) I/F I/F PMS-TC PMD SRU PMD PMS-TC I/F I/F Application Interaces) optional optional optional Application Speciic Section Application Invariant Section Application Invariant Section Application Speciic Section T1541130-00 Figure 4-1/G.991. STU-x unctional model ITU-T Rec. G.991. 0/001) 5
Figure 4-1 is a block diagram o an SHDSL Transceiver Unit STU) transmitter showing the unctional blocks and interaces that are reerenced in this Recommendation. It illustrates the basic unctionality o the STU-R and the STU-C. Each STU contains both an application invariant section and an application speciic section. The application invariant section consists o the PMD and PMS-TC layers, while the application speciic aspects are conined to the TPS-TC layer and device interaces. As shown in the igure, one or more optional signal regenerators may also be included in an SHDSL span. Management unctions, which are typically controlled by the operator's network management system, are not shown in the igure. See clause 9 or details on management. Remote power eeding, which is optionally provided across the span by the STU-C, is not illustrated in the igure. The unctions at the central oice side constitute the STU-C or Line Termination LT)). The STU-C acts as the master both to the customer side unctions o the STU-R or Network Termination NT)) and to any regenerators. The STU-C and STU-R, along with the DLL Digital Local Line) and any regenerators, make up an SHDSL span. The DLL may consist o a single copper twisted pair, or, in optional conigurations, two copper twisted pairs. In the two-pair cases, each STU contains two separate PMD layers, interacing to a common PMS-TC layer. I enhanced transmission range is required, one or more signal regenerators may be inserted into the loop at intermediate points. These points shall be chosen to meet applicable criteria or insertion loss and loop transmission characteristics. The principal unctions o the PMD layer are: symbol timing generation and recovery; coding and decoding; modulation and demodulation; echo cancellation; line equalization; link startup. The PMD layer unctionality is described in detail in clause 6. The PMS-TC layer contains the raming and rame synchronization unctions, as well as the scrambler and descrambler. The PMS-TC layer is described in clause 7. The PMS-TC is connected across the α and β interaces in the STU-C and the STU-R, respectively, to the TPS-TC layer. The TPS-TC is application speciic and consists largely o the packaging o user data within the SHDSL rame. See clause 8 or details. This may include multiplexing, demultiplexing, and timing alignment o multiple user data channels. Supported TPS-TC user data raming ormats are described in Annex E. The TPS-TC layer communicates with the Interace blocks across the γ R and γ C interaces. Depending upon the speciic application, the TPS-TC layer may be required to support one or more channels o user data and associated interaces. The deinition o these interaces is beyond the scope o this Recommendation. Note that the α, β, γ R and γ C interaces are only intended as logical separations and need not be physically accessible. 6 ITU-T Rec. G.991. 0/001)
4. User plane protocol reerence model NT1, NT/1 STU-R STU-C LT Transport Protocol e.g. SDH) γ R γ C Transport Protocol e.g. SDH) Not Speciied TPS-TC PMS-TC PMD β α TPS-TC PMS-TC PMD Not Speciied User Data Interace Physical Transmission Media Internal Interace T1541140-00 S/T U Figure 4-/G.991. User plane protocol reerence model LT internal interace The user plane protocol reerence model, shown in Figure 4-, is an alternate representation o the inormation shown in Figure 4-1. This igure is included to emphasize the layered nature o this Recommendation and to provide a view that is consistent with the generic xdsl models shown in ITU-T G.995.1 [B], in Appendix IV. 4.3 Application models User Terminal S/T User Terminal S/T U-R U-C U-R U-C U-R U-C V STU-R DLL SRU DLL DLL STU-C Optional) CO Network Optional) T1541150-00 Figure 4-3/G.991. Application model Figure 4-3 is an application model or a typical SHDSL system, showing reerence points and attached equipment. In such an application, an STU-R will typically connect to one or more user terminals, which may include data terminals, telecommunications equipment, or other devices. These connections to these pieces o terminal equipment are designated S/T reerence points. The connection between STU-R and STU-C may optionally contain one or more SHDSL signal regenerators SRUs). The connections to the DLLs that interconnect STUs and SRUs are designated U reerence points. For each STU-x and SRU, the Network side connection is termed the U-R interace and the Customer side connection is termed the U-C interace. The STU-C typically connects to a Central Oice network at the V reerence point. ITU-T Rec. G.991. 0/001) 7
5 Transport capacity This Recommendation speciies a two-wire operational mode or SHDSL transceivers that is capable o supporting user payload) data rates rom 19 kbit/s to.31 Mbit/s in increments o 8 kbit/s. The allowed rates are given by n 64 + i 8 kbit/s, where 3 n 36 and 0 i 7. For n = 36, i is restricted to the values o 0 or 1. See Annexes A and B or details o speciic regional requirements. This Recommendation also speciies an optional our-wire operational mode that is capable o supporting user payload) data rates rom 384 kbit/s to 4.64 Mbit/s in increments o 16 kbit/s. Again, see Annexes A and B or details o speciic regional requirements. 6 PMD layer unctional characteristics 6.1 Data mode operation 6.1.1 STU data mode PMD reerence model A reerence model o the data mode PMD layer o an STU-C or STU-R transmitter is shown in Figure 6-1. TCM Spectral n) Scrambler sn) xm) Precoder ym) zt) Encoder Shaper input rom ramer output at loop interace T1541160-00 Figure 6-1/G.991. Data mode PMD reerence model The time index n represents the bit time, the time index m represents the symbol time, and t represents analogue time. The input rom the ramer is n), and sn) is the output o the scrambler. Both the ramer and the scrambler are contained within the PMS-TC layer and are shown here or clarity. xm) is the output o the TCM Trellis Coded Modulation) encoder, ym) is the output o the channel precoder, and zt) is the analogue output o the spectral shaper at the loop interace. When transerring K inormation bits per one-dimensional PAM symbol, the symbol duration is K times the bit duration, so the K values o n or a given value o m are {mk + 0, mk + 1,, mk + K 1}. In the optional our-wire mode, two separate PMD sublayers are active one or each wire pair. In this case, n represents the bit time or each wire pair rather than the aggregate system line rate. 6.1.1.1 PMD rates The operation o the PMD layer at the speciied inormation rate shall be as speciied in A.5.1 or B.5.1. 6.1. TCM encoder The block diagram o the TCM encoder is shown in Figure 6-. The serial bit stream rom the scrambler, sn), shall be converted to a K-bit parallel word at the mth symbol time, then processed by the convolutional encoder. The resulting K+1-bit word shall be mapped to one o K+1 predetermined levels orming xm). 8 ITU-T Rec. G.991. 0/001)
smk + K 1) = X K m) Y K m) sn) Serial to Parallel smk + 1) = X m) Y m) Mapper xm) smk + 0 ) = X 1 m) Convolutional Encoder Y 1 m) Y 0 m) T1541170-00 Figure 6-/G.991. Block diagram o the TCM encoder 6.1..1 Serial-to-parallel converter The serial bit stream rom the scrambler, sn), shall be converted to a K-bit parallel word {X 1 m) = smk + 0), X m) = smk + 1),, X K m) = smk + K 1)} at the mth symbol time, where X 1 m) is the irst input bit in time. 6.1.. Convolutional encoder Figure 6-3 shows the eedorward non-systematic convolutional encoder, where T s is a delay o one symbol time, " " is binary exclusive-or, and " " is binary AND. X 1 m) shall be applied to the convolutional encoder, Y 1 m) and Y 0 m) shall be computed, then X 1 m) shall be shited into the shit register.... Y 1 m) b 0 b 1 b b 19 b 0 X 1 m) T s X 1 m 1) X... 1 m 19) T s T s X 1 m 0) a 0 a 1 a a 19 a 0... Y 0 m) T1541180-00 Figure 6-3/G.991. Block diagram o the convolutional encoder The binary coeicients a i and b i shall be passed to the encoder rom the receiver during the activation phase speciied in 7..1.3. A numerical representation o these coeicients is A and B where: A = a 0 0 + a 19 19 + a 18 18 + + a 0 0, and B = b 0 0 + b 19 19 + b 18 18 + + b 0 0 ITU-T Rec. G.991. 0/001) 9
The choice o encoder coeicients is vendor speciic. They shall be chosen such that the system perormance requirements are satisied see Annex A and/or Annex B or perormance requirements). 6.1..3 Mapper The K + 1 bits Y K m),, Y 1 m), and Y 0 m) shall be mapped to a level xm). Table 6-1 gives the bit to level mapping or 16-level mapping. 6.1.3 Channel precoder Table 6-1/G.991. Mapping o bits to PAM levels Y 3 m) Y m) Y 1 m) Y 0 m) xm) or 16-PAM 0 0 0 0 15/16 0 0 0 1 13/16 0 0 1 0 11/16 0 0 1 1 9/16 0 1 0 0 7/16 0 1 0 1 5/16 0 1 1 0 3/16 0 1 1 1 1/16 1 1 0 0 1/16 1 1 0 1 3/16 1 1 1 0 5/16 1 1 1 1 7/16 1 0 0 0 9/16 1 0 0 1 11/16 1 0 1 0 13/16 1 0 1 1 15/16 The block diagram o channel precoder is shown in Figure 6-4, where T s is a delay o one symbol time. 10 ITU-T Rec. G.991. 0/001)
xm) + Σ um) Modulo ym) vm) ym N) ym ) ym 1) T s T s... T s T s C N C N+1 C C 1 Σ Precoder Filter T1544100-01 Figure 6-4/G.991. Block diagram o the channel precoder The coeicients o the precoder ilter, C k, shall be transerred to the channel precoder as described in 7..1.. The output o the precoder ilter, vm), shall be computed as ollows: ν m) = N k= 1 C k y m k) where 18 N 180. The unction o the modulo block shall be to determine ym) as ollows: or each value o um), ind an integer, dm), such that: 1 u m) + d m) < 1 and then: 6.1.4 Spectral shaper y m) = u m) + d m) The choice o spectral shape shall be region-speciic. The details o s or Regions A and B are given in A.3.3.8 and B.4. 6.1.5 Power backo SHDSL devices shall implement power backo, as speciied in this clause. The selected power backo value shall be communicated during pre-activation through the use o G.994.1 parameter selections. The power backo value shall be selected to meet the requirements shown in Table 6-. The power backo calculations are based on Estimated Power Loss EPL), which is deined as: Estimated power loss db) = Tx power dbm) estimated Rx power dbm), evaluated or the data mode. No explicit speciication is given herein or the method o calculating estimated Rx power. Depending upon the application, this value may be determined based on line probe results, a priori knowledge, or G.994.1 tone levels. The power backo that is applied shall be no less than the deault power backo, and it shall not exceed the maximum power backo value. ITU-T Rec. G.991. 0/001) 11
Estimated power loss db) Table 6-/G.991. Required power backo values Maximum power backo db) Deault power backo db) EPL > 6 31 0 6 EPL > 5 31 1 5 EPL > 4 31 4 EPL > 3 31 3 3 EPL > 31 4 EPL > 1 31 5 1 EPL > 0 31 6 6. PMD activation sequence This clause describes waveorms at the loop interace and associated procedures during activation mode. The direct speciication o the perormance o individual receiver elements is avoided when possible. Instead, the transmitter characteristics are speciied on an individual basis and the receiver perormance is speciied on a general basis as the aggregate perormance o all receiver elements. Exceptions are made or cases where the perormance o an individual receiver element is crucial to interoperability. In 6.., "convergence" reers to the state where all adaptive elements have reached steady-state. The declaration o convergence by a transceiver is thereore vendor dependent. Nevertheless, actions based on the state o convergence are speciied to improve interoperability. 6..1 PMD activation reerence model The reerence model o the activation mode o an STU-C or STU-R transmitter is shown in Figure 6-5. logical ones dm) precoder coeicients, encoder coeicients Activation Framer m) Scrambler Spectral sm) Mapper ym) zt) Shaper output at loop interace T154100-00 Figure 6-5/G.991. Activation reerence model The time index m represents the symbol time, and t represents analogue time. Startup uses -PAM modulation, so the bit time is equivalent to the symbol time. The output o the activation ramer is m), the ramed inormation bits. The output o the scrambler is sm). Both the ramer and the scrambler are contained within the PMS-TC layer and are shown here only or clarity. The output o the mapper is ym), and the output o the spectral shaper at the loop interace is zt). dm) is an initialization signal that shall be logical ones or all m. The modulation ormat shall be uncoded -PAM, at the symbol rate selected or data mode operation. In devices supporting the optional our-wire mode, the activation procedure shall be considered as an independent procedure or each pair. Such devices shall be capable o detecting the completion o activation or both pairs and upon completion shall initiate the transmission o user data over both pairs. 1 ITU-T Rec. G.991. 0/001)
6.. PMD activation sequence description The timing diagram or the activation sequence is given in Figure 6-6. The state transition diagram or the startup sequence is given in Figure 6-7. Each signal in the activation sequence shall satisy the tolerance values listed in Table 6-3. t Act S c T c F c Data c STU-C t crsc t cr STU-R t crsr C r S r T r Data r T154110-00 Figure 6-6/G.991. Timing diagram or activation sequence Figure 6-6a shows the total activation sequence at a high level or G.991., which includes preactivation and core activation. Included as an example in the pre-activation phase are two sessions o handshake per G.994.1 and line probe. t Pre_Activation t Core_Activation G.994.1 Line Probing G.994.1 Core Activation Data t p-total t Act t Act_Global T1544110-01 Figure 6-6a/G.991. G.991. total activation sequence The global activation time is the sum o the pre-activation and core activation times. Thereore, rom Figure 6-6a: t Pre-Activation + t Core-Activation t Act_Global where t Pre-Activation is the combined duration o the G.994.1 sessions see 6.4) and line probing see 6.3), t Core-Activation is the core activation duration see 6.). The values or t Act and t Act_Global are deined in Table 6-3. The value or t p-total is given in Table 6-5. ITU-T Rec. G.991. 0/001) 13
Table 6-3/G.991. Timing or activation signals Time Parameter Reerence Nominal value Tolerance t cr Duration o C r See 6...1 1 β s * ±0 ms t crsc Time rom end o C r to beginning o S c See 6... 500 ms ±0 ms t crsr Time rom end o C r to beginning o S r See 6...3 1.5 β s * ±0 ms t act Maximum time rom start o C r to Data r 15 β s * t payloadvalid t silence t PLL t act_global Maximum time rom start o Data c or Data r to valid SHDSL payload data Minimum silence time rom exception condition to start o train Maximum time rom start o S c to STU-R PLL lock Maximum time rom start o initial preactivation session 6.3) to Data r 1 s s 5 s 30 s * β is dependent on bit rate. β = 1 or n > 1, β = or n 1, where n is deined in clause 5. STU-C STU-R Power On Power On Pre-activation per 6.3 Pre-activation per 6.3 C r Detected Not Converged on S r S c C r Exception State T r Not Detected Receiver Converged on S r and S c Sent > t PLL T c S r Not Converged on T c or T c Not Detected Exception State Exception Detected T r Detected F c T c Detected T r F c Not Detected Exception Detected F c Detected Data c Data r T15410-00 Figure 6-7/G.991. STU-C and STU-R transmitter activation state transition diagram 14 ITU-T Rec. G.991. 0/001)
6...1 Signal C r Ater exiting the pre-activation sequence per ITU-T G.994.1 [], see 6.3 or details), the STU-R shall send C r. Waveorm C r shall be generated by connecting the signal dm) to the input o the STU-R scrambler as shown in Figure 6-5. The mask or C r shall be the upstream mask, as negotiated during pre-activation sequence. C r shall have a duration o t cr and shall be sent 0.3 s ater the end o pre-activation. 6... Signal S c Ater detecting C r, the STU-C shall send S c. Waveorm S c shall be generated by connecting the signal dm) to the input o the STU-C scrambler as shown in Figure 6-5. The mask or S c shall be the downstream mask, as negotiated during pre-activation sequence. S c shall be sent t crsc ater the end o C r. I the STU-C does not converge while S c is transmitted, it shall enter the exception state 6...8). 6...3 Signal S r The STU-R shall send S r, beginning t crsr ater the end o C r. Waveorm S r shall be generated by connecting the signal dm) to the input o the STU-R scrambler as shown in Figure 6-5. The mask or S r shall be the same as or C r. I the STU-R does not converge and detect T c while S r is transmitted, it shall enter the exception state 6...8). The method used to detect T c is vendor dependent. In timing modes supporting loop timing, waveorm S r and all subsequent signals transmitted rom the STU-R shall be loop timed, i.e. the STU-R symbol clock shall be locked to the STU-C symbol clock. 6...4 Signal T c Once the STU-C has converged and has been sending S c or at least t PLL Table 6-3 ), it shall send T c. Waveorm T c contains the precoder coeicients and other system inormation. T c shall be generated by connecting the signal m) to the input o the STU-C scrambler as shown in Figure 6-5. The mask or T c shall be the same as or S c. The signal m) is the activation rame inormation as described in 7..1. I the STU-C does not detect T r while sending T c, it shall enter the exception state 6...8). The method used to detect T r is vendor dependent. 6...5 Signal T r Once the STU-R has converged and has detected the T c signal, it shall send T r. Waveorm T r contains the precoder coeicients and other system inormation. T r shall be generated by connecting the signal m) to the input o the STU-R scrambler as shown in Figure 6-5. The mask or T r shall be the same as or C r. The signal m) is the activation rame inormation as described in 7..1. I the STU-R does not detect F c while sending T r, it shall enter the exception state 6...8). The method used to detect F c is vendor dependent. 6...6 Signal F c Once the STU-C has detected T r and completed sending the current T c rame, then it shall send F c. The irst bit o the irst F c rame shall ollow contiguously the last bit o the last T c rame. Signal F c shall be generated by connecting the signal m) to the input o the STU-C scrambler as shown in Figure 6-5. The mask or F c shall be the same as or S c. The signal m) is the activation rame inormation as described in 7..1, with the ollowing exceptions: the rame sync word shall be reversed in time, and the payload inormation bits shall be set to arbitrary values. The CRC shall be ITU-T Rec. G.991. 0/001) 15
calculated on this arbitrary-valued payload. The signal F c shall be transmitted or exactly two activation rames. As soon as the irst bit o F c is transmitted, the payload data in the T r signal shall be ignored. 6...7 Data c and Data r Within 00 symbols ater the end o the second rame o F c, the STU-C shall enter data mode and send Data c, and the STU-R shall enter data mode and send Data r. These TCPAM signals are described in 6.1. The mask or Data r and or Data c shall be according to A.4 or B.4, as negotiated during the pre-activation sequence. There is no required relationship between the end o the activation rame and any bit within the SHDSL data-mode rame. t PayloadValid Table 6-3) ater the end o F c, the SHDSL payload data shall be valid at the α or β interace. 6...8 Exception state I activation is not achieved within t act Table 6-3) or i pre-activation and activation are not completed within t act_global Table 6-3) or i any exception condition occurs, then the exception state shall be invoked. During the exception state the STU shall be silent or at least t silence Table 6-3), then wait or transmission rom the ar end to cease, then return to the corresponding initial startup state; the STU-R and STU-C shall begin pre-activation, as per 6.3. 6...9 Exception condition An exception condition shall be declared during activation i any o the timeouts in Table 6-3 expire or i any vendor-deined abnormal event occurs. An exception condition shall be declared during data mode i a vendor-deined abnormal event occurs. A vendor-deined abnormal event shall be deined as any event that requires a loop restart or recovery. 6..3 Framer and scrambler The activation mode ramer and scrambler are described in 7.. 6..4 Mapper The output bits rom the scrambler, sm), shall be mapped to the output level, ym), as ollows: Table 6-4/G.991. Bit-to-level mapping Scrambler output sm) Mapper output level, ym) Data mode index 0 9/16 0011 1 +9/16 1000 These levels, corresponding to the scrambler outputs 0 and 1, shall be identical to the levels in the 16-TCPAM constellation Table 6-1) corresponding to indexes 0011 and 1000, respectively. 6..5 Spectral shaper The same spectral shaper shall be used or data mode and activation mode as described in A.4 or B.4. 6..6 Timeouts Table 6-3 shows the system timeouts and their values. t act shall be the maximum time rom the start o C r to the start o Data r. It controls the overall time o the train. t PayloadValid is the time between the start o data mode and the instant at which the SHDSL payload data is valid this accounts or 16 ITU-T Rec. G.991. 0/001)
settling time, data lushing, rame synchronization, etc). t silence shall be the minimum time in the exception state in which the STU-C or STU-R is silent beore returning to pre-activation per ITU-T G.994.1 [], see 6.3 or details). t PLL shall be the time allocated or the STU-R to pull in the STU-C timing. The STU-C shall transmit S c or at least t PLL. 6.3 PMD pre-activation sequence This clause describes waveorms at the loop interace and associated procedures during preactivation mode. The direct speciication o the perormance o individual receiver elements is avoided when possible. Instead, the transmitter characteristics are speciied on an individual basis and the receiver perormance is speciied on a general basis as the aggregate perormance o all receiver elements. Exceptions are made or cases where the perormance o an individual receiver element is crucial to interoperability. In the optional our-wire mode, Pair 1 and Pair shall be determined during the pre-activation sequence. Pair 1 shall be deined as the pair on which the inal G.994.1 transaction is conducted. 6.3.1 PMD pre-activation reerence model The reerence model o the pre-activation mode o an STU-C or STU-R transmitter is shown in Figure 6-8. logical ones dm) Scrambler sm) G.994.1 Mapper ym) Spectral Shaper Handshake zt) Probe output at loop interace T154130-00 Figure 6-8/G.991. Pre-activation reerence model The time index m represents the symbol time, and t represents analogue time. Since the probe signal uses -PAM modulation, the bit time is equivalent to the symbol time. The output o the scrambler is sm). The scrambler used in the PMD pre-activation may dier rom the PMS-TC scrambler used in activation and data modes. See 6.3.3 or details o the pre-activation scrambler. The output o the mapper is ym), and the output o the spectral shaper at the loop interace is zt). dm) is an initialization signal that shall be logical ones or all m. The probe modulation ormat shall be uncoded -PAM, with the symbol rate, spectral shape, duration and power backo selected by G.994.1. Probe results shall be exchanged by ITU-T G.994.1. In the optional our-wire mode, the G.994.1 exchange shall ollow the deined procedures or multi-pair operation. In this case, signals P ri and P ci, as described below, shall be sent in parallel on both wire pairs. ITU-T Rec. G.991. 0/001) 17
6.3. PMD pre-activation sequence description A typical timing diagram or the pre-activation sequence is given in Figure 6-9. Each signal in the pre-activation sequence shall satisy the tolerance values listed in Table 6-5. P c1 P c STU-C STU-R G.994.1 t pcd t ps t pcd t ph t hp t prd t ps t prd t ps t prd t prc G.994.1 P r1 P r P r3 T154140-00 Figure 6-9/G.991. Typical timing diagram or pre-activation sequence Table 6-5/G.991. Timing or pre-activation signals Note) Time Parameter Nominal value Tolerance t hp Time rom end o handshake to start o remote probe 0. s ±10 ms t prd Duration o remote probe Selectable rom 50 ms to 3.1 s ±10 ms t ps Time separating two probe sequences 0. s ±10 ms t prc Time separating last remote and irst central probe sequences 0. s ±10 ms t pcd Duration o central probe Selectable rom 50 ms to 3.1 s ±10 ms t ph Time rom end o central probe to start o handshake 0. s ±10 ms t p-total Total probe duration, rom end o the irst G.994.1 session to the start o the second G.994.1 session 10 s maximum NOTE Tolerances are relative to the nominal or ideal value. They are not cumulative across the preactivation sequence. 6.3..1 Signal P ri I the optional line probe is selected during the G.994.1 session see ITU-T G.994.1 [] or details), the STU-R shall send the remote probe signal. The symbol rate or the remote probe signal shall be negotiated during the G.994.1 session, and shall correspond to the symbol rate used during activation or the speciied data rate. I multiple remote probe symbol rates are negotiated during the G.994.1 session, then multiple probe signals will be generated, starting with the lowest symbol rate negotiated and ending with the highest symbol rate negotiated. P ri is the ith probe signal corresponding to the ith symbol rate negotiated). Waveorm P ri shall be generated by connecting the signal dm) to the input o the STU-R scrambler as shown in Figure 6-8. The mask or P ri shall be the upstream mask used or signal C r at the same symbol rate, and shall be selectable between the s or activating at data rates o 19 kbit/s to 304 kbit/s in steps o 64 kbit/s. Alternatively, waveorm P ri can be selected to transmit silence. The duration t prd ) and power backo shall be the same or all P ri, and shall be negotiated during the G.994.1 session. The duration 18 ITU-T Rec. G.991. 0/001)
shall be selectable between 50 ms and 3.1 s in steps o 50 ms, and the power backo shall be selectable between 0 db and 15 db in steps o 1 db. The probe signal power backo can be selected using either the received G.994.1 signal power or a priori knowledge. I no inormation is available, implementors are encouraged to select a probe power backo o at least 6 db. The irst remote probe signal shall begin t hp ater the end o the G.994.1 session. There shall be a t ps second silent interval between successive remote probe signals. In the optional our-wire mode, P ri shall be sent in parallel on both wire pairs. 6.3.. Signal P ci The STU-C shall send the central probe signal t prc ater the end o the last remote probe signal. The symbol rate or the central probe signal shall be negotiated during the G.994.1 session, and shall correspond to the symbol rate used during activation or the speciied data rate. I multiple central probe symbol rates are negotiated during the G.994.1 session, then multiple probe signals will be generated, starting with the lowest symbol rate negotiated and ending with the highest symbol rate negotiated. Waveorm P ci is the ith probe signal corresponding to the ith symbol rate negotiated). Waveorm P ci shall be generated by connecting the signal dm) to the input o the STU-C scrambler as shown in Figure 6-8. The mask or P ci shall be the downstream mask used or signal S c at the same symbol rate, and shall be selectable between the s or activating at data rates o 19 kbit/s to 304 kbit/s in steps o 64 kbit/s. Alternatively, waveorm P ri can be selected to transmit silence. The duration t pcd ) and power backo shall be the same or all P ci, and shall be negotiated during the G.994.1 session. The duration shall be selectable between 50 ms and 3.1 s in steps o 50 ms, and the power backo shall be selectable between 0 db and 15 db in steps o 1 db. The probe signal power backo can be selected using either the received G.994.1 signal power or a priori knowledge. I no inormation is available, implementors are encouraged to select a probe power backo o at least 6 db. There shall be a t ps silent interval between successive central probe signals, and there shall be a t ph second silent interval between the last central probe signal and the start o the ollowing G.994.1 session. In the optional our-wire mode, P ci shall be sent in parallel on both wire pairs. 6.3.3 Scrambler The pre-activation mode scrambler shall have the same basic structure as the data mode scrambler, but may employ a dierent scrambler polynomial. During the G.994.1 session, the scrambler polynomial or the line probe sequence shall be selected by the receiver rom the set o allowed scrambler polynomials listed in Table 6-6. The transmitter shall support all the polynomials in Table 6-6. During the line probe sequence, the transmit scrambler shall use the scrambler polynomial selected by the receiver during the G.994.1 session. The scrambler shall be initialized to all zeros. ITU-T Rec. G.991. 0/001) 19