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G.984.6-200803

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G.984.6-200803

    International Telecommunication Union

    ITU-T G.984.6

    (03/2008) TELECOMMUNICATION

    STANDARDIZATION SECTOR

    OF ITU

SERIES G: TRANSMISSION SYSTEMS AND MEDIA,

    DIGITAL SYSTEMS AND NETWORKS

    Digital sections and digital line system Optical line systems for local and access networks

     Gigabit-capable passive optical networks (GPON): Reach extension

Recommendation ITU-T G.984.6

    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-G.200G.299 TRANSMISSION SYSTEMS

    INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE G.300G.399 SYSTEMS ON METALLIC LINES

    GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS G.400G.449 ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES

    COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 General G.900G.909 Parameters for optical fibre cable systems G.910G.919 Digital sections at hierarchical bit rates based on a bit rate of 2048 kbit/s G.920G.929 Digital line transmission systems on cable at non-hierarchical bit rates G.930G.939 Digital line systems provided by FDM transmission bearers G.940G.949 Digital line systems G.950G.959 Digital section and digital transmission systems for customer access to ISDN G.960G.969 Optical fibre submarine cable systems G.970G.979 Optical line systems for local and access networks G.980G.989 Access networks G.990G.999 QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED G.1000G.1999 ASPECTS

    TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999 ACCESS NETWORKS G.9000G.9999

For further details, please refer to the list of ITU-T Recommendations.

Recommendation ITU-T G.984.6

    Gigabit-capable passive optical networks (GPON): Reach extension

Summary

    Recommendation ITU-T G.984.6 outlines the architecture and interface parameters for GPON

    systems with extended reach using a physical layer reach extension device such as a regenerator or

    optical amplifier in the fibre link between the optical line termination (OLT) and optical network termination (ONT). The maximum reach is up to 60 km with loss budgets of in excess of 27.5 dB being achievable in both spans.

Source

    Recommendation ITU-T G.984.6 was approved on 29 March 2008 by ITU-T Study Group 15 (2005-2008) under Recommendation ITU-T A.8 procedure.

     Rec. ITU-T G.984.6 (03/2008) i

    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-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 years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.

    The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall 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 for conciseness to indicate both a telecommunication administration and a recognized operating agency.

    Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.

    INTELLECTUAL PROPERTY RIGHTS?

    ITU draws attention to the 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 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 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/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.

    ii Rec. ITU-T G.984.6 (03/2008)

    CONTENTS

     Page

    1 Scope ........................................................................................................................ 1

    2 References ................................................................................................................ 1

    3 Definitions ................................................................................................................ 2

    4 Abbreviations and acronyms ..................................................................................... 2

    5 Conventions .............................................................................................................. 2

    6 Optical extension schemes and architectures ............................................................. 2

    6.1 OA-based reach extenders ........................................................................... 5

    6.2 OEO-based reach extenders ......................................................................... 6

    6.3 Hybrid architectures .................................................................................... 7

    7 General requirements on GPON reach extenders ....................................................... 9

    7.1 Compatibility .............................................................................................. 9

    7.2 Management ................................................................................................ 9

    7.3 Power .......................................................................................................... 10

    7.4 Out-of-scope issues ..................................................................................... 10

    8 Specifications for mid-span extenders ....................................................................... 10

    8.1 Optical trunk line ......................................................................................... 10

    8.2 Optical trunk line interface (R'/S') and OLT interface (S/R) ......................... 11

    8.3 Optical distribution network ........................................................................ 17

    8.4 Extender interface to optical distribution network (S'/R') and ONU

    interface (R/S) ............................................................................................. 18

    8.5 TC layer impacts ......................................................................................... 24

    Appendix I Implications on OLT receivers due to insertion of OA type extenders ............. 25 Appendix II Possible realization of an OA-based extender ................................................ 27

    II.1 Introduction ................................................................................................. 27

    II.2 Constraints on the link budget ..................................................................... 27

    II.3 Amplifier design parameters ........................................................................ 27

    Appendix III Protection ..................................................................................................... 31

    III.1 Introduction ................................................................................................. 31

    Appendix IV Class C+ operation ....................................................................................... 31 Appendix V Optical time domain reflectometer................................................................. 32

    V.1 Introduction ................................................................................................. 32

    V.2 Solution ....................................................................................................... 32

     Rec. ITU-T G.984.6 (03/2008) iii

Recommendation ITU-T G.984.6

    Gigabit-capable passive optical networks (GPON): Reach extension

    1 Scope

    This Recommendation concerns GPON systems with optical link budgets up to the logical limits of

    the transmission convergence (TC) layer. The increased optical capability, which includes both

    increased overall fibre length and increased overall splitting ratio, is referred to in this

    Recommendation as "reach extension". The primary concerns addressed are the increase of the loss

    budget and the management of optical impairments.

    This Recommendation considers mid-span extension, which uses an active extension node placed in

    the middle of the optical network. The recommended parameters for the ODN(s) involved in this

    scheme are specified. Single-sided extension is considered as an improvement to the OLT interface,

    and is described in [ITU-T G.984.2] as amended.

    The systems considered here must remain compatible with existing ONTs. Furthermore, the

    approaches should maintain compatibility with existing OLTs to the maximum extent possible. It is

    recognized that some modification of the OLT equipment may be necessary, but this should be

    minimized.

    Two system architectures are considered: optical amplification, and opto-electronic regeneration.

    These can be viewed as providing reach extension at the physical layer. The key interfaces and

    functional blocks in each of these architectures are identified and specified.

    2 References

    The following ITU-T Recommendations and other references contain provisions which, through

    reference in this text, constitute provisions of this Recommendation. At the time of publication, the

    editions indicated were valid. All Recommendations and other references are subject to revision;

    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 valid ITU-T Recommendations is regularly published. The reference to a document within

    this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.

    [ITU-T G.652] Recommendation ITU-T G.652 (2005), Characteristics of a single-mode

    optical fibre and cable.

    [ITU-T G.983.1] Recommendation ITU-T G.983.1 (1998), Broadband optical access systems

    based on Passive Optical Networks (PON). [ITU-T G.983.3] Recommendation ITU-T G.983.3 (2001), A broadband optical access system

    with increased service capability by wavelength allocation. [ITU-T G.984.2] Recommendation ITU-T G.984.2 (2003), Gigabit-capable Passive Optical

    Networks (GPON): Physical Media Dependent (PMD) layer specification.

    [ITU-T G.984.3] Recommendation ITU-T G.984.3 (2004), Gigabit-capable Passive Optical

    Networks (GPON): Transmission Convergence layer specification.

    [ITU-T G.984.4] Recommendation ITU-T G.984.4 (2004), Gigabit-capable Passive Optical

    Networks (GPON): ONT management and control interface specification.

    [ITU-T G.984.5] Recommendation ITU-T G.984.5 (2007), Gigabit-capable Passive Optical

    Networks (GPON): Enhancement band.

     Rec. ITU-T G.984.6 (03/2008) 1

3 Definitions

    None.

    4 Abbreviations and acronyms

    This Recommendation uses the following abbreviations and acronyms: ASE Amplified Spontaneous Emission

    BER Bit Error Ratio

    BW BandWidth

    CW Continuous Wave

    EONT Embedded Optical Network Termination for management of the extender GPON Gigabit-capable Passive Optical Network

    NGA Next Generation Access

    OA Optical Amplifier

    OBF Optical Bandpass Filter

    ODN Optical Distribution Network

    OEO Optical-Electrical-Optical converter

    OLT Optical Line Termination

    ONT Optical Network Termination

    ONU Optical Network Unit

    OTDR Optical Time Domain Reflectometer

    OTL Optical Trunk Line

    PLOAM Physical Layer Operations, Administration and Maintenance PMD Physical Media Dependent

    PON Passive Optical Network

    R/S Optical network unit interface to optical distribution network R'/S' Extender interface to optical trunk line

    SOA Semiconductor Optical Amplifiers

    S/R Optical line termination interface to optical trunk line S'/R' Extender interface to optical distribution network WBF Wavelength Blocking Filter

    5 Conventions

    None.

    6 Optical extension schemes and architectures

    The basic PON architecture is shown in Figure 1. The OLT interfaces with multiple ONTs via the

    ODN. The OLT also provides interfaces to one or more SNIs, as well as the management system.

    The ONT interfaces with various UNIs. The only interfaces of interest to this Recommendation are

    those that face the ODN. Amendment 2 to [ITU-T G.983.3] and Amendment 1 to [ITU-T G.984.2]

    2 Rec. ITU-T G.984.6 (03/2008)

specify the best practice loss profile for the ODN to be between 13 and 28 dB. The OLT-ODN and

    ONT-ODN interfaces for GPON are specified in [ITU-T G.984.2] (as amended). Indeed, most

    ITU-compliant PONs deployed today adhere to these Recommendations.

    ONUONU

    UNIUNIR/SR/SODNODNOLTOLT

    SNISNIS/RS/RONUONUR/SR/S

    UNIUNI

    Figure 1 Basic PON architecture The architecture considered in this Recommendation is illustrated in Figure 2. A mid-span extender

    device is inserted between the ODN (compliant with existing PON Recommendations) and an

    optical trunk line (OTL), which is connected to the OLT. This architecture extends the reach of the

    PON by the length of the OTL, and may also increase the split ratio of the PON. However, it does

    require electrical power for the mid-span extender.

    ONU

    UNIMid-SpanR/SODNOLTOTLExtender

    SNIS/RS'/R'R'/S'ONUR/S

    UNI

    Figure 2 Mid-span reach extension

     Rec. ITU-T G.984.6 (03/2008) 3

There are several ways to implement an optical reach extender. There are two general classes of

    extenders. The first is an optical amplifier (OA), shown in Figure 3a, which provides gain in optical

    power. The second is an optical-electrical-optical (OEO) regenerator (Figure 3b), which receives an

    optical signal, reshapes and retimes it in the electrical domain and retransmits in the optical domain.

    Further hybrid schemes are possible, for example, to use optical amplification in the downstream

    and regeneration in the upstream, as shown in Figure 4a, or the reverse as shown in Figure 4b.

     a)

    OBFOA

    (optional)

    DiplexerDiplexer

    S'/R'R'/S'

    OBFOA

    (optional)

     b)

    RxTx

    DiplexerDiplexer

    ClockS'/R'R'/S'

    TxRx

    Figure 3 The two basic extender architectures: Optical amplifier, repeater

    4 Rec. ITU-T G.984.6 (03/2008)

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