1、 International Telecommunication Union ITU-T G.984.6TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (03/2008) 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 opt
2、ical 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-TRANSMISSION SYSTEMS G.200
3、G.299 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 TEL
4、EPHONY 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 hier
5、archical 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 f
6、or 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 ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.
7、6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T G.984.6 (03/2008) i Recommendation ITU-T G.984.6 Gigabit-capable passive optical networks (G
8、PON): 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
9、 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. ii Rec. ITU-T
10、 G.984.6 (03/2008) 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 r
11、esponsible 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 t
12、he ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collabo
13、rative 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
14、 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
15、. 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
16、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 pr
17、operty, 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 reserv
18、ed. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T G.984.6 (03/2008) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Conventions 2 6 Optical extension schemes and architectur
19、es . 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
20、.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 A
21、ppendix 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 Introduct
22、ion 32 V.2 Solution. 32 Rec. ITU-T G.984.6 (03/2008) 1 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 in
23、creased 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 Recomme
24、ndation 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
25、-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
26、 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
27、 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
28、 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 doe
29、s 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 (PO
30、N). 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.
31、 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. I
32、TU-T G.984.5 Recommendation ITU-T G.984.5 (2007), Gigabit-capable Passive Optical Networks (GPON): Enhancement band. 2 Rec. ITU-T G.984.6 (03/2008) 3 Definitions None. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: ASE Amplified Spontaneous Emission B
33、ER 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
34、-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
35、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 No
36、ne. 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 i
37、nterest 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 Rec. ITU-T G.984.6 (03/2008) 3 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
38、.984.2 (as amended). Indeed, most ITU-compliant PONs deployed today adhere to these Recommendations. ONUONUODN OLTUNIUNISNIR/SR/SS/RFigure 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 (c
39、ompliant 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.
40、ONUONUODN OLTUNIUNISNIR/SR/SS/RMid-SpanExtenderOTLS/R R/SFigure 2 Mid-span reach extension 4 Rec. ITU-T G.984.6 (03/2008) 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 provi
41、des 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 amplificati
42、on in the downstream and regeneration in the upstream, as shown in Figure 4a, or the reverse as shown in Figure 4b. a) DiplexerDiplexerOAOAOBF(optional)S/R R/SOBF(optional)b) DiplexerDiplexerRx TxTx RxS/R R/SClockFigure 3 The two basic extender architectures: Optical amplifier, repeater Rec. ITU-T G
43、.984.6 (03/2008) 5 a) Rx TxDiplexerDiplexerOAOBF(optional)S/R R/Sb) DiplexerDiplexerTx RxOAOBF(optional)S/R R/SClockOA Optical Amplifier OBF Optical Bandpass Filter Figure 4 Examples for hybrid extender architectures 6.1 OA-based reach extenders Reach extenders based on optical amplifiers optionally
44、 may include optical bandpass filters (OBFs) in order to restrict the bandwidth of amplified spontaneous emission (ASE) generated by the optical amplifier, and thus reduce ASE-ASE beat noise and ASE-based power-offset (see Appendix I) in the optical receiver and achieve higher performance. If OBFs a
45、re used, restricted wavelength range for transmitters may be necessary. For options on restricted upstream bands, refer to ITU-T G.984.5. Due to the nature of OA-based reach extenders, the application range (useable trunk and ODN loss range) varies according to the parameters of the optical amplifie
46、rs used. The vendor has to provide sufficient data showing the key parameters (such as, e.g., maximum gain, minimum gain, saturated output power), the application range and applicable penalties due to ASE. As there is no signal regeneration provided by OA-based reach extenders, ONT and OLT transmitt
47、ers must provide a dispersion reach of up to 60 km. 6 Rec. ITU-T G.984.6 (03/2008) An optical amplifier-based extender should include a complete embedded ONT (EONT) for management purposes, as shown in Figure 5. The EONT is connected internally by means of an optical tap coupler at the interface fac
48、ing the OTL in order to keep the RE accessible even in case an optical amplifier fails. upstream amplifierEONTS/R R/SLocalcontrollertapdiplexerdownstream amplifierdiplexerFigure 5 OA-type reach extender with embedded ONT (EONT) for management purposes 6.2 OEO-based reach extenders The signals passin
49、g through the OEO extender are re-timed (2R regenerators are not specified by this Recommendation). The timing reference for this function is the downstream receiver of the extender (see Figure 6). This timing is used to drive both transmitters and as a reference for the other receiver. This arrangement is identical to that used in SDH regenerator devices. The presence of an OEO-based extender may require extension of burst overhead, which is automatically handled by the OLT via PLOAM
