1、 International Telecommunication Union ITU-T G.984.6TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 1(11/2009) 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
2、passive optical networks (GPON): Reach extension Amendment 1: Wavelength-converting, continuous mode, and 1:N-protected range extenders Recommendation ITU-T G.984.6 (2008) Amendment 1 15ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHON
3、E CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-
4、RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 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 L
5、INE 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
6、 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.989Access networks G.990G.999 MULTIM
7、EDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 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
8、 of ITU-T Recommendations. Rec. ITU-T G.984.6 (2008)/Amd.1 (11/2009) i Recommendation ITU-T G.984.6 Gigabit-capable passive optical networks (GPON): Reach extension Amendment 1 Wavelength-converting, continuous mode, and 1:N-protected range extenders Summary Amendment 1 to Recommendation ITU-T G.984
9、.6 is aimed at defining several additional features or types of reach extender units, including: Wavelength-converting reach extenders. Continuous mode reach extenders. 1:N protected reach extenders. History Edition Recommendation Approval Study Group 1.0 ITU-T G.984.6 2008-03-29 15 1.1 ITU-T G.984.
10、6 (2008) Amend. 1 2009-11-13 15 ii Rec. ITU-T G.984.6 (2008)/Amd.1 (11/2009) 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 Standardizat
11、ion 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 mee
12、ts 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-Ts
13、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
14、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
15、 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 invo
16、lve 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 Reco
17、mmendation, 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 a
18、t http:/www.itu.int/ITU-T/ipr/. ITU 2010 All rights reserved. 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 (2008)/Amd.1 (11/2009) iii CONTENTS Page 1) Changes to clause 1 “Scope“ 1 2) Changes to clause 3 “Defi
19、nitions“ 1 3) Changes to clause 4 “Abbreviations and acronyms“ 2 4) Changes to clause 6 “Optical extension schemes and architectures“ . 2 5) New clause 6.4 “Wavelength conversion reach extenders“ 5 6) New clause 6.5 “Wavelength re-conversion at OLT“ 6 7) New clause 8.6 “WDM wavelength allocation pla
20、n for OTL“ . 9 8) New Appendix VI “Extender-based type B protection scheme“ 10 9) New Appendix VII “Possible realization of OA and OEO-based extenders using wavelength conversion“ 12 10) New Appendix VIII “Transport of BM-to-CM converted signals over OTN“ 18 Rec. ITU-T G.984.6 (2008)/Amd.1 (11/2009)
21、 1 Recommendation ITU-T G.984.6 Gigabit-capable passive optical networks (GPON): Reach extension Amendment 1 Wavelength-converting, continuous mode, and 1:N-protected range extenders This amendment lists the changes necessary to accommodate the wavelength conversion (WC) function in the ITU-T G.984.
22、6 architecture. 1) Changes to clause 1 “Scope“ Add the following after the last paragraph of clause 1: Optionally, optical-electrical-optical converter (OEO) type reach extender (RE) units may support a burst mode (BM) to continuous mode (CM) conversion function, as specified in clause 6.2. In this
23、case, it is also necessary to introduce a CM to BM conversion function before the S/R interface at the OLT. Optionally, both optical amplifier (OA) and OEO type RE units may support the WC function, as specified in clause 6.4. In case of WC-enabled RE units, it is also necessary to introduce a WC fu
24、nction block before the S/R interface. The optional support of type B protection in RE units is described in Appendix VI. 2) Changes to clause 3 “Definitions“ Replace the text of clause 3 with the following: This Recommendation defines the following term: 3.1 wavelength conversion (WC): Any type of
25、technology used to convert the frequency (wavelength) of the incoming optical signal inputinto any outputfrom a predefined wavelength grid. In case of output input, true wavelength conversion takes place, while if output= input, a wavelength-transparent WC function is used, where the frequency of th
26、e optical signal does not change when passing through the WC function. Utilization of a wavelength-transparent WC function does not imply the optical path transparency to data rate modulation format. Several WC technologies are available, including wavelength-tuneable lasers, laser arrays, all-optic
27、al wavelength conversion and seed wavelength modulation. CMGPON_D The name given to the continuous mode GPON downstream bit-stream signal. CMGPON_U The name given to the continuous mode GPON upstream bit-stream signal. 2 Rec. ITU-T G.984.6 (2008)/Amd.1 (11/2009) 3) Changes to clause 4 “Abbreviations
28、 and acronyms“ Add the following to clause 4: AWG Arrayed Waveguide Grating BC Burst Mode BLS Broadband Light Source BM-to-CM Burst Mode to Continuous Mode CID Consecutive Identical Digits CM Continuous Mode CM-to-BM Continuous Mode to Burst Mode DWDM Dense wavelength Division Multiplexing LC Local
29、Controller NRZ Non-Return to Zero OWC Optical Wavelength Conversion RE Reach Extender/Reach Extension SNI Service Node Interface UNI User Network Interface WC Wavelength Conversion WC-RE Wavelength Conversion-enabled Reach Extender unit WDM Wavelength Division Multiplexing XGM Cross-Grain Modulation
30、 4) Changes to clause 6 “Optical extension schemes and architectures“ Add the following text immediately after Figure 2: An extended architecture considered in this Recommendation is presented in Figure 2a. A WC-enabled RE unit is inserted between the ODN (compliant with existing PON Recommendations
31、) 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. Additionally, the WC-RE unit may aggregate several GPON-class ODNs, enabled by the wavelength division multiple
32、xing (WDM) multiplexing over OTL to achieve more cost-efficient use of existing fibre infrastructure. The WC function block inserted before the S/R interface at the OLT performs adaptation between the WDM optical signals transmitted over the OTL and the ITU-T G.984.x-series compliant OLT interfaces.
33、 Rec. ITU-T G.984.6 (2008)/Amd.1 (11/2009) 3 OLTOTLWC+REODNONUONUSNIS/R R/SS/RR/SR/SUNIUNIWCS/RODNONUONUS/RR/SR/SUNIUNIOLTSNI S/RFigure 2a Wavelength conversion reach extender architecture An additional extended architecture considered in this architecture is shown in Figure 2b. A BM-to-CM converter
34、 is used at the remote PON reach extender to convert the bursty upstream signal into a conventional continuous mode signal. A CM-to-BM converter is theoretically present at the OLT location, although it will most likely be integrated within the OLT itself. Figure 2b BM-to-CM conversion reach extende
35、r architecture Add the following text at the end of clause 6.2: The continuous mode OEO RE is a subtype of OEO RE. The S/R interface of CM OEO RE is the same as the one of OEO RE. In CM RE, a BM-to-CM converter is used to convert the burst signal to a continuous signal. The downstream signal (denote
36、d CMGPON_D) has a bit rate of 2.48832 Gbit/s, and a frequency accuracy of 32 ppm in the worst case (where the OLT is in free-running mode). The upstream signal (denoted CMGPON_U) has a bit rate of 1.24416 Gbit/s, and a frequency accuracy of 32 ppm in the worst case (where the OLT is in free-running
37、mode). It must be noted, however, that the upstream signal is always synchronous to the downstream signal. The CMGPON_U signal is composed of the regenerated upstream bursts and some filler signal inserted between the bursts. The filler signal is a bit pattern that is well balanced in order to avoid
38、 long consecutive identical digits (CID). This continuous signal is transmitted by the R/S interface. The filling bit_pattern is configured by the management system at both the transmitter and receiver. The pattern is subject to the control of the OLT; however, it does need to satisfy a few basic re
39、quirements to avoid impacting the physical layer: it should have approximately a 1:1 mark to space ratio, and it should have approximately a 50% transition density. The OEO RE regenerates the received data from ONUs, and therefore does not unscramble the data from the ONUs. OLT OTLBMToCMREODNONUONUS
40、NIS/R R/SS/RR/SR/SUNIUNICMToBMS/R4 Rec. ITU-T G.984.6 (2008)/Amd.1 (11/2009) The upstream frame is depicted in Figure 6a. It is important to note that the incoming upstream bursts each have a unique and independent bit clock phase. The BM-to-CM converter produces at its output a signal that has a si
41、ngle continuous bit clock phase. Therefore, the BM-to-CM converter must buffer each incoming burst of data and re-time it with its output clock. G.984.6(08)Amd.1(09)_F06aONT A ONT B data ONT A data ONT BPreamblePreambleStuffing patternThere may be between 0 and7 zeros between the end ofdata from ONT
42、 A and thestart of the stuffing patternBetween 0 and 7 bits ofthe preamble from ONT Bmay be overwritten bythe stuffing patternBufferingdelayFigure 6a Frame of the upstream CMGPON_U signal Specific techniques for implementing BM-to-CM are beyond the scope of this Recommendation; however, there are a
43、couple of basic methods for detecting the gaps between bursts. Detecting the gap at the optical layer (fibre to PHY interface). On the OEO RE, the optical power is detected, and a control signal is generated accordingly which can be used to control the insertion. Detecting the gap at the logical lay
44、er (PHY to MAC interface). There are some regular patterns (typically the all-zeroes pattern) in the burst gaps which can be detected and used to generate the control signal. Upon the completion of data synchronization, the receiver accepts the burst data while at the same time it is searching for t
45、he end of the burst. When it detects the burst termination by finding the expected pattern, it can reset the burst receiver. Detecting the beginning of bursts requires 32 bit pattern matching, except for cases where the receiver produces random data between bursts, in which case 96 bit patterns are
46、required for a reliable result. Also, 96 bit pattern matching is required to detect the end of bursts for a reliable result. These numbers of required digits are based on statistical calculations of the probability of missing a burst event or creating a false burst event. Shorter or longer pattern m
47、atching is possible, with the concomitant change in error probability. The gap detector will require a logical buffer to store the upstream data to compensate for the non-zero response time of the gap detector, so as to avoid long gaps of all-zero data. However, the stuffing pattern is typically byt
48、e-oriented, while the aligned bursts can be at any arbitrary bit timing. Therefore, in this case an integral number of 0 to 7 bits of zeroes should be expected at the end of each burst, and the last byte of the stuffing pattern will overwrite an integral number of 0 to 7 bits of the following bursts
49、 preamble. The CM-to-BM converter can find the boundaries of the bursts using the logical layer detection method. Importantly, the pattern between the bursts is known to be filled with the stuffing pattern, and so the detection algorithm can be quite simple and should require only 32 bits of pattern matching to detect the start of a burst, and 96 bits to detect the end of a burst. The comment given above on lengths of bit pattern matching apply here as well. As with the ordinar
