1、 International Telecommunication Union ITU-T G.987.1TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 1(04/2012) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital sections and digital line system Optical line systems for local and access networks 10-Gigabit-capab
2、le passive optical networks (XG-PON): General requirements Amendment 1 Recommendation ITU-T G.987.1 (2010) Amendment 1 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMO
3、N 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-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.
4、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 LINE SYSTEM G.900G.999 General G.900G.909 Parameters for optical fib
5、re 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.95
6、9 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 MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED AS
7、PECTS 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 of ITU-T Recommendations. Rec. ITU-T G.987.1 (2010)/Amd.1 (04/2012
8、) i Recommendation ITU-T G.987.1 10-Gigabit-capable passive optical networks (XG-PON): General requirements Amendment 1 Summary Amendment 1 to Recommendation ITU-T G.987.1 (2010) includes: 1) text describing the operation of XG-PON with IEEE 1588; 2) use cases for XG-PON frequency and time-of-day sy
9、nchronization; 3) transport of ESMC messages over PON; and 4) clarification of the reference optical configuration for XG-PON coexistence through splitters. History Edition Recommendation Approval Study Group 1.0 ITU-T G.987.1 2010-01-13 15 1.1 ITU-T G.987.1 (2010) Amd. 1 2012-04-22 15 ii Rec. ITU-T
10、 G.987.1 (2010)/Amd.1 (04/2012) 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 IT
11、U. 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 f
12、or 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 purview, the necessary standards are prepared
13、 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 co
14、ntain 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 expre
15、ss 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 Prope
16、rty 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
17、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 2012 Al
18、l 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.987.1 (2010)/Amd.1 (04/2012) iii Table of Contents Page 1 Scope 1 2 Additional acronyms . 1 3 New Appendix IV . 1 4 New Appendix V 2 5 New Appendix VI
19、. 6 6 Revised Figure 5-6 and new note . 7 7 Additional references 8 Rec. ITU-T G.987.1 (2010)/Amd.1 (04/2012) 1 Recommendation ITU-T G.987.1 10-Gigabit-capable passive optical networks (XG-PON): General requirements Amendment 1 1 Scope Amendment 1 of ITU-T G.987.1 includes: 1) text describing the op
20、eration of XG-PON with IEEE 1588, 2) use cases for XG-PON frequency and time-of-day synchronization, 3) text describing the transport of ESMC messages over PON and 4) clarification of the reference optical configuration for XG-PON coexistence through splitters. 2 Additional acronyms Insert the follo
21、wing acronyms alphanumerically in the list of abbreviations and acronyms within clause 4: ESMC Ethernet Synchronization Messaging Channel OSSP Organization Specific Slow Protocol PRC Primary Reference Clock PTP Precision Timing Protocol RNC Radio Network Controller ToD Time-of-Day 3 New Appendix IV
22、Add the following material as a new Appendix IV: Appendix IV Operation with IEEE 1588 (This appendix does not form an integral part of this Recommendation.) IEEE 1588 describes a protocol for transferring time and/or frequency information through a packet network. A good explanation of this can be f
23、ound in b-Garner. XG-PON distributes the IEEE 1588 master and slave functionality between the OLT and the ONU. The OLT will perform the slave port function; or, in the case of a shelf, the OLT will receive the frequency and time information from the function in the shelf that performs the slave port
24、 function. The OLT synchronizes the PON line rate to the network clock frequency, and transfers the time-of-day information to the ONU using the method in clause 13.2 of ITU-T G.987.3. The ONU uses 2 Rec. ITU-T G.987.1 (2010)/Amd.1 (04/2012) the methods specified in ITU-T G.987.2 to recover frequenc
25、y and ITU-T G.987.3 to recover time. The ONU will then either function as a master port to subsequent nodes or output the time and frequency information through another interface. 4 New Appendix V Add the following material as a new Appendix V: Appendix V Use cases for frequency and time-of-day sync
26、hronization (This appendix does not form an integral part of this Recommendation.) There are many applications where precise time and/or frequency information must be transferred through a packet network from a source to a destination. In this appendix, several use cases are described in terms of th
27、e methods used to deliver frequency and/or time information. Since most of the use cases mentioned are related to mobile backhauling applications, examples will use the RNC and Node B network elements; however, these use cases are not intended to be exhaustive. Frequency and/or time-of-day synchroni
28、zation is provided to the OLT via either: 1) Physical timing interface (e.g., synchronous Ethernet (SyncE) (frequency only) 2) IEEE 1588 + synchronous Ethernet 3) IEEE 1588 + non-synchronous Ethernet 4) Physical time-of-day (ToD) interface + SyncE Frequency and/or time-of-day synchronization is supp
29、lied from the ONU via either: 1) Physical timing interface (e.g., synchronous Ethernet (SyncE) (frequency only) 2) IEEE 1588 + synchronous Ethernet 3) IEEE 1588 + non-synchronous Ethernet 4) Physical ToD interface + SyncE The use cases are described in terms of various combinations of these synchron
30、ization inputs and outputs, as shown in Table V.1. Table V.1 XG-PON synchronization use cases Use case Network synchronization to OLT UNI synchronization from ONU 1 SyncE (frequency only) SyncE (frequency only) 2 IEEE 1588 and SyncE IEEE 1588 and SyncE 3 IEEE 1588 IEEE 1588 4 IEEE 1588 IEEE 1588 and
31、 SyncE 5 IEEE 1588 and SyncE ToD interface and SyncE 6 IEEE 1588 ToD interface and SyncE 7 ToD interface and SyncE ToD interface and SyncE Figure V.1 depicts use case 1 where frequency only is transferred through the XG-PON network. The clock interface at the OLT input and the ONU output is a physic
32、al timing interface such as synchronous Ethernet (SyncE), defined in ITU-T G.8262. The OLT synchronizes the PON line Rec. ITU-T G.987.1 (2010)/Amd.1 (04/2012) 3 rate to this physical interface. The ONU outputs a physical timing interface such as SyncE, which is synchronous to the PON line rate. Figu
33、re V.1 Using synchronous Ethernet in XG-PON (use case 1) There are several use cases of interest (use cases 2 through 6) that use IEEE 1588, with the following assumptions. The PRC provides a frequency reference. The OLT network interface is Ethernet, with the Ethernet line rate either synchronous t
34、o a network frequency reference (synchronous Ethernet) or not synchronous to a network frequency reference. The OLT obtains time-of-day using IEEE 1588, usually through intervening nodes between the OLT and the PRC. The OLT synchronizes to the network frequency reference either using synchronous Eth
35、ernet, IEEE 1588, or some other physical layer synchronous interface. The OLT transfers the time-of-day to the ONU using the method specified in chapter 13 of ITU-T G.987.3. The OLT transfers the network frequency reference to the ONU via its downstream line rate, which is synchronous to the network
36、 frequency reference. The ONU user interface is Ethernet, with the Ethernet line rate either synchronous to a network frequency reference (synchronous Ethernet) or not synchronous to a network frequency reference. The ONU may also have a physical time interface (e.g., 1pps). Figure V.2a PTP use case
37、 2: ONU as IEEE 1588 master, OLT as IEEE 1588 slave with SyncE at both SNI and UNI 4 Rec. ITU-T G.987.1 (2010)/Amd.1 (04/2012) Figure V.2b PTP use case 3: ONU as IEEE 1588 master, OLT as IEEE 1588 slave without SyncE Figure V.2c PTP use case 4: ONU as IEEE 1588 master, OLT as IEEE 1588 slave, with S
38、yncE at UNI Figures V.2a and V.2b show use cases 2 and 3 for wireless backhaul. The OLT has an IEEE 1588 slave port at the SNI, which obtains the time of day from the network. This time of day is passed to the ONU as described above, and the ONU passes the time of day from an IEEE 1588 master port t
39、o the Node B. If the OLT network feed is synchronous Ethernet (use cases 2), then the OLT will synchronize its downstream PON line rate to the synchronous Ethernet line rate; otherwise the OLT will synchronize its downstream PON line rate to the IEEE 1588 time-of-day (use cases 3). If the link betwe
40、en the ONU and the Node B is synchronous Ethernet (use cases 2), then the synchronous Ethernet line rate will be synchronized to the downstream PON line rate. Synchronous Ethernet ESMC messages would be used in conjunction with the synchronous Ethernet to indicate clock quality. Figure V.3a below sh
41、ows use case 5, while Figure V.3b illustrates use case 6 for wireless backhaul. The only difference between Figure V.2 and Figure V.3 is that the ONU has a physical interface for transferring time information to the Node B, such as a ToD interface. If the OLT network feed is synchronous Ethernet (us
42、e case 5), then the OLT will synchronize its downstream PON line rate to Rec. ITU-T G.987.1 (2010)/Amd.1 (04/2012) 5 the synchronous Ethernet line rate; otherwise the OLT will synchronize its downstream PON line rate to the IEEE 1588 time-of-day (use cases 6). Figure V.2c illustrates use case 4 wher
43、e the OLT does not receive synchronous Ethernet and derives the downstream PON line rate from IEEE 1588. In this case the ESMC messages would correspond to the IEEE 1588 clock quality and not a clock quality received via ESMC at the OLT. Figure V.4 shows use case 7, where a physical ToD interface is
44、 provided as an input to the OLT. The OLT processes the ToD information and sends timing information to the ONU according to the description provided in clause 13.2 of ITU-T G.987.3. The ONU processes the received timing information and outputs the timing information using a physical ToD interface.
45、NOTE The details of the physical ToD interface are for further study. Figure V.3a PTP use case 5: ONU with physical time interface, OLT as IEEE 1588 slave with SyncE at both SNI and UNI Figure V.3b PTP use case 6: ONU with physical time interface, OLT as IEEE 1588 slave with SyncE at UNI only 6 Rec.
46、 ITU-T G.987.1 (2010)/Amd.1 (04/2012) Figure V.4 Use case 7, ONU and OLT with physical time interface 5 New Appendix VI Add the following material as a new Appendix V: Appendix VI Transport of ESMC messages over PON (This appendix does not form an integral part of this Recommendation.) In Appendix V
47、, the use case of synchronous Ethernet over the PON was described and the ESMC was introduced. Appendix VI addresses frequency synchronization over XG-PON, but focuses on a recommended method to transfer the SSM carried in the ESMC (as defined in b-ITU-T G.8264) that are used to send the synchronous
48、 Ethernet clock quality in a one-way fashion from the clock master to a base station or other end-device. Refer to Figure V.1, for this appendix. Within the physical layer, synchronous Ethernet is transferred over the OLT/ODN/ONU in the following way. A synchronous Ethernet-capable OLT will lock the
49、 XG-PON clock to the received Ethernet clock at the OLT SNI, and a synchronous Ethernet-capable ONU will, in turn, lock the Ethernet clock of one or more provisioned Ethernet port UNIs to the XG-PON clock. NOTE ITU-T G.8262 defines the types of UNIs capable of synchronous Ethernet. Characteristics of the ESMC include: Simple, stateless, unidirectional protocol for communicating the current reference clock quality between nodes. Uses the IEEE 802.3 Organization Specific Slow Pr
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