1、 I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n ITU-T Series G TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Supplement 51 (06/2017) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Passive optical network protection considerations ITU-T G-series Recomm
2、endations Supplement 51 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.200G.299 INDIVIDUAL CHARACTERISTICS OF INTERNA
3、TIONAL 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 TELEPHONY G.450G.499 TRANSMISSION MEDIA AND OP
4、TICAL 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 MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999
5、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. G series Supplement 51 (06/2017) i Supplement 51 to ITU-T G-series Recommendations Passive optical network
6、protection considerations Summary Passive optical networks (PONs) can generally be considered point-to-multipoint networks, much like wireless networks such as wireless fidelity (Wi-Fi), 2G4G or the hybrid fibre coax (HFC) networks used by multiple system operators. Redundancy is generally not funda
7、mental in these networks as contrasted with ring-based topologies. Nonetheless, there are services such as business services, mobile backhaul and high-density residential services, which may justify the addition of PON redundancy and protection switching. Recommendation ITU-T G.984.1 outlines severa
8、l topologies for achieving redundancy; these have been named type A, type B, type C and type D. Since the publication of ITU-T G.984.1, many other studies of various aspects of PON availability, redundancy and switching have been made available. The ITU-T G.987 series, ITU-T G.989 series and ITU-T G
9、.9807.1 describe the 10-Gigabit-capable passive optical network (XG-PON), the 40-Gigabit-capable passive optical network (NG-PON2) and the 10-Gigabit-capable symmetric passive optical network (XGS-PON) systems. Each of these further describe protection aspects of those systems. In particular, the de
10、tails of automatic protection switching in type B has been more fully worked out. This Supplement collects this information and, guided by input from operators, distils it into use cases and methods that are recommended for adding redundancy and increasing the reliability of PON networks. History Ed
11、ition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G Suppl. 51 2012-05-11 15 11.1002/1000/11652 2.0 ITU-T G Suppl. 51 2016-02-26 15 11.1002/1000/12841 3.0 ITU-T G Suppl. 51 2017-06-30 15 11.1002/1000/13342 * To access the Recommendation, type the URL http:/handle.itu.int/ in the address
12、field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii G series Supplement 51 (06/2017) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, inf
13、ormation 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 w
14、orldwide 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 i
15、n WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this publication, the expression “Administration“ is used for conciseness to indicate both a telecommunication admini
16、stration and a recognized operating agency. Compliance with this publication is voluntary. However, the publication may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the publication is achieved when all of these mandatory provisions are
17、 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 publication is required of any party. INTELLECTUAL PROPERTY RIGHTSITU draws attention to the possibi
18、lity that the practice or implementation of this publication 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 public
19、ation development process. As of the date of approval of this publication, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this publication. However, implementers are cautioned that this may not represent the latest information and are t
20、herefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2017 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. G series Supplement 51 (06/2017) iii Table of Contents Page 1
21、 Scope . 1 2 Abbreviations and acronyms 1 3 Background Fibre protection . 3 3.1 PON system components Failure rates 3 3.2 Failures in time and mean time between failures . 3 4 PON protection use cases . 4 4.1 Large numbers of subscribers per PON line card . 4 4.2 Business and mobile backhaul service
22、s 5 4.3 PON reach extenders 5 4.4 Emergency services 5 4.5 PON maintenance . 5 5 Protection architectures 6 5.1 Type A 6 5.2 Type B 7 5.3 Dual-parented type B protection 7 5.4 Type C protection . 8 5.5 Extra traffic for type C protection 9 5.6 Type C protection using link aggregation 9 5.7 Type D De
23、precated 9 5.8 Type B with N:1 . 9 6 Availability and switching speed goals 10 6.1 Availability in an unprotected PON . 10 6.2 Assumptions for availability calculations 11 6.3 Availability of an unprotected PON . 12 6.4 Protection path monitoring . 12 6.5 Switching speed and impact on availability .
24、 12 7 Fast failure detection . 14 8 Fast protection switchover mechanisms . 15 8.1 Ranging before switchover (pre-ranging) 16 8.2 Ranging after switchover (limited re-ranging) . 18 8.3 No pre-configuration of standby OLT EqD values per ONU (fast ranging) 19 8.4 Equalization-delay-agnostic protection
25、 switch . 20 8.5 Typical practice of fast protection switchover mechanisms and viability analysis . 20 9 Recommended architectures versus use cases 25 10 Ethernet linear protection switching to support type B PON protection 25 10.1 Protection switching service characteristics . 26 10.2 OLT PON port
26、type B Protection State Machine . 27 iv G series Supplement 51 (06/2017) Page 10.3 Initial connection configuration . 33 10.4 Description of end to end protection switching 34 Bibliography. 36 G series Supplement 51 (06/2017) 1 Supplement 51 to ITU-T G-series Recommendations Passive optical network
27、protection considerations 1 Scope Passive optical networks (PONs) are point-to-multipoint networks, much like wireless networks such as wireless fidelity (Wi-Fi), 2G4G or the hybrid fibre coax (HFC) networks used by multiple system operators. Redundancy is generally not fundamental in these networks
28、 when compared to ring-based topologies. Nonetheless, there are services such as business services, mobile backhaul and high-density residential services that may justify the addition of PON redundancy and protection switching. b-ITU-T G.984.1 outlines several topologies for achieving redundancy; th
29、ese have been named type A, type B, type C and type D. Since the publication of b-ITU-T G.984.1, many other studies of various aspects of PON availability, redundancy and switching have been made available. This Supplement collects this information and, guided by input from operators, distils it int
30、o use cases and methods that are recommended for adding redundancy and increasing the reliability of PON networks. 2 Abbreviations and acronyms This Supplement uses the following abbreviations and acronyms: 2G4G second Generation to fourth Generation 10G-EPON 10-Gigabit Ethernet Passive Optical Netw
31、ork BA Bandwidth Allocation BNG Broadband Network Gateway BW Bandwidth CCM Continuity Check Message EMS Element Management System E-PON Ethernet Passive Optical Network EqD Equalization Delay FIT Failure in Time FTTH Fibre to the Home FWI Forced Wakeup Indicator G-PON Gigabit-capable Passive Optical
32、 Network HFC Hybrid Fibre Coax IGMP Internet Group Management Protocol ISDN Integrated Services Digital Network LAG Link Aggregation LOF Loss of Frame LOS Loss of Signal LSB Least Significant Bit 2 G series Supplement 51 (06/2017) MAC Media Access Control MEG Maintenance Entity Group MEP Maintenance
33、 entity group Endpoint MTBF Mean Time Between Failures MTTR Mean Time to Repair NG-PON2 40-Gigabit-capable Passive Optical Network NMS Network Management System OAM Operations, Administration and Maintenance OAN Optical Access Network ODN Optical Distribution Network OLT Optical Line Terminal ONU Op
34、tical Network Unit PLOAM Physical Layer Operations, Administration and Maintenance PON Passive Optical Network POTS Plain Old Telephone Service QoS Quality of Service RE Reach Extender RTD Round-Trip Delay RTT Round-Trip Time SDi Signal Degrade SFi Signal Fail SLA Service Level Agreement SME Small t
35、o Medium-sized Enterprises SNI Server Node Interface S-VID Service VLAN Identifier TDM Time Division Multiplex TDMA Time Division Multiple Access UNI User Network Interface VID VLAN Identifier VLAN Virtual Local Area Network WDM Wavelength Division Multiplexing Wi-Fi Wireless Fidelity XG-PON 10-Giga
36、bit-capable Passive Optical Network XGS-PON 10-Gigabit-capable Symmetric Passive Optical Network G series Supplement 51 (06/2017) 3 3 Background Fibre protection Optical access networks (OANs) are now delivering multimedia services including data, voice and video. OANs also serve as mobile backhaul
37、connecting wireless towers to metro or core networks. Although the physical media in the last (or first) mile could be different from fibre, OANs are an integral part of any broadband access network. Most OANs use passive optical network (PON) architectures. As society moves towards everything in cl
38、oud, everything on a click, remote working, global collaboration, e-business and social networking, a single network failure can disrupt services of hundreds of users and have a cascading effect. Users will find it unacceptable because their survival and well-being are now highly dependent on the he
39、alth of the access networks. The access network will be considered an essential service. Thus, to meet service level agreements (SLAs) and guarantee the appropriate level of connection availability, fault management within any type of PON becomes more significant for reliable service delivery and bu
40、siness continuance. Failure of any network component will interrupt the service resulting in a significant loss of revenues. Service subscribers expect the quality of service (QoS) to be at least at the same level as that provided by the copper-based plant. Currently, PONs are mostly poorly protecte
41、d or not protected at all. Fibre cuts are not the only issue. Failure may occur in the optical line terminal (OLT), optical network unit (ONU) power splitter or optical amplifier, if employed. 3.1 PON system components Failure rates There have been several reports on failure rates and time to repair
42、 for PON system components. Failure rates differ widely and depend on geography, environment, assumptions and component design, at a minimum. Table 1 is a compilation of the component failure rates taken from these references and has references to the various sources used for failure rates and times
43、 to repair for the different elements of the network. 3.2 Failures in time and mean time between failures The failure of some network elements has more impact on services than others. For example, ONU failure or distribution fibre cuts affects only one user. But a failure of OLT, feeder fibre or a r
44、emote node can shut down the entire PON. Mean time to repair (MTTR) will also be different for different network elements. Table 1 summarizes some statistical data relating to unavailability of the network due to failure of network components. Here, the FIT column lists the failure frequency over 10
45、9 h and MTTR applies to each failure. Unavailability is defined as the probability that the equipment, service or fibre is unavailable at any time and can be defined mathematically as: Network unavailability due to a component failure = FIT MTTR 109 Another measure of failure rates is the mean time
46、between failures (MTBF). This is the average time between failures for an MTBF (h) = 109/FIT. FIT versus MTBF will be used for the rest of this Supplement. 4 G series Supplement 51 (06/2017) Table 1 Survey of failure rates and repair times for PON components in published literature Equipment Referen
47、ce FIT MTTR (h) Unavailability OLT b-Alcoa NA NA NA b-Chen, 2008 2 500 4 1 105 b-Hajduczenia 7 000 5 3.5 105 b-Chen, 2010, b-Tsubokawa NA NA NA ONU b-Alcoa NA NA NA b-Chen, 2008 256 24 6.1 106 b-Hajduczenia 2 500 12 3 105 b-Chen, 2010, b-Tsubokawa NA NA NA Deployed optical fibre cable (Note 1) b-Alc
48、oa 10/km250/km (Note 2) NA NA b-Chen, 2008 NA NA NA b-Hajduczenia 200/km 14 2.8 106 b-Chen, 2010, b-Tsubokawa 18/km 6 6 1011 Splitter b-Alcoa NA NA NA b-Chen, 2008 50120 24 1.2 107 to 2.9 106 b-Hajduczenia 200 12 2.4 106/km b-Chen, 2010, b-Tsubokawa 50100 6 3 107 to 6 107 Optical switch b-Alcoa NA N
49、A NA b-Chen, 2008 200 14 4.8 106 b-Hajduczenia NA NA NA b-Chen, 2010, b-Tsubokawa NA NA NA NOTE 1 b-GR-418 requires no more than 400 FIT/mile, equal to 250 FIT/km. Also, the MTTR for b-GR-418 is 6 h not 24 h. NOTE 2 b-Alcoa distinguished between aerial and buried fibre. Aerial = 10 FIT/km, buried 250 FIT/km. The 250 FIT/km may be a result of poor control of utility digging policies; it should be s
