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 (02/2016) 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 (02/2016) 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), 2G-4G or the hybrid fibre coax (HFC) networks used by multiple system operators. Redundancy is generally not fund
7、amental 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 sever
8、al 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
9、G.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 d
10、etails 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 E
11、dition 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 * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendat
12、ions unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii G series Supplement 51 (02/2016) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The IT
13、U 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 Standardiz
14、ation 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 tech
15、nology 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 administration and a recognized operating agency. Compliance
16、 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 met. The words “shall“ or some other obligatory langu
17、age 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 possibility that the practice or implementation of this publi
18、cation 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 publication development process. As of the date of approval
19、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 therefore strongly urged to consult the TSB patent data
20、base at http:/www.itu.int/ITU-T/ipr/. ITU 2016 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 (02/2016) iii Table of Contents Page 1 Scope . 1 2 Abbreviations and acronyms 1 3 Background
21、 Fibre protection . 2 3.1 PON system components Failure rates 3 3.2 FIT Failures in time and MTBF 3 4 PON protection use cases . 4 4.1 Large numbers of subscribers per PON line card . 4 4.2 Business and mobile backhaul services 4 4.3 PON reach extenders 4 4.4 Emergency services 5 4.5 PON maintenance
22、 . 5 5 Protection architectures 5 5.1 Type A 6 5.2 Type B 6 5.3 Dual-parented Type B protection . 7 5.4 Type C protection . 7 5.5 Extra traffic for Type C protection . 8 5.6 Type C protection using link aggregation 8 5.7 Type D Deprecated 8 5.8 Type B with N:1 . 9 6 Availability and switching speed
23、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 . 12 7 Fast failure detection . 14 8 Fast protection switchover mechani
24、sms . 16 8.1 Ranging before switchover (pre-ranging) 17 8.2 Ranging after switchover (limited re-ranging) . 18 8.3 No pre-configuration of standby OLT EqD values per ONU (fast ranging) 20 8.4 Equalization-delay-agnostic protection switch . 20 8.5 Typical practice of fast protection switchover mechan
25、isms and viability analysis . 21 9 Recommended architectures versus use cases 26 iv G series Supplement 51 (02/2016) Page 10 Ethernet linear protection switching to support dual-parenting Type B PON protection 26 10.1 Protection switching service characteristics . 27 10.2 Initial connection configur
26、ation . 28 10.3 Description of the end to end protection switching 29 Bibliography. 35 G series Supplement 51 (02/2016) 1 Supplement 51 to ITU-T G-series Recommendations Passive optical network protection considerations 1 Scope Passive optical networks (PONs) are point-to-multipoint networks, much l
27、ike wireless networks such as wireless fidelity (Wi-Fi), 2G-4G or the hybrid fibre coax (HFC) networks used by multiple system operators. Redundancy is generally not fundamental in these networks when compared to ring-based topologies. Nonetheless, there are services such as business services, mobil
28、e backhaul and high-density residential services, which may justify the addition of PON redundancy and protection switching. b-ITU-T G.984.1 outlines several topologies for achieving redundancy; these have been named Type A, Type B, Type C and Type D. Since the publication of that Recommendation, ma
29、ny 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 into use cases and methods that are recommended for adding redundancy and increasing the reliability o
30、f PON networks. 2 Abbreviations and acronyms This Supplement uses the following abbreviations and acronyms: 10G-EPON 10 Gigabit Ethernet Passive Optical Network BA Bandwidth Allocation BNG Broadband Network Gateway BW Bandwidth CCM Continuity Check Message EMS Element Management System EqD Equalizat
31、ion Delay FIT Failures in Time FTTH Fibre to the Home FWI Forced Wakeup Indicator 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 MAC Media Access Control MEG Ma
32、intenance Entity Group MEP Maintenance entity group End Point 2 G series Supplement 51 (02/2016) MTBF Mean Time Between Failures MTTR Mean Time to Repair NG-PON2 40-Gigabit-capable Passive Optical Network NMS Network Management System OAN Optical Access Network ODN Optical Distribution Network OLT O
33、ptical Line Terminal ONU Optical 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 SLA Service Level Agreement SNI Server Node Int
34、erface TDM Time Division Multiplex TDMA Time Division Multiple Access UNI User Network Interface VID VLAN Identifier VLAN Virtual Local Area Network XG-PON 10-Gigabit-capable Passive Optical Network XGS-PON 10-Gigabit-capable Symmetric Passive Optical Network WDM Wavelength Division Multiplexing Wi-
35、Fi Wireless Fidelity 3 Background Fibre protection Optical access networks (OANs) are now delivering multimedia services including data, voice and video. OANs also serve as mobile backhaul connecting wireless towers to metro or core networks. Although the physical media in the last (or first) mile c
36、ould 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 cloud, everything on a click, remote working, global collaboration, e-business and social networking, a single ne
37、twork failure can disrupt services of hundreds of users and will have a cascading effect. Users will find it unacceptable because their survival and well-being are now highly dependent on the health of the access networks. The access network will be considered an essential service. Thus, to meet ser
38、vice 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 business continuance. Failure of G series Supplement 51 (02/2016) 3 any network component will interrupt the
39、 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. Presently, PONs are mostly poorly protected or not protected at all. Fibre cuts are not the only issue. Failure m
40、ay 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 the failure rates and time to repair for PON system components (see the bibliography). The failure rate
41、s 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. The table has references for the various sources used for the failure rates and times to repair for the different
42、 elements of the network. 3.2 FIT Failures in time and MTBF 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 remote node can shut down the entire PON. Mean
43、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, failures in time (FIT) is the failure frequency in 109 hours and MTTR is the mean time to repair
44、 for 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 between failures (M
45、TBF). This is the average time between failures for an MTBF (hrs) = 109/FIT. FIT versus MTBF will be used for the rest of this Supplement. Table 1 Survey of failure rates and repair times for PON components in published literature Equipment Reference FIT MTTR (h) Unavailability OLT b-Alcoa NA NA NA
46、b-Chen1 2500 4 1 105 b-Hajduczenia 7000 5 3.5 105 b-Chen2, b-Tsubokawa NA NA NA ONU b-Alcoa NA NA NA b-Chen1 256 24 6.1 106 b-Hajduczenia 2500 12 3 105 b-Chen2, b-Tsubokawa NA NA NA Deployed optical fibre cable (Note 1) b-Alcoa 10-250/km (Note 2) NA NA b-Chen1 NA NA NA b-Hajduczenia 200/km 14 2.8 10
47、6 b-Chen2, b-Tsubokawa 18/km 6 6 1011 4 G series Supplement 51 (02/2016) Table 1 Survey of failure rates and repair times for PON components in published literature Equipment Reference FIT MTTR (h) Unavailability Splitter b-Alcoa NA NA NA b-Chen1 50-120 24 1.2 107 to 2.9 106 b-Hajduczenia 200 12 2.4
48、 106/km b-Chen2, b-Tsubokawa 50-100 6 3 107 to 6 107 Optical switch b-Alcoa NA NA NA b-Chen1 200 14 4.8 106 b-Hajduczenia NA NA NA b-Chen2, b-Tsubokawa NA NA NA NOTE 1 b-GR-CORE-418 requires no more than 400 FIT per mile, equal to 250 FIT per kilometre. Also, the MTTR for b-GR-CORE-418 is 6 hours no
49、t 24 hours. 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 seen as an upper bound (as evidenced by the fact that b-GR-CORE-418 has a requirement of less than 250 FIT/km). NOTE 3 Some data shown are based on Table 5.1 of b-Chen1, and b-Alcoa. 4 PON
