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 G.873.2 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (08/2015) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital networks Optical transport networks ODUk shared ring protection Recommendation
2、 ITU-T G.873.2 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 INTERNATIONAL CA
3、RRIER 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 OPTICAL SYS
4、TEMS CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 General aspects G.800G.809 Design objectives for digital networks G.810G.819 Synchronization, quality and availability targets G.820G.829 Network capabilities and functions G.830G.839 SDH network chara
5、cteristics G.840G.849 Management of transport network G.850G.859 SDH radio and satellite systems integration G.860G.869 Optical transport networks G.870G.879 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.199
6、9 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.873.2 (08/2015) i Recommendation ITU-T G.873
7、.2 ODUk shared ring protection Summary Recommendation ITU-T G.873.2 provides the first set of necessary equipment-level specifications to implement shared ring protection architectures in optical transport networks (OTNs). In this version of the Recommendation shared ring protection on base of wrapp
8、ing method is specified. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.873.2 2012-04-22 15 11.1002/1000/7505 1.1 ITU-T G.873.2 (2012) Amd.1 2012-10-29 15 11.1002/1000/11791 2.0 ITU-T G.873.2 2015-08-13 15 11.1002/1000/12530 _ * To access the Recommendation, type the URL
9、http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T G.873.2 (08/2015) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the
10、 field of telecommunications, information 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 standa
11、rdizing telecommunications on a worldwide 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 cov
12、ered 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 collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indi
13、cate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achiev
14、ed 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. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL P
15、ROPERTY RIGHTSITU draws attention to the possibility that the practice or implementation of this Recommendation 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 asse
16、rted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that
17、 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 2016 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec.
18、ITU-T G.873.2 (08/2015) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation . 2 4 Abbreviations and acronyms 2 5 Conventions 3 6 Applications of OTN shared ring protection 3 6.1 Attributes of shared ring prote
19、ction 3 6.2 Protection classifications 4 6.3 Applications considerations 8 6.4 Use of extra traffic 14 7 ODU SRP 14 7.1 Two and four-fibre ODU SRP types 14 7.2 Wrapping application of ODU SRP . 18 7.3 Steering application of ODU shared ring protection 44 8 Interworking architectures 44 8.1 Single no
20、de interconnection . 44 8.2 Dual node interconnection 45 Annex A Network objectives 60 Appendix I Examples of protection switching in an ODU SRP . 61 I.1 Unidirectional signal fail (span) in a four-fibre ring 61 I.2 Unidirectional signal fail (ring) 63 I.3 Bidirectional signal fail (ring) 66 I.4 Uni
21、directional signal degrade (ring) . 69 I.5 Node failure 71 I.6 Unidirectional SF-R pre-empting a unidirectional SD-S on non-adjacent spans . 74 I.7 Unidirectional SF-S pre-empting a unidirectional SF-R on adjacent spans SF-S and SF-R detected at non-adjacent nodes . 77 I.8 Unidirectional SF-R pre-em
22、pting a unidirectional SD-S on adjacent spans 79 I.9 Unidirectional SF-R coexisting with a unidirectional SF-R on non-adjacent spans . 82 I.10 Node failure on a ring with extra traffic capability 84 I.11 Unidirectional SF-S pre-empting a unidirectional SF-R on adjacent spans SF-S and SF-R detected a
23、t adjacent nodes 86 iv Rec. ITU-T G.873.2 (08/2015) Page Appendix II Generalized squelching logic 90 II.1 Squelching for unidirectional (and bidirectional) circuits 90 II.2 Squelching of multiply dropped and multiply sourced unidirectional circuits 91 Appendix III Ring configuration examples 94 III.
24、1 2-fibre/2-lambda, 2-fibre/4-lambda and 4-fibre/4-lambda SRP-p Ring (22SRP-p, 24SRP-p, 44SRP-p) configurations example . 94 III.2 2 fibres/4 lambda, 4-fibre/4-lambda SRP-1 Ring (24SRP-1, 44SRP-1) configuration example 95 III.3 ODU SRP group protection example . 96 Rec. ITU-T G.873.2 (08/2015) 1 Rec
25、ommendation ITU-T G.873.2 ODUk shared ring protection 1 Scope This Recommendation describes the automatic protection switching (APS) protocol to support optical channel data unit k (ODUk) shared ring protection (SRP) in the optical transport network (OTN). Shared ring protection provides two types o
26、f switching: SRP-1 with 1 ODU per lambda, and SRP-p with p ODUs per lambda. SRP protects ODUs within a physical ring with ODU cross-connects. The interconnects are in general of type optical transport module-n (OTM-n), as specified in ITU-T G.709. The network objectives are given in Annex A. 2 Refer
27、ences The 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; user
28、s of this 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 Recommend
29、ation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.709 Recommendation ITU-T G.709/Y.1331 (2012), Interfaces for the optical transport network. ITU-T G.798 Recommendation ITU-T G.798 (2010), Characteristics of optical transport network hierarchy equipment funct
30、ional blocks. ITU-T G.805 Recommendation ITU-T G.805 (2000), Generic functional architecture of transport networks. ITU-T G.806 Recommendation ITU-T G.806 (2006), Characteristics of transport equipment Description methodology and generic functionality. ITU-T G.808.1 Recommendation ITU-T G.808.1 (201
31、4), Generic protection switching Linear trail and subnetwork protection. ITU-T G.841 Recommendation ITU-T G.841 (1998), Types and characteristics of SDH network protection architectures. ITU-T G.870 Recommendation ITU-T G.870/Y.1352 (2012), Terms and definitions for optical transport networks. ITU-T
32、 G.872 Recommendation ITU-T G.872 (2001), Architecture of optical transport networks. ITU-T G.873.1 Recommendation ITU-T G.873.1 (2006), Optical Transport Network (OTN): Linear protection. ITU-T G.874 Recommendation ITU-T G.874 (2001), Management aspects of the optical transport network element. 2 R
33、ec. ITU-T G.873.2 (08/2015) 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the following terms defined elsewhere: 3.1.1 APS-byte pass-through: See ITU-T G.870. 3.1.2 APS channel: See ITU-T G.870. 3.1.3 crossing APS-bytes: See ITU-T G.870. 3.1.4 default APS code: See ITU-T G.870.
34、3.1.5 entity: See ITU-T G.870. 3.1.6 extra traffic signal: See ITU-T G.870. 3.1.7 full pass-through: See ITU-T G.870. 3.1.8 head end: See ITU-T G.870. 3.1.9 normal traffic signal: See ITU-T G.870. 3.1.10 null signal: See ITU-T G.870. 3.1.11 protection communication channel: See ITU-T G.870. 3.1.12 p
35、rotection group: See ITU-T G.870. 3.1.13 signal: See ITU-T G.870. 3.1.14 SRP-1: See ITU-T G.870. 3.1.15 SRP-p: See ITU-T G.870. 3.1.16 steering: See ITU-T G.870. 3.1.17 tail end: See ITU-T G.870. 3.1.18 pass-through: See ITU-T G.841. 3.1.19 ring switch: See ITU-T G.841. 3.1.20 span switch: See ITU-T
36、 G.841. 3.1.21 wrapping: See ITU-T Rec. G.870. 3.2 Terms defined in this Recommendation None. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: AIS Alarm Indication Signal APS Automatic Protection Switching DNR Do Not Revert ET Extra Traffic EXER Exercis
37、e FS Forced Switch Rec. ITU-T G.873.2 (08/2015) 3 GCC General Communication Channel HO Highest Order LO Lowest Order MS Manual Switch NE Network Element NIM Non-Intrusive Monitor NR No Request NUT Non-pre-emptible Unprotected Traffic ODUk Optical channel Data Unit k OPU Optical channel Payload Unit
38、OTN Optical Transport Network OTUk Optical channel Transport Unit k PCC Protection Communication Channel RR Reverse Request SD Signal Degrade SF Signal Fail SNC Sub-Network Connection SNC/N Sub-Network Connection with Non-intrusive monitoring SNCP Sub-Network Connection Protection SRP-n Shared Ring
39、Protection of n ODU per Lambda (n=1, p) TCM Tandem Connection Monitoring WTR Wait-To-Restore 5 Conventions As used in this Recommendation, highest order (HO) and lowest order (LO) are referring to the shared ring sub-network viewpoint. 6 Applications of OTN shared ring protection 6.1 Attributes of s
40、hared ring protection Shared ring protection of p optical channel data unit (ODU) per lambda (SRP-p) protection switching is on a per-highest order (HO) ODU basis between all nodes in the ring. A bundle of lowest order (LO) ODU signals is switched when LO ODUk is carried by an HO ODUk around the rin
41、g. Automatic protection switching (APS) is used for each HO ODUk. SRP-1 protection switching is on a per-LO ODUk sub-network connection (SNC) or tandem connection basis between the ingress/egress points on the ring for that ODUk when the LO ODU is carried by an OTUk or as the client of a higher orde
42、r (HO) ODU server around the ring. 4 Rec. ITU-T G.873.2 (08/2015) For SRP-p, the payload type considered is PT21. While, in principle, PT20 could also be supported, the use of mixed payload structures creates interworking issues and is not recommended. There are no two-/four-fibre architectural diff
43、erences for LO ODU SRP. Whether working/protection are on the same or different, diversely routed fibres across a span affects the ultimate reliability, but not the architecture or switching. There are two-/four-lambda architectural differences for SRP-p (also quoted as HO ODU). In the two-lambda ar
44、chitecture, the HO OPU payload must be split into working, protection and a non-pre-emptible parts. In the four-lambda architecture, all working traffic is carried in one HO ODU and all protection traffic is carried in another HO ODU. In ITU-T G.709 OTN, per-wavelength failure modes provide value fo
45、r span switches even when working and protection ODUks are on the same fibre. Each connection between adjacent nodes in a given ring consists of a working and a protection entity. These entities may either be provided over the same fibre, or over two diversely routed fibres between the adjacent node
46、s. When many ODUks in one fibre belong to one group, group protection can reduce the number of APS instances in one fibre. Group protection can be triggered on the basis of signal fail group/signal degrade group (SFG/SDG) specifications as described in clauses 11.1.2 and 11.3.1 of ITU-T G.808.1. 6.2
47、 Protection classifications This clause describes, in general terms, the types of ODU SRP architectures described within this Recommendation. ODU SRP is an ODU ring-based sub-network connection group protection with inherent monitoring (SNCG/I). Figure 6-1 illustrates the model of a two-fibre/two-la
48、mbda ODUj SRP node with an N OPUk tributary slot capacity (ODU SRP-p). OTUk section monitoring and ODUk path monitoring endpoints terminate the OTUk and ODUk signals. ODUj signals within the ODUk are either protected by means of SRP, or are pre-emptible or non-pre-emptible unprotected. Figure 6-2 il
49、lustrates the model of a four-lambda ODUj SRP with a 2N OPUk tributary slot capacity. The four-lambdas may be transported over either four-fibres or two-fibres. When transported over two-fibres, working and protection are part of the same shared risk group and provide a double capacity version of the two-fibre/two-lambda ODU SRP case. OTUk section monitoring and ODUk path monitoring endpoints are terminating the OTUk a
