1、 International Telecommunication Union ITU-T G.808.2TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/2013) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital networks General aspects Generic protection switching Ring protection Recommendation ITU-T G.808.2 ITU-T G-SERI
2、ES 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 CARRIER TELEPHONE SYSTEMS ON
3、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 SYSTEMS CHARACTERISTICS G.600G
4、.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 General aspects G.800G.809Design objectives for digital networks G.810G.819 Quality and availability targets G.820G.829 Network capabilities and functions G.830G.839 SDH network characteristics G.840G.849 Management of transport
5、 network G.850-G.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.1000-G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000
6、G.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.808.2 (11/2013) i Recommendation ITU-T G.808.2 Generic protection switching Ring protec
7、tion Summary Recommendation ITU-T G.808.2 defines the generic functional models, characteristics and processes associated with various ring protection schemes for connection oriented networks; e.g., optical transport networks (OTNs), synchronous digital hierarchy (SDH) networks. It also defines the
8、objectives and applications for these schemes. The protection scheme described in this Recommendation is shared ring protection. Generic functional models, characteristics and processes for linear protection and interconnected subnetwork protection schemes are defined in other Recommendations. Histo
9、ry Edition Recommendation Approval Study Group Unique ID*1.0 ITU-T G.808.2 2013-11-22 15 11.1002/1000/7504-en _ *To access the Recommendation, type the URL 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.
10、1002/1000/11830-en. ii Rec. ITU-T G.808.2 (11/2013) 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 p
11、ermanent 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 meets every four years, esta
12、blishes 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 purview, the necessary st
13、andards 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 voluntary. However, the R
14、ecommendation 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 the negative equivalen
15、ts 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 involve the use of a claime
16、d 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 Recommendation, ITU had not
17、 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 at http:/www.itu.int/ITU
18、-T/ipr/. ITU 2014 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.808.2 (11/2013) iii Table of Contents Page 1 Scope 1 2 References. 1 3 Definitions 1 3.1 Terms defined elsewhere 1 3.2 Terms define
19、d in this Recommendation . 2 4 Abbreviations and acronyms 2 5 Conventions 3 6 Individual and group protection concept 3 6.1 Individual protection 3 6.2 Group protection . 3 7 Architecture types . 3 7.1 Wrapping protection . 4 7.2 Steering protection 5 8 Switching types . 6 9 Operation types . 6 10 S
20、witching protocol 6 11 Protection classes and subclasses . 7 11.1 Shared section link ring protection (SLRing) . 7 11.2 Dedicated section link ring protection (DLRing) . 7 11.3 Description . 8 12 Multi-ring scenario . 10 13 Protection switching performance 10 14 Hold-off timer . 11 15 Wait-to-restor
21、e timer 12 16 Automatic protection switching (APS) signal 12 17 Non-pre-emptible unprotected traffic (NUT) and extra traffic (ET) 13 18 External commands 13 19 Automatic commands . 14 20 Priority 15 21 SF and SD trigger conditions 16 22 How to avoid misconnections . 16 22.1 Squelching 16 22.2 Steeri
22、ng . 16 Bibliography. 17 Rec. ITU-T G.808.2 (11/2013) 1 Recommendation ITU-T G.808.2 Generic protection switching Ring protection 1 Scope This Recommendation describes the generic aspects of ring protection switching. It covers synchronous digital hierarchy (SDH) and optical transport network (OTN)
23、based protection schemes. Overviews of ring protection and dual node subnetwork (e.g., dual ring) interconnect schemes will be provided in other Recommendations. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute
24、 provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recomme
25、ndations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.783 Recommendation ITU-T G.783 (2006), C
26、haracteristics of synchronous digital hierarchy (SDH) equipment functional blocks. ITU-T G.798 Recommendation ITU-T G.798 (2012), Characteristics of optical transport network hierarchy equipment functional blocks. ITU-T G.841 Recommendation ITU-T G.841 (1998), Types and characteristics of SDH networ
27、k protection architectures. ITU-T G.870 Recommendation ITU-T G.870/Y.1352 (2012), Terms and definitions for optical transport networks. ITU-T M.495 Recommendation ITU-T M.495 (1988), Transmission restoration and transmission route diversity: terminology and general principles. 3 Definitions 3.1 Term
28、s defined elsewhere This Recommendation uses the following terms defined elsewhere: 3.1.1 long path: ITU-T G.841. 3.1.2 non-revertive (protection) operation: ITU-T G.870. 3.1.3 protection class: individual: ITU-T G.870. 3.1.4 revertive (protection) operation: ITU-T G.870. 3.1.5 ring switching: ITU-T
29、 G.841. 3.1.6 short path: ITU-T G.841. 3.1.7 span switching: ITU-T G.841. 3.1.8 steering: ITU-T G.870. 3.1.9 wrapping: ITU-T G.870. 2 Rec. ITU-T G.808.2 (11/2013) 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 extra traffic: This is the traffic that w
30、ill be discarded as soon as protection of the normal traffic is required. It will have the lowest availability of the three types of traffic because every protection switch in the ring affects it. 3.2.2 nonpre-emptible unprotected traffic: This is the traffic that will not be affected by the protect
31、ion switch. It will have availability between that of the Normal traffic and the Extra traffic as it will be affected only by a defect in a section it passes. 3.2.3 normal traffic: This is the traffic that will be protected and will have the highest availability. 3.2.4 ring map: This is a map (table
32、) present in each node on a ring that contains information regarding the order in which the nodes appear on the ring including their node IDs. NOTE Also present in each node is a ring circuit map, containing the cross-connection (added, dropped, and passed-through client traffic) maps of all nodes i
33、n the ring with the squelch table per node as a subset. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: AIS Alarm Indication Signal APS Automatic Protection Switching BER Bit Error Rate DEG Degraded DLRing Dedicated section Link Ring ET Extra Traffic (
34、signal) EXER-R Exercise Ring EXER-S Exercise Span FS-R Forced Switch to protection Ring FS-S Forced Switch to protection Span HO Hold-Off LOW-R Lockout of Working channels Ring switch LOW-S Lockout of Working channels Span switch LP-S Lockout of Protection Span MS-R Manual Switch to protection Ring
35、MS-S Manual Switch to protection Span NR No Request NUT Non-pre-emptible Unprotected Traffic (signal) OAM Operations, Administration and Maintenance OTN Optical Transport Network RR-R Reverse Request Ring RR-S Reverse Request Span Rec. ITU-T G.808.2 (11/2013) 3 SD Signal Degrade SDH Synchronous Digi
36、tal Hierarchy SD-P Signal Degrade Protection SD-R Signal Degrade Ring SD-S Signal Degrade Span SF Signal Fail SF-P Signal Fail Protection SF-R Signal Fail Ring SF-S Signal Fail Span SLRing Shared section Link Ring protection SPRing Shared Protection Ring SSD Server Signal Degrade SSF Server Signal F
37、ail TSD Trail Signal Degrade TSF Trail Signal Fail TT Trail Termination WTR Wait-To-Restore 5 Conventions No conventions are used. 6 Individual and group protection concept 6.1 Individual protection In individual protection, the protection mechanism relies on defects detected in the server layer tha
38、t affect all individual protected entities in the physical section at the same time. In general, individual protection is used in SDH and OTN technologies in physical rings. 6.2 Group protection In group protection, the protection mechanism relies on defects detected by one of the members of the gro
39、up or by the whole group in a logical section. 7 Architecture types The only applicable architecture is a ring. A ring consists of three or more nodes. Each node is connected to two other adjacent nodes in the ring, see Figure 7-1. Two adjacent nodes are connected by a bidirectional span. Each bidir
40、ectional span provides in each direction a working entity, a protection entity and, optionally, an entity to transport non-pre-emptible unprotected traffic (NUT) signals. 4 Rec. ITU-T G.808.2 (11/2013) G.808.2(13)_F7-1ProtectionNUTWorkingTributariesNode #5Node #4SpanNode #2 Node #3Node #1Node #6Figu
41、re 7-1 Ring topology The normal traffic signal transported by the working entity of a section in one direction is protected by the protection entity in the opposite direction of the same section. The NUT is not protected; it is affected if a section or node it passes through fails. The protection en
42、tity can be used to transport extra traffic signals. Extra traffic signals are not protected; they are affected if any section or node in the ring fails. 7.1 Wrapping protection The normal traffic signal is wrapped from the working entity to the protection entity in the nodes adjacent to the failed
43、section or node. During a ring protection switch, normal traffic signal transmitted toward the failed section/node is switched (wrapped) at the node just before the failure to the protection entity in the opposite direction (away from the failure). This bridged traffic signal travels around the ring
44、 on the protection entities to the node just after the failure where the normal traffic signal from the protection entity is switched (wrapped) back onto the working entity. In the other direction, the normal traffic signal is bridged and switched in the same manner. Figure 7-2 illustrates a ring pr
45、otection switch in response to a section failure. Since the protection entity of each section (except the failed section) is used for recovery, the protection capacity is effectively shared by all sections. Rec. ITU-T G.808.2 (11/2013) 5 G.808.2(13)_F7-2FailureNode #5Node #4Node #2 Node #3Node #1Nod
46、e #6wrapwrapProtection pathWorking pathFigure 7-2 Wrapping 7.2 Steering protection The normal traffic signal is switched to the protection entity at its ingress and egress nodes. During a ring protection switch, normal traffic signal transmitted toward the failed section/node is switched (steered) a
47、t the node where it enters the ring to the protection entity in the opposite direction (away from the failure). This bridged traffic signal travels around the ring on the protection entities to the node where the normal traffic signal exits the ring and where the normal traffic signal from the prote
48、ction entity is switched (steered) back to the output. In the other direction, the normal traffic signal is bridged and switched in the same manner. Figure 7-3 illustrates a ring protection switch in response to a section failure. Since the protection entity of each section (except the failed sectio
49、n) is used for recovery, the protection capacity is effectively shared by all spans. 6 Rec. ITU-T G.808.2 (11/2013) G.808.2(13)_F7-3FailureNode #5Node #4Node #2 Node #3Node #1Node #6steerProtection pathWorking pathsteerFigure 7-3 Steering 8 Switching types Shared ring protection switching is bidirectional. 9 Operation types The protection operation types can be a revertive operation type or a non-revertive operation type. In revertive (protection)
