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.873.1 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (10/2017) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital networks Optical transport networks Optical transport network: Linear protecti
2、on Recommendation ITU-T G.873.1 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
3、 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.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TRANSMISSION MEDI
4、A AND OPTICAL SYSTEMS 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
5、SDH network characteristics 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 AS
6、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.873.1 (10/2017) i Recommend
7、ation ITU-T G.873.1 Optical transport network: Linear protection Summary Recommendation ITU-T G.873.1 defines the automatic protection switching (APS) protocol and protection switching operation for the linear protection schemes for the optical transport network at the optical data unit k (ODUk) lev
8、el. Protection schemes considered in this Recommendation are: ODUk subnetwork connection protection with inherent monitoring (1+1, 1:n); ODUk subnetwork connection protection with non-intrusive monitoring (1+1); ODUk subnetwork connection protection with sublayer monitoring (1+1, 1:n). ODUk compound
9、 link subnetwork connection group protection with inherent monitoring (1+1, 1:1). In addition, client-related protection architectures are described. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.873.1 2003-03-29 15 11.1002/1000/6306 2.0 ITU-T G.873.1 2006-03-29 15 11.10
10、02/1000/8762 3.0 ITU-T G.873.1 2011-07-22 15 11.1002/1000/11120 3.1 ITU-T G.873.1 (2011) Amd. 1 2012-10-29 15 11.1002/1000/11790 4.0 ITU-T G.873.1 2014-05-14 15 11.1002/1000/12181 4.1 ITU-T G.873.1 (2014) Amd. 1 2014-12-05 15 11.1002/1000/12368 5.0 ITU-T G.873.1 2017-10-07 15 11.1002/1000/13302 * To
11、 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/11.1002/1000/ 11830-en. ii Rec. ITU-T G.873.1 (10/2017) FOREWORD The International Telecommunication Union (ITU) is th
12、e 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 ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Rec
13、ommendations 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 for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. Th
14、e 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 on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Admin
15、istration“ 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 contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and co
16、mpliance 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 express requirements. The use of such words does not suggest that compliance with the Recommendatio
17、n is required of any party. INTELLECTUAL PROPERTY 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
18、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 intellectual property, protected by patents, which may be required to implement this Recommenda
19、tion. 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 2017 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, with
20、out the prior written permission of ITU. Rec. ITU-T G.873.1 (10/2017) iii Table of Contents Page 1 Scope 1 2 References 1 3 Definitions . 1 3.1 Terms defined elsewhere . 1 3.2 Terms defined in this Recommendation 2 4 Abbreviations and acronyms . 2 5 Conventions . 3 6 Protection characteristics . 4 6
21、.1 Monitoring methods and conditions 4 6.2 Protection switching performance . 6 7 Protection group commands 6 7.1 End-to-end commands and states 6 7.2 Local commands 7 8 Protection architectures . 8 8.1 Unidirectional and bidirectional switching . 8 8.2 Need for an APS/PCC channel 9 8.3 Revertive an
22、d non-revertive switching 9 8.4 Provisioning mismatches . 9 8.5 Overview of protection architectures for OTN linear protection 10 9 APS protocol 11 9.1 APS channel format . 11 9.2 Transmission and acceptance of APS protocol . 12 9.3 Request type 13 9.4 Protection types . 14 9.5 Requested signal 14 9
23、.6 Bridged signal 15 9.7 Control of bridge . 15 9.8 Control of selector . 15 9.9 Signal Fail of the protection entity 15 9.10 Equal priority requests . 15 9.11 Command acceptance and retention 16 9.12 Hold-off timer 16 9.13 Exercise operation . 16 9.14 APS channel alarming . 17 iv Rec. ITU-T G.873.1
24、 (10/2017) Page 9.15 SF persistency timer 17 Appendix I Examples of operation 18 I.1 1+1 unidirectional switching . 18 I.2 1+1 bidirectional switching . 18 I.3 1:n bidirectional switching 19 I.4 Exercise command operation 20 Appendix II ODUk client protection . 23 II.1 Overview over protection archi
25、tectures of OTN linear client protection 23 II.2 Model of client SNC/Nc protection architecture of OTN linear client protection . 23 II.3 Model of client SNC/I protection architectures of OTN linear client protection . 24 Appendix III Media layer protection . 27 III.1 Overview of media layer protect
26、ion 27 III.2 Media layer protection types . 27 Bibliography 32 Rec. ITU-T G.873.1 (10/2017) 1 Recommendation ITU-T G.873.1 Optical transport network: Linear protection 1 Scope This Recommendation defines the automatic protection switching (APS) protocol and protection switching operation for the lin
27、ear protection schemes for the optical transport network (OTN) at the optical data unit k (ODUk) level. These schemes are based on the generic linear protection specifications in ITU-T G.808.1. Linear protection schemes considered in this Recommendation are: ODUk subnetwork connection protection wit
28、h inherent monitoring (1+1, 1:n); ODUk subnetwork connection protection with non-intrusive monitoring (1+1); ODUk subnetwork connection protection with sublayer monitoring (1+1, 1:n); ODUk compound link subnetwork connection group protection with inherent monitoring (1+1, 1:1). In addition, client-r
29、elated protection architectures are described. 2 References 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 Recommendati
30、ons 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 Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly publis
31、hed. 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.709 Recommendation ITU-T G.709/Y.1331 (2016), Interfaces for the optical transport network. ITU-T G.798 Recommendation ITU-T G.798 (2017), Characteristics
32、of optical transport network hierarchy equipment functional blocks. ITU-T G.798.1 Recommendation ITU-T G.798.1 (2013), Types and characteristics of optical transport network equipment. ITU-T G.806 Recommendation ITU-T G.806 (2012), Characteristics of transport equipment Description methodology and g
33、eneric functionality. ITU-T G.808 Recommendation ITU-T G.808 (2016), Terms and definitions for network protection and restoration. ITU-T G.808.1 Recommendation ITU-T G.808.1 (2014), Generic protection switching Linear trail and subnetwork protection. 3 Definitions 3.1 Terms defined elsewhere This Re
34、commendation uses the following terms defined elsewhere: Terms defined in ITU-T G.808: APS channel; 2 Rec. ITU-T G.873.1 (10/2017) extra traffic signal; head-end; normal traffic signal; null signal; protection communication channel; protection group; signal; tail-end. 3.2 Terms defined in this Recom
35、mendation None. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: AIS Alarm Indication Signal APS Automatic Protection Switching CBR Constant Bit Rate signal CL_SNCG/I Compound Link Subnetwork Connection Group protection with Inherent monitoring CSF Clie
36、nt Signal Fail DNR Do Not Revert ETC3 Ethernet Coding 1000BASE-X EXER Exercise FDI Forward Defect Indication FS Forced Switch HO Higher Order LCK Locked defect LO Lower Order LoP Lockout for Protection MFAS Multiframe Alignment Signal MS Manual Switch NIM Non-Intrusive Monitor NR No Request OCI Open
37、 Connection Indication ODUij_A ODUkP to ODUij Adaptation function ODUij_A_SK ODUkP to ODUij Adaptation Sink function ODUj-21_A ODUj payload type 21 Adaptation function ODUk Optical Data Unit k ODUk_A Optical Data Unit Adaptation of rate K Rec. ITU-T G.873.1 (10/2017) 3 ODUk_A_Sk ODUk Adaptation Sink
38、 function ODUkij ODUj/i Optical Data Unit of level j or i (i is optional; i 1, it cannot be known which of the normal traffic signals should be bridged onto the protection entity, until a defect is detected on one of the protected signals. 1:n architectures are capable of carrying an extra (low prio
39、rity, pre-emptable) traffic signal on the protection entity when it is not being used to protect any normal traffic signal. A 1:n architecture can be used even for n = 1 (1:1). This might be chosen over the simpler 1+1 architecture (which requires no head-end actions of the protection algorithm) sin
40、ce 1:1 is capable of carrying extra traffic, where 1+1 is not. m:n In this architecture, m protection entities are used to protect n working entities. This is for further study. With the assumption of a larger APS channel, the coding for the entity number “n“ will use a full byte rather than the few
41、 bits in synchronous digital hierarchy (SDH). Two of the 256 values are reserved: 0 is used to indicate a null signal or the protection entity and 0xFF (255) is used to indicate extra traffic. The architecture at each end of the connection must match. 8.1 Unidirectional and bidirectional switching I
42、n the case of bidirectional transmission, it is possible to choose either unidirectional or bidirectional switching. With unidirectional switching, the selectors at each end are fully independent. With bidirectional switching, an attempt is made to coordinate the two ends so that both have the same
43、bridge and selector settings, even for a unidirectional failure. Bidirectional switching always requires an APS and/or protection communication channel (PCC) to coordinate the two endpoints. Unidirectional switching can protect two unidirectional failures in opposite directions on different entities
44、. Rec. ITU-T G.873.1 (10/2017) 9 8.2 Need for an APS/PCC channel The only switching type that does not require an APS and/or PCC channel is 1+1 unidirectional switching. With a permanent bridge at the head-end and no need to coordinate selector positions at the two ends, the tail-end selector can be
45、 operated entirely according to defects and commands received at the tail-end. Bidirectional switching always requires an APS channel. 1:n unidirectional switching requires an APS channel to coordinate the head-end bridge with the tail-end selector. 8.3 Revertive and non-revertive switching In rever
46、tive operation, traffic is restored to the working entities after a switch reason has cleared. In the case of clearing a command (e.g., Forced Switch), this happens immediately. In the case of clearing of a defect, this generally happens after the expiry of a “Wait-to-Restore“ timer, which is used t
47、o avoid chattering of selectors in the case of intermittent defects. In non-revertive operation, normal traffic is allowed to remain on the protection entity even after a switch reason has cleared. This is generally accomplished by replacing the previous switch request with a “do not revert (DNR)“ r
48、equest, which is low priority. 1+1 protection is often provisioned as non-revertive, as the protection is fully dedicated in any case and this avoids a second “glitch“ to the traffic. There may, however, be reasons to provision this to be revertive (e.g., so that the traffic uses the “short“ directi
49、on around a ring except during failure conditions. Certain operator policies also dictate revertive operation even for 1+1). Usually, 1:n protection is revertive. Certainly in the case where an extra traffic signal is carried on the protection entity, the operation would always be revertive so that the pre-empted extra traffic signal can be restored. It is certainly possible to define the protocol in a way that would permit non-revertive operation for 1:n protec
