1、 International Telecommunication Union ITU-T G.808.3TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (10/2012) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital networks General aspects Generic protection switching Shared mesh protection Recommendation ITU-T G.808.3 ITU-T
2、 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 CARRIER TELEPHONE SYST
3、EMS 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 SYSTEMS CHARACTERISTICS
4、 G.600G.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 tr
5、ansport 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.1999 TRANSMISSION MEDIA CHARACTERISTICS G
6、.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.808.3 (10/2012) i Recommendation ITU-T G.808.3 Generic protection switching Shared
7、 mesh protection Summary Recommendation ITU-T G.808.3 provides an overview of generic aspects of a shared mesh protection (SMP) mechanism for connection-oriented layer networks that does not depend upon the presence of a control plane. SMP provides a method for sharing resources in the mesh network
8、for protection against one or more failures in the network. History Edition Recommendation Approval Study Group 1.0 ITU-T G.808.3 2012-10-29 15 ii Rec. ITU-T G.808.3 (10/2012) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommun
9、ications, 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 standardizing telecommunic
10、ations 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 covered by the procedur
11、e 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 indicate both a telecomm
12、unication 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 achieved when all of these
13、 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 PROPERTY RIGHTS ITU d
14、raws 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 asserted by ITU members
15、 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 this may not repre
16、sent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2013 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.808.3 (10/2
17、012) iii Table of Contents Page 1 Scope 1 2 References. 1 3.1 Terms defined elsewhere 1 3.2 Terms defined in this Recommendation . 2 4 Abbreviations and acronyms 2 5 Conventions 3 6 Overview 3 6.1 Mesh topologies 3 6.2 Capacity efficiency considerations . 4 7 SMP architecture types . 4 7.1 SMP archi
18、tecture overview 4 8 Switching types . 9 9 Operation types . 9 10 Non-pre-emptible unprotected traffic (NUT) and extra traffic . 9 11 Automatic switch 9 12 Pre-emption principle . 9 13 Path status monitoring 10 14 Automatic protection switching (APS) protocol 10 Annex A Objectives 11 Appendix I SMP
19、scenarios 13 I.1 A simple SMP scenario 13 I.2 SMP in mesh network 13 Appendix II Overview of shared mesh restoration (SMR) and shared mesh protection (SMP) operation . 18 Bibliography. 19 Rec. ITU-T G.808.3 (10/2012) 1 Recommendation ITU-T G.808.3 Generic protection switching Shared mesh protection
20、1 Scope This Recommendation provides an overview of generic aspects of a shared mesh protection (SMP) mechanism for connection-oriented layer networks that does not depend upon the presence of a control plane. This mechanism is targeted for mesh network architectures, which offer further efficiencie
21、s in protection resource utilization. The primary characteristics of this path-based protection approach involve usage of pre-computation and pre-allocation of resources to maximize speed of recovery. The technology-specific shared mesh protection mechanisms will be defined in technology-specific Re
22、commendation(s). This version of the Recommendation provides an architecture framework for SMP. 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, th
23、e 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 Recommendations and other references listed below. A list of the currentl
24、y 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.780 Recommendation ITU-T G.780/Y.1351 (2010), Terms and definitions for synchronous digital hierarchy (SDH
25、) networks. 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 (2010)
26、, Generic protection switching Linear trail and subnetwork protection. ITU-T G.870 Recommendation ITU-T G.870/Y.1352 (2010), Terms and definitions for optical transport network. 3.1 Terms defined elsewhere This Recommendation uses the following terms defined elsewhere: 3.1.1 Terms related to actions
27、 3.1.1.1 switch ITU-T G.870 3.1.2 Terms related to components 3.1.2.1 bridge ITU-T G.870 3.1.2.2 selector ITU-T G.870 3.1.2.3 intermediate node ITU-T G.870 3.1.3 Terms related to fault conditions 3.1.3.1 signal degrade (SD) ITU-T G.805 2 Rec. ITU-T G.808.3 (10/2012) 3.1.3.2 signal fail (SF) ITU-T G.
28、805 3.1.4 Terms related to architecture 3.1.4.1 m:n (protection) architecture ITU-T G.870 3.1.5 Terms related to operation 3.1.5.1 revertive (protection) operation ITU-T G.870 3.1.6 Terms related to signals 3.1.6.1 traffic signal ITU-T G.870 3.1.6.2 normal traffic signal ITU-T G.870 3.1.6.3 extra tr
29、affic signal ITU-T G.870 3.1.7 Terms related to switching 3.1.7.1 bidirectional (protection) switching ITU-T G.780 3.1.7.2 unidirectional (protection) switching ITU-T G.780 3.1.8 Terms related to transport entities 3.1.8.1 link ITU-T G.805 3.1.8.2 transport entity ITU-T G.870 3.1.8.3 protection tran
30、sport entity ITU-T G.870 3.1.8.4 working transport entity ITU-T G.870 3.1.9 protection ITU-T G.870 3.1.10 restoration ITU-T G.870 3.1.11 switch event ITU-T G.870 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 protection segment: A link between two SMP
31、 nodes on a protection transport entity. 3.2.2 shared mesh protection: A shared mesh protection (SMP) architecture involves multiple normal traffic signals, where each signal has one corresponding working transport entity and one or more protection transport entities, in a meshed network. In an SMP,
32、 the protection resources are shared among two or more protection transport entities. Only one of these protection transport entities can use the shared protection resources at any point of time. 3.2.3 shared protection segment: A link between two SMP nodes, where the bandwidth resource on the link
33、is shared by multiple protection transport entities. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: APS Automatic Protection Switching NUT Non-pre-emptible Unprotected Traffic OTN Optical Transport Network P Protection Rec. ITU-T G.808.3 (10/2012) 3 S
34、D Signal Degrade SDH Synchronous Digital Hierarchy SF Signal Fail SMP Shared Mesh Protection W Working 5 Conventions None. 6 Overview 6.1 Mesh topologies A meshed transport network is one in which each node in the network is interconnected by at least two links whose remote ends are on different nod
35、es from each other (see example a) of Figure 1). It should be noted that while the overall transport network may contain nodes that do not satisfy the above criteria (see left two nodes in example b) of Figure 1), such nodes would not be considered part of the portion of the transport network define
36、d as being a mesh. A fully meshed topology is one in which each node is directly connected to every other node in a network (see example c) of Figure 1). a) b) c) 1-a: Example of a mesh network 1-b: Example of a network, only a portion of which is meshed 1-c: Example of a fully meshed network Figure
37、 1 Examples of mesh network Most mesh transport networks are only partially meshed (as in example a) of Figure 1), with some nodes fully meshed and others connecting to one or more nodes, but not to all of them (i.e., their maximum number being less than the total number of nodes 1). While fully mes
38、hed network topologies offer the highest degree of survivability in the event of failures, they have the highest degree of transport resource redundancy. Most mesh transport networks are only partially meshed and generally require traversing intermediate nodes to go from each node to every other nod
39、e. 4 Rec. ITU-T G.808.3 (10/2012) 6.2 Capacity efficiency considerations Increased sharing of protection resources in mesh network architectures inherently allows for reduction of network costs by eliminating dedicated protection resources. Such architectures may also be designed according to the le
40、vel of “guaranteed protection“ and capacity efficiency desired by the operator, according to the grades of services offered. Capacity efficiency in mesh network architectures can be measured in various ways, including b-BLTJ.1999: i) The fraction of demands that can be protected given the network ca
41、pacities, point-to-point demands, and working path for each demand; ii) The needed network capacities for providing 100% protection given point-to-point demands and working path for each demand; or iii) The total network capacities for working and protection paths given point-to-point demands and pr
42、ovided 100% protection. The first approach involves finding protection paths for as many demands as possible under link capacity constraints in an existing network. This is distinguished from the latter two approaches, which assume that capacity planning is underway to assure 100% protection for all
43、 demands. It should be noted that at some point the desired degree of network resource optimization (resulting in insufficient link capacity) becomes inversely proportional to the degree of “guaranteed protection“ that can be offered. In real capacity-constrained situations, it is necessary to be ca
44、pable of prioritizing the demands and ensuring that those demands with high availability requirements are always assigned protection paths. Within this Recommendation, the focus is upon achieving maximal possible protection considering a given networks capabilities, including mechanisms for prioriti
45、zing demands to enable those demands with high availability requirements to be assigned protection paths. 7 SMP architecture types 7.1 SMP architecture overview SMP may be employed in fully meshed and partially meshed transport networks, which include, but are not limited to, long-haul and metro net
46、works. Depending on the degree of inter-connection between network nodes, SMP protection can significantly improve network resource utilization, as compared with alternative 1:1 protection mechanisms. An SMP architecture involves multiple normal traffic signals, where each signal is associated with
47、a working transport entity and one or more protection transport entities. SMP architecture is based upon m:1 protection (where m may be greater than or equal to one). In the m:1 SMP architecture, each working transport entity is protected by m protection transport entities. In this architecture, the
48、 working transport entity can be protected when one of the m protection transport entities is available. Each protection transport entity is constructed of one or multiple protection segments. The bandwidth of each protection segment can be shared by multiple protection transport entities. To preven
49、t a network failure from interrupting the protected normal traffic signal, it is recommended that all working transport entities that share protection resources should be disjoint. The shared bandwidth for the protection segment should be capable of supporting the largest of the corresponding protection transport entities. Rec. ITU-T G.808.3 (10/2012) 5 NOTE The protection resources and the information of protection transport ent
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