1、 International Telecommunication Union ITU-T G.8131/Y.1382TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 1(09/2007) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Packet over Transport aspects MPLS over Transport aspects SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE,
2、 INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Internet protocol aspects Transport Linear protection switching for transport MPLS (T-MPLS) networks Amendment 1 ITU-T Recommendation G.8131/Y.1382 (2007) Amendment 1 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEM
3、S 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 METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONA
4、L 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.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.80
5、0G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999Ethernet over Transpo
6、rt aspects G.8000G.8099 MPLS over Transport aspects G.8100G.8199 Quality and availability targets G.8200G.8299 Service Management G.8600G.8699 ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. G.8131/Y.1382 (2007)/Amd.1 (09/2007) i ITU-T
7、Recommendation G.8131/Y.1382 Linear protection switching for transport MPLS (T-MPLS) networks Amendment 1 Summary Amendment 1 to ITU-T Recommendation G.8131/Y.1382 contains additional material to be incorporated into ITU-T Recommendation G.8131/Y.1382, Linear protection switching for transport MPLS
8、(T-MPLS) networks. It presents further specification of the APS protocol. Source Amendment 1 to ITU-T Recommendation G.8131/Y.1382 (2007) was approved on 22 September 2007 by ITU-T Study Group 15 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. G.8131/Y.1382 (2007)/Amd.1 (09/2
9、007) 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 permanent organ of ITU. ITU-T is responsible for
10、 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, establishes the topics for study by the ITU-T study
11、 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 standards are prepared on a collaborative basis w
12、ith 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 Recommendation may contain certain mandatory pro
13、visions (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 equivalents are used to express requirements. The use of s
14、uch 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 claimed Intellectual Property Right. ITU takes no posit
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16、ted 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-T/ipr/. ITU 2008 All rights reserved. No part of
17、 this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. G.8131/Y.1382 (2007)/Amd.1 (09/2007) 1 ITU-T Recommendation G.8131/Y.1382 Linear protection switching for transport MPLS (T-MPLS) networks Amendment 1 Modifications introduced by thi
18、s amendment are shown in revision marks. Unchanged text is replaced by ellipsis (). Some parts of unchanged texts (clause numbers, etc.) may be kept to indicate the correct insertion points. 6 Network objectives 10) Mismatch detection A mismatch between the bridge/selector positions of the near end
19、and the far end should be detected. The bridge/selector mismatch for the local network element should be detected and reported. The bridge/selector mismatch should be cleared by a network operator. 7 Protection aArchitecture types and characteristics Protection switching is a fully allocated protect
20、ion mechanism that can be used on any topology. It is fully allocated in the sense that the route and bandwidth of the protection connection is reserved for a selected working connection. To be effective under all possible failures of the working connection, however, the protection connection must b
21、e known to have complete physical diversity over all common-failure modes. This may not always be possible. Also, this might require the working connection not to follow its shortest path. The T-MPLS linear protection switching architecture can be trail protection and SNC/S protection as defined in
22、ITU-T G.808.1. Other types are for further study. 7.1 T-MPLS trail protection T-MPLS trail protection is used to protect a T-MPLS connection. That means the client layer of a T-MPLS protected domain is also a T-MPLS layer (TMC or TMP). It is a dedicated end-to-end protection architecture, which can
23、be used in different network structures, meshed networks, rings, etc. 7.1.1 1+1 trail protection In the 1+1 architecture type, a protection connection is dedicated to each working connection with the working connection bridged onto the protection connection at the source of the protection domain. Th
24、e traffic on working and protection connection is transmitted simultaneously to the sink of the protection domain, where a selection between the working and protection connection is made, based on some predetermined criteria, such as defect indication. NOTE To avoid a single point of failure, the wo
25、rking connection and the protection connection shall be routedprovisioned along disjoint paths. 2 ITU-T Rec. G.8131/Y.1382 (2007)/Amd.1 (09/2007) 7.1.2 1:1 trail protection In the 1:1 architecture type, a protection connection is dedicated to each working connection. The protected or working traffic
26、 is transmitted either by working or protection connection. The method for a selection between the working and protection connection depends on the mechanism. NOTE To avoid a single point of failure, the working connection and the protection connection shall be routedprovisioned along disjoint paths
27、. 7.2 T-MPLS SNC protection 87.3 Switching types The protection switching types can be a unidirectional switching type or a bidirectional switching type. 8.17.3.1 Unidirectional switching type In unidirectional switching, only the affected direction of the connection is switched to protection; the s
28、electors at each end are independent. This type is applicable for 1+1 T-MPLS trail and SNC/S protection. 8.27.3.2 Bidirectional switching type In bidirectional switching, both directions of the connection, including the affected direction and the unaffected direction, are switched to protection. For
29、 bidirectional switching, automatic protection switching (APS) protocol is required to coordinate the two endpoints. This type is applicable for 1:1 T-MPLS trail and SNC/S protection. 97.4 Operation types The protection operation types can be a non-revertive operation type or a revertive operation t
30、ype. 97.4.1 Non-revertive operation In non-revertive types, the service will not be switched back to the working connection if the switch requests are terminated. In non-revertive mode of operation, when the failed connection is no longer in an SF or SD condition, and no other externally initiated c
31、ommands are present, a No Request state is entered. During this state, switching does not occur. 97.4.2 Revertive operation In revertive types, the service will always return to (or remain on) the working connection if the switch requests are terminated. In revertive mode of operation, under conditi
32、ons where working traffic is being transmitted via the protection connection and when the working connection is restored, if local protection switching requests have been previously active and now become inactive, a local Wait-to-Restore state is entered. This state normally times out and becomes a
33、No Request state after the Wait-to-Restore timer has expired. Then, reversion back to select the working connection occurs. The Wait-to-Restore timer deactivates earlier if any local request of higher priority pre-empts this state. ITU-T Rec. G.8131/Y.1382 (2007)/Amd.1 (09/2007) 3 Clause 12 has been
34、 moved and renumbered as clause 7.5. 127.5 Protection switching trigger mechanism Protection switching action shall be conducted when: 1) initiated by operator control (e.g., manual switch, forced switch, and lockout of protection) without a higher priority switch request being in effect; 2) SF or S
35、D is declared on the associated connection (i.e., working connection or protection connection) and is not declared on the other connection and the hold-off timer has expired; or 3) the Wait-to-Restore timer expires (in revertive mode) and SF or SD is not declared on the working connection.; 4) in th
36、e bidirectional 1:1 architecture, the received APS protocol requests to switch and it has a higher priority than any other local request. 127.5.1 Manual control Manual control of the protection switching function may be transferred from the element or network management system. 127.5.2 Signal fail d
37、eclaration conditions Protection switching will occur based on the detection of certain defects on the transport entities (working and protection) within the protected domain. How these defects are detected is the subject of the equipment Recommendations (e.g., ITU-T Rec. G.8121/Y.1381). For the pur
38、pose of the protection switching process, a transport entity within the protected domain has a condition of OK, failed (signal fail = SF), or degraded (signal degrade = SD) if applicable. In Trail protection switching, Signal fail (SF) is declared when the TMT_TT_Sk function in the protected domain
39、detects a trail signal fail as defined in b-ITU-T G.8110.1 Amd.1ITU-T Rec. G.8121/Y.1381. Signal Degrade (SD) is declared when the TMT_TT_Sk function in the protected domain detects a trail signal degrade as defined in b-ITU-T G.8110.1 Amd.1 ITU-T Rec. G.8121/Y.1381. In SNC/S protection switching, S
40、ignal Fail (SF) is declared when the TMT_TT_Sk function in the protected domain detects a trail signal fail as defined in ITU-T Rec. G.8121/Y.1381. Signal Degrade (SD) is declared when the TMT_TT_Sk function in the protected domain detects a trail signal degrade as defined in ITU-T Rec. G.8121/Y.138
41、1. 7.6 Provisioning mismatches With all of the options for provisioning of protection groups, there are opportunities for mismatches between the provisioning at the two ends. These provisioning mismatches take one of several forms: Mismatches where proper operation is not possible. Mismatches where
42、one or both sides can adapt their operation to provide a degree of interworking in spite of the mismatch. Mismatches that do not prevent interworking. An example is the revertive/non-revertive mismatch discussed in clauses 7.4 and 9.4. 4 ITU-T Rec. G.8131/Y.1382 (2007)/Amd.1 (09/2007) Not all provis
43、ioning mismatches can be conveyed and detected by information passed through the APS communication. There are simply too many combinations of valid entity numbers to easily provide full visibility of all of the configuration options. What is desirable, however, is to provide visibility for the middl
44、e category, where the sides can adapt their operation to interwork in spite of the mismatch. The user could still be informed of the provisioning mismatch, but a level of protection could still be provided by the equipment. 8 Protection group commands and states Clause 13.1 has been moved and renumb
45、ered as clause 8.1. 138.1 Externally initiated commands 8.2 Local commands These commands apply only to the near end of the protection group. Even when an APS protocol is supported, they are not signalled to the far end. Lockout-normal-traffic signal from protection Prevents normal traffic signal fr
46、om being selected from the protection entity. Commands for normal traffic signal will be rejected. For normal traffic, any indication of SF (or SD if applicable) will be ignored. In bidirectional switching, remote bridge requests for normal traffic signal will still be honoured to prevent protocol f
47、ailures. As a result, a normal traffic signal must be locked out from the protection transport entity at both ends to prevent it being selected from the protection transport entity as a result of a command or failure at either end. Clear lockout-normal-traffic signal from protection Clause 13.2 has
48、been moved and renumbered as clause 8.3. 13.28.3 States 109 Automatic protection switching (APS) protocol Except for the case of 1+1 unidirectional switching, an APS signal is used to synchronize the action at the A and Z ends of the protected domain. Communicated are: Request/State type, Requested
49、signal, Bridged signal, Protection configuration. The only switching type that does NOT require APS protocol 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 operated entirely according to defects and commands received at the tail end. Bidirectional switching always requires APS protocol. 109.1 APS payload information structure The APS payload structure (see Table 10-1) in a T-MPLS OAM frame is for further
