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+Internet Engineering Task Force (IETF) J. He
+Request for Comments: 9270 I. Busi
+Updates: 4872, 4873 Huawei Technologies
+Category: Standards Track J. Ryoo
+ISSN: 2070-1721 B. Yoon
+ ETRI
+ P. Park
+ KT
+ August 2022
+
+
+ GMPLS Signaling Extensions for Shared Mesh Protection
+
+Abstract
+
+ ITU-T Recommendation G.808.3 defines the generic aspects of a Shared
+ Mesh Protection (SMP) mechanism, where the difference between SMP and
+ Shared Mesh Restoration (SMR) is also identified. ITU-T
+ Recommendation G.873.3 defines the protection switching operation and
+ associated protocol for SMP at the Optical Data Unit (ODU) layer.
+ RFC 7412 provides requirements for any mechanism that would be used
+ to implement SMP in a Multi-Protocol Label Switching - Transport
+ Profile (MPLS-TP) network.
+
+ This document updates RFCs 4872 and 4873 to provide extensions for
+ Generalized Multi-Protocol Label Switching (GMPLS) signaling to
+ support the control of the SMP mechanism.
+
+Status of This Memo
+
+ This is an Internet Standards Track document.
+
+ This document is a product of the Internet Engineering Task Force
+ (IETF). It represents the consensus of the IETF community. It has
+ received public review and has been approved for publication by the
+ Internet Engineering Steering Group (IESG). Further information on
+ Internet Standards is available in Section 2 of RFC 7841.
+
+ Information about the current status of this document, any errata,
+ and how to provide feedback on it may be obtained at
+ https://www.rfc-editor.org/info/rfc9270.
+
+Copyright Notice
+
+ Copyright (c) 2022 IETF Trust and the persons identified as the
+ document authors. All rights reserved.
+
+ This document is subject to BCP 78 and the IETF Trust's Legal
+ Provisions Relating to IETF Documents
+ (https://trustee.ietf.org/license-info) in effect on the date of
+ publication of this document. Please review these documents
+ carefully, as they describe your rights and restrictions with respect
+ to this document. Code Components extracted from this document must
+ include Revised BSD License text as described in Section 4.e of the
+ Trust Legal Provisions and are provided without warranty as described
+ in the Revised BSD License.
+
+ This document may contain material from IETF Documents or IETF
+ Contributions published or made publicly available before November
+ 10, 2008. The person(s) controlling the copyright in some of this
+ material may not have granted the IETF Trust the right to allow
+ modifications of such material outside the IETF Standards Process.
+ Without obtaining an adequate license from the person(s) controlling
+ the copyright in such materials, this document may not be modified
+ outside the IETF Standards Process, and derivative works of it may
+ not be created outside the IETF Standards Process, except to format
+ it for publication as an RFC or to translate it into languages other
+ than English.
+
+Table of Contents
+
+ 1. Introduction
+ 2. Conventions Used in This Document
+ 3. SMP Definition
+ 4. Operation of SMP with GMPLS Signaling Extensions
+ 5. GMPLS Signaling Extensions for SMP
+ 5.1. Identifiers
+ 5.2. Signaling Primary LSPs
+ 5.3. Signaling Secondary LSPs
+ 5.4. SMP Preemption Priority
+ 5.5. Availability of Shared Resources: The Notify Message
+ 5.6. SMP APS Configuration
+ 6. Updates to PROTECTION Object
+ 6.1. New Protection Type
+ 6.2. Updates to Definitions of Notification and Operational Bits
+ 6.3. Preemption Priority
+ 7. IANA Considerations
+ 8. Security Considerations
+ 9. References
+ 9.1. Normative References
+ 9.2. Informative References
+ Acknowledgements
+ Contributors
+ Authors' Addresses
+
+1. Introduction
+
+ RFC 4872 [RFC4872] defines extensions for Resource Reservation
+ Protocol - Traffic Engineering (RSVP-TE) to support Shared Mesh
+ Restoration (SMR) mechanisms. SMR can be seen as a particular case
+ of preplanned Label Switched Path (LSP) rerouting that reduces the
+ recovery resource requirements by allowing multiple protecting LSPs
+ to share common link and node resources. The recovery resources for
+ the protecting LSPs are pre-reserved during the provisioning phase,
+ and explicit restoration signaling is required to activate (i.e.,
+ commit resource allocation at the data plane) a specific protecting
+ LSP that was instantiated during the provisioning phase. RFC 4873
+ [RFC4873] details the encoding of the last 32-bit Reserved field of
+ the PROTECTION object defined in [RFC4872].
+
+ ITU-T Recommendation G.808.3 [G808.3] defines the generic aspects of
+ a Shared Mesh Protection (SMP) mechanism, which are not specific to a
+ particular network technology in terms of architecture types,
+ preemption principle, path monitoring methods, etc. ITU-T
+ Recommendation G.873.3 [G873.3] defines the protection switching
+ operation and associated protocol for SMP at the Optical Data Unit
+ (ODU) layer. RFC 7412 [RFC7412] provides requirements for any
+ mechanism that would be used to implement SMP in a Multi-Protocol
+ Label Switching - Transport Profile (MPLS-TP) network.
+
+ SMP differs from SMR in the activation/protection switching
+ operation. The former activates a protecting LSP via the Automatic
+ Protection Switching (APS) protocol in the data plane when the
+ working LSP fails, while the latter does it via control plane
+ signaling. It is therefore necessary to distinguish SMP from SMR
+ during provisioning so that each node involved behaves appropriately
+ in the recovery phase when activation of a protecting LSP is done.
+ SMP has advantages with regard to the recovery speed compared with
+ SMR.
+
+ This document updates [RFC4872] and [RFC4873] to provide extensions
+ for Generalized Multi-Protocol Label Switching (GMPLS) signaling to
+ support the control of the SMP mechanism. Specifically, it
+
+ * defines a new LSP Protection Type, "Shared Mesh Protection", for
+ the LSP Flags field [RFC4872] of the PROTECTION object (see
+ Section 6.1),
+
+ * updates the definitions of the Notification (N) and Operational
+ (O) fields [RFC4872] of the PROTECTION object to take the new SMP
+ type into account (see Section 6.2), and
+
+ * updates the definition of the 16-bit Reserved field [RFC4873] of
+ the PROTECTION object to allocate 8 bits to signal the SMP
+ preemption priority (see Section 6.3).
+
+ Only the generic aspects for signaling SMP are addressed by this
+ document. The technology-specific aspects are expected to be
+ addressed by other documents.
+
+ RFC 8776 [RFC8776] defines a collection of common YANG data types for
+ Traffic Engineering (TE) configuration and state capabilities. It
+ defines several identities for LSP Protection Types. As this
+ document introduces a new LSP Protection Type, [RFC8776] is expected
+ to be updated to support the SMP mechanism specified in this
+ document. [YANG-TE] defines a YANG data model for the provisioning
+ and management of TE tunnels, LSPs, and interfaces. It includes some
+ protection and restoration data nodes relevant to this document.
+ Management aspects of the SMP mechanism are outside the scope of this
+ document, and they are expected to be addressed by other documents.
+
+2. Conventions Used in This Document
+
+ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
+ "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
+ "OPTIONAL" in this document are to be interpreted as described in
+ BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
+ capitals, as shown here.
+
+ In addition, the reader is assumed to be familiar with the
+ terminology used in [RFC4872], RFC 4426 [RFC4426], and RFC 6372
+ [RFC6372].
+
+3. SMP Definition
+
+ [G808.3] defines the generic aspects of an SMP mechanism. [G873.3]
+ defines the protection switching operation and associated protocol
+ for SMP at the ODU layer. [RFC7412] provides requirements for any
+ mechanism that would be used to implement SMP in an MPLS-TP network.
+
+ The SMP mechanism is based on precomputed protecting LSPs that are
+ preconfigured into the network elements. Preconfiguration here means
+ pre-reserving resources for the protecting LSPs without activating a
+ particular protecting LSP (e.g., in circuit networks, the cross-
+ connects in the intermediate nodes of the protecting LSP are not
+ preestablished). Preconfiguring but not activating protecting LSPs
+ allows link and node resources to be shared by the protecting LSPs of
+ multiple working LSPs (which are themselves disjoint and thus
+ unlikely to fail simultaneously). Protecting LSPs are activated in
+ response to failures of working LSPs or operator commands by means of
+ the APS protocol, which operates in the data plane. The APS protocol
+ messages are exchanged along the protecting LSP. SMP is always
+ revertive.
+
+ SMP is very similar to SMR, except that activation in the case of SMR
+ is achieved by control plane signaling during the recovery operation,
+ while the same is done for SMP by the APS protocol in the data plane.
+
+4. Operation of SMP with GMPLS Signaling Extensions
+
+ Consider the network topology shown in Figure 1:
+
+ A---B---C---D
+ \ /
+ E---F---G
+ / \
+ H---I---J---K
+
+ Figure 1: An Example of an SMP Topology
+
+ The working LSPs [A,B,C,D] and [H,I,J,K] could be protected by the
+ protecting LSPs [A,E,F,G,D] and [H,E,F,G,K], respectively. Per RFC
+ 3209 [RFC3209], in order to achieve resource sharing during the
+ signaling of these protecting LSPs, they have the same Tunnel
+ Endpoint Address (as part of their SESSION object). However, these
+ addresses are not the same in this example. Similar to SMR, this
+ document defines a new LSP Protection Type of the secondary LSP as
+ "Shared Mesh Protection" (see Section 6.1) to allow resource sharing
+ along nodes E, F, and G. Examples of shared resources include the
+ capacity of a link and the cross-connects in a node. In this case,
+ the protecting LSPs are not merged (which is useful, since the paths
+ diverge at G), but the resources along E, F, and G can be shared.
+
+ When a failure, such as Signal Fail (SF) or Signal Degrade (SD),
+ occurs on one of the working LSPs (say, working LSP [A,B,C,D]), the
+ end node (say, node A) that detects the failure initiates the
+ protection switching operation. End node A will send a protection
+ switching request APS message (for example, SF) to its adjacent
+ (downstream) intermediate node (say, node E) to activate the
+ corresponding protecting LSP and will wait for a confirmation message
+ from node E.
+
+ If the protection resource is available, node E will send the
+ confirmation APS message to the end node (node A) and forward the
+ switching request APS message to its adjacent (downstream) node (say,
+ node F). When the confirmation APS message is received by node A,
+ the cross-connection on node A is established. At this time, traffic
+ is bridged to and selected from the protecting LSP at node A. After
+ forwarding the switching request APS message, node E will wait for a
+ confirmation APS message from node F, which triggers node E to set up
+ the cross-connection for the protecting LSP being activated.
+
+ If the protection resource is not available (due to failure or being
+ used by higher-priority connections), the switching will not be
+ successful; the intermediate node (node E) MUST send a message to
+ notify the end node (node A) (see Section 5.5). If the resource is
+ in use by a lower-priority protecting LSP, the lower-priority service
+ will be removed, and the intermediate node will then follow the
+ procedure as described for the case when the protection resource is
+ available for the higher-priority protecting LSP.
+
+ If node E fails to allocate the protection resource, it MUST send a
+ message to notify node A (see Section 5.5). Then, node A will stop
+ bridging and selecting traffic to/from the protecting LSP and proceed
+ with the procedure of removing the protection allocation according to
+ the APS protocol.
+
+5. GMPLS Signaling Extensions for SMP
+
+ The following subsections detail how LSPs using SMP can be signaled
+ in an interoperable fashion using GMPLS RSVP-TE extensions (see RFC
+ 3473 [RFC3473]). This signaling enables:
+
+ (1) the ability to identify a "secondary protecting LSP" (LSP
+ [A,E,F,G,D] or LSP [H,E,F,G,K] from Figure 1, here called the
+ "secondary LSP") used to recover another "primary working LSP"
+ (LSP [A,B,C,D] or LSP [H,I,J,K] from Figure 1, here called the
+ "protected LSP"),
+
+ (2) the ability to associate the secondary LSP with the protected
+ LSP,
+
+ (3) the capability to include information about the resources used
+ by the protected LSP while instantiating the secondary LSP,
+
+ (4) the capability to instantiate several secondary LSPs efficiently
+ during the provisioning phase, and
+
+ (5) the capability to support activation of a secondary LSP via the
+ APS protocol in the data plane if a failure occurs.
+
+5.1. Identifiers
+
+ To simplify association operations, both LSPs (i.e., the protected
+ LSP and the secondary LSP) belong to the same session. Thus, the
+ SESSION object MUST be the same for both LSPs. The LSP ID, however,
+ MUST be different to distinguish between the protected LSP and the
+ secondary LSP.
+
+ A new LSP Protection Type, "Shared Mesh Protection", is defined (see
+ Section 6.1) for the LSP Flags field of the PROTECTION object (see
+ [RFC4872]) to set up the two LSPs. This LSP Protection Type value is
+ only applicable to bidirectional LSPs as required in [G808.3].
+
+5.2. Signaling Primary LSPs
+
+ The PROTECTION object (see [RFC4872]) is included in the Path message
+ during signaling of the primary working LSPs, with the LSP Protection
+ Type value set to "Shared Mesh Protection".
+
+ Primary working LSPs are signaled by setting in the PROTECTION object
+ the S bit to 0, the P bit to 0, and the N bit to 1; and setting in
+ the ASSOCIATION object the Association ID to the associated secondary
+ protecting LSP_ID.
+
+ | Note: The N bit is set to indicate that the protection
+ | switching signaling is done via the data plane.
+
+5.3. Signaling Secondary LSPs
+
+ The PROTECTION object (see [RFC4872]) is included in the Path message
+ during signaling of the secondary protecting LSPs, with the LSP
+ Protection Type value set to "Shared Mesh Protection".
+
+ Secondary protecting LSPs are signaled by setting in the PROTECTION
+ object the S bit, the P bit, and the N bit to 1; and setting in the
+ ASSOCIATION object the Association ID to the associated primary
+ working LSP_ID, which MUST be known before signaling of the secondary
+ LSP. Moreover, the Path message used to instantiate the secondary
+ LSP MUST include at least one PRIMARY_PATH_ROUTE object (see
+ [RFC4872]) that further allows for recovery resource sharing at each
+ intermediate node along the secondary path.
+
+ With this setting, the resources for the secondary LSP MUST be pre-
+ reserved but not committed at the data plane level, meaning that the
+ internals of the switch need not be established until explicit action
+ is taken to activate this LSP. Activation of a secondary LSP and
+ protection switching to the activated protecting LSP is done using
+ the APS protocol in the data plane.
+
+ After protection switching completes, the protecting LSP MUST be
+ signaled by setting the S bit to 0 and the O bit to 1 in the
+ PROTECTION object. At this point, the link and node resources MUST
+ be allocated for this LSP, which becomes a primary LSP (ready to
+ carry traffic). The formerly working LSP MAY be signaled with the A
+ bit set in the ADMIN_STATUS object (see [RFC3473]).
+
+ Support for extra traffic in SMP is left for further study.
+ Therefore, mechanisms to set up LSPs for extra traffic are outside
+ the scope of this document.
+
+5.4. SMP Preemption Priority
+
+ The SMP preemption priority of a protecting LSP is used by the APS
+ protocol to resolve competition for shared resources among multiple
+ protecting LSPs and is indicated in the Preemption Priority field of
+ the PROTECTION object in the Path message of the protecting LSP.
+
+ The Setup and Holding priorities in the SESSION_ATTRIBUTE object can
+ be used by GMPLS to control LSP preemption, but they are not used by
+ the APS to resolve competition among multiple protecting LSPs. This
+ avoids the need to define a complex policy for defining Setup and
+ Holding priorities when used for both GMPLS control plane LSP
+ preemption and SMP shared resource competition resolution.
+
+ When an intermediate node on the protecting LSP receives the Path
+ message, the priority value in the Preemption Priority field MUST be
+ stored for that protecting LSP. When resource competition among
+ multiple protecting LSPs occurs, the APS protocol will use their
+ priority values to resolve this competition. A lower value has a
+ higher priority.
+
+ In SMP, a preempted LSP MUST NOT be terminated even after its
+ resources have been deallocated. Once the working LSP and the
+ protecting LSP are configured or preconfigured, the end node MUST
+ keep refreshing both working and protecting LSPs, regardless of
+ failure or preemption status.
+
+5.5. Availability of Shared Resources: The Notify Message
+
+ When a lower-priority protecting LSP is preempted, the intermediate
+ node that performed the preemption MUST send a Notify message with
+ error code "Notify Error" (25) (see [RFC4872]) and error sub-code
+ "Shared resources unavailable" (17) to the end nodes of that
+ protecting LSP. Upon receipt of this Notify message, the end node
+ MUST stop sending and selecting traffic to/from its protecting LSP
+ and try switching the traffic to another protecting LSP, if
+ available.
+
+ When a protecting LSP occupies the shared resources and they become
+ unavailable, the same Notify message MUST be generated by the
+ intermediate node to all the end nodes of the protecting LSPs that
+ have lower SMP preemption priorities than the one that has occupied
+ the shared resources. If the shared resources become unavailable due
+ to a failure in the shared resources, the same Notify message MUST be
+ generated by the intermediate node to all the end nodes of the
+ protecting LSPs that have been configured to use the shared
+ resources. In the case of a failure of the working LSP, these end
+ nodes MUST avoid trying to switch traffic to these protecting LSPs
+ that have been configured to use the shared resources and try
+ switching the traffic to other protecting LSPs, if available.
+
+ When the shared resources become available, a Notify message with
+ error code "Notify Error" (25) and error sub-code "Shared resources
+ available" (18) MUST be generated by the intermediate node. The
+ recipients of this Notify message are the end nodes of the lower-
+ priority protecting LSPs that have been preempted and/or all the end
+ nodes of the protecting LSPs that have lower SMP preemption
+ priorities than the one that does not need the shared resources
+ anymore. Upon receipt of this Notify message, the end node is
+ allowed to reinitiate the protection switching operation as described
+ in Section 4, if it still needs the protection resource.
+
+5.6. SMP APS Configuration
+
+ SMP relies on APS protocol messages being exchanged between the nodes
+ along the path to activate a protecting LSP.
+
+ In order to allow the exchange of APS protocol messages, an APS
+ channel has to be configured between adjacent nodes along the path of
+ the protecting LSP. This is done by means other than GMPLS
+ signaling, before any protecting LSP has been set up. Therefore,
+ there are likely additional requirements for APS configuration that
+ are outside the scope of this document.
+
+ Depending on the APS protocol message format, the APS protocol may
+ use different identifiers than GMPLS signaling to identify the
+ protecting LSP.
+
+ Since the APS protocol is left for further study per [G808.3], it can
+ be assumed that the APS message format and identifiers are technology
+ specific and/or vendor specific. Therefore, additional requirements
+ for APS configuration are outside the scope of this document.
+
+6. Updates to PROTECTION Object
+
+ GMPLS extension requirements for SMP introduce several updates to the
+ PROTECTION object (see [RFC4872]), as detailed below.
+
+6.1. New Protection Type
+
+ A new LSP Protection Type, "Shared Mesh Protection", is added in the
+ PROTECTION object. This LSP Protection Type value is only applicable
+ to bidirectional LSPs.
+
+ LSP (Protection Type) Flags:
+
+ 0x20: Shared Mesh Protection
+
+ The rules defined in Section 14.2 of [RFC4872] ensure that all the
+ nodes along an SMP LSP are SMP aware. Therefore, there are no
+ backward-compatibility issues.
+
+6.2. Updates to Definitions of Notification and Operational Bits
+
+ The definitions of the N and O bits in Section 14.1 of [RFC4872] are
+ replaced as follows:
+
+ Notification (N): 1 bit
+
+ When set to 1, this bit indicates that the control plane message
+ exchange is only used for notification during protection
+ switching. When set to 0 (default), it indicates that the control
+ plane message exchanges are used for purposes of protection
+ switching. The N bit is only applicable when the LSP Protection
+ Type Flag is set to 0x04 (1:N Protection with Extra-Traffic), 0x08
+ (1+1 Unidirectional Protection), 0x10 (1+1 Bidirectional
+ Protection), or 0x20 (Shared Mesh Protection). The N bit MUST be
+ set to 0 in any other case. If 0x20 (SMP), the N bit MUST be set
+ to 1.
+
+ Operational (O): 1 bit
+
+ When set to 1, this bit indicates that the protecting LSP is
+ carrying traffic after protection switching. The O bit is only
+ applicable when (1) the P bit is set to 1 and (2) the LSP
+ Protection Type Flag is set to 0x04 (1:N Protection with Extra-
+ Traffic), 0x08 (1+1 Unidirectional Protection), 0x10 (1+1
+ Bidirectional Protection), or 0x20 (Shared Mesh Protection). The
+ O bit MUST be set to 0 in any other case.
+
+6.3. Preemption Priority
+
+ [RFC4872] reserved a 32-bit field in the PROTECTION object header.
+ Subsequently, [RFC4873] allocated several bits from that field and
+ left the remainder of the bits reserved. This specification further
+ allocates the Preemption Priority field from the remaining formerly
+ reserved bits. The 32-bit field in the PROTECTION object as defined
+ in [RFC4872] and modified by [RFC4873] is updated by this document as
+ follows:
+
+ 0 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ |I|R| Reserved | Seg.Flags | Reserved | Preempt Prio |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Preemption Priority (Preempt Prio): 8 bits
+
+ This field indicates the SMP preemption priority of a protecting
+ LSP, when the LSP Protection Type field indicates "Shared Mesh
+ Protection". The SMP preemption priority value is configured at
+ the end nodes of the protecting LSP by a network operator. A
+ lower value has a higher priority. The decision regarding how
+ many priority levels should be implemented in an SMP network is
+ left to network operators.
+
+ See [RFC4873] for the definitions of the other fields.
+
+7. IANA Considerations
+
+ IANA maintains a group of registries called "Resource Reservation
+ Protocol (RSVP) Parameters", which includes the "Error Codes and
+ Globally-Defined Error Value Sub-Codes" registry. IANA has added the
+ following values to the "Sub-Codes - 25 Notify Error" subregistry,
+ which lists error value sub-codes that may be used with error code
+ 25. IANA has allocated the following error value sub-codes (Table 1)
+ for use with this error code as described in this document.
+
+ +=======+==============================+===========+
+ | Value | Description | Reference |
+ +=======+==============================+===========+
+ | 17 | Shared resources unavailable | RFC 9270 |
+ +-------+------------------------------+-----------+
+ | 18 | Shared resources available | RFC 9270 |
+ +-------+------------------------------+-----------+
+
+ Table 1: New Error Sub-Codes
+
+8. Security Considerations
+
+ Since this document makes use of the exchange of RSVP messages that
+ include a Notify message, the security threats discussed in [RFC4872]
+ also apply to this document.
+
+ Additionally, it may be possible to cause disruption to traffic on
+ one protecting LSP by targeting a link used by the primary LSP of
+ another, higher-priority LSP somewhere completely different in the
+ network. For example, in Figure 1, assume that the preemption
+ priority of LSP [A,E,F,G,D] is higher than that of LSP [H,E,F,G,K]
+ and the protecting LSP [H,E,F,G,K] is being used to transport
+ traffic. If link B-C is attacked, traffic on LSP [H,E,F,G,K] can be
+ disrupted. For this reason, it is important not only to use security
+ mechanisms as discussed in [RFC4872] but also to acknowledge that
+ detailed knowledge of a network's topology, including routes and
+ priorities of LSPs, can help an attacker better target or improve the
+ efficacy of an attack.
+
+9. References
+
+9.1. Normative References
+
+ [G808.3] International Telecommunication Union, "Generic protection
+ switching - Shared mesh protection", ITU-T Recommendation
+ G.808.3, October 2012,
+ <https://www.itu.int/rec/T-REC-G.808.3>.
+
+ [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
+ Requirement Levels", BCP 14, RFC 2119,
+ DOI 10.17487/RFC2119, March 1997,
+ <https://www.rfc-editor.org/info/rfc2119>.
+
+ [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
+ and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
+ Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
+ <https://www.rfc-editor.org/info/rfc3209>.
+
+ [RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
+ Switching (GMPLS) Signaling Resource ReserVation Protocol-
+ Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
+ DOI 10.17487/RFC3473, January 2003,
+ <https://www.rfc-editor.org/info/rfc3473>.
+
+ [RFC4426] Lang, J., Ed., Rajagopalan, B., Ed., and D. Papadimitriou,
+ Ed., "Generalized Multi-Protocol Label Switching (GMPLS)
+ Recovery Functional Specification", RFC 4426,
+ DOI 10.17487/RFC4426, March 2006,
+ <https://www.rfc-editor.org/info/rfc4426>.
+
+ [RFC4872] Lang, J P., Ed., Rekhter, Y., Ed., and D. Papadimitriou,
+ Ed., "RSVP-TE Extensions in Support of End-to-End
+ Generalized Multi-Protocol Label Switching (GMPLS)
+ Recovery", RFC 4872, DOI 10.17487/RFC4872, May 2007,
+ <https://www.rfc-editor.org/info/rfc4872>.
+
+ [RFC4873] Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
+ "GMPLS Segment Recovery", RFC 4873, DOI 10.17487/RFC4873,
+ May 2007, <https://www.rfc-editor.org/info/rfc4873>.
+
+ [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
+ 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
+ May 2017, <https://www.rfc-editor.org/info/rfc8174>.
+
+9.2. Informative References
+
+ [G873.3] International Telecommunication Union, "Optical transport
+ network - Shared mesh protection", ITU-T Recommendation
+ G.873.3, September 2017,
+ <https://www.itu.int/rec/T-REC-G.873.3-201709-I/en>.
+
+ [RFC6372] Sprecher, N., Ed. and A. Farrel, Ed., "MPLS Transport
+ Profile (MPLS-TP) Survivability Framework", RFC 6372,
+ DOI 10.17487/RFC6372, September 2011,
+ <https://www.rfc-editor.org/info/rfc6372>.
+
+ [RFC7412] Weingarten, Y., Aldrin, S., Pan, P., Ryoo, J., and G.
+ Mirsky, "Requirements for MPLS Transport Profile (MPLS-TP)
+ Shared Mesh Protection", RFC 7412, DOI 10.17487/RFC7412,
+ December 2014, <https://www.rfc-editor.org/info/rfc7412>.
+
+ [RFC8776] Saad, T., Gandhi, R., Liu, X., Beeram, V., and I. Bryskin,
+ "Common YANG Data Types for Traffic Engineering",
+ RFC 8776, DOI 10.17487/RFC8776, June 2020,
+ <https://www.rfc-editor.org/info/rfc8776>.
+
+ [YANG-TE] Saad, T., Gandhi, R., Liu, X., Beeram, V.P., Bryskin, I.,
+ and O. Gonzalez de Dios, "A YANG Data Model for Traffic
+ Engineering Tunnels, Label Switched Paths and Interfaces",
+ Work in Progress, Internet-Draft, draft-ietf-teas-yang-te-
+ 30, 11 July 2022, <https://datatracker.ietf.org/doc/html/
+ draft-ietf-teas-yang-te-30>.
+
+Acknowledgements
+
+ The authors would like to thank Adrian Farrel, Vishnu Pavan Beeram,
+ Tom Petch, Ines Robles, John Scudder, Dale Worley, Dan Romascanu,
+ Éric Vyncke, Roman Danyliw, Paul Wouters, Lars Eggert, Francesca
+ Palombini, and Robert Wilton for their valuable comments and
+ suggestions on this document.
+
+Contributors
+
+ The following person contributed significantly to the content of this
+ document and should be considered a coauthor.
+
+ Yuji Tochio
+ Fujitsu
+ Email: tochio@fujitsu.com
+
+
+Authors' Addresses
+
+ Jia He
+ Huawei Technologies
+ F3-1B, R&D Center, Huawei Industrial Base
+ Bantian, Longgang District
+ Shenzhen
+ China
+ Email: hejia@huawei.com
+
+
+ Italo Busi
+ Huawei Technologies
+ Email: italo.busi@huawei.com
+
+
+ Jeong-dong Ryoo
+ ETRI
+ 218 Gajeongno
+ Yuseong-gu
+ Daejeon
+ 34129
+ South Korea
+ Phone: +82-42-860-5384
+ Email: ryoo@etri.re.kr
+
+
+ Bin Yeong Yoon
+ ETRI
+ Email: byyun@etri.re.kr
+
+
+ Peter Park
+ KT
+ Email: peter.park@kt.com