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GMPLS Signaling Extensions for Shared Mesh Protection
draft-ietf-teas-gmpls-signaling-smp-12

Document Type Active Internet-Draft (teas WG)
Authors He Jia , Italo Busi , Jeong-dong Ryoo , Bin-Yeong Yoon , Peter Choongul Park
Last updated 2022-04-19
Replaces draft-he-teas-gmpls-signaling-smp
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draft-ietf-teas-gmpls-signaling-smp-12
TEAS Working Group                                                 J. He
Internet-Draft                                                   I. Busi
Updates: 4872, 4873 (if approved)                    Huawei Technologies
Intended status: Standards Track                                 J. Ryoo
Expires: October 21, 2022                                        B. Yoon
                                                                    ETRI
                                                                 P. Park
                                                                      KT
                                                          April 19, 2022

         GMPLS Signaling Extensions for Shared Mesh Protection
                 draft-ietf-teas-gmpls-signaling-smp-12

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 RFC 4872 and RFC 4873 to provide the extensions
   to the Generalized Multi-Protocol Label Switching (GMPLS) signaling
   to support the control of the SMP.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 21, 2022.

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Copyright Notice

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   document authors.  All rights reserved.

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   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   4
   3.  SMP Definition  . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Operation of SMP with GMPLS Signaling Extension . . . . . . .   5
   5.  GMPLS Signaling Extension for SMP . . . . . . . . . . . . . .   6
     5.1.  Identifiers . . . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  Signaling Primary LSPs  . . . . . . . . . . . . . . . . .   7
     5.3.  Signaling Secondary LSPs  . . . . . . . . . . . . . . . .   7
     5.4.  SMP Preemption Priority . . . . . . . . . . . . . . . . .   8
     5.5.  Notifying Availability of Shared Resources  . . . . . . .   8
     5.6.  SMP APS Configuration . . . . . . . . . . . . . . . . . .   9
   6.  Updates to PROTECTION Object  . . . . . . . . . . . . . . . .  10
     6.1.  New Protection Type . . . . . . . . . . . . . . . . . . .  10
     6.2.  Updates on Notification and Operational Bits  . . . . . .  10
     6.3.  Preemption Priority . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   10. Contributor . . . . . . . . . . . . . . . . . . . . . . . . .  12

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   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     11.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   RFC 4872 [RFC4872] defines extension of Resource Reservation Protocol
   - Traffic Engineering (RSVP-TE) to support Shared Mesh Restoration
   (SMR) mechanisms.  SMR can be seen as a particular case of pre-
   planned 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, and 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 the
   extensions to the Generalized Multi-Protocol Label Switching (GMPLS)
   signaling to support the control of the SMP mechanism.  Specifically,
   it;

   o  defines a new LSP protection type, "Shared Mesh Protection," for
      the LSP Flags field [RFC4872] of the PROTECTION object (see
      Section 6.1),

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   o  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

   o  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 specified in this document.
   [I-D.ietf-teas-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 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 a MPLS-TP network.

   The SMP mechanism is based on pre-computed protecting LSPs that are
   pre-configured into the network elements.  Pre-configuration 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

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   are not pre-established).  Pre-configuring but not activating
   protecting LSPs allows link and node resources to be shared by the
   protecting LSPs of multiple working LSPs (that are themselves
   disjoint and thus unlikely to fail simultaneously).  Protecting LSPs
   are activated in response to failures of working LSPs or operator's
   commands by means of the APS protocol that operates in the data
   plane.  The APS protocol messages are exchanged along the protecting
   LSP.  SMP is always revertive.

   SMP has a lot of similarity to SMR except that the activation in case
   of SMR is achieved by control plane signaling during the recovery
   operation, while SMP is done by the APS protocol in the data plane.

4.  Operation of SMP with GMPLS Signaling Extension

   Consider the following network topology:

                             A---B---C---D
                              \         /
                               E---F---G
                              /         \
                             H---I---J---K

                   Figure 1: An example of 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 MUST 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, G can be shared.

   When a failure, such as Signal Fail (SF) and 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.

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   If the protection resource is available, node E will send the
   confirmation APS message to the end 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 then the intermediate node will 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 Extension 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, hereby 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, hereby 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 during the provisioning phase
      several secondary LSPs efficiently, and

      (5) the capability to support activation of a secondary LSP after
      failure occurrence via APS protocol in the data plane.

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5.1.  Identifiers

   To simplify association operations, both LSPs (i.e., the protected
   and the secondary LSPs) 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 of PROTECTION object (see [RFC4872])
   to set up the two LSPs.  This LSP Protection Type value is applicable
   only 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 in the
   ASSOCIATION object, the Association ID to the associated secondary
   protecting LSP_ID.

   Note: N bit is set to indicate that the protection switching
   signaling is done via 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 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
   APS protocol in the data plane.

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   After protection switching completes the protecting LSP MUST be
   signaled with the S bit set to 0 and O bit set to 1 in the PROTECTION
   object.  At this point, the link and node resources MUST be allocated
   for this LSP that 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 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 that the APS protocol
   uses to resolve the competition for shared resources among multiple
   protecting LSPs, is indicated in 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 the 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 the 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 pre-configured, the end node MUST
   keep refreshing both working and protecting LSPs regardless of
   failure or preempted situation.

5.5.  Notifying Availability of Shared Resources

   When a lower priority protecting LSP is preempted, the intermediate
   node that performed preemption MUST send a Notify message with error
   code "Notify Error" (25) (see [RFC4872]) and error sub-code "Shared
   resources unavailable" (TBA1) 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.

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   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.  In case 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.  These end nodes, in case of a failure of the
   working LSP, 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" (TBA2) 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 an SMP 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 SMP protecting LSP.  This is done by other means than GMPLS
   signaling, before any SMP protecting LSP has been set up.  Therefore,
   there are likely additional requirements for APS configuration which
   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 SMP
   protecting LSP.

   Since APS protocol is for further study in [G808.3], it can be
   assumed that 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.

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6.  Updates to PROTECTION Object

   GMPLS extension requirements for SMP introduce several updates to the
   Protection Object (see [RFC4872]).

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 applicable to
   only 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 on 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 protection-switching
      purposes.  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 the P bit is set to 1, and 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.

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6.3.  Preemption Priority

   [RFC4872] reserved a 32-bit field in the PROTECTION object header.
   Subsequently, [RFC4873] allocated several fields from that field, and
   left the remainder of the bits reserved.  This specification further
   allocates the preemption priority field from those formerly-reserved
   bits.  The 32-bit field in the PROTECTION object defined in [RFC4873]
   are updated 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 bit

      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 of how many
      priority levels to be operated in an SMP network is a network
      operator's choice.

   See [RFC4873] for the definition of other fields.

7.  IANA Considerations

   IANA maintains a registry called "Resource Reservation Protocol
   (RSVP) Parameters" with a subregistry called "Error Codes and
   Globally-Defined Error Value Sub-Codes".  Within this subregistry
   there is a definition of the "Notify Error" error code (25).  The
   definition lists a number of error value sub-codes that may be used
   with this error code.  IANA is requested to allocate further error
   value sub-codes for use with this error code as described in this
   document.

      Value        Description              Reference
      ----- ---------------------------- ---------------
      TBA1  Shared resources unavailable (this document)
      TBA2  Shared resources available   (this document)

8.  Security Considerations

   Since this document makes use of the exchange of RSVP messages
   including a Notify message, the security threats discussed in
   [RFC4872] also apply to this document.

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   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.  Acknowledgements

   The authors would like to thank Adrian Farrel, Vishnu Pavan Beeram,
   Tom Petch, Ines Robles, John Scudder, Dale Worley, Dan Romascanu,
   Eric Vyncke, Roman Danyliw, Paul Wouters, Lars Eggert, Francesca
   Palombini, and Robert Wilton for their valuable comments and
   suggestions on this document.

10.  Contributor

   The following person contributed significantly to the content of this
   document and should be considered as a co-author.

   Yuji Tochio
   Fujitsu
   Email: tochio@fujitsu.com

11.  References

11.1.  Normative References

   [G808.3]   International Telecommunication Union, "Generic protection
              switching - Shared mesh protection", ITU-T Recommendation
              G.808.3, October 2012.

   [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>.

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   [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., 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>.

11.2.  Informative References

   [G873.3]   International Telecommunication Union, "Optical transport
              network - Shared mesh protection", ITU-T Recommendation
              G.873.3, September 2017.

   [I-D.ietf-teas-yang-te]
              Saad, T., Gandhi, R., Liu, X., Beeram, V. P., Bryskin, I.,
              and O. G. D. Dios, "A YANG Data Model for Traffic
              Engineering Tunnels, Label Switched Paths and Interfaces",
              draft-ietf-teas-yang-te-29 (work in progress), February
              2022.

   [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>.

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   [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>.

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

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