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rfc:rfc8131

Internet Engineering Task Force (IETF) X. Zhang Request for Comments: 8131 H. Zheng, Ed. Category: Informational Huawei Technologies ISSN: 2070-1721 R. Gandhi, Ed.

                                                                Z. Ali
                                                   Cisco Systems, Inc.
                                                         P. Brzozowski
                                                          ADVA Optical
                                                            March 2017
                    RSVP-TE Signaling Procedure for
           End-to-End GMPLS Restoration and Resource Sharing

Abstract

 In non-packet transport networks, there are requirements where the
 Generalized Multiprotocol Label Switching (GMPLS) end-to-end recovery
 scheme needs to employ a restoration Label Switched Path (LSP) while
 keeping resources for the working and/or protecting LSPs reserved in
 the network after the failure occurs.
 This document reviews how the LSP association is to be provided using
 Resource Reservation Protocol - Traffic Engineering (RSVP-TE)
 signaling in the context of a GMPLS end-to-end recovery scheme when
 using restoration LSP where failed LSP is not torn down.  In
 addition, this document discusses resource sharing-based setup and
 teardown of LSPs as well as LSP reversion procedures.  No new
 signaling extensions are defined by this document, and it is strictly
 informative in nature.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 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).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see 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
 http://www.rfc-editor.org/info/rfc8131.

Zhang, et al. Informational [Page 1] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

Copyright Notice

 Copyright (c) 2017 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
 (http://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 Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1. Introduction ....................................................3
 2. Conventions Used in This Document ...............................4
    2.1. Terminology ................................................4
    2.2. Abbreviations ..............................................4
 3. Overview ........................................................4
    3.1. Examples of Restoration Schemes ............................5
         3.1.1. 1+R Restoration .....................................5
         3.1.2. 1+1+R Restoration ...................................6
                3.1.2.1. 1+1+R Restoration - Variants ...............7
    3.2. Resource Sharing by Restoration LSP ........................7
 4. RSVP-TE Signaling Procedure .....................................8
    4.1. Restoration LSP Association ................................8
    4.2. Resource Sharing-Based Restoration LSP Setup ...............8
    4.3. LSP Reversion .............................................10
         4.3.1. Make-While-Break Reversion .........................10
         4.3.2. Make-Before-Break Reversion ........................11
 5. Security Considerations ........................................12
 6. IANA Considerations ............................................13
 7. References .....................................................13
    7.1. Normative References ......................................13
    7.2. Informative References ....................................13
 Acknowledgements  .................................................14
 Contributors ......................................................14
 Authors' Addresses ................................................15

Zhang, et al. Informational [Page 2] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

1. Introduction

 Generalized Multiprotocol Label Switching (GMPLS) [RFC3945] defines a
 set of protocols, including Open Shortest Path First - Traffic
 Engineering (OSPF-TE) [RFC4203] and Resource Reservation Protocol -
 Traffic Engineering (RSVP-TE) [RFC3473].  These protocols can be used
 to set up Label Switched Paths (LSPs) in non-packet transport
 networks.  The GMPLS protocol extends MPLS to support interfaces
 capable of Time Division Multiplexing (TDM), Lambda Switching and
 Fiber Switching.  These switching technologies provide several
 protection schemes [RFC4426] [RFC4427] (e.g., 1+1, 1:N, and M:N).
 RSVP-TE signaling has been extended to support various GMPLS recovery
 schemes, such as end-to-end recovery [RFC4872] and segment recovery
 [RFC4873].  As described in [RFC6689], an ASSOCIATION object with
 Association Type "Recovery" [RFC4872] can be signaled in the RSVP
 Path message to identify the LSPs for restoration.  Also, an
 ASSOCIATION object with Association Type "Resource Sharing" [RFC4873]
 can be signaled in the RSVP Path message to identify the LSPs for
 resource sharing.  Section 2.2 of [RFC6689] reviews the procedure for
 providing LSP associations for GMPLS end-to-end recovery, and Section
 2.4 of that document reviews the procedure for providing LSP
 associations for sharing resources.
 Generally, GMPLS end-to-end recovery schemes have the restoration LSP
 set up after the failure has been detected and notified on the
 working LSP.  For a recovery scheme with revertive behavior, a
 restoration LSP is set up while the working LSP and/or protecting LSP
 are not torn down in the control plane due to a failure.  In non-
 packet transport networks, because working LSPs are typically set up
 over preferred paths, service providers would like to keep resources
 associated with the working LSPs reserved.  This is to make sure that
 the service can be reverted to the preferred path (working LSP) when
 the failure is repaired to provide deterministic behavior and a
 guaranteed Service Level Agreement (SLA).
 In this document, we review procedures for GMPLS LSP associations,
 resource-sharing-based LSP setup, teardown, and LSP reversion for
 non-packet transport networks, including the following:
 o  The procedure for providing LSP associations for the GMPLS end-to-
    end recovery using restoration LSP where working and protecting
    LSPs are not torn down and resources are kept reserved in the
    network after the failure.
 o  The procedure for resource sharing using the Shared Explicit (SE)
    flag in conjunction with an ASSOCIATION object.  In [RFC3209], the
    Make-Before-Break (MBB) method assumes the old and new LSPs share

Zhang, et al. Informational [Page 3] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

    the SESSION object and signal SE flag in the SESSION_ATTRIBUTE
    object for sharing resources.  According to [RFC6689], an
    ASSOCIATION object with Association Type "Resource Sharing" in the
    Path message enables the sharing of resources across LSPs with
    different SESSION objects.
 o  The procedures for LSP reversion and resource sharing, when using
    end-to-end recovery scheme with revertive behavior.
 This document is strictly informative in nature and does not define
 any RSVP-TE signaling extensions.

2. Conventions Used in This Document

2.1. Terminology

 The reader is assumed to be familiar with the terminology in
 [RFC3209], [RFC3473], [RFC4872], and [RFC4873].  The terminology for
 GMPLS recovery is defined in [RFC4427].

2.2. Abbreviations

 GMPLS: Generalized Multiprotocol Label Switching
 LSP: Label Switched Path
 MBB: Make-Before-Break
 MPLS: Multiprotocol Label Switching
 RSVP: Resource Reservation Protocol
 SE: Shared Explicit (flag)
 TDM: Time Division Multiplexing
 TE: Traffic Engineering

3. Overview

 The GMPLS end-to-end recovery scheme, as defined in [RFC4872] and
 discussed in this document, switches normal traffic to an alternate
 LSP that is not even partially established only after the working LSP
 failure occurs.  The new alternate route is selected at the LSP head-
 end node, it may reuse resources of the failed LSP at intermediate
 nodes and may include additional intermediate nodes and/or links.

Zhang, et al. Informational [Page 4] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

3.1. Examples of Restoration Schemes

 Two forms of end-to-end recovery schemes, 1+R restoration and 1+1+R
 restoration, are described in the following sections.  Other forms of
 end-to-end recovery schemes also exist, and they can use these
 signaling techniques.

3.1.1. 1+R Restoration

 One example of the recovery scheme considered in this document is 1+R
 recovery.  The 1+R recovery scheme is exemplified in Figure 1.  In
 this example, a working LSP on path A-B-C-Z is pre-established.
 Typically, after a failure detection and notification on the working
 LSP, a second LSP on path A-H-I-J-Z is established as a restoration
 LSP.  Unlike a protecting LSP, which is set up before the failure, a
 restoration LSP is set up when needed, after the failure.
        +-----+    +-----+     +-----+     +-----+
        |  A  +----+  B  +-----+  C  +-----+  Z  |
        +--+--+    +-----+     +-----+     +--+--+
            \                                /
             \                              /
           +--+--+       +-----+        +--+--+
           |  H  +-------+  I  +--------+  J  |
           +-----+       +-----+        +-----+
        Figure 1: An Example of 1+R Recovery Scheme
 During failure switchover with 1+R recovery scheme, in general,
 working LSP resources are not released so that working and
 restoration LSPs coexist in the network.  Nonetheless, working and
 restoration LSPs can share network resources.  Typically, when the
 failure has recovered on the working LSP, the restoration LSP is no
 longer required and is torn down while the traffic is reverted to the
 original working LSP.

Zhang, et al. Informational [Page 5] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

3.1.2. 1+1+R Restoration

 Another example of the recovery scheme considered in this document is
 1+1+R.  In 1+1+R, a restoration LSP is set up for the working LSP
 and/or the protecting LSP after the failure has been detected; this
 recovery scheme is exemplified in Figure 2.
           +-----+       +-----+        +-----+
           |  D  +-------+  E  +--------+  F  |
           +--+--+       +-----+        +--+--+
             /                              \
            /                                \
        +--+--+    +-----+     +-----+     +--+--+
        |  A  +----+  B  +-----+  C  +-----+  Z  |
        +--+--+    +-----+     +-----+     +--+--+
            \                                /
             \                              /
           +--+--+       +-----+        +--+--+
           |  H  +-------+  I  +--------+  J  |
           +-----+       +-----+        +-----+
        Figure 2: An Example of 1+1+R Recovery Scheme
 In this example, a working LSP on path A-B-C-Z and a protecting LSP
 on path A-D-E-F-Z are pre-established.  After a failure detection and
 notification on the working LSP or protecting LSP, a third LSP on
 path A-H-I-J-Z is established as a restoration LSP.  The restoration
 LSP, in this case, provides protection against failure of both the
 working and protecting LSPs.  During failure switchover with the
 1+1+R recovery scheme, in general, failed LSP resources are not
 released so that working, protecting, and restoration LSPs coexist in
 the network.  The restoration LSP can share network resources with
 the working LSP, and it can share network resources with the
 protecting LSP.  Typically, the restoration LSP is torn down when the
 traffic is reverted to the original LSP and is no longer needed.
 There are two possible models when using a restoration LSP with 1+1+R
 recovery scheme:
 o  A restoration LSP is set up after either a working or a protecting
    LSP fails.  Only one restoration LSP is present at a time.
 o  A restoration LSP is set up after both the working and protecting
    LSPs fail.  Only one restoration LSP is present at a time.

Zhang, et al. Informational [Page 6] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

3.1.2.1. 1+1+R Restoration - Variants

 Two other possible variants exist when using a restoration LSP with
 1+1+R recovery scheme:
 o  A restoration LSP is set up after either a working or protecting
    LSP fails.  Two different restoration LSPs may be present, one for
    the working LSP and one for the protecting LSP.
 o  Two different restoration LSPs are set up after both working and
    protecting LSPs fail, one for the working LSP and one for the
    protecting LSP.
 In all these models, if a restoration LSP also fails, it is torn down
 and a new restoration LSP is set up.

3.2. Resource Sharing by Restoration LSP

                            +-----+      +-----+
                            |  F  +------+  G  +--------+
                            +--+--+      +-----+        |
                               |                        |
                               |                        |
     +-----+    +-----+     +--+--+      +-----+     +--+--+
     |  A  +----+  B  +-----+  C  +--X---+  D  +-----+  E  |
     +-----+    +-----+     +-----+      +-----+     +-----+
       Figure 3: Resource Sharing in 1+R Recovery Scheme
 Using the network shown in Figure 3 as an example using 1+R recovery
 scheme, LSP1 (A-B-C-D-E) is the working LSP; assume it allows for
 resource sharing when the LSP traffic is dynamically restored.  Upon
 detecting the failure of a link along the LSP1, e.g., Link C-D, node
 A needs to decide which alternative path it will use to signal
 restoration LSP and reroute traffic.  In this case, A-B-C-F-G-E is
 chosen as the restoration LSP path, and the resources on the path
 segment A-B-C are reused by this LSP.  The working LSP is not torn
 down and coexists with the restoration LSP.  When the head-end node A
 signals the restoration LSP, nodes C, F, G, and E reconfigure the
 resources (as listed in Table 1 of this document) to set up the LSP
 by sending cross-connection command to the data plane.
 In the recovery scheme employing revertive behavior, after the
 failure is repaired, the resources on nodes C and E need to be
 reconfigured to set up the working LSP (using a procedure described
 in Section 4.3 of this document) by sending cross-connection command
 to the data plane.  The traffic is then reverted back to the original
 working LSP.

Zhang, et al. Informational [Page 7] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

4. RSVP-TE Signaling Procedure

4.1. Restoration LSP Association

 Where GMPLS end-to-end recovery scheme needs to employ a restoration
 LSP while keeping resources for the working and/or protecting LSPs
 reserved in the network after the failure, the restoration LSP is set
 up with an ASSOCIATION object that has the Association Type set to
 "Recovery" [RFC4872], the Association ID and the Association Source
 set to the corresponding Association ID and the Association Source
 signaled in the Path message of the LSP it is restoring.  For
 example, when a restoration LSP is signaled for a failed working LSP,
 the ASSOCIATION object in the Path message of the restoration LSP
 contains the Association ID and Association Source set to the
 Association ID and Association Source signaled in the working LSP for
 the "Recovery" Association Type.  Similarly, when a restoration LSP
 is set up for a failed protecting LSP, the ASSOCIATION object in the
 Path message of the restoration LSP contains the Association ID and
 Association Source is set to the Association ID and Association
 Source signaled in the protecting LSP for the "Recovery" Association
 Type.
 The procedure for signaling the PROTECTION object is specified in
 [RFC4872].  Specifically, the restoration LSP used for a working LSP
 is set up with the P bit cleared in the PROTECTION object in the Path
 message of the restoration LSP and the restoration LSP used for a
 protecting LSP is set up with the P bit set in the PROTECTION object
 in the Path message of the restoration LSP.

4.2. Resource Sharing-Based Restoration LSP Setup

 GMPLS LSPs can share resources during LSP setup if they have the
 Shared Explicit (SE) flag set in the SESSION_ATTRIBUTE objects
 [RFC3209] in the Path messages that create them and:
 o  As defined in [RFC3209], LSPs have identical SESSION objects,
    and/or
 o  As defined in [RFC6689], LSPs have matching ASSOCIATION objects
    with the Association Type set to "Resource Sharing" signaled in
    their Path messages.  In this case, LSPs can have different
    SESSION objects i.e., a different Tunnel ID, Source and/or
    Destination signaled in their Path messages.
 As described in Section 2.5 of [RFC3209], the purpose of make-before-
 break is not to disrupt traffic, or adversely impact network
 operations while TE tunnel rerouting is in progress.  In non-packet
 transport networks, during the RSVP-TE signaling procedure, the nodes

Zhang, et al. Informational [Page 8] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

 set up cross-connections along the LSP accordingly.  Because the
 cross-connection cannot simultaneously connect a shared resource to
 different resources in two alternative LSPs, nodes may not be able to
 fulfill this request when LSPs share resources.
 For LSP restoration upon failure, as explained in Section 11 of
 [RFC4872], the reroute procedure may reuse existing resources.  The
 action of the intermediate nodes during the rerouting process to
 reconfigure cross-connections does not further impact the traffic
 since it has been interrupted due to the already failed LSP.
 The node actions for setting up the restoration LSP can be
 categorized into the following:
  1. ———————————-+———————————

| Category | Action |

  1. ———————————-+———————————

| Reusing existing resource on | This type of node needs to |

 | both input and output interfaces | reserve the existing resources |
 | (nodes A & B in Figure 3).       | and no cross-connection        |
 |                                  | command is needed.             |
 -----------------------------------+---------------------------------
 | Reusing an existing resource only| This type of node needs to     |
 | on one of the interfaces, either | reserve the resources and send |
 | input or output interfaces, and  | the reconfiguration            |
 | using new resource on the        | cross-connection command to its|
 | other interfaces.                | corresponding data plane       |
 | (nodes C & E in Figure 3).       | node on the interfaces where   |
 |                                  | new resources are needed, and  |
 |                                  | it needs to reuse the existing |
 |                                  | resources on the other         |
 |                                  | interfaces.                    |
 -----------------------------------+---------------------------------
 | Using new resources on both      | This type of node needs to     |
 | interfaces.                      | reserve the new resources      |
 | (nodes F & G in Figure 3).       | and send the cross-connection  |
 |                                  | command on both interfaces.    |
 -----------------------------------+---------------------------------
       Table 1: Node Actions during Restoration LSP Setup
 Depending on whether or not the resource is reused, the node actions
 differ.  This deviates from normal LSP setup, since some nodes do not
 need to reconfigure the cross-connection.  Also, the judgment of
 whether the control plane node needs to send a cross-connection setup
 or modification command to its corresponding data plane node(s)
 relies on the check whether the LSPs are sharing resources.

Zhang, et al. Informational [Page 9] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

4.3. LSP Reversion

 If the end-to-end LSP recovery scheme employs the revertive behavior,
 as described in Section 3 of this document, traffic can be reverted
 from the restoration LSP to the working or protecting LSP after its
 failure is recovered.  The LSP reversion can be achieved using two
 methods:
 1. Make-While-Break Reversion: resources associated with a working or
    protecting LSP are reconfigured while removing reservations for
    the restoration LSP.
 2. Make-Before-Break Reversion: resources associated with a working
    or protecting LSP are reconfigured before removing reservations
    for the restoration LSP.
 In non-packet transport networks, both of the above reversion methods
 will result in some traffic disruption when the restoration LSP and
 the LSP being restored are sharing resources and the cross-
 connections need to be reconfigured on intermediate nodes.

4.3.1. Make-While-Break Reversion

 In this reversion method, restoration LSP is simply requested to be
 deleted by the head-end.  Removing reservations for restoration LSP
 triggers reconfiguration of resources associated with a working or
 protecting LSP on every node where resources are shared.  The working
 or protecting LSP state was not removed from the nodes when the
 failure occurred.  Whenever reservation for restoration LSP is
 removed from a node, data plane configuration changes to reflect
 reservations of working or protecting LSP as signaling progresses.
 Eventually, after the whole restoration LSP is deleted, data plane
 configuration will fully match working or protecting LSP reservations
 on the whole path.  Thus, reversion is complete.
 Make-while-break, while being relatively simple in its logic, has a
 few limitations as follows which may not be acceptable in some
 networks:
 o  No rollback
 If, for some reason, reconfiguration of the data plane on one of the
 nodes, to match working or protecting LSP reservations, fails,
 falling back to restoration LSP is no longer an option, as its state
 might have already been removed from other nodes.

Zhang, et al. Informational [Page 10] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

 o  No completion guarantee
 Deletion of an LSP provides no guarantees of completion.  In
 particular, if RSVP packets are lost due to a node or link failure,
 it is possible for an LSP to be only partially deleted.  To mitigate
 this, RSVP could maintain soft state reservations and, hence,
 eventually remove remaining reservations due to refresh timeouts.
 This approach is not feasible in non-packet transport networks,
 however, where control and data channels are often separated; hence,
 soft state reservations are not useful.
 Finally, one could argue that graceful LSP deletion [RFC3473] would
 provide a guarantee of completion.  While this is true for most
 cases, many implementations will time out graceful deletion if LSP is
 not removed within certain amount of time, e.g., due to a transit
 node fault.  After that, deletion procedures that provide no
 completion guarantees will be attempted.  Hence, in corner cases a
 completion guarantee cannot be provided.
 o  No explicit notification of completion to head-end node
 In some cases, it may be useful for a head-end node to know when the
 data plane has been reconfigured to match working or protecting LSP
 reservations.  This knowledge could be used for initiating operations
 like enabling alarm monitoring, power equalization, and others.
 Unfortunately, for the reasons mentioned above, make-while-break
 reversion lacks such explicit notification.

4.3.2. Make-Before-Break Reversion

 This reversion method can be used to overcome limitations of make-
 while-break reversion.  It is similar in spirit to the MBB concept
 used for re-optimization.  Instead of relying on deletion of the
 restoration LSP, the head-end chooses to establish a new reversion
 LSP that duplicates the configuration of the resources on the working
 or protecting LSP and uses identical ASSOCIATION and PROTECTION
 objects in the Path message of that LSP.  Only if the setup of this
 LSP is successful will other (restoration and working or protecting)
 LSPs be deleted by the head-end.  MBB reversion consists of two
 parts:
 A) Make part:
 Creating a new reversion LSP following working or protecting the LSP.
 The reversion LSP shares all of the resources of the working or
 protecting LSP and may share resources with the restoration LSP.  As
 the reversion LSP is created, resources are

Zhang, et al. Informational [Page 11] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

 reconfigured to match its reservations.  Hence, after the reversion
 LSP is created, data plane configuration reflects working or
 protecting LSP reservations.
 B) Break part:
 After the "make" part is finished, the original working or protecting
 and restoration LSPs are torn down, and the reversion LSP becomes the
 new working or protecting LSP.  Removing reservations for working or
 restoration LSPs does not cause any resource reconfiguration on the
 reversion LSP -- nodes follow same procedures for the "break" part of
 any MBB operation.  Hence, after working or protecting and
 restoration LSPs are removed, the data plane configuration is exactly
 the same as before starting restoration.  Thus, reversion is
 complete.
 MBB reversion uses make-before-break characteristics to overcome
 challenges related to make-while-break reversion as follow:
 o  Rollback
 If the "make" part fails, the (existing) restoration LSP will still
 be used to carry existing traffic as the restoration LSP state was
 not removed.  Same logic applies here as for any MBB operation
 failure.
 o  Completion guarantee
 LSP setup is resilient against RSVP message loss, as Path and Resv
 messages are refreshed periodically.  Hence, given that the network
 recovers from node and link failures eventually, reversion LSP setup
 is guaranteed to finish with either success or failure.
 o  Explicit notification of completion to head-end node
 The head-end knows that the data plane has been reconfigured to match
 working or protecting LSP reservations on the intermediate nodes when
 it receives a Resv message for the reversion LSP.

5. Security Considerations

 This document reviews procedures defined in [RFC3209], [RFC4872],
 [RFC4873], and [RFC6689] and does not define any new procedures.
 This document does not introduce any new security issues; security
 issues were already covered in [RFC3209], [RFC4872], [RFC4873], and
 [RFC6689].

Zhang, et al. Informational [Page 12] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

6. IANA Considerations

 This document does not require any IANA actions.

7. References

7.1. Normative References

 [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,
             <http://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,
             <http://www.rfc-editor.org/info/rfc3473>.
 [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,
             <http://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,
             <http://www.rfc-editor.org/info/rfc4873>.
 [RFC6689]   Berger, L., "Usage of the RSVP ASSOCIATION Object",
             RFC 6689, DOI 10.17487/RFC6689, July 2012,
             <http://www.rfc-editor.org/info/rfc6689>.

7.2. Informative References

 [RFC3945]   Mannie, E., Ed., "Generalized Multi-Protocol Label
             Switching (GMPLS) Architecture", RFC 3945,
             DOI 10.17487/RFC3945, October 2004,
             <http://www.rfc-editor.org/info/rfc3945>.
 [RFC4203]   Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF Extensions
             in Support of Generalized Multi-Protocol Label Switching
             (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
             <http://www.rfc-editor.org/info/rfc4203>.

Zhang, et al. Informational [Page 13] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

 [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,
             <http://www.rfc-editor.org/info/rfc4426>.
 [RFC4427]   Mannie, E., Ed., and D. Papadimitriou, Ed., "Recovery
             (Protection and Restoration) Terminology for Generalized
             Multi-Protocol Label Switching (GMPLS)", RFC 4427,
             DOI 10.17487/RFC4427, March 2006,
             <http://www.rfc-editor.org/info/rfc4427>.

Acknowledgements

 The authors would like to thank:
  1. George Swallow for the discussions on the GMPLS restoration.
  1. Lou Berger for the guidance on this work.
  1. Lou Berger, Vishnu Pavan Beeram, and Christian Hopps for reviewing

this document and providing valuable comments.

 A special thanks to Dale Worley for his thorough review of this
 document.

Contributors

 Gabriele Maria Galimberti
 Cisco Systems, Inc.
 Email: ggalimbe@cisco.com

Zhang, et al. Informational [Page 14] RFC 8131 GMPLS Restoration and Resource Sharing March 2017

Authors' Addresses

 Xian Zhang
 Huawei Technologies
 F3-1-B R&D Center, Huawei Base
 Bantian, Longgang District
 Shenzhen 518129
 China
 Email: zhang.xian@huawei.com
 Haomian Zheng (editor)
 Huawei Technologies
 F3-1-B R&D Center, Huawei Base
 Bantian, Longgang District
 Shenzhen 518129
 China
 Email: zhenghaomian@huawei.com
 Rakesh Gandhi (editor)
 Cisco Systems, Inc.
 Email: rgandhi@cisco.com
 Zafar Ali
 Cisco Systems, Inc.
 Email: zali@cisco.com
 Pawel Brzozowski
 ADVA Optical
 Email: PBrzozowski@advaoptical.com

Zhang, et al. Informational [Page 15]

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