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rfc:rfc7271

Internet Engineering Task Force (IETF) J. Ryoo, Ed. Request for Comments: 7271 ETRI Updates: 6378 E. Gray, Ed. Category: Standards Track Ericsson ISSN: 2070-1721 H. van Helvoort

                                                   Huawei Technologies
                                                       A. D'Alessandro
                                                        Telecom Italia
                                                             T. Cheung
                                                                  ETRI
                                                            E. Osborne
                                                             June 2014
  MPLS Transport Profile (MPLS-TP) Linear Protection to Match the
     Operational Expectations of Synchronous Digital Hierarchy,
Optical Transport Network, and Ethernet Transport Network Operators

Abstract

 This document describes alternate mechanisms to perform some of the
 functions of MPLS Transport Profile (MPLS-TP) linear protection
 defined in RFC 6378, and also defines additional mechanisms.  The
 purpose of these alternate and additional mechanisms is to provide
 operator control and experience that more closely models the behavior
 of linear protection seen in other transport networks.
 This document also introduces capabilities and modes for linear
 protection.  A capability is an individual behavior, and a mode is a
 particular combination of capabilities.  Two modes are defined in
 this document: Protection State Coordination (PSC) mode and Automatic
 Protection Switching (APS) mode.
 This document describes the behavior of the PSC protocol including
 priority logic and state machine when all the capabilities associated
 with the APS mode are enabled.
 This document updates RFC 6378 in that the capability advertisement
 method defined here is an addition to that document.

Ryoo, et al. Standards Track [Page 1] RFC 7271 MPLS-TP LP for ITU-T June 2014

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 5741.
 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/rfc7271.

Copyright Notice

 Copyright (c) 2014 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  . . . . . . . . . . . . . . . . . . . . . . . .   4
 2.  Conventions Used in This Document . . . . . . . . . . . . . .   5
 3.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
 4.  Capability 1: Priority Modification . . . . . . . . . . . . .   6
   4.1.  Motivation for Swapping Priorities of FS and SF-P . . . .   6
   4.2.  Motivation for Raising the Priority of SFc  . . . . . . .   7
   4.3.  Motivation for Introducing the Freeze Command . . . . . .   7
   4.4.  Procedures in Support of Priority Modification  . . . . .   8
 5.  Capability 2: Non-revertive Behavior Modification . . . . . .   8
 6.  Capability 3: Support of the MS-W Command . . . . . . . . . .   8
   6.1.  Motivation for adding MS-W  . . . . . . . . . . . . . . .   8
   6.2.  Terminology to Support MS-W . . . . . . . . . . . . . . .   9
   6.3.  Behavior of MS-P and MS-W . . . . . . . . . . . . . . . .   9
   6.4.  Equal-Priority Resolution for MS  . . . . . . . . . . . .  10
 7.  Capability 4: Support of Protection against SD  . . . . . . .  10
   7.1.  Motivation for Supporting Protection against SD . . . . .  10
   7.2.  Terminology to Support SD . . . . . . . . . . . . . . . .  10

Ryoo, et al. Standards Track [Page 2] RFC 7271 MPLS-TP LP for ITU-T June 2014

   7.3.  Behavior of Protection against SD . . . . . . . . . . . .  11
   7.4.  Equal-Priority Resolution . . . . . . . . . . . . . . . .  12
 8.  Capability 5: Support of EXER Command . . . . . . . . . . . .  13
 9.  Capabilities and Modes  . . . . . . . . . . . . . . . . . . .  14
   9.1.  Capabilities  . . . . . . . . . . . . . . . . . . . . . .  14
     9.1.1.  Sending and Receiving the Capabilities TLV  . . . . .  15
   9.2.  Modes . . . . . . . . . . . . . . . . . . . . . . . . . .  16
     9.2.1.  PSC Mode  . . . . . . . . . . . . . . . . . . . . . .  16
     9.2.2.  APS Mode  . . . . . . . . . . . . . . . . . . . . . .  16
 10. PSC Protocol in APS Mode  . . . . . . . . . . . . . . . . . .  17
   10.1.  Request Field in PSC Protocol Message  . . . . . . . . .  17
   10.2.  Priorities of Local Inputs and Remote Requests . . . . .  17
     10.2.1.  Equal-Priority Requests  . . . . . . . . . . . . . .  18
   10.3.  Acceptance and Retention of Local Inputs . . . . . . . .  20
 11. State Transition Tables in APS Mode . . . . . . . . . . . . .  20
   11.1.  State Transition by Local Inputs . . . . . . . . . . . .  23
   11.2.  State Transition by Remote Messages  . . . . . . . . . .  25
   11.3.  State Transition for 1+1 Unidirectional Protection . . .  27
 12. Provisioning Mismatch and Protocol Failure in APS Mode  . . .  27
 13. Security Considerations . . . . . . . . . . . . . . . . . . .  28
 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  29
   14.1.  MPLS PSC Request Registry  . . . . . . . . . . . . . . .  29
   14.2.  MPLS PSC TLV Registry  . . . . . . . . . . . . . . . . .  29
   14.3.  MPLS PSC Capability Flag Registry  . . . . . . . . . . .  29
 15. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  30
 16. References  . . . . . . . . . . . . . . . . . . . . . . . . .  30
   16.1.  Normative References . . . . . . . . . . . . . . . . . .  30
   16.2.  Informative References . . . . . . . . . . . . . . . . .  30
 Appendix A.  An Example of an Out-of-Service Scenario . . . . . .  32
 Appendix B.  An Example of a Sequence Diagram Showing
              the Problem with the Priority Level of SFc . . . . .  33
 Appendix C.  Freeze Command . . . . . . . . . . . . . . . . . . .  34
 Appendix D.  Operation Examples of the APS Mode . . . . . . . . .  35

Ryoo, et al. Standards Track [Page 3] RFC 7271 MPLS-TP LP for ITU-T June 2014

1. Introduction

 Linear protection mechanisms for the MPLS Transport Profile (MPLS-TP)
 are described in RFC 6378 [RFC6378] to meet the requirements
 described in RFC 5654 [RFC5654].
 This document describes alternate mechanisms to perform some of the
 functions of linear protection, and also defines additional
 mechanisms.  The purpose of these alternate and additional mechanisms
 is to provide operator control and experience that more closely
 models the behavior of linear protection seen in other transport
 networks, such as Synchronous Digital Hierarchy (SDH), Optical
 Transport Network (OTN), and Ethernet transport networks.  Linear
 protection for SDH, OTN, and Ethernet transport networks is defined
 in ITU-T Recommendations G.841 [G841], G.873.1 [G873.1], and G.8031
 [G8031], respectively.
 The reader of this document is assumed to be familiar with [RFC6378].
 The alternative mechanisms described in this document are for the
 following capabilities:
 1.  Priority modification,
 2.  non-revertive behavior modification,
 and the following capabilities have been added to define additional
 mechanisms:
 3.  support of the Manual Switch to Working path (MS-W) command,
 4.  support of protection against Signal Degrade (SD), and
 5.  support of the Exercise (EXER) command.
 The priority modification includes raising the priority of Signal
 Fail on Protection path (SF-P) relative to Forced Switch (FS), and
 raising the priority level of Clear Signal Fail (SFc) above SF-P.
 Non-revertive behavior is modified to align with the behavior defined
 in RFC 4427 [RFC4427] as well as to follow the behavior of linear
 protection seen in other transport networks.
 Support of the MS-W command to revert traffic to the working path in
 non-revertive operation is covered in this document.

Ryoo, et al. Standards Track [Page 4] RFC 7271 MPLS-TP LP for ITU-T June 2014

 Support of the protection-switching protocol against SD is covered in
 this document.  The specifics for the method of identifying SD are
 out of the scope for this document and are treated similarly to
 Signal Fail (SF) in [RFC6378].
 Support of the EXER command to test if the Protection State
 Coordination (PSC) communication is operating correctly is also
 covered in this document.  Without actually switching traffic, the
 EXER command tests and validates the linear protection mechanism and
 PSC protocol including the aliveness of the priority logic, the PSC
 state machine, the PSC message generation and reception, and the
 integrity of the protection path.
 This document introduces capabilities and modes.  A capability is an
 individual behavior.  The capabilities of a node are advertised using
 the method given in this document.  A mode is a particular
 combination of capabilities.  Two modes are defined in this document:
 PSC mode and Automatic Protection Switching (APS) mode.
 Other modes may be defined as new combinations of the capabilities
 defined in this document or through the definition of additional
 capabilities.  In either case, the specification defining a new mode
 will be responsible for documenting the behavior, the priority logic,
 and the state machine of the PSC protocol when the set of
 capabilities in the new mode is enabled.
 This document describes the behavior, the priority logic, and the
 state machine of the PSC protocol when all the capabilities
 associated with the APS mode are enabled.  The PSC protocol behavior
 for the PSC mode is as defined in [RFC6378].
 This document updates [RFC6378] by adding a capability advertisement
 mechanism.  It is recommended that existing implementations of the
 PSC protocol be updated to support this capability.  Backward
 compatibility with existing implementations that do not support this
 mechanism is described in Section 9.2.1.
 Implementations are expected to be configured to support a specific
 set of capabilities (a mode) and to reject messages that indicate the
 use of a different set of capabilities (a different mode).  Thus, the
 capability advertisement is not a negotiation but a verification that
 peers are using the same mode.

2. Conventions Used in This Document

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [RFC2119].

Ryoo, et al. Standards Track [Page 5] RFC 7271 MPLS-TP LP for ITU-T June 2014

3. Acronyms

 This document uses the following acronyms:
 APS     Automatic Protection Switching
 DNR     Do-not-Revert
 EXER    Exercise
 FS      Forced Switch
 LO      Lockout of protection
 MS      Manual Switch
 MS-P    Manual Switch to Protection path
 MS-W    Manual Switch to Working path
 MPLS-TP MPLS Transport Profile
 NR      No Request
 OC      Operator Clear
 OTN     Optical Transport Network
 PSC     Protection State Coordination
 RR      Reverse Request
 SD      Signal Degrade
 SD-P    Signal Degrade on Protection path
 SD-W    Signal Degrade on Working path
 SDH     Synchronous Digital Hierarchy
 SF      Signal Fail
 SF-P    Signal Fail on Protection path
 SF-W    Signal Fail on Working path
 SFc     Clear Signal Fail
 SFDc    Clear Signal Fail or Degrade
 WTR     Wait-to-Restore

4. Capability 1: Priority Modification

 [RFC6378] defines the priority of FS to be higher than that of SF-P.
 That document also defines the priority of Clear SF (SFc) to be low.
 This document defines the priority modification capability whereby
 the relative priorities of FS and SF-P are swapped, and the priority
 of Clear SF (SFc) is raised.  In addition, this capability introduces
 the Freeze command as described in Appendix C.  The rationale for
 these changes is detailed in the following subsections from both the
 technical and network operational aspects.

4.1. Motivation for Swapping Priorities of FS and SF-P

 Defining the priority of FS higher than that of SF-P can result in a
 situation where the protected traffic is taken out of service.  When
 the protection path fails, PSC communication may stop as a result.
 In this case, if any input that is supposed to be signaled to the
 other end has a higher priority than SF-P, then this can result in an

Ryoo, et al. Standards Track [Page 6] RFC 7271 MPLS-TP LP for ITU-T June 2014

 unpredictable protection-switching state.  An example scenario that
 may result in an out-of-service situation is presented in Appendix A
 of this document.
 According to Section 2.4 of [RFC5654], it MUST be possible to operate
 an MPLS-TP network without using a control plane.  This means that
 the PSC communication channel is very important for the transfer of
 external switching commands (e.g., FS), and these commands should not
 rely on the presence of a control plane.  In consequence, the failure
 of the PSC communication channel has higher priority than FS.
 In other transport networks (such as SDH, OTN, and Ethernet transport
 networks), the priority of SF-P has been higher than that of FS.  It
 is therefore important to offer network operators the option of
 having the same behavior in their MPLS-TP networks so that they can
 have the same operational protection-switching behavior to which they
 have become accustomed.  Typically, an FS command is issued before
 network maintenance jobs (e.g., replacing optical cables or other
 network components).  When an operator pulls out a cable on the
 protection path, by mistake, the traffic should continue to be
 protected, and the operator expects this behavior based on his/her
 experience with traditional transport network operations.

4.2. Motivation for Raising the Priority of SFc

 The priority level of SFc defined in [RFC6378] can cause traffic
 disruption when a node that has experienced local signal fails on
 both the working and the protection paths is recovering from these
 failures.
 A sequence diagram highlighting the problem with the priority level
 of SFc as defined in [RFC6378] is presented in Appendix B.

4.3. Motivation for Introducing the Freeze Command

 With the priority swapping between FS and SF-P, the traffic is always
 moved back to the working path when SF-P occurs in Protecting
 Administrative state.  In case network operators need an option to
 control their networks so that the traffic can remain on the
 protection path even when the PSC communication channel is broken,
 the Freeze command can be used.  Freeze is defined to be a "local"
 command that is not signaled to the remote node.  The use of the
 Freeze command is described in Appendix C.

Ryoo, et al. Standards Track [Page 7] RFC 7271 MPLS-TP LP for ITU-T June 2014

4.4. Procedures in Support of Priority Modification

 When the modified priority order specified in this document is in
 use, the list of local requests in order of priority SHALL be as
 follows (from highest to lowest):
 o  Clear Signal Fail
 o  Signal Fail on Protection path
 o  Forced Switch
 o  Signal Fail on Working path
 This requires modification of the PSC Control Logic (including the
 state machine) relative to that described in [RFC6378].  Sections 10
 and 11 present the PSC Control Logic when all capabilities of APS
 mode are enabled.

5. Capability 2: Non-revertive Behavior Modification

 Non-revertive operation of protection switching is defined in
 [RFC4427].  In this operation, the traffic does not return to the
 working path when switch-over requests are terminated.
 However, the PSC protocol defined in [RFC6378] supports this
 operation only when recovering from a defect condition: it does not
 support the non-revertive function when an operator's switch-over
 command, such as FS or Manual Switch (MS), is cleared.  To be aligned
 with the behavior in other transport networks and to be consistent
 with [RFC4427], a node should go into the Do-not-Revert (DNR) state
 not only when a failure condition on the working path is cleared, but
 also when an operator command that requested switch-over is cleared.
 This requires modification to the PSC Control Logic (including the
 state machine) relative to that described in [RFC6378].  Sections 10
 and 11 present the PSC Control Logic when all capabilities of APS
 mode are enabled.

6. Capability 3: Support of the MS-W Command

6.1. Motivation for adding MS-W

 Changing the non-revertive operation as described in Section 5
 introduces the necessity of a new operator command to revert traffic
 to the working path in the DNR state.  When the traffic is on the
 protection path in the DNR state, a Manual Switch to Working (MS-W)
 command is issued to switch the normal traffic back to the working

Ryoo, et al. Standards Track [Page 8] RFC 7271 MPLS-TP LP for ITU-T June 2014

 path.  According to Section 4.3.3.6 (Do-not-Revert State) in
 [RFC6378], "To revert back to the Normal state, the administrator
 SHALL issue a Lockout of protection command followed by a Clear
 command."  However, using the Lockout of protection (LO) command
 introduces the potential risk of an unprotected situation while the
 LO is in effect.
 The "Manual switch-over for recovery LSP/span" command is defined in
 [RFC4427].  Requirement 83 in [RFC5654] states that the external
 commands defined in [RFC4427] MUST be supported.  Since there is no
 support for this external command in [RFC6378], this functionality
 should be added to PSC.  This support is provided by introducing the
 MS-W command.  The MS-W command, as described here, corresponds to
 the "Manual switch-over for recovery LSP/span" command.

6.2. Terminology to Support MS-W

 [RFC6378] uses the term "Manual Switch" and its acronym "MS".  This
 document uses the term "Manual Switch to Protection path" and "MS-P"
 to have the same meaning, while avoiding confusion with "Manual
 Switch to Working path" and its acronym "MS-W".
 Similarly, we modify the name of "Protecting Administrative" state
 (as defined in [RFC6378]) to be "Switching Administrative" state to
 include the case where traffic is switched to the working path as a
 result of the external MS-W command.

6.3. Behavior of MS-P and MS-W

 MS-P and MS-W SHALL have the same priority.  We consider different
 instances of determining the priority of the commands when they are
 received either in succession or simultaneously.
 o  When two commands are received in succession, the command that is
    received after the initial command SHALL be cancelled.
 o  If two nodes simultaneously receive commands that indicate
    opposite operations (i.e., one node receives MS-P and the other
    node receives MS-W) and transmit the indications to the remote
    node, the MS-W SHALL be considered to have a higher priority, and
    the MS-P SHALL be cancelled and discarded.
 Two commands, MS-P and MS-W, are transmitted using the same Request
 field value but SHALL indicate in the Fault Path (FPath) value the
 path from which the traffic is being diverted.  When traffic is
 switched to the protection path, the FPath field value SHALL be set
 to 1, indicating that traffic is being diverted from the working
 path.  When traffic is switched to the working path, the FPath field

Ryoo, et al. Standards Track [Page 9] RFC 7271 MPLS-TP LP for ITU-T June 2014

 value SHALL be set to 0, indicating that traffic is being diverted
 from the protection path.  The Data Path (Path) field SHALL indicate
 where user data traffic is being transported (i.e., if the working
 path is selected, then Path is set to 0; if the protection path is
 selected, then Path is set to 1).
 When an MS command is in effect at a node, any subsequent MS or EXER
 command and any other lower-priority requests SHALL be ignored.

6.4. Equal-Priority Resolution for MS

 [RFC6378] defines only one rule for the equal-priority condition in
 Section 4.3.2 as "The remote message from the far-end LER is assigned
 a priority just below the similar local input."  In order to support
 the Manual Switch behavior described in Section 6.3, additional rules
 for equal-priority resolution are required.  Since the support of
 protection against signal degrade also requires a similar equal-
 priority resolution, the rules are described in Section 7.4.
 Support of this function requires changes to the PSC Control Logic
 (including the state machine) relative to that shown in [RFC6378].
 Sections 10 and 11 present the PSC Control Logic when all
 capabilities of APS mode are enabled.

7. Capability 4: Support of Protection against SD

7.1. Motivation for Supporting Protection against SD

 In the MPLS-TP Survivability Framework [RFC6372], both SF and SD
 fault conditions can be used to trigger protection switching.
 [RFC6378], which defines the protection-switching protocol for
 MPLS-TP, does not specify how the SF and SD are detected, and
 specifies the protection-switching protocol associated with SF only.
 The PSC protocol associated with SD is covered in this document, but
 the specifics for the method of identifying SD is out of scope for
 the protection protocol in the same way that SF detection and MS or
 FS command initiation are out of scope.

7.2. Terminology to Support SD

 In this document, the term Clear Signal Fail or Degrade (SFDc) is
 used to indicate the clearance of either a degraded condition or a
 failure condition.

Ryoo, et al. Standards Track [Page 10] RFC 7271 MPLS-TP LP for ITU-T June 2014

 The second paragraph of Section 4.3.3.2 (Unavailable State) in
 [RFC6378] shows the intention of including Signal Degrade on
 Protection path (SD-P) in the Unavailable state.  Even though the
 protection path can be partially available under the condition of
 SD-P, this document follows the same state grouping as [RFC6378] for
 SD-P.
 The bulleted item on the Protecting Failure state in Section 3.6 of
 [RFC6378] includes the degraded condition in the Protecting Failure
 state.  This document follows the same state grouping as [RFC6378]
 for Signal Degrade on Working path (SD-W).

7.3. Behavior of Protection against SD

 To better align the behavior of MPLS-TP networks with that of other
 transport networks (such as SDH, OTN, and Ethernet transport
 networks), we define the following:
 o  The priorities of SD-P and SD-W SHALL be equal.
 o  Once a switch has been completed due to SD on one path, it will
    not be overridden by SD on the other path (first come, first
    served behavior), to avoid protection switching that cannot
    improve signal quality.
 The SD message indicates that the transmitting node has identified
 degradation of the signal or integrity of the packet received on
 either the working path or the protection path.  The FPath field
 SHALL identify the path that is reporting the degraded condition
 (i.e., if the protection path, then FPath is set to 0; if the working
 path, then FPath is set to 1), and the Path field SHALL indicate
 where the data traffic is being transported (i.e., if the working
 path is selected, then Path is set to 0; if the protection path is
 selected, then Path is set to 1).
 When the SD condition is cleared and the protected domain is
 recovering from the situation, the Wait-to-Restore (WTR) timer SHALL
 be used if the protected domain is configured for revertive behavior.
 The WTR timer SHALL be started at the node that recovers from a local
 degraded condition on the working path.
 Protection switching against SD is always provided by a selector
 bridge duplicating user data traffic and feeding it to both the
 working path and the protection path under SD condition.  When a
 local or remote SD occurs on either the working path or the
 protection path, the node SHALL duplicate user data traffic and SHALL
 feed it to both the working path and the protection path.  The packet
 duplication SHALL continue as long as any SD condition exists in the

Ryoo, et al. Standards Track [Page 11] RFC 7271 MPLS-TP LP for ITU-T June 2014

 protected domain.  When the SD condition is cleared, in revertive
 operation, the packet duplication SHALL continue in the WTR state and
 SHALL stop when the node leaves the WTR state; while in non-revertive
 operation, the packet duplication SHALL stop immediately.
 The selector bridge with the packet duplication under SD condition,
 which is a non-permanent bridge, is considered to be a 1:1 protection
 architecture.
 Protection switching against SD does not introduce any modification
 to the operation of the selector at the sink node described in
 [RFC6378].  The selector chooses either the working or protection
 path from which to receive the normal traffic in both 1:1 and 1+1
 architectures.  The position of the selector, i.e., which path to
 receive the traffic, is determined by the PSC protocol in
 bidirectional switching or by the local input in unidirectional
 switching.

7.4. Equal-Priority Resolution

 In order to support the MS behavior described in Section 6.3 and the
 protection against SD described in Section 7.3, it is necessary to
 expand rules for treating equal-priority inputs.
 For equal-priority local inputs, such as MS and SD, apply a simple
 first-come, first-served rule.  Once a local input is determined as
 the highest priority local input, then a subsequent equal-priority
 local input requesting a different action, i.e., the action results
 in the same PSC Request field but different FPath value, will not be
 presented to the PSC Control Logic as the highest local request.
 Furthermore, in the case of an MS command, the subsequent local MS
 command requesting a different action will be cancelled.
 If a node is in a remote state due to a remote SD (or MS) message, a
 subsequent local input having the same priority but requesting a
 different action to the PSC Control Logic will be considered as
 having lower priority than the remote message and will be ignored.
 For example, if a node is in remote Switching Administrative state
 due to a remote MS-P, then any subsequent local MS-W SHALL be ignored
 and automatically cancelled.  If a node is in remote Unavailable
 state due to a remote SD-P, then any subsequent local SD-W input will
 be ignored.  However, the local SD-W SHALL continue to appear in the
 Local Request Logic as long as the SD condition exists, but it SHALL
 NOT be the top-priority global request, which determines the state
 transition at the PSC Control Logic.

Ryoo, et al. Standards Track [Page 12] RFC 7271 MPLS-TP LP for ITU-T June 2014

 Cases where two end-points of the protected domain simultaneously
 receive local triggers of the same priority that request different
 actions may occur (for example, one node receives SD-P and the other
 receives SD-W).  Subsequently, each node will receive a remote
 message with the opposing action indication.  To address these cases,
 we define the following priority resolution rules:
 o  When MS-W and MS-P occur simultaneously at both nodes, MS-W SHALL
    be considered as having higher priority than MS-P at both nodes.
 o  When SD-W and SD-P occur simultaneously at both nodes, the SD on
    the standby path (the path from which the selector does not select
    the user data traffic) is considered as having higher priority
    than the SD on the active path (the path from which the selector
    selects the user data traffic) regardless of its origin (local or
    remote message).  Therefore, no unnecessary protection switching
    is performed, and the user data traffic continues to be selected
    from the active path.
 In the preceding paragraphs, "simultaneously" refers to the case a
 sent SD (or MS) request has not been confirmed by the remote end in
 bidirectional protection switching.  When a local node that has
 transmitted an SD message receives an SD (or MS) message that
 indicates a different value of Path field from the value of Path
 field in the transmitted SD (or MS) message, both the local and
 remote SD requests are considered to occur simultaneously.
 The addition of support for protection against SD requires
 modification to the PSC Control Logic (including the state machine)
 relative to that described in [RFC6378].  Sections 10 and 11 present
 the PSC Control Logic when all capabilities of APS mode are enabled.

8. Capability 5: Support of EXER Command

 The EXER command is used to verify the correct operation of the PSC
 communication, such as the aliveness of the Local Request Logic, the
 integrity of the PSC Control Logic, the PSC message generation and
 reception mechanism, and the integrity of the protection path.  EXER
 does not trigger any actual traffic switching.
 The command is only relevant for bidirectional protection switching,
 since it is dependent upon receiving a response from the remote node.
 The EXER command is assigned lower priority than any switching
 message.  It may be used regardless of the traffic usage of the
 working path.

Ryoo, et al. Standards Track [Page 13] RFC 7271 MPLS-TP LP for ITU-T June 2014

 When a node receives a remote EXER message, it SHOULD respond with a
 Reverse Request (RR) message with the FPath and Path fields set
 according to the current condition of the node.  The RR message SHALL
 be generated only in response to a remote EXER message.
 This command is documented in R84 of [RFC5654].
 If EXER commands are input at both ends, then a race condition may
 arise.  This is resolved as follows:
 o  If a node has issued EXER and receives EXER before receiving RR,
    it MUST treat the received EXER as it would an RR, and it SHOULD
    NOT respond with RR.
 The following PSC Requests are added to the PSC Request field to
 support the Exercise command (see also Section 14.1):
    (3) Exercise - indicates that the transmitting end-point is
    exercising the protection channel and mechanism.  FPath and Path
    are set to the same value of the No Request (NR), RR, or DNR
    message whose transmission is stopped by EXER.
    (2) Reverse Request - indicates that the transmitting end-point is
    responding to an EXER command from the remote node.  FPath and
    Path are set to the same value of the NR or DNR message whose
    transmission is stopped by RR.
 The relative priorities of EXER and RR are defined in Section 10.2.

9. Capabilities and Modes

9.1. Capabilities

 A Capability is an individual behavior whose use is signaled in a
 Capabilities TLV, which is placed in Optional TLVs field inside the
 PSC message shown in Figure 2 of [RFC6378].  The format of the
 Capabilities TLV is:
 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Type = Capabilities          |    Length                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Value = Flags                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 Figure 1: Format of Capabilities TLV

Ryoo, et al. Standards Track [Page 14] RFC 7271 MPLS-TP LP for ITU-T June 2014

 The value of the Type field is 1.
 The value of the Length field is the length of the Flags field in
 octets.  The length of the Flags field MUST be a multiple of 4 octets
 and MUST be the minimum required to signal all the required
 capabilities.
 Section 4 to Section 8 discuss five capabilities that are signaled
 using the five most significant bits; if a node wishes to signal
 these five capabilities, it MUST send a Flags field of 4 octets.  A
 node would send a Flags field greater than 4 octets only if it had
 more than 32 Capabilities to indicate.  All unused bits MUST be set
 to zero.
 If the bit assigned for an individual capability is set to 1, it
 indicates the sending node's intent to use that capability in the
 protected domain.  If a bit is set to 0, the sending node does not
 intend to use the indicated capability in the protected domain.  Note
 that it is not possible to distinguish between the intent not to use
 a capability and a node's complete non-support (i.e., lack of
 implementation) of a given capability.
 This document defines five specific capabilities that are described
 in Section 4 to Section 8.  Each capability is assigned bit as
 follows:
    0x80000000: priority modification
    0x40000000: non-revertive behavior modification
    0x20000000: support of MS-W command
    0x10000000: support of protection against SD
    0x08000000: support of EXER command
 If all the five capabilities should be used, a node SHALL set the
 Flags field to 0xF8000000.

9.1.1. Sending and Receiving the Capabilities TLV

 A node MUST include its Capabilities TLV in every PSC message that it
 transmits.  The transmission and acceptance of the PSC message is
 described in Section 4.1 of [RFC6378].
 When a node receives a Capabilities TLV, it MUST compare the Flags
 value to its most recent Flags value transmitted by the node.  If the
 two are equal, the protected domain is said to be running in the mode

Ryoo, et al. Standards Track [Page 15] RFC 7271 MPLS-TP LP for ITU-T June 2014

 indicated by that set of capabilities (see Section 9.2).  If the sent
 and received Capabilities TLVs are not equal, this indicates a
 Capabilities TLV mismatch.  When this happens, the node MUST alert
 the operator and MUST NOT perform any protection switching until the
 operator resolves the mismatch between the two end-points.

9.2. Modes

 A mode is a given set of Capabilities.  Modes are shorthand;
 referring to a set of capabilities by their individual values or by
 the name of their mode does not change the protocol behavior.  This
 document defines two modes -- PSC and APS.  Capabilities TLVs with
 other combinations than the one specified by a mode are not supported
 in this specification.

9.2.1. PSC Mode

 PSC mode is defined as the lack of support for any of the additional
 capabilities defined in this document -- that is, a Capabilities set
 of 0x0.  It is the behavior specified in [RFC6378].
 There are two ways to declare PSC mode.  A node can send no
 Capabilities TLV at all since there are no TLV units defined in
 [RFC6378], or it can send a Capabilities TLV with Flags value set to
 0x0.  In order to allow backward compatibility between two end-points
 -- one which supports sending the Capabilities TLV, and one which
 does not, the node that has the ability to send and process the PSC
 mode Capabilities TLV MUST be able to both send the PSC mode
 Capabilities TLV and send no Capabilities TLV at all.  An
 implementation MUST be configurable between these two options.

9.2.2. APS Mode

 APS mode is defined as the use of all the five specific capabilities,
 which are described in Sections 4 to 8 in this document.  APS mode is
 indicated with the Flags value of 0xF8000000.

Ryoo, et al. Standards Track [Page 16] RFC 7271 MPLS-TP LP for ITU-T June 2014

10. PSC Protocol in APS Mode

 This section and the following section define the behavior of the PSC
 protocol when all of the aforementioned capabilities are enabled,
 i.e., APS mode.

10.1. Request Field in PSC Protocol Message

 This document defines two new values for the "Request" field in the
 PSC protocol message that is shown in Figure 2 of [RFC6378] as
 follows:
    (2) Reverse Request
    (3) Exercise
 See also Section 14.1 of this document.

10.2. Priorities of Local Inputs and Remote Requests

 Based on the description in Sections 3 and 4.3.2 in [RFC6378], the
 priorities of multiple outstanding local inputs are evaluated in the
 Local Request Logic, where the highest priority local input (highest
 local request) is determined.  This highest local request is passed
 to the PSC Control Logic that will determine the higher-priority
 input (top-priority global request) between the highest local request
 and the last received remote message.  When a remote message comes to
 the PSC Control Logic, the top-priority global request is determined
 between this remote message and the highest local request that is
 present.  The top-priority global request is used to determine the
 state transition, which is described in Section 11.  In this
 document, in order to simplify the description on the PSC Control
 Logic, we strictly decouple the priority evaluation from the state
 transition table lookup.
 The priorities for both local and remote requests are defined as
 follows from highest to lowest:
 o  Operator Clear (Local only)
 o  Lockout of protection (Local and Remote)
 o  Clear Signal Fail or Degrade (Local only)
 o  Signal Fail on Protection path (Local and Remote)
 o  Forced Switch (Local and Remote)

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 o  Signal Fail on Working path (Local and Remote)
 o  Signal Degrade on either Protection path or Working path (Local
    and Remote)
 o  Manual Switch to either Protection path or Working path (Local and
    Remote)
 o  WTR Timer Expiry (Local only)
 o  WTR (Remote only)
 o  Exercise (Local and Remote)
 o  Reverse Request (Remote only)
 o  Do-Not-Revert (Remote only)
 o  No Request (Remote and Local)
 Note that the "Local only" requests are not transmitted to the remote
 node.  Likewise, the "Remote only" requests do not exist in the Local
 Request Logic as local inputs.  For example, the priority of WTR only
 applies to the received WTR message, which is generated from the
 remote node.  The remote node that is running the WTR timer in the
 WTR state has no local request.
 The remote SF and SD on either the working path or the protection
 path and the remote MS to either the working path or the protection
 path are indicated by the values of the Request and FPath fields in
 the PSC message.
 The remote request from the remote node is assigned a priority just
 below the same local request except for NR and equal-priority
 requests, such as SD and MS.  Since a received NR message needs to be
 used in the state transition table lookup when there is no
 outstanding local request, the remote NR request SHALL have a higher
 priority than the local NR.  For the equal-priority requests, see
 Section 10.2.1.

10.2.1. Equal-Priority Requests

 As stated in Section 10.2, the remote request from the remote node is
 assigned a priority just below the same local request.  However, for
 equal-priority requests, such as SD and MS, the priority SHALL be
 evaluated as described in this section.

Ryoo, et al. Standards Track [Page 18] RFC 7271 MPLS-TP LP for ITU-T June 2014

 For equal-priority local requests, the first-come, first-served rule
 SHALL be applied.  Once a local request appears in the Local Request
 Logic, a subsequent equal-priority local request requesting a
 different action, i.e., the action results in the same Request value
 but a different FPath value, SHALL be considered to have a lower
 priority.  Furthermore, in the case of an MS command, the subsequent
 local MS command requesting a different action SHALL be rejected and
 cleared.
 When the priority is evaluated in the PSC Control Logic between the
 highest local request and a remote request, the following equal-
 priority resolution rules SHALL be applied:
 o  If two requests request the same action, i.e., the same Request
    and FPath values, then the local request SHALL be considered to
    have a higher priority than the remote request.
 o  When the highest local request comes to the PSC Control Logic, if
    the remote request that requests a different action exists, then
    the highest local request SHALL be ignored and the remote request
    SHALL remain to be the top-priority global request.  In the case
    of an MS command, the local MS command requesting a different
    action SHALL be cancelled.
 o  When the remote request comes to the PSC Control Logic, if the
    highest local request that requests a different action exists,
    then the top-priority global request SHALL be determined by the
    following rules:
  • For MS requests, the MS-W request SHALL be considered to have a

higher priority than the MS-P request. The node that has the

       local MS-W request SHALL maintain the local MS-W request as the
       top-priority global request.  The other node that has the local
       MS-P request SHALL cancel the MS-P command and SHALL generate
       "Operator Clear" internally as the top-priority global request.
  • For SD requests, the SD on the standby path (the path from

which the selector does not select the user data traffic) SHALL

       be considered to have a higher priority than the SD on the
       active path (the path from which the selector selects the user
       data traffic) regardless of its origin (local or remote
       message).  The node that has the SD on the standby path SHALL
       maintain the local SD on the standby path request as the top-
       priority global request.  The other node that has local SD on
       the active path SHALL use the remote SD on the standby path as
       the top-priority global request to lookup the state transition

Ryoo, et al. Standards Track [Page 19] RFC 7271 MPLS-TP LP for ITU-T June 2014

       table.  The differentiation of the active and standby paths is
       based upon which path had been selected for the user data
       traffic when each node detected its local SD.

10.3. Acceptance and Retention of Local Inputs

 A local input indicating a defect, such as SF-P, SF-W, SD-P, and
 SD-W, SHALL be accepted and retained persistently in the Local
 Request Logic as long as the defect condition exists.  If there is
 any higher-priority local input than the local defect input, the
 higher-priority local input is passed to the PSC Control Logic as the
 highest local request, but the local defect input cannot be removed
 but remains in the Local Request Logic.  When the higher-priority
 local input is cleared, the local defect will become the highest
 local request if the defect condition still exists.
 The Operator Clear (OC) command, SFDc, and WTR Timer Expiry are not
 persistent.  Once they appear to the Local Request Logic and complete
 all the operations in the protection-switching control, they SHALL
 disappear.
 The LO, FS, MS, and EXER commands SHALL be rejected if there is any
 higher-priority local input in the Local Request Logic.  If a new
 higher-priority local request (including an operator command) is
 accepted, any previous lower-priority local operator command SHALL be
 cancelled.  When any higher-priority remote request is received, a
 lower-priority local operator command SHALL be cancelled.  The
 cancelled operator command is cleared.  If the operators wish to
 renew the cancelled command, then they should reissue the command.

11. State Transition Tables in APS Mode

 When there is a change in the highest local request or in remote PSC
 messages, the top-priority global request SHALL be evaluated, and the
 state transition tables SHALL be looked up in the PSC Control Logic.
 The following rules are applied to the operation related to the state
 transition table lookup.
 o  If the top-priority global request, which determines the state
    transition, is the highest local request, the local state
    transition table in Section 11.1 SHALL be used to decide the next
    state of the node.  Otherwise, the remote state transition table
    in Section 11.2 SHALL be used.
 o  If in remote state, the highest local defect condition (SF-P,
    SF-W, SD-P, or SD-W) SHALL always be reflected in the Request and
    FPath fields.

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 o  For the node currently in the local state, if the top-priority
    global request is changed to OC or SFDc, causing the next state to
    be Normal, WTR, or DNR, then all the local and remote requests
    SHALL be re-evaluated as if the node is in the state specified in
    the footnotes to the state transition tables, before deciding the
    final state.  If there are no active requests, the node enters the
    state specified in the footnotes to the state transition tables.
    This re-evaluation is an internal operation confined within the
    local node, and the PSC messages are generated according to the
    final state.
 o  The WTR timer is started only when the node that has recovered
    from a local failure or degradation enters the WTR state.  A node
    that is entering into the WTR state due to a remote WTR message
    does not start the WTR timer.  The WTR timer SHALL be stopped when
    any local or remote request triggers the state change out of the
    WTR state.
 The extended states, as they appear in the table, are as follows:
 N        Normal state
 UA:LO:L  Unavailable state due to local LO command
 UA:P:L   Unavailable state due to local SF-P
 UA:DP:L  Unavailable state due to local SD-P
 UA:LO:R  Unavailable state due to remote LO message
 UA:P:R   Unavailable state due to remote SF-P message
 UA:DP:R  Unavailable state due to remote SD-P message
 PF:W:L   Protecting Failure state due to local SF-W
 PF:DW:L  Protecting Failure state due to local SD-W
 PF:W:R   Protecting Failure state due to remote SF-W message
 PF:DW:R  Protecting Failure state due to remote SD-W message
 SA:F:L   Switching Administrative state due to local FS command
 SA:MW:L  Switching Administrative state due to local MS-W command
 SA:MP:L  Switching Administrative state due to local MS-P command
 SA:F:R   Switching Administrative state due to remote FS message
 SA:MW:R  Switching Administrative state due to remote MS-W message
 SA:MP:R  Switching Administrative state due to remote MS-P message
 WTR      Wait-to-Restore state
 DNR      Do-not-Revert state
 E::L     Exercise state due to local EXER command
 E::R     Exercise state due to remote EXER message
 Each state corresponds to the transmission of a particular set of
 Request, FPath, and Path fields.  The table below lists the message
 that is generally sent in each particular state.  If the message to
 be sent in a particular state deviates from the table below, it is
 noted in the footnotes of the state transition tables.

Ryoo, et al. Standards Track [Page 21] RFC 7271 MPLS-TP LP for ITU-T June 2014

 State    Request(FPath,Path)
 -------  ------------------------------------
 N        NR(0,0)
 UA:LO:L  LO(0,0)
 UA:P:L   SF(0,0)
 UA:DP:L  SD(0,0)
 UA:LO:R  highest local request(local FPath,0)
 UA:P:R   highest local request(local FPath,0)
 UA:DP:R  highest local request(local FPath,0)
 PF:W:L   SF(1,1)
 PF:DW:L  SD(1,1)
 PF:W:R   highest local request(local FPath,1)
 PF:DW:R  highest local request(local FPath,1)
 SA:F:L   FS(1,1)
 SA:MW:L  MS(0,0)
 SA:MP:L  MS(1,1)
 SA:F:R   highest local request(local FPath,1)
 SA:MW:R  NR(0,0)
 SA:MP:R  NR(0,1)
 WTR      WTR(0,1)
 DNR      DNR(0,1)
 E::L     EXER(0,x), where x is the existing Path value
                     when Exercise command is issued.
 E::R     RR(0,x), where x is the existing Path value
                   when RR message is generated.
 Some operation examples of APS mode are shown in Appendix D.
 In the state transition tables below, the letter 'i' stands for
 "ignore" and is an indication to remain in the current state and
 continue transmitting the current PSC message

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11.1. State Transition by Local Inputs

         | OC  | LO      | SFDc | SF-P   | FS     | SF-W   |
 --------+-----+---------+------+--------+--------+--------+
 N       | i   | UA:LO:L | i    | UA:P:L | SA:F:L | PF:W:L |
 UA:LO:L | (1) | i       | i    | i      | i      | i      |
 UA:P:L  | i   | UA:LO:L | (1)  | i      | i      | i      |
 UA:DP:L | i   | UA:LO:L | (1)  | UA:P:L | SA:F:L | PF:W:L |
 UA:LO:R | i   | UA:LO:L | i    | UA:P:L | i      | PF:W:L |
 UA:P:R  | i   | UA:LO:L | i    | UA:P:L | i      | PF:W:L |
 UA:DP:R | i   | UA:LO:L | i    | UA:P:L | SA:F:L | PF:W:L |
 PF:W:L  | i   | UA:LO:L | (2)  | UA:P:L | SA:F:L | i      |
 PF:DW:L | i   | UA:LO:L | (2)  | UA:P:L | SA:F:L | PF:W:L |
 PF:W:R  | i   | UA:LO:L | i    | UA:P:L | SA:F:L | PF:W:L |
 PF:DW:R | i   | UA:LO:L | i    | UA:P:L | SA:F:L | PF:W:L |
 SA:F:L  | (3) | UA:LO:L | i    | UA:P:L | i      | i      |
 SA:MW:L | (1) | UA:LO:L | i    | UA:P:L | SA:F:L | PF:W:L |
 SA:MP:L | (3) | UA:LO:L | i    | UA:P:L | SA:F:L | PF:W:L |
 SA:F:R  | i   | UA:LO:L | i    | UA:P:L | SA:F:L | PF:W:L |
 SA:MW:R | i   | UA:LO:L | i    | UA:P:L | SA:F:L | PF:W:L |
 SA:MP:R | i   | UA:LO:L | i    | UA:P:L | SA:F:L | PF:W:L |
 WTR     | (4) | UA:LO:L | i    | UA:P:L | SA:F:L | PF:W:L |
 DNR     | i   | UA:LO:L | i    | UA:P:L | SA:F:L | PF:W:L |
 E::L    | (5) | UA:LO:L | i    | UA:P:L | SA:F:L | PF:W:L |
 E::R    | i   | UA:LO:L | i    | UA:P:L | SA:F:L | PF:W:L |

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(Continued)

         | SD-P    | SD-W    | MS-W    | MS-P    | WTRExp | EXER
 --------+---------+---------+---------+---------+--------+------
 N       | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | i      | E::L
 UA:LO:L | i       | i       | i       | i       | i      | i
 UA:P:L  | i       | i       | i       | i       | i      | i
 UA:DP:L | i       | i       | i       | i       | i      | i
 UA:LO:R | UA:DP:L | PF:DW:L | i       | i       | i      | i
 UA:P:R  | UA:DP:L | PF:DW:L | i       | i       | i      | i
 UA:DP:R | UA:DP:L | PF:DW:L | i       | i       | i      | i
 PF:W:L  | i       | i       | i       | i       | i      | i
 PF:DW:L | i       | i       | i       | i       | i      | i
 PF:W:R  | UA:DP:L | PF:DW:L | i       | i       | i      | i
 PF:DW:R | UA:DP:L | PF:DW:L | i       | i       | i      | i
 SA:F:L  | i       | i       | i       | i       | i      | i
 SA:MW:L | UA:DP:L | PF:DW:L | i       | i       | i      | i
 SA:MP:L | UA:DP:L | PF:DW:L | i       | i       | i      | i
 SA:F:R  | UA:DP:L | PF:DW:L | i       | i       | i      | i
 SA:MW:R | UA:DP:L | PF:DW:L | SA:MW:L | i       | i      | i
 SA:MP:R | UA:DP:L | PF:DW:L | i       | SA:MP:L | i      | i
 WTR     | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | (6)    | i
 DNR     | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | i      | E::L
 E::L    | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | i      | i
 E::R    | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | i      | E::L
 NOTES:
 (1)  Re-evaluate to determine the final state as if the node is in
      the Normal state.  If there are no active requests, the node
      enters the Normal State.
 (2)  In the case that both local input after SFDc and the last
      received remote message are NR, the node enters into the WTR
      state when the domain is configured for revertive behavior, or
      the node enters into the DNR state when the domain is configured
      for non-revertive behavior.  In all the other cases, where one
      or more active requests exist, re-evaluate to determine the
      final state as if the node is in the Normal state.
 (3)  Re-evaluate to determine final state as if the node is in the
      Normal state when the domain is configured for revertive
      behavior, or as if the node is in the DNR state when the domain
      is configured for non-revertive behavior.  If there are no
      active requests, the node enters either the Normal state when
      the domain is configured for revertive behavior or the DNR state
      when the domain is configured for non-revertive behavior.

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 (4)  Remain in the WTR state and send an NR(0,1) message.  Stop the
      WTR timer if it is running.  In APS mode, OC can cancel the WTR
      timer and hasten the state transition to the Normal state as in
      other transport networks.
 (5)  If Path value is 0, re-evaluate to determine final state as if
      the node is in the Normal state.  If Path value is 1,
      re-evaluate to determine final state as if the node is in the
      DNR state.  If there are no active requests, the node enters the
      Normal state when Path value is 0, or the DNR state when Path
      value is 1.
 (6)  Remain in the WTR state and send an NR(0,1) message.

11.2. State Transition by Remote Messages

         | LO      | SF-P   | FS     | SF-W   | SD-P    | SD-W    |
 --------+---------+--------+--------+--------+---------+---------+
 N       | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
 UA:LO:L | i       | i      | i      | i      | i       | i       |
 UA:P:L  | UA:LO:R | i      | i      | i      | i       | i       |
 UA:DP:L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | i       | (7)     |
 UA:LO:R | i       | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
 UA:P:R  | UA:LO:R | i      | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
 UA:DP:R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | i       | PF:DW:R |
 PF:W:L  | UA:LO:R | UA:P:R | SA:F:R | i      | i       | i       |
 PF:DW:L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | (8)     | i       |
 PF:W:R  | UA:LO:R | UA:P:R | SA:F:R | i      | UA:DP:R | PF:DW:R |
 PF:DW:R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | i       |
 SA:F:L  | UA:LO:R | UA:P:R | i      | i      | i       | i       |
 SA:MW:L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
 SA:MP:L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
 SA:F:R  | UA:LO:R | UA:P:R | i      | PF:W:R | UA:DP:R | PF:DW:R |
 SA:MW:R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
 SA:MP:R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
 WTR     | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
 DNR     | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
 E::L    | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
 E::R    | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |

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(Continued)

         | MS-W    | MS-P    | WTR | EXER | RR | DNR  | NR
 --------+---------+---------+-----+------+----+------+----
 N       | SA:MW:R | SA:MP:R | i   | E::R | i  | i    | i
 UA:LO:L | i       | i       | i   | i    | i  | i    | i
 UA:P:L  | i       | i       | i   | i    | i  | i    | i
 UA:DP:L | i       | i       | i   | i    | i  | i    | i
 UA:LO:R | SA:MW:R | SA:MP:R | i   | E::R | i  | i    | N
 UA:P:R  | SA:MW:R | SA:MP:R | i   | E::R | i  | i    | N
 UA:DP:R | SA:MW:R | SA:MP:R | i   | E::R | i  | i    | N
 PF:W:L  | i       | i       | i   | i    | i  | i    | i
 PF:DW:L | i       | i       | i   | i    | i  | i    | i
 PF:W:R  | SA:MW:R | SA:MP:R | (9) | E::R | i  | (10) | (11)
 PF:DW:R | SA:MW:R | SA:MP:R | (9) | E::R | i  | (10) | (11)
 SA:F:L  | i       | i       | i   | i    | i  | i    | i
 SA:MW:L | i       | i       | i   | i    | i  | i    | i
 SA:MP:L | i       | i       | i   | i    | i  | i    | i
 SA:F:R  | SA:MW:R | SA:MP:R | i   | E::R | i  | DNR  | N
 SA:MW:R | i       | SA:MP:R | i   | E::R | i  | i    | N
 SA:MP:R | SA:MW:R | i       | i   | E::R | i  | DNR  | N
 WTR     | SA:MW:R | SA:MP:R | i   | i    | i  | i    | (12)
 DNR     | SA:MW:R | SA:MP:R | (13)| E::R | i  | i    | i
 E::L    | SA:MW:R | SA:MP:R | i   | i    | i  | i    | i
 E::R    | SA:MW:R | SA:MP:R | i   | i    | i  | DNR  | N
 NOTES:
 (7)  If the received SD-W message has Path=0, ignore the message.  If
      the received SD-W message has Path=1, go to the PF:DW:R state
      and transmit an SD(0,1) message.
 (8)  If the received SD-P message has Path=1, ignore the message.  If
      the received SD-P message has Path=0, go to the UA:DP:R state
      and transmit an SD(1,0) message.
 (9)  Transition to the WTR state and continue to send the current
      message.
 (10) Transition to the DNR state and continue to send the current
      message.
 (11) If the received NR message has Path=1, transition to the WTR
      state if the domain is configured for revertive behavior, else
      transition to the DNR state.  If the received NR message has
      Path=0, transition to the Normal state.

Ryoo, et al. Standards Track [Page 26] RFC 7271 MPLS-TP LP for ITU-T June 2014

 (12) If the receiving node's WTR timer is running, maintain the
      current state and message.  If the WTR timer is not running,
      transition to the Normal state.
 (13) Transit to the WTR state and send an NR(0,1) message.  The WTR
      timer is not initiated.

11.3. State Transition for 1+1 Unidirectional Protection

 The state transition tables given in Sections 11.1 and 11.2 are for
 bidirectional protection switching, where remote PSC protocol
 messages are used to determine the protection-switching actions.  1+1
 unidirectional protection switching does not require the remote
 information in the PSC protocol message and acts upon local inputs
 only.  The state transition by local inputs in Section 11.1 SHALL be
 reused for 1+1 unidirectional protection under the following
 conditions:
 o  The value of Request field in the received remote message is
    ignored and always assumed to be no request.
 o  Replace footnote (4) with "Stop the WTR timer and transit to the
    Normal state."
 o  Replace footnote (6) with "Transit to the Normal state."
 o  Exercise command is not relevant.

12. Provisioning Mismatch and Protocol Failure in APS Mode

 The remote PSC message that is received from the remote node is
 subject to the detection of provisioning mismatch and protocol
 failure conditions.  In APS mode, provisioning mismatches are handled
 as follows:
 o  If the PSC message is received from the working path due to
    working/protection path configuration mismatch, the node MUST
    alert the operator and MUST NOT perform any protection switching
    until the operator resolves this path configuration mismatch.
 o  In the case that the mismatch happens in the two-bit "Protection
    Type (PT)" field, which indicates permanent/selector bridge type
    and uni/bidirectional switching type:

Ryoo, et al. Standards Track [Page 27] RFC 7271 MPLS-TP LP for ITU-T June 2014

  • If the value of the PT field of one side is 2 (i.e., selector

bridge) and that of the other side is 1 or 3 (i.e., permanent

       bridge), then this event MUST be notified to the operator and
       each node MUST NOT perform any protection switching until the
       operator resolves this bridge type mismatch.
  • If the bridge type matches but the switching type mismatches,

i.e., one side has PT=1 (unidirectional switching) while the

       other side has PT=2 or 3 (bidirectional switching), then the
       node provisioned for bidirectional switching SHOULD fall back
       to unidirectional switching to allow interworking.  The node
       SHOULD notify the operator of this event.
 o  If the "Revertive (R)" bit mismatches, two sides will interwork
    and traffic is protected according to the state transition
    definition given in Section 11.  The node SHOULD notify the
    operator of this event.
 o  If the Capabilities TLV mismatches, the node MUST alert the
    operator and MUST NOT perform any protection switching until the
    operator resolves the mismatch in the Capabilities TLV.
 The following are the protocol failure situations and the actions to
 be taken:
 o  No match in sent "Data Path (Path)" and received "Data Path
    (Path)" for more than 50 ms: The node MAY continue to perform
    protection switching and SHOULD notify the operator of this event.
 o  No PSC message is received on the protection path during at least
    3.5 times the long PSC message interval (e.g., at least 17.5
    seconds with a default message interval of 5 seconds), and there
    is no defect on the protection path: The node MUST alert the
    operator and MUST NOT perform any protection switching until the
    operator resolves this defect.

13. Security Considerations

 This document introduces no new security risks.  [RFC6378] points out
 that MPLS relies on assumptions about the difficulty of traffic
 injection and assumes that the control plane does not have end-to-end
 security.  [RFC5920] describes MPLS security issues and generic
 methods for securing traffic privacy and integrity.  MPLS use should
 conform to such advice.

Ryoo, et al. Standards Track [Page 28] RFC 7271 MPLS-TP LP for ITU-T June 2014

14. IANA Considerations

14.1. MPLS PSC Request Registry

 In the "Generic Associated Channel (G-ACh) Parameters" registry, IANA
 maintains the "MPLS PSC Request Registry".
 IANA has assigned the following two new code points from this
 registry.
    Value Description           Reference
    ----- --------------------- ---------------
     2    Reverse Request       (this document)
     3    Exercise              (this document)

14.2. MPLS PSC TLV Registry

 In the "Generic Associated Channel (G-ACh) Parameters" registry, IANA
 maintains the "MPLS PSC TLV Registry".
 This document defines the following new value for the Capabilities
 TLV type in the "MPLS PSC TLV Registry".
    Value  Description           Reference
    ------ --------------------- ---------------
      1    Capabilities          (this document)

14.3. MPLS PSC Capability Flag Registry

 IANA has created and now maintains a new registry within the "Generic
 Associated Channel (G-ACh) Parameters" registry called "MPLS PSC
 Capability Flag Registry".  All flags within this registry SHALL be
 allocated according to the "Standards Action" procedures as specified
 in RFC 5226 [RFC5226].
 The length of each flag MUST be a multiple of 4 octets.  This
 document defines 4-octet flags.  Flags greater than 4 octets SHALL be
 used only if more than 32 Capabilities need to be defined.  The flags
 defined in this document are:
 Bit  Hex Value  Capability                          Reference
 ---- ---------- ----------------------------------- ---------------
  0   0x80000000 priority modification               (this document)
  1   0x40000000 non-revertive behavior modification (this document)
  2   0x20000000 support of MS-W command             (this document)
  3   0x10000000 support of protection against SD    (this document)
  4   0x08000000 support of EXER command             (this document)
 5-31            Unassigned                          (this document)

Ryoo, et al. Standards Track [Page 29] RFC 7271 MPLS-TP LP for ITU-T June 2014

15. Acknowledgements

 The authors would like to thank Yaacov Weingarten, Yuji Tochio,
 Malcolm Betts, Ross Callon, Qin Wu, and Xian Zhang for their valuable
 comments and suggestions on this document.
 We would also like to acknowledge explicit text provided by Loa
 Andersson and Adrian Farrel.

16. References

16.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            May 2008.
 [RFC5654]  Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N.,
            and S. Ueno, "Requirements of an MPLS Transport Profile",
            RFC 5654, September 2009.
 [RFC6378]  Weingarten, Y., Bryant, S., Osborne, E., Sprecher, N., and
            A. Fulignoli, "MPLS Transport Profile (MPLS-TP) Linear
            Protection", RFC 6378, October 2011.

16.2. Informative References

 [G8031]    International Telecommunication Union, "Ethernet Linear
            Protection Switching", ITU-T Recommendation G.8031/Y.1342,
            June 2011.
 [G841]     International Telecommunication Union, "Types and
            characteristics of SDH network protection architectures",
            ITU-T Recommendation G.841, October 1998.
 [G873.1]   International Telecommunication Union, "Optical Transport
            Network (OTN): Linear protection", ITU-T Recommendation
            G.873.1, July 2011.
 [RFC4427]  Mannie, E. and D. Papadimitriou, "Recovery (Protection and
            Restoration) Terminology for Generalized Multi-Protocol
            Label Switching (GMPLS)", RFC 4427, March 2006.
 [RFC5920]  Fang, L., "Security Framework for MPLS and GMPLS
            Networks", RFC 5920, July 2010.

Ryoo, et al. Standards Track [Page 30] RFC 7271 MPLS-TP LP for ITU-T June 2014

 [RFC6372]  Sprecher, N. and A. Farrel, "MPLS Transport Profile
            (MPLS-TP) Survivability Framework", RFC 6372, September
            2011.

Ryoo, et al. Standards Track [Page 31] RFC 7271 MPLS-TP LP for ITU-T June 2014

Appendix A. An Example of an Out-of-Service Scenario

 The sequence diagram shown is an example of the out-of-service
 scenarios based on the priority level defined in [RFC6378].  The
 first PSC message that differs from the previous PSC message is
 shown.
                     A                  Z
                     |                  |
                 (1) |-- NR(0,0) ------>| (1)
                     |<----- NR(0,0) ---|
                     |                  |
                     |                  |
                     | (FS issued at Z) | (2)
                 (3) |<------ FS(1,1) --|
                     |-- NR(0,1) ------>|
                     |                  |
                     |                  |
                 (4) | (SF on P(A<-Z))  |
                     |                  |
                     |                  |
                     | (Clear FS at Z)  | (5)
                 (6) |   X <- NR(0,0) --|
                     |                  |
                     |                  |
 (1)  Each end is in the Normal state and transmits NR(0,0) messages.
 (2)  When a FS command is issued at node Z, node Z goes into local
      Protecting Administrative state (PA:F:L) and begins transmission
      of an FS(1,1) message.
 (3)  A remote FS message causes node A to go into remote Protecting
      Administrative state (PA:F:R), and node A begins transmitting
      NR(0,1) messages.
 (4)  When node A detects a unidirectional SF-P, node A keeps sending
      an NR(0,1) message because SF-P is ignored under the PA:F:R
      state.
 (5)  When a Clear command is issued at node Z, node Z goes into the
      Normal state and begins transmission of NR(0,0) messages.
 (6)  But, node A cannot receive PSC message because of local
      unidirectional SF-P.  Because no valid PSC message is received
      over a period of several successive message intervals, the last
      valid received message remains applicable, and the node A
      continue to transmit an NR(0,1) message in the PA:F:R state.

Ryoo, et al. Standards Track [Page 32] RFC 7271 MPLS-TP LP for ITU-T June 2014

 Now, there exists a mismatch between the selector and bridge
 positions of node A (transmitting an NR(0,1) message) and node Z
 (transmitting an NR(0,0) message).  It results in an out-of-service
 situation even when there is neither SF-W nor FS.

Appendix B. An Example of a Sequence Diagram Showing the Problem with

           the Priority Level of SFc
 An example of a sequence diagram showing the problem with the
 priority level of SFc defined in [RFC6378] is given below.  The
 following sequence diagram depicts the case when the bidirectional
 signal fails.  However, other cases with unidirectional signal fails
 can result in the same problem.  The first PSC message that differs
 from the previous PSC message is shown.
                     A                  Z
                     |                  |
                 (1) |-- NR(0,0) ------>| (1)
                     |<----- NR(0,0) ---|
                     |                  |
                     |                  |
                 (2) | (SF on P(A<->Z)) | (2)
                     |-- SF(0,0) ------>|
                     |<------ SF(0,0) --|
                     |                  |
                     |                  |
                 (3) | (SF on W(A<->Z)) | (3)
                     |                  |
                     |                  |
                 (4) |   (Clear SF-P)   | (4)
                     |                  |
                     |                  |
                 (5) |   (Clear SF-W)   | (5)
                     |                  |
                     |                  |
 (1)  Each end is in the Normal state and transmits NR(0,0) messages.
 (2)  When SF-P occurs, each node enters into the UA:P:L state and
      transmits SF(0,0) messages.  Traffic remains on the working
      path.
 (3)  When SF-W occurs, each node remains in the UA:P:L state as SF-W
      has a lower priority than SF-P.  Traffic is still on the working
      path.  Traffic cannot be delivered, as both the working path and
      the protection path are experiencing signal fails.

Ryoo, et al. Standards Track [Page 33] RFC 7271 MPLS-TP LP for ITU-T June 2014

 (4)  When SF-P is cleared, the local "Clear SF-P" request cannot be
      presented to the PSC Control Logic, which takes the highest
      local request and runs the PSC state machine, since the priority
      of "Clear SF-P" is lower than that of SF-W.  Consequently, there
      is no change in state, and the selector and/or bridge keep
      pointing at the working path, which has SF condition.
 Now, traffic cannot be delivered while the protection path is
 recovered and available.  It should be noted that the same problem
 will occur in the case that the sequence of SF-P and SF-W events is
 changed.
 If we further continue with this sequence to see what will happen
 after SF-W is cleared:
 (5)  When SF-W is cleared, the local "Clear SF-W" request can be
      passed to the PSC Control Logic, as there is no higher-priority
      local input, but it will be ignored in the PSC Control Logic
      according to the state transition definition in [RFC6378].
      There will be no change in state or protocol message
      transmitted.
 As SF-W is now cleared and the selector and/or bridge are still
 pointing at the working path, traffic delivery is resumed.  However,
 each node is in the UA:P:L state and transmitting SF(0,0) messages,
 while there exists no outstanding request for protection switching.
 Moreover, any future legitimate protection-switching requests, such
 as SF-W, will be rejected as each node thinks the protection path is
 unavailable.

Appendix C. Freeze Command

 The "Freeze" command applies only to the local node of the protection
 group and is not signaled to the remote node.  This command freezes
 the state of the protection group.  Until the Freeze is cleared,
 additional local commands are rejected, and condition changes and
 received PSC information are ignored.
 The "Clear Freeze" command clears the local freeze.  When the Freeze
 command is cleared, the state of the protection group is recomputed
 based on the persistent condition of the local triggers.
 Because the freeze is local, if the freeze is issued at one end only,
 a failure of protocol can occur as the other end is open to accept
 any operator command or a fault condition.

Ryoo, et al. Standards Track [Page 34] RFC 7271 MPLS-TP LP for ITU-T June 2014

Appendix D. Operation Examples of the APS Mode

 The sequence diagrams shown in this section are only a few examples
 of the APS mode operations.  The first PSC protocol message that
 differs from the previous message is shown.  The operation of the
 hold-off timer is omitted.  The Request, FPath, and Path fields whose
 values are changed during PSC message exchange are shown.  For an
 example, SF(1,0) represents a PSC message with the following field
 values: Request=SF, FPath=1, and Path=0.  The values of the other
 fields remain unchanged from the initial configuration.  W(A->Z) and
 P(A->Z) indicate the working path and the protection path in the
 direction of A to Z, respectively.
 Example 1.  1:1 bidirectional protection switching (revertive
 operation) - Unidirectional SF case
                     A                  Z
                     |                  |
                 (1) |<---- NR(0,0)---->| (1)
                     |                  |
                     |                  |
                 (2) | (SF on W(Z->A))  |
                     |---- SF(1,1)----->| (3)
                 (4) |<----- NR(0,1)----|
                     |                  |
                     |                  |
                 (5) |  (Clear SF-W)    |
                     |---- WTR(0,1)---->|
                    /|                  |
                   | |                  |
           WTR timer |                  |
                   | |                  |
                    \|                  |
                 (6) |---- NR(0,1)----->| (7)
                 (8) |<----- NR(0,0)----|
                     |---- NR(0,0)----->| (9)
                     |                  |
 (1)  The protected domain is operating without any defect, and the
      working path is used for delivering the traffic in the Normal
      state.
 (2)  SF-W occurs in the Z to A direction.  Node A enters into the
      PF:W:L state and generates an SF(1,1) message.  Both the
      selector and bridge of node A are pointing at the protection
      path.

Ryoo, et al. Standards Track [Page 35] RFC 7271 MPLS-TP LP for ITU-T June 2014

 (3)  Upon receiving an SF(1,1) message, node Z sets both the selector
      and bridge to the protection path.  As there is no local request
      in node Z, node Z generates an NR(0,1) message in the PF:W:R
      state.
 (4)  Node A confirms that the remote node is also selecting the
      protection path.
 (5)  Node A detects clearing of SF condition, starts the WTR timer,
      and sends a WTR(0,1) message in the WTR state.
 (6)  Upon expiration of the WTR timer, node A sets both the selector
      and bridge to the working path and sends an NR(0,1) message.
 (7)  Node Z is notified that the remote request has been cleared.
      Node Z transits to the Normal state and sends an NR(0,0)
      message.
 (8)  Upon receiving an NR(0,0) message, node A transits to the Normal
      state and sends an NR(0,0) message.
 (9)  It is confirmed that the remote node is also selecting the
      working path.

Ryoo, et al. Standards Track [Page 36] RFC 7271 MPLS-TP LP for ITU-T June 2014

 Example 2.  1:1 bidirectional protection switching (revertive
 operation) - Bidirectional SF case - Inconsistent WTR timers
                     A                  Z
                     |                  |
                 (1) |<---- NR(0,0)---->| (1)
                     |                  |
                     |                  |
                 (2) | (SF on W(A<->Z)) | (2)
                     |<---- SF(1,1)---->|
                     |                  |
                     |                  |
                 (3) |   (Clear SF-W)   | (3)
                     |<---- NR(0,1)---->|
                 (4) |<--- WTR(0,1) --->| (4)
                    /|                  |\
                   | |                  | |
           WTR timer |                  | WTR timer
                   | |                  | |
                   | |                  |/
                   | |<------ NR(0,1)---| (5)
                   | |                  |
                    \|                  |
                 (6) |--- NR(0,1)------>|
                     |<------ NR(0,0)---| (7)
                 (8) |--- NR(0,0)------>|
                     |                  |
 (1)  Each end is in the Normal state and transmits NR(0,0) messages.
 (2)  When SF-W occurs, each node enters into the PF:W:L state and
      transmits SF(1,1) messages.  Traffic is switched to the
      protection path.  Upon receiving an SF(1,1) message, each node
      confirms that the remote node is also sending and receiving the
      traffic from the protection path.
 (3)  When SF-W is cleared, each node transits to the PF:W:R state and
      transmits NR(0,1) messages as the last received message is SF-W.
 (4)  Upon receiving NR(0,1) messages, each node goes into the WTR
      state, starts the WTR timer, and sends the WTR(0,1) messages.
 (5)  Upon expiration of the WTR timer in node Z, node Z sends an
      NR(0,1) message as the last received APS message was WTR.  When
      the NR(0,1) message arrives at node A, node A maintains the WTR
      state and keeps sending current WTR messages as described in the
      state transition table.

Ryoo, et al. Standards Track [Page 37] RFC 7271 MPLS-TP LP for ITU-T June 2014

 (6)  Upon expiration of the WTR timer in node A, node A sends an
      NR(0,1) message.
 (7)  When the NR(0,1) message arrives at node Z, node Z moves to the
      Normal state, sets both the selector and bridge to the working
      path, and sends an NR(0,0) message.
 (8)  The received NR(0,0) message causes node A to go to the Normal
      state.  Now, the traffic is switched back to the working path.
 Example 3.  1:1 bidirectional protection switching - R bit mismatch
 This example shows that both sides will interwork and the traffic is
 protected when one side (node A) is configured as revertive operation
 and the other (node Z) is configured as non-revertive operation.  The
 interworking is covered in the state transition tables.
         (revertive) A                  Z (non-revertive)
                     |                  |
                 (1) |<---- NR(0,0)---->| (1)
                     |                  |
                     |                  |
                 (2) | (SF on W(A<->Z)) | (2)
                     |<---- SF(1,1)---->|
                     |                  |
                     |                  |
                 (3) |   (Clear SF-W)   | (3)
                     |<---- NR(0,1)---->|
                 (4) |<----- DNR(0,1)---| (4)
                    /|-- WTR(0,1)------>|
                   | |<----- NR(0,1)----| (5)
                   | |                  |
           WTR timer |                  |
                   | |                  |
                   | |                  |
                    \|                  |
                 (6) |--- NR(0,1)------>|
                     |<------ NR(0,0)---| (7)
                 (8) |--- NR(0,0)------>|
                     |                  |
 (1)  Each end is in the Normal state and transmits NR(0,0) messages.
 (2)  When SF-W occurs, each node enters into the PF:W:L state and
      transmits SF(l,l) messages.  Traffic is switched to the
      protection path.  Upon receiving an SF(1,1) message, each node
      confirms that the remote node is also sending and receiving the
      traffic on the protection path.

Ryoo, et al. Standards Track [Page 38] RFC 7271 MPLS-TP LP for ITU-T June 2014

 (3)  When SF-W is cleared, each node transits to the PF:W:R state and
      transmits NR(0,1) messages as the last received message is SF-W.
 (4)  Upon receiving NR(0,1) messages, node A goes into the WTR state,
      starts the WTR timer, and sends WTR(0,1) messages.  At the same
      time, node Z transits to the DNR state and sends a DNR(0,1)
      message.
 (5)  When the WTR message arrives at node Z, node Z transits to the
      WTR state and sends an NR(0,1) message according to the state
      transition table.  At the same time, the DNR message arrived at
      node Z is ignored according to the state transition table.
      Therefore, node Z, which is configured as non-revertive
      operation, is operating as if in revertive operation.
 (6)  Upon expiration of the WTR timer in node A, node A sends an
      NR(0,1) message.
 (7)  When the NR(0,1) message arrives at node Z, node Z moves to the
      Normal state, sets both the selector and bridge to the working
      path, and sends an NR(0,0) message.
 (8)  The received NR(0,0) message causes node A to transit to the
      Normal state.  Now, the traffic is switched back to the working
      path.

Ryoo, et al. Standards Track [Page 39] RFC 7271 MPLS-TP LP for ITU-T June 2014

Authors' Addresses

 Jeong-dong Ryoo (editor)
 ETRI
 218 Gajeongno
 Yuseong-gu, Daejeon  305-700
 South Korea
 Phone: +82-42-860-5384
 EMail: ryoo@etri.re.kr
 Eric Gray (editor)
 Ericsson
 EMail: eric.gray@ericsson.com
 Huub van Helvoort
 Huawei Technologies
 Karspeldreef 4,
 Amsterdam 1101 CJ
 The Netherlands
 Phone: +31 20 4300936
 EMail: huub.van.helvoort@huawei.com
 Alessandro D'Alessandro
 Telecom Italia
 via Reiss Romoli, 274
 Torino  10148
 Italy
 Phone: +39 011 2285887
 EMail: alessandro.dalessandro@telecomitalia.it
 Taesik Cheung
 ETRI
 218 Gajeongno
 Yuseong-gu, Daejeon  305-700
 South Korea
 Phone: +82-42-860-5646
 EMail: cts@etri.re.kr
 Eric Osborne
 EMail: eric.osborne@notcom.com

Ryoo, et al. Standards Track [Page 40]

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