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Versions: 00 01 draft-ryoogray-mpls-tp-psc-itu

MPLS Working Group                                               J. Ryoo
Internet-Draft                                                      ETRI
Intended status: Standards Track                         H. van Helvoort
Expires: March 15, 2014                              Huawei Technologies
                                                         A. D'Alessandro
                                                          Telecom Italia
                                                      September 11, 2013


           Supporting Signal Degrade in PSC Linear Protection
                    draft-rhd-mpls-tp-psc-sd-01.txt

Abstract

   This document optionally updates [RFC6378], "MPLS Transport Profile
   (MPLS-TP) Linear Protection", to support protection against signal
   degrade (SD) in an effort to satisfy the ITU-T's protection switching
   requirements.

Status of This Memo

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

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

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

   This Internet-Draft will expire on March 15, 2014.

Copyright Notice

   Copyright (c) 2013 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



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   3.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Operation of Protection Switching against Signal Degrade  . .   3
   5.  Updates to the PSC RFC  . . . . . . . . . . . . . . . . . . .   4
     5.1.  Updates to Section 3.1. Local Request Logic . . . . . . .   4
     5.2.  Updates to Section 3.5. Wait-to-Restore (WTR) Timer . . .   5
     5.3.  Updates to Section 3.6. PSC Control States  . . . . . . .   5
     5.4.  Updates to Section 4.2.2. PSC Request Field . . . . . . .   5
     5.5.  Updates to Section 4.2.3. Protection Type (PT) Field  . .   6
     5.6.  Updates to Section 4.2.6. Data Path (Path) Field  . . . .   6
     5.7.  Updates to Section 4.3.2. Priority of Inputs  . . . . . .   7
     5.8.  Updates to Section 4.3.3.1 Normal State . . . . . . . . .   9
     5.9.  Updates to Section 4.3.3.2 Unavailable State  . . . . . .  10
     5.10. Updates to Section 4.3.3.3 Protecting Administrative
           State . . . . . . . . . . . . . . . . . . . . . . . . . .  15
     5.11. Updates to Section 4.3.3.4 Protecting Failure State . . .  16
     5.12. Updates to Section 4.3.3.5 Wait-to-Restore State  . . . .  19
     5.13. Updates to Section 4.3.3.6 Do-not-Revert State  . . . . .  20
     5.14. Updates to Appendix A. PSC State Machine Tables . . . . .  21
   6.  Security considerations . . . . . . . . . . . . . . . . . . .  25
   7.  IANA considerations . . . . . . . . . . . . . . . . . . . . .  26
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  26
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  26
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  26
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   This document optionally updates [RFC6378], "MPLS Transport Profile
   (MPLS-TP) Linear Protection", to support protection against signal
   degrade in an effort to satisfy the ITU-T's protection switching
   requirements shown in the ITU-T's liaison statements [LIAISON1205]
   and [LIAISON1234].  In MPLS-TP survivability framework [RFC6372],
   fault conditions include both Signal Fail (SF) and Signal Degrade
   (SD) that can be used to trigger protection switching.

   [RFC6378], which defines the Protection State Coordination (PSC)
   protocol, does not specify how the SF and SD are declared and
   specifies the protection switching protocol associated with SF only.





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   This document is intended to cover the protection switching protocol
   associated with SD, and the specifics for the method of identifying
   SD is out of the scope of this document similarly to SF for
   [RFC6378].  The updates specified in this document do not require any
   changes to the protocol's packet format.

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 [RFC2119].

3.  Acronyms

   This draft uses the following acronyms:

   FS      Forced Switch
   LO      Lockout of protection
   MS      Manual Switch
   MPLS-TP Transport Profile for MPLS
   PSC     Protection State Coordination
   SD      Signal Degrade
   SD-P    Signal Degrade on the Protection path
   SD-W    Signal Degrade on the Working path
   SF      Signal Fail
   SF-P    Signal Fail on the Protection path
   SF-W    Signal Fail on the Working path
   SFc     Clear Signal Fail


4.  Operation of Protection Switching against Signal Degrade

   In order to maintain the network operation behavior to which
   transport network operators have become accustomed, the priorities of
   SD-P and SD-W are defined to be equal as in other transport networks,
   such as OTN and Ethernet.  Once a switch has been completed due to
   signal degrade on one path, it will not be overridden by signal
   degrade on the other path (first come, first served behavior), to
   avoid protection switching that cannot improve signal quality and
   flapping.











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   When multiple SDs are detected simultaneously, either as local or
   remote requests on both working and protection paths, 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).  Therefore, no unnecessary protection switching
   is performed and the user data traffic continues to be selected from
   the active path.

   In the preceding paragraph, "simultaneously" relates to the
   occurrence of SD on both the active and standby paths at input to the
   PSC Protection State Control Logic at the same time, or as long as a
   SD request has not been acknowledged by the remote end in
   bidirectional protection switching.  In other words, when a local
   node that has transmitted a SD message receives a SD message that
   indicates a different value of data path (Path) field than the value
   of the Path field in the transmitted SD message, both the local and
   the remote SD requests are considered to occur simultaneously.

5.  Updates to the PSC RFC

   This section describes the changes required to support protection
   against SD in the PSC protocol defined in [RFC6378]

5.1.  Updates to Section 3.1.  Local Request Logic

   Replace the following two bullet item text:

   o  Signal Degrade (SD) - if any of the server-layer, control-plane,
      or OAM indications signaled a degraded transmission condition on
      either the protection path or one of the working paths.  The
      determination and actions for SD are for further study and may
      appear in a separate document.  All references to SD input are
      placeholders for this extension.

   o  Clear Signal Fail (SFc) - if all of the server-layer,
      controlplane, or OAM indications are no longer indicating a
      failure condition on a path that was previously indicating a
      failure condition.

   With:

   o  Signal Degrade (SD) - if any of the server-layer, control-plane,
      or OAM indications signaled a degraded transmission condition on
      either the protection path or one of the working paths.

   o  Clear Signal Fail (SFc) - if all of the server-layer,
      controlplane, or OAM indications are no longer indicating a



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      failure/degradation condition on a path that was previously
      indicating a failure/degradation condition.

5.2.  Updates to Section 3.5.  Wait-to-Restore (WTR) Timer

   Replace the following text in the first paragraph:

      The WTR timer is used to delay reversion to Normal state when
      recovering from a failure condition on the working path and the
      protection domain is configured for revertive behavior.

   With:

      The WTR timer is used to delay reversion to Normal state when the
      protection domain is configured for revertive behavior and
      recovering from a failure or a degradation condition on the
      working path.

5.3.  Updates to Section 3.6.  PSC Control States

   The second paragraph of Section 4.3.3.2 Unavailable State in
   [RFC6378] shows the intention of including the signal degrade on the
   protection in the Unavailable state.  Even though the protection path
   can be partially available under the condition of the signal degrade
   on the protection path, this document follows the same state grouping
   as [RFC6378] for SD on the protection.

   Replace the following bullet item text:

   o  Unavailable state - The protection path is unavailable -- either
      as a result of an operator Lockout command or a failure condition
      detected on the protection path.

   With:

   o  Unavailable state - The protection path is unavailable -- either
      as a result of an operator Lockout command or a failure/
      degradation condition detected on the protection path.

5.4.  Updates to Section 4.2.2.  PSC Request Field

   Replace the following bullet item text:

   o  (7) Signal Degrade - indicates that the transmitting end point has
      identified a degradation of the signal, or integrity of the packet
      transmission on either the working or protection path.  This
      request is presented here only as a placeholder.  The specifics
      for the method of identifying this degradation is out of scope for



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      this document.  The details of the actions to be taken for this
      situation are left for future specification.

   With:

   o  (7) Signal Degrade - indicates that the transmitting end point has
      identified a degradation of the signal, or integrity of the packet
      transmission on either the working or protection path.  The FPath
      field SHALL identify the path that is reporting the degrade
      condition (i.e., if protection path, then FPath is set to 0; if
      working path, then FPath is set to 1), and the Path field SHALL
      indicate where the data traffic is being transported (i.e., if
      working path is selected, then Path is set to 0; if protection
      path is selected, then Path is set to 1).

5.5.  Updates to Section 4.2.3.  Protection Type (PT) Field

   Add the following text at the end of Section 4.2.3:

      If the detection of a SD depends on the presence of user data
      packets, such a condition declared on the working path is cleared
      following protection switching to the protection path if a
      selector bridge is used, possibly resulting in flapping.  To avoid
      flapping, the selector bridge should duplicate the user data
      traffic and feed it to both working and protection paths under SD
      condition.

5.6.  Updates to Section 4.2.6.  Data Path (Path) Field

   Replace the following bullet item text:

   o  0: indicates that the protection path is not transporting user
      data traffic (in 1:n architecture) or transporting redundant user
      data traffic (in 1+1 architecture).

   With:

   o  0: indicates that the protection path is not transporting user
      data traffic (in 1:n architecture) or transporting redundant user
      data traffic (in 1+1 architecture or under SD condition in 1:n
      architecture when the detection of a SD depends on the presence of
      user data packets)









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5.7.  Updates to Section 4.3.2.  Priority of Inputs

   Replace the following bullet item text:

   o  Signal Degrade on working (OAM / control-plane / server
      indication)

   With:

   o  Signal Degrade on either working or protection (OAM / control-
      plane / server indication)

   Replace the following two paragraphs:

      As was noted above, the Local Request logic SHALL always select
      the local input indicator with the highest priority as the current
      local request, i.e., only the highest priority local input will be
      used to affect the control logic.  All local inputs with lower
      priority than this current local request will be ignored.

      The remote message from the far-end LER is assigned a priority
      just below the similar local input.  For example, a remote Forced
      Switch would have a priority just below a local Forced Switch but
      above a local Signal Fail on protection input.  As mentioned in
      Section 3.6.1, the state transition is determined by the higher
      priority input between the highest priority local input and the
      remote message.  This also determines the classification of the
      state as local or remote.  The following subsections detail the
      transition based on the current state and the higher priority of
      these two inputs.

   With:

      As was noted above, the Local Request logic SHALL always select
      the local input indicator with the highest priority as the current
      local request, i.e., only the highest priority local input will be
      used to affect the control logic.  All local inputs with lower
      priority than this current local request will be ignored.  For
      local inputs with same priority, first-come, first-served rule is
      applied.  For example, once SD-P (or SD-W) local input is
      determined as the highest priority local input, then subsequent
      SD-W (or SD-P) local input will not be presented to the PSC
      Control logic as the highest local request.

      The remote message from the far-end LER is assigned a priority
      just below the same local input.  For example, a remote Forced
      Switch would have a priority just below a local Forced Switch but
      above a local Signal Fail on protection input.



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      However, if the LER is in a remote state due to a remote message,
      a subsequent local input having the same priority but requesting
      different action to the control logic, will be considered as
      having lower priority than the remote message, and will be
      ignored.  For example, if the LER is in remote Unavailable state
      due to a remote SD-P, then subsequent local SD-W input will be
      ignored.

      It should be noted that there is a reverse case where one LER
      receives a local input and the other LER receives, simultaneously,
      a local input with the same priority but requesting different
      action.  In this case, each of the two LERs receives a subsequent
      remote message having the same priority but requesting different
      action, while the LER is in a local state due to the local input.
      In this case, a priority must be set for the inputs with the same
      priority regardless of its origin (local input or remote message).
      For example, one LER receives SD-P as a local input and the other
      LER receives SP-W as a local input, simultaneously.  In this case,
      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.  Giving the higher priority to the
      SD on the standby path SHALL also be applied to the Local Request
      logic when two SDs for different paths happen to be presented to
      the Local Request logic exactly at the same time.

      In order to resolve the equal priority conditions described above,
      following rules are defined:

      (a)  If two local inputs having same priority but requesting
            different action come to the Local Request logic, then the
            input coming first SHALL be considered to have a higher
            priority than the other coming later (first-come, first-
            served).

      (b)  If the LER receives both a local input and a remote message
            with the same priority and requesting the same action, i.e.,
            the same PSC Request Field and the same FPath value, then
            the local input SHALL be considered to have a higher
            priority than the remote message.

      (c)  If the LER receives both a local input and a remote message
            with the same priority but requesting different actions,
            i.e., the same PSC Request Field but different FPath value,
            then the first-come, first-served rule SHALL be applied.  If



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            the remote message comes first, then the state SHALL be a
            remote state and subsequent local input is ignored.
            However, if the local input comes first, the first-come,
            first-served rule cannot be applied and must be viewed as
            simultaneous condition.  This is because the subsequent
            remote message will not be an acknowledge of the local input
            by the far-end node.  In this case, the priority SHALL be
            determined by rules for each simultaneous conditions.

      (d)  If the LER receives both SD-P and SD-W request either as
            local input or remote message and the LER is in a local
            state, then 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).  This rule of giving the higher priority to the SD
            on the standby path SHALL also be applied to the Local
            Request logic when two SDs for different paths happen to be
            presented to the Local Request logic exactly at the same
            time

      As mentioned in Section 3.6.1, the state transition is determined
      by the higher priority input between the highest priority local
      input and the remote message.  This also determines the
      classification of the state as local or remote.  The following
      subsections detail the transition based on the current state and
      the higher priority of these two inputs.

5.8.  Updates to Section 4.3.3.1 Normal State

   Add the following bullet item text to the transitions in reaction to
   a local input to the LER:

   o  A local Signal Degrade indication on the protection path (SD-P)
      SHALL cause the LER to go into local Unavailable state and begin
      transmission of an SD(0,0) message.

   o  A local Signal Degrade indication on the working path (SD-W) SHALL
      cause the LER to go into local Protecting failure state and begin
      transmission of an SD(1,1) message.

   Add the following bullet item text to the transitions in reaction to
   a remote message:

   o  A remote SD-P message SHALL cause the LER (LER-A) to go into
      remote Unavailable state, while continuing to transmit the NR(0,0)
      message.



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   o  A remote SD-W message SHALL cause the LER to go into remote
      Protecting failure state, and transmit an NR(0,1) message.

5.9.  Updates to Section 4.3.3.2 Unavailable State

   The second paragraph of Section 4.3.3.2 Unavailable State in
   [RFC6378] shows the intention of including the signal degrade on the
   protection in the Unavailable state.  This document follows the same
   state grouping as [RFC6378] for SD-P, even though the protection path
   can be partially available under the condition of the signal degrade
   on the protection path.

   Replace the following text in the first paragraph of Section 4.3.3.2
   Unavailable State for further clarification on SD on the protection
   path:

      When the protection path is unavailable -- either as a result of a
      Lockout operator command, or as a result of a SF detected on the
      protection path -- then the protection domain is in the
      Unavailable state.

   With:

      When the protection path is unavailable -- either as a result of a
      Lockout operator command, or as a result of a SF/SD detected on
      the protection path -- then the protection domain is in the
      Unavailable state.

      When an LER is in this state due to degradation condition, the
      user traffic should be duplicated and fed to both working and
      protection paths if the detection of a SD depends on the presence
      of user data packets.

   Replace the following bullet item text in the transitions in reaction
   to a local input:

   o  A local Forced Switch SHALL be ignored by the PSC Control logic
      when in Unavailable state as a result of a (local or remote)
      Lockout of protection.  If in Unavailable state due to an SF on
      protection, then the FS SHALL cause the LER to go into local
      Protecting administrative state and begin transmitting an FS(1,1)
      message.  It should be noted that due to the unavailability of the
      protection path (i.e., due to the SF condition) that this FS may
      not be received by the far-end until the SF condition is cleared.

   With:





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   o  A local Forced Switch SHALL be ignored by the PSC Control logic
      when in Unavailable state as a result of a (local or remote)
      Lockout of protection.  If in Unavailable state due to an SF/SD on
      protection, then the FS SHALL cause the LER to go into local
      Protecting administrative state and begin transmitting an FS(1,1)
      message.  It should be noted that due to the unavailability of the
      protection path (i.e., due to the SF condition) that this FS may
      not be received by the far-end until the SF condition is cleared.

   Replace the following bullet item text in the transitions in reaction
   to a local input:

   o  A local Signal Fail on the protection path input when in local
      Unavailable state (by implication, this is due to a local SF on
      protection) SHALL cause the LER to remain in local Unavailable
      state and transmit an SF(0,0) message.

   With:

   o  A local Signal Fail on the protection path input when in local
      Unavailable state SHALL cause the LER to remain in local
      Unavailable state and transmit an SF(0,0) message.

   Replace the following bullet item text in the transitions in reaction
   to a local input:

   o  A local Signal Fail on the working path input when in remote
      Unavailable state SHALL cause the LER to remain in remote
      Unavailable state and transmit an SF(1,0) message.

   With:

   o  A local Signal Fail on the working path input when in local or
      remote Unavailable state due to SD-P SHALL cause the LER to go to
      local Protecting failure state.  If the LER is in remote
      Unavailable state due to SF-P or Lockout of protection, the LER
      SHALL remain in remote Unavailable state and transmit an SF(1,0)
      message.

   Add the following bullet item text to the transitions in reaction to
   a local input:










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   o  A local Clear SD of the protection path in local Unavailable state
      that is due to an SD on the protection path SHALL cause the LER to
      go to Normal state.  If the LER is in remote Unavailable state but
      has an active local SD condition, then the local Clear SD SHALL
      clear the SD local condition and the LER SHALL remain in remote
      Unavailable state and begin transmitting NR(0,0) messages.  In all
      other cases, the local Clear SD SHALL be ignored.

   o  A local SD-P input when in local Unavailable state (by
      implication, this is due to a local SD on protection) SHALL cause
      the LER to remain in local Unavailable state and transmit an
      SD(0,0) message.  When in remote Unavailable state due to LO or
      SF-P, the LER SHALL remain in remote unavailable state and begin
      transmitting SD(0,0) messages.  When in remote Unavailable state
      due to SD-P, the LER SHALL enter to local Unavailable state and
      begin transmitting SD(0,0) messages.

   o  A local SD-W input when in remote Unavailable state SHALL cause
      the LER to remain in remote Unavailable state and transmit an
      SD(1,0) message.

   Replace the following bullet item text in the transitions in reaction
   to a remote message:

   o  A remote Lockout of protection message SHALL cause the LER to
      remain in Unavailable state (note that if the LER was previously
      in local Unavailable state due to a Signal Fail on the protection
      path, then it will now be in remote Unavailable state) and
      continue transmission of the current message (either NR(0,0) or
      LO(0,0) or SF(0,0)).

   With:

   o  A remote Lockout of protection message SHALL cause the LER to
      remain in Unavailable state (note that if the LER was previously
      in local Unavailable state due to a Signal Fail on the protection
      path or a Signal Degrade on the protection path, then it will now
      be in remote Unavailable state) and continue transmission of the
      current message (either NR(0,0) or LO(0,0) or SF(0,0) or SF(1,0)
      or SD(0,0) or SD(1,0)).

   Replace the following bullet item text in the transitions in reaction
   to a remote message:

   o  A remote Forced Switch message SHALL be ignored by the PSC Control
      logic when in Unavailable state as a result of a (local or remote)
      Lockout of protection.  If in Unavailable state due to a local or
      remote SF on protection, then the FS SHALL cause the LER to go



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      into remote Protecting administrative state; if in Unavailable
      state due to local SF, begin transmitting an SF(0,1) message.

   With:

   o  A remote Forced Switch message SHALL be ignored by the PSC Control
      logic when in Unavailable state as a result of a local Lockout of
      protection.  If in Unavailable state due to a remote Lockout of
      protection, the LER SHALL go to remote Protecting Administrative
      state and begin transmitting a message reflecting its local input
      with Path=1.  If in Unavailable state due to a local or remote
      SF-P/SD-P, then the FS SHALL cause the LER to go into remote
      Protecting administrative state; if in Unavailable state due to
      local SF-P and SD-P, begin transmitting an SF(0,1) and SD(0,1)
      message, respectively.

   Replace the following bullet item text in the transitions in reaction
   to a remote message:

   o  A remote Signal Fail message that indicates that the failure is on
      the protection path SHALL cause the LER to remain in Unavailable
      state and continue transmission of the current message (either
      NR(0,0) or SF(0,0) or LO(0,0)).

   With:

   o  A remote Signal Fail message that indicates that the failure is on
      the protection path SHALL cause the LER to remain in Unavailable
      state and continue transmission of the current message (either
      NR(0,0) or LO(0,0) or SF(0,0) or SF(1,0) or SD(0,0) or SD(1,0)

   Replace the following bullet item text in the transitions in reaction
   to a remote message:

   o  A remote No Request, when the LER is in remote Unavailable state
      and there is no active local Signal Fail SHALL cause the LER to go
      into Normal state and continue transmission of the current
      message.  If there is a local Signal Fail on the protection path,
      the LER SHALL remain in local Unavailable state and transmit an
      SF(0,0) message.  If there is a local Signal Fail on the working
      path, the LER SHALL go into local Protecting Failure state and
      transmit an SF(1,1) message.  When in local Unavailable state, the
      remote message SHALL be ignored.

   With:

   o  A remote No Request, when the LER is in remote Unavailable state
      and there is no active local Signal Fail or Signal Degrade SHALL



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      cause the LER to go into Normal state and continue transmission of
      the current message.  If there is a local Signal Fail on the
      protection path, the LER SHALL remain in local Unavailable state
      and transmit an SF(0,0) message.  If there is a local Signal Fail
      on the working path, the LER SHALL go into local Protecting
      Failure state and transmit an SF(1,1) message.  If there is a
      local Signal Degrade on the protection path, the LER SHALL remain
      in local Unavailable state and transmit an SD(0,0) message.  If
      there is a local Signal Degrade on the working path, the LER SHALL
      go into local Protecting Failure state and transmit an SD(1,1)
      message.  When in local Unavailable state, the remote message
      SHALL be ignored.

   Add the following bullet item text to the transitions in reaction to
   a remote message:

   o  A remote SF-W message SHALL be ignored if the LER is in local
      Unavailable state due to LO or SF-P.  When in local Unavailable
      state due to SD-P, the LER SHALL enter to remote Protecting
      Failure state and begin transmitting SD(0,1) messages.  If the LER
      is in remote Unavailable state, then the SF-W message and the
      local input are reevaluated as if the LER is in the Normal state.
      In the case that the LER is in remote Unavailable state due to
      remote SD-P, the reevaluation will cause the LER to enter remote
      Protecting Failure state and continue to send the current messages
      with Path=1.

   o  A remote MS message SHALL be ignored if the LER is in local
      Unavailable state.  If the LER is in remote Unavailable state,
      then the MS message and the local input are reevaluated as if the
      LER is in the Normal state.

   o  A remote SD-P message shall be ignored if the LER is in local
      Unavailable state.  If the LER is in remote Unavailable state due
      to LO or SF-P, then the SD-P message and the local input are
      reevaluated as if the LER is in the Normal state.  If the LER is
      in remote Unavailable state due to SD-P, then the remote SD-P
      message will be ignored













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   o  A remote SD-W message shall be reevaluated with the local input as
      if the LER is in the Normal state, A remote SD-W message shall be
      ignored if the LER is in local Unavailable state due to LO or
      SF-P.  When in local Unavailable state due to SD-P, the LER shall
      examine the Path value in the remote SD-W message.  If the Path
      value of the received SD-W message is the same as the Path value
      that the LER indicates in its current outgoing PSC message, then
      the LER shall ignore the SD-W message.  Otherwise, as the local
      SD-P and the remote SD-W are considered to occur simultaneously,
      perform the followings:

      *  If the working path was the active path at the time when local
         SD-P was selected as the highest local request, the LER remains
         in the local Unavailabe state and continue transmission of the
         current message.

      *  If the working path was the standby path at the time when local
         SD-P was selected as the highest local request, the LER enters
         into the remote Protection Failure state and begin transmitting
         SD(0,1) messages.

5.10.  Updates to Section 4.3.3.3 Protecting Administrative State

   Add the following bullet item text to the transitions in reaction to
   a local input:

   o  A local SD-P SHALL cause the LER to go to local Unavailabe state
      and begin transmitting an SD(0,0) message, if the current state is
      due to a (local or remote) MS command.  If the LER is in remote
      Protecting administrative state due to a remote Forced Switch
      command, then this local indication SHALL cause the LER to remain
      in remote Protecting administrative state and transmit an SD(0,1)
      message.  If the LER is in local Protecting administrative state
      due to a local FS command, then this indication SHALL be ignored
      (i.e., the indication should have been blocked by the Local
      Request logic).

   o  A local SD-W SHALL cause the LER to go to local Unavailabe state
      and begin transmitting an SD(1,1) message, it the current state is
      due to a (local or remote) MS command.  If the LER is in remote
      Protecting administrative state due to a remote Forced Switch
      command, then this local indication SHALL cause the LER to remain
      in remote Protecting administrative state and transmit an SD(1,1)
      message.  If the LER is in local Protecting administrative state
      due to a local FS command, then this indication SHALL be ignored
      (i.e., the indication should have been blocked by the Local
      Request logic).




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   Add the following bullet item text to the transitions in reaction to
   a remote message:

   o  A remote SD-P SHALL cause the LER to go into remote Unavailable
      state and begin transmitting an NR(0,0) message, if the Protecting
      administrative state is due to a (local or remote) MS command.  It
      should be noted that this automatically cancels the current MS
      command and data traffic is reverted to the working path.  If the
      LER is in remote Protecting administrative state due to a remote
      FS command, then the SD-P message and the local input are
      reevaluated as if the LER is in the Normal state.  If the LER is
      in local Protecting administrative state due to a local FS
      command, then this indication SHALL be ignored (i.e., the
      indication should have been blocked by the Local Request logic).

   o  A remote SD-W message SHALL cause the LER to go into remote
      Unavailable state and begin transmitting an NR(0,1) message, if
      the Protecting administrative state is due to a (local or remote)
      MS command.  If the LER is in remote Protecting administrative
      state due to a remote FS command, then the SD-W message and the
      local input are reevaluated as if the LER is in the Normal state.
      If the LER is in local Protecting administrative state due to a
      local FS command, then this indication SHALL be ignored

5.11.  Updates to Section 4.3.3.4 Protecting Failure State

   The bullet item of "Protecting failure state" in Section 3.6.  PSC
   Control States in [RFC6378] includes the degrade condition in
   Protection failure state.  This document follows the same state
   grouping as [RFC6378] for SD on the working path.

   Replace the following text in the first paragraph of Section 4.3.3.4
   Protecting Failure State for further clarification on the SD on the
   working path:

      When the protection mechanism has been triggered and the
      protection domain has performed a protection switch, the domain is
      in the Protecting failure state.  In this state, the normal data
      traffic SHALL be transported on the protection path.  When an LER
      is in this state, it implies that there either was a local SF
      condition or it received a remote SF PSC message.  The SF
      condition or message indicated that the failure is on the working
      path.

      This state may be overridden by the Unavailable state triggers,
      i.e., Lockout of protection or SF on the protection path, or by
      issuing an FS operator command.  This state will be cleared when
      the SF condition is cleared.  In order to prevent flapping due to



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      an intermittent fault, the LER SHOULD employ a Wait-to-Restore
      timer to delay return to Normal state until the network has
      stabilized (see Section 3.5).

   With:

      When the protection mechanism has been triggered and the
      protection domain has performed a protection switch, the domain is
      in the Protecting failure state.  In this state, the normal data
      traffic SHALL be transported on the protection path.  When an LER
      is in this state, it implies that there either was a local SF/SD
      condition or it received a remote SF/SD PSC message.  The SF/SD
      condition or message indicated that the failure/degradation is on
      the working path.

      This state may be overridden by the Unavailable state triggers,
      i.e., Lockout of protection or SF on the protection path, or by
      issuing an FS operator command.  This state will be cleared when
      the SF/SD condition is cleared.  In order to prevent flapping due
      to an intermittent fault, the LER SHOULD employ a Wait-to-Restore
      timer to delay return to Normal state until the network has
      stabilized (see Section 3.5).

      When an LER is in this state due to degradation condition, the
      user traffic should be duplicated and fed to both working and
      protection paths if the detection of a SD depends on the presence
      of user data packets.

   Replace the following bullet item text in the transitions in reaction
   to a local input:

   o  A local Clear SF SHALL be ignored if in remote Protecting failure
      state.  If in local Protecting failure state and the LER is
      configured for revertive behavior, then this input SHALL cause the
      LER to go into Wait-to-Restore state, start the WTR timer, and
      begin transmitting a WTR(0,1) message.  If in local Protecting
      failure state and the LER is configured for non-revertive
      behavior, then this input SHALL cause the LER to go into Do-not-
      Revert state and begin transmitting a DNR(0,1) message.

   With:

   o  A local Clear SF for clearing local SF-W SHALL be ignored if in
      remote Protecting failure state due to remote SF-W.  In local
      Protecting failure state due to local SF-W, clearing local SF-W
      SHALL cause the LER to go into WTR state, start the WTR timer, and
      begin transmitting a WTR(0,1) message, if the LER is configured
      for revertive behavior.  Clear local SF-W in local Protecting



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      failure state due to local SF-W SHALL cause the LER to go into Do-
      not- Revert state and begin transmitting a DNR(0,1) message for
      non-revertive configuration.  In local Protecting Failure state
      due to local SD-W, if the SF/SD being cleared is SD-W and there is
      no local SD-P, then go to WTR or DNR state depending on the
      configuration for revertive behavior.  If there is local SD-P when
      local SD-W is cleared in local Protecting Failure state due to
      SD-W, go to local Unavailable state and begin transmitting SD(0.0)
      message.  If the SF/SD being cleared is SD-P in local Protecting
      Failure due to SD-W, then ignore.  In remote Protection Failure
      state due to remote SD-W, if the SF/SD being cleared is SD-P, then
      remain in current state and begin transmitting NR(0,1), otherwise,
      ignore.

   Add the following bullet item text to the transitions in reaction to
   a local input:

   o  A local SD-P SHALL be ignored if the LER is in local Protecting
      Failure state.  If in remote Protecting Failure state,the LER
      SHALL remain in the current state and begin transmission of an
      SD(0,1) message.

   o  A local SD-W SHALL be ignored if the LER is in local Protecting
      Failure state.  If in remote Protecting Failure state, the LER
      SHALL remain in the current state and begin transmission of an
      SD(1,1) message.

   Add the following SD related sentences to the end of each bullet item
   text for describing the reaction to remote PSC messages:

   remote Lockout of protection:  If the LER is in local Protecting
      Failure state due to local SD-W, then go to remote Unavailable
      state and begin sending SD(1,0) If in remote Protecting Failure
      state due to remote SD-W, then go to remote Unavailable state and
      continue to send the current message with Path=0.

   remote Forced Switch:  If the LER is in the Protecting Failure state
      due to local or remote SD-W, go to remote Protecting
      Administrative state and continue to send the current message.

   remote Signal Fail on the protection path:  If the LER is in the
      Protecting Failure state due to local or remote SD-W, go to remote
      Unavailable state and continue to send the current message with
      Path=0.

   Add the following bullet item text to the transitions in reaction to
   a remote message:




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   o  A remote SF-W message received in Protecting Failure state due to
      local or remote SD-W SHALL cause the LER to remain in Protecting
      Failure state and continue to send the current message.

   o  A remote SD-P message can cause the LER to react differently
      depending on the cause and locality of current state as follows:

      *  In Protecting Failure state due to remote SF-W, if there is no
         local request, transition to remote Unavailable state and send
         NR(0,0).  If there is local SD-W input, then transition to
         remote Unavailable state and send SD(1,0) message.  If the
         local input is SD-P, then transition to local Unavailable state
         and send SD(0,0) message.

      *  In Protecting Failure state due to remote SD-W, if the local
         input is SD-P, then transition to local Unavailable state.
         Else, transition to N state.

      *  In Protecting Failure state due to local SD-W, if the received
         SD-P message has Path=1, ignore the message.  If the received
         SD-P message has Path=0 and the active path just before the
         SD-W is selected as the highest local input was the working
         path, then go to remote Unavailable state and transmit SD(1,0).
         If the received SD-P message has Path=0 and the active path
         just before the SD-W is selected as the highest local input was
         the protection path, then ignore the received SD-P message.

   o  A remote Manual Switch message received in Protecting Failure due
      to remote SD-W SHALL cause the LER to reevaluate the MS message
      and local input as if the LER is in the Normal state.

5.12.  Updates to Section 4.3.3.5 Wait-to-Restore State

   Replace the following paragraph in Section 4.3.3.5 Wait-to-Restore
   State:

   o  When recovering from a failure condition on the working path, the
      Wait-to-Restore state is used by the PSC protocol to delay
      reverting to the Normal state, for the period of the WTR timer to
      allow the recovering failure to stabilize.  While in the Wait-to-
      Restore state, the data traffic SHALL continue to be transported
      on the protection path.  The natural transition from the Wait-to-
      Restore state to Normal state will occur when the WTR timer
      expires.

   With:





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   o  When recovering from a failure or degradation condition on the
      working path, the Wait-to-Restore state is used by the PSC
      protocol to delay reverting to the Normal state, for the period of
      the WTR timer to allow the recovering failure/degradation to
      stabilize.  While in the Wait-to-Restore state, the data traffic
      SHALL continue to be transported on the protection path.  The
      natural transition from the Wait-to-Restore state to Normal state
      will occur when the WTR timer expires.

   o  When an LER is in this state following the recovery of degradation
      condition, the user traffic will continue to be duplicated and fed
      to both working and protection paths if the detection of a SD
      depends on the presence of user data packets.

   Add the following bullet item text to the transitions in reaction to
   a local input:

   o  A local SD-P SHALL send the Stop command to the WTR timer, go into
      local Unavailable state, and begin transmission of an SD(0,0)
      message.

   o  A local SD-W SHALL send the Stop command to the WTR timer, go into
      local Protecting failure state, and begin transmission of an
      SD(1,1) message.

   Add the following bullet item text to the transitions in reaction to
   a remote PSC message:

   o  A remote SD-P message SHALL send the Stop command to the WTR
      timer, go into remote Unavailable state, and begin transmission of
      an NR(0,0) message.

   o  A remote SD-W message SHALL send the Stop command to the WTR
      timer, go into remote Protecting failure state, and begin
      transmission of an NR(0,1) message.

5.13.  Updates to Section 4.3.3.6 Do-not-Revert State

   Add the following bullet item text to the transitions in reaction to
   a local input:

   o  A local SD-P SHALL cause the LER to go into local Unavailable
      state, and begin transmission of an SD(0,0) message.

   o  A local SD-W SHALL cause the LER go into local Protecting failure
      state, and begin transmission of an SD(1,1) message.





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   Add the following bullet item text to the transitions in reaction to
   a remote PSC message:

   o  A remote SD-P message SHALL cause the LER to go into remote
      Unavailable state, and begin transmission of an NR(0,0) message.

   o  A remote SD-W message SHALL cause the LER to go into remote
      Protecting failure state, and begin transmission of an NR(0,1)
      message.

5.14.  Updates to Appendix A. PSC State Machine Tables

   Add the following extended states:

      UA:DP:L Unavailable state due to local SD on protection path
      UA:DP:R Unavailable state due to remote SD-P message
      PF:DW:L Protecting failure state due to local SD on working path
      PF:DW:R Protecting failure state due to remote SD-W message

   Add the following default messages:

      State   REQ(FP, P)
      ------- ----------
      UA:DP:L SD(0,0)
      UA:DP:R NR(0,0)
      PF:DW:L SD(1,1)
      PF:DW:R NR(0,1)

   Add the following text before the state machine table:

      The letter 'r' in the table below stands for reevaluation, and is
      an indication to reevaluate all inputs (both the local input and
      the remote message) as if the LER is in the Normal state.  See
      4.3.3.

   Modify the state machine as follows (only modified cells are shown):

   Part 1: Local input state machine

   +---------+----+---------+--------+--------+--------+
   |         | OC | LO      | SF-P   | FS     | SF-W   |
   +---------+----+---------+--------+--------+--------+
   | N       |    |         |        |        |        |
   | UA:LO:L |    |         |        |        |        |
   | UA:P:L  |    |         |        |        |        |
   | UA:DP:L | i  | UA:LO:L | UA:P:L | PA:F:L | PA:W:L |
   | UA:LO:R |    |         |        |        |        |
   | UA:P:R  |    |         |        |        |        |



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   | UA:DP:R | i  | UA:LO:L | UA:P:L | PA:F:L | PF:W:L |
   | PF:W:L  |    |         |        |        |        |
   | PF:DW:L | i  | UA:LO:L | UA:P:L | PA:F:L | PF:W:L |
   | PF:W:R  |    |         |        |        |        |
   | PF:DW:R | i  | UA:LO:L | UA:P:L | PA:F:L | PF:W:L |
   | PA:F:L  |    |         |        |        |        |
   | PA:M:L  |    |         |        |        |        |
   | PA:F:R  |    |         |        |        |        |
   | PA:M:R  |    |         |        |        |        |
   | WTR     |    |         |        |        |        |
   | DNR     |    |         |        |        |        |
   +---------+----+---------+--------+--------+--------+


   +---------+---------+---------+------+----+--------+
   |         | SD-P    | SD-W    | SFc  | MS | WTRExp |
   +---------+---------+---------+------+----+--------+
   | N       | UA:DP:L | PF:DW:L |      |    |        |
   | UA:LO:L | i       | i       |      |    |        |
   | UA:P:L  | i       | i       | [5]  |    |        |
   | UA:DP:L | i       | i       | [20] | i  | i      |
   | UA:LO:R | [21]    | [22]    |      |    |        |
   | UA:P:R  | [21]    | [22]    |      |    |        |
   | UA:DP:R | UA:DP:L | [22]    | [23] | i  | i      |
   | PF:W:L  | i       | i       |      |    |        |
   | PF:DW:L | i       | i       | [24] | i  | i      |
   | PF:W:R  | [25]    | [26]    |      |    |        |
   | PF:DW:R | [25]    | PF:DW:L | [27] | i  | i      |
   | PA:F:L  | i       | i       |      |    |        |
   | PA:M:L  | UA:DP:L | PF:DW:L |      |    |        |
   | PA:F:R  | [25]    | [26]    |      |    |        |
   | PA:M:R  | UA:DP:L | PF:DW:L |      |    |        |
   | WTR     | UA:DP:L | PF:DW:L |      |    |        |
   | DNR     | UA:DP:L | PF:DW:L |      |    |        |
   +---------+---------+---------+------+----+--------+


   Part 2: Remote messages state machine

   +---------+------+------+------+------+---------+---------+
   |         | LO   | SF-P | FS   | SF-W | SD-P    | SD-W    |
   +---------+------+------+------+------+---------+---------+
   | N       |      |      |      |      | UA:DP:R | PF:DW:R |
   | UA:LO:L |      |      |      |      | i       | i       |
   | UA:P:L  |      |      |      |      | i       | i       |
   | UA:DP:L | [28] | [29] | [30] | [31] | i       | [32]    |
   | UA:LO:R |      |      |      |      | r       | r       |
   | UA:P:R  |      |      |      |      | r       | r       |



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   | UA:DP:R | [33] | [34] | [35] | [36] | i       | r       |
   | PF:W:L  |      |      |      |      | i       | i       |
   | PF:DW:L | [37] | [38] | [39] | [40] | [41]    | i       |
   | PF:W:R  |      |      |      |      | [42]    | i       |
   | PF:DW:R | [43] | [44] | [45] | [46] | [47]    | i       |
   | PA:F:L  |      |      |      |      | i       | i       |
   | PA:M:L  |      |      |      |      | UA:DP:R | PF:DW:R |
   | PA:F:R  |      |      |      |      | r       | r       |
   | PA:M:R  |      |      |      |      | UA:DP:R | PF:DW:R |
   | WTR     |      |      |      |      | UA:DP:R | PF:DW:R |
   | DNR     |      |      |      |      | UA:DP:R | PF:DW:R |
   +---------+------+------+------+------+---------+---------+


   +---------+----+------+------+----+
   |         | MS | WTR  | DNR  | NR |
   +---------+----+------+------+----+
   | N       |    |      |      |    |
   | UA:LO:L |    |      |      |    |
   | UA:P:L  |    |      |      |    |
   | UA:DP:L | i  | i    | i    | i  |
   | UA:LO:R |    |      |      |    |
   | UA:P:R  |    |      |      |    |
   | UA:DP:R | r  | i    | i    | r  |
   | PF:W:L  |    |      |      |    |
   | PF:DW:L | i  | i    | i    | i  |
   | PF:W:R  |    |      |      |    |
   | PF:DW:R | r  | [14] | [15] | N  |
   | PA:F:L  |    |      |      |    |
   | PA:M:L  |    |      |      |    |
   | PA:F:R  |    |      |      |    |
   | PA:M:R  |    |      |      |    |
   | WTR     |    |      |      |    |
   | DNR     |    |      |      |    |
   +---------+----+------+------+----+


   Replace the following footnote:

   5    If the SF being cleared is SF-P, transition to N.  If it's SF-W,
        ignore the clear.

   With:

   5    If the SF being cleared is SF-P, transition to N.  Otherwise,
        ignore the clear.

   Add the following footnotes for the table:



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   20   If the SF/SD being cleared is SD-P, transition to N.  Otherwise,
        ignore the clear.

   21   Remain in the current state and transmit SD(0,0).

   22   Remain in the current state and transmit SD(1,0).

   23   If the SF/SD being cleared is SD-W, then remain in current state
        (UA:DP:R) and begin transmitting NR(0,0).  Otherwise, ignore the
        SFc.

   24   If the SF/SD being cleared is SD-W and there is no local SD-P,
        then go to WTR or DNR depending on the configuration for
        revertive behavior.  If there is local SD-P when local SD-W is
        cleared, go to UA:DP:L state.  If the SF/SD being cleared is
        SD-P then ignore.

   25   Remain in the current state and transmit SD(0,1).

   26   Remain in the current state and transmit SD(1,1).

   27   If the SF/SD being cleared is SD-P, then remain in current state
        (PF:DW:R) and begin transmitting NR(0,1).  Otherwise, ignore.

   28   Transition to (UA:LO:R) and continue sending SD(0,0)

   29   Transition to (UA:P:R) and continue sending SD(0,0)

   30   Transition to (PA:F:R) and send SD(0,1).

   31   Transition to (PF:W:R) and send SD(0,1)

   32   If the active path just before the SD is selected as the highest
        local input was the working path, then ignore.  Otherwise, go to
        PF:DW:R and transmit SD(0,1)

   33   Transition to (UA:LO:R) state and continue to send the current
        message.

   34   Transition to (UA:P:R) state and continue to send the current
        message.

   35   Transition to (PA:F:R) state and continue to send the current
        message with Path=1.

   36   Transition to (PF:W:R) state and continue to send the current
        message with Path=1.




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   37   Transition to (UA:LO:R) and send SD(1,0)

   38   Transition to (UA:P:R) and send SD(1,0)

   39   Transition to (PA:F:R) and continue to send the current message,
        SD(1,1).

   40   Transition to (PF:W:R) and continue to send the current message,
        SD(1,1).

   41   If the received SD-P message has Path=1, ignore the message.  If
        the received SD-P message has Path=0 and the active path just
        before the SD is selected as the highest local input was the
        working path, then go to UA:DP:R and transmit SD(1,0).  If the
        received SD-P message has Path=0 and the active path just before
        the SD is selected as the highest local input was the protection
        path, then ignore the received SD-P message.

   42   If there is no local request, transition to UA:DP:R and send
        NR(0,0).  If the local input is SD-W, then transition to UA:DP:R
        and send SD(1,0) message.  If the local input is SD-P, then
        transition to UA:DP:L and send SD(0,0) message.

   43   Transition to (UA:LO:R) state and continue to send the current
        message with Path=0.

   44   Transition to (UA:P:R) state and continue to send the current
        Message with Path=0.

   45   Transition to (PA:F:R) state and continue to send the current
        message.

   46   Transition to (PF:W:R) state and continue to send the current
        message.

   47   If the local input is SD-P, then transition to UA:DP:L.  Else,
        transition to N state.

6.  Security considerations

   No specific security issue is raised in addition to those ones
   already documented in [RFC6378]









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7.  IANA considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

8.  Acknowledgements

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

   [RFC6378]  Weingarten, Y., Bryant, S., Osborne, E., Sprecher, N., and
              A. Fulignoli, "MPLS Transport Profile (MPLS-TP) Linear
              Protection", RFC 6378, October 2011.

9.2.  Informative References

   [LIAISON1205]
              ITU-T SG15, ., "Liaison Statement: Recommendation ITU-T
              G.8131/Y.1382 revision - Linear protection switching for
              MPLS-TP networks ", https://datatracker.ietf.org/liaison/
              1205/ , October 2012.

   [LIAISON1234]
              ITU-T SG15, ., "Liaison Statement: Recommendation ITU-T
              G.8131 revision - Linear protection switching for MPLS-TP
              networks ", https://datatracker.ietf.org/liaison/1234/ ,
              February 2013.

Authors' Addresses

   Jeong-dong Ryoo
   ETRI
   218 Gajeongno
   Yuseong-gu, Daejeon  305-700
   South Korea

   Phone: +82-42-860-5384
   Email: ryoo@etri.re.kr




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   Huub van Helvoort
   Huawei Technologies
   Karspeldreef 4,
   Amsterdam 1101 CJ
   the Netherlands

   Phone: +31 20 4300832
   Email: huub.van.helvoort@huawei.com


   Alessandro D'Alessandro
   Telecom Italia
   via Reiss Romoli, 274
   Torino  10141
   Italy

   Phone: +39 011 2285887
   Email: alessandro.dalessandro@telecomitalia.it

































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