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RFC 8227

 
 
 

MPLS-TP Shared-Ring Protection (MSRP) Mechanism for Ring Topology

Part 4 of 4, p. 36 to 56
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5.3.  RPS State Machine

5.3.1.  Switch Initiation Criteria

5.3.1.1.  Administrative Commands

   Administrative commands can be initiated by the network operator
   through the Network Management System (NMS).  The operator command
   may be transmitted to the appropriate node via the MPLS-TP RPS
   message.

   The following commands can be transferred by the RPS message:

   o  Lockout of Protection (LP): This command prevents any protection
      activity and prevents using ring switches anywhere in the ring.
      If any ring switches exist in the ring, this command causes the
      switches to drop.

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   o  Forced Switch (FS) to protection: This command performs the ring
      switch of normal traffic from the working entity to the protection
      entity for the link between the node at which the command is
      initiated and the adjacent node to which the command is directed.
      This switch occurs regardless of the state of the MPLS-TP section
      for the requested link, unless a higher-priority switch request
      exists.

   o  Manual Switch (MS) to protection: This command performs the ring
      switch of the normal traffic from the working entity to the
      protection entity for the link between the node at which the
      command is initiated and the adjacent node to which the command is
      directed.  This occurs if the MPLS-TP section for the requested
      link is not satisfying an equal or higher priority switch request.

   o  Exercise (EXER): This command exercises ring protection switching
      on the addressed link without completing the actual switch.  The
      command is issued and the responses (RRs) are checked, but no
      normal traffic is affected.

   The following commands are not transferred by the RPS message:

   o  Clear: This command clears the administrative command and WTR
      timer at the node to which the command was addressed.  The
      node-to-node signaling after the removal of the externally
      initiated commands is performed using the NR code.

   o  Lockout of Working (LW): This command prevents the normal traffic
      transported over the addressed link from being switched to the
      protection entity by disabling the node's capability of requesting
      a switch for this link in case of failure.  If any normal traffic
      is already switched on the protection entity, the switch is
      dropped.  If no other switch requests are active on the ring, the
      NR code is transmitted.  This command has no impact on any other
      link.  If the node receives the switch request from the adjacent
      node from any side, it will perform the requested switch.  If the
      node receives the switch request addressed to the other node, it
      will enter the pass-through state.

5.3.1.2.  Automatically Initiated Commands

   Automatically initiated commands can be initiated based on MPLS-TP
   section-layer OAM indication and the received switch requests.

   The node can initiate the following switch requests automatically:

   o  Signal Fail (SF): This command is issued when the MPLS-TP section-
      layer OAM detects a signal failure condition.

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   o  Wait-to-Restore (WTR): This command is issued when the MPLS-TP
      section detects that the SF condition has cleared.  It is used to
      maintain the state during the WTR period unless it is preempted by
      a higher-priority switch request.  The WTR time may be configured
      by the operator in 1 minute steps between 0 and 12 minutes; the
      default value is 5 minutes.

   o  Reverse Request (RR): This command is transmitted to the source
      node of the received RPS message over the short path as an
      acknowledgment for receiving the switch request.

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5.3.2.  Initial States

   This section describes the possible states of a ring node, the
   corresponding action of the working and protection ring tunnels on
   the node, and the RPS request that should be generated in that state.

            +-----------------------------------+----------------+
            |        State                      |  Signaled RPS  |
            +-----------------------------------+----------------+
            |  A  |  Idle                       |  NR            |
            |     |  Working: no switch         |                |
            |     |  Protection: no switch      |                |
            +-----+-----------------------------+----------------+
            |  B  |  Pass-through               |  N/A           |
            |     |  Working: no switch         |                |
            |     |  Protection: pass-through   |                |
            +-----+-----------------------------+----------------+
            |  C  |  Switching - LP             |  LP            |
            |     |  Working: no switch         |                |
            |     |  Protection: no switch      |                |
            +-----+-----------------------------+----------------+
            |  D  |  Idle - LW                  |  NR            |
            |     |  Working: no switch         |                |
            |     |  Protection: no switch      |                |
            +-----+-----------------------------+----------------+
            |  E  |  Switching - FS             |  FS            |
            |     |  Working: switched          |                |
            |     |  Protection: switched       |                |
            +-----+-----------------------------+----------------+
            |  F  |  Switching - SF             |  SF            |
            |     |  Working: switched          |                |
            |     |  Protection: switched       |                |
            +-----+-----------------------------+----------------+
            |  G  |  Switching - MS             |  MS            |
            |     |  Working: switched          |                |
            |     |  Protection: switched       |                |
            +-----+-----------------------------+----------------+
            |  H  |  Switching - WTR            |  WTR           |
            |     |  Working: switched          |                |
            |     |  Protection: switched       |                |
            +-----+-----------------------------+----------------+
            |  I  |  Switching - EXER           |  EXER          |
            |     |  Working: no switch         |                |
            |     |  Protection: no switch      |                |
            +-----+-----------------------------+----------------+

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5.3.3.  State Transitions When Local Request Is Applied

   In the state description below, 'O' means that a new local request
   will be rejected because of an existing request.

   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   A (Idle)             LP                C (Switching - LP)
                        LW                D (Idle - LW)
                        FS                E (Switching - FS)
                        SF                F (Switching - SF)
                        Recover from SF   N/A
                        MS                G (Switching - MS)
                        Clear             N/A
                        WTR expires       N/A
                        EXER              I (Switching - EXER)
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   B (Pass-through)     LP                C (Switching - LP)
                        LW                B (Pass-through)
                        FS                O - if current state is due to
                                              LP sent by another node
                                          E (Switching - FS) - otherwise
                        SF                O - if current state is due to
                                              LP sent by another node
                                          F (Switching - SF) - otherwise
                        Recover from SF   N/A
                        MS                O - if current state is due to
                                              LP, SF, or FS sent by
                                              another node
                                          G (Switching - MS) - otherwise
                        Clear             N/A
                        WTR expires       N/A
                        EXER              O

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   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   C (Switching - LP)   LP                N/A
                        LW                O
                        FS                O
                        SF                O
                        Recover from SF   N/A
                        MS                O
                        Clear             A (Idle) - if there is no
                                             failure in the ring
                                          F (Switching - SF) - if there
                                             is a failure at this node
                                          B (Pass-through) - if there is
                                             a failure at another node
                        WTR expires       N/A
                        EXER              O
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   D (Idle - LW)        LP                C (Switching - LP)
                        LW                N/A - if on the same link
                                          D (Idle - LW) - if on another
                                             link
                        FS                O - if on the same link
                                          E (Switching - FS) - if on
                                             another link
                        SF                O - if on the addressed link
                                          F (Switching - SF) - if on
                                             another link
                        Recover from SF   N/A
                        MS                O - if on the same link
                                          G (Switching - MS) - if on
                                             another link
                        Clear             A (Idle) - if there is no
                                             failure on addressed link
                                          F (Switching - SF) - if there
                                             is a failure on this link
                        WTR expires       N/A
                        EXER              O

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   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   E (Switching - FS)   LP                C (Switching - LP)
                        LW                O - if on another link
                                          D (Idle - LW) - if on the same
                                             link
                        FS                N/A - if on the same link
                                          E (Switching - FS) - if on
                                             another link
                        SF                O - if on the addressed link
                                          E (Switching - FS) - if on
                                             another link
                        Recover from SF   N/A
                        MS                O
                        Clear             A (Idle) - if there is no
                                             failure in the ring
                                          F (Switching - SF) - if there
                                             is a failure at this node
                                          B (Pass-through) - if there is
                                             a failure at another node
                        WTR expires       N/A
                        EXER              O
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   F (Switching - SF)   LP                C (Switching - LP)
                        LW                O - if on another link
                                          D (Idle - LW) - if on the same
                                             link
                        FS                E (Switching - FS)
                        SF                N/A - if on the same link
                                          F (Switching - SF) - if on
                                             another link
                        Recover from SF   H (Switching - WTR)
                        MS                O
                        Clear             N/A
                        WTR expires       N/A
                        EXER              O

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   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   G (Switching - MS)   LP                C (Switching - LP)
                        LW                O - if on another link
                                          D (Idle - LW) - if on the same
                                             link
                        FS                E (Switching - FS)
                        SF                F (Switching - SF)
                        Recover from SF   N/A
                        MS                N/A - if on the same link
                                          G (Switching - MS) - if on
                                             another link, release the
                                             switches but signal MS
                        Clear             A
                        WTR expires       N/A
                        EXER              O
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   H (Switching - WTR)  LP                C (Switching - LP)
                        LW                D (Idle - W)
                        FS                E (Switching - FS)
                        SF                F (Switching - SF)
                        Recover from SF   N/A
                        MS                G (Switching - MS)
                        Clear             A
                        WTR expires       A
                        EXER              O
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   I (Switching - EXER) LP                C (Switching - LP)
                        LW                D (Idle - W)
                        FS                E (Switching - FS)
                        SF                F (Switching - SF)
                        Recover from SF   N/A
                        MS                G (Switching - MS)
                        Clear             A
                        WTR expires       N/A
                        EXER              N/A - if on the same link
                                          I (Switching - EXER)
   =====================================================================

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5.3.4.  State Transitions When Remote Request is Applied

   The priority of a remote request does not depend on the side from
   which the request is received.

   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   A (Idle)             LP                C (Switching - LP)
                        FS                E (Switching - FS)
                        SF                F (Switching - SF)
                        MS                G (Switching - MS)
                        WTR               N/A
                        EXER              I (Switching - EXER)
                        RR                N/A
                        NR                A (Idle)
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   B (Pass-through)     LP                C (Switching - LP)
                        FS                N/A - cannot happen when there
                                                is an LP request in the
                                                ring
                                          E (Switching - FS) - otherwise
                        SF                N/A - cannot happen when there
                                                is an LP request in the
                                                ring
                                          F (Switching - SF) - otherwise
                        MS                N/A - cannot happen when there
                                                is an LP, FS, or SF
                                                request in the ring
                                          G (Switching - MS) - otherwise
                        WTR               N/A - cannot happen when there
                                                is an LP, FS, SF, or MS
                                                request in the ring
                        EXER              N/A - cannot happen when there
                                                is an LP, FS, SF, MS, or
                                                a WTR request in the
                                                ring
                                          I (Switching - EXER) -
                                                otherwise
                        RR                N/A
                        NR                A (Idle) - if received from
                                                     both sides

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   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   C (Switching - LP)   LP                C (Switching - LP)

                        FS                N/A - cannot happen when there
                                                is an LP request in the
                                                ring
                        SF                N/A - cannot happen when there
                                                is an LP request in the
                                                ring
                        MS                N/A - cannot happen when there
                                                is an LP request in the
                                                ring
                        WTR               N/A
                        EXER              N/A - cannot happen when there
                                                is an LP request in the
                                                ring
                        RR                C (Switching - LP)
                        NR                N/A
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   D (Idle - LW)        LP                C (Switching - LP)
                        FS                E (Switching - FS)
                        SF                F (Switching - SF)
                        MS                G (Switching - MS)
                        WTR               N/A
                        EXER              I (Switching - EXER)
                        RR                N/A
                        NR                D (Idle - LW)
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   E (Switching - FS)   LP                C (Switching - LP)
                        FS                E (Switching - FS)
                        SF                E (Switching - FS)
                        MS                N/A - cannot happen when there
                                                is an FS request in the
                                                ring
                        WTR               N/A
                        EXER              N/A - cannot happen when there
                                                is an FS request in the
                                                ring
                        RR                E (Switching - FS)
                        NR                N/A

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   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   F (Switching - SF)   LP                C (Switching - LP)
                        FS                F (Switching - SF)
                        SF                F (Switching - SF)
                        MS                N/A - cannot happen when there
                                                is an SF request in the
                                                ring
                        WTR               N/A
                        EXER              N/A - cannot happen when there
                                                is an SF request in the
                                                ring
                        RR                F (Switching - SF)
                        NR                N/A
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   G (Switching - MS)   LP                C (Switching - LP)
                        FS                E (Switching - FS)
                        SF                F (Switching - SF)
                        MS                G (Switching - MS) - release
                                             the switches but signal MS
                        WTR               N/A
                        EXER              N/A - cannot happen when there
                                                is an MS request in the
                                                ring
                        RR                G (Switching - MS)
                        NR                N/A
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   H (Switching - WTR)  LP                C (Switching - LP)
                        FS                E (Switching - FS)
                        SF                F (Switching - SF)
                        MS                G (Switching - MS)
                        WTR               H (Switching - WTR)
                        EXER              N/A - cannot happen when there
                                                is a WTR request in the
                                                ring
                        RR                H (Switching - WTR)
                        NR                N/A

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   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   I (Switching - EXER) LP                C (Switching - LP)
                        FS                E (Switching - FS)
                        SF                F (Switching - SF)
                        MS                G (Switching - MS)
                        WTR               N/A
                        EXER              I (Switching - EXER)
                        RR                I (Switching - EXER)
                        NR                N/A
   =====================================================================


5.3.5.  State Transitions When Request Addresses to Another Node is
        Received

   The priority of a remote request does not depend on the side from
   which the request is received.

   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   A (Idle)             LP                B (Pass-through)
                        FS                B (Pass-through)
                        SF                B (Pass-through)
                        MS                B (Pass-through)
                        WTR               B (Pass-through)
                        EXER              B (Pass-through)
                        RR                N/A
                        NR                N/A

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   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   B (Pass-through)     LP                B (Pass-through)
                        FS                N/A - cannot happen when there
                                                is an LP request in the
                                                ring
                                          B (Pass-through) - otherwise
                        SF                N/A - cannot happen when there
                                                is an LP request in the
                                                ring
                                          B (Pass-through) - otherwise
                        MS                N/A - cannot happen when there
                                                is an LP, FS, or SF
                                                request in the ring
                                          B (Pass-through) - otherwise
                        WTR               N/A - cannot happen when there
                                                is an LP, FS, SF, or MS
                                                request in the ring
                                          B (Pass-through) - otherwise
                        EXER              N/A - cannot happen when there
                                                is an LP, FS, SF, MS, or
                                                a WTR request in the
                                                ring
                                          B (Pass-through) - otherwise
                        RR                N/A
                        NR                N/A
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   C (Switching - LP)   LP                C (Switching - LP)
                        FS                N/A - cannot happen when there
                                                is an LP request in the
                                                ring
                        SF                N/A - cannot happen when there
                                                is an LP request in the
                                                ring
                        MS                N/A - cannot happen when there
                                                is an LP request in the
                                                ring
                        WTR               N/A - cannot happen when there
                                                is an LP request in the
                                                ring
                        EXER              N/A - cannot happen when there
                                                is an LP request in the
                                                ring
                        RR                N/A
                        NR                N/A

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   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   D (Idle - LW)        LP                B (Pass-through)
                        FS                B (Pass-through)
                        SF                B (Pass-through)
                        MS                B (Pass-through)
                        WTR               B (Pass-through)
                        EXER              B (Pass-through)
                        RR                N/A
                        NR                N/A
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   E (Switching - FS)   LP                B (Pass-through)
                        FS                E (Switching - FS)
                        SF                E (Switching - FS)
                        MS                N/A - cannot happen when there
                                                is an FS request in the
                                                ring
                        WTR               N/A - cannot happen when there
                                                is an FS request in the
                                                ring
                        EXER              N/A - cannot happen when there
                                                is an FS request in the
                                                ring
                        RR                N/A
                        NR                N/A
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   F (Switching - SF)   LP                B (Pass-through)
                        FS                F (Switching - SF)
                        SF                F (Switching - SF)
                        MS                N/A - cannot happen when there
                                                is an SF request in the
                                                ring
                        WTR               N/A - cannot happen when there
                                                is an SF request in the
                                                ring
                        EXER              N/A - cannot happen when there
                                                is an SF request in the
                                                ring
                        RR                N/A
                        NR                N/A

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   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   G (Switching - MS)   LP                B (Pass-through)
                        FS                B (Pass-through)
                        SF                B (Pass-through)
                        MS                G (Switching - MS) - release
                                             the switches but signal MS
                        WTR               N/A - cannot happen when there
                                                is an MS request in the
                                                ring
                        EXER              N/A - cannot happen when there
                                                is an MS request in the
                                                ring
                        RR                N/A
                        NR                N/A
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   H (Switching - WTR)  LP                B (Pass-through)
                        FS                B (Pass-through)
                        SF                B (Pass-through)
                        MS                B (Pass-through)
                        WTR               N/A
                        EXER              N/A - cannot happen when there
                                                is a WTR request in the
                                                ring
                        RR                N/A
                        NR                N/A
   =====================================================================
   Initial state        New request       New state
   -------------        -----------       ---------
   I (Switching - EXER) LP                B (Pass-through)
                        FS                B (Pass-through)
                        SF                B (Pass-through)
                        MS                B (Pass-through)
                        WTR               N/A
                        EXER              I (Switching - EXER)
                        RR                N/A
                        NR                N/A
   =====================================================================

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6.  IANA Considerations

   IANA has assigned the values listed in the sections below.

6.1.  G-ACh Channel Type

   The Channel Types for G-ACh are allocated from the PW Associated
   Channel Type registry defined in [RFC4446] and updated by [RFC5586].

   IANA has allocated the following new G-ACh Channel Type in the "MPLS
   Generalized Associated Channel (G-ACh) Types (including Pseudowire
   Associated Channel Types)" registry:

      Value |          Description            | Reference
     -------+---------------------------------+--------------
     0x002A | Ring Protection Switching (RPS) | this document
            | Protocol                        |
     -------+---------------------------------+--------------

6.2.  RPS Request Codes

   IANA has created the subregistry "MPLS RPS Request Code Registry"
   under the "Generic Associated Channel (G-ACh) Parameters" registry.
   All code points within this registry shall be allocated according to
   the "Specification Required" procedure as specified in [RFC8126].

   The RPS request field is 8 bits; the allocated values are as follows:

      Value    Description                  Reference
      -------  ---------------------------  -------------
         0     No Request (NR)              this document
         1     Reverse Request (RR)         this document
         2     Unassigned
         3     Exercise (EXER)              this document
         4     Unassigned
         5     Wait-to-Restore (WTR)        this document
         6     Manual Switch (MS)           this document
        7-10   Unassigned
        11     Signal Fail (SF)             this document
        12     Unassigned
        13     Forced Switch (FS)           this document
        14     Unassigned
        15     Lockout of Protection (LP)   this document
      16-254   Unassigned
        255    Reserved

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7.  Operational Considerations

   This document describes three protection modes of the RPS protocol.
   Operators could choose the appropriate protection mode according to
   their network and service requirement.

   Wrapping mode provides a ring protection mechanism in which the
   protected traffic will reach every node of the ring and is applicable
   to protect both the point-to-point LSPs and LSPs that need to be
   dropped in several ring nodes, i.e., the point-to-multipoint
   applications.  When protection is inactive, the protected traffic is
   switched (wrapped) to/from the protection ring tunnel at both sides
   of the defective link/node.  Due to the wrapping, the additional
   propagation delay and bandwidth consumption of the protection tunnel
   are considerable.  For bidirectional LSPs, the protected traffic in
   both directions is co-routed.

   Short-wrapping mode provides a ring protection mechanism that can be
   used to protect only point-to-point LSPs.  When protection is
   inactive, the protected traffic is wrapped to the protection ring
   tunnel at the defective link/node and leaves the ring when the
   protection ring tunnel reaches the egress node.  Compared with the
   wrapping mode, short-wrapping can reduce the propagation latency and
   bandwidth consumption of the protection tunnel.  However, the two
   directions of a protected bidirectional LSP are not totally co-
   routed.

   Steering mode provides a ring protection mechanism that can be used
   to protect only point-to-point LSPs.  When protection is inactive,
   the protected traffic is switched to the protection ring tunnel at
   the ingress node and leaves the ring when the protection ring tunnel
   reaches the egress node.  The steering mode has the least propagation
   delay and bandwidth consumption of the three modes, and the two
   directions of a protected bidirectional LSP can be kept co-routed.

   Note that only one protection mode can be provisioned in the whole
   ring for all protected traffic.

8.  Security Considerations

   MPLS-TP is a subset of MPLS, thus it builds upon many of the aspects
   of the security model of MPLS.  Please refer to [RFC5920] for generic
   MPLS security issues and methods for securing traffic privacy and
   integrity.

   The RPS message defined in this document is used for protection
   coordination on the ring; if it is injected or modified by an
   attacker, the ring nodes might not agree on the protection action,

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   and the improper protection-switching action may cause a temporary
   break to services traversing the ring.  It is important that the RPS
   message is used within a trusted MPLS-TP network domain as described
   in [RFC6941].

   The RPS message is carried in the G-ACh [RFC5586], so it is dependent
   on the security of the G-ACh itself.  The G-ACh is a generalization
   of the Associated Channel defined in [RFC4385].  Thus, this document
   relies on the security mechanisms provided for the Associated Channel
   as described in those two documents.

   As described in the security considerations of [RFC6378], the G-ACh
   is essentially connection oriented, so injection or modification of
   control messages requires the subversion of a transit node.  Such
   subversion is generally considered hard in connection-oriented MPLS
   networks and impossible to protect against at the protocol level.
   Management-level techniques are more appropriate.  The procedures and
   protocol extensions defined in this document do not affect the
   security model of MPLS-TP linear protection as defined in [RFC6378].

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

   [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,
              "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
              Use over an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385,
              February 2006, <https://www.rfc-editor.org/info/rfc4385>.

   [RFC4446]  Martini, L., "IANA Allocations for Pseudowire Edge to Edge
              Emulation (PWE3)", BCP 116, RFC 4446,
              DOI 10.17487/RFC4446, April 2006,
              <https://www.rfc-editor.org/info/rfc4446>.

   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586,
              DOI 10.17487/RFC5586, June 2009,
              <https://www.rfc-editor.org/info/rfc5586>.

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   [RFC5654]  Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
              Sprecher, N., and S. Ueno, "Requirements of an MPLS
              Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
              September 2009, <https://www.rfc-editor.org/info/rfc5654>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

9.2.  Informative References

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
              <https://www.rfc-editor.org/info/rfc5920>.

   [RFC6371]  Busi, I., Ed. and D. Allan, Ed., "Operations,
              Administration, and Maintenance Framework for MPLS-Based
              Transport Networks", RFC 6371, DOI 10.17487/RFC6371,
              September 2011, <https://www.rfc-editor.org/info/rfc6371>.

   [RFC6378]  Weingarten, Y., Ed., Bryant, S., Osborne, E., Sprecher,
              N., and A. Fulignoli, Ed., "MPLS Transport Profile (MPLS-
              TP) Linear Protection", RFC 6378, DOI 10.17487/RFC6378,
              October 2011, <https://www.rfc-editor.org/info/rfc6378>.

   [RFC6941]  Fang, L., Ed., Niven-Jenkins, B., Ed., Mansfield, S., Ed.,
              and R. Graveman, Ed., "MPLS Transport Profile (MPLS-TP)
              Security Framework", RFC 6941, DOI 10.17487/RFC6941, April
              2013, <https://www.rfc-editor.org/info/rfc6941>.

   [RFC6974]  Weingarten, Y., Bryant, S., Ceccarelli, D., Caviglia, D.,
              Fondelli, F., Corsi, M., Wu, B., and X. Dai,
              "Applicability of MPLS Transport Profile for Ring
              Topologies", RFC 6974, DOI 10.17487/RFC6974, July 2013,
              <https://www.rfc-editor.org/info/rfc6974>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

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Acknowledgements

   The authors would like to thank Gregory Mirsky, Yimin Shen, Eric
   Osborne, Spencer Jackson, and Eric Gray for their valuable comments
   and suggestions.

Contributors

   The following people contributed significantly to the content of this
   document and should be considered co-authors:

   Kai Liu
   Huawei Technologies
   Email: alex.liukai@huawei.com

   Jia He
   Huawei Technologies
   Email: hejia@huawei.com

   Fang Li
   China Academy of Telecommunication Research MIIT
   China
   Email: lifang@catr.cn

   Jian Yang
   ZTE Corporation
   China
   Email: yang.jian90@zte.com.cn

   Junfang Wang
   Fiberhome Telecommunication Technologies Co., LTD.
   Email: wjf@fiberhome.com.cn

   Wen Ye
   China Mobile
   Email: yewen@chinamobile.com

   Minxue Wang
   China Mobile
   Email: wangminxue@chinamobile.com

   Sheng Liu
   China Mobile
   Email: liusheng@chinamobile.com

   Guanghui Sun
   Huawei Technologies
   Email: sunguanghui@huawei.com

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Authors' Addresses

   Weiqiang Cheng
   China Mobile

   Email: chengweiqiang@chinamobile.com


   Lei Wang
   China Mobile

   Email: wangleiyj@chinamobile.com


   Han Li
   China Mobile

   Email: lihan@chinamobile.com


   Huub van Helvoort
   Hai Gaoming BV

   Email: huubatwork@gmail.com


   Jie Dong
   Huawei Technologies

   Email: jie.dong@huawei.com