





Network Working Group                                       J. Lang, Ed.
Request for Comments: 4426                           B. Rajagopalan, Ed.
Category: Standards Track                          D. Papadimitriou, Ed.
                                                              March 2006


           Generalized Multi-Protocol Label Switching (GMPLS)
                   Recovery Functional Specification

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document presents a functional description of the protocol
   extensions needed to support Generalized Multi-Protocol Label
   Switching (GMPLS)-based recovery (i.e., protection and restoration).
   Protocol specific formats and mechanisms will be described in
   companion documents.

Table of Contents

   1.  Introduction .................................................  2
       1.1.  Conventions Used in This Document ......................  3
   2.  Span Protection ..............................................  3
       2.1.  Unidirectional 1+1 Dedicated Protection ................  4
       2.2.  Bi-directional 1+1 Dedicated Protection ................  5
       2.3.  Dedicated 1:1 Protection with Extra Traffic ............  6
       2.4.  Shared M:N Protection ..................................  8
       2.5.  Messages ............................................... 10
             2.5.1.  Failure Indication Message ..................... 10
             2.5.2.  Switchover Request Message ..................... 11
             2.5.3.  Switchover Response Message .................... 11
       2.6.  Preventing Unintended Connections ...................... 12
   3.  End-to-End (Path) Protection and Restoration ................. 12
       3.1.  Unidirectional 1+1 Protection .......................... 12
       3.2.  Bi-directional 1+1 Protection .......................... 12
             3.2.1.  Identifiers .................................... 13
             3.2.2.  Nodal Information .............................. 14



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             3.2.3.  End-to-End Failure Indication Message .......... 14
             3.2.4.  End-to-End Failure Acknowledgement Message ..... 15
             3.2.5.  End-to-End Switchover Request Message .......... 15
             3.2.6.  End-to-End Switchover Response Message ......... 15
       3.3.  Shared Mesh Restoration ................................ 15
             3.3.1.  End-to-End Failure Indication and
                     Acknowledgement Message ........................ 16
             3.3.2.  End-to-End Switchover Request Message .......... 16
             3.3.3.  End-to-End Switchover Response Message ......... 17
   4.  Reversion and Other Administrative Procedures ................ 17
   5.  Discussion ................................................... 18
       5.1.  LSP Priorities During Protection ....................... 18
   6.  Security Considerations ...................................... 19
   7.  Contributors ................................................. 20
   8.  References ................................................... 21
       8.1.  Normative References ................................... 21
       8.2.  Informative References ................................. 22

1.  Introduction

   A requirement for the development of a common control plane for both
   optical and electronic switching equipment is that there must be
   signaling, routing, and link management mechanisms that support data
   plane fault recovery.  In this document, the term "recovery" is
   generically used to denote both protection and restoration; the
   specific terms "protection" and "restoration" are used only when
   differentiation is required.  The subtle distinction between
   protection and restoration is made based on the resource allocation
   done during the recovery period (see [RFC4427]).

   A label-switched path (LSP) may be subject to local (span), segment,
   and/or end-to-end recovery.  Local span protection refers to the
   protection of the link (and hence all the LSPs marked as required for
   span protection and routed over the link) between two neighboring
   switches.  Segment protection refers to the recovery of an LSP
   segment (i.e., an SNC in the ITU-T terminology) between two nodes,
   i.e., the boundary nodes of the segment.  End-to-end protection
   refers to the protection of an entire LSP from the ingress to the
   egress port.  The end-to-end recovery models discussed in this
   document apply to segment protection where the source and destination
   refer to the protected segment rather than the entire LSP.  Multiple
   recovery levels may be used concurrently by a single LSP for added
   resiliency; however, the interaction between levels affects any one
   direction of the LSP results in both directions of the LSP being
   switched to a new span, segment, or end-to-end path.






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   Unless otherwise stated, all references to "link" in this document
   indicate a bi-directional link (which may be realized as a pair of
   unidirectional links).

   Consider the control plane message flow during the establishment of
   an LSP.  This message flow proceeds from an initiating (or source)
   node to a terminating (or destination) node, via a sequence of
   intermediate nodes.  A node along the LSP is said to be "upstream"
   from another node if the former occurs first in the sequence.  The
   latter node is said to be "downstream" from the former node.  That
   is, an "upstream" node is closer to the initiating node than a node
   further "downstream".  Unless otherwise stated, all references to
   "upstream" and "downstream" are in terms of the control plane message
   flow.

   The flow of the data traffic is defined from ingress (source node) to
   egress (destination node).  Note that for bi-directional LSPs, there
   are two different data plane flows, one for each direction of the
   LSP.  This document presents a protocol functional description to
   support Generalized Multi-Protocol Label Switching (GMPLS)-based
   recovery (i.e., protection and restoration).  Protocol-specific
   formats, encoding, and mechanisms will be described in companion
   documents.

1.1.  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].

   In addition, the reader is assumed to be familiar with the
   terminology used in [RFC3945], [RFC3471] and referenced as well as
   [RFC4427].

2.  Span Protection

   Consider a (working) link i between two nodes A and B.  There are two
   fundamental models for span protection.  The first is referred to as
   1+1 protection.  Under this model, a dedicated link j is pre-assigned
   to protect link i.  LSP traffic is permanently bridged onto both
   links i and j at the ingress node, and the egress node selects the
   signal (i.e., normal traffic) from i or j, based on a selection
   function (e.g., signal quality).  Under unidirectional 1+1 span
   protection (Section 2.1), each node A and B acts autonomously to
   select the signal from the working link i or the protection link j.
   Under bi-directional 1+1 span protection (Section 2.2) the two nodes
   A and B coordinate the selection function such that they select the
   signal from the same link, i or j.



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   Under the second model, a set of N working links are protected by a
   set of M protection links, usually with M =< N.  A failure in any of
   the N working links results in traffic being switched to one of the M
   protection links that is available.  This is typically a three-step
   process: first the data plane failure is detected at the egress node
   and reported (notification), then a protection link is selected, and
   finally, the LSPs on the failed link are moved to the protection
   link.  If reversion is supported, a fourth step is included, i.e.,
   return of the traffic to the working link (when the working link has
   recovered from the failure).  In Section 2.3, 1:1 span protection is
   described.  In Section 2.4, M:N span protection is described, where
   M =< N.

2.1.  Unidirectional 1+1 Dedicated Protection

   Suppose a bi-directional LSP is routed over link i between two nodes
   A and B.  Under unidirectional 1+1 protection, a dedicated link j is
   pre-assigned to protect the working link i.  LSP traffic is
   permanently bridged on both links at the ingress node, and the egress
   node selects the normal traffic from one of the links, i or j.  If a
   node (A or B) detects a failure of a span, it autonomously invokes a
   process to receive the traffic from the protection span.  Thus, it is
   possible that node A selects the signal from link i in the B to A
   direction of the LSP, and node B selects the signal from link j in
   the A to B direction.

   The following functionality is required for 1+1 unidirectional span
   protection:

      o  Routing: A single TE link encompassing both working and
         protection links SHOULD be announced with a Link Protection
         Type "Dedicated 1+1", along with the bandwidth parameters for
         the working link.  As the resources are consumed/released, the
         bandwidth parameters of the TE link are adjusted accordingly.
         Encoding of the Link Protection Type and bandwidth parameters
         in IS-IS is specified in [RFC4205].  Encoding of this
         information in OSPF is specified in [RFC4203].

      o  Signaling: The Link Protection object/TLV SHOULD be used to
         request "Dedicated 1+1" link protection for that LSP.  This
         object/TLV is defined in [RFC3471].  If the Link Protection
         object/TLV is not used, link selection is a matter of local
         policy.  No additional signaling is required when a fail-over
         occurs.







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      o  Link management: Both nodes MUST have a consistent view of the
         link protection association for the spans.  This can be done
         using the Link Management Protocol (LMP) [RFC4204], or if LMP
         is not used, this MUST be configured manually.

2.2.  Bi-directional 1+1 Dedicated Protection

   Suppose a bi-directional LSP is routed over link i between two nodes
   A and B.  Under bi-directional 1+1 protection, a dedicated link j is
   pre-assigned to protect the working link i.  LSP traffic is
   permanently duplicated on both links, and under normal conditions,
   the traffic from link i is received by nodes A and B (in the
   appropriate directions).  A failure affecting link i results in both
   A and B switching to the traffic on link j in the respective
   directions.  Note that some form of signaling is required to ensure
   that both A and B start receiving traffic from the protection link.

   The basic steps in 1+1 bi-directional span protection are as follows:

      1. If a node (A or B) detects the failure of the working link (or
         a degradation of signal quality over the working link), it
         SHOULD begin receiving on the protection link and send a
         Switchover Request message reliably to the other node (B or A,
         respectively).  This message SHOULD indicate the identity of
         the failed working link and provide other relevant information.

      2. Upon receipt of the Switchover Request message, a node MUST
         begin receiving from the protection link and send a Switchover
         Response message to the other node (A or B, respectively).
         Because both the working/protect spans are exposed to routing
         and signaling as a single link, the switchover SHOULD be
         transparent to routing and signaling.

   The following functionality is required for 1+1 bi-directional span
   protection:

      o  The routing procedures are the same as in 1+1 unidirectional.

      o  The signaling procedures are the same as in 1+1 unidirectional.

      o  In addition to the procedures described in 1+1
         (unidirectional), a Switchover Request message MUST be used to
         signal the Switchover Request.  This can be done using LMP
         [RFC4204].  Note that GMPLS-based mechanisms MAY not be
         necessary when the underlying span (transport) technology
         provides such a mechanism.





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2.3.  Dedicated 1:1 Protection with Extra Traffic

   Consider two adjacent nodes, A and B.  Under 1:1 protection, a
   dedicated link j between A and B is pre-assigned to protect working
   link i.  Link j may be carrying (pre-emptable) Extra Traffic.  A
   failure affecting link i results in the corresponding LSP(s) being
   restored to link j.  Extra Traffic being routed over link j may need
   to be pre-empted to accommodate the LSPs that have to be restored.

   Once a fault is isolated/localized, the affected LSP(s) must be moved
   to the protection link.  The process of moving an LSP from a failed
   (working) link to a protection link must be initiated by one of the
   nodes, A or B.  This node is referred to as the "master".  The other
   node is called the "slave".  The determination of the master and the
   slave may be based on configured information or protocol specific
   requirements.

   The basic steps in dedicated 1:1 span protection (ignoring reversion)
   are as follows:

      1. If the master detects/localizes a link failure event, it
         invokes a process to allocate the protection link to the
         affected LSP(s).

      2. If the slave detects a link failure event, it informs the
         master of the failure using a failure indication message.  The
         master then invokes the same procedure as (1) to move the LSPs
         to the protection link.  If the protection link is carrying
         Extra Traffic, the slave stops using the span for the Extra
         Traffic.

      3. Once the span protection procedure is invoked in the master, it
         requests the slave to switch the affected LSP(s) to the
         protection link.  Prior to this, if the protection link is
         carrying Extra Traffic, the master stops using the span for
         this traffic (i.e., the traffic is dropped by the master and
         not forwarded into or out of the protection link).

      4. The slave sends an acknowledgement to the master.  Prior to
         this, the slave stops using the link for Extra Traffic (i.e.,
         the traffic is dropped by the slave and not forwarded into or
         out of the protection link).  It then starts sending the normal
         traffic on the selected protection link.

      5. When the master receives the acknowledgement, it starts sending
         and receiving the normal traffic over the new link.  The
         switchover of the LSPs is thus completed.




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      Note: Although this mechanism implies more traffic dropped than
      necessary, it is preferred over possible misconnections during the
      recovery process.

   From the description above, it is clear that 1:1 span protection may
   require up to three signaling messages for each failed span: a
   failure indication message, an LSP Switchover Request message, and an
   LSP Switchover Response message.  Furthermore, it may be possible to
   switch multiple LSPs from the working span to the protection span
   simultaneously.

   The following functionality is required for dedicated 1:1 span
   protection:

      o  Pre-emption MUST be supported to accommodate Extra Traffic.

      o  Routing: A single TE link encompassing both working and
         protection links is announced with a Link Protection Type
         "Dedicated 1:1".  If Extra Traffic is supported over the
         protection link, then the bandwidth parameters for the
         protection link MUST also be announced.  The differentiation
         between bandwidth for working and protect links is made using
         priority mechanisms.  In other words, the network MUST be
         configured such that bandwidth at priority X or lower is
         considered Extra Traffic.

         If there is a failure on the working link, then the normal
         traffic is switched to the protection link, pre-empting Extra
         Traffic if necessary.  The bandwidth for the protection link
         MUST be adjusted accordingly.

      o  Signaling: To establish an LSP on the working link, the Link
         Protection object/TLV indicating "Dedicated 1:1" SHOULD be
         included in the signaling request message for that LSP.  To
         establish an LSP on the protection link, the appropriate
         priority (indicating Extra Traffic) SHOULD be used for that
         LSP.  These objects/TLVs are defined in [RFC3471].  If the Link
         Protection object/TLV is not used, link selection is a matter
         of local policy.

      o  Link management: Both nodes MUST have a consistent view of the
         link protection association for the spans.  This can be done
         using LMP [RFC4204] or via manual configuration.

      o  When a link failure is detected at the slave, a failure
         indication message MUST be sent to the master informing the
         node of the link failure.




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2.4.  Shared M:N Protection

   Shared M:N protection is described with respect to two neighboring
   nodes, A and B.  The scenario considered is as follows:

      o  At any point in time, there are two sets of links between A and
         B, i.e., a working set of N (bi-directional) links carrying
         traffic subject to protection and a protection set of M (bi-
         directional) links.  A protection link may be carrying Extra
         Traffic.  There is no a priori relationship between the two
         sets of links, but the value of M and N MAY be pre-configured.
         The specific links in the protection set MAY be pre-configured
         to be physically diverse to avoid the possibility of failure
         events affecting a large proportion of protection links (along
         with working links).

      o  When a link in the working set is affected by a failure, the
         normal traffic is diverted to a link in the protection set, if
         such a link is available.  Note that such a link might be
         carrying more than one LSP, e.g., an OC-192 link carrying four
         STS-48 LSPs.

      o  More than one link in the working set may be affected by the
         same failure event.  In this case, there may not be an adequate
         number of protection links to accommodate all of the affected
         traffic carried by failed working links.  The set of affected
         working links that are actually restored over available
         protection links is then subject to policies (e.g., based on
         relative priority of working traffic).  These policies are not
         specified in this document.

      o  When normal traffic must be diverted from a failed link in the
         working set to a protection link, the decision as to which
         protection link is chosen is always made by one of the nodes, A
         or B.  This node is considered the "master" and it is required
         to both apply any policies and select specific protection links
         to divert working traffic.  The other node is considered the
         "slave".  The determination of the master and the slave MAY be
         based on configured information, protocol-specific
         requirements, or as a result of running a neighbor discovery
         procedure.

      o  Failure events are detected by transport layer mechanisms, if
         available (e.g., SONET Alarm Indication Signal (AIS)/Remote
         Defect Indication (RDI)).  Since the bi-directional links are
         formed by a pair of unidirectional links, a failure in the link
         from A to B is typically detected by B, and a failure in the
         opposite direction is detected by A.  It is possible for a



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         failure to simultaneously affect both directions of the bi-
         directional link.  In this case, A and B will concurrently
         detect failures, in the B-to-A direction and in the A-to-B
         direction, respectively.

   The basic steps in M:N protection (ignoring reversion) are as
   follows:

      1. If the master detects a failure of a working link, it
         autonomously invokes a process to allocate a protection link to
         the affected traffic.

      2. If the slave detects a failure of a working link, it MUST
         inform the master of the failure using a failure indication
         message.  The master then invokes the same procedure as above
         to allocate a protection link.  (It is possible that the master
         has itself detected the same failure, for example, a failure
         simultaneously affecting both directions of a link.)

      3. Once the master has determined the identity of the protection
         link, it indicates this to the slave and requests the
         switchover of the traffic (using a "Switchover Request"
         message).  Prior to this, if the protection link is carrying
         Extra Traffic, the master stops using the link for this traffic
         (i.e., the traffic is dropped by the master and not forwarded
         into or out of the protection link).

      4. The slave sends a "Switchover Response" message back to the
         master.  Prior to this, if the selected protection link is
         carrying traffic that could be pre-empted, the slave stops
         using the link for this traffic (i.e., the traffic is dropped
         by the slave and not forwarded into or out of the protection
         link).  It then starts sending the normal traffic on the
         selected protection link.

      5. When the master receives the Switchover Response, it starts
         sending and receiving the traffic that was previously carried
         on the now-failed link over the new link.

      Note: Although this mechanism implies more traffic dropped than
      necessary, it is preferred over possible misconnections during the
      recovery process.

   From the description above, it is clear that M:N span restoration
   (involving LSP local recovery) MAY require up to three messages for
   each working link being switched: a failure indication message, a
   Switchover Request message, and a Switchover Response message.




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   The following functionality is required for M:N span restoration:

      o  Pre-emption MUST be supported to accommodate Extra Traffic.

      o  Routing: A single TE link encompassing both sets of working and
         protect links should be announced with a Link Protection Type
         "Shared M:N".  If Extra Traffic is supported over a set of the
         protection links, then the bandwidth parameters for the set of
         protection links MUST also be announced.  The differentiation
         between bandwidth for working and protect links is made using
         priority mechanisms.

         If there is a failure on a working link, then the affected
         LSP(s) MUST be switched to a protection link, pre-empting Extra
         Traffic if necessary.  The bandwidth for the protection link
         MUST be adjusted accordingly.

      o  Signaling: To establish an LSP on the working link, the Link
         Protection object/TLV indicating "Shared M:N" SHOULD be
         included in the signaling request message for that LSP.  To
         establish an LSP on the protection link, the appropriate
         priority (indicating Extra Traffic) SHOULD be used.  These
         objects/TLVs are defined in [RFC3471].  If the Link Protection
         object/TLV is not used, link selection is a matter of local
         policy.

      o  For link management, both nodes MUST have a consistent view of
         the link protection association for the links.  This can be
         done using LMP [RFC4204] or via manual configuration.

2.5.  Messages

   The following messages are used in local span protection procedures.

   These messages SHOULD be delivered reliably.  Therefore, the protocol
   mechanisms used to deliver these messages SHOULD provide sequencing,
   acknowledgement, and retransmission.  The protocol SHOULD also handle
   situations where the message(s) cannot be delivered.

   The messages described in the following subsections are abstract;
   their format and encoding will be described in separate documents.

2.5.1.  Failure Indication Message

   This message is sent from the slave to the master to indicate the
   identities of one or more failed working links.  This message MAY not
   be necessary when the transport plane technology itself provides for
   such a notification.



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   The number of links included in the message depends on the number of
   failures detected within a window of time by the sending node.  A
   node MAY choose to send separate failure indication messages in the
   interest of completing the recovery for a given link within an
   implementation-dependent time constraint.

2.5.2.  Switchover Request Message

   Under bi-directional 1+1 span protection, this message is used to
   coordinate the selecting function at both nodes.  This message
   originated at the node that detected the failure.

   Under dedicated 1:1 and shared M:N span protection, this message is
   used as an LSP Switchover Request.  This message is sent from the
   master node to the slave node (reliably) to indicate that the LSP(s)
   on the (failed) working link can be switched to an available
   protection link.  If so, the ID of the protection link, as well as
   the LSP labels (if necessary), MUST be indicated.  These identifiers
   MUST be consistent with those used in GMPLS signaling.

   A working link may carry multiple LSPs.  Since the normal traffic
   carried over the working link is switched to the protection link, it
   MAY be possible for the LSPs on the working link to be mapped to the
   protection link without re-signaling each individual LSP.  For
   example, if link bundling [RFC4201] is used where the working and
   protect links are mapped to component links, and the labels are the
   same on the working and protection links, it MAY be possible to
   change the component links without needing to re-signal each
   individual LSP.  Optionally, the labels MAY need to be explicitly
   coordinated between the two nodes.  In this case, the Switchover
   Request message SHOULD carry the new label mappings.

   The master may not be able to find protection links to accommodate
   all failed working links.  Thus, if this message is generated in
   response to a Failure Indication message from the slave, then the set
   of failed links in the message MAY be a sub-set of the links received
   in the Failure Indication message.  Depending on time constraints,
   the master may switch the normal traffic from the set of failed links
   in smaller batches.  Thus, a single failure indication message MAY
   result in the master sending more than one Switchover Request message
   to the same slave node.

2.5.3.  Switchover Response Message

   This message is sent from the slave to the master (reliably) to
   indicate the completion (or failure) of switchover at the slave.  In
   this message, the slave MAY indicate that it cannot switch over to
   the corresponding free link for some reason.  In this case, the



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   master and slave notify the user (operator) of the failed switchover.
   A notification of the failure MAY also be used as a trigger in an
   end-to-end recovery.

2.6.  Preventing Unintended Connections

   An unintended connection occurs when traffic from the wrong source is
   delivered to a receiver.  This MUST be prevented during protection
   switching.  This is primarily a concern when the protection link is
   being used to carry Extra Traffic.  In this case, it MUST be ensured
   that the LSP traffic being switched from the (failed) working link to
   the protection link is not delivered to the receiver of the pre-
   empted traffic.  Thus, in the message flow described above, the
   master node MUST disconnect (any) pre-empted traffic on the selected
   protection link before sending the Switchover Request.  The slave
   node MUST also disconnect pre-empted traffic before sending the
   Switchover Response.  In addition, the master node SHOULD start
   receiving traffic for the protected LSP from the protection link.
   Finally, the master node SHOULD start sending protected traffic on
   the protection link upon receipt of the Switchover Response.

3.  End-to-End (Path) Protection and Restoration

   End-to-end path protection and restoration refer to the recovery of
   an entire LSP from the initiator to the terminator.  Suppose the
   primary path of an LSP is routed from the initiator (Node A) to the
   terminator (Node B) through a set of intermediate nodes.

   The following subsections describe three previously proposed end-to-
   end protection schemes and the functional steps needed to implement
   them.

3.1.  Unidirectional 1+1 Protection

   A dedicated, resource-disjoint alternate path is pre-established to
   protect the LSP.  Traffic is simultaneously sent on both paths and
   received from one of the functional paths by the end nodes A and B.

   There is no explicit signaling involved with this mode of protection.

3.2.  Bi-directional 1+1 Protection

   A dedicated, resource-disjoint alternate path is pre-established to
   protect the LSP.  Traffic is simultaneously sent on both paths; under
   normal conditions, the traffic from the working path is received by
   nodes A and B (in the appropriate directions).  A failure affecting
   the working path results in both A and B switching to the traffic on
   the protection path in the respective directions.



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   Note that this requires coordination between the end nodes to switch
   to the protection path.

   The basic steps in bi-directional 1+1 path protection are as follows:

      o  Failure detection: There are two possibilities for this.

            1. A node in the working path detects a failure event.  Such
               a node MUST send a Failure Indication message toward the
               upstream or/and downstream end node of the LSP (node A or
               B).  This message MAY be forwarded along the working path
               or routed over a different path if the network has
               general routing intelligence.

               Mechanisms provided by the data transport plane MAY also
               be used for this, if available.

            2. The end nodes (A or B) detect the failure themselves
               (e.g., loss of signal).

      o  Switchover: The action taken when an end node detects a failure
         in the working path is as follows: Start receiving from the
         protection path; at the same time, send a Switchover Request
         message to the other end node to enable switching at the other
         end.

         The action taken when an end node receives a Switchover Request
         message is as follows:

            -  Start receiving from the protection path; at the same
               time, send a Switchover Response message to the other end
               node.

   GMPLS signaling mechanisms MAY be used to (reliably) signal the
   Failure Indication message, as well as the Switchover Request and
   Response message.  These messages MAY be forwarded along the
   protection path if no other routing intelligence is available in the
   network.

3.2.1.  Identifiers

   LSP Identifier: A unique identifier for each LSP.  The LSP identifier
   is within the scope of the Source ID and Destination ID.

   Source ID: ID of the source (e.g., IP address).

   Destination ID: ID of the destination (e.g., IP address).




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3.2.2.  Nodal Information

   Each node that is on the working or protection path of an LSP MUST
   have knowledge of the LSP identifier.  If the network does not
   provide routing intelligence, nodal information MAY also include
   previous and next nodes in the LSP so that restoration-related
   messages can be forwarded properly.  When the network provides
   general routing intelligence, messages MAY be forwarded along paths
   other than that of the LSP.

   At the end-point nodes, the working and protection paths MUST be
   associated.  The association of these paths MAY be either provisioned
   using signaling or MAY be configured when LSP provisioning does not
   involve signaling (e.g., provisioning through a management system).
   The related association information MUST remain until the LSP is
   explicitly de-provisioned.

3.2.3.  End-to-End Failure Indication Message

   This message is sent (reliably) by an intermediate node toward the
   source of an LSP.  For instance, such a node might have attempted
   local span protection and failed.  This message MAY not be necessary
   if the data transport layer provides mechanisms for the notification
   of LSP failure by the endpoints (i.e., if LSP endpoints are co-
   located with a corresponding data (transport) maintenance/recovery
   domain).

   Consider a node that detects a link failure.  The node MUST determine
   the identities of all LSPs that are affected by the failure of the
   link and send an End-to-End Failure Indication message to the source
   of each LSP.  For scalability reasons, Failure Indication messages
   MAY contain the identity and the status of multiple LSPs rather than
   a single one.  Each intermediate node receiving such a message MUST
   forward the message to the appropriate next node such that the
   message would ultimately reach the LSP source.  However, there is no
   requirement that this message flows toward the source along the same
   path as the failed LSP.  Furthermore, if an intermediate node is
   itself generating a Failure Indication message, there SHOULD be a
   mechanism to suppress all but one source of Failure Indication
   messages.  Finally, the Failure Indication message MUST be sent
   reliably from the node detecting the failure to the LSP source.
   Reliability MAY be achieved, for example, by retransmitting the
   message until an acknowledgement is received.  However,
   retransmission of Failure Indication messages SHOULD not cause
   further message drops.  This MAY be achieved through the appropriate
   configuration and use of congestion and flow control mechanisms.





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3.2.4.  End-to-End Failure Acknowledgement Message

   This message is sent by the source node to acknowledge the receipt of
   an End-to-End Failure Indication message.  This message is sent to
   the originator of the Failure Indication message.  The Acknowledge
   message SHOULD be sent for each Failure Indication Message received.
   Each intermediate node receiving the Failure Acknowledgement message
   MUST forward it toward the destination of the message.  However,
   there is no requirement that this message flows toward the
   destination along the same path as the failed LSP.

   This message MAY not be required if other means of ensuring reliable
   message delivery are used.

3.2.5.  End-to-End Switchover Request Message

   This message is generated by the source node receiving an indication
   of failure in an LSP.  It is sent to the LSP destination, and it
   carries the identifier of the LSP being restored.  The End-to-End
   Switchover Request message MUST be sent reliably from the source to
   the destination of the LSP.

3.2.6.  End-to-End Switchover Response Message

   This message is sent by the destination node receiving an End-to-End
   Switchover Request message toward the source of the LSP.  This
   message SHOULD identify the LSP being switched over.  This message
   MUST be transmitted in response to each End-to-End Switchover Request
   message received and MAY indicate either a positive or negative
   outcome.

3.3.  Shared Mesh Restoration

   Shared mesh restoration refers to schemes under which protection
   paths for multiple LSPs share common link and node resources.  Under
   these schemes, the protection capacity is pre-reserved, i.e., link
   capacity is allocated to protect one or more LSPs, but explicit
   action is required to instantiate a specific protection LSP.  This
   requires restoration signaling along the protection path.  Typically,
   the protection capacity is shared only amongst LSPs whose working
   paths are physically diverse.  This criterion can be enforced when
   provisioning the protection path.  Specifically, provisioning-related
   signaling messages may carry information about the working path to
   nodes along the protection path.  This can be used as call admission
   control to accept/reject connections along the protection path based
   on the identification of the resources used for the primary path.





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   Thus, shared mesh restoration is designed to protect an LSP after a
   single failure event, i.e., a failure that affects the working path
   of at most one LSP sharing the protection capacity.  It is possible
   that a protection path may not be successfully activated when
   multiple, concurrent failure events occur.  In this case, shared mesh
   restoration capacity may be claimed for more than one failed LSP and
   the protection path can be activated only for one of them (at most).

   For implementing shared mesh restoration, the identifier and nodal
   information related to signaling along the control path are as
   defined for 1+1 protection in Sections 3.2.1 and 3.2.2.  In addition,
   each node MUST also keep (local) information needed to establish the
   data plane of the protection path.  This information MUST indicate
   the local resources to be allocated, the fabric cross-connect to be
   established to activate the path, etc.  The precise nature of this
   information would depend on the type of node and LSP (the GMPLS
   signaling document describes different type of switches [RFC3471]).
   It would also depend on whether the information is fine or coarse-
   grained.  For example, fine-grained information would indicate pre-
   selection of all details pertaining to protection path activation,
   such as outgoing link, labels, etc.  Coarse-grained information, on
   the other hand, would allow some details to be determined during
   protection path activation.  For example, protection resources may be
   pre-selected at the level of a TE link, while the selection of the
   specific component link and label occurs during protection path
   activation.

   While the coarser specification allows some flexibility in the
   selection of the precise resource to activate, it also adds
   complexity in decision making and signaling during the time-critical
   restoration phase.  Furthermore, the procedures for the assignment of
   bandwidth to protection paths MUST take into account the total
   resources in a TE link so that single-failure survivability
   requirements are satisfied.

3.3.1.  End-to-End Failure Indication and Acknowledgement Message

   The End-to-End failure indication and acknowledgement procedures and
   messages are as defined in Sections 3.2.3 and 3.2.4.

3.3.2.  End-to-End Switchover Request Message

   This message is generated by the source node receiving an indication
   of failure in an LSP.  It is sent to the LSP destination along the
   protection path, and it identifies the LSP being restored.  If any
   intermediate node is unable to establish cross-connects for the
   protection path, then it is desirable that no other node in the path




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   establishes cross-connects for the path.  This would allow shared
   mesh restoration paths to be efficiently utilized.

   The End-to-End Switchover message MUST be sent reliably from the
   source to the destination of the LSP along the protection path.

3.3.3.  End-to-End Switchover Response Message

   This message is sent by the destination node receiving an End-to-End
   Switchover Request message toward the source of the LSP, along the
   protection path.  This message SHOULD identify the LSP that is being
   switched over.  Prior to activating the secondary bandwidth at each
   hop along the path, Extra Traffic (if used) MUST be dropped and not
   forwarded.

   This message MUST be transmitted in response to each End-to-End
   Switchover Request message received.

4.  Reversion and Other Administrative Procedures

   Reversion refers to the process of moving an LSP back to the original
   working path after a failure is cleared and the path is repaired.
   Reversion applies both to local span and end-to-end path-protected
   LSPs.  Reversion is desired for the following reasons.  First, the
   protection path may not be optimal in comparison to the working path
   from a routing and resource consumption point of view.  Second,
   moving an LSP to its working path allows the protection resources to
   be used to protect other LSPs.  Reversion has the disadvantage of
   causing a second service disruption.  Use of reversion is at the
   option of the operator.  Reversion implies that a working path
   remains allocated to the LSP that was originally routed over it, even
   after a failure.  It is important to have mechanisms that allow
   reversion to be performed with minimal service disruption to the
   customer.  This can be achieved using a "bridge-and-switch" approach
   (often referred to as make-before-break).

   The basic steps involved in bridge-and-switch are as follows:

      1. The source node commences the process by "bridging" the normal
         traffic onto both the working and the protection paths (or
         links in the case of span protection).

      2. Once the bridging process is complete, the source node sends a
         Bridge and Switch Request message to the destination,
         identifying the LSP and other information necessary to perform
         reversion.  Upon receipt of this message, the destination





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         selects the traffic from the working path.  At the same time,
         it bridges the transmitted traffic onto both the working and
         protection paths.

      3. The destination then sends a Bridge and Switch Response message
         to the source confirming the completion of the operation.

      4. When the source receives this message, it switches to receive
         from the working path, and stops transmitting traffic on the
         protection path.  The source then sends a Bridge and Switch
         Completed message to the destination confirming that the LSP
         has been reverted.

      5. Upon receipt of this message, the destination stops
         transmitting along the protection path and de-activates the LSP
         along this path.  The de-activation procedure should remove the
         crossed connections along the protection path (and frees the
         resources to be used for restoring other failures).

   Administrative procedures other than reversion include the ability to
   force a switchover (from working to protection or vice versa) and
   locking out switchover, i.e., preventing an LSP from moving from
   working to protection administratively.  These administrative
   conditions have to be supported by signaling.

5.  Discussion

5.1.  LSP Priorities During Protection

   Under span protection, a failure event could affect more than one
   working link and there could be fewer protection links than the
   number of failed working links.  Furthermore, a working link may
   contain multiple LSPs of varying priority.  Under this scenario, a
   decision must be made as to which working links (and therefore LSPs)
   should be protected.  This decision MAY be based on LSP priorities.

   In general, a node might detect failures sequentially, i.e., all
   failed working links may not be detected simultaneously, but only
   sequentially.  In this case, as per the proposed signaling
   procedures, LSPs on a working link MAY be switched over to a given
   protection link, but another failure (of a working link carrying
   higher priority LSPs) may be detected soon afterward.  In this case,
   the new LSPs may bump the ones previously switched over the
   protection link.

   In the case of end-to-end shared mesh restoration, priorities MAY be
   implemented for allocating shared link resources under multiple
   failure scenarios.  As described in Section 3.3, more than one LSP



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   can claim shared resources under multiple failure scenarios.  If such
   resources are first allocated to a lower-priority LSP, they MAY have
   to be reclaimed and allocated to a higher-priority LSP.

6.  Security Considerations

   There are a number of security threats that MAY be experienced due to
   the exchange of messages and information, as detailed in this
   document.  Some examples include interception, spoofing,
   modification, and replay of control messages.  Therefore, the
   following security requirements are applicable to the mechanisms of
   this document.

      o  Signaling MUST be able to provide authentication, integrity,
         and protection against replay attacks.

      o  Privacy and confidentiality are not required.  Only
         authentication is required to ensure that the signaling
         messages are originating from the right place and have not been
         modified in transit.

      o  Protection of the identity of the data plane end-points (in
         Failure Indication messages) is not required

   The consequences of poorly secured protection may increase the risk
   of triggering recovery actions under false Failure Indication
   messages, including LSP identifiers that are not under failure.  Such
   information could subsequently trigger the initiation of "false"
   recovery actions while there are no reasons to do so.  Additionally,
   if the identification of the LSP is tampered with from a Failure
   Indication message, recovery actions will involve nodes for which the
   LSPs do not indicate any failure condition or for which no Failure
   Indication message has been received.  The consequences of such
   actions is unpredictable and MAY lead to de-synchronisation between
   the control and the data plane, as well as increase the risk of
   misconnections.  Moreover, the consequences of poorly applied
   protection may increase the risk of misconnection.  In particular,
   when Extra Traffic is involved, it is easily possible to deliver the
   wrong traffic to the wrong destination.  Similarly, an intrusion that
   sets up what appears to be a valid protection LSP and then causes a
   fault may be able to divert traffic.

   Moreover, tampering with a routing information exchange may also have
   an effect on traffic engineering.  Therefore, any mechanisms used for
   securing and authenticating the transmission of routing information
   SHOULD be applied in the present context.





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7.  Contributors

   This document was the product of many individuals working together in
   the CCAMP WG Protection and Restoration design team.  The following
   are the authors that contributed to this document:

   Deborah Brungard (AT&T)
   200 S. Laurel Ave.
   Middletown, NJ 07748, USA

   EMail: dbrungard@att.com


   Sudheer Dharanikota

   EMail: sudheer@ieee.org


   Jonathan P. Lang (Sonos)
   223 East De La Guerra Street
   Santa Barbara, CA 93101, USA

   EMail: jplang@ieee.org


   Guangzhi Li (AT&T)
   180 Park Avenue,
   Florham Park, NJ 07932, USA

   EMail: gli@research.att.com


   Eric Mannie

   EMail: eric_mannie@hotmail.com


   Dimitri Papadimitriou (Alcatel)
   Francis Wellesplein, 1
   B-2018 Antwerpen, Belgium

   EMail: dimitri.papadimitriou@alcatel.be









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RFC 4426        GMPLS Recovery Functional Specification       March 2006


   Bala Rajagopalan
   Microsoft India Development Center
   Hyderabad, India

   EMail: balar@microsoft.com


   Yakov Rekhter (Juniper)
   1194 N. Mathilda Avenue
   Sunnyvale, CA 94089, USA

   EMail: yakov@juniper.net

8.  References

8.1.  Normative References

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

   [RFC3471]    Berger, L., "Generalized Multi-Protocol Label Switching
                (GMPLS) Signaling Functional Description", RFC 3471,
                January 2003.

   [RFC4201]    Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling
                in MPLS Traffic Engineering (TE)", RFC 4201, October
                2005.

   [RFC4203]    Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions
                in Support of Generalized Multi-Protocol Label Switching
                (GMPLS)", RFC 4203, October 2005.

   [RFC4204]    Lang, J., Ed., "Link Management Protocol (LMP)", RFC
                4204, October 2005.

   [RFC4205]    Kompella, K., Ed. and Y. Rekhter, Ed., "Intermediate
                System to Intermediate System (IS-IS) Extensions in
                Support of Generalized Multi-Protocol Label Switching
                (GMPLS)", RFC 4205, October 2005.












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8.2.  Informative References

   [RFC3945]    Mannie, E., "Generalized Multi-Protocol Label Switching
                (GMPLS) Architecture", RFC 3945, October 2004.

   [RFC4427]    Mannie, E., Ed. and D. Papadimitriou, Ed., "Recovery
                (Protection and Restoration) Terminology for Generalized
                Multi-Protocol Label Switching (GMPLS)", RFC 4427, March
                2006.

Editors' Addresses

   Jonathan P. Lang
   Sonos, Inc.
   223 East De La Guerra Street
   Santa Barbara, CA 93101

   EMail: jplang@ieee.org


   Bala Rajagopalan
   Microsoft India Development Center
   Hyderabad, India

   Ph: +91-40-5502-7423
   EMail: balar@microsoft.com


   Dimitri Papadimitriou
   Alcatel
   Francis Wellesplein, 1
   B-2018 Antwerpen, Belgium

   Phone: +32 3 240-8491
   EMail: dimitri.papadimitriou@alcatel.be
















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Full Copyright Statement

   Copyright (C) The Internet Society (2006).

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Acknowledgement

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