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Versions: (draft-busi-mpls-tp-oam-framework) 00 01 02 03 04 05 06 07 08 09 10 11 RFC 6371

MPLS Working Group                                        I. Busi (Ed)
Internet Draft                                          Alcatel-Lucent
Intended status: Informational                    B. Niven-Jenkins (Ed)
                                                                   BT
                                                         D. Allan (Ed)
                                                             Ericsson

Expires: January 12, 2011                                July 12, 2010


                        MPLS-TP OAM Framework
                draft-ietf-mpls-tp-oam-framework-07.txt


Abstract

   The Transport Profile of Multi-Protocol Label Switching
   (MPLS-TP) is a packet-based transport technology based on the
   MPLS Traffic Engineering (MPLS-TE) and Pseudowire (PW) data
   plane architectures.

   This document describes a framework to support a comprehensive
   set of Operations, Administration and Maintenance (OAM)
   procedures that fulfill the MPLS-TP OAM requirements for fault,
   performance and protection-switching management and that do not
   rely on the presence of a control plane.

   This document is a product of a joint Internet Engineering Task
   Force (IETF) / International Telecommunications Union
   Telecommunication Standardization Sector (ITU-T) effort to
   include an MPLS Transport Profile within the IETF MPLS and PWE3
   architectures to support the capabilities and functionalities of
   a packet transport network as defined by the ITU-T.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet
   Engineering Task Force (IETF), its areas, and its working
   groups. Note that other groups may also distribute working
   documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other
   documents at any time. It is inappropriate to use Internet-




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   Drafts as reference material or to cite them other than as "work
   in progress".

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on January 12, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with
   respect to this document. Code Components extracted from this
   document must include Simplified BSD License text as described
   in Section 4.e of the Trust Legal Provisions and are provided
   without warranty as described in the BSD License.























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Table of Contents

   1. Introduction................................................5
      1.1. Contributing Authors....................................6
   2. Conventions used in this document............................6
      2.1. Terminology............................................6
      2.2. Definitions............................................7
   3. Functional Components.......................................10
      3.1. Maintenance Entity and Maintenance Entity Group.........10
      3.2. Nested MEGs: SPMEs and Tandem Connection Monitoring.....12
      3.3. MEG End Points (MEPs)..................................14
      3.4. MEG Intermediate Points (MIPs).........................17
      3.5. Server MEPs...........................................18
      3.6. Configuration Considerations...........................19
      3.7. P2MP considerations....................................20
   4. Reference Model............................................21
      4.1. MPLS-TP Section Monitoring (SME).......................23
      4.2. MPLS-TP LSP End-to-End Monitoring (LME)................24
      4.3. MPLS-TP PW Monitoring (PME)............................24
      4.4. MPLS-TP LSP SPME Monitoring (LSME).....................25
      4.5. MPLS-TP MS-PW SPME Monitoring (PSME)...................26
      4.6. Fate sharing considerations for multilink..............28
   5. OAM Functions for proactive monitoring......................29
      5.1. Continuity Check and Connectivity Verification..........30
         5.1.1. Defects identified by CC-V........................31
         5.1.2. Consequent action.................................33
         5.1.3. Configuration considerations......................34
      5.2. Remote Defect Indication...............................35
         5.2.1. Configuration considerations......................36
      5.3. Alarm Reporting........................................36
      5.4. Lock Reporting........................................38
      5.5. Packet Loss Measurement................................39
         5.5.1. Configuration considerations......................40
         5.5.2. Sampling skew.....................................40
         5.5.3. Multilink issues..................................40
      5.6. Packet Delay Measurement...............................41
         5.6.1. Configuration considerations......................41
      5.7. Client Failure Indication..............................41
         5.7.1. Configuration considerations......................42
   6. OAM Functions for on-demand monitoring......................42
      6.1. Connectivity Verification..............................43
         6.1.1. Configuration considerations......................44
      6.2. Packet Loss Measurement................................45
         6.2.1. Configuration considerations......................45
         6.2.2. Sampling skew.....................................45
         6.2.3. Multilink issues..................................46
      6.3. Diagnostic Tests.......................................46


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         6.3.1. Throughput Estimation.............................46
         6.3.2. Data plane Loopback...............................47
      6.4. Route Tracing.........................................48
         6.4.1. Configuration considerations......................48
      6.5. Packet Delay Measurement...............................48
         6.5.1. Configuration considerations......................49
   7. OAM Functions for administration control....................49
      7.1. Lock Instruct.........................................49
         7.1.1. Locking a transport path..........................50
         7.1.2. Unlocking a transport path........................50
   8. Security Considerations.....................................51
   9. IANA Considerations........................................51
   10. Acknowledgments...........................................52
   11. References................................................53
      11.1. Normative References..................................53
      11.2. Informative References................................54
































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Editors' Note:

   This Informational Internet-Draft is aimed at achieving IETF
   Consensus before publication as an RFC and will be subject to an
   IETF Last Call.

   [RFC Editor, please remove this note before publication as an
   RFC and insert the correct Streams Boilerplate to indicate that
   the published RFC has IETF Consensus.]

1. Introduction

   As noted in [8], the transport profile of multi-protocol label
   switching (MPLS-TP) is a packet-based transport technology based on
   the MPLS Traffic Engineering (MPLS-TE) and Pseudo Wire (PW) data
   plane architectures defined in RFC 3031 [1], RFC 3985 [2] and RFC
   5659 [4].

   MPLS-TP supports a comprehensive set of Operations,
   Administration and Maintenance (OAM) procedures for fault,
   performance and protection-switching management and that do not
   rely on the presence of a control plane.

   In line with [13], existing MPLS OAM mechanisms will be used
   wherever possible and extensions or new OAM mechanisms will be
   defined only where existing mechanisms are not sufficient to
   meet the requirements. Extensions do not deprecate support for
   existing MPLS OAM capabilities.

   The MPLS-TP OAM framework defined in this document provides a
   comprehensive set of OAM procedures that satisfy the MPLS-TP OAM
   requirements of RFC 5860 [10]. In this regard, it defines
   similar OAM functionality as for existing SONET/SDH and OTN OAM
   mechanisms (e.g. [17]).

   The MPLS-TP OAM framework is applicable to both LSPs and
   (MS-)PWs and supports co-routed and associated bidirectional p2p
   transport paths as well as unidirectional p2p and p2mp transport
   paths.

   This document is a product of a joint Internet Engineering Task
   Force (IETF) / International Telecommunication Union
   Telecommunication Standardization Sector (ITU-T) effort to
   include an MPLS Transport Profile within the IETF MPLS and PWE3
   architectures to support the capabilities and functionalities of
   a packet transport network as defined by the ITU-T.



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1.1. Contributing Authors

   Dave Allan, Italo Busi, Ben Niven-Jenkins, Annamaria Fulignoli,
   Enrique Hernandez-Valencia, Lieven Levrau, Vincenzo Sestito,
   Nurit Sprecher, Huub van Helvoort, Martin Vigoureux, Yaacov
   Weingarten, Rolf Winter

2. Conventions used in this document

2.1. Terminology

   AC   Attachment Circuit

   DBN  Domain Border Node

   LER  Label Edge Router

   LME  LSP Maintenance Entity

   LMEG LSP ME Group

   LSP  Label Switched Path

   LSR  Label Switching Router

   LSME LSP SPME ME

   LSMEG LSP SPME ME Group

   ME   Maintenance Entity

   MEG  Maintenance Entity Group

   MEP  Maintenance Entity Group End Point

   MIP  Maintenance Entity Group Intermediate Point

   PHB  Per-hop Behavior

   PME  PW Maintenance Entity

   PMEG PW ME Group

   PSME PW SPME ME

   PSMEG PW SPME ME Group



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   PW   Pseudowire

   SLA  Service Level Agreement

   SME  Section Maintenance Entity Group

   SPME Sub-path Maintenance Element

2.2. Definitions

   This document uses the terms defined in RFC 5654 [5].

   This document uses the term 'Per-hop Behavior' as defined in RFC
   2474 [14].

   This document uses the term LSP to indicate either a service LSP
   or a transport LSP (as defined in [8]).

   Where appropriate, the following definitions are aligned with
   ITU-T recommendation Y.1731 [19] in order to have a common,
   unambiguous terminology. They do not however intend to imply a
   certain implementation but rather serve as a framework to
   describe the necessary OAM functions for MPLS-TP.

   Adaptation function: The adaptation function is the interface
   between the client (sub)-layer and the server (sub-layer).

   Data plane loopback: An out-of-service test where an interface
   at either an intermediate or terminating node in a path is
   placed into a data plane loopback state, such that all traffic
   (including user data and OAM) received on the looped back
   interface is sent on the reverse direction of the transport
   path.

   Note - The only way to send an OAM packet to a node set in the data
   plane loopback mode is via TTL expiry, irrespectively on whether the
   node is hosting MIPs or MEPs.

   Domain Border Node (DBN): An intermediate node in an MPLS-TP LSP
   that is at the boundary between two MPLS-TP OAM domains. Such a
   node may be present on the edge of two domains or may be
   connected by a link to the DBN at the edge of another OAM
   domain.

   Down MEP: A MEP that receives OAM packets from, and transmits
   them towards, the direction of a server layer.



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   In-Service: The administrative status of a transport path when
   it is unlocked.

   Intermediate Node: An intermediate node transits traffic for an
   LSP or a PW. An intermediate node may originate OAM flows
   directed to downstream intermediate nodes or MEPs.

   Loopback: See data plane loopback and OAM loopback definitions.

   Maintenance Entity (ME): Some portion of a transport path that
   requires management bounded by two points (called MEPs), and the
   relationship between those points to which maintenance and
   monitoring operations apply (details in section 3.1).

   Maintenance Entity Group (MEG): The set of one or more
   maintenance entities that maintain and monitor a transport path
   in an OAM domain.

   MEP: A MEG end point (MEP) is capable of initiating (MEP Source)
   and terminating (MEP Sink) OAM messages for fault management and
   performance monitoring. MEPs define the boundaries of an ME
   (details in section 3.3).

   MEP Source: A MEP acts as MEP source for an OAM message when it
   originates and inserts the message into the transport path for
   its associated MEG.

   MEP Sink: A MEP acts as a MEP sink for an OAM message when it
   terminates and processes the messages received from its
   associated MEG.

   MIP: A MEG intermediate point (MIP) terminates and processes OAM
   messages that are sent to this particular MIP and may generate
   OAM messages in reaction to received OAM messages. It never
   generates unsolicited OAM messages itself. A MIP resides within
   a MEG between MEPs (details in section 3.3).

   MPLS-TP Section: As defined in [8], it is the link traversed by
   an MPLS-TP LSP.

   OAM domain: A domain, as defined in [5], whose entities are
   grouped for the purpose of keeping the OAM confined within that
   domain.

   Note - within the rest of this document the term "domain" is
   used to indicate an "OAM domain"



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   OAM flow: Is the set of all OAM messages originating with a
   specific MEP source that instrument one direction of a MEG.

   OAM information element: An atomic piece of information
   exchanged between MEPs and/or MIPs in MEG used by an OAM
   application.

   OAM loopback: It is the capability of a node to be directed by a
   received OAM message to generate a reply back to the sender. OAM
   loopback can work in-service and can support different OAM
   functions (e.g., bidirectional on-demand connectivity
   verification).

   OAM Message: One or more OAM information elements that when
   exchanged between MEPs or between MEPs and MIPs performs some
   OAM functionality (e.g. connectivity verification)

   OAM Packet: A packet that carries one or more OAM messages (i.e.
   OAM information elements).

   Out-of-Service: The administrative status of a transport path
   when it is locked.  When a path is in a locked condition, it is
   blocked from carrying client traffic.

   Path Segment: It is either a segment or a concatenated segment,
   as defined in RFC 5654 [5].

   Signal Degrade: A condition declared by a MEP when the data
   forwarding capability associated with a transport path has
   deteriorated, as determined by PM. See also ITU-T recommendation
   G.806 [12].

   Signal Fail: A condition declared by a MEP when the data
   forwarding capability associated with a transport path has
   failed, e.g. loss of continuity. See also ITU-T recommendation
   G.806 [12].

   Tandem Connection: A tandem connection is an arbitrary part of a
   transport path that can be monitored (via OAM) independent of
   the end-to-end monitoring (OAM). The tandem connection may also
   include the forwarding engine(s) of the node(s) at the
   boundaries of the tandem connection. Tandem connections may be
   nested but cannot overlap. See also ITU-T recommendation G.805
   [18].

   Up MEP: A MEP that transmits OAM packets towards, and receives
   them from, the direction of the forwarding engine.


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3. Functional Components

   MPLS-TP is a packet-based transport technology based on the MPLS
   and PW data plane architectures ([1], [2] and [4]) and is
   capable of transporting service traffic where the
   characteristics of information transfer between the transport
   path endpoints can be demonstrated to comply with certain
   performance and quality guarantees.

   In order to describe the required OAM functionality, this
   document introduces a set of functional components.

3.1. Maintenance Entity and Maintenance Entity Group

   MPLS-TP OAM operates in the context of Maintenance Entities
   (MEs) that define a relationship between any two points of a
   transport path to which maintenance and monitoring operations
   apply. The collection of one or more MEs that belongs to the
   same transport path and that are maintained and monitored as a
   group are known as a maintenance entity group (MEG) and the two
   points that define a maintenance entity are called Maintenance
   Entity Group (MEG) End Points (MEPs). In between these two
   points zero or more intermediate points, called Maintenance
   Entity Group Intermediate Points (MIPs), can exist and can be
   shared by more than one ME in a MEG.

   An abstract reference model for an ME is illustrated in Figure 1
   below:


                            +-+    +-+    +-+    +-+
                            |A|----|B|----|C|----|D|
                            +-+    +-+    +-+    +-+

                 Figure 1 ME Abstract Reference Model

   The instantiation of this abstract model to different MPLS-TP
   entities is described in section 4. In Figure 1, nodes A and D
   can be LERs for an LSP or the T-PEs for a MS-PW, nodes B and C
   are LSRs for a LSP or S-PEs for a MS-PW. MEPs reside in nodes A
   and D while MIPs reside in nodes B and C and may reside in A and
   D. The links connecting adjacent nodes can be physical links,
   (sub-)layer LSPs/SPMEs, or serving layer paths.

   This functional model defines the relationships between all OAM
   entities from a maintenance perspective, to allow each



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   Maintenance Entity to monitor and manage the (sub-)layer network
   under its responsibility and to localize problems efficiently.

   An MPLS-TP Maintenance Entity Group may be defined to monitor
   the transport path for fault and/or performance management.

   The MEPs that form a MEG bound the scope of an OAM flows to the
   MEG (i.e. within the domain of the transport path that is being
   monitored and managed). There are two exceptions to this:

   1) A misbranching fault may cause OAM packets to be delivered to
      a MEP that is not in the MEG of origin.

   2) An out-of-band return path may be used between a MIP or a MEP
      and the originating MEP.

   In case of unidirectional point-to-point transport paths, a
   single unidirectional Maintenance Entity is defined to monitor
   it.

   In case of associated bi-directional point-to-point transport
   paths, two independent unidirectional Maintenance Entities are
   defined to independently monitor each direction. This has
   implications for transactions that terminate at or query a MIP,
   as a return path from MIP to source MEP does not necessarily
   exist in the MEG.

   In case of co-routed bi-directional point-to-point transport
   paths, a single bidirectional Maintenance Entity is defined to
   monitor both directions congruently.

   In case of unidirectional point-to-multipoint transport paths, a
   single unidirectional Maintenance entity for each leaf is
   defined to monitor the transport path from the root to that
   leaf.

   In all cases, portions of the transport path may be monitored by
   the instantiation of SPMEs (see section 3.2).

   The reference model for the p2mp MEG is represented in Figure 2.








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                                             +-+
                                          /--|D|
                                         /   +-+
                                      +-+
                                   /--|C|
                        +-+    +-+/   +-+\   +-+
                        |A|----|B|        \--|E|
                        +-+    +-+\   +-+    +-+
                                   \--|F|
                                      +-+

                 Figure 2 Reference Model for p2mp MEG

   In case of p2mp transport paths, the OAM measurements are
   independent for each ME (A-D, A-E and A-F):

   o Fault conditions - some faults may impact more than one ME
      depending from where the failure is located;

   o Packet loss - packet dropping may impact more than one ME
      depending from where the packets are lost;

   o Packet delay - will be unique per ME.

   Each leaf (i.e. D, E and F) terminates OAM flows to monitor the
   ME from itself and the root while the root (i.e. A) generates
   OAM messages common to all the MEs of the p2mp MEG. All nodes
   may implement a MIP in the corresponding MEG.

3.2. Nested MEGs: SPMEs and Tandem Connection Monitoring

   In order to verify and maintain performance and quality
   guarantees, there is a need to not only apply OAM functionality
   on a transport path granularity (e.g. LSP or MS-PW), but also on
   arbitrary parts of transport paths, defined as Tandem
   Connections, between any two arbitrary points along a transport
   path.

   Sub-path Maintenance Elements (SPMEs), as defined in [8], are
   instantiated to provide monitoring of a portion of a set of co-
   routed transport paths (LSPs or MS-PWs). The operational aspects
   of instantiating SPMEs are out of scope of this memo.

   SPMEs can also be employed to meet the requirement to provide
   tandem connection monitoring (TCM).



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   TCM for a given path segment of a transport path is implemented
   by creating an SPME that has a 1:1 association with the path
   segment of the transport path that is to be monitored.

   In the TCM case, this means that the SPME used to provide TCM
   can carry only one and only one transport path thus allowing
   direct correlation between all fault management and performance
   monitoring information gathered for the SPME and the monitored
   path segment of the end-to-end transport path. The SPME is
   monitored using normal LSP monitoring.

   Where resiliency is required across an arbitrary portion of a
   transport path, this may be implemented by more than one
   diversely routed SPMEs with common end points where only one
   SPME is active at any given time.

   There are a number of implications to this approach:

   1) The SPME would use the uniform model of TC code point copying
      between sub-layers for diffserv such that the E2E markings
      and PHB treatment for the transport path was preserved by the
      SPMEs.

   2) The SPME normally would use the short-pipe model for TTL
      handling [6] such that MIP addressing for the E2E entity
      would be not be impacted by the presence of the SPME, but it
      should be possible for an operator to specify use of the
      uniform model.

   3) PM statistics need to be adjusted for the encapsulation
      overhead of the additional SPME sub-layer.

   Note that points 1 an 2 above assume that the TTL copying mode
   and TC copying modes are independently configurable for an LSP.

   There are specific issues with the use of the uniform model of
   TTL copying for an SPME:

   1. As any MIP in the SPME sub-layer is not part of the transport path
      MEG, hence only an out of band return path would be available.

   2. The instantiation of a lower level MEG or protection switching
      actions within a lower level MEG may change the TTL distances to
      MIPs in the higher level MEGs.





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   The endpoints of the SPME are MEPs and limit the scope of an OAM
   flow within each MEG to the MEPs belong to (i.e. within the
   domain of the SPME that is being monitored and managed).

   When considering SPMEs, it is important to consider that the
   following properties apply to all MPLS-TP MEGs:

   o They can be nested but not overlapped, e.g. a MEG may cover a
      segment or a concatenated segment of another MEG, and may
      also include the forwarding engine(s) of the node(s) at the
      edge(s) of the segment or concatenated segment. However when
      MEGs are nested, the MEPs and MIPs in the nested MEG are no
      longer part of the encompassing MEG.

   o It is possible that MEPs of nested MEGs reside on a single
      node but again implemented in such a way that they do not
      overlap.

   o Each OAM flow is associated with a single MEG

   o OAM packets that instrument a particular direction of a
      transport path are subject to the same forwarding treatment
      (i.e. fate share) as the data traffic and in some cases may
      be required to have common queuing discipline E2E with the
      class of traffic monitored. OAM packets can be distinguished
      from the data traffic using the GAL and ACH constructs [7]
      for LSP and Section or the ACH construct [3]and [7] for
      (MS-)PW.

   o When a SPME is instantiated after the transport path has been
      instantiated the addressing of the MIPs will change.

3.3. MEG End Points (MEPs)

   MEG End Points (MEPs) are the source and sink points of a MEG.
   In the context of an MPLS-TP LSP, only LERs can implement MEPs
   while in the context of an SPME LSRs for the MPLS-TP LSP can be
   LERs for SPMEs that contribute to the overall monitoring
   infrastructure for the transport path. Regarding PWs, only T-PEs
   can implement MEPs while for SPMEs supporting one or more PWs
   both T-PEs and S-PEs can implement SPME MEPs. Any MPLS-TP LSR
   can implement a MEP for an MPLS-TP Section.

   MEPs are responsible for activating and controlling all of the
   proactive and on-demand monitoring OAM functionality for the
   MEG. There is a separate class of notifications (such as LKR and
   AIS) that are originated by intermediate nodes and triggered by


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   server layer events. A MEP is capable of originating and
   terminating OAM messages for fault management and performance
   monitoring. These OAM messages are encapsulated into an OAM
   packet using the G-ACh as defined in RFC 5586 [7]. In this case
   the G-ACh message is an OAM message and the channel type
   indicates an OAM message. A MEP terminates all the OAM packets
   it receives from the MEG it belongs to and silently discards
   those that do not (note in the case of a mis-connectivity defect
   there are further actions taken). The MEG the OAM packet belongs
   to is inferred from the MPLS or PW label or, in case of an
   MPLS-TP section, the MEG is inferred from the port on which an
   OAM packet was received with the GAL at the top of the label
   stack.

   OAM packets may require the use of an available "out-of-band"
   return path (as defined in [8]). In such cases sufficient
   information is required in the originating transaction such that
   the OAM reply packet can be constructed (e.g. IP address).

   Each OAM solution will further detail its applicability as a
   pro-active or on-demand mechanism as well as its usage when:

   o The "in-band" return path exists and it is used;

   o An "out-of-band" return path exists and it is used;

   o Any return path does not exist or is not used.

   Once a MEG is configured, the operator can configure which
   proactive OAM functions to use on the MEG but the MEPs are
   always enabled. A node at the edge of a MEG always supports a
   MEP.

   MEPs terminate all OAM packets received from the associated MEG.
   As the MEP corresponds to the termination of the forwarding path
   for a MEG at the given (sub-)layer, OAM packets never leak
   outside of a MEG in a properly configured fault-free
   implementation.

   A MEP of an MPLS-TP transport path coincides with transport path
   termination and monitors it for failures or performance
   degradation (e.g. based on packet counts) in an end-to-end
   scope. Note that both MEP source and MEP sink coincide with
   transport paths' source and sink terminations.

   The MEPs of an SPME are not necessarily coincident with the
   termination of the MPLS-TP transport path and monitor a path


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   segment of the transport path for failures or performance
   degradation (e.g. based on packet counts) only within the
   boundary of the MEG for the SPME.

   An MPLS-TP MEP sink passes a fault indication to its client
   (sub-)layer network as a consequent action of fault detection.

   A node at the edge of a MEG can either support per-node MEP or
   per-interface MEP(s). A per-node MEP resides in an unspecified
   location within the node while a per-interface MEP resides on a
   specific side of the forwarding engine. In particular a per-
   interface MEP is called "Up MEP" or "Down MEP" depending on its
   location relative to the forwarding engine.

         Source node                         Destination node
       ------------------------         ------------------------
      |                        |       |                        |
      |-----              -----|       |-----              -----|
      | MEP |            |     |       |     |            | MEP |
      |     |    ----    |     |       |     |    ----    |     |
      | In  |->-| FW |->-| Out |->- ->-| In  |->-| FW |->-| Out |
      | i/f |    ----    | i/f |       | i/f |    ----    | i/f |
      |-----              -----|       |-----              -----|
      |                        |       |                        |
       ------------------------         ------------------------
                  (1)                               (2)

               Figure 3 Example of per-interface Up MEPs

   Figure 3 describes two examples of per-interface Up MEPs: An Up
   Source MEP in a source node (case 1) and an Up Sink MEP in a
   destination node (case 2).

   The usage of per-interface Up MEPs extends the coverage of the
   ME for both fault and performance monitoring closer to the edge
   of the domain and allows the isolation of failures or
   performance degradation to being within a node or either the
   link or interfaces.

   Each OAM solution will further detail the implications when used
   with per-interface or per-node MEPs, if necessary.

   It may occur that the Up MEPs of an SPME are set on both sides
   of the forwarding engine such that the MEG is entirely internal
   to the node.




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   It should be noted that a ME may span nodes that implement per
   node MEPs and per-interface MEPs. This guarantees backward
   compatibility with most of the existing LSRs that can implement
   only a per-node MEP as in current implementations label
   operations are largely performed on the ingress interface, hence
   the exposure of the GAL as top label will occur at the ingress
   interface.

   Note that a MEP can only exist at the beginning and end of a
   (sub-)layer in MPLS-TP. If there is a need to monitor some
   portion of that LSP or PW, a new sub-layer in the form of an
   SPME is created which permits MEPs and associated MEGs to be
   created.

   In the case where an intermediate node sends a message to a MEP,
   it uses the top label of the stack at that point.

3.4. MEG Intermediate Points (MIPs)

   A MEG Intermediate Point (MIP) is a function located at a point
   between the MEPs of a MEG for a PW, LSP or SPME.

   A MIP is capable of reacting to some OAM packets and forwarding all
   the other OAM packets while ensuring fate sharing with data plane
   packets. However, a MIP does not initiate unsolicited OAM packets,
   but may be addressed by OAM packets initiated by one of the MEPs of
   the MEG. A MIP can generate OAM packets only in response to OAM
   packets that are sent on the MEG it belongs to. The OAM messages
   generated by the MIP are sent in the direction of the source MEP and
   not forwarded to the sink MEP.

   An intermediate node within a MEG can either:

   o Support per-node MIP (i.e. a single MIP per node in an
      unspecified location within the node);

   o Support per-interface MIP (i.e. two or more MIPs per node on
      both sides of the forwarding engine).










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                            Intermediate node
                        ------------------------
                       |                        |
                       |-----              -----|
                       | MIP |            | MIP |
                       |     |    ----    |     |
                    ->-| In  |->-| FW |->-| Out |->-
                       | i/f |    ----    | i/f |
                       |-----              -----|
                       |                        |
                        ------------------------
                Figure 4 Example of per-interface MIPs

   Figure 4 describes an example of two per-interface MIPs at an
   intermediate node of a point-to-point MEG.

   The usage of per-interface MIPs allows the isolation of failures
   or performance degradation to being within a node or either the
   link or interfaces.

   When sending an OAM packet to a MIP, the source MEP should set
   the TTL field to indicate the number of hops necessary to reach
   the node where the MIP resides. It is always assumed that the
   "short pipe" model of TTL handling is used by the MPLS transport
   profile.

   The source MEP should also include Target MIP information in the
   OAM packets sent to a MIP to allow proper identification of the
   MIP within the node. The MEG the OAM packet is associated with
   is inferred from the MPLS label.

   A node at the edge of a MEG can also support per-interface Up
   MEPs and per-interface MIPs on either side of the forwarding
   engine.

   Once a MEG is configured, the operator can enable/disable the
   MIPs on the nodes within the MEG. All the intermediate nodes and
   possibly the end nodes host MIP(s). Local policy allows them to
   be enabled per function and per MEG. The local policy is
   controlled by the management system, which may delegate it to
   the control plane.

3.5.  Server MEPs

   A server MEP is a MEP of a MEG that is either:




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   o Defined in a layer network that is "below", which is to say
      encapsulates and transports the MPLS-TP layer network being
      referenced, or

   o Defined in a sub-layer of the MPLS-TP layer network that is
      "below" which is to say encapsulates and transports the sub-
      layer being referenced.

   A server MEP can coincide with a MIP or a MEP in the client
   (MPLS-TP) (sub-)layer network.

   A server MEP also interacts with the client/server adaptation
   function between the client (MPLS-TP) (sub-)layer network and
   the server (sub-)layer network. The adaptation function
   maintains state on the mapping of MPLS-TP transport paths that
   are setup over that server (sub-)layer's transport path.

   For example, a server MEP can be either:

   o A termination point of a physical link (e.g. 802.3), an SDH
      VC or OTN ODU, for the MPLS-TP Section layer network, defined
      in section 4.1;

   o An MPLS-TP Section MEP for MPLS-TP LSPs, defined in section
      4.2;

   o An MPLS-TP LSP MEP for MPLS-TP PWs, defined in section 4.3;

   o An MPLS-TP SPME MEP used for LSP path segment monitoring, as
      defined in section 4.4, for MPLS-TP LSPs or higher-level
      SPMEs providing LSP path segment monitoring;

   o An MPLS-TP SPME MEP used for PW path segment monitoring, as
      defined in section 4.5, for MPLS-TP PWs or higher-level SPMEs
      providing PW path segment monitoring.

   The server MEP can run appropriate OAM functions for fault
   detection within the server (sub-)layer network, and provides a
   fault indication to its client MPLS-TP layer network. Server MEP
   OAM functions are outside the scope of this document.

3.6. Configuration Considerations

   When a control plane is not present, the management plane
   configures these functional components. Otherwise they can be
   configured either by the management plane or by the control
   plane.


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   Local policy allows disabling the usage of any available "out-
   of-band" return path, as defined in [8], irrespective of what is
   requested by the node originating the OAM packet.

   SPMEs are usually instantiated when the transport path is
   created by either the management plane or by the control plane
   (if present). Sometimes an SPME can be instantiated after the
   transport path is initially created.

3.7. P2MP considerations

   All the traffic sent over a p2mp transport path, including OAM
   packets generated by a MEP, is sent (multicast) from the root to
   all the leaves. As a consequence:

      o To send an OAM packet to all leaves, the source MEP can
        send a single OAM packet that will be delivered by the
        forwarding plane to all the leaves and processed by all the
        leaves.

      o To send an OAM packet to a single leaf, the source MEP
        sends a single OAM packet that will be delivered by the
        forwarding plane to all the leaves but contains sufficient
        information to identify a target leaf, and therefore is
        processed only by the target leaf and ignored by the other
        leaves.

      o To send an OAM packet to a single MIP, the source MEP sends
        a single OAM packet with the TTL field indicating the
        number of hops necessary to reach the node where the MIP
        resides. This packet will be delivered by the forwarding
        plane to all intermediate nodes at the same TTL distance of
        the target MIP and to any leaf that is located at a shorter
        distance. The OAM message must contain sufficient
        information to identify the target MIP and therefore is
        processed only by the target MIP.

      o In order to send an OAM packet to M leaves (i.e., a subset
        of all the leaves), the source MEP sends M different OAM
        packets targeted to each individual leaf in the group of M
        leaves. Aggregated or subsetting mechanisms are outside the
        scope of this document.

   P2MP paths are unidirectional, therefore any return path to a
   source MEP for on-demand transactions will be out-of-band. A
   mechanism to scope the set of MEPs or MIPs expected to respond
   to a given "on-demand" transaction is useful as it relieves the


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   source MEP of the requirement to filter and discard undesired
   responses as normally TTL exhaustion will address all MIPs at a
   given distance from the source, and failure to exhaust TTL will
   address all MEPs.

4. Reference Model

   The reference model for the MPLS-TP framework builds upon the
   concept of a MEG, and its associated MEPs and MIPs, to support
   the functional requirements specified in RFC 5860 [10].

   The following MPLS-TP MEGs are specified in this document:

   o A Section Maintenance Entity Group (SME), allowing monitoring
      and management of MPLS-TP Sections (between MPLS LSRs).

   o An LSP Maintenance Entity Group (LME), allowing monitoring
      and management of an end-to-end LSP (between LERs).

   o A PW Maintenance Entity Group (PME), allowing monitoring and
      management of an end-to-end SS/MS-PWs (between T-PEs).

   o An LSP SPME ME Group (LSMEG), allowing monitoring and
      management of an SPME (between any LERs/LSRs along an LSP).

   o A PW SPME ME Group (PSMEG), allowing monitoring and
      management of an SPME (between any T-PEs/S-PEs along the
      (MS-)PW).

   The MEGs specified in this MPLS-TP framework are compliant with
   the architecture framework for MPLS-TP MS-PWs [4] and LSPs [1].

   Hierarchical LSPs are also supported in the form of SPMEs. In
   this case, each LSP in the hierarchy is a different sub-layer
   network that can be monitored, independently from higher and
   lower level LSPs in the hierarchy, on an end-to-end basis (from
   LER to LER) by a SPME. It is possible to monitor a portion of a
   hierarchical LSP by instantiating a hierarchical SPME between
   any LERs/LSRs along the hierarchical LSP.









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    Native |<------------------ MS-PW1Z ---------------->|  Native
    Layer  |                                             |   Layer
   Service |    |<LSP13>|    |<-LSP3X->|    |<LSPXZ>|    |  Service
    (AC1)  V    V  LSP  V    V   LSP   V    V  LSP  V    V   (AC2)
           +----+  +-+  +----+         +----+  +-+  +----+
   +----+  |TPE1|  | |  |SPE3|         |SPEX|  | |  |TPEZ|   +----+
   |    |  |    |=======|    |=========|    |=======|    |   |    |
   | CE1|--|.......PW13......|...PW3X..|......PWXZ.......|---|CE2 |
   |    |  |    |=======|    |=========|    |=======|    |   |    |
   +----+  | 1  |  |2|  | 3  |         | X  |  |Y|  | Z  |   +----+
           +----+  +-+  +----+         +----+  +-+  +----+
           .                 .         .                 .
           |                 |         |                 |
           |<--- Domain 1 -->|         |<--- Domain Z -->|
           ^----------------- PW1Z  PME -----------------^
           ^--- PW13 PSME ---^         ^--- PWXZ PSME ---^
                ^-------^                   ^-------^
                 LSP13 LME                  LSPXZ LME
                ^--^ ^--^    ^---------^    ^--^ ^--^
               Sec12 Sec23       Sec3X     SecXY SecYZ
                 SME   SME         SME       SME   SME

   TPE1: Terminating Provider Edge 1  SPE2: Switching Provider Edge
   3
   TPEX: Terminating Provider Edge X  SPEZ: Switching Provider Edge
   Z

   ^---^ ME   ^     MEP  ====   LSP      .... PW

        Figure 5 Reference Model for the MPLS-TP OAM Framework

   Figure 5 depicts a high-level reference model for the MPLS-TP
   OAM framework. The figure depicts portions of two MPLS-TP
   enabled network domains, Domain 1 and Domain Z. In Domain 1,
   LSR1 is adjacent to LSR2 via the MPLS-TP Section Sec12 and LSR2
   is adjacent to LSR3 via the MPLS-TP Section Sec23. Similarly, in
   Domain Z, LSRX is adjacent to LSRY via the MPLS-TP Section SecXY
   and LSRY is adjacent to LSRZ via the MPLS-TP Section SecYZ. In
   addition, LSR3 is adjacent to LSRX via the MPLS-TP Section 3X.

   Figure 5 also shows a bi-directional MS-PW (PW1Z) between AC1 on
   TPE1 and AC2 on TPEZ. The MS-PW consists of three bi-directional
   PW path segments: 1) PW13 path segment between T-PE1 and S-PE3
   via the bi-directional LSP13 LSP, 2) PW3X path segment between
   S-PE3 and S-PEX, via the bi-directional LSP3X LSP, and 3) PWXZ



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   path segment between S-PEX and T-PEZ via the bi-directional
   LSPXZ LSP.

   The MPLS-TP OAM procedures that apply to a MEG are expected to
   operate independently from procedures on other MEGs. Yet, this
   does not preclude that multiple MEGs may be affected
   simultaneously by the same network condition, for example, a
   fiber cut event.

   Note that there are no constrains imposed by this OAM framework
   on the number, or type (p2p, p2mp, LSP or PW), of MEGs that may
   be instantiated on a particular node. In particular, when
   looking at Figure 5, it should be possible to configure one or
   more MEPs on the same node if that node is the endpoint of one
   or more MEGs.

   Figure 5 does not describe a PW3X PSME because typically SPMEs
   are used to monitor an OAM domain (like PW13 and PWXZ PSMEs)
   rather than the segment between two OAM domains. However the OAM
   framework does not pose any constraints on the way SPMEs are
   instantiated as long as they are not overlapping.

   The subsections below define the MEGs specified in this MPLS-TP
   OAM architecture framework document. Unless otherwise stated,
   all references to domains, LSRs, MPLS-TP Sections, LSPs,
   pseudowires and MEGs in this section are made in relation to
   those shown in Figure 5.

4.1. MPLS-TP Section Monitoring (SME)

   An MPLS-TP Section ME (SME) is an MPLS-TP maintenance entity
   intended to monitor an MPLS-TP Section as defined in RFC 5654
   [5]. An SME may be configured on any MPLS-TP section. SME OAM
   packets must fate share with the user data packets sent over the
   monitored MPLS-TP Section.

   An SME is intended to be deployed for applications where it is
   preferable to monitor the link between topologically adjacent
   (next hop in this layer network) MPLS-TP LSRs rather than
   monitoring the individual LSP or PW path segments traversing the
   MPLS-TP Section and the server layer technology does not provide
   adequate OAM capabilities.

   Figure 5 shows five Section MEs configured in the network
   between AC1 and AC2:




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   1. Sec12 ME associated with the MPLS-TP Section between LSR 1
      and LSR 2,

   2. Sec23 ME associated with the MPLS-TP Section between LSR 2
      and LSR 3,

   3. Sec3X ME associated with the MPLS-TP Section between LSR 3
      and LSR X,

   4. SecXY ME associated with the MPLS-TP Section between LSR X
      and LSR Y, and

   5. SecYZ ME associated with the MPLS-TP Section between LSR Y
      and LSR Z.

4.2. MPLS-TP LSP End-to-End Monitoring (LME)

   An MPLS-TP LSP ME (LME) is an MPLS-TP maintenance entity
   intended to monitor an end-to-end LSP between two LERs. An LME
   may be configured on any MPLS LSP. LME OAM packets must fate
   share with user data packets sent over the monitored MPLS-TP
   LSP.

   An LME is intended to be deployed in scenarios where it is
   desirable to monitor an entire LSP between its LERs, rather
   than, say, monitoring individual PWs.

   Figure 5 depicts two LMEs configured in the network between AC1
   and AC2: 1) the LSP13 LME between LER 1 and LER 3, and 2) the
   LSPXZ LME between LER X and LER Y. Note that the presence of a
   LSP3X LME in such a configuration is optional, hence, not
   precluded by this framework. For instance, the SPs may prefer to
   monitor the MPLS-TP Section between the two LSRs rather than the
   individual LSPs.

4.3. MPLS-TP PW Monitoring (PME)

   An MPLS-TP PW ME (PME) is an MPLS-TP maintenance entity intended
   to monitor a SS-PW or MS-PW between a pair of T-PEs. A PME can
   be configured on any SS-PW or MS-PW. PME OAM packets must fate
   share with the user data packets sent over the monitored PW.

   A PME is intended to be deployed in scenarios where it is
   desirable to monitor an entire PW between a pair of MPLS-TP
   enabled T-PEs rather than monitoring the LSP aggregating
   multiple PWs between PEs.



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           |<----------------- MS-PW1Z ----------------->|
           |                                             |
           |    |<LSP13>|    |<-LSP3X->|    |<LSPXZ>|    |
           V    V  LSP  V    V   LSP   V    V  LSP  V    V
           +----+  +-+  +----+         +----+  +-+  +----+
   +---+   |TPE1|  | |  |SPE3|         |SPEX|  | |  |TPEZ|   +---+
   |   |AC1|    |=======|    |=========|    |=======|    |AC2|   |
   |CE1|---|.......PW13......|...PW3X..|.......PWXZ......|---|CE2|
   |   |   |    |=======|    |=========|    |=======|    |   |   |
   +---+   | 1  |  |2|  | 3  |         | X  |  |Y|  | Z  |   +---+
           +----+  +-+  +----+         +----+  +-+  +----+
           ^-------------------PW1Z PME------------------^

                     Figure 6 MPLS-TP PW ME (PME)

   Figure 6 depicts a MS-PW (MS-PW1Z) consisting of three path
   segments: PW13, PW3X and PWXZ and its associated end-to-end PME
   (PW1Z PME).

4.4. MPLS-TP LSP SPME Monitoring (LSME)

   An MPLS-TP LSP SPME ME (LSME) is an MPLS-TP LSP with associated
   maintenance entity intended to monitor an arbitrary part of an
   LSP between the pair of MEPs instantiated for the SPME
   independent from the end-to-end monitoring (LME). An LSME can
   monitor an LSP segment or concatenated segment and it may also
   include the forwarding engine(s) of the node(s) at the edge(s)
   of the segment or concatenated segment.

   Multiple LSMEs can be configured on any LSP. The LSRs that
   terminate the LSME may or may not be immediately adjacent at the
   MPLS-TP layer. LSME OAM packets must fate share with the user
   data packets sent over the monitored LSP path segment.

   A LSME can be defined between the following entities:

   o The end node and any intermediate node of a given LSP.

   o Any two intermediate nodes of a given LSP.

   An LSME is intended to be deployed in scenarios where it is
   preferable to monitor the behaviour of a part of an LSP or set
   of LSPs rather than the entire LSP itself, for example when
   there is a need to monitor a part of an LSP that extends beyond
   the administrative boundaries of an MPLS-TP enabled
   administrative domain.



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         |<-------------------- PW1Z ------------------->|
         |                                               |
         |    |<-------------LSP1Z LSP------------->|    |
         |    |<-LSP13->|    |<LSP3X>|    |<-LSPXZ->|    |
         V    V  S-LSP  V    V S-LSP V    V  S-LSP  V    V
         +----+   +-+   +----+       +----+   +-+   +----+
+----+   | PE1|   | |   |DBN3|       |DBNX|   | |   | PEZ|   +----+
|    |AC1|    |=====================================|    |AC2|    |
| CE1|---|.....................PW1Z......................|---|CE2 |
|    |   |    |=====================================|    |   |    |
+----+   | 1  |   |2|   | 3  |       | X  |   |Y|   | Z  |   +----+
         +----+   +-+   +----+       +----+   +-+   +----+
         .                   .       .                   .
         |                   |       |                   |
         |<---- Domain 1 --->|       |<---- Domain Z --->|

              ^---------^                 ^---------^
              LSP13 LSME                   LSPXZ LSME
              ^-------------------------------------^
                              LSP1Z LME

   DBN: Domain Border Node

                  Figure 7 MPLS-TP LSP SPME ME (LSME)

   Figure 7 depicts a variation of the reference model in Figure 5
   where there is an end-to-end LSP (LSP1Z) between PE1 and PEZ.
   LSP1Z consists of, at least, three LSP Concatenated Segments:
   LSP13, LSP3X and LSPXZ. In this scenario there are two separate
   LSMEs configured to monitor the LSP1Z: 1) a LSME monitoring the
   LSP13 Concatenated Segment on Domain 1 (LSP13 LSME), and 2) a
   LSME monitoring the LSPXZ Concatenated Segment on Domain Z
   (LSPXZ LSME).

   It is worth noticing that LSMEs can coexist with the LME
   monitoring the end-to-end LSP and that LSME MEPs and LME MEPs
   can be coincident in the same node (e.g. PE1 node supports both
   the LSP1Z LME MEP and the LSP13 LSME MEP).

4.5. MPLS-TP MS-PW SPME Monitoring (PSME)

   An MPLS-TP MS-PW SPME Monitoring ME (PSME) is an MPLS-TP
   maintenance entity intended to monitor an arbitrary part of an
   MS-PW between a given pair of PEs independently from the end-to-
   end monitoring (PME). A PSME can monitor a PW segment or
   concatenated segment and it may also include the forwarding


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   engine(s) of the node(s) at the edge(s) of the segment or
   concatenated segment.

   S-PE placement is typically dictated by considerations other
   than OAM. S-PEs will frequently reside at operational boundaries
   such as the transition from distributed (CP) to centralized
   (NMS) control or at a routing area boundary. As such the
   architecture would superficially appear not to have the
   flexibility that arbitrary placement of SPME segments would
   imply. More arbitrary placement of MEs for a PW would require
   additional hierarchical components, beyond the SPMEs between PEs
   Multiple PSMEs can be configured on any MS-PW. The PEs may or
   may not be immediately adjacent at the MS-PW layer. PSME OAM
   packets fate share with the user data packets sent over the
   monitored PW path Segment.

   A PSME can be defined between the following entities:

   o T-PE and any S-PE of a given MS-PW

   o Any two S-PEs of a given MS-PW. It can span several PW
      segments.

   Note that, in line with the SPME description in section 3.2, when a
   PW SPME is instantiated after the MS-PW has been instantiated, the
   addressing of the MIPs will change and MIPs in the nested MEG are no
   longer part of the encompassing MEG. This means that the S-PE nodes
   hosting these MIPs are no longer S-PEs but P nodes at the SPME LSP
   level. The consequences are that the S-PEs hosting the PSME MEPs
   become adjacent S-PEs.

   A PSME is intended to be deployed in scenarios where it is
   preferable to monitor the behaviour of a part of a MS-PW rather
   than the entire end-to-end PW itself, for example to monitor an
   MS-PW path segment within a given network domain of an inter-
   domain MS-PW.












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           |<----------------- MS-PW1Z ----------------->|
           |                                             |
           |    |<LSP13>|    |<-LSP3X->|    |<LSPXZ>|    |
           V    V  LSP  V    V   LSP   V    V  LSP  V    V
           +----+  +-+  +----+         +----+  +-+  +----+
   +---+   |TPE1|  | |  |SPE3|         |SPEX|  | |  |TPEZ|   +---+
   |   |AC1|    |=======|    |=========|    |=======|    |AC2|   |
   |CE1|---|.......PW13......|...PW3X..|.......PWXZ......|---|CE2|
   |   |   |    |=======|    |=========|    |=======|    |   |   |
   +---+   | 1  |  |2|  | 3  |         | X  |  |Y|  | Z  |   +---+
           +----+  +-+  +----+         +----+  +-+  +----+

           ^--- PW1 PSME ----^         ^--- PW5 PSME ----^
           ^-------------------PW1Z PME------------------^

             Figure 8 MPLS-TP MS-PW SPME Monitoring (PSME)

   Figure 8 depicts the same MS-PW (MS-PW1Z) between AC1 and AC2 as
   in Figure 6. In this scenario there are two separate PSMEs
   configured to monitor MS-PW1Z: 1) a PSME monitoring the PW13 MS-
   PW path segment on Domain 1 (PW13 PSME), and 2) a PSME
   monitoring the PWXZ MS-PW path segment on Domain Z with (PWXZ
   PSME).

   It is worth noticing that PSMEs can coexist with the PME
   monitoring the end-to-end MS-PW and that PSME MEPs and PME MEPs
   can be coincident in the same node (e.g. TPE1 node supports both
   the PW1Z PME MEP and the PW13 PSME MEP).

4.6. Fate sharing considerations for multilink

   Multilink techniques are in use today and are expected to
   continue to be used in future deployments. These techniques
   include Ethernet Link Aggregations [20], the use of Link
   Bundling for MPLS [16] where the option to spread traffic over
   component links is supported and enabled. While the use of Link
   Bundling can be controlled at the MPLS-TP layer, use of Link
   Aggregation (or any server layer specific multilink) is not
   necessarily under control of the MPLS-TP layer. Other techniques
   may emerge in the future. These techniques share the
   characteristic that an LSP may be spread over a set of component
   links and therefore be reordered but no flow within the LSP is
   reordered (except when very infrequent and minimally disruptive
   load rebalancing occurs).

   The use of multilink techniques may be prohibited or permitted
   in any particular deployment. If multilink techniques are used,


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   the deployment can be considered to be only partially MPLS-TP
   compliant, however this is unlikely to prevent its use.

   The implications for OAM is that not all components of a
   multilink will be exercised, independent server layer OAM being
   required to exercise the aggregated link components. This has
   further implications for MIP and MEP placement, as per-interface
   MIPs or "down" MEPs on a multilink interface are akin to a layer
   violation, as they instrument at the granularity of the server
   layer. The implications for reduced OAM loss measurement
   functionality is documented in sections 5.5.3 and 6.2.3.

5. OAM Functions for proactive monitoring

   In this document, proactive monitoring refers to OAM operations
   that are either configured to be carried out periodically and
   continuously or preconfigured to act on certain events such as
   alarm signals.

   Proactive monitoring is usually performed "in-service". Such
   transactions are universally MEP to MEP in operation while
   notifications emerging from the serving layer are MIP to MEP or
   can be MIP to MIP. The control and measurement considerations
   are:

   1. Proactive monitoring for a MEG is typically configured at
      transport path creation time.

   2. The operational characteristics of in-band measurement
      transactions (e.g., CV, LM etc.) are configured at the MEPs.

   3. Server layer events are reported by transactions originating
      at intermediate nodes.

   4. The measurements resulting from proactive monitoring are
      typically only reported outside of the MEG as unsolicited
      notifications for "out of profile" events, such as faults or
      loss measurement indication of excessive impairment of
      information transfer capability.

   5. The measurements resulting from proactive monitoring may be
      periodically harvested by an EMS/NMS.

   For statically provisioned transport paths the above information
   is statically configured; for dynamically established transport
   paths the configuration information is signaled via the control
   plane or configured via the management plane.


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   The operator enables/disables some of the consequent actions
   defined in section 5.1.2.

5.1. Continuity Check and Connectivity Verification

   Proactive Continuity Check functions, as required in section
   2.2.2 of RFC 5860 [10], are used to detect a loss of continuity
   defect (LOC) between two MEPs in a MEG.

   Proactive Connectivity Verification functions, as required in
   section 2.2.3 of RFC 5860 [10], are used to detect an unexpected
   connectivity defect between two MEGs (e.g. mismerging or
   misconnection), as well as unexpected connectivity within the
   MEG with an unexpected MEP.

   Both functions are based on the (proactive) generation of OAM
   packets by the source MEP that are processed by the sink MEP. As
   a consequence these two functions are grouped together into
   Continuity Check and Connectivity Verification (CC-V) OAM
   packets.

   In order to perform pro-active Connectivity Verification, each
   CC-V OAM packet also includes a globally unique Source MEP
   identifier. When used to perform only pro-active Continuity
   Check, the CC-V OAM packet will not include any globally unique
   Source MEP identifier. Different formats of MEP identifiers are
   defined in [9] to address different environments. When MPLS-TP
   is deployed in transport network environments where IP
   addressing is not used in the forwarding plane, the ICC-based
   format for MEP identification is used. When MPLS-TP is deployed
   in an IP-based environment, the IP-based MEP identification is
   used.

   As a consequence, it is not possible to detect misconnections
   between two MEGs monitored only for continuity as neither the
   OAM message type nor OAM message content provides sufficient
   information to disambiguate an invalid source. To expand:

   o For CC leaking into a CC monitored MEG - undetectable

   o For CV leaking into a CC monitored MEG - presence of
      additional Source MEP identifier allows detecting the fault

   o For CC leaking into a CV monitored MEG - lack of additional
      Source MEP identifier allows detecting the fault.




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   o For CV leaking into a CV monitored MEG - different Source MEP
      identifier permits fault to be identified.

   CC-V OAM packets are transmitted at a regular, operator's
   configurable, rate. The default CC-V transmission periods are
   application dependent (see section 5.1.3).

   Proactive CC-V OAM packets are transmitted with the "minimum
   loss probability PHB" within the transport path (LSP, PW) they
   are monitoring. This PHB is configurable on network operator's
   basis. PHBs can be translated at the network borders by the same
   function that translates it for user data traffic. The
   implication is that CC-V fate shares with much of the forwarding
   implementation, but not all aspects of PHB processing are
   exercised. Either on-demand tools are used for finer grained
   fault finding or an implementation may utilize a CC-V flow per
   PHB with the entire E-LSP fate sharing with any individual PHB.

   In a bidirectional point-to-point transport path, when a MEP is
   enabled to generate pro-active CC-V OAM packets with a
   configured transmission rate, it also expects to receive pro-
   active CC-V OAM packets from its peer MEP at the same
   transmission rate as a common SLA applies to all components of
   the transport path. In a unidirectional transport path (either
   point-to-point or point-to-multipoint), only the source MEP is
   enabled to generate CC-V OAM packets and only the sink MEP is
   configured to expect these packets at the configured rate.

   MIPs, as well as intermediate nodes not supporting MPLS-TP OAM,
   are transparent to the pro-active CC-V information and forward
   these pro-active CC-V OAM packets as regular data packets.

   During path setup and tear down, situations arise where CC-V
   checks would give rise to alarms, as the path is not fully
   instantiated. In order to avoid these spurious alarms the
   following procedures are recommended. At initialization, the MEP
   source function (generating pro-active CC-V packets) should be
   enabled prior to the corresponding MEP sink function (detecting
   continuity and connectivity defects).  When disabling the CC-V
   proactive functionality, the MEP sink function should be
   disabled prior to the corresponding MEP source function.

5.1.1. Defects identified by CC-V

   Pro-active CC-V functions allow a sink MEP to detect the defect
   conditions described in the following sub-sections. For all of



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   the described defect cases, the sink MEP should notify the
   equipment fault management process of the detected defect.

5.1.1.1. Loss Of Continuity defect

   When proactive CC-V is enabled, a sink MEP detects a loss of
   continuity (LOC) defect when it fails to receive pro-active CC-V
   OAM packets from the source MEP.

   o Entry criteria:  If no pro-active CC-V OAM packets from the
      source MEP with the correct encapsulation (and in the case of
      CV, this includes the requirement to have a correct globally
      unique Source MEP identifier) are received within the
      interval equal to 3.5 times the receiving MEP's configured
      CC-V reception period.

   o Exit criteria: A pro-active CC-V OAM packet from the source
      MEP with the correct encapsulation (and again in the case of
      CV, with the correct globally unique Source MEP identifier)
      is received.

5.1.1.2. Mis-connectivity defect

   When a pro-active CC-V OAM packet is received, a sink MEP
   identifies a mis-connectivity defect (e.g. mismerge,
   misconnection or unintended looping) when the received packet
   carries an incorrect globally unique Source MEP identifier.

   o Entry criteria: The sink MEP receives a pro-active CC-V OAM
      packet with an incorrect globally unique Source MEP
      identifier or receives a CC or CC/CV OAM packet with an
      unexpected encapsulation.

     It should be noted that there are practical limitations to
     detecting unexpected encapsulation. It is possible that there
     are mis-connectivity scenarios where OAM frames can alias as
     payload IF a transport path can carry an arbitrary payload
     without a pseudo wire.

   o Exit criteria: The sink MEP does not receive any pro-active
      CC-V OAM packet with an incorrect globally unique Source MEP
      identifier for an interval equal at least to 3.5 times the
      longest transmission period of the pro-active CC-V OAM
      packets received with an incorrect globally unique Source MEP
      identifier since this defect has been raised. This requires
      the OAM message to self identify the CC-V periodicity as not
      all MEPs can be expected to have knowledge of all MEGs.


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5.1.1.3. Period Misconfiguration defect

   If pro-active CC-V OAM packets are received with a correct
   globally unique Source MEP identifier but with a transmission
   period different than the locally configured reception period,
   then a CV period mis-configuration defect is detected.

   o Entry criteria: A MEP receives a CC-V pro-active packet with
      correct globally unique Source MEP identifier but with a
      Period field value different than its own CC-V configured
      transmission period.

   o Exit criteria: The sink MEP does not receive any pro-active
      CC-V OAM packet with a correct globally unique Source MEP
      identifier and an incorrect transmission period for an
      interval equal at least to 3.5 times the longest transmission
      period of the pro-active CC-V OAM packets received with a
      correct globally unique Source MEP identifier and an
      incorrect transmission period since this defect has been
      raised.

5.1.2. Consequent action

   A sink MEP that detects one of the defect conditions defined in
   section 5.1.1 performs the following consequent actions.

   If a MEP detects an unexpected globally unique Source MEP
   Identifier, it blocks all the traffic (including also the user
   data packets) that it receives from the misconnected transport
   path.

   If a MEP detects LOC defect that is not caused by a period
   mis-configuration, it should block all the traffic (including
   also the user data packets) that it receives from the transport
   path, if this consequent action has been enabled by the
   operator.

   It is worth noticing that the OAM requirements document [10]
   recommends that CC-V proactive monitoring be enabled on every
   MEG in order to reliably detect connectivity defects. However,
   CC-V proactive monitoring can be disabled by an operator for a
   MEG. In the event of a misconnection between a transport path
   that is pro-actively monitored for CC-V and a transport path
   which is not, the MEP of the former transport path will detect a
   LOC defect representing a connectivity problem (e.g. a
   misconnection with a transport path where CC-V proactive
   monitoring is not enabled) instead of a continuity problem, with


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   a consequent wrong traffic delivering. For these reasons, the
   traffic block consequent action is applied even when a LOC
   condition occurs. This block consequent action can be disabled
   through configuration. This deactivation of the block action may
   be used for activating or deactivating the monitoring when it is
   not possible to synchronize the function activation of the two
   peer MEPs.

   If a MEP detects a LOC defect (section 5.1.1.1), a
   mis-connectivity defect (section 5.1.1.2) it declares a signal
   fail condition at the transport path level.

   It is a matter if local policy if a MEP detecting a period
   misconfiguration defect (section 5.1.1.3) declares a signal fail
   condition at the transport path level.

5.1.3. Configuration considerations

   At all MEPs inside a MEG, the following configuration
   information needs to be configured when a proactive CC-V
   function is enabled:

   o MEG ID; the MEG identifier to which the MEP belongs;

   o MEP-ID; the MEP's own identity inside the MEG;

   o list of the other MEPs in the MEG. For a point-to-point MEG
      the list would consist of the single MEP ID from which the
      OAM packets are expected. In case of the root MEP of a p2mp
      MEG, the list is composed by all the leaf MEP IDs inside the
      MEG. In case of the leaf MEP of a p2mp MEG, the list is
      composed by the root MEP ID (i.e. each leaf needs to know the
      root MEP ID from which it expect to receive the CC-V OAM
      packets).

   o PHB; it identifies the per-hop behaviour of CC-V packet.
      Proactive CC-V packets are transmitted with the "minimum loss
      probability PHB" previously configured within a single
      network operator. This PHB is configurable on network
      operator's basis. PHBs can be translated at the network
      borders.

   o transmission rate; the default CC-V transmission periods are
      application dependent (depending on whether they are used to
      support fault management, performance monitoring, or
      protection switching applications):



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        o Fault Management: default transmission period is 1s (i.e.
          transmission rate of 1 packet/second).

        o Performance Monitoring: default transmission period is
          100ms (i.e. transmission rate of 10 packets/second).
          Performance monitoring is only relevant when the
          transport path is defect free. CC-V contributes to the
          accuracy of PM statistics by permitting the defect free
          periods to be properly distinguished.

        o Protection Switching: default transmission period is
          3.33ms (i.e. transmission rate of 300 packets/second), in
          order to achieve sub-50ms the CC-V defect entry criteria
          should resolve in less than 10msec, and complete a
          protection switch within a subsequent period of 50 msec.
          It is also possible to lengthen the transmission period
          to 10ms (i.e. transmission rate of 100 packets/second):
          in this case the CC-V defect entry criteria is reached
          later (i.e. 30msec).

   It should be possible for the operator to configure these
   transmission rates for all applications, to satisfy his internal
   requirements.

   Note that the reception period is the same as the configured
   transmission rate.

   For statically provisioned transport paths the above parameters
   are statically configured; for dynamically established transport
   paths the configuration information are signaled via the control
   plane.

   The operator should be able to enable/disable some of the
   consequent actions. Which consequent action can be
   enabled/disabled are described in section 5.1.2.

5.2. Remote Defect Indication

   The Remote Defect Indication (RDI) function, as required in
   section 2.2.9 of RFC  5860 [10], is an indicator that is
   transmitted by a sink MEP to communicate to its source MEP that
   a signal fail condition exists.  RDI is only used for
   bidirectional connections and is associated with proactive CC-V.
   The RDI indicator is piggy-backed onto the CC-V packet.

   When a MEP detects a signal fail condition (e.g. in case of a
   continuity or connectivity defect), it should begin transmitting


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   an RDI indicator to its peer MEP.  The RDI information will be
   included in all pro-active CC-V packets that it generates for
   the duration of the signal fail condition's existence.

   A MEP that receives packets from a peer MEP (as best can be
   validated with the CC or CV tool in use) with the RDI
   information should determine that its peer MEP has encountered a
   defect condition associated with a signal fail.

   MIPs as well as intermediate nodes not supporting MPLS-TP OAM
   are transparent to the RDI indicator and forward these proactive
   CC-V packets that include the RDI indicator as regular data
   packets, i.e. the MIP should not perform any actions nor examine
   the indicator.

   When the signal fail defect condition clears, the MEP should
   clear the RDI indicator from subsequent transmission of pro-
   active CC-V packets.  A MEP should clear the RDI defect upon
   reception of a pro-active CC-V packet from the source MEP with
   the RDI indicator cleared.

5.2.1. Configuration considerations

   In order to support RDI indication, this may be a unique OAM
   message or an OAM information element embedded in a CV message.
   In this case the RDI transmission rate and PHB of the OAM
   packets carrying RDI should be the same as that configured for
   CC-V.

5.3. Alarm Reporting

   The Alarm Reporting function, as required in section 2.2.8 of
   RFC 5860 [10], relies upon an Alarm Indication Signal (AIS)
   message to suppress alarms following detection of defect
   conditions at the server (sub-)layer.

   When a server MEP asserts signal fail, the co-located MPLS-TP
   client (sub-)layer adaptation function generates packets with
   AIS information in the downstream direction to allow the
   suppression of secondary alarms at the MEP in the client (sub-
   )layer.

   The generation of packets with AIS information starts
   immediately when the server MEP asserts signal fail. These
   periodic packets, with AIS information, continue to be
   transmitted until the signal fail condition is cleared. It is
   assumed that to avoid race conditions a MEP detecting loss of


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   continuity will wait for a hold off interval prior to asserting
   an alarm to the management system.

   Upon receiving a packet with AIS information an MPLS-TP MEP
   enters an AIS defect condition and suppresses loss of continuity
   alarms associated with its peer MEP but does not block traffic
   received from the transport path. A MEP resumes loss of
   continuity alarm generation upon detecting loss of continuity
   defect conditions in the absence of AIS condition.

   MIPs, as well as intermediate nodes, do not process AIS
   information and forward these AIS OAM packets as regular data
   packets.

   For example, let's consider a fiber cut between LSR 1 and LSR 2
   in the reference network of Figure 5. Assuming that all the MEGs
   described in Figure 5 have pro-active CC-V enabled, a LOC defect
   is detected by the MEPs of Sec12 SME, LSP13 LME, PW1 PSME and
   PW1Z PME, however in a transport network only the alarm
   associated to the fiber cut needs to be reported to an NMS while
   all secondary alarms should be suppressed (i.e. not reported to
   the NMS or reported as secondary alarms).

   If the fiber cut is detected by the MEP in the physical layer
   (in LSR2), LSR2 can generate the proper alarm in the physical
   layer and suppress the secondary alarm associated with the LOC
   defect detected on Sec12 SME. As both MEPs reside within the
   same node, this process does not involve any external protocol
   exchange. Otherwise, if the physical layer has not enough OAM
   capabilities to detect the fiber cut, the MEP of Sec12 SME in
   LSR2 will report a LOC alarm.

   In both cases, the MEP of Sec12 SME in LSR 2 notifies the
   adaptation function for LSP13 LME that then generates AIS
   packets on the LSP13 LME in order to allow its MEP in LSR3 to
   suppress the LOC alarm. LSR3 can also suppress the secondary
   alarm on PW13 PSME because the MEP of PW13 PSME resides within
   the same node as the MEP of LSP13 LME. The MEP of PW13 PSME in
   LSR3 also notifies the adaptation function for PW1Z PME that
   then generates AIS packets on PW1Z PME in order to allow its MEP
   in LSRZ to suppress the LOC alarm.

   The generation of AIS packets for each MEG in the MPLS-TP client
   (sub-)layer is configurable (i.e. the operator can
   enable/disable the AIS generation).




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   AIS packets are transmitted with the "minimum loss probability
   PHB" within a single network operator. This PHB is configurable
   on network operator's basis.

   AIS condition is cleared if no AIS message has been received in
   3.5 times the AIS transmission period.

5.4. Lock Reporting

   The Lock Reporting function, as required in section 2.2.7 of RFC
   5860 [10], relies upon a Locked Report (LKR) message used to
   suppress alarms following administrative locking action in the
   server (sub-)layer.

   When a server MEP is locked, the MPLS-TP client (sub-)layer
   adaptation function generates packets with LKR information in
   both directions to allow the suppression of secondary alarms at
   the MEPs in the client (sub-)layer. Again it is assumed that
   there is a hold off for any loss of continuity alarms in the
   client layer MEPs downstream of the node originating the locked
   report.

   The generation of packets with LKR information starts
   immediately when the server MEP is locked. These periodic
   packets, with LKR information, continue to be transmitted until
   the locked condition is cleared.

   Upon receiving a packet with LKR information an MPLS-TP MEP
   enters an LKR defect condition and suppresses loss of continuity
   alarm associated with its peer MEP but does not block traffic
   received from the transport path. A MEP resumes loss of
   continuity alarm generation upon detecting loss of continuity
   defect conditions in the absence of LKR condition.

   MIPs, as well as intermediate nodes, do not process the LKR
   information and forward these LKR OAM packets as regular data
   packets.











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   For example, let's consider the case where the MPLS-TP Section
   between LSR 1 and LSR 2 in the reference network of Figure 5 is
   administrative locked at LSR2 (in both directions).

   Assuming that all the MEGs described in Figure 5 have pro-active
   CC-V enabled, a LOC defect is detected by the MEPs of LSP13 LME,
   PW1 PSME and PW1Z PME, however in a transport network all these
   secondary alarms should be suppressed (i.e. not reported to the
   NMS or reported as secondary alarms).

   The MEP of Sec12 SME in LSR 2 notifies the adaptation function
   for LSP13 LME that then generates LKR packets on the LSP13 LME
   in order to allow its MEPs in LSR1 and LSR3 to suppress the LOC
   alarm. LSR3 can also suppress the secondary alarm on PW13 PSME
   because the MEP of PW13 PSME resides within the same node as the
   MEP of LSP13 LME. The MEP of PW13 PSME in LSR3 also notifies the
   adaptation function for PW1Z PME that then generates AIS packets
   on PW1Z PME in order to allow its MEP in LSRZ to suppress the
   LOC alarm.

   The generation of LKR packets for each MEG in the MPLS-TP client
   (sub-)layer is configurable (i.e. the operator can
   enable/disable the LKR generation).

   LKR packets are transmitted with the "minimum loss probability
   PHB" within a single network operator. This PHB is configurable
   on network operator's basis.

   Locked condition is cleared if no LKR packet has been received
   for 3.5 times the transmission period.

5.5. Packet Loss Measurement

   Packet Loss Measurement (LM) is one of the capabilities
   supported by the MPLS-TP Performance Monitoring (PM) function in
   order to facilitate reporting of QoS information for a transport
   path as required in section 2.2.11 of RFC 5860 [10]. LM is used
   to exchange counter values for the number of ingress and egress
   packets transmitted and received by the transport path monitored
   by a pair of MEPs.

   Proactive LM is performed by periodically sending LM OAM packets
   from a MEP to a peer MEP and by receiving LM OAM packets from
   the peer MEP (if a bidirectional transport path) during the life
   time of the transport path. Each MEP performs measurements of
   its transmitted and received packets. These measurements are
   then correlated with the peer MEP in the ME to derive the impact


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   of packet loss on a number of performance metrics for the ME in
   the MEG. The LM transactions are issued such that the OAM
   packets will experience the same queuing discipline as the
   measured traffic while transiting between the MEPs in the ME.

   For a MEP, near-end packet loss refers to packet loss associated
   with incoming data packets (from the far-end MEP) while far-end
   packet loss refers to packet loss associated with egress data
   packets (towards the far-end MEP).

   MIPs, as well as intermediate nodes, do not process the LM
   information and forward these pro-active LM OAM packets as
   regular data packets.

5.5.1. Configuration considerations

   In order to support proactive LM, the transmission rate and PHB
   class associated with the LM OAM packets originating from a MEP
   need be configured as part of the LM provisioning. LM OAM
   packets should be transmitted with the PHB that yields the
   lowest discard probability within the measured PHB Scheduling
   Class (see RFC 3260 [15]).

   If that PHB class is not an ordered aggregate where the ordering
   constraint is all packets with the PHB class being delivered in
   order, LM can produce inconsistent results.

5.5.2. Sampling skew

   If an implementation makes use of a hardware forwarding path
   which operates in parallel with an OAM processing path, whether
   hardware or software based, the packet and byte counts may be
   skewed if one or more packets can be processed before the OAM
   processing samples counters. If OAM is implemented in software
   this error can be quite large.

5.5.3. Multilink issues

   If multilink is used at the LSP ingress or egress, there may be
   no single packet processing engine where to inject or extract a
   LM packet as an atomic operation to which accurate packet and
   byte counts can be associated with the packet.

   In the case where multilink is encountered in the LSP path, the
   reordering of packets within the LSP can cause inaccurate LM
   results.



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5.6. Packet Delay Measurement

   Packet Delay Measurement (DM) is one of the capabilities
   supported by the MPLS-TP PM function in order to facilitate
   reporting of QoS information for a transport path as required in
   section 2.2.12 of RFC 5860 [10]. Specifically, pro-active DM is
   used to measure the long-term packet delay and packet delay
   variation in the transport path monitored by a pair of MEPs.

   Proactive DM is performed by sending periodic DM OAM packets
   from a MEP to a peer MEP and by receiving DM OAM packets from
   the peer MEP (if a bidirectional transport path) during a
   configurable time interval.

   Pro-active DM can be operated in two ways:

   o One-way: a MEP sends DM OAM packet to its peer MEP containing
      all the required information to facilitate one-way packet
      delay and/or one-way packet delay variation measurements at
      the peer MEP. Note that this requires synchronized precision
      time at either MEP by means outside the scope of this
      framework.

   o Two-way: a MEP sends DM OAM packet with a DM request to its
      peer MEP, which replies with a DM OAM packet as a DM
      response. The request/response DM OAM packets containing all
      the required information to facilitate two-way packet delay
      and/or two-way packet delay variation measurements from the
      viewpoint of the source MEP.

   MIPs, as well as intermediate nodes, do not process the DM
   information and forward these pro-active DM OAM packets as
   regular data packets.

5.6.1. Configuration considerations

   In order to support pro-active DM, the transmission rate and PHB
   associated with the DM OAM packets originating from a MEP need
   be configured as part of the DM provisioning. DM OAM packets
   should be transmitted with the PHB that yields the lowest
   discard probability within the measured PHB Scheduling Class
   (see RFC 3260 [15]).

5.7. Client Failure Indication

   The Client Failure Indication (CFI) function, as required in
   section 2.2.10 of RFC 5860 [10], is used to help process client


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   defects and propagate a client signal defect condition from the
   process associated with the local attachment circuit where the
   defect was detected (typically the source adaptation function
   for the local client interface) to the process associated with
   the far-end attachment circuit (typically the source adaptation
   function for the far-end client interface) for the same
   transmission path in case the client of the transport path does
   not support a native defect/alarm indication mechanism, e.g.
   AIS.

   A source MEP starts transmitting a CFI indication to its peer
   MEP when it receives a local client signal defect notification
   via its local CSF function. Mechanisms to detect local client
   signal fail defects are technology specific. Similarly
   mechanisms to determine when to cease originating client signal
   fail indication are also technology specific.

   A sink MEP that has received a CFI indication report this
   condition to its associated client process via its local CFI
   function. Consequent actions toward the client attachment
   circuit are technology specific.

   Either there needs to be a 1:1 correspondence between the client
   and the MEG, or when multiple clients are multiplexed over a
   transport path, the CFI message requires additional information
   to permit the client instance to be identified.

   MIPs, as well as intermediate nodes, do not process the CFI
   information and forward these pro-active CFI OAM packets as
   regular data packets.

5.7.1. Configuration considerations

   In order to support CFI indication, the CFI transmission rate
   and PHB of the CFI OAM message/information element should be
   configured as part of the CFI configuration.

6. OAM Functions for on-demand monitoring

   In contrast to proactive monitoring, on-demand monitoring is
   initiated manually and for a limited amount of time, usually for
   operations such as e.g. diagnostics to investigate into a defect
   condition.

   On-demand monitoring covers a combination of "in-service" and
   "out-of-service" monitoring functions. The control and
   measurement implications are:


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   1. A MEG can be directed to perform an "on-demand" functions at
      arbitrary times in the lifetime of a transport path.

   2. "out-of-service" monitoring functions may require a-priori
      configuration of both MEPs and intermediate nodes in the MEG
      (e.g., data plane loopback) and the issuance of notifications
      into client layers of the transport path being removed from
      service (e.g., lock-reporting)

   3. The measurements resulting from on-demand monitoring are
      typically harvested in real time, as these are frequently
      initiated manually. These do not necessarily require
      different harvesting mechanisms that for harvesting proactive
      monitoring telemetry.

   The functions that are exclusive out-of-service are those
   described in section 6.3. The remainder are applicable to both
   in-service and out-of-service transport paths.

6.1. Connectivity Verification

   In order to preserve network resources, e.g. bandwidth,
   processing time at switches, it may be preferable to not use
   proactive CC-V. In order to perform fault management functions,
   network management may invoke periodic on-demand bursts of on-
   demand CV packets, as required in section 2.2.3 of RFC 5860
   [10].

   On demand connectivity verification is a transaction that flows
   from the source MEP to a target MIP or MEP.

   Use of on-demand CV is dependent on the existence of either a
   bi-directional ME, or an associated return ME, or the
   availability of an out-of-band return path because it requires
   the ability for target MIPs and MEPs to direct responses to the
   originating MEPs.

   An additional use of on-demand CV would be to detect and locate
   a problem of connectivity when a problem is suspected or known
   based on other tools.  In this case the functionality will be
   triggered by the network management in response to a status
   signal or alarm indication.

   On-demand CV is based upon generation of on-demand CV packets
   that should uniquely identify the MEG that is being checked.
   The on-demand functionality may be used to check either an
   entire MEG (end-to-end) or between a source MEP and a specific


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   MIP. This functionality may not be available for associated
   bidirectional transport paths or unidirectional paths, as the
   MIP may not have a return path to the source MEP for the on-
   demand CV transaction.

   On-demand CV may generate a one-time burst of on-demand CV
   packets, or be used to invoke periodic, non-continuous, bursts
   of on-demand CV packets.  The number of packets generated in
   each burst is configurable at the MEPs, and should take into
   account normal packet-loss conditions.

   When invoking a periodic check of the MEG, the source MEP should
   issue a burst of on-demand CV packets that uniquely identifies
   the MEG being verified.  The number of packets and their
   transmission rate should be pre-configured and known to both the
   source MEP and the target MEP or MIP.  The source MEP should use
   the mechanisms defined in sections 3.3 and 3.4 when sending an
   on-demand CV packet to a target MEP or target MIP respectively.
   The target MEP/MIP shall return a reply on-demand CV packet for
   each packet received.  If the expected number of on-demand CV
   reply packets is not received at source MEP, the LOC defect
   state is entered.

   On-demand CV should have the ability to carry padding such that
   a variety of MTU sizes can be originated to verify the MTU
   transport capability of the transport path.

   MIPs that are not target by on-demand CV packets, as well as
   intermediate nodes, do not process the CV information and
   forward these on-demand CV OAM packets as regular data packets.

6.1.1. Configuration considerations

   For on-demand CV the MEP should support the configuration of the
   number of packets to be transmitted/received in each burst of
   transmissions and their packet size. The transmission rate
   should be configured between the different nodes.

   In addition, when the CV packet is used to check connectivity
   toward a target MIP, the number of hops to reach the target MIP
   should be configured.

   The PHB of the on-demand CV packets should be configured as
   well. This permits the verification of correct operation of QoS
   queuing as well as connectivity.




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6.2. Packet Loss Measurement

   On-demand Packet Loss Measurement (LM) is one of the
   capabilities supported by the MPLS-TP Performance Monitoring
   function in order to facilitate diagnostic of QoS performance
   for a transport path, as required in section 2.2.11 of RFC 5860
   [10]. As proactive LM, on-demand LM is used to exchange counter
   values for the number of ingress and egress packets transmitted
   and received by the transport path monitored by a pair of MEPs.
   LM is not performed MEP to MIP or between a pair of MIPs.

   On-demand LM is performed by periodically sending LM OAM packets
   from a MEP to a peer MEP and by receiving LM OAM packets from
   the peer MEP (if a bidirectional transport path) during a pre-
   defined monitoring period. Each MEP performs measurements of its
   transmitted and received packets. These measurements are then
   correlated to evaluate the packet loss performance metrics of
   the transport path.

   Use of packet loss measurement in an out-of-service transport
   path requires a traffic source such as a tester.

   MIPs, as well as intermediate nodes, do not process the LM
   information and forward these on-demand LM OAM packets as
   regular data packets.

6.2.1. Configuration considerations

   In order to support on-demand LM, the beginning and duration of
   the LM procedures, the transmission rate and PHB associated with
   the LM OAM packets originating from a MEP must be configured as
   part of the on-demand LM provisioning. LM OAM packets should be
   transmitted with the PHB that yields the lowest discard
   probability within the measured PHB Scheduling Class (see RFC
   3260 [15]).

6.2.2. Sampling skew

   If an implementation makes use of a hardware forwarding path
   which operates in parallel with an OAM processing path, whether
   hardware or software based, the packet and byte counts may be
   skewed if one or more packets can be processed before the OAM
   processing samples counters.  If OAM is implemented in software
   this error can be quite large.





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6.2.3. Multilink issues

   Multi-link Issues are as described in section 5.5.3.

6.3. Diagnostic Tests

   Diagnostic tests are tests performed on a MEG that has been taken
   out-of-service.

6.3.1. Throughput Estimation

   Throughput estimation is an on-demand out-of-service function,
   as required in section 2.2.5 of RFC 5860 [10], that allows
   verifying the bandwidth/throughput of an MPLS-TP transport path
   (LSP or PW) before it is put in-service.

   Throughput estimation is performed between MEPs and can be
   performed in one-way or two-way modes.

   According to RFC 2544 [11], this test is performed by sending
   OAM test packets at increasing rate (up to the theoretical
   maximum), graphing the percentage of OAM test packets received
   and reporting the rate at which OAM test packets begin to drop.
   In general, this rate is dependent on the OAM test packet size.

   When configured to perform such tests, a MEP source inserts OAM
   test packets with a specified packet size and transmission
   pattern at a rate to exercise the throughput.

   For a one-way test, the remote MEP sink receives the OAM test
   packets and calculates the packet loss. For a two-way test, the
   remote MEP loopbacks the OAM test packets back to original MEP
   and the local MEP sink calculates the packet loss. However, a
   two-way test will return the minimum of available throughput in
   the two directions. Alternatively it is possible to run two
   individual one-way tests to get a distinct measurement in the
   two directions.

   It is worth noting that two-way throughput estimation can only
   evaluate the minimum of available throughput of the two
   directions. In order to estimate the throughput of each
   direction uniquely, two one-way throughput estimation sessions
   have to be setup.

   MIPs, as well as intermediate nodes, do not process the
   throughput test information and forward these on-demand test OAM
   packets as regular data packets.


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6.3.1.1. Configuration considerations

   Throughput estimation is an out-of-service tool. The diagnosed
   MEG should be put into a Lock status before the diagnostic test
   is started.

   A MEG can be put into a Lock status either via an NMS action or
   using the Lock Instruct OAM tool as defined in section 7.

   At the transmitting MEP, provisioning is required for a test
   signal generator, which is associated with the MEP. At a
   receiving MEP, provisioning is required for a test signal
   detector which is associated with the MEP.

6.3.1.2. Limited OAM processing rate

   If an implementation is able to process payload at much higher
   data rates than OAM packets, then accurate measurement of
   throughput using OAM packets is not achievable.  Whether OAM
   packets can be processed at the same rate as payload is
   implementation dependent.

6.3.1.3. Multilink considerations

   If multilink is used, then it may not be possible to perform
   throughput measurement, as the throughput test may not have a
   mechanism for utilizing more than one component link of the
   aggregated link.

6.3.2. Data plane Loopback

   Data plane loopback is an out-of-service function, as required
   in section 2.2.5 of RFC 5860 [10], that permits all traffic
   (including user data and OAM, with the exception of the disable
   loopback command) originated at the ingress of a transport path
   or inserted by the test equipment to be looped back unmodified
   (other than normal per hop processing such as TTL decrement) in
   the direction of the point of origin by an interface at either
   an intermediate node or a terminating node. TTL is decremented
   normally during this process. It is also normal to disable
   proactive monitoring of the path as the source MEP will see all
   source MEP originated OAM messages returned to it.

   If the loopback function is to be performed at an intermediate
   node it is only applicable to co-routed bi-directional paths. If
   the loopback is to be performed end to end, it is applicable to



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   both co-routed bi-directional or associated bi-directional
   paths.

   Where a node implements data plane loopback capability and
   whether it implements more than one point is implementation
   dependent.

6.4. Route Tracing

   It is often necessary to trace a route covered by a MEG from a
   source MEP to the sink MEP including all the MIPs in-between
   after e.g., provisioning an MPLS-TP transport path or for
   trouble shooting purposes such as fault localization.

   The route tracing function, as required in section 2.2.4 of RFC
   5860 [10], is providing this functionality. Based on the fate
   sharing requirement of OAM flows, i.e. OAM packets receive the
   same forwarding treatment as data packet, route tracing is a
   basic means to perform connectivity verification and, to a much
   lesser degree, continuity check. For this function to work
   properly, a return path must be present.

   Route tracing might be implemented in different ways and this
   document does not preclude any of them.

   Route tracing should always discover the full list of MIPs and
   of the peer MEPs. In case a defect exist, the route trace
   function needs to be able to detect it and stop automatically
   returning the incomplete list of OAM entities that it was able
   to trace.

6.4.1. Configuration considerations

   The configuration of the route trace function must at least
   support the setting of the number of trace attempts before it
   gives up.

6.5. Packet Delay Measurement

   Packet Delay Measurement (DM) is one of the capabilities
   supported by the MPLS-TP PM function in order to facilitate
   reporting of QoS information for a transport path, as required
   in section 2.2.12 of RFC 5860 [10]. Specifically, on-demand DM
   is used to measure packet delay and packet delay variation in
   the transport path monitored by a pair of MEPs during a pre-
   defined monitoring period.



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   On-Demand DM is performed by sending periodic DM OAM packets
   from a MEP to a peer MEP and by receiving DM OAM packets from
   the peer MEP (if a bidirectional transport path) during a
   configurable time interval.

   On-demand DM can be operated in two ways:

   o One-way: a MEP sends DM OAM packet to its peer MEP containing
      all the required information to facilitate one-way packet
      delay and/or one-way packet delay variation measurements at
      the peer MEP. Note that this requires synchronized precision
      time at either MEP by means outside the scope of this
      framework.

   o Two-way: a MEP sends DM OAM packet with a DM request to its
      peer MEP, which replies with an DM OAM packet as a DM
      response. The request/response DM OAM packets containing all
      the required information to facilitate two-way packet delay
      and/or two-way packet delay variation measurements from the
      viewpoint of the source MEP.

   MIPs, as well as intermediate nodes, do not process the DM
   information and forward these on-demand DM OAM packets as
   regular data packets.

6.5.1. Configuration considerations

   In order to support on-demand DM, the beginning and duration of
   the DM procedures, the transmission rate and PHB associated with
   the DM OAM packets originating from a MEP need be configured as
   part of the DM provisioning. DM OAM packets should be
   transmitted with the PHB that yields the lowest discard
   probability within the measured PHB Scheduling Class (see RFC
   3260 [15]).

   In order to verify different performances between long and short
   packets (e.g., due to the processing time), it should be
   possible for the operator to configure the packet size of the
   on-demand OAM DM packet.

7. OAM Functions for administration control

7.1. Lock Instruct

   Lock Instruct (LKI) function, as required in section 2.2.6 of
   RFC 5860 [10], is a command allowing a MEP to instruct the peer



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   MEP(s) to put the MPLS-TP transport path into a locked
   condition.

   This function allows single-side provisioning for
   administratively locking (and unlocking) an MPLS-TP transport
   path.

   Note that it is also possible to administratively lock (and
   unlock) an MPLS-TP transport path using two-side provisioning,
   where the NMS administratively put both MEPs into ad
   administrative lock condition. In this case, the LKI function is
   not required/used.

   MIPs, as well as intermediate nodes, do not process the lock
   instruct information and forward these on-demand LKI OAM packets
   as regular data packets.

7.1.1. Locking a transport path

   A MEP, upon receiving a single-side administrative lock command
   from an NMS, sends an LKI request OAM packet to its peer MEP(s).
   It also puts the MPLS-TP transport path into a locked state and
   notifies its client (sub-)layer adaptation function upon the
   locked condition.

   A MEP, upon receiving an LKI request from its peer MEP, can
   accept or not the instruction and replies to the peer MEP with
   an LKI reply OAM packet indicating whether it has accepted or
   not the instruction.

   If the lock instruction has been accepted, it also puts the
   MPLS-TP transport path into a locked and notifies its client
   (sub-)layer adaptation function upon the locked condition.

   Note that if the client (sub-)layer is also MPLS-TP, Lock
   Reporting (LKR) generation at the client MPLS-TP (sub-)layer is
   started, as described in section 5.4.

7.1.2. Unlocking a transport path

   A MEP, upon receiving a single-side administrative unlock
   command from NMS, sends an LKI removal request OAM packet to its
   peer MEP(s).

   The peer MEP, upon receiving an LKI removal request, can accept
   or not the removal instruction and replies with an LKI removal



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   reply OAM packet indicating whether it has accepted or not the
   instruction.

   If the lock removal instruction has been accepted, it also
   clears the locked condition on the MPLS-TP transport path and
   notifies this event to its client (sub-)layer adaptation
   function.

   The MEP that has initiated the LKI clear procedure, upon
   receiving a positive LKI removal reply, also clears the locked
   condition on the MPLS-TP transport path and notifies this event
   to its client (sub-)layer adaptation function.

   Note that if the client (sub-)layer is also MPLS-TP, Lock
   Reporting (LKR) generation at the client MPLS-TP (sub-)layer is
   terminated, as described in section 5.4.

8. Security Considerations

   A number of security considerations are important in the context
   of OAM applications.

   OAM traffic can reveal sensitive information such as passwords,
   performance data and details about e.g. the network topology.
   The nature of OAM data therefore suggests to have some form of
   authentication, authorization and encryption in place. This will
   prevent unauthorized access to vital equipment and it will
   prevent third parties from learning about sensitive information
   about the transport network. However it should be observed that
   the combination of all permutations of unique MEP to MEP, MEP to
   MIP, and intermediate system originated transactions mitigates
   against the practical establishment and maintenance of a large
   number of security associations per MEG.

   For this reason it is assumed that the network is physically
   secured against man-in-the-middle attacks. Further, this
   document describes OAM functions that, if a man-in-the-middle
   attack was possible, could be exploited to significantly disrupt
   proper operation of the network.

   Mechanisms that the framework does not specify might be subject
   to additional security considerations.

9. IANA Considerations

   No new IANA considerations.



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10. Acknowledgments

   The authors would like to thank all members of the teams (the
   Joint Working Team, the MPLS Interoperability Design Team in
   IETF and the Ad Hoc Group on MPLS-TP in ITU-T) involved in the
   definition and specification of MPLS Transport Profile.

   The editors gratefully acknowledge the contributions of Adrian
   Farrel, Yoshinori Koike, Luca Martini, Yuji Tochio and Manuel
   Paul for the definition of per-interface MIPs and MEPs.

   The editors gratefully acknowledge the contributions of Malcolm
   Betts, Yoshinori Koike, Xiao Min, and Maarten Vissers for the
   lock report and lock instruction description.

   The authors would also like to thank Alessandro D'Alessandro,
   Loa Andersson, Malcolm Betts, Stewart Bryant, Rui Costa, Xuehui
   Dai, John Drake, Adrian Farrel, Dan Frost, Liu Gouman, Peng He,
   Feng Huang, Su Hui, Yoshionori Koike, George Swallow, Yuji
   Tochio, Curtis Villamizar, Maarten Vissers and Xuequin Wei for
   their comments and enhancements to the text.

   This document was prepared using 2-Word-v2.0.template.dot.

























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11. References

11.1. Normative References

   [1]  Rosen, E., Viswanathan, A., Callon, R., "Multiprotocol
         Label Switching Architecture", RFC 3031, January 2001

   [2]  Bryant, S., Pate, P., "Pseudo Wire Emulation Edge-to-Edge
         (PWE3) Architecture", RFC 3985, March 2005

   [3]  Nadeau, T., Pignataro, S., "Pseudowire Virtual Circuit
         Connectivity Verification (VCCV): A Control Channel for
         Pseudowires", RFC 5085, December 2007

   [4]  Bocci, M., Bryant, S., "An Architecture for Multi-Segment
         Pseudo Wire Emulation Edge-to-Edge", RFC 5659, October
         2009

   [5]  Niven-Jenkins, B., Brungard, D., Betts, M., sprecher, N.,
         Ueno, S., "MPLS-TP Requirements", RFC 5654, September 2009

   [6]  Agarwal, P., Akyol, B., "Time To Live (TTL) Processing in
         Multiprotocol Label Switching (MPLS) Networks", RFC 3443,
         January 2003

   [7]  Vigoureux, M., Bocci, M., Swallow, G., Ward, D., Aggarwal,
         R., "MPLS Generic Associated Channel", RFC 5586, June 2009

   [8]  Bocci, M., et al., "A Framework for MPLS in Transport
         Networks", RFC 5921, July 2010

   [9]  Swallow, G., Bocci, M., "MPLS-TP Identifiers", draft-ietf-
         mpls-tp-identifiers-01 (work in progress), April 2010

   [10] Vigoureux, M., Betts, M., Ward, D., "Requirements for OAM
         in MPLS Transport Networks", RFC 5860, May 2010

   [11] Bradner, S., McQuaid, J., "Benchmarking Methodology for
         Network Interconnect Devices", RFC 2544, March 1999

   [12] ITU-T Recommendation G.806 (01/09), "Characteristics of
         transport equipment - Description methodology and generic
         functionality ", January 2009






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11.2. Informative References

   [13] Sprecher, N., Nadeau, T., van Helvoort, H., Weingarten,
         Y., "MPLS-TP OAM Analysis", draft-ietf-mpls-tp-oam-
         analysis-02 (work in progress), July 2010

   [14] Nichols, K., Blake, S., Baker, F., Black, D., "Definition
         of the Differentiated Services Field (DS Field) in the
         IPv4 and IPv6 Headers", RFC 2474, December 1998

   [15] Grossman, D., "New terminology and clarifications for
         Diffserv", RFC 3260, April 2002.

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

   [17] ITU-T Recommendation G.707/Y.1322 (01/07), "Network node
         interface for the synchronous digital hierarchy (SDH)",
         January 2007

   [18] ITU-T Recommendation G.805 (03/00), "Generic functional
         architecture of transport networks", March 2000

   [19] ITU-T Recommendation Y.1731 (02/08), "OAM functions and
         mechanisms for Ethernet based networks", February 2008

   [20] IEEE Standard 802.1AX-2008, "IEEE Standard for Local and
         Metropolitan Area Networks - Link Aggregation", November
         2008

Authors' Addresses

   Dave Allan
   Ericsson

   Email: david.i.allan@ericsson.com


   Italo Busi
   Alcatel-Lucent

   Email: Italo.Busi@alcatel-lucent.com







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   Ben Niven-Jenkins
   BT

   Email: benjamin.niven-jenkins@bt.com


   Annamaria Fulignoli
   Ericsson

   Email: annamaria.fulignoli@ericsson.com


   Enrique Hernandez-Valencia
   Alcatel-Lucent

   Email: Enrique.Hernandez@alcatel-lucent.com


   Lieven Levrau
   Alcatel-Lucent

   Email: Lieven.Levrau@alcatel-lucent.com


   Vincenzo Sestito
   Alcatel-Lucent

   Email: Vincenzo.Sestito@alcatel-lucent.com


   Nurit Sprecher
   Nokia Siemens Networks

   Email: nurit.sprecher@nsn.com


   Huub van Helvoort
   Huawei Technologies

   Email: hhelvoort@huawei.com


   Martin Vigoureux
   Alcatel-Lucent

   Email: Martin.Vigoureux@alcatel-lucent.com



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   Yaacov Weingarten
   Nokia Siemens Networks

   Email: yaacov.weingarten@nsn.com


   Rolf Winter
   NEC

   Email: Rolf.Winter@nw.neclab.eu






































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