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Versions: (draft-blb-mpls-tp-framework) 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 5921

MPLS Working Group                                         M. Bocci, Ed.
Internet-Draft                                            Alcatel-Lucent
Intended status: Informational                            S. Bryant, Ed.
Expires: June 25, 2010                                          D. Frost
                                                           Cisco Systems
                                                               L. Levrau
                                                          Alcatel-Lucent
                                                               L. Berger
                                                                    LabN
                                                       December 22, 2009


               A Framework for MPLS in Transport Networks
                    draft-ietf-mpls-tp-framework-07

Abstract

   This document specifies an architectural framework for the
   application of Multiprotocol Label Switching (MPLS) to the
   construction of packet-switched equivalents of traditional circuit-
   switched carrier networks.  It describes a common set of protocol
   functions - the MPLS Transport Profile (MPLS-TP) - that supports the
   operational models and capabilities typical of such networks,
   including signaled or explicitly provisioned bi-directional
   connection-oriented paths, protection and restoration mechanisms,
   comprehensive Operations, Administration and Maintenance (OAM)
   functions, and network operation in the absence of a dynamic control
   plane or IP forwarding support.  Some of these functions are defined
   in existing MPLS specifications, while others require extensions to
   existing specifications to meet the requirements of the MPLS-TP.

   This document defines the subset of the MPLS-TP applicable in general
   and to point-to-point paths.  The remaining subset, applicable
   specifically to point-to-multipoint paths, are out of scope of this
   document.

   This document is a product of a joint Internet Engineering Task Force
   (IETF) / International Telecommunications Union Telecommunications
   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.




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Copyright Notice

   Copyright (c) 2009 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
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   described in the BSD License.



















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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Motivation and Background  . . . . . . . . . . . . . . . .  4
     1.2.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  6
       1.3.1.  Transport Network  . . . . . . . . . . . . . . . . . .  6
       1.3.2.  MPLS Transport Profile . . . . . . . . . . . . . . . .  7
       1.3.3.  MPLS-TP Section  . . . . . . . . . . . . . . . . . . .  7
       1.3.4.  MPLS-TP Label Switched Path  . . . . . . . . . . . . .  7
       1.3.5.  MPLS-TP Label Switching Router (LSR) and Label
               Edge Router (LER)  . . . . . . . . . . . . . . . . . .  7
       1.3.6.  Customer Edge (CE) . . . . . . . . . . . . . . . . . .  8
       1.3.7.  Additional Definitions and Terminology . . . . . . . .  8
     1.4.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  8
   2.  MPLS Transport Profile Requirements  . . . . . . . . . . . . . 11
   3.  MPLS Transport Profile Overview  . . . . . . . . . . . . . . . 12
     3.1.  Packet Transport Services  . . . . . . . . . . . . . . . . 12
     3.2.  Scope of the MPLS Transport Profile  . . . . . . . . . . . 13
     3.3.  Architecture . . . . . . . . . . . . . . . . . . . . . . . 14
       3.3.1.  MPLS-TP Client Adaptation Functions  . . . . . . . . . 14
       3.3.2.  MPLS-TP Forwarding Functions . . . . . . . . . . . . . 15
     3.4.  MPLS-TP Native Services  . . . . . . . . . . . . . . . . . 16
       3.4.1.  MPLS-TP Client/Server Relationship . . . . . . . . . . 17
       3.4.2.  Pseudowire Adaptation  . . . . . . . . . . . . . . . . 17
       3.4.3.  Network Layer Adaptation . . . . . . . . . . . . . . . 20
     3.5.  Identifiers  . . . . . . . . . . . . . . . . . . . . . . . 24
     3.6.  Generic Associated Channel (G-ACh) . . . . . . . . . . . . 24
     3.7.  Operations, Administration and Maintenance (OAM) . . . . . 27
       3.7.1.  OAM Architecture . . . . . . . . . . . . . . . . . . . 28
       3.7.2.  OAM Functions  . . . . . . . . . . . . . . . . . . . . 31
     3.8.  Control Plane  . . . . . . . . . . . . . . . . . . . . . . 32
       3.8.1.  PW Control Plane . . . . . . . . . . . . . . . . . . . 34
       3.8.2.  LSP Control Plane  . . . . . . . . . . . . . . . . . . 34
     3.9.  Static Operation of LSPs and PWs . . . . . . . . . . . . . 35
     3.10. Survivability  . . . . . . . . . . . . . . . . . . . . . . 35
     3.11. Network Management . . . . . . . . . . . . . . . . . . . . 37
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 38
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 38
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 38
   7.  Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . . 39
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 40
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 42







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1.  Introduction

1.1.  Motivation and Background

   This document describes an architectural framework for the
   application of MPLS to the construction of packet-switched transport
   networks.  It specifies the common set of protocol functions that
   meet the requirements in [RFC5654], and that together constitute the
   MPLS Transport Profile (MPLS-TP) for point-to-point paths.  The
   remaining MPLS-TP functions, applicable specifically to point-to-
   multipoint paths, are out of scope of this document.

   Historically the optical transport infrastructure - Synchronous
   Optical Network/Synchronous Digital Hierarchy (SONET/SDH) and Optical
   Transport Network (OTN) - has provided carriers with a high benchmark
   for reliability and operational simplicity.  To achieve this,
   transport technologies have been designed with specific
   characteristics:

   o  Strictly connection-oriented connectivity, which may be long-lived
      and may be provisioned manually (i.e. configuration of the node
      via a command line interface) or by network management.

   o  A high level of availability.

   o  Quality of service.

   o  Extensive OAM capabilities.

   Carriers wish to evolve such transport networks to take advantage of
   the flexibility and cost benefits of packet switching technology and
   to support packet based services more efficiently.  While MPLS is a
   maturing packet technology that already plays an important role in
   transport networks and services, not all MPLS capabilities and
   mechanisms are needed in or consistent with the transport network
   operational model.  There are also transport technology
   characteristics that are not currently reflected in MPLS.

   There are thus two objectives for MPLS-TP:

   1.  To enable MPLS to be deployed in a transport network and operated
       in a similar manner to existing transport technologies.

   2.  To enable MPLS to support packet transport services with a
       similar degree of predictability to that found in existing
       transport networks.

   In order to achieve these objectives, there is a need to define a



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   common set of MPLS protocol functions - an MPLS Transport Profile -
   for the use of MPLS in transport networks and applications.  Some of
   the necessary functions are provided by existing MPLS specifications,
   while others require additions to the MPLS tool-set.  Such additions
   should, wherever possible, be applicable to MPLS networks in general
   as well as those that conform strictly to the transport network
   model.

   This document is a product of a joint Internet Engineering Task Force
   (IETF) / International Telecommunications Union Telecommunications
   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.

1.2.  Scope

   This document describes an architectural framework for the
   application of MPLS to the construction of packet-switched transport
   networks.  It specifies the common set of protocol functions that
   meet the requirements in [RFC5654], and that together constitute the
   MPLS Transport Profile (MPLS-TP) for point-to-point MPLS-TP transport
   paths.  The remaining MPLS-TP functions, applicable specifically to
   point-to-multipoint transport paths, are out of scope of this
   document.


























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1.3.  Terminology

   Term       Definition
   ---------- ----------------------------------------------------------
   LSP        Label Switched Path
   MPLS-TP    MPLS Transport Profile
   SDH        Synchronous Digital Hierarchy
   ATM        Asynchronous Transfer Mode
   OTN        Optical Transport Network
   cl-ps      Connectionless - Packet Switched
   co-cs      Connection Oriented - Circuit Switched
   co-ps      Connection Oriented - Packet Switched
   OAM        Operations, Administration and Maintenance
   G-ACh      Generic Associated Channel
   GAL        Generic Alert Label
   MEP        Maintenance End Point
   MIP        Maintenance Intermediate Point
   APS        Automatic Protection Switching
   SCC        Signaling Communication Channel
   MCC        Management Communication Channel
   EMF        Equipment Management Function
   FM         Fault Management
   CM         Configuration Management
   PM         Performance Management
   LSR        Label Switching Router
   MPLS-TP PE MPLS-TP Provider Edge LSR
   MPLS-TP P  MPLS-TP Provider LSR
   PW         Pseudowire
   Adaptation The mapping of client information into a format suitable
              for transport by the server layer
   Native     The traffic belonging to the client of the MPLS-TP network
   Service
   T-PE       PW Terminating Provider Edge
   S-PE       PW Switching provider Edge

1.3.1.  Transport Network

   A Transport Network provides transparent transmission of client user
   plane traffic between attached client devices by establishing and
   maintaining point-to-point or point-to-multipoint connections between
   such devices.  The architecture of networks supporting point to
   multipoint connections is out of scope of this document.  A Transport
   Network is independent of any higher-layer network that may exist
   between clients, except to the extent required to supply this
   transmission service.  In addition to client traffic, a Transport
   Network may carry traffic to facilitate its own operation, such as
   that required to support connection control, network management, and
   Operations, Administration and Maintenance (OAM) functions.



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   See also the definition of Packet Transport Service in Section 3.1.

1.3.2.  MPLS Transport Profile

   The MPLS Transport Profile (MPLS-TP) is the subset of MPLS functions
   that meet the requirements in [RFC5654].  Note that MPLS is defined
   to include any present and future MPLS capability specified by the
   IETF, including those capabilities specifically added to support
   transport network requirements [RFC5654].

1.3.3.  MPLS-TP Section

   An MPLS-TP Section is defined in Section 1.2.2 of [RFC5654].

1.3.4.  MPLS-TP Label Switched Path

   An MPLS-TP Label Switched Path (MPLS-TP LSP) is an LSP that uses a
   subset of the capabilities of an MPLS LSP in order to meet the
   requirements of an MPLS transport network as set out in [RFC5654].
   The characteristics of an MPLS-TP LSP are primarily that it:

   1.  Uses a subset of the MPLS OAM tools defined as described in
       [I-D.ietf-mpls-tp-oam-framework].

   2.  Supports 1+1, 1:1, and 1:N protection functions.

   3.  Is traffic engineered.

   4.  May be established and maintained via the management plane, or
       using GMPLS protocols when a control plane is used.

   5.  Is either point-to-point or point-to-multipoint.  Multipoint to
       point and multipoint to multipoint LSPs are not permitted.

   Note that an MPLS LSP is defined to include any present and future
   MPLS capability, including those specifically added to support the
   transport network requirements.

1.3.5.  MPLS-TP Label Switching Router (LSR) and Label Edge Router (LER)

   Editor's Note: These terms are here for clarity - but this is not the
   authoritative definition - (need to find a definition)

   An MPLS-TP Label Switching Router (LSR) is either an MPLS-TP Provider
   Edge (PE) router or an MPLS-TP Provider (P) router for a given LSP,
   as defined below.  The terms MPLS-TP PE router and MPLS-TP P router
   describe logical functions; a specific node may undertake only one of
   these roles on a given LSP.



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   Note that the use of the term "router" in this context is historic
   and neither requires nor precludes the ability to perform IP
   forwarding.

1.3.5.1.  MPLS-TP Provider Edge (PE) Router

   An MPLS-TP Provider Edge (PE) router is an MPLS-TP LSR that adapts
   client traffic and encapsulates it to be transported over an MPLS-TP
   LSP.  Encapsulation may be as simple as pushing a label, or it may
   require the use of a pseudowire.  An MPLS-TP PE exists at the
   interface between a pair of layer networks.  For an MS-PW, an MPLS-TP
   PE may be either an S-PE or a T-PE, as defined in [RFC5659].

   A layer network is defined in [G.805].

1.3.5.2.  MPLS-TP Provider (P) Router

   An MPLS-TP Provider router is an MPLS-TP LSR that does not provide
   MPLS-TP PE functionality for a given LSP.  An MPLS-TP P router
   switches LSPs which carry client traffic, but does not adapt client
   traffic and encapsulate it to be carried over an MPLS-TP LSP.

1.3.6.  Customer Edge (CE)

   A Customer Edge (CE) is the client function sourcing or sinking
   native service traffic to or from the MPLS-TP network.  CEs on either
   side of the MPLS-TP network are peers and view the MPLS-TP network as
   a single point-to-point or point-to-multipoint link.

1.3.7.  Additional Definitions and Terminology

   Detailed definitions and additional terminology may be found in
   [RFC5654].

1.4.  Applicability

   MPLS-TP can be used to construct packet transport networks and is
   therefore applicable in any packet transport network context.  It is
   also applicable to subsets of a packet network where the transport
   network operational model is deemed attractive.  The following are
   examples of MPLS-TP applicability models:

   1.  MPLS-TP provided by a network that only supports MPLS-TP LSPs and
       PWs (i.e.  Only MPLS-TP LSPs and PWs exist between the PEs or
       LSRs), acting as a server for other layer 1, layer 2 and layer 3
       networks (Figure 1).





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   2.  MPLS-TP provided by a network that also supports non-MPLS-TP LSPs
       and PWs (i.e. both LSPs and PWs that conform to the transport
       profile and those that do not, exist between the PEs), acting as
       a server for other layer 1, layer 2 and layer 3 networks
       (Figure 2).

   3.  MPLS-TP as a server layer for client layer traffic of IP or MPLS
       networks which do not use functions of the MPLS transport
       profile.  For MPLS traffic, the MPLS-TP server layer network uses
       PW switching or LSP stitching at the PE that terminates the
       MPLS-TP server layer (Figure 3). - See notes in word document -
       ref = rfc5150

   These models are not mutually exclusive.

MPLS-TP LSP, provided by a network that only supports MPLS-TP, acting as
    a server for other layer 1, layer 2 and layer 3 networks.

            |<-- L1/2/3 -->|<-- MPLS-TP-->|<-- L1/2/3 -->|
                                 Only

                               MPLS-TP
                         +---+   LSP    +---+
          +---+  Client  |   |----------|   | Client   +---+
          |CE1|==Traffic=|PE2|==========|PE3|=Traffic==|CE1|
          +---+          |   |----------|   |          +---+
                         +---+          +---+

  Example  a)  [Ethernet]     [Ethernet]     [Ethernet]
  layering                    [   PW   ]
                              [-TP LSP ]

           b)  [   IP   ]     [  IP    ]     [  IP   ]
                              [ Demux  ]
                              [-TP LSP ]


                  Figure 1: MPLS-TP Server Layer Example













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   MPLS-TP LSP, provided by a network that also supports non-MPLS-TP
       functions, acting as a server for other layer 1, layer 2 and
       layer 3 networks.

               |<-- L1/2/3 -->|<-- MPLS -->|<-- L1/2/3 -->|

                                  MPLS-TP
                            +---+   LSP    +---+
             +---+  Client  |   |----------|   | Client   +---+
             |CE1|==Traffic=|PE2|==========|PE3|=Traffic==|CE1|
             +---+          |   |----------|   |          +---+
                            +---+          +---+

   Example  a)  [Ethernet]       [Ethernet]     [Ethernet]
   layering                      [   PW   ]
                                 [-TP LSP ]

            b)  [   IP   ]       [  IP    ]     [  IP   ]
                                 [ Demux  ]
                                 [-TP LSP ]

                 Figure 2: MPLS-TP in MPLS Network Example





























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MPLS-TP as a server layer for client layer traffic of IP or MPLS
    networks which do not use functions of the MPLS transport
    profile.


              |<-- MPLS ---->|<-- MPLS-TP-->|<--- MPLS --->|
                                   Only

  +---+   +----+  Non-TP  +----+  MPLS-TP +----+  Non-TP  +----+   +---+
  |CE1|---|T-PE|====LSP===|S-PE|====LSP===|S-PE|====LSP===|S-PE|---|CE2|
  +---+   +----+          +----+          +----+          +----+   +---+
                       (PW switching)  (PW switching)

(a)  [ Eth ]   [   Eth  ]       [  Eth   ]     [   Eth  ]     [ Eth ]
               [PW Seg't]       [PW Seg't]     [PW Seg't]
               [   LSP  ]       [-TP LSP ]     [   LSP  ]



             |<-- MPLS ---->|<-- MPLS-TP-->|<--- MPLS --->|
                                  Only

  +---+   +----+  Non-TP  +----+  MPLS-TP +----+  Non-TP  +----+   +---+
  |CE1|---| PE |====LSP===| PE |====LSP===| PE |====LSP===| PE |---|CE2|
  +---+   +----+          +----+          +----+          +----+   +---+
                       (LSP stitching) (LSP stitching)

(b)  [ IP ]      [  IP  ]       [   IP   ]     [  IP   ]     [ IP  ]
                 [  LSP ]       [-TP LSP ]     [  LSP  ]

           Figure 3: MPLS-TP Transporting Client Service Traffic

2.  MPLS Transport Profile Requirements

   The requirements for MPLS-TP are specified in [RFC5654],
   [I-D.ietf-mpls-tp-oam-requirements], and [I-D.ietf-mpls-tp-nm-req].
   This section provides a brief reminder to guide the reader and is
   therefore not normative.  It is not intended as a substitute for
   these documents.

   MPLS-TP must not modify the MPLS forwarding architecture and must be
   based on existing pseudowire and LSP constructs.

   Point to point LSPs may be unidirectional or bi-directional, and it
   must be possible to construct congruent Bi-directional LSPs.

   MPLS-TP LSPs do not merge with other LSPs at an MPLS-TP LSR and it
   must be possible to detect if a merged LSP has been created.



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   It must be possible to forward packets solely based on switching the
   MPLS or PW label.  It must also be possible to establish and maintain
   LSPs and/or pseudowires both in the absence or presence of a dynamic
   control plane.  When static provisioning is used, there must be no
   dependency on dynamic routing or signaling.

   OAM, protection and forwarding of data packets must be able to
   operate without IP forwarding support.

   It must be possible to monitor LSPs and pseudowires through the use
   of OAM in the absence of control plane or routing functions.  In this
   case information gained from the OAM functions is used to initiate
   path recovery actions at either the PW or LSP layers.

3.  MPLS Transport Profile Overview

3.1.  Packet Transport Services

   One objective of MPLS-TP is to enable MPLS networks to provide packet
   transport services with a similar degree of predictability to that
   found in existing transport networks.  Such packet transport services
   inherit a number of characteristics, defined in [RFC5654]:

   o  In an environment where an MPLS-TP layer network is supporting a
      client layer network, and the MPLS-TP layer network is supported
      by a server layer network then operation of the MPLS-TP layer
      network must be possible without any dependencies on either the
      server or client layer network.

   o  The service provided by the MPLS-TP network to the client is
      guaranteed not to fall below the agreed level regardless of other
      client activity.

   o  The control and management planes of any client network layer that
      uses the service is isolated from the control and management
      planes of the MPLS-TP layer network, where the client network
      layer is considered to be the native service of the MPLS-TP
      network.

   o  Where a client network makes use of an MPLS-TP server that
      provides a packet transport service, the level of co-ordination
      required between the client and server layer networks is minimal
      (preferably no co-ordination will be required).

   o  The complete set of packets generated by a client MPLS(-TP) layer
      network using the packet transport service, which may contain
      packets that are not MPLS packets (e.g.  IP or CNLS packets used
      by the control/management plane of the client MPLS(-TP) layer



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      network), are transported by the MPLS-TP server layer network.

   o  The packet transport service enables the MPLS-TP layer network
      addressing and other information (e.g. topology) to be hidden from
      any client layer networks using that service, and vice-versa.

   These characteristics imply that a packet transport service does not
   support a connectionless packet-switched forwarding mode.  However,
   this does not preclude it carrying client traffic associated with a
   connectionless service.

   Such packet transport services are very similar to Layer 2 Virtual
   Private Networks as defined by the IETF.

3.2.  Scope of the MPLS Transport Profile

   Figure 4 illustrates the scope of MPLS-TP.  MPLS-TP solutions are
   primarily intended for packet transport applications.  MPLS-TP is a
   strict subset of MPLS, and comprises only those functions that are
   necessary to meet the requirements of [RFC5654].  This includes MPLS
   functions that were defined prior to [RFC5654] but that meet the
   requirements of [RFC5654], together with additional functions defined
   to meet those requirements.  Some MPLS functions defined before
   [RFC5654] such as Equal Cost Multi-Path, LDP signaling used in such a
   way that it creates multipoint-to-point LSPs, and IP forwarding in
   the data plane are explicitly excluded from MPLS-TP by that
   requirements specification.

   Note that MPLS as a whole will continue to evolve to include
   additional functions that do not conform to the MPLS Transport
   Profile or its requirements, and thus fall outside the scope of
   MPLS-TP.

  |<============================== MPLS ==============================>|


  |<============= Pre-RFC5654 MPLS ================>|
    {      ECMP       }
    { LDP/non-TE LSPs }
    {     IP fwd      }

                      |<================ MPLS-TP ====================>|
                                                      { Additional }
                                                      {  Transport }
                                                      {  Functions }






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                        Figure 4: Scope of MPLS-TP

3.3.  Architecture

   MPLS-TP comprises the following architectural elements:

   o  Sections, LSPs and PWs that provide a packet transport service for
      a client network.

   o  Proactive and on-demand Operations, Administration and Maintenance
      (OAM) functions to monitor and diagnose the MPLS-TP network, such
      as connectivity check, connectivity verification, performance
      monitoring and fault localisation.

   o  Optional control planes for LSPs and PWs, as well as support for
      static provisioning and configuration.

   o  Optional path protection mechanisms to ensure that the packet
      transport service survives anticipated failures and degradations
      of the MPLS-TP network.

   o  Network management functions.

   The MPLS-TP architecture for LSPs and PWs includes the following two
   sets of functions:

   o  MPLS-TP client adaptation

   o  MPLS-TP forwarding

   The adaptation functions interface the native service to MPLS-TP.
   This includes the case where the native service is an MPLS-TP LSP.

   The forwarding functions comprise the mechanisms required for
   forwarding the encapsulated client traffic over an MPLS-TP server
   layer network, for example PW and LSP labels.

3.3.1.  MPLS-TP Client Adaptation Functions

   The MPLS-TP native service adaptation functions interface the client
   service to MPLS-TP.  For pseudowires, these adaptation functions are
   the payload encapsulation described in Section 4.4 of [RFC3985] and
   Section 6 of [RFC5659].  For network layer client services, the
   adaptation function uses the MPLS encapsulation format as defined in
   [RFC3032].

   The purpose of this encapsulation is to abstract the client service
   data plane from the MPLS-TP data plane, thus contributing to the



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   independent operation of the MPLS-TP network.

   MPLS-TP is itself a client of an underlying server layer.  MPLS-TP is
   thus also bounded by a set of adaptation functions to this server
   layer network, which may itself be MPLS-TP.  These adaptation
   functions provide encapsulation of the MPLS-TP frames and for the
   transparent transport of those frames over the server layer network.
   The MPLS-TP client inherits its Quality of Service (QoS) from the
   MPLS-TP network, which in turn inherits its QoS from the server
   layer.  The server layer must therefore provide the necessary QoS to
   ensure that the MPLS-TP client QoS commitments can be satisfied.

3.3.2.  MPLS-TP Forwarding Functions

   The forwarding functions comprise the mechanisms required for
   forwarding the encapsulated client over an MPLS-TP server layer
   network, for example PW and LSP labels.

   MPLS-TP LSPs use the MPLS label switching operations and TTL
   processing procedures defined in [RFC3031] and [RFC3032].  These
   operations are highly optimised for performance and are not modified
   by the MPLS-TP profile.

   In addition, MPLS-TP PWs use the SS-PW and MS-PW forwarding
   operations defined in [RFC3985] and [RFC5659].  The PW label is
   processed by a PW forwarder and is always at the bottom of the label
   stack for a given MPLS-TP layer network.

   Per-platform label space is used for PWs.  Either per-platform, per-
   interface or other context-specific label space [RFC5331] may be used
   for LSPs.

   MPLS-TP forwarding is based on the label that identifies the
   transport path (LSP or PW).  The label value specifies the processing
   operation to be performed by the next hop at that level of
   encapsulation.  A swap of this label is an atomic operation in which
   the contents of the packet after the swapped label are opaque to the
   forwarder.  The only event that interrupts a swap operation is TTL
   expiry.  This is a fundamental architectural construct of MPLS to be
   taken into account when designing protocol extensions that require
   packets (e.g.  OAM packets) to be sent to an intermediate LSR.

   Further processing to determine the context of a packet occurs when a
   swap operation is interrupted in this manner, or a pop operation
   exposes a specific reserved label at the top of the stack.  Otherwise
   the packet is forwarded according to the procedures in [RFC3032].

   Point-to-point MPLS-TP LSPs can be either unidirectional or



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   bidirectional.

   It must be possible to configure an MPLS-TP LSP such that the forward
   and backward directions of a bidirectional MPLS-TP LSP are co-routed,
   i.e. follow the same path.  The pairing relationship between the
   forward and the backward directions must be known at each LSR or LER
   on a bidirectional LSP.

   In normal conditions, all the packets sent over a PW or an LSP follow
   the same path through the network and those that belong to a common
   ordered aggregate are delivered in order.  For example per-packet
   equal cost multi-path (ECMP) load balancing is not applicable to
   MPLS-TP LSPs.

   Penultimate hop popping (PHP) is disabled on MPLS-TP LSPs by default.

   MPLS-TP supports Quality of Service capabilities via the MPLS
   Differentiated Services (DiffServ) architecture [RFC3270].  Both
   E-LSP and L-LSP MPLS DiffServ modes are supported.  The Traffic Class
   field (formerly the EXP field) of an MPLS label follows the
   definition and processing rules of [RFC5462] and [RFC3270].  Note
   that packet reordering between flows belonging to different traffic
   classes may occur if more than one traffic class is supported on a
   single LSP.

   Only the Pipe and Short Pipe DiffServ tunnelling and TTL processing
   models described in [RFC3270] and [RFC3443] are supported in MPLS-TP.

3.4.  MPLS-TP Native Services

   This document specifies the architecture for two types of native
   service adaptation:

   o  A PW: PW Demultiplexer and PW encapsulation

   o  An MPLS Label

   A PW can carry any emulated service defined by the IETF to be
   provided by a PW, for example Ethernet, Frame Relay, or PPP/HDLC.  A
   registry of PW types is maintained by IANA.  When the client
   adaptation is via a PW, the mechanisms described in Section 3.4.2 are
   used.

   An MPLS LSP Label can also be used as the adaptation, in which case
   any network layer client supported by MPLS is allowed, for example an
   MPLS LSP, PW, or IP.  When the client adaptation is via an MPLS
   label, the mechanisms described in Section 3.4.3 are used.




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3.4.1.  MPLS-TP Client/Server Relationship

   The relationship of MPLS-TP to its clients is illustrated in
   Figure 5.


      PW-Based                          MPLS Labelled
      Services                            Services

   Emulated             PW              LSP             IP
   Service
                  +------------+
                  | PW Payload |
 +------------+   +------------+  +------------+               (CLIENTS)
 | PW Payload |   |PW Lbl(S=1) |  |     IP     |
~~~~~~~~~~~~~~~~~ +------------+  +------------+  +------------+
 |PW Lbl (S=1)| | |LSP Lbl(S=0)|  |LSP Lbl(S=1)|  |     IP     |
 +------------+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 |LSP Lbl(S=0)|   |LSP Lbl(S=0)|  |LSP Lbl(S=0)|  |LSP Lbl(S=1)|
 +------------+   +------------+  +------------+  +------------+

                                                               (MPLS-TP)

~~~~~~~~~~~ = Client - MPLS-TP layer boundary

                  Figure 5: MPLS-TP - Client Relationship

   The data plane behaviour of MPLS-TP is the same as the best current
   practise for MPLS.  This includes the setting of the S-Bit.  In each
   case, the S-bit is set to indicate the bottom (i.e. inner-most) label
   in the label stack that is contiguous between the MPLS-TP server and
   the client layer.

   Note that this best current practise differs slightly from [RFC3032]
   which uses the S-bit to identify when MPLS label processing stops and
   network layer processing starts.

   Note that the label stacks shown above are those inside MPLS-TP
   network.  They illustrate the smallest number of labels possible.
   These label stacks could also include more labels.

3.4.2.  Pseudowire Adaptation

   The architecture for an MPLS-TP client adaptation that uses PWs is
   based on the MPLS [RFC3031] and pseudowire [RFC3985] architectures.
   If multi-segment pseudowires are used to provide a packet transport
   service, motivated by, for example, the requirements specified in
   [RFC5254], then the MS-PW architecture [RFC5659] also applies.



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   Figure 6 shows the architecture for an MPLS-TP network using single-
   segment PWs.

            |<--------------- Emulated Service ----------------->|
            |                                                    |
            |          |<-------- Pseudowire -------->|          |
            |          |      encapsulated packet     |          |
            |          |      transport service       |          |
            |          |                              |          |
            |          |    |<------ LSP ------->|    |          |
            |          V    V                    V    V          |
            V    AC    +----+      +-----+       +----+     AC   V
      +-----+    |     | PE1|=======\   /========| PE2|     |    +-----+
      |     |----------|.......PW1.| \ / |............|----------|     |
      | CE1 |    |     |    |      |  X  |       |    |     |    | CE2 |
      |     |----------|.......PW2.| / \ |............|----------|     |
      +-----+  ^ |     |    |=======/   \========|    |     | ^  +-----+
            ^  |       +----+      +-----+       +----+       |  ^
            |  |   Provider Edge 1    ^     Provider Edge 2   |  |
            |  |                      |                       |  |
     Customer  |                  P Router                    | Customer
      Edge 1   |                                              |  Edge 2
               |                                              |
               |                                              |
         Native service                                 Native service


            Figure 6: MPLS-TP Architecture (Single Segment PW)

   Figure 7 shows the architecture for an MPLS-TP network when multi-
   segment pseudowires are used.  Note that as in the SS-PW case,
   P-routers may also exist.



















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           |<----------- Pseudowire encapsulated ------------->|
           |             packet transport service              |
           |                                                   |
           |                                                   |
           |                                                   |
        AC |     |<-------- LSP1 -------->|    |<--LSP2-->|    | AC
         | V     V                        V    V          V    V |
         | +----+              +-----+    +----+          +----+ |
   +---+ | |TPE1|===============\   /=====|SPE1|==========|TPE2| | +---+
   |   |---|......PW.Seg't1... | \ / | ......X...PW.Seg't3.....|---|   |
   |CE1| | |    |              |  X  |    |    |          |    | | |CE2|
   |   |---|......PW.Seg't2... | / \ | ......X...PW.Seg't4.....|---|   |
   +---+ | |    |===============/   \=====|    |==========|    | | +---+
       ^   +----+     ^        +-----+    +----+     ^    +----+   ^
       |              |          ^                   |             |
       |           TE LSP        |                TE LSP           |
       |                      P-router                             |
       |                                                           |
       |<-------------------- Emulated Service ------------------->|


             Figure 7: MPLS-TP Architecture (Multi-Segment PW)

   The corresponding domain of the MPLS-TP protocol stack including PWs
   is shown in Figure 8.


 +-------------------+
 |  Client Layer     |
 /===================\     /===================\
 H     PW Encap      H     H     PW OAM        H
 H-------------------H     H-------------------H   /===================\
 H   PW Demux (S=1)  H     H PW Demux (S=1)    H   H      LSP OAM      H
 H-------------------H     H-------------------H   H-------------------H
 H     LSP Demux(s)  H     H  LSP Demux(s)     H   H  LSP Demux(s)     H
 \===================/     \===================/   \===================/
 |    Server Layer   |     |   Server Layer    |   |   Server Layer    |
 +-------------------+     +-------------------+   +-------------------+

     User Traffic                 PW OAM                  LSP OAM

Note: Transport Service Layer = PW Demux
      Transport Path Layer = LSP Demux

             Figure 8: MPLS-TP Layer Network using Pseudowires

   When providing a Virtual Private Wire Service (VPWS), Virtual Private
   Local Area Network Service (VPLS), Virtual Private Multicast Service



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   (VPMS) or Internet Protocol Local Area Network Service (IPLS),
   pseudowires must be used to carry the client service.

   [Editors' note add references for the terms in this para].

   PWs and their underlying labels may be configured or signaled.  See
   Section 3.9 for additional details related to configured service
   types.  See Section 3.8 for additional details related to signaled
   service types.

3.4.3.  Network Layer Adaptation

   MPLS-TP LSPs can be used to transport network layer clients.  Any
   network layer protocol can be transported between service interfaces.
   Examples of network layer protocols include IP, MPLS and MPLS-TP.
   Support for network layer clients follows the MPLS architecture for
   support of network layer protocols as defined in [RFC3031] and
   supported in [RFC3032].

   With network layer adaptation, the MPLS-TP domain provides a
   bidirectional point-to-point connection between two PEs in order to
   deliver a packet transport service to attached customer edge (CE)
   nodes.  For example, a CE may be an IP, MPLS or MPLS-TP node.  As
   shown in Figure 9, there is an attachment circuit between the CE node
   on the left and its corresponding provider edge (PE) node which
   provides the service interface, a bidirectional LSP across the
   MPLS-TP network to the corresponding PE node on the right, and an
   attachment circuit between that PE node and the corresponding CE node
   for this service.






















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              |<------------- Client Network Layer-------------->|
              |                                                  |
              |          |<---- Pkt Xport Service --->|
              |          |                            |          |
              |          |    |<-- PSN Tunnel -->|    |          |
              |          V    V                  V    V          |
              V     AC   +----+      +---+       +----+    AC    V
        +-----+     |    |PE1 |      |   |       |PE2 |    |     +-----+
        |     |     |LSP |    |      |   |       |    |    |     |     |
        | CE1 |----------|    |========X=========|    |----------| CE2 |
        |     |  ^  |IP  |    |  ^   |   |   ^   |    |    |  ^  |     |
        +-----+  |  |    |    |  |   |   |   |   |    |    |  |  +-----+
              ^  |       +----+  |   +---+   |   +----+    |  |  ^
              |  |      Provider |     ^     |  Provider      |  |
              |  |       Edge    |     |     |   Edge         |  |
        Customer |        1      | P-router  |    2           | Customer
        Edge 1   |             TE           TE                | Edge 2
                 |             LSP          LSP               |
                 |                                            |
           Native service                               Native service


         Figure 9: MPLS-TP Architecture for Network Layer Clients

   At the ingress service interface, the PE pushes one or more labels
   onto the ingress packets which are label switched over the transport
   network, and similarly the corresponding service interface at the
   egress PE pops any labels added by the MPLS-TP networks and delivers
   the packets to the attached CE.  The attachment circuits may be
   heterogeneous (e.g., any combination of SDH, PPP, Frame Relay, etc.)
   and network layer protocol payloads arrive at the service interface
   encapsulated in the Layer1/Layer2 encoding defined for that access
   link type.  It should be noted that the set of network layer
   protocols includes MPLS and hence MPLS encoded packets with an MPLS
   label stack (the client MPLS stack), may appear at the service
   interface.















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 +-------------------+
 |  Client Layer     |
 /===================\     /===================\
 H    Encap Label    H     H     SvcLSP OAM    H
 H-------------------H     H-------------------H   /===================\
 H   SvcLSP Demux    H     H SvcLSP Demux (S=1)H   H      LSP OAM      H
 H-------------------H     H-------------------H   H-------------------H
 H     LSP Demux(s)  H     H  LSP Demux(s)     H   H  LSP Demux(s)     H
 \===================/     \===================/   \===================/
 |   Server Layer    |     |   Server Layer    |   |   Server Layer    |
 +-------------------+     +-------------------+   +-------------------+

     User Traffic            Service LSP OAM                  LSP OAM

Note: Transport Service Layer = SvcLSP Demux
      Transport Path Layer = LSP Demux

Note that the functions of the Encap label and the Service Label may be
represented by a single label or omitted. Additionally, the S-bit will
always be zero when the client layer is MPLS labelled.

     Figure 10: Domain of MPLS-TP Layer Network for IP and LSP Clients

   Within the MPLS-TP transport network, the network layer protocols are
   carried over the MPLS-TP network using a logically separate MPLS
   label stack (the server stack).  The server stack is entirely under
   the control of the nodes within the MPLS-TP transport network and it
   is not visible outside that network.  Figure 10 shows how a client
   network protocol stack (which may be an MPLS label stack and payload)
   is carried over a network layer client service over an MPLS-TP
   transport network.

   A label per network layer protocol payload type that is to be
   transported is required.  Such labels are referred to as
   "Encapsulation Labels", one of which is shown in Figure 10.
   Encapsulation Label is either configured or signaled.

   A Service Label should be used when a particular packet transport
   service is supporting more than one network layer protocol payload
   type (and more than one Encapsulation Label is used).  An example
   Service Label is shown in Figure 10.  A Service Label may be omitted
   when only one encapsulation label is used in support of a particular
   service.  For example, if only MPLS labelled packets are carried over
   a service, then a single Encapsulation Label would be used to provide
   both payload type indication and service identification.
   Alternatively, if both IP and MPLS is to be carried, as shown in
   Figure 9, then two Encapsulation Labels could be mapped on to a
   common Service Label.



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   Service labels are typically carried over an MPLS-TP edge-to-edge (or
   transport path layer) LSP, which is also shown in Figure 10.  The use
   of an edge-to-edge LSP is recommended when more than one service
   exists between two PEs.  An edge-to-edge LSP may be omitted when only
   one service label is used in between two PEs.  For example, if only
   one service is carried between two PEs then a single Service Label
   could be used to provided both service indication and the MPLS-TP
   edge-to-edge LSP.  Alternatively, if multiple services exist between
   a pair of PEs then a per-client Service Label would be mapped on to a
   common MPLS-TP edge-to-edge LSP.

   As noted above, the layer 2 and layer 1 protocols used to carry the
   network layer protocol over the attachment circuits are not
   transported across the MPLS-TP network.  This enables the use of
   different layer 2 and layer 1 protocols on the two attachment
   circuits.

   At each service interface, Layer 2 addressing must be used to ensure
   the proper delivery of a network layer packet to the adjacent node.
   This is typically only an issue for LAN media technologies (e.g.,
   Ethernet) which have Media Access Control (MAC) addresses.  In cases
   where a MAC address is needed, the sending node must set the
   destination MAC address to an address that ensures delivery to the
   adjacent node.  That is the CE sets the destination MAC address to an
   address that ensures delivery to the PE, and the PE sets the
   destination MAC address to an address that ensures delivery to the
   CE.  The specific address used is technology type specific and is not
   covered in this document.  In some technologies the MAC address will
   need to be configured (Examples for the Ethernet case include a
   configured unicast MAC address for the adjacent node, or even using
   the broadcast MAC address when the CE-PE service interface is
   dedicated.  The configured address is then used as the MAC
   destination address for all packets sent over the service interface.)

   Note that when the two CEs operating over the network layer transport
   service are running a routing protocol such as IS-IS or OSPF some
   care should be taken to configure the routing protocols to use point-
   to-point adjacencies.  The specifics of such configuration is outside
   the scope of this document.  See [RFC5309] for additional details.

   The CE to CE service types and corresponding labels may be configured
   or signaled.  See Section 3.9 for additional details related to
   configured service types.  See Section 3.8 for additional details
   related to signaled service types.







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3.5.  Identifiers

   Identifiers are used to uniquely distinguish entities in an MPLS-TP
   network.  These include operators, nodes, LSPs, pseudowires, and
   their associated maintenance entities.
   [I-D.ietf-mpls-tp-identifiers] defines a set of identifiers that are
   compatible with existing MPLS control plane identifiers, as well as a
   set of identifiers that may be used when no IP control plane is
   available.

3.6.  Generic Associated Channel (G-ACh)

   For correct operation of the OAM it is important that the OAM packets
   fate-share with the data packets.  In addition in MPLS-TP it is
   necessary to discriminate between user data payloads and other types
   of payload.  For example, a packet may be associated with a Signaling
   Communication Channel (SCC), or a channel used for Automatic
   Protection Switching (APS) data.  This is achieved by carrying such
   packets on a generic control channel associated to the LSP, PW or
   section.

   MPLS-TP makes use of such a generic associated channel (G-ACh) to
   support Fault, Configuration, Accounting, Performance and Security
   (FCAPS) functions by carrying packets related to OAM, APS, SCC, MCC
   or other packet types in-band over LSPs or PWs.  The G-ACh is defined
   in [RFC5586] and is similar to the Pseudowire Associated Channel
   [RFC4385], which is used to carry OAM packets over pseudowires.  The
   G-ACh is indicated by a generic associated channel header (ACH),
   similar to the Pseudowire VCCV control word; this header is present
   for all Sections, LSPs and PWs making use of FCAPS functions
   supported by the G-ACh.

   For pseudowires, the G-ACh uses the first four bits of the pseudowire
   control word to provide the initial discrimination between data
   packets and packets belonging to the associated channel, as described
   in [RFC4385].  When this first nibble of a packet, immediately
   following the label at the bottom of stack, has a value of '1', then
   this packet belongs to a G-ACh.  The first 32 bits following the
   bottom of stack label then have a defined format called an associated
   channel header (ACH), which further defines the content of the
   packet.  The ACH is therefore both a demultiplexer for G-ACh traffic
   on the PW, and a discriminator for the type of G-ACh traffic.

   When the OAM or other control message is carried over an LSP, rather
   than over a pseudowire, it is necessary to provide an indication in
   the packet that the payload is something other than a user data
   packet.  This is achieved by including a reserved label with a value
   of 13 in the label stack.  This reserved label is referred to as the



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   'Generic Alert Label (GAL)', and is defined in [RFC5586].  When a GAL
   is found, it indicates that the payload begins with an ACH.  The GAL
   is thus a demultiplexer for G-ACh traffic on the LSP, and the ACH is
   a discriminator for the type of traffic carried on the G-ACh.  Note
   however that MPLS-TP forwarding follows the normal MPLS model, and
   that a GAL is invisible to an LSR unless it is the top label in the
   label stack.  The only other circumstance under which the label stack
   may be inspected for a GAL is when the TTL has expired.  Any MPLS-TP
   component that intentionally performs this inspection must assume
   that it is asynchronous with respect to the forwarding of other
   packets.  All operations on the label stack are in accordance with
   [RFC3031] and [RFC3032].

   In MPLS-TP, the 'G-ACh Alert Label (GAL)' always appears at the
   bottom of the label stack (i.e.  S bit set to 1).

   The G-ACh must only be used for channels that are an adjunct to the
   data service.  Examples of these are OAM, APS, MCC and SCC, but the
   use is not restricted to these services.  The G-ACh must not be used
   to carry additional data for use in the forwarding path, i.e. it must
   not be used as an alternative to a PW control word, or to define a PW
   type.

   At the server layer, bandwidth and QoS commitments apply to the gross
   traffic on the LSP, PW or section.  Since the G-ACh traffic is
   indistinguishable from the user data traffic, protocols using the
   G-ACh must take into consideration the impact they have on the user
   data that they are sharing resources with.  Conversely, capacity must
   be made available for important G-ACh uses such as protection and
   OAM.  In addition, protocols using the G-ACh must conform to the
   security and congestion considerations described in [RFC5586].

   Figure 11 shows the reference model depicting how the control channel
   is associated with the pseudowire protocol stack.  This is based on
   the reference model for VCCV shown in Figure 2 of [RFC5085].
















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          +-------------+                                +-------------+
          |  Payload    |       < Service / FCAPS >      |  Payload    |
          +-------------+                                +-------------+
          |   Demux /   |       < CW / ACH for PWs >     |   Demux /   |
          |Discriminator|                                |Discriminator|
          +-------------+                                +-------------+
          |     PW      |             < PW >             |     PW      |
          +-------------+                                +-------------+
          |    PSN      |             < LSP >            |    PSN      |
          +-------------+                                +-------------+
          |  Physical   |                                |  Physical   |
          +-----+-------+                                +-----+-------+
                |                                              |
                |             ____     ___       ____          |
                |           _/    \___/   \    _/    \__       |
                |          /               \__/         \_     |
                |         /                               \    |
                +--------|      MPLS/MPLS-TP Network       |---+
                          \                               /
                           \   ___      ___     __      _/
                            \_/   \____/   \___/  \____/


    Figure 11: PWE3 Protocol Stack Reference Model including the G-ACh

   PW associated channel messages are encapsulated using the PWE3
   encapsulation, so that they are handled and processed in the same
   manner (or in some cases, an analogous manner) as the PW PDUs for
   which they provide a control channel.

   Figure 12 shows the reference model depicting how the control channel
   is associated with the LSP protocol stack.



















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          +-------------+                                +-------------+
          |  Payload    |          < Service >           |   Payload   |
          +-------------+                                +-------------+
          |Discriminator|         < ACH on LSP >         |Discriminator|
          +-------------+                                +-------------+
          |Demultiplexer|         < GAL on LSP >         |Demultiplexer|
          +-------------+                                +-------------+
          |    PSN      |            < LSP >             |    PSN      |
          +-------------+                                +-------------+
          |  Physical   |                                |  Physical   |
          +-----+-------+                                +-----+-------+
                |                                              |
                |             ____     ___       ____          |
                |           _/    \___/   \    _/    \__       |
                |          /               \__/         \_     |
                |         /                               \    |
                +--------|      MPLS/MPLS-TP Network       |---+
                          \                               /
                           \   ___      ___     __      _/
                            \_/   \____/   \___/  \____/

     Figure 12: MPLS Protocol Stack Reference Model including the LSP
                        Associated Control Channel

3.7.  Operations, Administration and Maintenance (OAM)

   MPLS-TP must be able to operate in environments where IP is not used
   in the forwarding plane.  Therefore, the default mechanism for OAM
   demultiplexing in MPLS-TP LSPs and PWs is the Generic Associated
   Channel (Section 3.6).  Forwarding based on IP addresses for user or
   OAM packets is not required for MPLS-TP.

   [RFC4379] and BFD for MPLS LSPs [I-D.ietf-bfd-mpls] have defined
   alert mechanisms that enable an MPLS LSR to identify and process MPLS
   OAM packets when the OAM packets are encapsulated in an IP header.
   These alert mechanisms are based on TTL expiration and/or use an IP
   destination address in the range 127/8 for IPv4 and that same range
   embedded as IPv4 mapped IPv6 addresses for IPv6 [RFC4379].  When the
   OAM packets are encapsulated in an IP header, these mechanisms are
   the default mechanisms for MPLS networks in general for identifying
   MPLS OAM packets.  MPLS-TP must be able to operate in an environments
   where IP forwarding is not supported, and thus the GACH/GAL is the
   default mechanism to demultiplex OAM packets in MPLS-TP.

   MPLS-TP supports a comprehensive set of OAM capabilities for packet
   transport applications, with equivalent capabilities to those
   provided in SONET/SDH.




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   MPLS-TP defines mechanisms to differentiate specific packets (e.g.
   OAM, APS, MCC or SCC) from those carrying user data packets on the
   same transport path (i.e. section, LSP or PW).  These mechanisms are
   described in [RFC5586].

   MPLS-TP requires [I-D.ietf-mpls-tp-oam-requirements] that a set of
   OAM capabilities is available to perform fault management (e.g. fault
   detection and localisation) and performance monitoring (e.g. packet
   delay and loss measurement) of the LSP, PW or section.  The framework
   for OAM in MPLS-TP is specified in [I-D.ietf-mpls-tp-oam-framework].

   MPLS-TP OAM packets share the same fate as their corresponding data
   packets, and are identified through the Generic Associated Channel
   mechanism [RFC5586].  This uses a combination of an Associated
   Channel Header (ACH) and a Generic Alert Label (GAL) to create a
   control channel associated to an LSP, Section or PW.

3.7.1.  OAM Architecture

   OAM and monitoring in MPLS-TP is based on the concept of maintenance
   entities, as described in [I-D.ietf-mpls-tp-oam-framework].  A
   Maintenance Entity can be viewed as the association of two
   Maintenance End Points (MEPs) (see example in Figure 13 ).  Another
   OAM construct is referred to as Maintenance Entity Group (MEG), which
   is a collection of one or more MEs that belongs to the same transport
   path and that are maintained and monitored as a group.  The MEPs that
   form an ME should be configured and managed to limit the OAM
   responsibilities of an OAM flow within the domain of a transport path
   or segment, in the specific layer network that is being monitored and
   managed.

   Each OAM flow is associated with a single ME.  Each MEP within an ME
   resides at the boundaries of that ME.  An ME may also include a set
   of zero or more Maintenance Intermediate Points (MIPs), which reside
   within the Maintenance Entity.  Maintenance End Points (MEPs) are
   capable of sourcing and sinking OAM flows, while Maintenance
   Intermediate Points (MIPs) can only sink or respond to OAM flows from
   within a MEG, or originate notifications as a result of specific
   network conditions.












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========================== End to End LSP OAM ==========================
     .....                     .....         .....            .....
-----|MIP|---------------------|MIP|---------|MIP|------------|MIP|-----
     '''''                     '''''         '''''            '''''

     |<-------- Carrier 1 --------->|        |<--- Carrier 2 ----->|
      ----     ---     ---      ----          ----     ---     ----
 NNI |    |   |   |   |   |    |    |  NNI   |    |   |   |   |    | NNI
-----| PE |---| P |---| P |----| PE |--------| PE |---| P |---| PE |----
     |    |   |   |   |   |    |    |        |    |   |   |   |    |
      ----     ---     ---      ----          ----     ---     ----

      ==== Segment LSP OAM ======  == Seg't ==  === Seg't LSP OAM ===
            (Carrier 1)             LSP OAM         (Carrier 2)
                                (inter-carrier)
      .....   .....   .....  ..........   ..........  .....    .....
      |MEP|---|MIP|---|MIP|--|MEP||MEP|---|MEP||MEP|--|MIP|----|MEP|
      '''''   '''''   '''''  ''''''''''   ''''''''''  '''''    '''''
      <------------ ME ----------><--- ME ----><------- ME -------->

Note: MEPs for End-to-end LSP OAM exist outside of the scope
      of this figure.


   Figure 13: Example of MPLS-TP OAM showing end-to-end and segment OAM

   Figure 14 illustrates how the concept of Maintenance Entities can be
   mapped to sections, LSPs and PWs in an MPLS-TP network that uses MS-
   PWs.






















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   Native  |<-------------------- PW15 --------------------->| Native
    Layer  |                                                 |  Layer
  Service  |    |<-PSN13->|    |<-PSN3X->|    |<-PSNXZ->|    | Service
     (AC1) V    V   LSP   V    V   LSP   V    V   LSP   V    V  (AC2)
           +----+   +-+   +----+         +----+   +-+   +----+
+---+      |TPE1|   | |   |SPE3|         |SPEX|   | |   |TPEZ|     +---+
|   |      |    |=========|    |=========|    |=========|    |     |   |
|CE1|------|........PW1.....X..|...PW3...|.X......PW5........|-----|CE2|
|   |      |    |=========|    |=========|    |=========|    |     |   |
+---+      | 1  |   |2|   | 3  |         | X  |   |Y|   | Z  |     +---+
           +----+   +-+   +----+         +----+   +-+   +----+

           |<- Subnetwork 123->|         |<- Subnetwork XYZ->|

           .------------------- PW15  PME -------------------.
           .---- PW1 PTCME ----.         .---- PW5 PTCME ---.
                .---------.                   .---------.
                 PSN13 LME                     PSNXZ LME

                 .--.  .--.     .--------.     .--.  .--.
             Sec12 SME Sec23 SME Sec3X SME SecXY SME SecYZ 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

SME: Section Maintenance Entity
LME: LSP Maintenance Entity
PME: PW Maintenance Entity


    Figure 14: MPLS-TP OAM architecture showing PWs, LSPs and Sections

   The following MPLS-TP MEs are specified in
   [I-D.ietf-mpls-tp-oam-framework]:

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

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

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





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   o  An LSP Tandem Connection Maintenance Entity (LTCME).

   A G-ACH packet may be directed to an individual MIP along the path of
   an LSP or MS-PW by setting the appropriate TTL in the label for the
   G-ACH packet, as per the traceroute mode of LSP Ping [RFC4379] and
   the vccv-trace mode of[I-D.ietf-pwe3-segmented-pw].  Note that this
   works when the location of MIPs along the LSP or PW path is known by
   the MEP.  There may be circumstances where this is not the case, e.g.
   following restoration using a facility bypass LSP.  In these cases,
   tools to trace the path of the LSP may be used to determine the
   appropriate setting for the TTL to reach a specific MIP.

   Within an LSR or PE, MEPs and MIPs can only be placed where MPLS
   layer processing is performed on a packet.  The architecture mandates
   that this must occur at least once.

   MEPs may only act as a sink of OAM packets when the label associated
   with the LSP or PW for that ME is popped.  MIPs can only be placed
   where an exception to the normal forwarding operation occurs.  A MEP
   may act as a source of OAM packets wherever a label is pushed or
   swapped.  For example, on an MS-PW, a MEP may source OAM within an
   S-PE or a T-PE, but a MIP may only be associated with a S-PE and a
   sink MEP can only be associated with a T-PE.

3.7.2.  OAM Functions

   The MPLS-TP OAM architecture supports a wide range of OAM functions,
   including the following:

   o  Continuity Check

   o  Connectivity Verification

   o  Performance Monitoring (e.g. packet loss and delay measurement)

   o  Alarm Suppression

   o  Remote Integrity

   These functions are applicable to any layer defined within MPLS-TP,
   i.e. to MPLS-TP Sections, LSPs and PWs.

   The MPLS-TP OAM tool-set must be able to operate without relying on a
   dynamic control plane or IP functionality in the datapath.  In the
   case of an MPLS-TP deployment in a network in which IP functionality
   is available, all existing IP/MPLS OAM functions, e.g.  LSP-Ping, BFD
   and VCCV, may be used.




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   One use of OAM mechanisms is to detect link failures, node failures
   and performance outside the required specification which then may be
   used to trigger recovery actions, according to the requirements of
   the service.

3.8.  Control Plane

   Editors note: This section will be updated based on text supplied by
   the control plane framework draft editors.

   A distributed dynamic control plane may be used to enable dynamic
   service provisioning in an MPLS-TP network.  Where the requirements
   specified in [RFC5654] can be met, the MPLS Transport Profile uses
   existing standard control plane protocols for LSPs and PWs.

   Note that a dynamic control plane is not required in an MPLS-TP
   network.  See Section 3.9 for further details on statically
   configured and provisioned MPLS-TP services.

   Figure 15 illustrates the relationship between the MPLS-TP control
   plane, the forwarding plane, the management plane, and OAM for point-
   to-point MPLS-TP LSPs or PWs.





























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    +------------------------------------------------------------------+
    |                                                                  |
    |                Network Management System and/or                  |
    |                                                                  |
    |           Control Plane for Point to Point Connections           |
    |                                                                  |
    +------------------------------------------------------------------+
                  |     |         |     |          |     |
     .............|.....|...  ....|.....|....  ....|.....|............
     :          +---+   |  :  : +---+   |   :  : +---+   |           :
     :          |OAM|   |  :  : |OAM|   |   :  : |OAM|   |           :
     :          +---+   |  :  : +---+   |   :  : +---+   |           :
     :            |     |  :  :   |     |   :  :   |     |           :
    \: +----+   +--------+ :  : +--------+  :  : +--------+   +----+ :/
   --+-|Edge|<->|Forward-|<---->|Forward-|<----->|Forward-|<->|Edge|-+--
    /: +----+   |ing     | :  : |ing     |  :  : |ing     |   +----+ :\
     :          +--------+ :  : +--------+  :  : +--------+          :
     '''''''''''''''''''''''  '''''''''''''''  '''''''''''''''''''''''

   Note:
      1) NMS may be centralised or distributed. Control plane is
         distributed.
      2) 'Edge' functions refers to those functions present at
         the edge of a PSN domain, e.g. NSP or classification.
      3) The control plane may be transported over the server
         layer, an LSP or a G-ACh.


           Figure 15: MPLS-TP Control Plane Architecture Context

   The MPLS-TP control plane is based on a combination of the LDP-based
   control plane for pseudowires [RFC4447] and the RSVP-TE-based control
   plane for MPLS-TP LSPs [RFC3471].  Some of the RSVP-TE functions that
   are required for MPLS-TP LSP signaling are based on Generalized MPLS
   (GMPLS) ([RFC3945], [RFC3471], [RFC3473]).

   The distributed MPLS-TP control plane may provide the following
   functions:

   o  Signaling

   o  Routing

   o  Traffic engineering and constraint-based path computation

   In a multi-domain environment, the MPLS-TP control plane supports
   different types of interfaces at domain boundaries or within the
   domains.  These include the User-Network Interface (UNI), Internal



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   Network Node Interface (I-NNI), and External Network Node Interface
   (E-NNI).  Note that different policies may be defined that control
   the information exchanged across these interface types.

   The MPLS-TP control plane is capable of activating MPLS-TP OAM
   functions as described in the OAM section of this document
   Section 3.7, e.g. for fault detection and localisation in the event
   of a failure in order to efficiently restore failed transport paths.

   The MPLS-TP control plane supports all MPLS-TP data plane
   connectivity patterns that are needed for establishing transport
   paths, including protected paths as described in Section 3.10.
   Examples of the MPLS-TP data plane connectivity patterns are LSPs
   utilising the fast reroute backup methods as defined in [RFC4090] and
   ingress-to-egress 1+1 or 1:1 protected LSPs.

   The MPLS-TP control plane provides functions to ensure its own
   survivability and to enable it to recover gracefully from failures
   and degradations.  These include graceful restart and hot redundant
   configurations.  Depending on how the control plane is transported,
   varying degrees of decoupling between the control plane and data
   plane may be achieved.

3.8.1.  PW Control Plane

   An MPLS-TP network provides many of its transport services using
   single-segment or multi-segment pseudowires, in compliance with the
   PWE3 architecture ([RFC3985] and [RFC5659]).  The setup and
   maintenance of single-segment or multi-segment pseudowires uses the
   Label Distribution Protocol (LDP) as per [RFC4447] and extensions for
   MS-PWs ([I-D.ietf-pwe3-segmented-pw] and
   [I-D.ietf-pwe3-dynamic-ms-pw]).

3.8.2.  LSP Control Plane

   MPLS-TP Provider Edge LSRs aggregate multiple pseudowires and carry
   them across the MPLS-TP network through MPLS-TP tunnels (MPLS-TP
   LSPs).  Applicable functions from the Generalized MPLS (GMPLS)
   ([RFC3945]) protocol suite supporting packet-switched capable (PSC)
   technologies are used as the control plane for MPLS-TP transport
   paths (LSPs).

   The LSP control plane includes:

   o  RSVP-TE for signaling

   o  OSPF-TE or ISIS-TE for routing




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   RSVP-TE signaling in support of GMPLS, as defined in [RFC3473], is
   used for the setup, modification, and release of MPLS-TP transport
   paths and protection paths.  It supports unidirectional and
   bidirectional point-to-point LSPs as well as unidirectional point-to-
   multipoint LSPs.  The architecture for MPLS-TP supporting point-to-
   multipoint packet transport services is out of scope of this
   document.

   The route of a transport path is typically calculated in the ingress
   node of a domain and the RSVP explicit route object (ERO) is utilised
   for the setup of the transport path exactly following the given
   route.  GMPLS-based MPLS-TP LSPs must be able to inter-operate with
   RSVP-TE-based MPLS-TE LSPs, as per [RFC5146]

   OSPF and IS-IS for GMPLS ([RFC4203] and [RFC5307]) are used for
   carrying link state routing information in an MPLS-TP network.

3.9.  Static Operation of LSPs and PWs

   An MPLS-TP LSP or PW may be statically configured without the support
   of a dynamic control plane.  This may be either by direct
   configuration of the LSRs, or via a network management system.
   Static operation is independent of a specific PW or LSP instance -
   for example it should be possible for a PW to be statically
   configured, while the LSP supporting it setup by a dynamic control
   plane.

   Persistent forwarding loops can cause significant additional resource
   utilisation, above that budgeted for the transport path.  Therefore,
   when static configuration mechanisms are used, care must be taken to
   ensure that loops do not form.

3.10.  Survivability

   Editors note: This section will be updated based on text supplied by
   the survivability draft editors.

   Survivability requirements for MPLS-TP are specified in
   [I-D.ietf-mpls-tp-survive-fwk].

   A wide variety of resiliency schemes have been developed to meet the
   various network and service survivability objectives.  For example,
   as part of the MPLS/PW paradigms, MPLS provides methods for local
   repair using back-up LSP tunnels ([RFC4090]), while pseudowire
   redundancy [I-D.ietf-pwe3-redundancy] supports scenarios where the
   protection for the PW cannot be fully provided by the PSN layer (i.e.
   where the backup PW terminates on a different target PE node than the
   working PW).  Additionally, GMPLS provides a well known set of



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   control plane driven protection and restoration mechanisms [RFC4872].
   MPLS-TP provides additional protection mechanisms that are optimised
   for both linear topologies and ring topologies, and that operate in
   the absence of a dynamic control plane.  These are specified in
   [I-D.ietf-mpls-tp-survive-fwk].

   Different protection schemes apply to different deployment topologies
   and operational considerations.  Such protection schemes may provide
   different levels of resiliency, for example:

   o  Two concurrent traffic paths (1+1).

   o  one active and one standby path with guaranteed bandwidth on both
      paths (1:1).

   o  one active path and a standby path the resources or which are
      shared by one or more other active paths (shared protection).

   The applicability of any given scheme to meet specific requirements
   is outside the current scope of this document.

   The characteristics of MPLS-TP resiliency mechanisms are as follows:

   o  Optimised for linear, ring or meshed topologies.

   o  Use OAM mechanisms to detect and localise network faults or
      service degenerations.

   o  Include protection mechanisms to coordinate and trigger protection
      switching actions in the absence of a dynamic control plane.  This
      is known as an Automatic Protection Switching (APS) mechanism.

   o  MPLS-TP recovery schemes are applicable to all levels in the
      MPLS-TP domain (i.e.  MPLS section, LSP and PW), providing segment
      and end-to-end recovery.

   o  MPLS-TP recovery mechanisms support the coordination of protection
      switching at multiple levels to prevent race conditions occurring
      between a client and its server layer.

   o  MPLS-TP recovery mechanisms can be data plane, control plane or
      management plane based.

   o  MPLS-TP supports revertive and non-revertive behaviour.







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3.11.  Network Management

   The network management architecture and requirements for MPLS-TP are
   specified in [I-D.ietf-mpls-tp-nm-framework] and
   [I-D.ietf-mpls-tp-nm-req].  These derive from the generic
   specifications described in ITU-T G.7710/Y.1701 [G.7710] for
   transport technologies.  It also incorporates the OAM requirements
   for MPLS Networks [RFC4377] and MPLS-TP Networks
   [I-D.ietf-mpls-tp-oam-requirements] and expands on those requirements
   to cover the modifications necessary for fault, configuration,
   performance, and security in a transport network.

   The Equipment Management Function (EMF) of an MPLS-TP Network Element
   (NE) (i.e.  LSR, LER, PE, S-PE or T-PE) provides the means through
   which a management system manages the NE.  The Management
   Communication Channel (MCC), realised by the G-ACh, provides a
   logical operations channel between NEs for transferring Management
   information.  For the management interface from a management system
   to an MPLS-TP NE, there is no restriction on which management
   protocol is used.  The MCC is used to provision and manage an end-to-
   end connection across a network where some segments are created/
   managed by, for example, Netconf or SNMP and other segments by XML or
   CORBA interfaces.  Maintenance operations are run on a connection
   (LSP or PW) in a manner that is independent of the provisioning
   mechanism.  An MPLS-TP NE is not required to offer more than one
   standard management interface.  In MPLS-TP, the EMF must be capable
   of statically provisioning LSPs for an LSR or LER, and PWs for a PE,
   as well as any associated MEPs and MIPs, as per Section 3.9.

   Fault Management (FM) functions within the EMF of an MPLS-TP NE
   enable the supervision, detection, validation, isolation, correction,
   and alarm handling of abnormal conditions in the MPLS-TP network and
   its environment.  FM must provide for the supervision of transmission
   (such as continuity, connectivity, etc.), software processing,
   hardware, and environment.  Alarm handling includes alarm severity
   assignment, alarm suppression/aggregation/correlation, alarm
   reporting control, and alarm reporting.

   Configuration Management (CM) provides functions to control,
   identify, collect data from, and provide data to MPLS-TP NEs.  In
   addition to general configuration for hardware, software protection
   switching, alarm reporting control, and date/time setting, the EMF of
   the MPLS-TP NE also supports the configuration of maintenance entity
   identifiers (such as MEP ID and MIP ID).  The EMF also supports the
   configuration of OAM parameters as a part of connectivity management
   to meet specific operational requirements.  These may specify whether
   the operational mode is one-time on-demand or is periodic at a
   specified frequency.



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   The Performance Management (PM) functions within the EMF of an
   MPLS-TP NE support the evaluation and reporting of the behaviour of
   the NEs and the network.  One particular requirement for PM is to
   provide coherent and consistent interpretation of the network
   behaviour in a hybrid network that uses multiple transport
   technologies.  Packet loss measurement and delay measurements may be
   collected and used to detect performance degradation.  This is
   reported via fault management to enable corrective actions to be
   taken (e.g. protection switching), and via performance monitoring for
   Service Level Agreement (SLA) verification and billing.  Collection
   mechanisms for performance data should be capable of operating on-
   demand or pro-actively.

4.  Security Considerations

   The introduction of MPLS-TP into transport networks means that the
   security considerations applicable to both MPLS and PWE3 apply to
   those transport networks.  Furthermore, when general MPLS networks
   that utilise functionality outside of the strict MPLS Transport
   Profile are used to support packet transport services, the security
   considerations of that additional functionality also apply.

   For pseudowires, the security considerations of [RFC3985] and
   [RFC5659] apply.

   Packets that arrive on an interface with a given label value should
   not be forwarded unless that label value is assigned to an LSP or PW
   to a peer LSR or PE that is reachable via that interface.

   Each MPLS-TP solution must specify the additional security
   considerations that apply.

5.  IANA Considerations

   IANA considerations resulting from specific elements of MPLS-TP
   functionality will be detailed in the documents specifying that
   functionality.

   This document introduces no additional IANA considerations in itself.

6.  Acknowledgements

   The editors wish to thank the following for their contribution to
   this document:

   o  Rahul Aggarwal





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   o  Dieter Beller

   o  Malcolm Betts

   o  Italo Busi

   o  John E Drake

   o  Hing-Kam Lam

   o  Marc Lasserre

   o  Vincenzo Sestito

   o  Martin Vigoureux

   o  The participants of ITU-T SG15

7.  Open Issues

   This section contains a list of issues that must be resolved before
   last call.

   o  There is some text missing from the network layer clients section.
      Text is invited covering the use of out of band signaling
      associated with the AC.

   o  Need text to address how the LSR next hop MAC address is
      determined for Ethernet link layers when no IP (i.e.  ARP) is
      available.  If statically configured, what is the default? 181209:
      this will be addressed in the normative data plane draft

   o  Need to add section (Appendix) describing stack optizations for
      LSP and PWs

   o  Add a section clarify what options are used for interdomain
      operation e.g. inter-AS TE LSPs, MS-PW, LSP stitching, back-to-
      back ACs

   o  Text reduction for the OAM, survivability and NM sections.

   o  Include summarised PST text

8.  References







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8.1.  Normative References

   [G.7710]                             "ITU-T Recommendation G.7710/
                                        Y.1701 (07/07), "Common
                                        equipment management function
                                        requirements"", 2005.

   [G.805]                              "ITU-T Recommendation G.805
                                        (11/95), "Generic Functional
                                        Architecture of Transport
                                        Networks"", November 1995.

   [RFC3031]                            Rosen, E., Viswanathan, A., and
                                        R. Callon, "Multiprotocol Label
                                        Switching Architecture",
                                        RFC 3031, January 2001.

   [RFC3032]                            Rosen, E., Tappan, D., Fedorkow,
                                        G., Rekhter, Y., Farinacci, D.,
                                        Li, T., and A. Conta, "MPLS
                                        Label Stack Encoding", RFC 3032,
                                        January 2001.

   [RFC3270]                            Le Faucheur, F., Wu, L., Davie,
                                        B., Davari, S., Vaananen, P.,
                                        Krishnan, R., Cheval, P., and J.
                                        Heinanen, "Multi-Protocol Label
                                        Switching (MPLS) Support of
                                        Differentiated Services",
                                        RFC 3270, May 2002.

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

   [RFC3473]                            Berger, L., "Generalized Multi-
                                        Protocol Label Switching (GMPLS)
                                        Signaling Resource ReserVation
                                        Protocol-Traffic Engineering
                                        (RSVP-TE) Extensions", RFC 3473,
                                        January 2003.

   [RFC3985]                            Bryant, S. and P. Pate, "Pseudo
                                        Wire Emulation Edge-to-Edge
                                        (PWE3) Architecture", RFC 3985,
                                        March 2005.



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   [RFC4090]                            Pan, P., Swallow, G., and A.
                                        Atlas, "Fast Reroute Extensions
                                        to RSVP-TE for LSP Tunnels",
                                        RFC 4090, May 2005.

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

   [RFC4385]                            Bryant, S., Swallow, G.,
                                        Martini, L., and D. McPherson,
                                        "Pseudowire Emulation Edge-to-
                                        Edge (PWE3) Control Word for Use
                                        over an MPLS PSN", RFC 4385,
                                        February 2006.

   [RFC4447]                            Martini, L., Rosen, E., El-
                                        Aawar, N., Smith, T., and G.
                                        Heron, "Pseudowire Setup and
                                        Maintenance Using the Label
                                        Distribution Protocol (LDP)",
                                        RFC 4447, April 2006.

   [RFC4872]                            Lang, J., Rekhter, Y., and D.
                                        Papadimitriou, "RSVP-TE
                                        Extensions in Support of End-to-
                                        End Generalized Multi-Protocol
                                        Label Switching (GMPLS)
                                        Recovery", RFC 4872, May 2007.

   [RFC5085]                            Nadeau, T. and C. Pignataro,
                                        "Pseudowire Virtual Circuit
                                        Connectivity Verification
                                        (VCCV): A Control Channel for
                                        Pseudowires", RFC 5085,
                                        December 2007.

   [RFC5307]                            Kompella, K. and Y. Rekhter,
                                        "IS-IS Extensions in Support of
                                        Generalized Multi-Protocol Label
                                        Switching (GMPLS)", RFC 5307,
                                        October 2008.

   [RFC5462]                            Andersson, L. and R. Asati,
                                        "Multiprotocol Label Switching
                                        (MPLS) Label Stack Entry: "EXP"



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                                        Field Renamed to "Traffic Class"
                                        Field", RFC 5462, February 2009.

   [RFC5586]                            Bocci, M., Vigoureux, M., and S.
                                        Bryant, "MPLS Generic Associated
                                        Channel", RFC 5586, June 2009.

8.2.  Informative References

   [I-D.ietf-bfd-mpls]                  Aggarwal, R., Kompella, K.,
                                        Nadeau, T., and G. Swallow, "BFD
                                        For MPLS LSPs",
                                        draft-ietf-bfd-mpls-07 (work in
                                        progress), June 2008.

   [I-D.ietf-mpls-tp-identifiers]       Bocci, M. and G. Swallow,
                                        "MPLS-TP Identifiers", draft-
                                        ietf-mpls-tp-identifiers-00
                                        (work in progress),
                                        November 2009.

   [I-D.ietf-mpls-tp-nm-framework]      Mansfield, S., Gray, E., and H.
                                        Lam, "MPLS-TP Network Management
                                        Framework", draft-ietf-mpls-tp-
                                        nm-framework-02 (work in
                                        progress), November 2009.

   [I-D.ietf-mpls-tp-nm-req]            Mansfield, S. and K. Lam, "MPLS
                                        TP Network Management
                                        Requirements",
                                        draft-ietf-mpls-tp-nm-req-06
                                        (work in progress),
                                        October 2009.

   [I-D.ietf-mpls-tp-oam-framework]     Allan, D., Busi, I., and B.
                                        Niven-Jenkins, "MPLS-TP OAM
                                        Framework", draft-ietf-mpls-tp-
                                        oam-framework-04 (work in
                                        progress), December 2009.

   [I-D.ietf-mpls-tp-oam-requirements]  Vigoureux, M., Ward, D., and M.
                                        Betts, "Requirements for OAM in
                                        MPLS Transport Networks", draft-
                                        ietf-mpls-tp-oam-requirements-04
                                        (work in progress),
                                        December 2009.

   [I-D.ietf-mpls-tp-survive-fwk]       Sprecher, N. and A. Farrel,



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                                        "Multiprotocol Label Switching
                                        Transport Profile Survivability
                                        Framework", draft-ietf-mpls-tp-
                                        survive-fwk-03 (work in
                                        progress), November 2009.

   [I-D.ietf-pwe3-dynamic-ms-pw]        Martini, L., Bocci, M., Balus,
                                        F., Bitar, N., Shah, H.,
                                        Aissaoui, M., Rusmisel, J.,
                                        Serbest, Y., Malis, A., Metz,
                                        C., McDysan, D., Sugimoto, J.,
                                        Duckett, M., Loomis, M., Doolan,
                                        P., Pan, P., Pate, P., Radoaca,
                                        V., Wada, Y., and Y. Seo,
                                        "Dynamic Placement of Multi
                                        Segment Pseudo Wires",
                                        draft-ietf-pwe3-dynamic-ms-pw-10
                                        (work in progress),
                                        October 2009.

   [I-D.ietf-pwe3-redundancy]           Muley, P. and V. Place,
                                        "Pseudowire (PW) Redundancy",
                                        draft-ietf-pwe3-redundancy-02
                                        (work in progress),
                                        October 2009.

   [I-D.ietf-pwe3-segmented-pw]         Martini, L., Nadeau, T., Metz,
                                        C., Duckett, M., Bocci, M.,
                                        Balus, F., and M. Aissaoui,
                                        "Segmented Pseudowire",
                                        draft-ietf-pwe3-segmented-pw-13
                                        (work in progress), August 2009.

   [RFC3443]                            Agarwal, P. and B. Akyol, "Time
                                        To Live (TTL) Processing in
                                        Multi-Protocol Label Switching
                                        (MPLS) Networks", RFC 3443,
                                        January 2003.

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

   [RFC4377]                            Nadeau, T., Morrow, M., Swallow,
                                        G., Allan, D., and S.
                                        Matsushima, "Operations and
                                        Management (OAM) Requirements



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                                        for Multi-Protocol Label
                                        Switched (MPLS) Networks",
                                        RFC 4377, February 2006.

   [RFC4379]                            Kompella, K. and G. Swallow,
                                        "Detecting Multi-Protocol Label
                                        Switched (MPLS) Data Plane
                                        Failures", RFC 4379,
                                        February 2006.

   [RFC5146]                            Kumaki, K., "Interworking
                                        Requirements to Support
                                        Operation of MPLS-TE over GMPLS
                                        Networks", RFC 5146, March 2008.

   [RFC5254]                            Bitar, N., Bocci, M., and L.
                                        Martini, "Requirements for
                                        Multi-Segment Pseudowire
                                        Emulation Edge-to-Edge (PWE3)",
                                        RFC 5254, October 2008.

   [RFC5309]                            Shen, N. and A. Zinin, "Point-
                                        to-Point Operation over LAN in
                                        Link State Routing Protocols",
                                        RFC 5309, October 2008.

   [RFC5331]                            Aggarwal, R., Rekhter, Y., and
                                        E. Rosen, "MPLS Upstream Label
                                        Assignment and Context-Specific
                                        Label Space", RFC 5331,
                                        August 2008.

   [RFC5654]                            Niven-Jenkins, B., Brungard, D.,
                                        Betts, M., Sprecher, N., and S.
                                        Ueno, "Requirements of an MPLS
                                        Transport Profile", RFC 5654,
                                        September 2009.

   [RFC5659]                            Bocci, M. and S. Bryant, "An
                                        Architecture for Multi-Segment
                                        Pseudowire Emulation Edge-to-
                                        Edge", RFC 5659, October 2009.









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Authors' Addresses

   Matthew Bocci (editor)
   Alcatel-Lucent
   Voyager Place, Shoppenhangers Road
   Maidenhead, Berks  SL6 2PJ
   United Kingdom

   Phone:
   EMail: matthew.bocci@alcatel-lucent.com


   Stewart Bryant (editor)
   Cisco Systems
   250 Longwater Ave
   Reading  RG2 6GB
   United Kingdom

   Phone:
   EMail: stbryant@cisco.com


   Dan Frost
   Cisco Systems


   Phone:
   Fax:
   EMail: danfrost@cisco.com
   URI:


   Lieven Levrau
   Alcatel-Lucent
   7-9, Avenue Morane Sulnier
   Velizy  78141
   France

   Phone:
   EMail: lieven.levrau@alcatel-lucent.com











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   Lou Berger
   LabN


   Phone: +1-301-468-9228
   Fax:
   EMail: lberger@labn.net
   URI:











































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