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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: October 4, 2010                                   D. Frost, Ed.
                                                           Cisco Systems
                                                               L. Levrau
                                                          Alcatel-Lucent
                                                               L. Berger
                                                                    LabN
                                                          April 02, 2010


               A Framework for MPLS in Transport Networks
                    draft-ietf-mpls-tp-framework-11

Abstract

   This document specifies an architectural framework for the
   application of Multiprotocol Label Switching (MPLS) to the
   construction of packet-switched transport 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 transport paths.  The remaining subset,
   applicable specifically to point-to-multipoint transport paths, is
   outside the 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 in full conformance with the
   provisions of BCP 78 and BCP 79.




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Copyright Notice

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

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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 . . . . . . . . . . . .  8
       1.3.6.  Customer Edge (CE) . . . . . . . . . . . . . . . . . .  8
       1.3.7.  Edge-to-Edge LSP . . . . . . . . . . . . . . . . . . .  9
       1.3.8.  Service LSP  . . . . . . . . . . . . . . . . . . . . .  9
       1.3.9.  Layer Network  . . . . . . . . . . . . . . . . . . . .  9
       1.3.10. Network Layer  . . . . . . . . . . . . . . . . . . . .  9
       1.3.11. Service Interface  . . . . . . . . . . . . . . . . . .  9
       1.3.12. Additional Definitions and Terminology . . . . . . . .  9
   2.  MPLS Transport Profile Requirements  . . . . . . . . . . . . . 10
   3.  MPLS Transport Profile Overview  . . . . . . . . . . . . . . . 10
     3.1.  Packet Transport Services  . . . . . . . . . . . . . . . . 10



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     3.2.  Scope of the MPLS Transport Profile  . . . . . . . . . . . 11
     3.3.  Architecture . . . . . . . . . . . . . . . . . . . . . . . 12
       3.3.1.  MPLS-TP Native Service Adaptation Functions  . . . . . 13
       3.3.2.  MPLS-TP Forwarding Functions . . . . . . . . . . . . . 13
     3.4.  MPLS-TP Native Service Adaptation  . . . . . . . . . . . . 14
       3.4.1.  MPLS-TP Client/Server Layer Relationship . . . . . . . 15
       3.4.2.  MPLS-TP Transport Layers . . . . . . . . . . . . . . . 16
       3.4.3.  MPLS-TP Transport Service Interfaces . . . . . . . . . 17
       3.4.4.  Pseudowire Adaptation  . . . . . . . . . . . . . . . . 23
       3.4.5.  Network Layer Adaptation . . . . . . . . . . . . . . . 26
     3.5.  Identifiers  . . . . . . . . . . . . . . . . . . . . . . . 30
     3.6.  Generic Associated Channel (G-ACh) . . . . . . . . . . . . 30
     3.7.  Operations, Administration and Maintenance (OAM) . . . . . 32
     3.8.  Return Path  . . . . . . . . . . . . . . . . . . . . . . . 34
       3.8.1.  Return Path Types  . . . . . . . . . . . . . . . . . . 35
       3.8.2.  Point-to-Point Unidirectional LSPs . . . . . . . . . . 35
       3.8.3.  Point-to-Point Associated Bidirectional LSPs . . . . . 36
       3.8.4.  Point-to-Point Co-Routed Bidirectional LSPs  . . . . . 36
     3.9.  Control Plane  . . . . . . . . . . . . . . . . . . . . . . 36
     3.10. Interdomain Connectivity . . . . . . . . . . . . . . . . . 39
     3.11. Static Operation of LSPs and PWs . . . . . . . . . . . . . 39
     3.12. Survivability  . . . . . . . . . . . . . . . . . . . . . . 39
     3.13. Path Segment Tunnels . . . . . . . . . . . . . . . . . . . 41
     3.14. Pseudowire Segment Tunnels . . . . . . . . . . . . . . . . 42
     3.15. Network Management . . . . . . . . . . . . . . . . . . . . 42
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 44
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 44
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 45
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 45
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 48




















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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 transport paths.
   The remaining MPLS-TP functions, applicable specifically to point-to-
   multipoint transport paths, are outside the 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, for example by network management
      systems or direct node configuration using a command line
      interface.

   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.




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   In order to achieve these objectives, there is a need to define a
   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 outside the 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        G-ACh Label
   MEG        Maintenance Entity Group
   MEP        Maintenance Entity Group End Point
   MIP        Maintenance Entity Group 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
   AC         Attachment Circuit
   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
   PST        Path Segment Tunnel

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 outside the 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



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   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.

   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

   MPLS-TP Sections are defined in [I-D.ietf-mpls-tp-data-plane].  See
   also the definition of "section layer network" 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 supported.

   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.

   See [I-D.ietf-mpls-tp-data-plane] for further details on the types
   and data-plane properties of MPLS-TP LSPs.

   The lowest server layer provided by MPLS-TP is an MPLS-TP LSP.  The



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   client layers of an MPLS-TP LSP may be network layer protocols, MPLS
   LSPs, or PWs.  The relationship of an MPLS-TP LSP to its client
   layers is described in detail in Section 3.4.

1.3.5.  MPLS-TP Label Switching Router

   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.

   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.  Label Edge Router

   An MPLS-TP Label Edge Router (LER) is an LSR that exists at the
   endpoints of an LSP and therefore pushes or pops the LSP label, i.e.
   does not perform a label swap on the particular LSP under
   consideration.

1.3.5.2.  MPLS-TP Provider Edge 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 PE
   that pushes or pops a label is an LER.

1.3.5.3.  MPLS-TP Provider 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 link.





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1.3.7.  Edge-to-Edge LSP

   An Edge-to-Edge LSP is an LSP between a pair of PEs that may transit
   zero or more provider LSRs.

1.3.8.  Service LSP

   A service LSP is an LSP that carries a single client service.

1.3.9.  Layer Network

   A layer network is defined in [G.805] and described in [RFC5654].

1.3.10.  Network Layer

   This document uses the term Network Layer in the same sense as it is
   used in [RFC3031] and [RFC3032].

1.3.11.  Service Interface

   The packet transport service provided by MPLS-TP is provided at a
   service interface.  Two types of service interfaces are defined (see
   :

   o  User-Network Interface (UNI) (see Section 3.4.3.1).

   o  Network-Network Interface (NNI) (see Section 3.4.3.2).

   A UNI service interface may be a layer 2 interface that carries only
   network layer clients.  MPLS-TP LSPs are both necessary and
   sufficient to support this service interface as described in section
   3.4.3.  Alternatively, it may be a layer 2 interface that carries
   both network layer and non-network layer clients.  To support this
   service interface, a PW is required to adapt the client traffic
   received over the service interface.  This PW in turn is a client of
   the MPLS-TP server layer.  This is described in section 3.4.2.

   An NNI service interface may be to an MPLS LSP or a PW.  To support
   this case an MPLS-TP PE participates in the service interface
   signaling.

1.3.12.  Additional Definitions and Terminology

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






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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.  It is
   not normative or 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.

   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.



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   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 CLNS packets used
      by the control/management plane of the client MPLS(-TP) layer
      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.

3.2.  Scope of the MPLS Transport Profile

   Figure 1 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.







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


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

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



                        Figure 1: Scope of MPLS-TP

3.3.  Architecture

   MPLS-TP comprises the following architectural elements:

   o  A standard MPLS data plane [RFC3031] as profiled in
      [I-D.ietf-mpls-tp-data-plane].

   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, as
      outlined in [I-D.ietf-mpls-tp-oam-framework].

   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, as outlined in
      [I-D.ietf-mpls-tp-survive-fwk].

   o  Network management functions, as outlined in
      [I-D.ietf-mpls-tp-nm-framework].

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

   o  MPLS-TP native service adaptation





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   o  MPLS-TP forwarding

   The adaptation functions interface the native service (i.e. the
   client layer network 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 native service traffic over an MPLS-TP
   server layer network, for example PW and LSP labels.

3.3.1.  MPLS-TP Native Service Adaptation Functions

   The MPLS-TP native service adaptation functions interface the client
   layer network 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 layer
   network data plane from the MPLS-TP data plane, thus contributing to
   the 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 native service traffic 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], [RFC3032] and [RFC3443],
   as profiled in [I-D.ietf-mpls-tp-data-plane].  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 optionally the MS-PW
   forwarding operations defined in [RFC3985] and [RFC5659].




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   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 (such as those
   for OAM) that require 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, or the
   packet is received with the GAL (Section 3.6) at the top of stack.
   Otherwise the packet is forwarded according to the procedures in
   [RFC3032].

   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.

   Further details of MPLS-TP forwarding can be found in
   [I-D.ietf-mpls-tp-data-plane].

3.4.  MPLS-TP Native Service Adaptation

   This document describes the architecture for two native service
   adaptation mechanisms, which provide encapsulation and demultiplexing
   for native service traffic traversing an MPLS-TP network:

   o  A PW

   o  An MPLS Label

   A PW provides any emulated service that the IETF has defined to be
   provided by a PW, for example Ethernet, Frame Relay, or PPP/HDLC.  A
   list of PW types is maintained by IANA in the the "MPLS Pseudowire
   Type" registry.  When the native service adaptation is via a PW, the
   mechanisms described in Section 3.4.4 are used.

   An MPLS LSP Label can also be used as the adaptation, in which case
   any native service traffic type supported by [RFC3031] and [RFC3032]
   is allowed.  Examples of such traffic types include IP, and MPLS-
   labeled packets.  Note that the latter case includes TE-LSPs



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   [RFC3209] and LSP based applications such as PWs, Layer 2 VPNs
   [RFC4664], and Layer 3 VPNs [RFC4364].  When the native service
   adaptation is via an MPLS label, the mechanisms described in
   Section 3.4.5 are used.

3.4.1.  MPLS-TP Client/Server Layer Relationship

   The relationship between the client layer network and the MPLS-TP
   server layer network is defined by the MPLS-TP network boundary and
   the label context.  It is not explicitly indicated in the packet.  In
   terms of the MPLS label stack, when the native service traffic type
   is itself MPLS-labeled, then the S bits of all the labels in the
   MPLS-TP label stack carrying that client traffic are zero; otherwise
   the bottom label of the MPLS-TP label stack has the S-bit set to 1.
   In other words, there can be only one S-bit set in a label stack.

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

   The relationship of MPLS-TP to its clients is illustrated in
   Figure 2.  Note that the label stacks shown in the figure are divided
   between those inside the MPLS-TP Network and those within the client
   network when the client network is MPLS(-TP).  They illustrate the
   smallest number of labels possible.  These label stacks could also
   include more labels.





















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   PW-Based               MPLS Labelled                IP
   Services                  Services                Transport
 |------------|  |-----------------------------|  |------------|

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

~~~~~~~~~~~ denotes Client <-> MPLS-TP layer boundary


                  Figure 2: MPLS-TP - Client Relationship

3.4.2.  MPLS-TP Transport Layers

   An MPLS-TP network consists logically of two layers: the Transport
   Service layer and the Transport Path layer.

   The Transport Service layer provides the interface between Customer
   Edge (CE) nodes and the MPLS-TP network.  Each packet transmitted by
   a CE node for transport over the MPLS-TP network is associated at the
   receiving MPLS-TP Provider Edge (PE) node with a single logical
   point-to-point connection at the Transport Service layer between this
   (ingress) PE and the corresponding (egress) PE to which the peer CE
   is attached.  Such a connection is called an MPLS-TP Transport
   Service Instance, and the set of client packets associated with such
   an instance on a particular CE-PE link is called a client flow.

   The Transport Path layer provides aggregation of Transport Service
   Instances over MPLS-TP transport paths (LSPs), as well as aggregation
   of transport paths (via LSP hierarchy).

   Awareness of the Transport Service layer need exist only at PE nodes.
   MPLS-TP Provider (P) nodes need have no awareness of this layer.
   Both PE and P nodes participate in the Transport Path layer.  A PE



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   terminates (i.e., is an LER with respect to) the transport paths it
   supports, and is responsible for multiplexing and demultiplexing of
   Transport Service Instance traffic over such transport paths.

3.4.3.  MPLS-TP Transport Service Interfaces

   An MPLS-TP PE node can provide two types of interface to the
   Transport Service layer.  The MPLS-TP User-Network Interface (UNI)
   provides the interface between a CE and the MPLS-TP network.  The
   MPLS-TP Network-Network Interface (NNI) provides the interface
   between two MPLS-TP PEs in different administrative domains.

   When providing a Virtual Private Wire Service (VPWS), Virtual Private
   Local Area Network Service (VPLS), Virtual Private Multicast Service
   (VPMS), or Internet Protocol Local Area Network Service (IPLS),
   pseudowires must be used to carry the client service.  VPWS, VLPS,
   and IPLS are described in [RFC4664].  VPMS is described in
   [I-D.ietf-l2vpn-vpms-frmwk-requirements].

   When MPLS-TP is used to provide a transport service for e.g.  IP
   services that are a part of a Layer 3 VPN, then packets are
   transported in the same manner as specified in [RFC4364].

3.4.3.1.  User-Network Interface

   The MPLS-TP User-Network interface (UNI) is illustrated in Figure 3.
   The UNI for a particular client flow may or may not involve signaling
   between the CE and PE, and if signaling is used, it may or may not
   traverse the same data-link that supports the client flow.

   :          User-Network Interface        :           MPLS-TP
    :<-------------------------------------->:           Network <----->
    :                                        :
   -:-------------             --------------:------------------
    :             |           |              : Transport        |
    :             |           |  Transport   :   Path           |
    :             |           |   Service    : Mux/Demux        |
    :             |           |   Control    :    --            |
    :             |           |    Plane     :   |  |  Transport|
    : ----------  | Signaling |  ----------  :   |  |    Path   |
    :|Signaling |_|___________|_|Signaling | :   |  |    --------->
    :|Controller| |           | |Controller| :   |  |   |
    : ----------  |           |  ----------  :   |  |    --------->
    :      :......|...........|......:       :   |  |           |
    :             |  Control  |              :   |  |  Transport|
    :             |  Channel  |              :   |  |    Path   |
    :             |           |              :   |  |    --------->
    :             |           |              :   |  |  -+----------->TSI



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    :             |           |  Transport   :   |  | |  --------->
    :             |  Client   |   Service    :   |  | |         |
    :             |  Traffic  |  Data Plane  :   |  | |         |
    : ----------  |  Flows    |  --------------  |  | |Transport|
    :|Signaling |-|-----------|-|Client/Service|-|  |-   Path   |
    :|Controller|=|===========|=|    Traffic   | |  |    --------->
    : ----------  |           | |  Processing  |=|  |===+===========>TSI
    :      |      |           |  --------------  |  |    --------->
    :      |______|___________|______|       :   |  |           |
    :             | Data Link |              :   |  |           |
    :             |           |              :    --            |
    :             |           |              :        Transport |
    :             |           |              :         Service  |
    :             |           |              :        Data Plane|
   ---------------             ---------------------------------
   Customer Edge Node              MPLS-TP Provider Edge Node


    TSI = Transport Service Instance



   Client/Service Traffic Processing Stages

                                               :
     --------------From UNI------->            :
    -------------------------------------------:------------------
   |                     | Client Traffic Unit :                  |
   | Link-Layer-Specific | Link Decapsulation  : Service Instance |
   |    Processing       |         &           :    Transport     |
   |                     |  Service Instance   :  Encapsulation   |
   |                     |   Identification    :                  |
    -------------------------------------------:------------------
                                               :
                                               :
    -------------------------------------------:------------------
   |                     |                     : Service Instance |
   |                     |                     :    Transport     |
   | Link-Layer-Specific | Client Traffic Unit :  Decapsulation   |
   |    Processing       | Link Encapsulation  :        &         |
   |                     |                     : Service Instance |
   |                     |                     :  Identification  |
    -------------------------------------------:------------------
     <-------------To UNI ---------            :


                   Figure 3: MPLS-TP PE Containing a UNI




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   The figure shows the logical processing steps involved in a PE both
   for traffic flowing from the CE to the MPLS-TP network (left to
   right), and from the network to the CE (right to left).

   In the first case, when a packet from a client flow is received by
   the PE from the CE over the data-link, the following steps occur:

   1.  Link-layer specific preprocessing, if any, is performed.  An
       example of such preprocessing is the PREP function illustrated in
       Figure 3 of [RFC3985].  Such preprocessing is outside the scope
       of MPLS-TP.

   2.  The packet is extracted from the data-link frame if necessary,
       and associated with a Transport Service Instance.  At this point,
       UNI processing has completed.

   3.  A transport service encapsulation is associated with the packet,
       if necessary, for transport over the MPLS-TP network.

   4.  The packet is mapped to a transport path based on its associated
       Transport Service Instance, the transport path encapsulation is
       added, if necessary, and the packet is transmitted over the
       transport path.

   In the second case, when a packet associated with a Transport Service
   Instance arrives over a transport path, the following steps occur:

   1.  The transport path encapsulation is disposed of.

   2.  The transport service encapsulation is disposed of and the
       Transport Service Instance and client flow identified.

   3.  At this point, UNI processing begins.  A data-link encapsulation
       is associated with the packet for delivery to the CE based on the
       client flow.

   4.  Link-layer-specific postprocessing, if any, is performed.  Such
       postprocessing is outside the scope of MPLS-TP.

3.4.3.2.  Network-Network Interface

   The MPLS-TP NNI is illustrated in Figure 4.  The NNI for a particular
   transport service instance may or may not involve signaling between
   the two PEs, and if signaling is used, it may or may not traverse the
   same data-link that supports the service instance.

                   :      Network-Network Interface    :
                   :<--------------------------------->:



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                   :                                   :
       ------------:-------------         -------------:------------
      |  Transport :             |       |             : Transport  |
      |    Path    : Transport   |       |  Transport  :   Path     |
      |  Mux/Demux :  Service    |       |   Service   : Mux/Demux  |
      |      --    :  Control    |       |   Control   :    --      |
      |     |  |   :   Plane     |Sig-   |    Plane    :   |  |     |
      |TP   |  |   : ----------  | naling|  ---------- :   |  |   TP|
    <---    |  |   :|Signaling |_|_______|_|Signaling |:   |  |    --->
   TSI<-+-  |  |   :|Controller| |       | |Controller|:   |  |   |
    <---  | |  |   : ----------  |       |  ---------- :   |  |    --->
      |   | |  |   :      :......|.......|......:      :   |  |     |
      |   | |  |   :             |Control|             :   |  |     |
      |TP | |  |   :             |Channel|             :   |  |   TP|
    <---  | |  |   :             |       |             :   |  |    --->
        | | |  |   :             |       |             :   |  |  -+->TSI
    <---  | |  |   : Transport   |       |  Transport  :   |  | |  --->
      |   | |  |   :  Service    |Service|   Service   :   |  | |   |
      |   | |  |   : Data Plane  |Traffic|  Data Plane :   |  | |   |
      |   | |  |  -------------  | Flows |  -------------  |  | |   |
      |TP  -|  |-|   Service   |-|-------|-|   Service   |-|  |-  TP|
    <---    |  | |   Traffic   | |       | |   Traffic   | |  |    --->
   TSI<=+===|  |=|  Processing |=|=======|=|  Processing |=|  |===+=>TSI
    <---    |  |  -------------  |       |  -------------  |  |    --->
      |     |  |   :      |______|_______|______|      :   |  |     |
      |     |  |   :             | Data  |             :   |  |     |
      |      --    :             | Link  |             :    --      |
      |            :             |       |             :            |
       --------------------------         --------------------------
       MPLS-TP Provider Edge Node         MPLS-TP Provider Edge Node


    TP  = Transport Path
    TSI = Transport Service Instance



   Service Traffic Processing Stages

                                                :
     --------------From NNI------->             :
    --------------------------------------------:------------------
   |                     | Service Traffic Unit :                  |
   | Link-Layer-Specific |  Link Decapsulation  : Service Instance |
   |    Processing       |          &           :  Encapsulation   |
   |                     |   Service Instance   :  Normalisation   |
   |                     |    Identification    :                  |
    --------------------------------------------:------------------



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                                                :
                                                :
    --------------------------------------------:------------------
   |                     |                      : Service Instance |
   |                     |                      :  Identification  |
   | Link-Layer-Specific | Service Traffic Unit :        &         |
   |    Processing       |  Link Encapsulation  : Service Instance |
   |                     |                      :  Encapsulation   |
   |                     |                      :  Normalisation   |
    --------------------------------------------:------------------
     <-------------To NNI ---------             :


                  Figure 4: MPLS-TP PE Containing an NNI

   The figure shows the logical processing steps involved in a PE for
   traffic flowing both from the peer PE (left to right) and to the peer
   PE (right to left).

   In the first case, when a packet from a transport service instance is
   received by the PE from the peer PE over the data-link, the following
   steps occur:

   1.  Link-layer specific preprocessing, if any, is performed.  Such
       preprocessing is outside the scope of MPLS-TP.

   2.  The packet is extracted from the data-link frame if necessary,
       and associated with a Transport Service Instance.  At this point,
       NNI processing has completed.

   3.  The transport service encapsulation of the packet is normalised
       for transport over the MPLS-TP network.  This step allows a
       different transport service encapsulation to be used over the NNI
       than that used in the internal MPLS-TP network.  An example of
       such normalisation is a swap of a label identifying the Transport
       Service Instance.

   4.  The packet is mapped to a transport path based on its associated
       Transport Service Instance, the transport path encapsulation is
       added, if necessary, and the packet is transmitted over the
       transport path.

   In the second case, when a packet associated with a Transport Service
   Instance arrives over a transport path, the following steps occur:

   1.  The transport path encapsulation is disposed of.





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   2.  The Transport Service Instance is identified from the transport
       service encapsulation, and this encapsulation is normalised for
       delivery over the NNI (see Step 3 above).

   3.  At this point, NNI processing begins.  A data-link encapsulation
       is associated with the packet for delivery to the peer PE based
       on the normalised Transport Service Instance.

   4.  Link-layer-specific postprocessing, if any, is performed.  Such
       postprocessing is outside the scope of MPLS-TP.

3.4.3.3.  Example Interfaces

   This section considers some special cases of UNI and NNI processing
   for particular transport service types.  These are illustrative, and
   do not preclude other transport service types.

3.4.3.3.1.  Layer 2 Transport Service

   In this example the MPLS-TP network is providing a point-to-point
   Layer 2 transport service between attached CE nodes.  This service is
   provided by a Transport Service Instance consisting of a PW
   established between the associated PE nodes.  The client flows
   associated with this Transport Service Instance are the sets of all
   Layer 2 frames transmitted and received over the attachment circuits.

   The processing steps in this case for a frame received from the CE
   are:

   1.  Link-layer specific preprocessing, if any, is performed,
       corresponding to the PREP function illustrated in Figure 3 of
       [RFC3985].

   2.  The frame is associated with a Transport Service Instance based
       on the attachment circuit over which it was received.

   3.  A transport service encapsulation, consisting of the PW control
       word and PW label, is associated with the frame.

   4.  The resulting packet is mapped to an LSP, the LSP label is
       pushed, and the packet is transmitted over the outbound interface
       associated with the LSP.

   The steps in the reverse direction for PW packets received over the
   LSP are analogous.






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3.4.3.4.  IP Transport Service

   In this example the MPLS-TP network is providing a point-to-point IP
   transport service between CE1, CE2, and CE3, as follows.  One point-
   to-point transport service instance delivers IPv4 packets between CE1
   and CE2, and another instance delivers IPv6 packets between CE1 and
   CE3.

   The processing steps in this case for an IP packet received from CE1
   are:

   A1.  No link-layer-specific processing is performed.

   A2.  The IP packet is extracted from the link-layer frame and
   associated with a Service LSP based on the source MAC address (CE1)
   and the IP protocol version.

   A3.  A transport service encapsulation, consisting of the Service LSP
   label, is associated with the packet.

   A4.  The resulting packet is mapped to a tunnel LSP, the tunnel LSP
   label is pushed, and the packet is transmitted over the outbound
   interface associated with the LSP.

   The steps in the reverse direction, for packets received over a
   tunnel LSP carrying the Service LSP label, are analogous.

3.4.4.  Pseudowire Adaptation

   If the MPLS-TP network provides a layer 2 interface, that can carry
   both network layer and non-network layer traffic, as a service
   interface, then a PW is required to support the service interface.
   The PW is a client of the MPLS-TP LSP server layer.  The architecture
   for an MPLS-TP network that provides such services is based on the
   MPLS [RFC3031] and pseudowire [RFC3985] architectures.  Multi-segment
   pseudowires may optionally be used to provide a packet transport
   service, and their use is consistent with the MPLS-TP architecture.
   The use of MS-PWs may be motivated by, for example, the requirements
   specified in [RFC5254].  If MS-PWs are used, then the MS-PW
   architecture [RFC5659] also applies.

   Figure 5 shows the architecture for an MPLS-TP network using single-
   segment PWs.  Note that, in this document, the client layer is
   equivalent to the emulated service described in [RFC3985], while the
   Transport LSP is equivalent to the Packet Switched Network (PSN)
   tunnel of [RFC3985].





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


            Figure 5: MPLS-TP Architecture (Single Segment PW)

   Figure 6 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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     |<--------------------- Client Layer ------------------------>|
     |                                                             |
     |                  Pseudowire encapsulated,                   |
     |    |<---------- Packet Transport Service ------------->|    |
     |    |                                                   |    |
     |    |              Transport               Transport    |    |
     | AC |     |<-------- LSP1 --------->|    |<--LSP2-->|   | AC |
     | |  V     V                         V    V          V   V |  |
     V |  +----+              +-----+    +----+          +----+ |  V
 +---+ |  |TPE1|===============\   /=====|SPE1|==========|TPE2| |  +---+
 |   |----|......PW1-Seg1.... | \ / | ......X...PW1-Seg2......|----|   |
 |CE1| |  |    |              |  X  |    |    |          |    | |  |CE2|
 |   |----|......PW2-Seg1.... | / \ | ......X...PW2-Seg2......|----|   |
 +---+  ^ |    |===============/   \=====|    |==========|    | | ^+---+
        | +----+     ^        +-----+    +----+     ^    +----+   |
        |            |           ^                  |             |
        |          TE LSP        |                TE LSP          |
        |                      P-router                           |
   Native Service                                          Native Service


PW1-segment1 and PW1-segment2 are segments of the same MS-PW,
while PW2-segment1 and PW2-segment2 are segments of another MS-PW


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

   The corresponding MPLS-TP protocol stacks including PWs are shown in
   Figure 7.  In this figure the Transport Service Layer [RFC5654] is
   identified by the PW demultiplexer (Demux) label and the Transport
   Path Layer [RFC5654] is identified by the LSP Demux Label.




















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

     User Traffic                 PW OAM                  LSP OAM

Note: H(ighlighted) indicates the part of the protocol stack considered
in this document.


              Figure 7: MPLS-TP label stack using pseudowires

   PWs and their associated labels may be configured or signaled.  See
   Section 3.11 for additional details related to configured service
   types.  See Section 3.9 for additional details related to signaled
   service types.

3.4.5.  Network Layer Adaptation

   MPLS-TP LSPs can be used to transport network layer clients.  This
   document uses the term Network Layer in the same sense as it is used
   in [RFC3031] and [RFC3032].  The network layer protocols supported by
   [RFC3031] and [RFC3032] can be transported between service
   interfaces.  Examples are shown in Figure 5 above.  Support for
   network layer clients follows the MPLS architecture for support of
   network layer protocols as specified in [RFC3031] and [RFC3032].

   With network layer adaptation, the MPLS-TP domain provides either a
   uni-directional or 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 8, 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.

   The attachment circuits may be heterogeneous (e.g., any combination
   of SDH, PPP, Frame Relay, etc.) and network layer protocol payloads



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   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.



            |<------------- Client Network Layer --------------->|
            |                                                    |
            |          |<----------- Packet --------->|          |
            |          |         Transport Service    |          |
            |          |                              |          |
            |          |                              |          |
            |          |          Transport           |          |
            |          |    |<------ LSP ------->|    |          |
            |          V    V                    V    V          |
            V    AC    +----+      +-----+       +----+     AC   V
      +-----+    |     | PE1|=======\   /========| PE2|     |    +-----+
      |     |----------|..Svc LSP1.| \ / |............|----------|     |
      | CE1 |    |     |    |      |  X  |       |    |     |    | CE2 |
      |     |----------|..Svc LSP2.| / \ |............|----------|     |
      +-----+  ^ |     |    |=======/   \========|    |     | ^  +-----+
            ^  |       +----+  ^   +-----+       +----+     | |  ^
            |  |      Provider |       ^         Provider     |  |
            |  |       Edge 1  |       |          Edge 2      |  |
      Customer |               |    P Router                  | Customer
       Edge 1  |             TE LSP                           |  Edge 2
               |                                              |
               |                                              |
         Native service                                 Native service


         Figure 8: MPLS-TP Architecture for Network Layer Clients

   At the ingress service interface the client packets are received.
   The PE pushes one or more labels onto the client packets which are
   then label switched over the transport network.  Correspondingly the
   egress PE pops any labels added by the MPLS-TP networks and transmits
   the packet for delivery to the attached CE via the egress service
   interface.










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                           /===================\
                           H     OAM PDU       H
 +-------------------+     H-------------------H   /===================\
 |  Client Layer     |     H      GACh         H   H     OAM PDU       H
 /===================\     H-------------------H   H-------------------H
 H    Encap Label    H     H      GAL (S=1)    H   H      GACh         H
 H-------------------H     H-------------------H   H-------------------H
 H   SvcLSP Demux    H     H SvcLSP Demux (S=0)H   H    GAL (S=1)      H
 H-------------------H     H-------------------H   H-------------------H
 H Trans LSP Demux(s)H     H Trans LSP Demux(s)H   H Trans LSP Demux(s)H
 \===================/     \===================/   \===================/
 |   Server Layer    |     |   Server Layer    |   |   Server Layer    |
 +-------------------+     +-------------------+   +-------------------+

     User Traffic            Service LSP OAM             LSP OAM


Note: H(ighlighted) indicates the part of the protocol stack considered
in this document.


           Figure 9: MPLS-TP Label Stack for IP and LSP Clients

   In this figure the Transport Service Layer [RFC5654] is identified by
   the Service LSP (SvcLSP) demultiplexer (Demux) label and the
   Transport Path Layer [RFC5654] is identified by the Transport (Trans)
   LSP Demux Label.  Note that the functions of the Encapsulation label
   (Encap Label) and the Service Label (SvcLSP Demux) shown above may
   alternatively be represented by a single label stack entry.  Note
   that the S-bit is always zero when the client layer is MPLS-labelled.

   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 9 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 may be used to identify the network layer protocol payload
   type.  Therefore, when multiple protocol payload types are to be
   carried over a single service LSP, a unique label stack entry must be
   present for each payload type.  Such labels are referred to as
   "Encapsulation Labels", one of which is shown in Figure 9.
   Encapsulation Label may be either configured or signaled.

   Both an Encapsulation Label and a Service Label should be present in



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   the label stack when a particular packet transport service is
   supporting more than one network layer protocol payload type.  For
   example, if both IP and MPLS are to be carried, as shown in Figure 8,
   then two Encapsulation Labels are mapped on to a common Service
   Label.

   Note: The Encapsulation Label may be omitted when the service LSP is
   supporting only one network layer protocol payload type.  For
   example, if only MPLS labeled packets are carried over a service,
   then the Service Label (stack entry) provides both the payload type
   indication and service identification.

   Service labels are typically carried over an MPLS-TP Transport LSP
   edge-to-edge (or transport path layer).  An MPLS-TP Transport LSP is
   represented as an LSP Transport Demux label, as shown in Figure 9.
   Transport LSP is commonly used when more than one service exists
   between two PEs.

   Note that, if only one service exists between two PEs, the functions
   of the Transport LSP label and the Service LSP Label may be combined
   into a single label stack entry.  For example, if only one service is
   carried between two PEs then a single label could be used to provide
   both the service indication and the MPLS-TP transport 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
   transport 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
   specified in this document.  In some technologies the MAC address
   will need to be configured.

   Note that when two CEs, which peer with each other, operate over a
   network layer transport service and run a routing protocol such as



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   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 .

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.  MPLS-TP defined two type of
   sets of identifiers: Those that are compatible with IP, and another
   set that is compatibple with ITU-T transport-based operations.  The
   definition of these sets of identifiers is outside the scope of this
   document and is provided by [I-D.ietf-mpls-tp-identifiers].

3.6.  Generic Associated Channel (G-ACh)

   For correct operation of OAM mechanisms it is important that 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
   Protection State Coordination (PSC) data.  This is achieved by
   carrying such packets in either:

   o  A generic control channel associated to the LSP, PW or section,
      with no IP encapsulation. e.g. in a similar manner to
      Bidirectional Forwarding Detection for Virtual Circuit
      Connectivity Verification (VCCV-BFD) with PW ACH encapsulation
      [I-D.ietf-pwe3-vccv-bfd]).

   o  An IP encapsulation where IP capabilities are present. e.g.  PW
      ACH encapsulation with IP headers for VCCV-BFD
      [I-D.ietf-pwe3-vccv-bfd], or IP encapsulation for MPLS BFD
      [I-D.ietf-bfd-mpls].

   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, PSC, SCC, MCC
   or other packet types in-band over LSPs, PWs or sections.  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 an 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



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   supported by the G-ACh.

   The G-ACh must only be used for channels that are an adjunct to the
   data service.  Examples of these are OAM, PSC, 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 with which they are sharing resources.  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 10 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].


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


     Figure 10: PWE3 Protocol Stack Reference Model showing the G-ACh




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


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



      Figure 11: MPLS Protocol Stack Reference Model showing the LSP
                        Associated Control Channel

3.7.  Operations, Administration and Maintenance (OAM)

   The MPLS-TP OAM architecture supports a wide range of OAM functions
   to check continuity, to verify connectivity, to monitor path
   performance, and to generate, filter and manage local and remote
   defect alarms.  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.  Since MPLS-TP must be able to operate in



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   environments where IP is not used in the forwarding plane, 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, although the mechanisms defined in [RFC5586] can
   also be used.  MPLS-TP must be able to operate in environments where
   IP forwarding is not supported, and thus the G-ACh/GAL is the default
   mechanism to demultiplex OAM packets in MPLS-TP in these
   environments.

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

   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 G-ACh Label (GAL) to create a control
   channel associated to an LSP, Section or PW.

   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 (ME) can be viewed as the association of two
   Maintenance Entity Group End Points (MEPs).  A Maintenance Entity
   Group (MEG) 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 limit the OAM responsibilities of an OAM
   flow to within the domain of a transport path or segment, in the
   specific layer network that is being monitored and managed.

   A MEG may also include a set of Maintenance Entity Group Intermediate
   Points (MIPs).  MEPs are capable of sourcing and sinking OAM flows,
   while MIPs can both react to OAM flows received from within a MEG.



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   Intermediate nodes can also originate notifications to the MEPs as a
   result of specific network conditions.

   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 MPLS architecture
   mandates that MPLS layer processing occurs at least once on an LSR.

   Any node on an LSP can send an OAM packet on that LSP.  Likewise, any
   node on a PW can send OAM packets on a PW, including S-PEs.

   An OAM packet can only be received to be processed at an LSP
   endpoint, a PW endpoint (T-PE), or on the expiry of the TTL of the
   LSP or PW label.

3.8.  Return Path

   Management, control and OAM protocol functions may require response
   packets to be delivered from the receiver back to the originator of a
   message exchange.  This section provides a summary of the return path
   options in MPLS-TP networks.  Although this section describes the
   case of an MPLS-TP LSP, it is also applicable to a PW.

   In this description, U and D are LSRs that terminate MPLS-TP LSPs
   (i.e.  LERs) and that Y is an intermediate LSR along the LSP.  In the
   unidirectional case, U is the upstream LER and D is the downstream
   LER with respect to the LSP.  This reference model is shown in
   Figure 12.


                 LSP         LSP

           U ========= Y ========= D

          LER         LSR         LER

           ---------> Direction of pcket flow

                  Figure 12: Return Path reference Model



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   The following cases are described for the various types of LSPs:

   Case 1  Packet transmission from D to U

   Case 2  Packet transmission from Y to U

   Case 3  Packet transmission from D to Y

   Note that a return path may not always exist, and that packet
   transmission in one or more of the above cases may not be possible.
   In general the existence and nature of return paths for MPLS-TP LSPs
   is determined by operational provisioning.

3.8.1.  Return Path Types

   There are two types of return path that may be used for the delivery
   of traffic from a downstream node D to an upstream node U. Either:

   a.  The LSP between U and D is bidirectional, and therefore D has a
       path via the MPLS-TP LSP to return traffic back to U, or

   b.  D has some other unspecified means of directing traffic back to
       U.

   The first option is referred to as an "in-band" return path, the
   second as an "out-of-band" return path.

   There are various possibilities for "out-of-band" return paths.  Such
   a path may, for example, be based on ordinary IP routing.  In this
   case packets would be forwarded as usual to a destination IP address
   associated with U. In an MPLS-TP network that is also an IP/MPLS
   network, such a forwarding path may traverse the same physical links
   or logical transport paths used by MPLS-TP.  An out-of-band return
   path may also be indirect, via a distinct Data Communication Network
   (DCN) (provided, for example, by the method specified in [RFC5718]);
   or it may be via one or more other MPLS-TP LSPs.

3.8.2.  Point-to-Point Unidirectional LSPs

   Case 1  In this situation, either an in-band or out-of-band return
           path may be used to deliver traffic from D back to U.

           It is recommended for reasons of operational simplicity that
           point-to-point unidirectional LSPs be provisioned as
           associated bidirectional LSPs (which may also be co-routed)
           whenever return traffic from D to U is required.  Note that
           the two directions of such an LSP may have differing
           bandwidth allocations and QoS characteristics.  In the in-



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           band case there is in essence an associated bidirectional LSP
           between U and D, and the discussion for such LSPs below
           applies.

   Case 2  In this case only the out-of-band return path option is
           available.  However, an additional out-of-band possibility is
           worthy of note here: if D is known to have a return path to
           U, then Y can arrange to deliver return traffic to U by first
           sending it to D along the original LSP.  The mechanism by
           which D recognises the need for and performs this forwarding
           operation is protocol-specific.

   Case 3  In this case only the out-of-band return path option is
           available.  However, if D has a return path to U, then in a
           manner analogous to the previous case D can arrange to
           deliver return traffic to Y by first sending it to U along
           that return path.  The mechanism by which U recognises the
           need for and performs this forwarding operation is protocol-
           specific.

3.8.3.  Point-to-Point Associated Bidirectional LSPs

   For Case 1, D has a natural in-band return path to U, the use of
   which is typically preferred for return traffic, although out-of-band
   return paths are also applicable.

   For Cases 2 and 3, the considerations are the same as those for
   point-to-point unidirectional LSPs.

3.8.4.  Point-to-Point Co-Routed Bidirectional LSPs

   For all of Cases 1, 2, and 3, a natural in-band return path exists in
   the form of the LSP itself, and its use is preferred for return
   traffic.  Out-of-band return paths, however, are also applicable,
   primarily as an alternative means of delivery in case the in-band
   return path has failed.

3.9.  Control Plane

   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 3.11 for further details on statically
   configured and provisioned MPLS-TP services.




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   Figure 13 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.

    +------------------------------------------------------------------+
    |                                                                  |
    |                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 13: MPLS-TP Control Plane Architecture Context

   The MPLS-TP control plane is based on existing MPLS and PW control
   plane protocols, and is consistent with the Automatically Switched
   Optical Networks (ASON) architecture [G.8080].  MPLS-TP uses
   Generalized MPLS (GMPLS) signaling ([RFC3945], [RFC3471], [RFC3473])
   for LSPs and Targeted LDP (T-LDP) [RFC4447]
   [I-D.ietf-pwe3-segmented-pw][I-D.ietf-pwe3-dynamic-ms-pw] for
   pseudowires.

   MPLS-TP requires that any control plane traffic be capable of being
   carried over an out-of-band signaling network or a signaling control
   channel such as the one described in [RFC5718].  Note that while
   T-LDP signaling is traditionally carried in-band in IP/MPLS networks,
   this does not preclude its operation over out-of-band channels.
   References to T-LDP in this document do not preclude the definition



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   of alternative PW control protocols for use in MPLS-TP.

   PW control (and maintenance) takes place separately from LSP tunnel
   signaling.  The main coordination between LSP and PW control will
   occur within the nodes that terminate PWs.  The control planes for
   PWs and LSPs may be used independently, and one may be employed
   without the other.  This translates into the four possible scenarios:
   (1) no control plane is employed; (2) a control plane is used for
   both LSPs and PWs; (3) a control plane is used for LSPs, but not PWs;
   (4) a control plane is used for PWs, but not LSPs.  The PW and LSP
   control planes, collectively, must satisfy the MPLS-TP control plane
   requirements reviewed in the MPLS-TP Control Plane Framework
   [I-D.ietf-ccamp-mpls-tp-cp-framework].  When client services are
   provided directly via LSPs, all requirements must be satisfied by the
   LSP control plane.  When client services are provided via PWs, the PW
   and LSP control planes operate in combination and some functions may
   be satisfied via the PW control plane while others are provided to
   PWs by the LSP control plane.

   Note that if MPLS-TP is being used in a multi-layer network, a number
   of control protocol types and instances may be used.  This is
   consistent with the MPLS architecture which permits each label in the
   label stack to be allocated and signaled by its own control protocol.

   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
   Network-Network Interface (I-NNI), and External Network-Network
   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 3.12.



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   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.  In all cases, however, the control plane is
   logically decoupled from the data plane such that a control plane
   failure does not imply a failure of the existing transport paths.

3.10.  Interdomain Connectivity

   A number of methods exist to support inter-domain operation of
   MPLS-TP, including the data plane, OAM and configuration aspects, for
   example:

   o  Inter-domain TE LSPs [RFC4216]

   o  Multi-segment Pseudowires [RFC5659]

   o  LSP stitching [RFC5150]

   o  back-to-back attachment circuits [RFC5659]

   An important consideration in selecting an inter-domain connectivity
   mechanism is the degree of layer network isolation and types of OAM
   required by the operator.  The selection of which technique to use in
   a particular deployment scenario is outside the scope of this
   document.

3.11.  Static Operation of LSPs and PWs

   A PW or LSP may be statically configured without the support of a
   dynamic control plane.  This may be either by direct configuration of
   the PEs/LSRs, or via a network management system.  Static operation
   is independent for a specific PW or LSP instance.  Thus it should be
   possible for a PW to be statically configured, while the LSP
   supporting it is set up by a dynamic control plane.  When static
   configuration mechanisms are used, care must be taken to ensure that
   loops are not created.

3.12.  Survivability

   The survivability architecture for MPLS-TP is specified in
   [I-D.ietf-mpls-tp-survive-fwk].



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   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 underlying LSP
   (i.e. where the backup PW terminates on a different target PE node
   than the working PW in dual homing scenarios, or where protection of
   the S-PE is required).  Additionally, GMPLS provides a well known set
   of 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 of 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 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 a Protection State Coordination (PSC) mechanism.

   o  MPLS-TP recovery schemes are applicable to all levels in the
      MPLS-TP domain (i.e. 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.



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

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

3.13.  Path Segment Tunnels

   In order to monitor, protect and manage a portion of an LSP, a new
   architectural element is defined called the Path Segment Tunnel
   (PST).  A PST is a hierarchical LSP [RFC3031] which is defined and
   used for the purposes of OAM monitoring, protection or management of
   LSP segments or concatenated LSP segments.

   A PST is defined between the edges of the portion of the LSP that
   needs to be monitored, protected or managed.  OAM messages can be
   initiated at the edge of the PST and sent to the peer edge of the PST
   or to a MIP along the PST by setting the TTL value at the PST level
   accordingly.  A P router only pushes or pops a label if it is at the
   end of a PST.  In this mode, it is an LER for the PST.

   For example in Figure 14, two PSTs are configured to allow
   monitoring, protection and management of the LSP concatenated
   segments.  One PST is defined between LER2 and LER3, and a second PST
   is set up between LER4 and LER5.  Each of these PSTs may be
   monitored, protected, or managed independently.

   ======================== End to End LSP ===========================

          |<---- Carrier 1 ---->|       |<---- Carrier 2 ---->|

 [LER1]---[LER2]---[LSR]---[LER3]-------[LER4]---[LSR]---[LER5]---[LER6]

          |======= PST =========|       |======= PST =========|
                 (Carrier 1)                 (Carrier 2)

 Note: LER2, LER3, LER4 and LER5 are with respect to the PST

                 Figure 14: PSTs in inter-carrier network

   The end-to-end traffic of the LSP, including data traffic and control
   traffic (OAM, Protection Switching Control, management and signaling
   messages) is tunneled within the PST by means of label stacking as
   defined in [RFC3031].

   The mapping between an LSP and a PST can be 1:1, in which case it is
   similar to the ITU-T Tandem Connection element [G.805].  The mapping
   can also be 1:N to allow aggregated monitoring, protection and
   management of a set of LSP segments or concatenated LSP segments.



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   Figure 15 shows a PST which is used to aggregate a set of
   concatenated LSP segments for the LSP from LERx to LERt and the LSP
   from LERa to LERd.  Note that such a construct is useful, for
   example, when the LSPs traverse a common portion of the network and
   they have the same Traffic Class.

  |LERx|--|LSRy|-+                                      +-|LSRz|--|LERt|
                 |                                      |
                 |  |<---------- Carrier 1 --------->|  |
                 |  +-----+   +---+   +---+    +-----+  |
                 +--|     |---|   |---|   |----|     |--+
                    |LER1 |   |LSR|   |LSR|    |LER2 |
                 +--|     |---|   |---|   |----|     |--+
                 |  +-----+   +---+   + P +    +-----+  |
                 |  |============= PST ==============|  |
  |LERa|--|LSRb|-+            (Carrier 1)               +-|LSRc|--|LERd|


           Figure 15: PST for a Set of Concatenated LSP Segments

   PSTs can be provisioned either statically or using control plane
   signaling procedures.  The make-before-break procedures which are
   supported by MPLS allow the creation of a PST on existing LSPs in-
   service without traffic disruption.  A PST can be defined
   corresponding to one or more end-to-end tunneled LSPs.  New end-to-
   end LSPs which are tunneled within the PST can be set up.  Traffic of
   the existing LSPs is switched over to the new end-to-end tunneled
   LSPs.  The old end-to-end LSPs can then be torn down.

3.14.  Pseudowire Segment Tunnels

   Hierarchical label stacking, in a similar manner to that described
   above, can be used to implement path segment tunnels on pseudowires.

3.15.  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.  They also incorporate the OAM requirements
   for MPLS Networks [RFC4377] and MPLS-TP Networks
   [I-D.ietf-mpls-tp-oam-requirements] and expand 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



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   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 Network Management System (NMS) is used to
   provision and manage an end-to-end connection across a network where
   some segments are created/managed by, for example, Netconf [RFC4741]
   or SNMP [RFC3411] 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 3.11.

   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 Maintenance Entity Group Endpoint (MEP) ID and
   MEG Intermediate Point (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.

   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-



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   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.

   Each MPLS-TP solution must specify the additional security
   considerations that apply.  This is discussed further in
   [I-D.fang-mpls-tp-security-framework].

   The security considerations in
   [I-D.ietf-mpls-mpls-and-gmpls-security-framework] 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

   o  Dieter Beller

   o  Malcolm Betts

   o  Italo Busi

   o  John E Drake

   o  Hing-Kam Lam

   o  Marc Lasserre




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   o  Vincenzo Sestito

   o  Nurit Sprecher

   o  Martin Vigoureux

   o  Yaacov Weingarten

   o  The participants of ITU-T SG15

7.  References

7.1.  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,



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                                                      "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.

   [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.

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



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                                                      RFC 4090,
                                                      May 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



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                                                      Pseudowires",
                                                      RFC 5085,
                                                      December 2007.

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

7.2.  Informative References

   [G.8080]                                           "ITU-T
                                                      Recommendation
                                                      G.8080/Y.1304,
                                                      "Architecture for
                                                      the automatically
                                                      switched optical
                                                      network (ASON)"",
                                                      2005.

   [I-D.fang-mpls-tp-security-framework]              Fang, L. and B.
                                                      Niven-Jenkins,
                                                      "Security
                                                      Framework for
                                                      MPLS-TP", draft-
                                                      fang-mpls-tp-
                                                      security-
                                                      framework-01 (work
                                                      in progress),
                                                      March 2010.

   [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-ccamp-mpls-tp-cp-framework]              Andersson, L.,
                                                      Berger, L., Fang,
                                                      L., Bitar, N.,
                                                      Takacs, A.,



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                                                      Vigoureux, M.,
                                                      Bellagamba, E.,
                                                      and E. Gray,
                                                      "MPLS-TP Control
                                                      Plane Framework",
                                                      draft-ietf-ccamp-
                                                      mpls-tp-cp-
                                                      framework-01 (work
                                                      in progress),
                                                      March 2010.

   [I-D.ietf-l2vpn-vpms-frmwk-requirements]           Kamite, Y.,
                                                      JOUNAY, F., Niven-
                                                      Jenkins, B.,
                                                      Brungard, D., and
                                                      L. Jin, "Framework
                                                      and Requirements
                                                      for Virtual
                                                      Private Multicast
                                                      Service (VPMS)", d
                                                      raft-ietf-l2vpn-
                                                      vpms-frmwk-
                                                      requirements-02
                                                      (work in
                                                      progress),
                                                      October 2009.

   [I-D.ietf-mpls-mpls-and-gmpls-security-framework]  Fang, L. and M.
                                                      Behringer,
                                                      "Security
                                                      Framework for MPLS
                                                      and GMPLS
                                                      Networks", draft-
                                                      ietf-mpls-mpls-
                                                      and-gmpls-
                                                      security-
                                                      framework-09 (work
                                                      in progress),
                                                      March 2010.

   [I-D.ietf-mpls-tp-data-plane]                      Frost, D., Bryant,
                                                      S., and M. Bocci,
                                                      "MPLS Transport
                                                      Profile Data Plane
                                                      Architecture", dra
                                                      ft-ietf-mpls-tp-
                                                      data-plane-01
                                                      (work in



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                                                      progress),
                                                      March 2010.

   [I-D.ietf-mpls-tp-identifiers]                     Bocci, M. and G.
                                                      Swallow, "MPLS-TP
                                                      Identifiers", draf
                                                      t-ietf-mpls-tp-
                                                      identifiers-01
                                                      (work in
                                                      progress),
                                                      March 2010.

   [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-05 (work
                                                      in progress),
                                                      February 2010.

   [I-D.ietf-mpls-tp-nm-req]                          Mansfield, S. and
                                                      K. Lam, "MPLS TP
                                                      Network Management
                                                      Requirements", dra
                                                      ft-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", dr
                                                      aft-ietf-mpls-tp-
                                                      oam-framework-05
                                                      (work in
                                                      progress),
                                                      March 2010.

   [I-D.ietf-mpls-tp-oam-requirements]                Vigoureux, M. and
                                                      D. Ward,
                                                      "Requirements for
                                                      OAM in MPLS
                                                      Transport
                                                      Networks", draft-
                                                      ietf-mpls-tp-oam-



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                                                      requirements-06
                                                      (work in
                                                      progress),
                                                      March 2010.

   [I-D.ietf-mpls-tp-survive-fwk]                     Sprecher, N. and
                                                      A. Farrel,
                                                      "Multiprotocol
                                                      Label Switching
                                                      Transport Profile
                                                      Survivability
                                                      Framework", draft-
                                                      ietf-mpls-tp-
                                                      survive-fwk-04
                                                      (work in
                                                      progress),
                                                      March 2010.

   [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", dra
                                                      ft-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



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                                                      (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.

   [I-D.ietf-pwe3-vccv-bfd]                           Nadeau, T. and C.
                                                      Pignataro,
                                                      "Bidirectional
                                                      Forwarding
                                                      Detection (BFD)
                                                      for the Pseudowire
                                                      Virtual Circuit
                                                      Connectivity
                                                      Verification
                                                      (VCCV)", draft-
                                                      ietf-pwe3-vccv-
                                                      bfd-07 (work in
                                                      progress),
                                                      July 2009.

   [RFC3209]                                          Awduche, D.,
                                                      Berger, L., Gan,
                                                      D., Li, T.,
                                                      Srinivasan, V.,
                                                      and G. Swallow,
                                                      "RSVP-TE:
                                                      Extensions to RSVP
                                                      for LSP Tunnels",
                                                      RFC 3209,
                                                      December 2001.

   [RFC3411]                                          Harrington, D.,
                                                      Presuhn, R., and
                                                      B. Wijnen, "An
                                                      Architecture for



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                                                      Describing Simple
                                                      Network Management
                                                      Protocol (SNMP)
                                                      Management
                                                      Frameworks",
                                                      STD 62, RFC 3411,
                                                      December 2002.

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

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

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

   [RFC4216]                                          Zhang, R. and J.
                                                      Vasseur, "MPLS
                                                      Inter-Autonomous
                                                      System (AS)
                                                      Traffic
                                                      Engineering (TE)
                                                      Requirements",
                                                      RFC 4216,
                                                      November 2005.

   [RFC4364]                                          Rosen, E. and Y.



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                                                      Rekhter, "BGP/MPLS
                                                      IP Virtual Private
                                                      Networks (VPNs)",
                                                      RFC 4364,
                                                      February 2006.

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

   [RFC4664]                                          Andersson, L. and
                                                      E. Rosen,
                                                      "Framework for
                                                      Layer 2 Virtual
                                                      Private Networks
                                                      (L2VPNs)",
                                                      RFC 4664,
                                                      September 2006.

   [RFC4741]                                          Enns, R., "NETCONF
                                                      Configuration
                                                      Protocol",
                                                      RFC 4741,
                                                      December 2006.

   [RFC5150]                                          Ayyangar, A.,
                                                      Kompella, K.,
                                                      Vasseur, JP., and



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                                                      A. Farrel, "Label
                                                      Switched Path
                                                      Stitching with
                                                      Generalized
                                                      Multiprotocol
                                                      Label Switching
                                                      Traffic
                                                      Engineering (GMPLS
                                                      TE)", RFC 5150,
                                                      February 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



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                                                      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.

   [RFC5718]                                          Beller, D. and A.
                                                      Farrel, "An In-
                                                      Band Data
                                                      Communication
                                                      Network For the
                                                      MPLS Transport
                                                      Profile",
                                                      RFC 5718,
                                                      January 2010.

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








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Internet-Draft      MPLS Transport Profile Framework          April 2010


   Dan Frost (editor)
   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


   Lou Berger
   LabN


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























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