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rfc:rfc5921

Internet Engineering Task Force (IETF) M. Bocci, Ed. Request for Comments: 5921 Alcatel-Lucent Category: Informational S. Bryant, Ed. ISSN: 2070-1721 D. Frost, Ed.

                                                         Cisco Systems
                                                             L. Levrau
                                                        Alcatel-Lucent
                                                             L. Berger
                                                                  LabN
                                                             July 2010
             A Framework for MPLS in Transport Networks

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
 bidirectional 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 Telecommunication Union Telecommunication
 Standardization Sector (ITU-T) effort to include an MPLS Transport
 Profile within the IETF MPLS and Pseudowire Emulation Edge-to-Edge
 (PWE3) architectures to support the capabilities and functionalities
 of a packet transport network as defined by the ITU-T.

Bocci, et al. Informational [Page 1] RFC 5921 MPLS Transport Profile Framework July 2010

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc5921.

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Bocci, et al. Informational [Page 2] RFC 5921 MPLS Transport Profile Framework July 2010

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   1.1.  Motivation and Background  . . . . . . . . . . . . . . . .  4
   1.2.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   1.3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
     1.3.1.  Transport Network  . . . . . . . . . . . . . . . . . .  7
     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) . . . . . . . . . . . . . . . . . . 10
     1.3.7.  Transport LSP  . . . . . . . . . . . . . . . . . . . . 10
     1.3.8.  Service LSP  . . . . . . . . . . . . . . . . . . . . . 10
     1.3.9.  Layer Network  . . . . . . . . . . . . . . . . . . . . 10
     1.3.10. Network Layer  . . . . . . . . . . . . . . . . . . . . 10
     1.3.11. Service Interface  . . . . . . . . . . . . . . . . . . 10
     1.3.12. Native Service . . . . . . . . . . . . . . . . . . . . 11
     1.3.13. Additional Definitions and Terminology . . . . . . . . 11
 2.  MPLS Transport Profile Requirements  . . . . . . . . . . . . . 11
 3.  MPLS Transport Profile Overview  . . . . . . . . . . . . . . . 12
   3.1.  Packet Transport Services  . . . . . . . . . . . . . . . . 12
   3.2.  Scope of the MPLS Transport Profile  . . . . . . . . . . . 13
   3.3.  Architecture . . . . . . . . . . . . . . . . . . . . . . . 14
     3.3.1.  MPLS-TP Native Service Adaptation Functions  . . . . . 14
     3.3.2.  MPLS-TP Forwarding Functions . . . . . . . . . . . . . 15
   3.4.  MPLS-TP Native Service Adaptation  . . . . . . . . . . . . 16
     3.4.1.  MPLS-TP Client/Server Layer Relationship . . . . . . . 16
     3.4.2.  MPLS-TP Transport Layers . . . . . . . . . . . . . . . 17
     3.4.3.  MPLS-TP Transport Service Interfaces . . . . . . . . . 18
     3.4.4.  Pseudowire Adaptation  . . . . . . . . . . . . . . . . 25
     3.4.5.  Network Layer Adaptation . . . . . . . . . . . . . . . 28
   3.5.  Identifiers  . . . . . . . . . . . . . . . . . . . . . . . 33
   3.6.  Generic Associated Channel (G-ACh) . . . . . . . . . . . . 33
   3.7.  Operations, Administration, and Maintenance (OAM)  . . . . 36
   3.8.  Return Path  . . . . . . . . . . . . . . . . . . . . . . . 38
     3.8.1.  Return Path Types  . . . . . . . . . . . . . . . . . . 39
     3.8.2.  Point-to-Point Unidirectional LSPs . . . . . . . . . . 39
     3.8.3.  Point-to-Point Associated Bidirectional LSPs . . . . . 40
     3.8.4.  Point-to-Point Co-Routed Bidirectional LSPs  . . . . . 40
   3.9.  Control Plane  . . . . . . . . . . . . . . . . . . . . . . 40
   3.10. Inter-Domain Connectivity  . . . . . . . . . . . . . . . . 43
   3.11. Static Operation of LSPs and PWs . . . . . . . . . . . . . 43
   3.12. Survivability  . . . . . . . . . . . . . . . . . . . . . . 44
   3.13. Sub-Path Maintenance . . . . . . . . . . . . . . . . . . . 45
   3.14. Network Management . . . . . . . . . . . . . . . . . . . . 47
 4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 48
 5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 49

Bocci, et al. Informational [Page 3] RFC 5921 MPLS Transport Profile Framework July 2010

 6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 50
 7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 50
   7.1.  Normative References . . . . . . . . . . . . . . . . . . . 50
   7.2.  Informative References . . . . . . . . . . . . . . . . . . 51

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 Operations, Administration, and Maintenance (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.

Bocci, et al. Informational [Page 4] RFC 5921 MPLS Transport Profile Framework July 2010

 There are thus two objectives for MPLS-TP:
 1.  To enable MPLS to be deployed in a transport network and operated
     in a similar manner to existing transport technologies.
 2.  To enable MPLS to support packet transport services with a
     similar degree of predictability to that found in existing
     transport networks.
 In order to achieve these objectives, there is a need to define a
 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 Telecommunication Union Telecommunication
 Standardization Sector (ITU-T) effort to include an MPLS Transport
 Profile within the IETF MPLS and PWE3 architectures to support the
 capabilities and functionalities of a packet transport network as
 defined by the ITU-T.

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.

1.3. Terminology

 Term       Definition
 ---------- ----------------------------------------------------------
 AC         Attachment Circuit
 ACH        Associated Channel Header
 Adaptation The mapping of client information into a format suitable
            for transport by the server layer
 APS        Automatic Protection Switching
 ATM        Asynchronous Transfer Mode
 BFD        Bidirectional Forwarding Detection
 CE         Customer Edge

Bocci, et al. Informational [Page 5] RFC 5921 MPLS Transport Profile Framework July 2010

 CL-PS      Connectionless - Packet Switched
 CM         Configuration Management
 CO-CS      Connection Oriented - Circuit Switched
 CO-PS      Connection Oriented - Packet Switched
 DCN        Data Communication Network
 EMF        Equipment Management Function
 FCAPS      Fault, Configuration, Accounting, Performance, and
            Security
 FM         Fault Management
 G-ACh      Generic Associated Channel
 GAL        G-ACh Label
 LER        Label Edge Router
 LSP        Label Switched Path
 LSR        Label Switching Router
 MAC        Media Access Control
 MCC        Management Communication Channel
 ME         Maintenance Entity
 MEG        Maintenance Entity Group
 MEP        Maintenance Entity Group End Point
 MIP        Maintenance Entity Group Intermediate Point
 MPLS       Multiprotocol Label Switching
 MPLS-TP    MPLS Transport Profile
 MPLS-TP P  MPLS-TP Provider LSR
 MPLS-TP PE MPLS-TP Provider Edge LSR
 MS-PW      Multi-Segment Pseudowire
 Native     The traffic belonging to the client of the MPLS-TP network
 Service
 OAM        Operations, Administration, and Maintenance (see
            [OAM-DEF])
 OSI        Open Systems Interconnection
 OTN        Optical Transport Network
 PDU        Protocol Data Unit
 PM         Performance Monitoring
 PSN        Packet Switching Network
 PW         Pseudowire
 SCC        Signaling Communication Channel
 SDH        Synchronous Digital Hierarchy
 S-PE       PW Switching Provider Edge
 SPME       Sub-Path Maintenance Element
 SS-PW      Single-Segment Pseudowire
 T-PE       PW Terminating Provider Edge
 TE LSP     Traffic Engineered Label Switched Path
 VCCV       Virtual Circuit Connectivity Verification

Bocci, et al. Informational [Page 6] RFC 5921 MPLS Transport Profile Framework July 2010

1.3.1. Transport Network

 A Transport Network provides transparent transmission of user 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
 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 [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 in [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.

Bocci, et al. Informational [Page 7] RFC 5921 MPLS Transport Profile Framework July 2010

 6.  It is either unidirectional, associated bidirectional, or co-
     routed bidirectional (i.e., the forward and reverse components of
     a bidirectional LSP follow the same path, and the intermediate
     nodes are aware of their association).  These are further defined
     in [DATA-PLANE].
 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 [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
 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] (see
 below).  A PE that pushes or pops an LSP label is an LER for that
 LSP.

Bocci, et al. Informational [Page 8] RFC 5921 MPLS Transport Profile Framework July 2010

 The term Provider Edge refers to the node's role within a provider's
 network.  A provider edge router resides at the edge of a given
 MPLS-TP network domain, in which case it has links to another MPLS-TP
 network domain or to a CE, except for the case of a pseudowire
 switching provider edge (S-PE) router, which is not restricted to the
 edge of an MPLS-TP network domain.

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 that carry client traffic, but does not adapt client
 traffic and encapsulate it to be carried over an MPLS-TP LSP.  The
 term Provider Router refers to the node's role within a provider's
 network.  A provider router does not have links to other MPLS-TP
 network domains.

1.3.5.4. Pseudowire Switching Provider Edge Router (S-PE)

 RFC 5659 [RFC5659] defines an S-PE as:
    A PE capable of switching the control and data planes of the
    preceding and succeeding PW segments in an MS-PW.  The S-PE
    terminates the PSN tunnels of the preceding and succeeding
    segments of the MS-PW.  It therefore includes a PW switching point
    for an MS-PW.  A PW switching point is never the S-PE and the T-PE
    for the same MS-PW.  A PW switching point runs necessary protocols
    to set up and manage PW segments with other PW switching points
    and terminating PEs.  An S-PE can exist anywhere a PW must be
    processed or policy applied.  It is therefore not limited to the
    edge of a provider network.
    Note that it was originally anticipated that S-PEs would only be
    deployed at the edge of a provider network where they would be
    used to switch the PWs of different service providers.  However,
    as the design of MS-PW progressed, other applications for MS-PW
    were recognized.  By this time S-PE had become the accepted term
    for the equipment, even though they were no longer universally
    deployed at the provider edge.

1.3.5.5. Pseudowire Terminating Provider Edge (T-PE) Router

 RFC 5659 [RFC5659] defines a T-PE as:
    A PE where the customer-facing attachment circuits (ACs) are bound
    to a PW forwarder.  A terminating PE is present in the first and
    last segments of an MS-PW.  This incorporates the functionality of
    a PE as defined in RFC 3985.

Bocci, et al. Informational [Page 9] RFC 5921 MPLS Transport Profile Framework July 2010

1.3.6. Customer Edge (CE)

 A Customer Edge (CE) is the client function that sources or sinks
 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.

1.3.7. Transport LSP

 A Transport LSP is an LSP between a pair of PEs that may transit zero
 or more MPLS-TP provider routers.  When carrying PWs, the Transport
 LSP is equivalent to the PSN tunnel LSP in [RFC3985] terminology.

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].  A
 layer network provides for the transfer of client information and
 independent operation of the client OAM.  A layer network may be
 described in a service context as follows: one layer network may
 provide a (transport) service to a higher client layer network and
 may, in turn, be a client to a lower-layer network.  A layer network
 is a logical construction somewhat independent of arrangement or
 composition of physical network elements.  A particular physical
 network element may topologically belong to more than one layer
 network, depending on the actions it takes on the encapsulation
 associated with the logical layers (e.g., the label stack), and thus
 could be modeled as multiple logical elements.  A layer network may
 consist of one or more sublayers.

1.3.10. Network Layer

 This document uses the term Network Layer in the same sense as it is
 used in [RFC3031] and [RFC3032].  Network-layer protocols are
 synonymous with those belonging to Layer 3 of the Open System
 Interconnect (OSI) network model [X.200].

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:
 o  User-Network Interface (UNI) (see Section 3.4.3.1).
 o  Network-Network Interface (NNI) (see Section 3.4.3.2).

Bocci, et al. Informational [Page 10] RFC 5921 MPLS Transport Profile Framework July 2010

 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. Native Service

 The native service is the client layer network service that is
 transported by the MPLS-TP network, whether a pseudowire or an LSP is
 used for the adaptation (see Section 3.4).

1.3.13. Additional Definitions and Terminology

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

2. MPLS Transport Profile Requirements

 The requirements for MPLS-TP are specified in [RFC5654], [RFC5860],
 and [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 bidirectional, and it
 must be possible to construct congruent bidirectional 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 and protection mechanisms, and forwarding of data packets, must
 be able to operate without IP forwarding support.

Bocci, et al. Informational [Page 11] RFC 5921 MPLS Transport Profile Framework July 2010

 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
 exhibit 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 a given client will
    not fall below the agreed level as a result of the traffic loading
    of other clients.
 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 coordination
    required between the client and server layer networks is minimal
    (preferably no coordination 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
    (Connectionless Network Service) 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.

Bocci, et al. Informational [Page 12] RFC 5921 MPLS Transport Profile Framework July 2010

 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 (ECMP), LDP signaling when
 used in such a way that it creates multipoint-to-point LSPs, and IP
 forwarding in the data plane are explicitly excluded from MPLS-TP by
 that requirements specification.
 Note that MPLS as a whole will continue to evolve to include
 additional functions that do not conform to the MPLS Transport
 Profile or its requirements, and thus fall outside the scope of
 MPLS-TP.
|<============================== MPLS ==============================>|
                                                   { Post-RFC5654    }
                                                   { non-Transport   }
                                                   {   Functions     }
|<========== Pre-RFC5654 MPLS ===========>|
{      ECMP       }
{ LDP/non-TE LSPs }
{  IP forwarding  }
                  |<======== MPLS-TP ============>|
                                     { Additional }
                                     {  Transport }
                                     {  Functions }
                      Figure 1: Scope of MPLS-TP
 MPLS-TP can be used to construct packet networks and is therefore
 applicable in any packet network context.  A subset of MPLS-TP is
 also applicable to ITU-T-defined packet transport networks, where the
 transport network operational model is deemed attractive.

Bocci, et al. Informational [Page 13] RFC 5921 MPLS Transport Profile Framework July 2010

3.3. Architecture

 MPLS-TP comprises the following architectural elements:
 o  A standard MPLS data plane [RFC3031] as profiled in [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 [OAM-FRAMEWORK].
 o  Control planes for LSPs and PWs, as well as support for static
    provisioning and configuration, as outlined in [CP-FRAMEWORK].
 o  Path protection mechanisms to ensure that the packet transport
    service survives anticipated failures and degradations of the
    MPLS-TP network, as outlined in [SURVIVE-FWK].
 o  Control-plane-based restoration mechanisms, as outlined in
    [SURVIVE-FWK].
 o  Network management functions, as outlined in [NM-FRAMEWORK].
 The MPLS-TP architecture for LSPs and PWs includes the following two
 sets of functions:
 o  MPLS-TP native service adaptation
 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].

Bocci, et al. Informational [Page 14] RFC 5921 MPLS Transport Profile Framework July 2010

 The purpose of this encapsulation is to abstract the data plane of
 the client layer network 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 therefore needs to 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 Time-to-Live
 (TTL) processing procedures defined in [RFC3031], [RFC3032], and
 [RFC3443], as profiled in [DATA-PLANE].  These operations are highly
 optimized 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].
 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

Bocci, et al. Informational [Page 15] RFC 5921 MPLS Transport Profile Framework July 2010

 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 [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 LSP
 MPLS-TP uses IETF-defined pseudowires to emulate certain services,
 for example, Ethernet, Frame Relay, or PPP / High-Level Data Link
 Control (HDLC).  A list of PW types is maintained by IANA in 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 can also provide the adaptation, in which case any native
 service traffic type supported by [RFC3031] and [RFC3032] is allowed.
 Examples of such traffic types include IP packets and MPLS-labeled
 packets.  Note that the latter case includes TE-LSPs [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 behavior of MPLS-TP is the same as the best current
 practice for MPLS.  This includes the setting of the S bit.  In each
 case, the S bit is set to indicate the bottom (i.e., innermost) label

Bocci, et al. Informational [Page 16] RFC 5921 MPLS Transport Profile Framework July 2010

 in the label stack that is contiguous between the MPLS-TP LSP and its
 payload, and only one label stack entry (LSE) contains the S bit
 (Bottom of Stack bit) set to 1.  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.
 PW-Based               MPLS Labeled                 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

Bocci, et al. Informational [Page 17] RFC 5921 MPLS Transport Profile Framework July 2010

 (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 belonging to the
 native service 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
 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 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 attachment circuit that supports the client flow.

Bocci, et al. Informational [Page 18] RFC 5921 MPLS Transport Profile Framework July 2010

  :          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
  :             |           |  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
                 Figure 3: MPLS-TP PE Containing a UNI

Bocci, et al. Informational [Page 19] RFC 5921 MPLS Transport Profile Framework July 2010

  1. ————-From UNI——→ :
  2. ——————————————:——————

| | 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 4: MPLS-TP UNI Client-Server Traffic Processing Stages
 Figure 4 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 pre-processing, if any, is performed.  An
     example of such pre-processing is the PREP function illustrated
     in Figure 3 of [RFC3985].  Such pre-processing 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.

Bocci, et al. Informational [Page 20] RFC 5921 MPLS Transport Profile Framework July 2010

 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 5.  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.

Bocci, et al. Informational [Page 21] RFC 5921 MPLS Transport Profile Framework July 2010

                 :      Network-Network Interface    :
                 :<--------------------------------->:
                 :                                   :
     ------------:-------------         -------------:------------
    |  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
                Figure 5: MPLS-TP PE Containing an NNI

Bocci, et al. Informational [Page 22] RFC 5921 MPLS Transport Profile Framework July 2010

                                                 :
      --------------From NNI------->             :
     --------------------------------------------:------------------
    |                     | Service Traffic Unit :                  |
    | Link-Layer-Specific |  Link Decapsulation  : Service Instance |
    |    Processing       |          &           :  Encapsulation   |
    |                     |   Service Instance   :  Normalization   |
    |                     |    Identification    :                  |
     --------------------------------------------:------------------
                                                 :
                                                 :
     --------------------------------------------:------------------
    |                     |                      : Service Instance |
    |                     |                      :  Identification  |
    | Link-Layer-Specific | Service Traffic Unit :        &         |
    |    Processing       |  Link Encapsulation  : Service Instance |
    |                     |                      :  Encapsulation   |
    |                     |                      :  Normalization   |
     --------------------------------------------:------------------
      <-------------To NNI ---------             :
        Figure 6: MPLS-TP NNI Service Traffic Processing Stages
 Figure 6 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 pre-processing, if any, is performed.  Such
     pre-processing 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 normalized
     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 normalization is a swap of a label identifying the Transport
     Service Instance.

Bocci, et al. Informational [Page 23] RFC 5921 MPLS Transport Profile Framework July 2010

 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 Instance is identified from the transport
     service encapsulation, and this encapsulation is normalized 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 normalized 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 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 pre-processing, 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.

Bocci, et al. Informational [Page 24] RFC 5921 MPLS Transport Profile Framework July 2010

 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.
 For PW packets received over the LSP, the steps are performed in the
 reverse order.

3.4.3.3.2. 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:
 1.  No link-layer-specific processing is performed.
 2.  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.
 3.  A transport service encapsulation, consisting of the Service LSP
     label, is associated with the packet.
 4.  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.
 For packets received over a tunnel LSP carrying the Service LSP
 label, the steps are performed in the reverse order.

3.4.4. Pseudowire Adaptation

 MPLS-TP uses pseudowires to provide a Virtual Private Wire Service
 (VPWS), a Virtual Private Local Area Network Service (VPLS), a
 Virtual Private Multicast Service (VPMS), and an Internet Protocol
 Local Area Network Service (IPLS).  VPWS, VLPS, and IPLS are
 described in [RFC4664].  VPMS is described in [VPMS-REQS].
 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

Bocci, et al. Informational [Page 25] RFC 5921 MPLS Transport Profile Framework July 2010

 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 7 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].
          |<----------------- 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 7: MPLS-TP Architecture (Single Segment PW)
 Figure 8 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.

Bocci, et al. Informational [Page 26] RFC 5921 MPLS Transport Profile Framework July 2010

   |<--------------------- 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 8: MPLS-TP Architecture (Multi-Segment PW)
 The corresponding MPLS-TP protocol stacks including PWs are shown in
 Figure 9.  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.

Bocci, et al. Informational [Page 27] RFC 5921 MPLS Transport Profile Framework July 2010

+-------------------+    /===================\   /===================\
|  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 9: 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.  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
 unidirectional 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 10, 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
 arrive at the service interface encapsulated in the Layer 1 / Layer 2

Bocci, et al. Informational [Page 28] RFC 5921 MPLS Transport Profile Framework July 2010

 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.
 The following figures illustrate the reference models for network-
 layer adaptation.  The details of these figures are described further
 in the following paragraphs.
          |<------------- 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 10: MPLS-TP Architecture for Network-Layer Clients

Bocci, et al. Informational [Page 29] RFC 5921 MPLS Transport Profile Framework July 2010

  |<--------------------- Client Layer ------------------------>|
  |                                                             |
  |                                                             |
  |    |<---------- Packet Transport Service ------------->|    |
  |    |                                                   |    |
  |    |              Transport               Transport    |    |
  | AC |     |<-------- LSP1 --------->|    |<--LSP2-->|   | AC |
  | |  V     V                         V    V          V   V |  |
  V |  +----+              +-----+    +----+          +----+ |  V

+—+ | | PE1|===============\ /=====| PE2|==========| PE3| | +—+

—-……svc-lsp1…. \ / …..X….svc-lsp1……—-
CE1 X CE2
—-……svc-lsp2…. / \ …..X….svc-lsp2……—-

+—+ ^ | |===============/ \=====| |==========| | | ^+—+

     | +----+     ^        +-----+    +----+     ^    +----+   |
     |            |           ^         ^        |             |
     |          TE LSP        |         |      TE LSP          |
     |                      P-router    |                      |

Native Service (LSR for | Native Service

                           T'port LSP1) |
                                        |
                                LSR for Service LSPs
                                LER for Transport LSPs
 Figure 11: MPLS-TP Architecture for Network Layer Adaptation, Showing
                         Service LSP Switching
 Client packets are received at the ingress service interface.  The PE
 pushes one or more labels onto the client packets that 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.

Bocci, et al. Informational [Page 30] RFC 5921 MPLS Transport Profile Framework July 2010

                         /===================\
                         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 12: MPLS-TP Label Stack for IP and LSP Clients
 In the figures above, 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-labeled.  It may be necessary to swap a service LSP
 label at an intermediate node.  This is shown in Figure 11.
 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 12 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 needs
 to be present for each payload type.  Such labels are referred to as
 "Encapsulation Labels", one of which is shown in Figure 12.  An
 Encapsulation Label may be either configured or signaled.

Bocci, et al. Informational [Page 31] RFC 5921 MPLS Transport Profile Framework July 2010

 Both an Encapsulation Label and a Service Label should be present in
 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, 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.  The Encapsulation Label
 cannot have any of the reserved label values [RFC3032].
 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 12.
 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 needs to 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) that have Media Access Control (MAC) addresses.  In
 cases where a MAC address is needed, the sending node sets 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.

Bocci, et al. Informational [Page 32] RFC 5921 MPLS Transport Profile Framework July 2010

 Note that when two CEs, which peer with each other, operate over a
 network layer transport service and run a routing protocol such as
 IS-IS or OSPF, some care should be taken to configure the routing
 protocols to use point-to-point adjacencies.  The specifics of such
 configuration is outside the scope of this document.  See [RFC5309]
 for additional details.
 The CE-to-CE service types and corresponding labels may be configured
 or signaled.

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 types of
 sets of identifiers: those that are compatible with IP, and those
 that are compatible with ITU-T transport-based operations.  The
 definition of these sets of identifiers is outside the scope of this
 document and is provided by [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 a
 protocol to coordinate path protection state.  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
    [RFC5885]).
 o  An IP encapsulation where IP capabilities are present, e.g., PW
    ACH encapsulation with IP headers for VCCV-BFD [RFC5885] or IP
    encapsulation for MPLS BFD [RFC5884].
 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, a protocol used
 to coordinate path protection state, 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

Bocci, et al. Informational [Page 33] RFC 5921 MPLS Transport Profile Framework July 2010

 the Pseudowire VCCV control word; this header is present for all
 sections, LSPs, and PWs that make use of FCAPS functions supported by
 the G-ACh.
 As specified in [RFC5586], the G-ACh must only be used for channels
 that are an adjunct to the data service.  Examples of these are OAM,
 a protocol used to coordinate path protection state, 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 need to take into consideration the impact they have on the
 user data with which they are sharing resources.  Conversely,
 capacity needs to be made available for important G-ACh uses such as
 protection and OAM.  In addition, the security and congestion
 considerations described in [RFC5586] apply to protocols using the
 G-ACh.
 Figure 13 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].

Bocci, et al. Informational [Page 34] RFC 5921 MPLS Transport Profile Framework July 2010

        +-------------+                                +-------------+
        |  Payload    |           < FCAPS >            |  Payload    |
        +-------------+                                +-------------+
        |   Demux /   |         < ACH for PW >         |   Demux /   |
        |Discriminator|                                |Discriminator|
        +-------------+                                +-------------+
        |     PW      |             < PW >             |     PW      |
        +-------------+                                +-------------+
        |    PSN      |             < LSP >            |    PSN      |
        +-------------+                                +-------------+
        |  Physical   |                                |  Physical   |
        +-----+-------+                                +-----+-------+
              |                                              |
              |             ____     ___       ____          |
              |           _/    \___/   \    _/    \__       |
              |          /               \__/         \_     |
              |         /                               \    |
              +--------|        MPLS-TP Network          |---+
                        \                               /
                         \   ___      ___     __      _/
                          \_/   \____/   \___/  \____/
   Figure 13: PWE3 Protocol Stack Reference Model Showing the G-ACh
 PW-associated channel messages are encapsulated using the PWE3
 encapsulation, so that they are handled and processed in the same
 manner (or in some cases, an analogous manner) as the PW PDUs for
 which they provide a control channel.
 Figure 14 shows the reference model depicting how the control channel
 is associated with the LSP protocol stack.

Bocci, et al. Informational [Page 35] RFC 5921 MPLS Transport Profile Framework July 2010

        +-------------+                                +-------------+
        |  Payload    |           < FCAPS >            |   Payload   |
        +-------------+                                +-------------+
        |Discriminator|         < ACH on LSP >         |Discriminator|
        +-------------+                                +-------------+
        |Demultiplexer|         < GAL on LSP >         |Demultiplexer|
        +-------------+                                +-------------+
        |    PSN      |            < LSP >             |    PSN      |
        +-------------+                                +-------------+
        |  Physical   |                                |  Physical   |
        +-----+-------+                                +-----+-------+
              |                                              |
              |             ____     ___       ____          |
              |           _/    \___/   \    _/    \__       |
              |          /               \__/         \_     |
              |         /                               \    |
              +--------|        MPLS-TP Network          |---+
                        \                               /
                         \   ___      ___     __      _/
                          \_/   \____/   \___/  \____/
    Figure 14: 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 is able to operate without relying on a
 dynamic control plane or IP functionality in the data path.  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 can operate in
 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 OAM or user data packets is not required for MPLS-TP.
 [RFC4379] and BFD for MPLS LSPs [RFC5884] 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

Bocci, et al. Informational [Page 36] RFC 5921 MPLS Transport Profile Framework July 2010

 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 is 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 [RFC5860] that a set of OAM capabilities is
 available to perform fault management (e.g., fault detection and
 localization) 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 [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 [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).
 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 stack
 entry for the G-ACh packet, as per the traceroute mode of LSP Ping
 [RFC4379] and the vccv-trace mode of [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.

Bocci, et al. Informational [Page 37] RFC 5921 MPLS Transport Profile Framework July 2010

 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 in the
 LSP or PW label stack entry.

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 Y is an intermediate LSR along the LSP.  Note that
 U is the upstream LER, and D is the downstream LER with respect to a
 particular direction of an LSP.  This reference model is shown in
 Figure 15.
               LSP         LSP
         U ========= Y ========= D
        LER         LSR         LER
  1. ——–> Direction of user traffic flow
                Figure 15: Return Path Reference Model
 The following cases are described for the various types of LSPs:
 Case 1  Return path packet transmission from D to U
 Case 2  Return path packet transmission from Y to U
 Case 3  Return path packet transmission from D to Y
 Note that a return path may not always exist (or may exist but be
 disabled), 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.

Bocci, et al. Informational [Page 38] RFC 5921 MPLS Transport Profile Framework July 2010

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  If an in-band return path is required 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.
         The discussion below for such LSPs applies.
 As an alternative, an out-of-band return path may be used.
 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 recognizes 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

Bocci, et al. Informational [Page 39] RFC 5921 MPLS Transport Profile Framework July 2010

         deliver return traffic to Y by first sending it to U along
         that return path.  The mechanism by which U recognizes 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.
 Figure 16 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.

Bocci, et al. Informational [Page 40] RFC 5921 MPLS Transport Profile Framework July 2010

  +------------------------------------------------------------------+
  |                                                                  |
  |                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 centralized or distributed.  Control plane is
       distributed.
    2) 'Edge' functions refers to those functions present at
       the edge of a PSN domain, e.g., native service processing or
       classification.
    3) The control plane may be transported over the server
       layer, an LSP, or a G-ACh.
         Figure 16: 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 Network (ASON) architecture [G.8080].  MPLS-TP uses:
 o  Generalized MPLS (GMPLS) signaling ([RFC3945], [RFC3471],
    [RFC3473]) for LSPs, and
 o  Targeted LDP (T-LDP) signaling ([RFC4447], [SEGMENTED-PW],
    [DYN-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
 of alternative PW control protocols for use in MPLS-TP.

Bocci, et al. Informational [Page 41] RFC 5921 MPLS Transport Profile Framework July 2010

 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, need to satisfy the MPLS-TP control
 plane requirements reviewed in the MPLS-TP Control Plane Framework
 [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 localization 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.

Bocci, et al. Informational [Page 42] RFC 5921 MPLS Transport Profile Framework July 2010

 Examples of the MPLS-TP data-plane connectivity patterns are LSPs
 utilizing 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. Inter-Domain 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 [RFC4726]
 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.  Note that the path of an LSP or PW may be
 dynamically computed, while the LSP or PW itself is established
 through static configuration.

Bocci, et al. Informational [Page 43] RFC 5921 MPLS Transport Profile Framework July 2010

3.12. Survivability

 The survivability architecture for MPLS-TP is specified in
 [SURVIVE-FWK].
 A wide variety of resiliency schemes have been developed to meet the
 various network and service survivability objectives.  For example,
 as part of the MPLS/PW paradigms, MPLS provides methods for local
 repair using back-up LSP tunnels ([RFC4090]), while pseudowire
 redundancy [PW-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 optimized
 for both linear topologies and ring topologies and that operate in
 the absence of a dynamic control plane.  These are specified in
 [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  Optimized for linear, ring, or meshed topologies.
 o  Use OAM mechanisms to detect and localize network faults or
    service degenerations.
 o  Include protection mechanisms to coordinate and trigger protection
    switching actions in the absence of a dynamic control plane.
 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.

Bocci, et al. Informational [Page 44] RFC 5921 MPLS Transport Profile Framework July 2010

 o  MPLS-TP recovery mechanisms support the coordination of protection
    switching at multiple levels to prevent race conditions occurring
    between a client and its server layer.
 o  MPLS-TP recovery mechanisms can be data-plane, control-plane, or
    management-plane based.
 o  MPLS-TP supports revertive and non-revertive behavior.

3.13. Sub-Path Maintenance

 In order to monitor, protect, and manage a portion (i.e., segment or
 concatenated segment) of an LSP, a hierarchical LSP [RFC3031] can be
 instantiated.  A hierarchical LSP instantiated for this purpose is
 called a Sub-Path Maintenance Element (SPME).  Note that by
 definition an SPME does not carry user traffic as a direct client.
 An SPME is defined between the edges of the portion of the LSP that
 needs to be monitored, protected or managed.  The SPME forms an
 MPLS-TP Section [DATA-PLANE] that carries the original LSP over this
 portion of the network as a client.  OAM messages can be initiated at
 the edge of the SPME and sent to the peer edge of the SPME or to a
 MIP along the SPME by setting the TTL value of the LSE at the
 corresponding hierarchical LSP level.  A P router only pushes or pops
 a label if it is at the end of a SPME.  In this mode, it is an LER
 for the SPME.
 For example, in Figure 17, two SPMEs are configured to allow
 monitoring, protection, and management of the LSP concatenated
 segments.  One SPME is defined between LER2 and LER3, and a second
 SPME is set up between LER4 and LER5.  Each of these SPMEs may be
 monitored, protected, or managed independently.
 |<============================= LSP =============================>|
        |<---- Carrier 1 ---->|       |<---- Carrier 2 ---->|

|LER1|—|LER2|—|LSR|—|LER3|——-|LER4|—|LSR|—|LER5|—|LER6|

        |====== SPME =========|       |====== SPME =========|
               (Carrier 1)                 (Carrier 2)

Note 1: LER2, LER3, LER4, and LER5 are with respect to the SPME,

       but LSRs with respect to the LSP.

Note 2: The LSP terminates in LERs outside of Carrier 1 and

       Carrier 2, for example, LER1 and LER6.
               Figure 17: SPMEs in Inter-Carrier Network

Bocci, et al. Informational [Page 45] RFC 5921 MPLS Transport Profile Framework July 2010

 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 hierarchical LSP by means of label
 stacking as defined in [RFC3031].
 The mapping between an LSP and a SPME 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.
 Figure 18 shows a SPME that 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.
 The QoS aspects of a SPME are network specific.  [OAM-FRAMEWORK]
 provides further considerations on the QoS aspects of OAM.
|LERx|--|LSRy|-+                                      +-|LSRz|--|LERt|
               |                                      |
               |  |<---------- Carrier 1 --------->|  |
               |  +-----+   +---+   +---+    +-----+  |
               +--|     |---|   |---|   |----|     |--+
                  |LER1 |   |LSR|   |LSR|    |LER2 |
               +--|     |---|   |---|   |----|     |--+
               |  +-----+   +---+   + P +    +-----+  |
               |  |============ SPME ==============|  |
|LERa|--|LSRb|-+            (Carrier 1)               +-|LSRc|--|LERd|
        Figure 18: SPME for a Set of Concatenated LSP Segments
 SPMEs 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 SPME on existing LSPs in-
 service without traffic disruption, as described in [SURVIVE-FWK].  A
 SPME can be defined corresponding to one or more end-to-end LSPs.
 New end-to-end LSPs that are tunneled within the SPME can be set up,
 which may require coordination across administrative boundaries.
 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.
 Hierarchical label stacking, in a similar manner to that described
 above, can be used to implement Sub-Path Maintenance Elements on
 pseudowires, as described in [OAM-FRAMEWORK].

Bocci, et al. Informational [Page 46] RFC 5921 MPLS Transport Profile Framework July 2010

3.14. Network Management

 The network management architecture and requirements for MPLS-TP are
 specified in [NM-FRAMEWORK] and [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 [RFC5860] 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
 which a management system manages the NE.  The Management
 Communication Channel (MCC), realized by the G-ACh, provides a
 logical operations channel between NEs for transferring management
 information.  The Network Management System (NMS) can be used to
 provision and manage an end-to-end connection across a network.
 Maintenance operations are run on a connection (LSP or PW) in a
 manner that is independent of the provisioning mechanism.  Segments
 may be created or managed by, for example, Netconf [RFC4741], SNMP
 [RFC3411], or CORBA (Common Object Request Broker Architecture)
 interfaces, but not all segments need to be created or managed using
 the same type of interface.  Where an MPLS-TP NE is managed by an
 NMS, at least one of these standard management mechanisms is required
 for interoperability, but this document imposes no restriction on
 which of these standard management protocols is used.  In MPLS-TP,
 the EMF needs to support 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 needs to 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

Bocci, et al. Informational [Page 47] RFC 5921 MPLS Transport Profile Framework July 2010

 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 behavior of
 the NEs and the network.  One particular requirement for PM is to
 provide coherent and consistent interpretation of the network
 behavior in a hybrid network that uses multiple transport
 technologies.  Packet loss measurement and delay measurements may be
 collected and used to detect performance degradation.  This is
 reported via fault management to enable corrective actions to be
 taken (e.g., protection switching) and via performance monitoring for
 Service Level Agreement (SLA) verification and billing.  Collection
 mechanisms for performance data should be capable of operating on-
 demand or proactively.

4. Security Considerations

 The introduction of MPLS-TP into transport networks means that the
 security considerations applicable to both MPLS [RFC3031] and PWE3
 [RFC3985] apply to those transport networks.  When an MPLS function
 is included in the MPLS transport profile, the security
 considerations pertinent to that function apply to MPLS-TP.
 Furthermore, when general MPLS networks that utilize 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.
 MPLS-TP nodes that implement the G-ACh create a Control Channel (CC)
 associated with a pseudowire, LSP, or section.  This control channel
 can be signaled or statically configured.  Over this control channel,
 control channel messages related to network maintenance functions
 such as OAM, signaling, or network management are sent.  Therefore,
 three different areas are of concern from a security standpoint.
 The first area of concern relates to control plane parameter and
 status message attacks, that is, attacks that concern the signaling
 of G-ACh capabilities.  MPLS-TP Control Plane security is discussed
 in [RFC5920].
 A second area of concern centers on data-plane attacks, that is,
 attacks on the G-ACh itself.  MPLS-TP nodes that implement the G-ACh
 mechanisms are subject to additional data-plane denial-of-service
 attacks as follows:

Bocci, et al. Informational [Page 48] RFC 5921 MPLS Transport Profile Framework July 2010

    An intruder could intercept or inject G-ACh packets effectively
    disrupting the protocols carried over the G-ACh.
    An intruder could deliberately flood a peer MPLS-TP node with
    G-ACh messages to deny services to others.
    A misconfigured or misbehaving device could inadvertently flood a
    peer MPLS-TP node with G-ACh messages that could result in denial
    of services.  In particular, if a node has either implicitly or
    explicitly indicated that it cannot support one or all of the
    types of G-ACh protocol, but is sent those messages in sufficient
    quantity, it could result in a denial of service.
 To protect against these potential (deliberate or unintentional)
 attacks, multiple mitigation techniques can be employed:
    G-ACh message throttling mechanisms can be used, especially in
    distributed implementations that have a centralized control-plane
    processor with various line cards attached by some control-plane
    data path.  In these architectures, G-ACh messages may be
    processed on the central processor after being forwarded there by
    the receiving line card.  In this case, the path between the line
    card and the control processor may become saturated if appropriate
    G-ACh traffic throttling is not employed, which could lead to a
    complete denial of service to users of the particular line card.
    Such filtering is also useful for preventing the processing of
    unwanted G-ACh messages, such as those which are sent on unwanted
    (and perhaps unadvertised) control channel types.
 A third and last area of concern relates to the processing of the
 actual contents of G-ACh messages.  It is necessary that the
 definition of the protocols using these messages carried over a G-ACh
 include appropriate security measures.
 Additional security considerations apply to each MPLS-TP solution.
 These are discussed further in [SEC-FRAMEWORK].
 The security considerations in [RFC5920] 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.

Bocci, et al. Informational [Page 49] RFC 5921 MPLS Transport Profile Framework July 2010

6. Acknowledgements

 The editors wish to thank the following for their contributions 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
 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, "Common equipment management function
                  requirements", ITU-T Recommendation G.7710/Y.1701,
                  July 2007.
 [G.805]          ITU-T, "Generic Functional Architecture of Transport
                  Networks", ITU-T Recommendation G.805, November
                  1995.
 [RFC3031]        Rosen, E., Viswanathan, A., and R. Callon,
                  "Multiprotocol Label Switching Architecture", RFC
                  3031, January 2001.
 [RFC3032]        Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
                  Farinacci, D., Li, T., and A. Conta, "MPLS Label
                  Stack Encoding", RFC 3032, January 2001.

Bocci, et al. Informational [Page 50] RFC 5921 MPLS Transport Profile Framework July 2010

 [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", 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 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

 [CP-FRAMEWORK]   Andersson, L., Berger, L., Fang, L., Bitar, N.,
                  Takacs, A., Vigoureux, M., Bellagamba, E., and E.
                  Gray, "MPLS-TP Control Plane Framework", Work in
                  Progress, March 2010.

Bocci, et al. Informational [Page 51] RFC 5921 MPLS Transport Profile Framework July 2010

 [DATA-PLANE]     Frost, D., Bryant, S., and M. Bocci, "MPLS Transport
                  Profile Data Plane Architecture", Work in Progress,
                  July 2010.
 [DYN-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", Work in
                  Progress, October 2009.
 [G.8080]         ITU-T, "Architecture for the automatically switched
                  optical network (ASON)", ITU-T Recommendation
                  G.8080/Y.1304, 2005.
 [IDENTIFIERS]    Bocci, M. and G. Swallow, "MPLS-TP Identifiers",
                  Work in Progress, March 2010.
 [NM-FRAMEWORK]   Mansfield, S., Ed., Gray, E., Ed., and H. Lam, Ed.,
                  "MPLS-TP Network Management Framework", Work in
                  Progress, February 2010.
 [NM-REQ]         Mansfield, S. and K. Lam, "MPLS TP Network
                  Management Requirements", Work in Progress, October
                  2009.
 [OAM-DEF]        Andersson, L., Helvoort, H., Bonica, R., Romascanu,
                  D., and S. Mansfield, "The OAM Acronym Soup", Work
                  in Progress, June 2010.
 [OAM-FRAMEWORK]  Busi, I., Ed., Niven-Jenkins, B., Ed., and D. Allan,
                  Ed., "MPLS-TP OAM Framework", Work in Progress,
                  April 2010.
 [PW-REDUNDANCY]  Muley, P., "Pseudowire (PW) Redundancy", Work in
                  Progress, May 2010.
 [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 Describing Simple Network
                  Management Protocol (SNMP) Management Frameworks",
                  STD 62, RFC 3411, December 2002.

Bocci, et al. Informational [Page 52] RFC 5921 MPLS Transport Profile Framework July 2010

 [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.
 [RFC4364]        Rosen, E. and Y. 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.
 [RFC4726]        Farrel, A., Vasseur, J., and A. Ayyangar, "A
                  Framework for Inter-Domain Multiprotocol Label
                  Switching Traffic Engineering", RFC 4726, November
                  2006.
 [RFC4741]        Enns, R., "NETCONF Configuration Protocol", RFC
                  4741, December 2006.
 [RFC5150]        Ayyangar, A., Kompella, K., Vasseur, JP., and 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.

Bocci, et al. Informational [Page 53] RFC 5921 MPLS Transport Profile Framework July 2010

 [RFC5331]        Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS
                  Upstream Label Assignment and Context-Specific Label
                  Space", RFC 5331, August 2008.
 [RFC5654]        Niven-Jenkins, B., Brungard, D., Betts, M.,
                  Sprecher, N., and S. Ueno, "Requirements of an MPLS
                  Transport Profile", RFC 5654, September 2009.
 [RFC5659]        Bocci, M. and S. Bryant, "An Architecture for Multi-
                  Segment Pseudowire Emulation Edge-to-Edge", RFC
                  5659, October 2009.
 [RFC5718]        Beller, D. and A. Farrel, "An In-Band Data
                  Communication Network For the MPLS Transport
                  Profile", RFC 5718, January 2010.
 [RFC5860]        Vigoureux, M., Ward, D., and M. Betts, "Requirements
                  for Operations, Administration, and Maintenance
                  (OAM) in MPLS Transport Networks", RFC 5860, May
                  2010.
 [RFC5884]        Aggarwal, R., Kompella, K., Nadeau, T., and G.
                  Swallow, "Bidirectional Forwarding Detection (BFD)
                  for MPLS Label Switched Paths (LSPs)", RFC 5884,
                  June 2010.
 [RFC5885]        Nadeau, T. and C. Pignataro, "Bidirectional
                  Forwarding Detection (BFD) for the Pseudowire
                  Virtual Circuit Connectivity Verification (VCCV)",
                  RFC 5885, June 2010.
 [RFC5920]        Fang, L., Ed., "Security Framework for MPLS and
                  GMPLS Networks", RFC 5920, July 2010.
 [ROSETTA-STONE]  Sprecher, N., "A Thesaurus for the Terminology used
                  in Multiprotocol Label Switching Transport Profile
                  (MPLS-TP) drafts/RFCs and ITU-T's Transport Network
                  Recommendations.", Work in Progress, May 2010.
 [SEC-FRAMEWORK]  Fang, L. and B. Niven-Jenkins, "Security Framework
                  for MPLS-TP", Work in Progress, March 2010.
 [SEGMENTED-PW]   Martini, L., Nadeau, T., Metz, C., Bocci, M., and M.
                  Aissaoui, "Segmented Pseudowire", Work in Progress,
                  June 2010.

Bocci, et al. Informational [Page 54] RFC 5921 MPLS Transport Profile Framework July 2010

 [SURVIVE-FWK]    Sprecher, N. and A. Farrel, "Multiprotocol Label
                  Switching Transport Profile Survivability
                  Framework", Work in Progress, June 2010.
 [VPMS-REQS]      Kamite, Y., JOUNAY, F., Niven-Jenkins, B., Brungard,
                  D., and L. Jin, "Framework and Requirements for
                  Virtual Private Multicast Service (VPMS)", Work in
                  Progress, October 2009.
 [X.200]          ITU-T, "Information Technology - Open Systems
                  Interconnection - Basic reference Model: The Basic
                  Model", ITU-T Recommendation X.200, 1994.

Bocci, et al. Informational [Page 55] RFC 5921 MPLS Transport Profile Framework July 2010

Authors' Addresses

 Matthew Bocci (editor)
 Alcatel-Lucent
 Voyager Place, Shoppenhangers Road
 Maidenhead, Berks  SL6 2PJ
 United Kingdom
 EMail: matthew.bocci@alcatel-lucent.com
 Stewart Bryant (editor)
 Cisco Systems
 250 Longwater Ave
 Reading  RG2 6GB
 United Kingdom
 EMail: stbryant@cisco.com
 Dan Frost (editor)
 Cisco Systems
 EMail: danfrost@cisco.com
 Lieven Levrau
 Alcatel-Lucent
 7-9, Avenue Morane Sulnier
 Velizy  78141
 France
 EMail: lieven.levrau@alcatel-lucent.com
 Lou Berger
 LabN Consulting, L.L.C.
 EMail: lberger@labn.net

Bocci, et al. Informational [Page 56]

/data/webs/external/dokuwiki/data/pages/rfc/rfc5921.txt · Last modified: 2010/07/09 23:12 (external edit)