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MPLS Transport Profile Data Plane Architecture
RFC 5960

Internet Engineering Task Force (IETF)                     D. Frost, Ed.
Request for Comments: 5960                                S. Bryant, Ed.
Category: Standards Track                                  Cisco Systems
ISSN: 2070-1721                                            M. Bocci, Ed.
                                                          Alcatel-Lucent
                                                             August 2010

             MPLS Transport Profile Data Plane Architecture

Abstract

   The Multiprotocol Label Switching Transport Profile (MPLS-TP) is the
   set of MPLS protocol functions applicable to the construction and
   operation of packet-switched transport networks.  This document
   specifies the subset of these functions that comprises the MPLS-TP
   data plane: the architectural layer concerned with the encapsulation
   and forwarding of packets within an MPLS-TP network.

   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.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc5960.

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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.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
     1.3.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
   2.  MPLS-TP Packet Encapsulation and Forwarding  . . . . . . . . .  4
   3.  MPLS-TP Transport Entities . . . . . . . . . . . . . . . . . .  5
     3.1.  Label Switched Paths . . . . . . . . . . . . . . . . . . .  5
       3.1.1.  LSP Packet Encapsulation and Forwarding  . . . . . . .  6
       3.1.2.  LSP Payloads . . . . . . . . . . . . . . . . . . . . .  7
       3.1.3.  LSP Types  . . . . . . . . . . . . . . . . . . . . . .  7
     3.2.  Sections . . . . . . . . . . . . . . . . . . . . . . . . .  8
     3.3.  Pseudowires  . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  MPLS-TP Generic Associated Channel . . . . . . . . . . . . . . 10
   5.  Server-Layer Considerations  . . . . . . . . . . . . . . . . . 11
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 14

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1.  Introduction

   The MPLS Transport Profile (MPLS-TP) is the set of functions that
   meet the requirements [RFC5654] for the application of MPLS to the
   construction and operation of packet-switched transport networks.
   MPLS-based packet-switched transport networks, and the overall
   architecture of the MPLS-TP, are defined and described in [RFC5921].
   It is assumed that the reader is familiar with that document.

   This document defines the set of functions that comprise the MPLS-TP
   data plane: the architectural layer concerned with the encapsulation
   and forwarding of packets within an MPLS-TP network.  This layer is
   based on the data plane architectures for MPLS ([RFC3031] and
   [RFC3032]) and for pseudowires [RFC3985].

   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.

1.1.  Scope

   This document has the following purposes:

   o  To identify the data plane functions within the MPLS Transport
      Profile; and

   o  To indicate which of these data plane functions an MPLS-TP
      implementation is required to support.

   This document defines the encapsulation and forwarding functions
   applicable to packets traversing an MPLS-TP Label Switched Path
   (LSP), pseudowire (PW), or section (see Section 3 for the definitions
   of these transport entities).  Encapsulation and forwarding functions
   for packets outside an MPLS-TP LSP, PW, or section, and mechanisms
   for delivering packets to or from MPLS-TP LSPs, PWs, and sections,
   are outside the scope of this document.

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1.2.  Terminology

   Term    Definition
   ------- -------------------------------------------
   ACH     Associated Channel Header
   G-ACh   Generic Associated Channel
   GAL     G-ACh Label
   LER     Label Edge Router
   LSE     Label Stack Entry
   LSP     Label Switched Path
   LSR     Label Switching Router
   MPLS-TP MPLS Transport Profile
   OAM     Operations, Administration, and Maintenance
   PW      Pseudowire
   QoS     Quality of Service
   S-PE    PW Switching Provider Edge
   T-PE    PW Terminating Provider Edge
   TTL     Time To Live

   Additional definitions and terminology can be found in [RFC5921] and
   [RFC5654].

1.3.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  MPLS-TP Packet Encapsulation and Forwarding

   MPLS-TP packet encapsulation and forwarding SHALL operate according
   to the MPLS data plane architecture described in [RFC3031] and
   [RFC3032] and to the data plane architectures for single-segment
   pseudowires and multi-segment pseudowires (see Section 3.3), except
   as noted otherwise in this document.  The MPLS-TP data plane
   satisfies the requirements specified in [RFC5654].

   Since an MPLS-TP packet is an MPLS packet as defined in [RFC3031] and
   [RFC3032], it will have an associated label stack, and the 'push',
   'pop', and 'swap' label processing operations specified in those
   documents apply.  The label stack represents a hierarchy of Label
   Switched Paths (LSPs).  A label is pushed to introduce an additional
   level of LSP hierarchy and popped to remove it.  Such an additional
   level may be introduced by any pair of LSRs, whereupon they become
   adjacent at this new level, and are then known as Label Edge Routers
   (LERs) with respect to the new LSP.

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   In contrast to, for example, Section 3.10 of [RFC3031], support for
   Internet Protocol (IP) host and router data plane functionality by
   MPLS-TP interfaces and in MPLS-TP networks is OPTIONAL.

   MPLS-TP forwarding is based on the label that identifies an 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 forwarding function.  The
   only event that interrupts a swap operation is Time To Live (TTL)
   expiry.

   At an LSR, S-PE, or T-PE, further processing to determine the context
   of a packet occurs when a swap operation is interrupted by TTL
   expiry.  If the TTL of an LSP label expires, then the label with the
   S (Bottom of Stack) bit set is inspected to determine if it is a
   reserved label.  If it is a reserved label, the packet is processed
   according to the rules of that reserved label.  For example, if it is
   a Generic Associated Channel Label (GAL), then it is processed as a
   packet on the Generic Associated Channel (G-ACh); see Section 4.  If
   the TTL of a PW expires at an S-PE or T-PE, then the packet is
   examined to determine if a Generic Associated Channel Header (ACH) is
   present immediately below the PW label.  If so, then the packet is
   processed as a packet on the G-ACh.

   Similarly, if a pop operation at an LER exposes a reserved label at
   the top of the label stack, then the packet is processed according to
   the rules of that reserved label.

   If no such exception occurs, the packet is forwarded according to the
   procedures in [RFC3031] and [RFC3032].

3.  MPLS-TP Transport Entities

   The MPLS Transport Profile includes the following data plane
   transport entities:

   o  Label Switched Paths (LSPs)

   o  sections

   o  pseudowires (PWs)

3.1.  Label Switched Paths

   MPLS-TP LSPs are ordinary MPLS LSPs as defined in [RFC3031], except
   as specifically noted otherwise in this document.

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3.1.1.  LSP Packet Encapsulation and Forwarding

   Encapsulation and forwarding of packets traversing MPLS-TP LSPs MUST
   follow standard MPLS packet encapsulation and forwarding as defined
   in [RFC3031], [RFC3032], [RFC5331], and [RFC5332], except as
   explicitly stated otherwise in this document.

   Data plane Quality of Service capabilities are included in the
   MPLS-TP in the form of Traffic Engineered (TE) LSPs [RFC3209] and the
   MPLS Differentiated Services (Diffserv) architecture [RFC3270].  Both
   E-LSP and L-LSP MPLS Diffserv modes are included.  The Traffic Class
   field (formerly the EXP field) of an MPLS label follows the
   definition of [RFC5462] and [RFC3270] and MUST be processed according
   to the rules specified in those documents.

   Except for transient packet reordering that may occur, for example,
   during fault conditions, packets are delivered in order on L-LSPs,
   and on E-LSPs within a specific ordered aggregate.

   The Uniform, Pipe, and Short Pipe Diffserv tunneling and TTL
   processing models described in [RFC3270] and [RFC3443] MAY be used
   for MPLS-TP LSPs.  Note, however, that support for the Pipe or Short
   Pipe models is REQUIRED for typical transport applications in which
   the topology and QoS characteristics of the MPLS-TP server layer are
   independent of the client layer.  Specific applications MAY place
   further requirements on the Diffserv tunneling and TTL processing
   models an LSP can use.

   Per-platform, per-interface, or other context-specific label space
   [RFC5331] MAY be used for MPLS-TP LSPs.  Downstream [RFC3031] or
   upstream [RFC5331] label allocation schemes MAY be used for MPLS-TP
   LSPs.  The requirements of a particular LSP type may, however,
   dictate which label spaces or allocation schemes LSPs of that type
   can use.

   Equal-Cost Multi-Path (ECMP) load-balancing MUST NOT be performed on
   an MPLS-TP LSP.  MPLS-TP LSPs as defined in this document MAY operate
   over a server layer that supports load-balancing, but this load-
   balancing MUST operate in such a manner that it is transparent to
   MPLS-TP.  This does not preclude the future definition of new MPLS-TP
   LSP types that have different requirements regarding the use of ECMP
   in the server layer.

   Penultimate Hop Popping (PHP) MUST be disabled by default on MPLS-TP
   LSPs.

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3.1.2.  LSP Payloads

   The MPLS-TP includes support for the following LSP payload types:

   o  Network-layer protocol packets (including MPLS-labeled packets)

   o  Pseudowire packets

   The rules for processing LSP payloads that are network-layer protocol
   packets SHALL be as specified in [RFC3032].

   The rules for processing LSP payloads that are pseudowire packets
   SHALL be as defined in the data plane pseudowire specifications (see
   Section 3.3).

   The payload of an MPLS-TP LSP may be a packet that itself contains an
   MPLS label stack.  This is true, for instance, when the payload is a
   pseudowire or an MPLS LSP.  In such cases, the label stack is
   contiguous between the MPLS-TP LSP and its payload, and exactly one
   LSE in this stack SHALL have the S (Bottom of Stack) bit set to 1.
   This behavior reflects best current practice in MPLS but differs
   slightly from [RFC3032], which uses the S bit to identify when MPLS
   label processing stops and network-layer processing starts.

3.1.3.  LSP Types

   The MPLS-TP includes the following LSP types:

   o  Point-to-point unidirectional

   o  Point-to-point associated bidirectional

   o  Point-to-point co-routed bidirectional

   o  Point-to-multipoint unidirectional

   Point-to-point unidirectional LSPs are supported by the basic MPLS
   architecture [RFC3031] and are REQUIRED to function in the same
   manner in the MPLS-TP data plane, except as explicitly stated
   otherwise in this document.

   A point-to-point associated bidirectional LSP between LSRs A and B
   consists of two unidirectional point-to-point LSPs, one from A to B
   and the other from B to A, which are regarded as a pair providing a
   single logical bidirectional transport path.

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   A point-to-point co-routed bidirectional LSP is a point-to-point
   associated bidirectional LSP with the additional constraint that its
   two unidirectional component LSPs in each direction follow the same
   path (in terms of both nodes and links).  An important property of
   co-routed bidirectional LSPs is that their unidirectional component
   LSPs share fate.

   A point-to-multipoint unidirectional LSP functions in the same manner
   in the data plane, with respect to basic label processing and packet-
   switching operations, as a point-to-point unidirectional LSP, with
   one difference: an LSR may have more than one (egress interface,
   outgoing label) pair associated with the LSP, and any packet it
   transmits on the LSP is transmitted out all associated egress
   interfaces.  Point-to-multipoint LSPs are described in [RFC4875] and
   [RFC5332].  TTL processing and exception handling for point-to-
   multipoint LSPs is the same as for point-to-point LSPs and is
   described in Section 2.

3.2.  Sections

   Two MPLS-TP LSRs are considered to be topologically adjacent at a
   particular layer n >= 0 of the MPLS-TP LSP hierarchy if there exists
   connectivity between them at the next lowest network layer, and if
   there is no MPLS layer processing at layer n between the two LSRs
   (other than at the LSRs themselves).  Such connectivity, if it
   exists, will be either an MPLS-TP LSP (if n > 0) or a data-link
   provided by the underlying server layer network (if n = 0), and is
   referred to as an MPLS-TP section at layer n of the MPLS-TP LSP
   hierarchy.  Thus, the links traversed by a layer n+1 MPLS-TP LSP are
   layer n MPLS-TP sections.  Such an LSP is referred to as a client of
   the section layer, and the section layer is referred to as the server
   layer with respect to its clients.

   The MPLS label stack associated with an MPLS-TP section at layer n
   consists of n labels, in the absence of stack optimization
   mechanisms.  In order for two LSRs to exchange non-IP MPLS-TP control
   packets over a section, an additional label, the G-ACh Label (GAL)
   (see Section 4) MUST appear at the bottom of the label stack.

   An MPLS-TP section may provide one or more of the following types of
   service to its client layer:

   o  Point-to-point bidirectional

   o  Point-to-point unidirectional

   o  Point-to-multipoint unidirectional

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   The manner in which a section provides such a service is outside the
   scope of the MPLS-TP.

   An LSP of any of the types listed in Section 3.1.3 may serve as a
   section for a client-layer transport entity as long as it supports
   the type of service the client requires.

   A section MUST provide a means of identifying the type of payload it
   carries.  If the section is a data-link, link-specific mechanisms
   such as a protocol type indication in the data-link header MAY be
   used.  If the section is an LSP, this information MAY be implied by
   the LSP label or, if the LSP payload is MPLS-labeled, by the setting
   of the S bit.  Additional labels MAY also be used if necessary to
   distinguish different payload types; see [RFC5921] for examples and
   further discussion.

3.3.  Pseudowires

   The data plane architectures for single-segment pseudowires [RFC3985]
   and multi-segment pseudowires [RFC5659] are included in the MPLS-TP.

   Data plane processing procedures for pseudowires are defined and
   described in a number of IETF documents.  Some example pseudowire
   data plane procedures include:

   o  Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over
      an MPLS PSN [RFC4385]

   o  Encapsulation Methods for Transport of Ethernet over MPLS Networks
      [RFC4448]

   o  Structure-Agnostic Time Division Multiplexing (TDM) over Packet
      (SAToP) [RFC4553]

   o  Encapsulation Methods for Transport of PPP/High-Level Data Link
      Control (HDLC) over MPLS Networks [RFC4618]

   o  Encapsulation Methods for Transport of Frame Relay over
      Multiprotocol Label Switching (MPLS) Networks [RFC4619]

   o  Encapsulation Methods for Transport of Asynchronous Transfer Mode
      (ATM) over MPLS Networks [RFC4717]

   o  Pseudowire Emulation Edge-to-Edge (PWE3) Asynchronous Transfer
      Mode (ATM) Transparent Cell Transport Service [RFC4816]

   o  Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/
      SDH) Circuit Emulation over Packet (CEP) [RFC4842]

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   o  Structure-Aware Time Division Multiplexed (TDM) Circuit Emulation
      Service over Packet Switched Network (CESoPSN) [RFC5086]

   o  Time Division Multiplexing over IP (TDMoIP) [RFC5087]

   o  Encapsulation Methods for Transport of Fibre Channel frames Over
      MPLS Networks [FC-ENCAP]

   This document specifies no modifications or extensions to pseudowire
   data plane architectures or protocols.

4.  MPLS-TP Generic Associated Channel

   The MPLS Generic Associated Channel (G-ACh) mechanism is specified in
   [RFC5586] and included in the MPLS-TP.  The G-ACh provides an
   auxiliary logical data channel associated with MPLS-TP sections,
   LSPs, and PWs in the data plane.  The primary purpose of the G-ACh in
   the context of MPLS-TP is to support control, management, and
   Operations, Administration, and Maintenance (OAM) traffic associated
   with MPLS-TP transport entities.  The G-ACh MUST NOT be used to
   transport client layer network traffic in MPLS-TP networks.

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

   When the control message is carried over a section or an LSP, rather
   than over a PW, it is necessary to provide an indication in the
   packet that the payload is something other than a client data packet.
   This is achieved by including a reserved label with a value of 13 at
   the bottom of the label stack.  This reserved label is referred to as
   the G-ACh Label (GAL) and is defined in [RFC5586].  When a GAL is
   found, it indicates that the payload begins with an ACH.  The GAL is
   thus a demultiplexer for G-ACh traffic on the section or the LSP, and
   the ACH is a discriminator for the type of traffic carried on the
   G-ACh.  MPLS-TP forwarding follows the normal MPLS model, and thus a
   GAL is invisible to an LSR unless it is the top label in the label
   stack.  The only other circumstance under which the label stack may
   be inspected for a GAL is when the TTL has expired.  Normal packet

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   forwarding MAY continue concurrently with this inspection.  All
   operations on the label stack are in accordance with [RFC3031] and
   [RFC3032].

   An application processing a packet received over the G-ACh may
   require packet-specific context (such as the receiving interface or
   received label stack).  Data plane implementations MUST therefore
   provide adequate context to the application that is to process a
   G-ACh packet.  The definition of the context required MUST be
   provided as part of the specification of the application using the
   G-ACh.

5.  Server-Layer Considerations

   The MPLS-TP network has no awareness of the internals of the server
   layer of which it is a client; it requires only that the server layer
   be capable of delivering the type of service required by the MPLS-TP
   transport entities that make use of it.  Note that what appears to be
   a single server-layer link to the MPLS-TP network may be a
   complicated construct underneath, such as an LSP or a collection of
   underlying links operating as a bundle.  Special care may be needed
   in network design and operation when such constructs are used as a
   server layer for MPLS-TP.

   Encapsulation of MPLS-TP packets for transport over specific server-
   layer media is outside the scope of this document.

6.  Security Considerations

   The MPLS data plane (and therefore the MPLS-TP data plane) does not
   provide any security mechanisms in and of itself.  Client layers that
   wish to secure data carried over MPLS-TP transport entities are
   REQUIRED to apply their own security mechanisms.

   Where management or control plane protocols are used to install
   label-switching operations necessary to establish MPLS-TP transport
   paths, those protocols are equipped with security features that
   network operators may use to securely create the transport paths.

   Where enhanced security is desirable, and a trust relationship exists
   between an LSR and its peer, the LSR MAY choose to implement the
   following policy for the processing of MPLS packets received from one
   or more of its neighbors:

      Upon receipt of an MPLS packet, discard the packet unless one of
      the following two conditions holds:

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      1.  Any MPLS label in the packet's label stack processed at the
          receiving LSR, such as an LSP or PW label, has a label value
          that the receiving LSR has distributed to that neighbor; or

      2.  Any MPLS label in the packet's label stack processed at the
          receiving LSR, such as an LSP or PW label, has a label value
          that the receiving LSR has previously distributed to the peer
          beyond that neighbor (i.e., when it is known that the path
          from the system to which the label was distributed to the
          receiving system is via that neighbor).

   Further details of MPLS and MPLS-TP security can be found in
   [RFC5921] and [RFC5920].

7.  References

7.1.  Normative References

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

   [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.

   [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.

   [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.

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

   [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.

   [RFC4448]   Martini, L., Rosen, E., El-Aawar, N., and G. Heron,
               "Encapsulation Methods for Transport of Ethernet over
               MPLS Networks", RFC 4448, April 2006.

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   [RFC4553]   Vainshtein, A. and YJ. Stein, "Structure-Agnostic Time
               Division Multiplexing (TDM) over Packet (SAToP)",
               RFC 4553, June 2006.

   [RFC4618]   Martini, L., Rosen, E., Heron, G., and A. Malis,
               "Encapsulation Methods for Transport of PPP/High-Level
               Data Link Control (HDLC) over MPLS Networks", RFC 4618,
               September 2006.

   [RFC4619]   Martini, L., Kawa, C., and A. Malis, "Encapsulation
               Methods for Transport of Frame Relay over Multiprotocol
               Label Switching (MPLS) Networks", RFC 4619,
               September 2006.

   [RFC4717]   Martini, L., Jayakumar, J., Bocci, M., El-Aawar, N.,
               Brayley, J., and G. Koleyni, "Encapsulation Methods for
               Transport of Asynchronous Transfer Mode (ATM) over MPLS
               Networks", RFC 4717, December 2006.

   [RFC4816]   Malis, A., Martini, L., Brayley, J., and T. Walsh,
               "Pseudowire Emulation Edge-to-Edge (PWE3) Asynchronous
               Transfer Mode (ATM) Transparent Cell Transport Service",
               RFC 4816, February 2007.

   [RFC4842]   Malis, A., Pate, P., Cohen, R., and D. Zelig,
               "Synchronous Optical Network/Synchronous Digital
               Hierarchy (SONET/SDH) Circuit Emulation over Packet
               (CEP)", RFC 4842, April 2007.

   [RFC4875]   Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
               "Extensions to Resource Reservation Protocol - Traffic
               Engineering (RSVP-TE) for Point-to-Multipoint TE Label
               Switched Paths (LSPs)", RFC 4875, May 2007.

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

   [RFC5332]   Eckert, T., Rosen, E., Aggarwal, R., and Y. Rekhter,
               "MPLS Multicast Encapsulations", RFC 5332, August 2008.

   [RFC5462]   Andersson, L. and R. Asati, "Multiprotocol Label
               Switching (MPLS) Label Stack Entry: "EXP" Field Renamed
               to "Traffic Class" Field", RFC 5462, February 2009.

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

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RFC 5960             MPLS-TP Data Plane Architecture         August 2010

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

7.2.  Informative References

   [FC-ENCAP]  Black, D. and L. Dunbar, "Encapsulation Methods for
               Transport of Fibre Channel frames Over MPLS Networks",
               Work in Progress, June 2010.

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

   [RFC5086]   Vainshtein, A., Sasson, I., Metz, E., Frost, T., and P.
               Pate, "Structure-Aware Time Division Multiplexed (TDM)
               Circuit Emulation Service over Packet Switched Network
               (CESoPSN)", RFC 5086, December 2007.

   [RFC5087]   Stein, Y(J)., Shashoua, R., Insler, R., and M. Anavi,
               "Time Division Multiplexing over IP (TDMoIP)", RFC 5087,
               December 2007.

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

   [RFC5920]   Fang, L., "Security Framework for MPLS and GMPLS
               Networks", RFC 5920, July 2010.

   [RFC5921]   Bocci, M., Bryant, S., Frost, D., Levrau, L., and L.
               Berger, "A Framework for MPLS in Transport Networks",
               RFC 5921, July 2010.

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Authors' Addresses

   Dan Frost (editor)
   Cisco Systems

   EMail: danfrost@cisco.com

   Stewart Bryant (editor)
   Cisco Systems

   EMail: stbryant@cisco.com

   Matthew Bocci (editor)
   Alcatel-Lucent

   EMail: matthew.bocci@alcatel-lucent.com

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