





Internet Engineering Task Force (IETF)                          M. Bocci
Request for Comments: 6215                                     L. Levrau
Updates: 5921                                             Alcatel-Lucent
Category: Informational                                         D. Frost
ISSN: 2070-1721                                                    Cisco
                                                              April 2011


                 MPLS Transport Profile User-to-Network
                   and Network-to-Network Interfaces

Abstract

   The framework for MPLS in transport networks (RFC 5921) provides
   reference models for the MPLS Transport Profile (MPLS-TP) Transport
   Service Interfaces, which are a User-to-Network Interface (UNI), and
   a Network-to-Network Interface (NNI).  This document updates those
   reference models to show detailed reference points for these
   interfaces, along with further clarification of the functional
   architecture of MPLS-TP at a UNI and NNI.

   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.

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/rfc6215.








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Copyright Notice

   Copyright (c) 2011 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.

1.  Introduction

   The framework for MPLS in transport networks [RFC5921] provides
   reference models for the MPLS Transport Profile (MPLS-TP) Transport
   Service Interfaces, which are a User-to-Network Interface (UNI) and a
   Network-to-Network Interface (NNI).  This document updates those
   reference models to show detailed reference points for these
   interfaces, along with further clarification of the functional
   architecture of MPLS-TP at a UNI and NNI.

   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.

1.1.  Updates to the MPLS-TP UNI and NNI

   The Transport Service Interfaces for MPLS-TP are defined in Section
   3.4.3 of [RFC5921].  These definitions are illustrated by showing
   MPLS-TP Provider Edges (PEs) containing a UNI and an NNI.  The
   figures illustrate the UNI and the NNI as a span.  However, it is
   convention to illustrate these interfaces as reference points.
   Furthermore, in the case of a UNI, it is useful to illustrate the
   distribution of UNI functions between the Customer Edge (CE) side and
   the PE side of the UNI, i.e., the UNI-C (User-to-User Interface,
   Client side) and UNI-N (User-to-Network Interface, Network side), in
   order to show their relationship to one another.







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   This document provides updated illustrations of the MPLS-TP UNI and
   MPLS-TP NNI to show these additional details.  These illustrations
   obsolete the corresponding ones in [RFC5921].  This document also
   defines additional terminology referenced in the illustrations.  No
   other updates are made by this document.

   Awareness of the Transport Service layer need exist only at PE nodes,
   and so only these nodes are illustrated in the figures.  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 a Label Edge Router (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.

1.2.  Terminology and Abbreviations

   The terminology and abbreviations of [RFC5921] apply.

   The following additional terminology is used in this document.

   Term  Definition
   ----- ---------------------------------------
   CP    Control Plane
   NNI   Network-to-Network Interface
   TSI   Transport Service Instance
   UNI   User-to-Network Interface
   UNI-C User-to-Network Interface, Client side
   UNI-N User-to-Network Interface, Network side

   Transport Service Instance:  A single logical point-to-point
      connection at the Transport Service layer between the ingress PE
      providing a packet transport service to a CE, and the
      corresponding egress PE to which the peer CE is attached.

2.  MPLS-TP User-to-Network Interface

   The MPLS-TP User-to-Network Interface (UNI) is illustrated in
   Figure 1.  This figure obsoletes Figure 3 of [RFC5921].  Note that
   the term "MPLS-TP UNI" is to be interpreted as a UNI to an MPLS-TP
   network and does not refer to the protocol transiting the UNI.  The
   UNI for a particular client flow may involve signaling between the CE
   and PE.  If signaling is used, it may traverse the same attachment
   circuit that supports the client flow.







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                       UNI
                        :                             MPLS-TP
    :<-- UNI-C -->:     :     :<-- UNI-N ->:          Network <----->
    :  function   :     :     :  function  :
   ---------------      :      ------------:--------------------
    :             |     :     |            :   Transport        |
    :             |     V     |    Client  :     Path           |
    :             |           |   Service  :   Mux/Demux        |
    :             |           |   Control  :      --            |
    : ----------  |           |  ----------:     |  |  Transport|
    :|          | |           | |          |     |  |    Path   |
    :|Signaling |_|___________|_|Signaling |     |  |    --------->
    :|Controller| |           | |Controller|     |  |   |
    : ----------  |           |  ----------      |  |    --------->
    :      :......|...........|......:     :     |  |           |
    :             |  Control  |            :     |  |  Transport|
    :             |  Channel  |            :     |  |    Path   |
    :             |           |            :     |  |    --------->
    :             |           |            :     |  |  -+----------->TSI
    :             |           |  Transport :     |  | |  --------->
    :             |  Client   |   Service  :     |  | |         |
    :             |  Traffic  |  Data Plane:     |  | |         |
    : ----------  |  Flows    |  --------------  |  | |Transport|
    :| Client   |-|-----------|-|Client/Service|-|  |-   Path   |
    :| Traffic  |=|===========|=|    Traffic   | |  |    --------->
    :|Processing| |           | |  Processing  |=|  |===+===========>TSI
    : ----------  |           |  --------------  |  |    --------->
    :      |______|___________|______|     :     |  |           |
    :             | Data Link |            :     |  |           |
    :             |           |            :      --            |
    :             |           |            :          Transport |
    :             |           |            :             Path   |
    :             |           |            :          Data Plane|
   ---------------             ---------------------------------

   Customer Edge Node              MPLS-TP Provider Edge Node

Note: The client service control plane may be a control protocol
      belonging to the native service, or GMPLS.

             Figure 1: UNI between CE Node and MPLS-TP PE Node










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3.  MPLS-TP Network-to-Network Interface

   The MPLS-TP Network-to-Network Interface (NNI) is illustrated in
   Figure 2.  This figure obsoletes Figure 5 of [RFC5921].  The NNI for
   a particular Transport Service Instance may involve signaling between
   the two PEs.  If signaling is used, it may traverse the same data-
   link that supports the service instance.
                                  NNI
                :<--- NNI --->:    :     :<--- NNI ---->:
                :  Function   :    :     :   Function   :
    ---------------------------    :      --------------------------
   |            :  Transport   |   :     |   Transport  :           |
   |            :  Service CP  |   V     |   Service CP :           |
   |            :  ----------  |Signaling|  ----------  :           |
   |            : |Signaling |_| _______ |_|Signaling | :           |
   |            : |Controller| |         | |Controller| :           |
   |            :  ----------  |         |  ----------  :           |
   |            :       :....... Control .......:       :           |
   |            :              | Channel |              :           |
   |   -        :   Transport  |         | Transport    :        -  |
   |  | |       :     Path CP  |         |  Path CP     :       | | |
   |  | |       :  ----------  |Signaling|  ----------  :       | | |
 -----| |       : |Signaling |_| _______ |_|Signaling | :       | |-----
 ---+-| |       : |Controller| |         | |Controller| :       | |-+---
 -----| |       :  ----------  |         |  ----------  :       | |-----
   |  | |       :       :....... Control .......:       :       | | |
   |  | |       :              | Channel |              :       | | |
   |  | |  Transport Path      |         |       Transport Path | | |
   |  | | /  mux/demux   \     |         |      /  mux/demux   \| | |
   |  | |/      :         \--  |         |  -- /        :       | | |
   |  | |   ----------    |  | |Transport| |  |    ----------   | | |
   |  | |--|Transport |---|  | |  Path   | |  |---|Transport |--| | |
 -----| |  | Service  |   |  |-------------|  |   | Service  |  | |-----
 TSI+=| |==|Processing|===|  |<+===TSI===+>|  |===|Processing|==| |=+TSI
 -----| |   ----------    |  |-------------|  |    ----------   | |-----
   |  | |       :         |  | |         | |  |         :       | | |
   |  | |       :         |  | |         | |  |         :       | | |
   |   -        :          --  |         |  --          :        -  |
   |            :              |         |              :           |
   |     Transport Path        |         |      Transport Path      |
   |       Data Plane                    |        Data Plane        |
    ---------------------------           --------------------------
         MPLS-TP Provider                        MPLS-TP Provider
           Edge Node A                             Edge Node B

                  Figure 2: NNI between MPLS-TP PE Nodes





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4.  Security Considerations

   The security considerations of [RFC5921] apply.  The updated
   reference models provided by this document introduce no new security
   considerations.

5.  Acknowledgements

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

   o  Eve Varma

   o  Dieter Beller

   o  Lou Berger

   o  Stewart Bryant

   o  Italo Busi

   o  The experts of ITU-T Study Group 15 and the IETF MPLS and PWE3
      working groups.

6.  Normative References

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

Authors' Addresses

   Matthew Bocci
   Alcatel-Lucent

   EMail: matthew.bocci@alcatel-lucent.com


   Lieven Levrau
   Alcatel-Lucent

   EMail: lieven.levrau@alcatel-lucent.com


   Dan Frost
   Cisco

   EMail: danfrost@cisco.com



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