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IETF RFC 6215
MPLS Transport Profile User-to-Network and Network-to-Network Interfaces
Last modified on Monday, April 11th, 2011
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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/RFC 6215.
Bocci, et al. Informational PAGE 1 
RFC 6215 MPLS-TP UNI and NNI April 2011
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 [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 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 [RFC 5921]. 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.
Bocci, et al. Informational PAGE 2
RFC 6215 MPLS-TP UNI and NNI April 2011
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 [RFC 5921]. 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 [RFC 5921] 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 [RFC 5921]. 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.
Bocci, et al. Informational PAGE 3
RFC 6215 MPLS-TP UNI and NNI April 2011
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
Bocci, et al. Informational PAGE 4
RFC 6215 MPLS-TP UNI and NNI April 2011
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 [RFC 5921]. 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
Bocci, et al. Informational PAGE 5
RFC 6215 MPLS-TP UNI and NNI April 2011
4. Security Considerations
The security considerations of [RFC 5921] 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
[RFC 5921] 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
Bocci, et al. Informational PAGE 6
MPLS Transport Profile User-to-Network and Network-to-Network Interfaces
RFC TOTAL SIZE: 13619 bytes
PUBLICATION DATE: Monday, April 11th, 2011
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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