MPLS-TP UNI and NNI: MPLS Transport Profile User-to-Network and Network-to-Network Interfaces
Redrawn reference models that show exactly where the customer-facing and network-facing interfaces sit in an MPLS-TP network.
Bocci, M., Levrau, L., and D. Frost, "MPLS Transport Profile User-to-Network and Network-to-Network Interfaces", RFC 6215, DOI 10.17487/RFC6215, April 2011, <https://www.rfc-editor.org/info/rfc6215>.
@misc{rfc6215,
series = {Request for Comments},
number = 6215,
howpublished = {RFC 6215},
publisher = {RFC Editor},
doi = {10.17487/RFC6215},
url = {https://www.rfc-editor.org/info/rfc6215},
author = {M. Bocci and L. Levrau and D. Frost},
title = {{MPLS Transport Profile User-to-Network and Network-to-Network Interfaces}},
pagetotal = 6,
year = 2011,
month = apr,
} RFC text
Contents
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.
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
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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.
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.
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
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
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
AI ELI5
On this page
§1What This Document Updates
The framework for MPLS in transport networks, RFC 5921, gives reference models for the two Transport Service Interfaces of the MPLS Transport Profile (MPLS-TP): a User-to-Network Interface (UNI) and a Network-to-Network Interface (NNI). RFC 6215 updates those models to show detailed reference points and to clarify the functional architecture of MPLS-TP at a UNI and an NNI.
The old figures drew the UNI and NNI as spans between nodes. The RFC points out that the convention is to draw interfaces as reference points. For the UNI it is also useful to show how the functions are shared between the Customer Edge (CE) side and the Provider Edge (PE) side. The new illustrations obsolete the matching ones in RFC 5921, and the document states that no other updates are made.
It is a product of a joint IETF and ITU-T effort to bring an MPLS Transport Profile into the IETF MPLS and PWE3 architectures, supporting the capabilities of a packet transport network as defined by the ITU-T.
The old picture drew a doorway as a long squiggle. The new picture draws it as a clear spot and shows which side of the door belongs to the customer and which to the network company.
§2Terms and Layers
The terminology of RFC 5921 applies. RFC 6215 adds CP (Control Plane), NNI, TSI, UNI, UNI-C (the client side of the UNI) and UNI-N (the network side of the UNI).
A Transport Service Instance (TSI) is a single logical point-to-point connection at the Transport Service layer. It runs between the ingress PE that provides a packet transport service to a CE and the matching egress PE to which the peer CE is attached.
Only PE nodes need to know about the Transport Service layer, so only PEs appear in the figures. Provider (P) nodes need no awareness of it. Both PE and P nodes take part in the Transport Path layer. A PE terminates the transport paths it supports, acting as a Label Edge Router (LER), and multiplexes and demultiplexes Transport Service Instance traffic over those paths.
A TSI is like a private pipe between two customers' doors. Only the stations at the ends need to know about the pipe; the stations in the middle just pass the traffic along.
§3The User-to-Network Interface
Figure 1 of the RFC, which obsoletes Figure 3 of RFC 5921, shows a UNI between a Customer Edge node and an MPLS-TP Provider Edge node. The UNI is split into a UNI-C function on the customer side and a UNI-N function on the network side.
Each side holds a signaling controller and client or service traffic processing. A control channel joins the two signaling controllers, and client traffic flows pass between the traffic processing blocks over a data link. On the PE, a client service control block and a transport path mux/demux function connect to the transport paths and the TSIs of the MPLS-TP network.
The RFC stresses that the term "MPLS-TP UNI" means a UNI to an MPLS-TP network. It does not name the protocol that crosses the UNI. Signaling between CE and PE may be used for a particular client flow, and if it is, it may travel over the same attachment circuit as the client flow. The client service control plane may be a control protocol of the native service, or GMPLS.
At the customer's door there are two helpers, one on each side, who talk to each other and pass the customer's packages through. Which helper does what is now clearly drawn.
§4The Network-to-Network Interface
Figure 2, which obsoletes Figure 5 of RFC 5921, shows an NNI between MPLS-TP Provider Edge Node A and Provider Edge Node B. Each node has an NNI function, and the figure shows a Transport Service control plane and a Transport Path control plane, each with its own signaling controller and a control channel to its peer.
On the data plane, each node has transport service processing and a transport path mux/demux. The transport path between the two nodes carries the Transport Service Instances (TSIs) across the interface.
For a particular Transport Service Instance, the NNI may involve signaling between the two PEs. If signaling is used, it may travel over the same data link that supports the service instance.
Where two network companies meet, each has a door, a signaling helper and a package handler. The helpers chat, and the packages ride a shared road between the two companies.
| Interface | Between | Functions shown | Replaces in RFC 5921 |
|---|---|---|---|
| UNI | CE node and MPLS-TP PE node | UNI-C (client side) and UNI-N (network side) | Figure 3 |
| NNI | Two MPLS-TP PE nodes (A and B) | An NNI function on each node | Figure 5 |
§5Security Considerations
The security considerations of RFC 5921 apply. The updated reference models in RFC 6215 introduce no new security considerations, which fits with a document that only redraws figures and adds terms.
Redrawing a map does not change who can walk through the doors, so nothing new needs guarding.