Network Working Group S. Bryant, Ed.
Request for Comments: 5317 Cisco Systems
Category: Informational L. Andersson, Ed.
February 2009 Joint Working Team (JWT) Report
on MPLS Architectural Considerations for a Transport Profile
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This RFC archives the report of the IETF - ITU-T Joint Working Team
(JWT) on the application of MPLS to transport networks. The JWT
recommended of Option 1: The IETF and the ITU-T jointly agree to work
together and bring transport requirements into the IETF and extend
IETF MPLS forwarding, OAM (Operations, Administration, and
Management), survivability, network management and control plane
protocols to meet those requirements through the IETF Standards
Process. This RFC is available in ASCII (which contains a summary of
the slides) and in PDF (which contains the summary and a copy of the
For a number of years, the ITU-T has been designing a connection-
oriented packet switched technology to be used in Transport Networks.
A Transport Network can be considered to be the network that provides
wide area connectivity upon which other services, such as IP or the
phone network, run. The ITU-T chose to adapt the IETF's MPLS to this
task, and introduced a protocol suite known as T-MPLS.
Quite late in the ITU-T design and specification cycle, there were a
number of liaison exchanges between the ITU-T and the IETF concerning
this technology. These liaisons can be found on the IETF Liaison
Statement web page [LIAISON]. In addition, the chairs of the MPLS,
PWE3, BFD, and CCAMP working groups as well as the Routing and
Internet Area Directors attended a number of ITU-T meetings. During
this process, the IETF became increasingly concerned that the
incompatibility of IETF MPLS and ITU-T T-MPLS would "represent a
mutual danger to both the Internet and the Transport network". These
concerns led the chairs of the IESG and IAB to take the step of
sending a liaison to the ITU-T, stating that either T-MPLS should
become fully compliant MPLS protocol, standardized under the IETF
process (the so-called "Option 1"), or it should become a completely
disjoint protocol with a new name and completely new set of code
points (the so-called "Option 2") [Ethertypes].
Option 1 and Option 2 were discussed at an ITU-T meeting of Question
12 Study Group 15 in Stuttgart [Stuttgart], where it was proposed
that a Joint (ITU-T - IETF) Team should be formed to evaluate the
issues, and make a recommendation to ITU-T management on the best way
Following discussion between the management of the IETF and the
ITU-T, a Joint Working Team (JWT) was established; this was supported
by an IETF Design Team and an Ad Hoc Group on T-MPLS in the ITU-T
[ahtmpls]. The first meeting of the Ad Hoc group occurred during the
ITU-T Geneva Plenary in February 2008. As a result of the work of
the JWT and the resulting agreement on a way forward, the fears that
a set of next-generation network transport specifications developed
by ITU-T could cause interoperability problems were allayed.
The JWT submitted their report to the ITU-T and IETF management in
the form of a set of Power Point slides [MPLS-TP-22]. (See the PDF
of this RFC.) The ITU-T have accepted the JWT recommendations, as
documented in [MPLS-TP]. This RFC archives the JWT report in a
format that is accessible to the IETF.
This RFC is available in ASCII (which contains a summary of the
slides) and in PDF (which contains the summary and a copy of the
slides). In the case of a conflict between the summary and the
slides, the slides take precedence. Since those slides were the
basis of an important agreement between the IETF and the ITU-T, it
should further be noted that in the event that the PDF version of the
slides differs from those emailed to ITU-T and IETF management on 18
April 2008 by the co-chairs of the JWT, the emailed slides take
2. Executive Summary
Slides 4 to 10 provide an executive summary of the JWT Report. The
following is a summary of those slides:
The JWT achieved consensus on the recommendation of Option 1: to
jointly agree to work together and bring transport requirements into
the IETF and extend IETF MPLS forwarding, OAM, survivability, network
management, and control plane protocols to meet those requirements
through the IETF Standards Process. The Joint Working Team believed
that this would fulfill the mutual goals of improving the
functionality of the transport networks and the Internet and
guaranteeing complete interoperability and architectural soundness.
This technology would be referred to as the Transport Profile for
The JWT recommended that future work should focus on:
In the IETF:
Definition of the MPLS "Transport Profile" (MPLS-TP).
In the ITU-T:
Integration of MPLS-TP into the transport network,
Alignment of the current T-MPLS ITU-T Recommendations with MPLS-TP
Termination of the work on current T-MPLS.
The technical feasibility analysis concluded there were no "show
stopper" issues in the recommendation of Option 1 and that the IETF
MPLS and Pseudowire architecture could be extended to support
transport functional requirements. Therefore, the team believed that
there was no need for the analysis of any other option.
The JWT proposed that the MPLS Interoperability Design Team (MEAD
Team), JWT, and Ad Hoc T-MPLS groups continue as described in SG15
TD515/PLEN [JWTcreation] with the following roles:
Facilitate the rapid exchange of information between the IETF and
Ensure that the work is progressing with a consistent set of
Identify gaps/inconsistencies in the solutions under development,
Propose solutions for consideration by the appropriate WG/
Provide guidance when work on a topic is stalled or a technical
decision must be mediated.
None of these groups would have the authority to create or modify
IETF RFCs or ITU-T Recommendations. Any such work would be
progressed via the normal process of the respective standards body.
Direct participation in the work by experts from the IETF and ITU-T
would be required.
The JWT recommended that the normative definition of the MPLS-TP that
supports the ITU-T transport network requirements be captured in IETF
RFCs. It proposed that the ITU-T should:
Develop ITU-T Recommendations to allow MPLS-TP to be integrated
with current transport equipment and networks, including in
agreement with the IETF, the definition of any ITU-T-specific
functionality within the MPLS-TP architecture via the MPLS change
Revise existing ITU-T Recommendations to align with MPLS-TP,
ITU-T Recommendations will make normative references to the
The executive summary contains a number of detailed JWT
recommendations to both IETF and ITU-T management together with
proposed document structure and timetable.
These JWT recommendations were accepted by ITU-T management
3. Introduction and Background Material
Slides 11 to 22 provide introductory and background material.
The starting point of the analysis was to attempt to satisfy Option 1
by showing the high-level architecture, any show stoppers, and the
design points that would need to be addressed after the decision had
been made to work together. Option 1 was stated as preferred by the
IETF and because Option 1 was shown to be feasible, Option 2 was not
The work was segmented into five groups looking at: Forwarding, OAM,
Protection, Control Plane, and Network Management. The outcome of
each review was reported in the following sections and is summarized
There follows a detailed description of the overall requirements and
architectural assumptions that would be used in the remainder of the
4. High-Level Architecture
Slides 23 to 28 provide a high-level architectural view of the
The spectrum of services that the MPLS-TP needs to address and the
wider MPLS context is described, together with the provisioning
issues. Some basic terminology needed in order to understand the
MPLS-TP is defined and some context examples are provided.
5. OAM and Forwarding
Slides 29 to 32 describe the OAM requirements and talk about segment
recovery and node identification.
Slides 33 to 38 introduce OAM hierarchy and describe Label Switched
Path (LSP) monitoring, the Maintenance End Point (MEP) and
Maintenance Intermediate Point (MIP) relationship and the LSP and
pseudowire (PW) monitoring relationship.
Sides 39 to 46 introduce the Associated Channel Header (ACH) and its
generalization to carry the OAM over LSPs through the use of the
"Label for You" (LFU).
Slides 47 to 48 provide a description of how the forwarding and the
ACH OAM mechanism work in detail. A significant number of scenarios
are described to work through the operation on a case-by-case basis.
These slides introduce a new textual notation to simplify the
description of complex MPLS stacks.
Note that the MPLS forwarding, as specified by IETF RFCs, requires no
changes to support MPLS-TP.
6. Control Plane
Sides 79 to 83 discuss various aspects of the control plane design.
Control plane sub-team stated that existing IETF protocols can be
used to provide required functions for transport network operation
and for data-communications-network/switched-circuit-network
operation. IETF GMPLS protocols have already applied to Automatic
Switched Optical Network (ASON) architecture, and the JWT considered
that any protocol extensions needed will be easy to make. The slides
provide a number of scenarios to demonstrate this conclusion.
The survivability considerations are provided in slides 95 to 104.
The survivability sub-team did not find any issues that prevented the
creation of an MPLS-TP, and therefore recommended that Option 1 be
selected. Three potential solutions were identified. Each solution
has different attributes and advantages, and it was thought that
further work in the design phase should eliminate one or more of
these options and/or provide an applicability statement.
After some clarifications and discussion, there follow in the slide
set a number of linear and ring protection scenarios with examples of
how they might be addressed.
8. Network Management
Slide 106 states the conclusion of the Network Management sub-team :
that it found no issues that prevent the creation of an MPLS-TP and
hence Option 1 can be selected.
Slide 113 provides a summary of the JWT report.
The JWT found no show stoppers and unanimously agreed that they had
identified a viable solution. They therefore recommend Option 1.
They stated that in their view, it is technically feasible that the
existing MPLS architecture can be extended to meet the requirements
of a Transport profile, and that the architecture allows for a single
OAM technology for LSPs, PWs, and a deeply nested network. From
probing various ITU-T Study Groups and IETF Working Groups it appears
that MPLS reserved label 14 has had wide enough implementation and
deployment that the solution may have to use a different reserved
label (e.g., Label 13). The JWT recommended that extensions to Label
14 should cease.
The JWT further recommended that this architecture appeared to
subsume Y.1711, since the requirements can be met by the mechanism
proposed in their report.
10. IANA Considerations
There are no IANA considerations that arise from this document.
Any IANA allocations needed to implement the JWT recommendation will
be requested in the Standards-Track RFCs that define the MPLS-TP
11. Security Considerations
The only security consideration that arises as a result of this
document is the need to ensure that this is a faithful representation
of the JWT report.
The protocol work that arises from this agreement will have technical
security requirements that will be identified in the RFCs that define
12. The JWT Report
In the PDF of this RFC, there follows the JWT report as a set of
Stewart Bryant (editor)
250, Longwater, Green Park,
Reading RG2 6GB
Loa Andersson (editor)