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RFC 5317 - Joint Working Team (JWT) Report on MPLS Architectural

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Network Working Group                                     S. Bryant, Ed.
Request for Comments: 5317                                 Cisco Systems
Category: Informational                                L. Andersson, Ed.
                                                                Acreo AB
                                                           February 2009

                    Joint Working Team (JWT) Report
      on MPLS Architectural Considerations for a Transport Profile

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

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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

Table of Contents

   1. Introduction ....................................................3
   2. Executive Summary ...............................................4
   3. Introduction and Background Material ............................6
   4. High-Level Architecture .........................................6
   5. OAM and Forwarding ..............................................6
   6. Control Plane ...................................................7
   7. Survivability ...................................................7
   8. Network Management ..............................................7
   9. Summary .........................................................7
   10. IANA Considerations ............................................8
   11. Security Considerations ........................................8
   12. The JWT Report .................................................8
   13. Informative References .........................................9

1.  Introduction

   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
      process [RFC4929],

      Revise existing ITU-T Recommendations to align with MPLS-TP,

      ITU-T Recommendations will make normative references to the
      appropriate RFCs.

   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
   proposed design.

   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.

7.  Survivability

   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.

9.  Summary

   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

13.  Informative References

   [Ethertypes]   IESG and IAB, "T-MPLS use of the MPLS Ethertypes",
                  2006, <https://datatracker.ietf.org/documents/LIAISON/

   [JWTcreation]  Chairman, ITU-T SG 15, "Proposal to establish an Ad
                  Hoc group on T-MPLS", 2008, <http://www.itu.int/md/

   [LIAISON]      Liaison statements to and from the IETF can be found
                  at: <https://datatracker.ietf.org/liaison/>.

   [MPLS-TP]      "IETF and ITU-T cooperation on extensions to MPLS for
                  transport network functionality", May 2008,

   [MPLS-TP-22]   IETF - ITU-T Joint Working Team, "MPLS Architectural
                  Considerations for a Transport Profile", April 2008,

   [MPLS-TP1]     "IETF and ITU-T cooperation on extensions to MPLS for
                  transport network functionality", ITU-T SG15,
                  May 2008, <https://datatracker.ietf.org/documents/

   [RFC4929]      Andersson, L. and A. Farrel, "Change Process for
                  Multiprotocol Label Switching (MPLS) and Generalized
                  MPLS (GMPLS) Protocols and Procedures", BCP 129,
                  RFC 4929, June 2007.

   [Stuttgart]    IETF - IESG and IAB Chairs, "Report of interim meeting
                  of Q.12 on T-MPLS", Stuttgart, Germany, Annex 4, 12-14
                  September 2007, 2008, <http://ties.itu.int/u//tsg15/
                  T-MPLS/wdt03_rapporteur_report-final.doc>.  This
                  document is available on request from the ITU-T.

   [ahtmpls]      "Ad Hoc group on T-MPLS", 2008, <http://www.itu.int/

Editors' Addresses

   Stewart Bryant (editor)
   Cisco Systems
   250, Longwater, Green Park,
   Reading  RG2 6GB

   EMail: stbryant@cisco.com

   Loa Andersson (editor)
   Acreo AB
   Isafjordsgatan 22

   EMail: loa@pi.nu


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