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RFC 6373


MPLS Transport Profile (MPLS-TP) Control Plane Framework

Part 4 of 4, p. 39 to 57
Prev RFC Part


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5.  Pseudowires

5.1.  LDP Functions and Pseudowires

   MPLS PWs are defined in [RFC3985] and [RFC5659], and provide for
   emulated services over an MPLS Packet Switched Network (PSN).
   Several types of PWs have been defined: (1) Ethernet PWs providing
   for Ethernet port or Ethernet VLAN transport over MPLS [RFC4448], (2)
   High-Level Data Link Control (HDLC) / PPP PW providing for HDLC/PPP
   leased line transport over MPLS [RFC4618], (3) ATM PWs [RFC4816], (4)
   Frame Relay PWs [RFC4619], and (5) circuit Emulation PWs [RFC4553].

   Today's transport networks based on Plesiochronous Digital Hierarchy
   (PDH), WDM, or SONET/SDH provide transport for PDH or SONET (e.g.,
   ATM over SONET or Packet PPP over SONET) client signals with no
   payload awareness.  Implementing PW capability allows for the use of
   an existing technology to substitute the Time-Division Multiplexing

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   (TDM) transport with packet-based transport, using well-defined PW
   encapsulation methods for carrying various packet services over MPLS,
   and providing for potentially better bandwidth utilization.

   There are two general classes of PWs: (1) Single-Segment Pseudowires
   (SS-PWs) [RFC3985] and (2) Multi-segment Pseudowires (MS-PWs)
   [RFC5659].  An MPLS-TP network domain may transparently transport a
   PW whose end points are within a client network.  Alternatively, an
   MPLS-TP edge node may be the Terminating PE (T-PE) for a PW,
   performing adaptation from the native attachment circuit technology
   (e.g., Ethernet 802.1Q) to an MPLS PW that is then transported in an
   LSP over an MPLS-TP network.  In this way, the PW is analogous to a
   transport channel in a TDM network, and the LSP is equivalent to a
   container of multiple non-concatenated channels, albeit they are
   packet containers.  An MPLS-TP network may also contain Switching PEs
   (S-PEs) for a Multi-Segment PW whereby the T-PEs may be at the edge
   of an MPLS-TP network or in a client network.  In the latter case, a
   T-PE in a client network performs the adaptation of the native
   service to MPLS and the MPLS-TP network performs pseudowire

   The SS-PW signaling control plane is based on targeted LDP (T-LDP)
   with specific procedures defined in [RFC4447].  The MS-PW signaling
   control plane is also based on T-LDP as allowed for in [RFC5659],
   [RFC6073], and [MS-PW-DYNAMIC].  An MPLS-TP network shall use the
   same PW signaling protocols and procedures for placing SS-PWs and
   MS-PWs.  This will leverage existing technology as well as facilitate
   interoperability with client networks with native attachment circuits
   or PW segments that are switched across an MPLS-TP network.

5.1.1.  Management-Plane Support

   There is no MPLS-TP requirement for a standardized management
   interface to the MPLS-TP control plane.  A general overview of MPLS-
   TP-related MIB modules can be found in [TP-MIB].  Network management
   requirements for MPLS-based transport networks are provided in

5.2.  PW Control (LDP) and MPLS-TP Requirements Table

   The following table shows how the MPLS-TP control-plane requirements
   can be met using the existing LDP control plane for pseudowires
   (targeted LDP).  Areas where additional specifications are required
   are also identified.  The table lists references based on the
   control-plane requirements as identified and numbered above in
   Section 2.

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   In the table below, several of the requirements shown are addressed
   -- in part or in full -- by the use of MPLS-TP LSPs to carry
   pseudowires.  This is reflected by including "TP-LSPs" as a reference
   for those requirements.  Section 5.3.2 provides additional context
   for the binding of PWs to TP-LSPs.

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   | Req # | References                                                |
   |    1  | Generic requirement met by using Standards Track RFCs     |
   |    2  | [RFC3985], [RFC4447], Together with TP-LSPs (Sec. 4.3)    |
   |    3  | [RFC3985], [RFC4447]                                      |
   |    4  | Generic requirement met by using Standards Track RFCs     |
   |    5  | [RFC3985], [RFC4447], Together with TP-LSPs               |
   |    6  | [RFC3985], [RFC4447], [PW-P2MPR], [PW-P2MPE] + TP-LSPs    |
   |    7  | [RFC3985], [RFC4447], + TP-LSPs                           |
   |    8  | [PW-P2MPR], [PW-P2MPE]                                    |
   |    9  | [RFC3985], end-node only involvement for PW               |
   |   10  | [RFC3985], proper vendor implementation                   |
   |   11  | [RFC3985], end-node only involvement for PW               |
   | 12-13 | [RFC3985], [RFC4447], See Section 5.3.4                   |
   |   14  | [RFC3985], [RFC4447]                                      |
   |   15  | [RFC4447], [RFC3478], proper vendor implementation        |
   |   16  | [RFC3985], [RFC4447]                                      |
   | 17-18 | [RFC3985], proper vendor implementation                   |
   | 19-26 | [RFC3985], [RFC4447], [RFC5659], implementation           |
   |   27  | [RFC4448], [RFC4816], [RFC4618], [RFC4619], [RFC4553]     |
   |       | [RFC4842], [RFC5287]                                      |
   |   28  | [RFC3985]                                                 |
   | 29-31 | [RFC3985], [RFC4447]                                      |
   |   32  | [RFC3985], [RFC4447], [RFC5659], See Section 5.3.6        |
   |   33  | [RFC4385], [RFC4447], [RFC5586]                           |
   |   34  | [PW-P2MPR], [PW-P2MPE]                                    |
   |   35  | [RFC4863]                                                 |
   | 36-37 | [RFC3985], [RFC4447], See Section 5.3.4                   |
   |   38  | Provided by TP-LSPs                                       |
   |   39  | [RFC3985], [RFC4447], + TP-LSPs                           |
   |   40  | [RFC3478]                                                 |
   | 41-42 | [RFC3985], [RFC4447]                                      |
   | 43-44 | [RFC3985], [RFC4447], + TP-LSPs - See Section 5.3.5       |
   |   45  | [RFC3985], [RFC4447], [RFC5659] + TP-LSPs                 |
   |   46  | [RFC3985], [RFC4447], + TP-LSPs - See Section 5.3.3       |
   |   47  | [PW-RED], [PW-REDB]                                       |
   | 48-49 | [RFC3985], [RFC4447], + TP-LSPs, implementation           |
   | 50-52 | Provided by TP-LSPs, and Section 5.3.5                    |
   | 53-55 | [RFC3985], [RFC4447], See Section 5.3.5                   |
   |   56  | [PW-RED], [PW-REDB]                                       |
   |       | revertive/non-revertive behavior is a local matter for PW |
   | 57-58 | [PW-RED], [PW-REDB]                                       |
   | 59-81 | [RFC3985], [RFC4447], [PW-RED], [PW-REDB], Section 5.3.5  |
   | 82-83 | [RFC5085], [RFC5586], [RFC5885]                           |
   | 84-89 | [RFC3985], [RFC4447], [PW-RED], [PW-REDB], Section 5.3.5  |
   | 90-95 | [RFC3985], [RFC4447], + TP-LSPs, implementation           |
   |   96  | [RFC4447], [MS-PW-DYNAMIC]                                |

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   |   97  | [RFC4447]                                                 |
   |  98 - |                                                           |
   |   99  | Not Applicable to PW                                      |
   |  100  | [RFC4447]                                                 |
   |  101  | [RFC3478]                                                 |
   |  102  | [RFC3985], + TP-LSPs                                      |
   |  103  | Not Applicable to PW                                      |
   |  104  | [PW-OAM]                                                  |
   |  105  | [PW-OAM]                                                  |
   | 106 - |                                                           |
   |   108 | [RFC5085], [RFC5586], [RFC5885]                           |
   |  109  | [RFC5085], [RFC5586], [RFC5885]                           |
   |       | fault reporting and protection triggering is a local      |
   |       | matter for PW                                             |
   |  110  | [RFC5085], [RFC5586], [RFC5885]                           |
   |       | fault reporting and protection triggering is a local      |
   |       | matter for PW                                             |
   |  111  | [RFC4447]                                                 |
   |  112  | [RFC4447], [RFC5085], [RFC5586], [RFC5885]                |
   |  113  | [RFC5085], [RFC5586], [RFC5885]                           |
   |  114  | [RFC5085], [RFC5586], [RFC5885]                           |
   |  115  | path traversed by PW is determined by LSP path; see       |
   |       | GMPLS and MPLS-TP Requirements Table, Section 4.3         |
   |  116  | [PW-RED], [PW-REDB], administrative control of redundant  |
   |       | PW is a local matter at the PW head-end                   |
   |  117  | [PW-RED], [PW-REDB], [RFC5085], [RFC5586], [RFC5885]      |
   |  118  | [RFC3985], [RFC4447], [PW-RED], [PW-REDB], Section 5.3.5  |
   |  119  | [RFC4447]                                                 |
   | 120 - |                                                           |
   |   125 | [RFC5085], [RFC5586], [RFC5885]                           |
   | 126 - |                                                           |
   |   130 | [PW-OAM]                                                  |
   |  131  | Section 5.3.5                                             |
   |  132  | [PW-OAM]                                                  |
   |  133  | [PW-OAM]                                                  |
   |  134  | Section 5.3.5                                             |
   |  135  | [PW-OAM]                                                  |
   |  136  | Not Applicable to PW                                      |
   |  137  | Not Applicable to PW                                      |
   |  138  | [RFC4447], [RFC5003], [MS-PW-DYNAMIC]                     |
   | 139 - |                                                           |
   |   143 | [PW-OAM]                                                  |

         Table 2: PW Control (LDP) and MPLS-TP Requirements Table

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5.3.  Anticipated MPLS-TP-Related Extensions

   Existing control protocol and procedures will be reused as much as
   possible to support MPLS-TP.  However, when using PWs in MPLS-TP, a
   set of new requirements is defined that may require extensions of the
   existing control mechanisms.  This section clarifies the areas where
   extensions are needed based on the requirements that are related to
   the PW control plane and documented in [RFC5654].

   Table 2 lists how requirements defined in [RFC5654] are expected to
   be addressed.

   The baseline requirement for extensions to support transport
   applications is that any new mechanisms and capabilities must be able
   to interoperate with existing IETF MPLS [RFC3031] and IETF PWE3
   [RFC3985] control and data planes where appropriate.  Hence,
   extensions of the PW control plane must be in-line with the
   procedures defined in [RFC4447], [RFC6073], and [MS-PW-DYNAMIC].

5.3.1.  Extensions to Support Out-of-Band PW Control

   For MPLS-TP, it is required that the data and control planes can be
   both logically and physically separated.  That is, the PW control
   plane must be able to operate out-of-band (OOB).  This separation
   ensures, among other things, that in the case of control-plane
   failures the data plane is not affected and can continue to operate
   normally.  This was not a design requirement for the current PW
   control plane.  However, due to the PW concept, i.e., PWs are
   connecting logical entities ('forwarders'), and the operation of the
   PW control protocol, i.e., only edge PE nodes (T-PE, S-PE) take part
   in the signaling exchanges: moving T-LDP out-of-band seems to be,
   theoretically, a straightforward exercise.

   In fact, as a strictly local matter, ensuring that targeted LDP
   (T-LDP) uses out-of-band signaling requires only that the local
   implementation is configured in such a way that reachability for a
   target LSR address is via the out-of-band channel.

   More precisely, if IP addressing is used in the MPLS-TP control
   plane, then T-LDP addressing can be maintained, although all
   addresses will refer to control-plane entities.  Both the PWid
   Forwarding Equivalence Class (FEC) and Generalized PWid FEC Elements
   can possibly be used in an OOB case as well.  (Detailed evaluation is
   outside the scope of this document.)  The PW label allocation and
   exchange mechanisms should be reused without change.

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5.3.2.  Support for Explicit Control of PW-to-LSP Binding

   Binding a PW to an LSP, or PW segments to LSPs, is left to nodes
   acting as T-PEs and S-PEs or a control-plane entity that may be the
   same one signaling the PW.  However, an extension of the PW signaling
   protocol is required to allow the LSR at the signal initiation end to
   inform the targeted LSR (at the signal termination end) to which LSP
   the resulting PW is to be bound, in the event that more than one such
   LSP exists and the choice of LSPs is important to the service being
   setup (for example, if the service requires co-routed bidirectional
   paths).  This is also particularly important to support transport
   path (symmetric and asymmetric) bandwidth requirements.

   For transport services, MPLS-TP requires support for bidirectional
   traffic that follows congruent paths.  Currently, each direction of a
   PW or a PW segment is bound to a unidirectional LSP that extends
   between two T-PEs, two S-PEs, or a T-PE and an S-PE.  The
   unidirectional LSPs in both directions are not required to follow
   congruent paths, and therefore both directions of a PW may not follow
   congruent paths, i.e., they are associated bidirectional paths.  The
   only requirement in [RFC5659] is that a PW or a PW segment shares the
   same T-PEs in both directions and the same S-PEs in both directions.

   MPLS-TP imposes new requirements on the PW control plane, in
   requiring that both end points map the PW or PW segment to the same
   transport path for the case where this is an objective of the
   service.  When a bidirectional LSP is selected on one end to
   transport the PW, a mechanism is needed that signals to the remote
   end which LSP has been selected locally to transport the PW.  This
   would be accomplished by adding a new TLV to PW signaling.

   Note that this coincides with the gap identified for OOB support: a
   new mechanism is needed to allow explicit binding of a PW to the
   supporting transport LSP.

   The case of unidirectional transport paths may also require
   additional protocol mechanisms, as today's PWs are always
   bidirectional.  One potential approach for providing a unidirectional
   PW-based transport path is for the PW to associate different
   (asymmetric) bandwidths in each direction, with a zero or minimal
   bandwidth for the return path.  This approach is consistent with
   Section 3.8.2 of [RFC5921] but does not address P2MP paths.

5.3.3.  Support for Dynamic Transfer of PW Control/Ownership

   In order to satisfy requirement 47 (as defined in Section 2), it will
   be necessary to specify methods for transfer of PW ownership from the
   management to the control plane (and vice versa).

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5.3.4.  Interoperable Support for PW/LSP Resource Allocation

   Transport applications may require resource guarantees.  For such
   transport LSPs, resource reservation mechanisms are provided via
   RSVP-TE and the use of Diffserv.  If multiple PWs are multiplexed
   into the same transport LSP resources, contention may occur.
   However, local policy at PEs should ensure proper resource sharing
   among PWs mapped into a resource-guaranteed LSP.  In the case of
   MS-PWs, signaling carries the PW traffic parameters [MS-PW-DYNAMIC]
   to enable admission control of a PW segment over a resource-
   guaranteed LSP.

   In conjunction with explicit PW-to-LSP binding, existing mechanisms
   may be sufficient; however, this needs to be verified in detailed

5.3.5.  Support for PW Protection and PW OAM Configuration

   Many of the requirements listed in Section 2 are intended to support
   connectivity and performance monitoring (grouped together as OAM), as
   well as protection conformant with the transport services model.

   In general, protection of MPLS-TP transported services is provided by
   way of protection of transport LSPs.  PW protection requires that
   mechanisms be defined to support redundant pseudowires, including a
   mechanism already described above for associating such pseudowires
   with specific protected ("working" and "protection") LSPs.  Also
   required are definitions of local protection control functions, to
   include test/verification operations, and protection status signals
   needed to ensure that PW termination points are in agreement as to
   which of a set of redundant pseudowires are in use for which
   transport services at any given point in time.

   Much of this work is currently being done in documents [PW-RED] and
   [PW-REDB] that define, respectively, how to establish redundant
   pseudowires and how to indicate which is in use.  Additional work may
   be required.

   Protection switching may be triggered manually by the operator, or as
   a result of loss of connectivity (detected using the mechanisms of
   [RFC5085] and [RFC5586]), or service degradation (detected using
   mechanisms yet to be defined).

   Automated protection switching is just one of the functions for which
   a transport service requires OAM.  OAM is generally referred to as
   either "proactive" or "on-demand", where the distinction is whether a
   specific OAM tool is being used continuously over time (for the
   purpose of detecting a need for protection switching, for example) or

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   is only used -- either a limited number of times or over a short
   period of time -- when explicitly enabled (for diagnostics, for

   PW OAM currently consists of connectivity verification defined by
   [RFC5085].  Work is currently in progress to extend PW OAM to include
   bidirectional forwarding detection (BFD) in [RFC5885], and work has
   begun on extending BFD to include performance-related monitor

5.3.6.  Client-Layer and Cross-Provider Interfaces to PW Control

   Additional work is likely to be required to define consistent access
   by a client-layer network, as well as between provider networks, to
   control information available to each type of network, for example,
   about the topology of an MS-PW.  This information may be required by
   the client-layer network in order to provide hints that may help to
   avoid establishment of fate-sharing alternate paths.  Such work will
   need to fit within the ASON architecture; see requirement 38 above.

5.4.  ASON Architecture Considerations

   MPLS-TP PWs are always transported using LSPs, and these LSPs will
   either have been statically provisioned or signaled using GMPLS.

   For LSPs signaled using the MPLS-TP LSP control plane (GMPLS),
   conformance with the ASON architecture is as described in Section 1.2
   ("Basic Approach"), bullet 4, of this framework document.

   As discussed above in Section 5.3, there are anticipated extensions
   in the following areas that may be related to ASON architecture:

      - PW-to-LSP binding (Section 5.3.2)
      - PW/LSP resource allocation (Section 5.3.4)
      - PW protection and OAM configuration (Section 5.3.5)
      - Client-layer interfaces for PW control (Section 5.3.6)

   This work is expected to be consistent with ASON architecture and may
   require additional specification in order to achieve this goal.

6.  Security Considerations

   This document primarily describes how existing mechanisms can be used
   to meet the MPLS-TP control-plane requirements.  The documents that
   describe each mechanism contain their own security considerations
   sections.  For a general discussion on MPLS- and GMPLS-related

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   security issues, see the MPLS/GMPLS security framework [RFC5920].  As
   mentioned above in Section 2.4, there are no specific MPLS-TP
   control-plane security requirements.

   This document also identifies a number of needed control-plane
   extensions.  It is expected that the documents that define such
   extensions will also include any appropriate security considerations.

7.  Acknowledgments

   The authors would like to acknowledge the contributions of Yannick
   Brehon, Diego Caviglia, Nic Neate, Dave Mcdysan, Dan Frost, and Eric
   Osborne to this work.  We also thank Dan Frost in his help responding
   to Last Call comments.

8.  References

8.1.  Normative References

   [RFC2210]  Wroclawski, J., "The Use of RSVP with IETF Integrated
              Services", RFC 2210, September 1997.

   [RFC2211]  Wroclawski, J., "Specification of the Controlled-Load
              Network Element Service", RFC 2211, September 1997.

   [RFC2212]  Shenker, S., Partridge, C., and R. Guerin, "Specification
              of Guaranteed Quality of Service", RFC 2212, September

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031, January 2001.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, December 2001.

   [RFC3471]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Functional Description", RFC
              3471, January 2003.

   [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Resource ReserVation Protocol-
              Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
              January 2003.

   [RFC3478]  Leelanivas, M., Rekhter, Y., and R. Aggarwal, "Graceful
              Restart Mechanism for Label Distribution Protocol", RFC
              3478, February 2003.

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   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630, September

   [RFC4124]  Le Faucheur, F., Ed., "Protocol Extensions for Support of
              Diffserv-aware MPLS Traffic Engineering", RFC 4124, June

   [RFC4202]  Kompella, K., Ed., and Y. Rekhter, Ed., "Routing
              Extensions in Support of Generalized Multi-Protocol Label
              Switching (GMPLS)", RFC 4202, October 2005.

   [RFC4203]  Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF Extensions
              in Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4203, October 2005.

   [RFC4206]  Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
              Hierarchy with Generalized Multi-Protocol Label Switching
              (GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.

   [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,
              "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
              Use over an MPLS PSN", RFC 4385, February 2006.

   [RFC4447]  Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
              G. Heron, "Pseudowire Setup and Maintenance Using the
              Label Distribution Protocol (LDP)", RFC 4447, April 2006.

   [RFC4448]  Martini, L., Ed., Rosen, E., El-Aawar, N., and G. Heron,
              "Encapsulation Methods for Transport of Ethernet over MPLS
              Networks", RFC 4448, April 2006.

   [RFC4842]  Malis, A., Pate, P., Cohen, R., Ed., and D. Zelig,
              "Synchronous Optical Network/Synchronous Digital Hierarchy
              (SONET/SDH) Circuit Emulation over Packet (CEP)", RFC
              4842, April 2007.

   [RFC4863]  Martini, L. and G. Swallow, "Wildcard Pseudowire Type",
              RFC 4863, May 2007.

   [RFC4872]  Lang, J., Ed., Rekhter, Y., Ed., and D. Papadimitriou,
              Ed., "RSVP-TE Extensions in Support of End-to-End
              Generalized Multi-Protocol Label Switching (GMPLS)
              Recovery", RFC 4872, May 2007.

   [RFC4873]  Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
              "GMPLS Segment Recovery", RFC 4873, May 2007.

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

   [RFC4974]  Papadimitriou, D. and A. Farrel, "Generalized MPLS (GMPLS)
              RSVP-TE Signaling Extensions in Support of Calls", RFC
              4974, August 2007.

   [RFC5063]  Satyanarayana, A., Ed., and R. Rahman, Ed., "Extensions to
              GMPLS Resource Reservation Protocol (RSVP) Graceful
              Restart", RFC 5063, October 2007.

   [RFC5151]  Farrel, A., Ed., Ayyangar, A., and JP. Vasseur, "Inter-
              Domain MPLS and GMPLS Traffic Engineering -- Resource
              Reservation Protocol-Traffic Engineering (RSVP-TE)
              Extensions", RFC 5151, February 2008.

   [RFC5287]  Vainshtein, A. and Y(J). Stein, "Control Protocol
              Extensions for the Setup of Time-Division Multiplexing
              (TDM) Pseudowires in MPLS Networks", RFC 5287, August

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, October 2008.

   [RFC5307]  Kompella, K., Ed., and Y. Rekhter, Ed., "IS-IS Extensions
              in Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 5307, October 2008.

   [RFC5316]  Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
              Support of Inter-Autonomous System (AS) MPLS and GMPLS
              Traffic Engineering", RFC 5316, December 2008.

   [RFC5392]  Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in
              Support of Inter-Autonomous System (AS) MPLS and GMPLS
              Traffic Engineering", RFC 5392, January 2009.

   [RFC5467]  Berger, L., Takacs, A., Caviglia, D., Fedyk, D., and J.
              Meuric, "GMPLS Asymmetric Bandwidth Bidirectional Label
              Switched Paths (LSPs)", RFC 5467, March 2009.

   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586, June 2009.

   [RFC5654]  Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
              Sprecher, N., and S. Ueno, "Requirements of an MPLS
              Transport Profile", RFC 5654, September 2009.

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   [RFC5860]  Vigoureux, M., Ed., Ward, D., Ed., and M. Betts, Ed.,
              "Requirements for Operations, Administration, and
              Maintenance (OAM) in MPLS Transport Networks", RFC 5860,
              May 2010.

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

   [RFC5960]  Frost, D., Ed., Bryant, S., Ed., and M. Bocci, Ed., "MPLS
              Transport Profile Data Plane Architecture", RFC 5960,
              August 2010.

   [RFC6370]  Bocci, M., Swallow, G., and E. Gray, "MPLS Transport
              Profile (MPLS-TP) Identifiers", RFC 6370, September 2011.

   [RFC6371]  Busi, I., Ed., and D. Allan, Ed., "Operations,
              Administration, and Maintenance Framework for MPLS-Based
              Transport Networks", RFC 6371, September 2011.

   [RFC6372]  Sprecher, N., Ed., and A. Farrel, Ed., "MPLS Transport
              Profile (MPLS-TP) Survivability Framework", RFC 6372,
              September 2011.

8.2.  Informative References

              Bellagamba, E., Ed., Andersson, L., Ed., Skoldstrom, P.,
              Ed., Ward, D., and A. Takacs, "Configuration of Pro-Active
              Operations, Administration, and Maintenance (OAM)
              Functions for MPLS-based Transport Networks using RSVP-
              TE", Work in Progress, July 2011.

              Takacs, A., Fedyk, D., and J. He, "GMPLS RSVP-TE
              extensions for OAM Configuration", Work in Progress, July

   [GMPLS-PS] Takacs, A., Fondelli, F., and B. Tremblay, "GMPLS RSVP-TE
              Recovery Extension for data plane initiated reversion and
              protection timer signalling", Work in Progress, April

              International Telecommunication Union, "Architecture for
              the automatically switched optical network (ASON)", ITU-T
              Recommendation G.8080, June 2006.

Top      Up      ToC       Page 52 
              International Telecommunication Union, "Architecture for
              the automatically switched optical network (ASON)
              Amendment 1", ITU-T Recommendation G.8080 Amendment 1,
              March 2008.

              Martini, L., Ed., Bocci, M., Ed., and F. Balus, Ed.,
              "Dynamic Placement of Multi Segment Pseudowires", Work in
              Progress, July 2011.

   [NO-PHP]   Ali, z., et al, "Non Penultimate Hop Popping Behavior and
              out-of-band mapping for RSVP-TE Label Switched Paths",
              Work in Progress, August 2011.

   [PW-OAM]   Zhang, F., Ed., Wu, B., Ed., and E. Bellagamba, Ed., "
              Label Distribution Protocol Extensions for Proactive
              Operations, Administration and Maintenance Configuration
              of Dynamic MPLS Transport Profile PseudoWire", Work in
              Progress, August 2011.

   [PW-P2MPE] Aggarwal, R. and F. Jounay, "Point-to-Multipoint Pseudo-
              Wire Encapsulation", Work in Progress, March 2010.

   [PW-P2MPR] Jounay, F., Ed., Kamite, Y., Heron, G., and M. Bocci,
              "Requirements and Framework for Point-to-Multipoint
              Pseudowire", Work in Progress, July 2011.

   [PW-RED]   Muley, P., Ed., Aissaoui, M., Ed., and M. Bocci,
              "Pseudowire Redundancy", Work in Progress, July 2011.

   [PW-REDB]  Muley, P., Ed., and M. Aissaoui, Ed., "Preferential
              Forwarding Status Bit", Work in Progress, March 2011.

   [RFC3270]  Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
              P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-
              Protocol Label Switching (MPLS) Support of Differentiated
              Services", RFC 3270, May 2002.

   [RFC3468]  Andersson, L. and G. Swallow, "The Multiprotocol Label
              Switching (MPLS) Working Group decision on MPLS signaling
              protocols", RFC 3468, February 2003.

   [RFC3472]  Ashwood-Smith, P., Ed., and L. Berger, Ed., "Generalized
              Multi-Protocol Label Switching (GMPLS) Signaling
              Constraint-based Routed Label Distribution Protocol (CR-
              LDP) Extensions", RFC 3472, January 2003.

Top      Up      ToC       Page 53 
   [RFC3477]  Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links
              in Resource ReSerVation Protocol - Traffic Engineering
              (RSVP-TE)", RFC 3477, January 2003.

   [RFC3812]  Srinivasan, C., Viswanathan, A., and T. Nadeau,
              "Multiprotocol Label Switching (MPLS) Traffic Engineering
              (TE) Management Information Base (MIB)", RFC 3812, June

   [RFC3813]  Srinivasan, C., Viswanathan, A., and T. Nadeau,
              "Multiprotocol Label Switching (MPLS) Label Switching
              Router (LSR) Management Information Base (MIB)", RFC 3813,
              June 2004.

   [RFC3945]  Mannie, E., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Architecture", RFC 3945, October 2004.

   [RFC3985]  Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation
              Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005.

   [RFC4139]  Papadimitriou, D., Drake, J., Ash, J., Farrel, A., and L.
              Ong, "Requirements for Generalized MPLS (GMPLS) Signaling
              Usage and Extensions for Automatically Switched Optical
              Network (ASON)", RFC 4139, July 2005.

   [RFC4201]  Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling
              in MPLS Traffic Engineering (TE)", RFC 4201, October 2005.

   [RFC4208]  Swallow, G., Drake, J., Ishimatsu, H., and Y. Rekhter,
              "Generalized Multiprotocol Label Switching (GMPLS) User-
              Network Interface (UNI): Resource ReserVation Protocol-
              Traffic Engineering (RSVP-TE) Support for the Overlay
              Model", RFC 4208, October 2005.

   [RFC4258]  Brungard, D., Ed., "Requirements for Generalized Multi-
              Protocol Label Switching (GMPLS) Routing for the
              Automatically Switched Optical Network (ASON)", RFC 4258,
              November 2005.

   [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol
              Label Switched (MPLS) Data Plane Failures", RFC 4379,
              February 2006.

   [RFC4426]  Lang, J., Ed., Rajagopalan, B., Ed., and D. Papadimitriou,
              Ed., "Generalized Multi-Protocol Label Switching (GMPLS)
              Recovery Functional Specification", RFC 4426, March 2006.

Top      Up      ToC       Page 54 
   [RFC4427]  Mannie, E., Ed., and D. Papadimitriou, Ed., "Recovery
              (Protection and Restoration) Terminology for Generalized
              Multi-Protocol Label Switching (GMPLS)", RFC 4427, March

   [RFC4553]  Vainshtein, A., Ed., and YJ. Stein, Ed., "Structure-
              Agnostic Time Division Multiplexing (TDM) over Packet
              (SAToP)", RFC 4553, June 2006.

   [RFC4618]  Martini, L., Rosen, E., Heron, G., and A. Malis,
              "Encapsulation Methods for Transport of PPP/High-Level
              Data Link Control (HDLC) over MPLS Networks", RFC 4618,
              September 2006.

   [RFC4619]  Martini, L., Ed., Kawa, C., Ed., and A. Malis, Ed.,
              "Encapsulation Methods for Transport of Frame Relay over
              Multiprotocol Label Switching (MPLS) Networks", RFC 4619,
              September 2006.

   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              August 2006.

   [RFC4783]  Berger, L., Ed., "GMPLS - Communication of Alarm
              Information", RFC 4783, December 2006.

   [RFC4802]  Nadeau, T., Ed., and A. Farrel, Ed., "Generalized
              Multiprotocol Label Switching (GMPLS) Traffic Engineering
              Management Information Base", RFC 4802, February 2007.

   [RFC4803]  Nadeau, T., Ed., and A. Farrel, Ed., "Generalized
              Multiprotocol Label Switching (GMPLS) Label Switching
              Router (LSR) Management Information Base", RFC 4803,
              February 2007.

   [RFC4816]  Malis, A., Martini, L., Brayley, J., and T. Walsh,
              "Pseudowire Emulation Edge-to-Edge (PWE3) Asynchronous
              Transfer Mode (ATM) Transparent Cell Transport Service",
              RFC 4816, February 2007.

   [RFC4875]  Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
              Yasukawa, Ed., "Extensions to Resource Reservation
              Protocol - Traffic Engineering (RSVP-TE) for Point-to-
              Multipoint TE Label Switched Paths (LSPs)", RFC 4875, May

Top      Up      ToC       Page 55 
   [RFC5003]  Metz, C., Martini, L., Balus, F., and J. Sugimoto,
              "Attachment Individual Identifier (AII) Types for
              Aggregation", RFC 5003, September 2007.

   [RFC5036]  Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
              "LDP Specification", RFC 5036, October 2007.

   [RFC5085]  Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire
              Virtual Circuit Connectivity Verification (VCCV): A
              Control Channel for Pseudowires", RFC 5085, December 2007.

   [RFC5145]  Shiomoto, K., Ed., "Framework for MPLS-TE to GMPLS
              Migration", RFC 5145, March 2008.

   [RFC5440]  Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              March 2009.

   [RFC5493]  Caviglia, D., Bramanti, D., Li, D., and D. McDysan,
              "Requirements for the Conversion between Permanent
              Connections and Switched Connections in a Generalized
              Multiprotocol Label Switching (GMPLS) Network", RFC 5493,
              April 2009.

   [RFC5659]  Bocci, M. and S. Bryant, "An Architecture for Multi-
              Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
              October 2009.

   [RFC5787]  Papadimitriou, D., "OSPFv2 Routing Protocols Extensions
              for Automatically Switched Optical Network (ASON)
              Routing", RFC 5787, March 2010.

   [RFC5852]  Caviglia, D., Ceccarelli, D., Bramanti, D., Li, D., and S.
              Bardalai, "RSVP-TE Signaling Extension for LSP Handover
              from the Management Plane to the Control Plane in a GMPLS-
              Enabled Transport Network", RFC 5852, April 2010.

   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
              "Bidirectional Forwarding Detection (BFD) for MPLS Label
              Switched Paths (LSPs)", RFC 5884, June 2010.

   [RFC5885]  Nadeau, T., Ed., and C. Pignataro, Ed., "Bidirectional
              Forwarding Detection (BFD) for the Pseudowire Virtual
              Circuit Connectivity Verification (VCCV)", RFC 5885, June

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, July 2010.

Top      Up      ToC       Page 56 
   [RFC5951]  Lam, K., Mansfield, S., and E. Gray, "Network Management
              Requirements for MPLS-based Transport Networks", RFC 5951,
              September 2010.

   [RFC6001]  Papadimitriou, D., Vigoureux, M., Shiomoto, K., Brungard,
              D., and JL. Le Roux, "Generalized MPLS (GMPLS) Protocol
              Extensions for Multi-Layer and Multi-Region Networks
              (MLN/MRN)", RFC 6001, October 2010.

   [RFC6073]  Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
              Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011.

   [RFC6107]  Shiomoto, K., Ed., and A. Farrel, Ed., "Procedures for
              Dynamically Signaled Hierarchical Label Switched Paths",
              RFC 6107, February 2011.

   [RFC6215]  Bocci, M., Levrau, L., and D. Frost, "MPLS Transport
              Profile User-to-Network and Network-to-Network
              Interfaces", RFC 6215, April 2011.

   [TE-MIB]   Miyazawa, M., Otani, T., Kumaki, K., and T. Nadeau,
              "Traffic Engineering Database Management Information Base
              in support of MPLS-TE/GMPLS", Work in Progress, July 2011.

   [TP-MIB]   King, D., Ed., and M. Venkatesan, Ed., "Multiprotocol
              Label Switching Transport Profile (MPLS-TP) MIB-based
              Management Overview", Work in Progress, August 2011.

              Frost, D., Ed., Bocci, M., Ed., and L. Berger, Ed., "A
              Framework for Point-to-Multipoint MPLS in Transport
              Networks", Work in Progress, July 2011.

   [TP-RING]  Weingarten, Y., Ed., "MPLS-TP Ring Protection", Work in
              Progress, June 2011

9.  Contributing Authors

   Attila Takacs
   1. Laborc u.
   Budapest 1037

   Martin Vigoureux

Top      Up      ToC       Page 57 
   Elisa Bellagamba
   Farogatan, 6
   164 40, Kista, Stockholm

Authors' Addresses

   Loa Andersson (editor)
   Phone: +46 10 717 52 13

   Lou Berger (editor)
   LabN Consulting, L.L.C.
   Phone: +1-301-468-9228

   Luyuan Fang (editor)
   Cisco Systems, Inc.
   111 Wood Avenue South
   Iselin, NJ 08830

   Nabil Bitar (editor)
   60 Sylvan Road
   Waltham, MA 02451

   Eric Gray (editor)
   900 Chelmsford Street
   Lowell, MA 01851
   Phone: +1 978 275 7470