A Framework for MPLS in Transport Networks
draft-ietf-mpls-tp-framework-01

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Abstract

This document specifies an archiectectural framework for the application of MPLS in transport networks. It describes a profile of MPLS that enables operational models typical in transport networks networks, while providing additional OAM, survivability and other maintenance functions not currently supported by MPLS.

Requirements Language

Although this document is not a protocol specification, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119] and are to be interpreted as instructions to the protocol designers producing solutions that satisfy the architectural concepts set out in this document..

Table of Contents

1.  Introduction
    1.1.  Motivation and Background
    1.2.  Applicability
    1.3.  Scope
    1.4.  Terminology
2.  Introduction to Requirements
3.  Transport Profile Overview
    3.1.  Packet Transport Services
    3.2.  Architecture
    3.3.  MPLS-TP Forwarding Domain
    3.4.  MPLS-TP Transport Domain
    3.5.  Addressing
    3.6.  Operations, Administration and Maintenance (OAM)
    3.7.  Generic Associated Channel (G-ACh)
    3.8.  Control Plane
        3.8.1.  PW Control Plane
        3.8.2.  LSP Control Plane
    3.9.  Static Operation of LSPs and PWs
    3.10.  Survivability
    3.11.  Network Management
4.  Security Considerations
5.  IANA Considerations
6.  Acknowledgements
7.  References
    7.1.  Normative References
    7.2.  Informative References

1.  Introduction

1.1.  Motivation and Background

This document describes a framework for a Multiprotocol Label Switching Transport Profile (MPLS-TP). It presents the architectural framework for MPLS-TP, definining those elements of MPLS applicable to supporting the requirements in [I‑D.ietf‑mpls‑tp‑requirements] (Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S. Ueno, “MPLS-TP Requirements,” August 2009.) and what new protocol elements are required.

Bandwidth demand continues to grow worldwide, stimulated by the accelerating growth and penetration of new packet based services and multimedia applications:

• Packet-based services such as Ethernet, Voice over IP (VoIP), Layer 2 (L2)/Layer 3 (L3) Virtual Private Networks (VPNs), IP Television (IPTV), Radio Access Network (RAN) backhauling, etc.,
• Applications with various bandwidth and Quality of Service (QoS) requirements.

This growth in demand has resulted in dramatic increases in access rates that are, in turn, driving dramatic increases in metro and core network bandwidth requirements.

Over the past two decades, the evolving optical transport infrastructure (Synchronous Optical Networking (SONET)/Synchronous Digital Hierarchy (SDH), Optical Transport Network (OTN)) has provided carriers with a high benchmark for reliability and operational simplicity. To achieve this, these existing transport technologies have been designed with specific characteristics :

• Strictly connection-oriented connectivity, which may be long-lived and may be provisioned manually or by network management.
• A high level of protection and availability.
• Quality of service.
• Extended OAM capabilities.

Carriers are looking to evolve such transport networks to support packet based services and networks, and to take advantage of the flexibility and cost benefits of packet switching technology. While MPLS is a maturing packet technology that is already playing an important role in transport networks and services, not all of MPLS's capabilities and mechanisms are needed and/or consistent with transport network operations. There are also transport technology characteristics that are not currently reflected in MPLS.

The types of packet transport services delivered by transport networks are very similar to Layer 2 Virtual Private Networks defined by the IETF.

There are thus two objectives for MPLS-TP:

1. To enable MPLS to be deployed in a transport network and operated in a similar manner to existing transport technologies.
2. To enable MPLS to support packet transport services with a similar degree of predictability to that found in existing transport networks.

In order to achieve these objectives, there is a need to create a common set of new functions that are applicable to both MPLS networks in general, and those blonging to the MPLS-TP profile.

MPLS-TP therefore defines a profile of MPLS targeted at transport applications and networks. This profile specifies the specific MPLS characteristics and extensions required to meet transport requirements. An equipment conforming to MPLS-TP MUST support this profile. An MPLS-TP conformant equipment MAY support additional MPLS features. A carrier may deploy some of those additional features in the transport layer of their network if they find them to be beneficial.

1.2.  Applicability

Figure 1 (MPLS-TP Applicability) illustrates the range of services that MPLS-TP is intended to address. MPLS-TP is intended to support a range of layer 1, layer 2 and layer 3 services, and is not limited to layer 3 services only. Networks implementing MPLS-TP may choose to only support a subset of these services.

                                          MPLS-TP Solution exists
                                           over this spectrum
                                  |<-------------------------------->|

cl-ps                      Multi-Service                     co-cs & co-ps
                          (cl-ps & co-ps)                      (Label is
  |                               |                        service context)
  |                               |                                  |
  |<------------------------------|--------------------------------->|
  |                               |                                  |
L3 Only                 L1, L2, L3 Services                 L1, L2 Services
                        Pt-Pt, Pt-MP, MP-MP                Pt-Pt and Pt-MP

The diagram above shows the spectrum of services that can be supported by MPLS. MPLS-TP solutions are primarily intended for packet transport applications. These can be deployed using a profile of MPLS that is strictly connection oriented and does not rely on IP forwarding or routing (shown on the right hand side of the figure), or in conjunction with an MPLS network that does use IP forwarding and that supports a broader range of IP services. This is the multi-service solution in the centre of the figure.

1.3.  Scope

This document describes a framework for a Tranport Profile of Multiprotocol Label Switching (MPLS-TP). It presents the architectural framework for MPLS-TP, definining those elements of MPLS applicable to supporting the requirements in [I‑D.ietf‑mpls‑tp‑requirements] (Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S. Ueno, “MPLS-TP Requirements,” August 2009.) and what new protocol elements are required.

This document describes the architecture for MPLS-TP when the LSP client is a PW. The transport of IP and MPLS, other than carried over a PW, is outside the scope of this document. This does not preclude the use of LSPs conforming to the MPLS transport profile from being used to carry IP or other MPLS LSPs by general purpose MPLS networks.

1.4.  Terminology

Detailed definitions and additional terminology may be found in [I‑D.ietf‑mpls‑tp‑requirements] (Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S. Ueno, “MPLS-TP Requirements,” August 2009.).

2.  Introduction to Requirements

The requirements for MPLS-TP are specified in [I‑D.ietf‑mpls‑tp‑requirements] (Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S. Ueno, “MPLS-TP Requirements,” August 2009.), [I‑D.ietf‑mpls‑tp‑oam‑requirements] (Vigoureux, M. and D. Ward, “Requirements for OAM in MPLS Transport Networks,” March 2010.), and [I‑D.ietf‑mpls‑tp‑nm‑req] (Mansfield, S. and K. Lam, “MPLS TP Network Management Requirements,” October 2009.). This section provides a brief reminder to guide the reader. It is not intended as a substitute for these documents.

MPLS-TP MUST NOT modify the MPLS forwarding architecture and MUST be based on existing pseudowire and LSP constructs. Any new mechanisms and capabilities added to support transport networks and packet transport services must be able to interoperate with existing MPLS and pseudowire control and forwarding planes.

Point to point LSPs MAY be unidirectional or bi-directional, and it MUST be possible to construct congruent Bi-directional LSPs. Point to multipoint LSPs are unidirectional.

MPLS-TP LSPs do not merge with other LSPs at an MPLS-TP LSR and it MUST be possible to detect if a merged LSP has been created.

It MUST be possible to forward packets solely based on switching the MPLS or PW label. It MUST also be possible to establish and maintain LSPs and/or pseudowires both in the absence or presence of a dynamic control plane. When static provisioning is used, there MUST be no dependency on dynamic routing or signaling.

OAM, protection and forwarding of data packets MUST be able to operate without IP forwarding support.

It MUST be possible to monitor LSPs and pseudowires through the use of OAM in the absence of control plane or routing functions. In this case information gained from the OAM functions is used to initiate path recovery actions at either the PW or LSP layers.

3.  Transport Profile Overview

3.1.  Packet Transport Services

The types of packet transport services provided by existing transport networks are similar to MPLS Layer 2 VPNs. A key characteristic of packet transport services is that the network used to provide the service does not participate in the any IP routing protocols present in the client, or use the IP addresses in client packets to forward those packets. The network is therefore transparent to IP in the client service.

MPLS-TP MUST use one of the Layer 2 VPN services defined in [PPVPN architecture] to provide a packet transport service.

MPLS-TP LSPs MAY also be used to transport traffic for which the immediate client of the MPLS-TP LSP is not a Layer 2 VPN. However, for the purposes of this document, we do not refer to these traffic types as belonging to a packet transport service. Such clients include IP and MPLS LSPs.

3.2.  Architecture

The architecture for a transport profile of MPLS (MPLS-TP) is based on the MPLS [RFC3031] (Rosen, E., Viswanathan, A., and R. Callon, “Multiprotocol Label Switching Architecture,” January 2001.), pseudowire [RFC3985] (Bryant, S. and P. Pate, “Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture,” March 2005.), and multi-segment pseudowire [I‑D.ietf‑pwe3‑ms‑pw‑arch] (Bocci, M. and S. Bryant, “An Architecture for Multi-Segment Pseudowire Emulation Edge-to-Edge,” July 2009.) architectures, as illustrated in Figure 2 (MPLS-TP Architecture (Single Segment PW)).

            |<-------------- Emulated Service ---------------->|
            |                                                  |
            |          |<------- Pseudo Wire ------>|          |
            |          |                            |          |
            |          |    |<-- PSN Tunnel -->|    |          |
            |          V    V                  V    V          |
            V    AC    +----+                  +----+     AC   V
      +-----+    |     | PE1|==================| PE2|     |    +-----+
      |     |----------|............PW1.............|----------|     |
      | CE1 |    |     |    |                  |    |     |    | CE2 |
      |     |----------|............PW2.............|----------|     |
      +-----+  ^ |     |    |==================|    |     | ^  +-----+
            ^  |       +----+                  +----+     | |  ^
            |  |   Provider Edge 1         Provider Edge 2  |  |
            |  |                                            |  |
      Customer |                                            | Customer
      Edge 1   |                                            | Edge 2
               |                                            |
               |                                            |
         Native service                               Native service

       Native  |<------------Pseudowire-------------->|  Native
       Service |         PSN              PSN         |  Service
        (AC)   |     |<--cloud->|     |<-cloud-->|    |   (AC)
          |    V     V          V     V          V    V     |
          |    +----+           +-----+          +----+     |
   +----+ |    |TPE1|===========|SPE1 |==========|TPE2|     | +----+
   |    |------|..... PW.Seg't1.........PW.Seg't3.....|-------|    |
   | CE1| |    |    |           |     |          |    |     | |CE2 |
   |    |------|..... PW.Seg't2.........PW.Seg't4.....|-------|    |
   +----+ |    |    |===========|     |==========|    |     | +----+
        ^      +----+     ^     +-----+     ^    +----+       ^
        |                 |                 |                 |
        |              TE LSP            TE LSP               |
        |                                                     |
        |                                                     |
        |<---------------- Emulated Service ----------------->|

The above figures illustrates the MPLS-TP architecture used to provide a point-to-point packet transport service, or VPWS. In this case, the MPLS-TP forwarding plane is a profile of the MPLS LSP and SS-PW or MS-PW forwarding architecture as detailed in section Section 3.3 (MPLS-TP Forwarding Domain).

This document describes the architecture for MPLS-TP when the LSP client is a PW. The transport of IP and MPLS, other than carried over a PW, is outside the scope of this document. This does not preclude the use of LSPs conforming to the MPLS transport profile from being used to carry IP or other MPLS LSPs by general purpose MPLS networks. LSP hierarchy MAY be used within the MPLS-TP network, so that more than one LSP label MAY appear in the label stack.

          +---------------------------+
          |     PW Native service     |
          /===========================\
          H     PW Encapsulation      H \   <---- PW Control word
          H---------------------------H  \  <---- Normalised client
          H         PW OAM            H     MPLS-TP channel
          H---------------------------H  /
          H     PW Demux (S=1)        H /
          H---------------------------H \
          H         LSP OAM           H  \
          H---------------------------H  / MPLS-TP Path(s)
          H     LSP Demultiplexer(s)  H /
          \===========================/
          |           Server          |
          +---------------------------+

When providing a VPWS, VPLS, VPMS or IPLS, pseudowires MUST be used to carry a client service. For compatibility with transport nomenclature, the PW may be referred to as the MPLS-TP Channel and the LSP may be referred to as the MPLS-TP Path.

Note that in MPLS-TP environments where IP is used for control or OAM purposes, IP MAY be carried over the LSP demultiplexers as per RFC3031 [RFC3031] (Rosen, E., Viswanathan, A., and R. Callon, “Multiprotocol Label Switching Architecture,” January 2001.), or directly over the server.

PW OAM, PSN OAM and PW client data are mutually exclusive and never exist in the same packet.

The MPLS-TP definition applies to the following two domains:

• MPLS-TP Forwarding Domain
• MPLS-TP Transport Domain

3.3.  MPLS-TP Forwarding Domain

A set of client-to-MPLS-TP adaptation functions interface the client to MPLS-TP. For pseudowires, this adaptation function is the PW forwarder shown in Figure 4a of [RFC3985] (Bryant, S. and P. Pate, “Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture,” March 2005.). The PW label is used for forwarding in this case and is always at the bottom of the label stack. The operation of the MPLS-TP network is independent of the payload carried by the MPLS-TP PW packet.

MPLS-TP is itself a client of an underlying server layer. MPLS-TP is thus bounded by a set of adaptation functions to this server layer network. These adaptation functions provide encapsulation of the MPLS-TP frames and for the transparent transport of those frames over the server layer network. The MPLS-TP client inherits its QoS from the MPLS-TP network, which in turn inherits its QoS from the server layer. The server layer must therefore provide the neccesary Quality of Service (QoS) to ensure that the MPLS-TP client QoS commitments are satisfied.

MPLS-TP LSPs use the MPLS label switching operations defined in [RFC3031] (Rosen, E., Viswanathan, A., and R. Callon, “Multiprotocol Label Switching Architecture,” January 2001.). These operations are highly optimized for performance and are not modified by the MPLS-TP profile.

During forwarding a label is pushed to associate a forwarding equivalence class (FEC) with the LSP or PW. This specifies the processing operaton to be performed by the next hop at that level of encapsulation. A swap of this label is an atomic operation in which the contents of the packet after the swapped label are opaque to the forwarder. The only event that interrupts a swap operation is TTL expiry, in which case the packet may be inspected and either discarded or subjected to further processing within the LSR. TTL expiry causes an exception which forces a packet to be further inspected and processed. While this occurs, the forwarding of succeeding packets continues without interruption. Therefore, the only way to cause a P (intermediate) LSR to inspect a packet (for example for OAM purposes) is to set the TTL to expire at that LSR.

MPLS-TP PWs support the PW and MS-PW forwarding operations defined in[RFC3985] (Bryant, S. and P. Pate, “Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture,” March 2005.) and [I‑D.ietf‑pwe3‑ms‑pw‑arch] (Bocci, M. and S. Bryant, “An Architecture for Multi-Segment Pseudowire Emulation Edge-to-Edge,” July 2009.).

The Traffic Class field (formerly the MPLS EXP field) follows the definition and processing rules of [RFC5462] (Andersson, L. and R. Asati, “Multiprotocol Label Switching (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic Class" Field,” February 2009.) and [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,” May 2002.). Only the pipe and short-pipe models are supported in MPLS-TP.

The MPLS encapsulation format is as defined in RFC 3032[RFC3032] (Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, “MPLS Label Stack Encoding,” January 2001.). Per-platform label space is used for PWs. Either per-platform or per-interface label space may be used for LSPs.

Point to point MPLS-TP LSPs can be either unidirectional or bidirectional. Point-to-multipoint MPLS-TP LSPs are unidirectional. Point-to-multipont PWs are currently being defined in the IETF and may be incorporated in MPLS-TP if required.

It MUST be possible to configure an MPLS-TP LSP such that the forward and backward directions of a bidirectional MPLS-TP LSP are co-routed i.e. they follow the same path. The pairing relationship between the forward and the backward directions must be known at each LSR or LER on a bidirectional LSP.

Per-packet equal cost multi-path (ECMP) load balancing is not applicable to MPLS-TP LSPs.

Penultimate hop popping (PHP) is disabled on MPLS-TP LSPs by default.

Both E-LSP and L-LSP are supported in MPLS-TP, as defined in RFC 3270 [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,” May 2002.)

3.4.  MPLS-TP Transport Domain

This document specifies the architecture when the client of the MPLS-TP LSP is a PW. Note, however, that in MPLS-TP environments where IP is used for control or OAM purposes, IP MAY be carried over the the LSPs or directly over the server, as described in Section 3.2 (Architecture). In this case, the MPLS-TP transport domain consists of the PW encapsulation mechanisms, including the PW control word.

3.5.  Addressing

Editor's note: This section will be updated after publication of the MPLS-TP Addressing Architecture draft.

MPLS-TP distinguishes between adressing used to identify nodes in the network, and identifiers used for demultiplexing and forwarding. This distinction is illustrated in Figure 4 (Addressing in MPLS-TP).

                          NMS                   Control/Signalling
                              .....         .....
                         [Address]|         |   [Address]
                                  |         |
                            +-----+---------+------+
    Address = Node          |     |         |      |
    ID in forwarding plane  |     V         V      |
                            |                      |
                            |     MEP or MIP       |
                            | dmux                 |
                            | svcid                |
                            | src                  |
                            +--^-------------------+
                               |
   OAM:                OAM     |
     dmux= [GAL/GACH]...........
              or       ________________________________________
             IP       (________________________________________)
     svc context=ID/FEC             PWE=ID1
     SRC=IP                           .
                                      .
                                     IDx

Editor's note: The figure above arose from discussions in the MPLS-TP design team. It will be clarified in a future verson of this draft.

IPv4 or IPv6 addresses are used to identify MPLS-TP nodes by default for network management and signaling purposes.

In the forwarding plane, identfiers are required for the service context (provided by the FEC), and for OAM. OAM requires both a demultiplexer and an address for the source of the OAM packet.

For MPLS in general where IP addressing is used, IPv4 or IPv6 is used by default. However, MPLS-TP must be able to operate in environments where IP is not used in the forwarding plane. Therefore, the default mechanism for OAM demultiplexing in MPLS-TP LSPs and PWs is the generic associated channel. Forwarding based on IP addresses for user or OAM packets is NOT REQUIRED for MPLS-TP.

RFC 4379 [RFC4379] (Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” February 2006.)and BFD for MPLS LSPs [I‑D.ietf‑bfd‑mpls] (Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, “BFD For MPLS LSPs,” June 2008.) have defined alert mechanisms that enable a MPLS LSR to identify and process MPLS OAM packets when the OAM packets are encapsulated in an IP header. These alert mechanisms are based on TTL expiration and/or use an IP destination address in the range 127/8. These mechanisms are the default mechanisms for MPLS networks in general for identifying MPLS OAM packets when the OAM packets are encapsulated in an IP header. MPLS-TP must not rely on these mechanisms, and thus relies on the GACH/GAL to demultiplex OAM packets.

3.6.  Operations, Administration and Maintenance (OAM)

MPLS-TP supports a comprehensive set of OAM capabilities for packet transport applications, with equivalent capabilities to those provided in SONET/SDH.

MPLS-TP defines mechanisms to differentiate specific packets (e.g. OAM, APS, MCC or SCC) from those carrying user data packets on the same LSP. These mechanisms are described in RFC5586 [RFC5586] (Bocci, M., Vigoureux, M., and S. Bryant, “MPLS Generic Associated Channel,” June 2009.).

MPLS-TP requires [I‑D.ietf‑mpls‑tp‑oam‑requirements] (Vigoureux, M. and D. Ward, “Requirements for OAM in MPLS Transport Networks,” March 2010.) that a set of OAM capabilities is available to perform fault management (e.g. fault detection and localization) and performance monitoring (e.g. packet delay and loss measurement) of the LSP, PW or section. The framework for OAM in MPLS-TP is specified in [I‑D.ietf‑mpls‑tp‑oam‑framework] (Allan, D., Busi, I., Niven-Jenkins, B., Fulignoli, A., Hernandez-Valencia, E., Levrau, L., Mohan, D., Sestito, V., Sprecher, N., Helvoort, H., Vigoureux, M., Weingarten, Y., and R. Winter, “MPLS-TP OAM Framework,” April 2010.).

OAM and monitoring in MPLS-TP is based on the concept of maintenance entities, as described in [I‑D.ietf‑mpls‑tp‑oam‑framework] (Allan, D., Busi, I., Niven-Jenkins, B., Fulignoli, A., Hernandez-Valencia, E., Levrau, L., Mohan, D., Sestito, V., Sprecher, N., Helvoort, H., Vigoureux, M., Weingarten, Y., and R. Winter, “MPLS-TP OAM Framework,” April 2010.). A Maintenance Entity can be viewed as the association of two (or more) Maintenance End Points (MEPs) (see example in Figure 5 (Example of MPLS-TP OAM ) ). The MEPs that form an ME should be configured and managed to limit the OAM responsibilities of an OAM flow within a network or sub- network, or a transport path or segment, in the specific layer network that is being monitored and managed.

Each OAM flow is associated with a single ME. Each MEP within an ME resides at the boundaries of that ME. An ME may also include a set of zero or more Maintenance Intermediate Points (MIPs), which reside within the Maintenance Entity. Maintenance end points (MEPs) are capable of sourcing and sinking OAM flows, while maintenance intermediate points (MIPs) can only sink or respond to OAM flows.

========================== End to End LSP OAM ============================
     .....                     .....         .....            .....
-----|MIP|---------------------|MIP|---------|MIP|------------|MIP|-----
     '''''                     '''''         '''''            '''''

     |<-------- Carrier 1 --------->|        |<--- Carrier 2 ----->|
      ----     ---     ---      ----          ----     ---     ----
 NNI |    |   |   |   |   |    |    |  NNI   |    |   |   |   |    | NNI
-----| PE |---| P |---| P |----| PE |--------| PE |---| P |---| PE |-----
     |    |   |   |   |   |    |    |        |    |   |   |   |    |
      ----     ---     ---      ----          ----     ---     ----

      ==== Segment LSP OAM ======  == Seg't ==  === Seg't LSP OAM ===
            (Carrier 1)             LSP OAM         (Carrier 2)
                                (inter-carrier)
      .....   .....   .....  ..........   ..........  .....    .....
      |MEP|---|MIP|---|MIP|--|MEP||MEP|---|MEP||MEP|--|MIP|----|MEP|
      '''''   '''''   '''''  ''''''''''   ''''''''''  '''''    '''''
      <------------ ME ----------><--- ME ----><------- ME -------->

Note: MEPs for End-to-end LSP OAM exist outside of the scope of this figure.

Figure 6 (MPLS-TP OAM archtecture) illustrates how the concept of Maintenance Entities can be mapped to sections, LSPs and PWs in an MPLS-TP network that uses MS-PWs.

     Native  |<-------------------- PW15 --------------------->| Native
      Layer  |                                                 |  Layer
    Service  |    |<-PSN13->|    |<-PSN3X->|    |<-PSNXZ->|    | Service
       (AC1) V    V   LSP   V    V   LSP   V    V   LSP   V    V  (AC2)
             +----+   +-+   +----+         +----+   +-+   +----+
+---+        |TPE1|   | |   |SPE3|         |SPEX|   | |   |TPEZ|     +---+
|   |        |    |=========|    |=========|    |=========|    |     |   |
|CE1|--------|........PW1........|...PW3...|........PW5........|-----|CE2|
|   |        |    |=========|    |=========|    |=========|    |     |   |
+---+        | 1  |   |2|   | 3  |         | X  |   |Y|   | Z  |     +---+
             +----+   +-+   +----+         +----+   +-+   +----+

             |<- Subnetwork 123->|         |<- Subnetwork XYZ->|

             .------------------- PW15  PME -------------------.
             .---- PW1 PTCME ----.         .---- PW5 PTCME ---.
                  .---------.                   .---------.
                   PSN13 LME                     PSNXZ LME

                   .--.  .--.     .--------.     .--.  .--.
               Sec12 SME Sec23 SME Sec3X SME SecXY SME SecYZ SME


TPE1: Terminating Provider Edge 1     SPE2: Switching Provider Edge 3
TPEX: Terminating Provider Edge X     SPEZ: Switching Provider Edge Z

   .---. ME     .     MEP    ====   LSP      .... PW

SME: Section Maintenance Entity
LME: LSP Maintenance Entity
PME: PW Maintenance Entity

The following MPLS-TP MEs are specified in [I‑D.ietf‑mpls‑tp‑oam‑framework] (Allan, D., Busi, I., Niven-Jenkins, B., Fulignoli, A., Hernandez-Valencia, E., Levrau, L., Mohan, D., Sestito, V., Sprecher, N., Helvoort, H., Vigoureux, M., Weingarten, Y., and R. Winter, “MPLS-TP OAM Framework,” April 2010.):

• A Section Maintenance Entity (SME), allowing monitoring and management of MPLS-TP Sections (between MPLS LSRs).
• A LSP Maintenance Entity (LME), allowing monitoring and management of an end-to-end LSP (between LERs).
• A PW Maintenance Entity (PME), allowing monitoring and management of an end-to-end SS/MS-PWs (between T-PEs).
• An LSP Tandem Connection Maintenance Entity (LTCME), allowing monitoring and management of an LSP Tandem Connection (or LSP Segment) between any LER/LSR along the LSP. o A MS-PW Tandem Connection Maintenance Entity (PTCME), allows monitoring and management of a SS/MS-PW Tandem Connection (or PW Segment) between any T-PE/S-PE along the (MS-)PW. Note that the term Tandem Connection Monitoring has historical significance dating back to the early days of the telephone network, but is equally applicable to the two-level hierarchal architectures commonly employed in todays packet networks.

Individual MIPs along the path of an LSP or PW are addressed by setting the appropriate TTL in the label for the OAM packet, as per [I‑D.ietf‑pwe3‑segmented‑pw] (Martini, L., Nadeau, T., Metz, C., Bocci, M., Aissaoui, M., Balus, F., and M. Duckett, “Segmented Pseudowire,” April 2010.). Note that this works when the location of MIPs along the LSP or PW path is known by the MEP. There may be cases where this is not the case in general MPLS networks e.g. following restoration using a facility bypass LSP.

MPLS-TP OAM packets share the same fate as their corresponding data packets, and are identified through the Generic Associated Channel mechanism [RFC5586] (Bocci, M., Vigoureux, M., and S. Bryant, “MPLS Generic Associated Channel,” June 2009.). This uses a combination of an Associated Channel Header (ACH) and a Generic Alert Label (GAL) to create a control channel associated to an LSP, Section or PW.

The MPLS-TP OAM architecture support a wide range of OAM functions, including the following

• Continuity Check
• Connectivity Verification
• Performance monitoring (e.g. loss and delay)
• Alarm suppression
• Remote Integrity

These are applicable to any layer defined within MPLS- TP, i.e. MPLS Section, LSP and PW.

The MPLS-TP OAM toolset needs to be able to operate without relying on a dynamic control plane or IP functionality in the datapath. In the case of MPLS-TP deployment with IP functionality, all existing IP-MPLS OAM functions, e.g. LSP-Ping, BFD and VCCV, may be used. This does not preculde the use of other OAM tools in an IP addressable network.

One use of OAM mechanisms is to detect link failures, node failures and performance outside the required specification which then may be used to trigger recovery actions, according to the requirements of the service.

3.7.  Generic Associated Channel (G-ACh)

For correct operation of the OAM it is important that the OAM packets fate share with the data packets. In addition in MPSL-TP it is necessary to discriminate between user data payloads and other types of payload. For example the packet may contain a Signaling Communication Channel (SCC), or a channel used for Automatic Protecton Switching (APS) data. Such packetets are carried on a control channel associated to the LSP, Section or PW. This is achieved by carrying such packets on a generic control channel associated to the LSP, PW or section.

MPLS-TP makes use of such a generic associated channel (G-ACh) to support Fault, Configuration, Accounting, Performance and Security (FCAPS) functions by carrying packets related to OAM, APS, SCC, MCC or other packet types in band over LSPs or PWs. The G-ACH is defined in [RFC5586] (Bocci, M., Vigoureux, M., and S. Bryant, “MPLS Generic Associated Channel,” June 2009.)and it is similar to the Pseudowire Associated Channel [RFC4385] (Bryant, S., Swallow, G., Martini, L., and D. McPherson, “Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over an MPLS PSN,” February 2006.), which is used to carry OAM packets across pseudowires. The G-ACH is indicated by a generic associated channel header (ACH), similar to the Pseudowire VCCV control word, and this is present for all Sections, LSPs and PWs making use of FCAPS functions supported by the G-ACH.

For pseudowires, the G-ACh use the first nibble of the pseudowire control word to provide the initial discrimination between data packets a packets belonging to the associated channel, as described in[RFC4385] (Bryant, S., Swallow, G., Martini, L., and D. McPherson, “Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over an MPLS PSN,” February 2006.). When the first nibble of a packet, immediately following the label at the bottom of stack, has a value of one, then this packet belongs to a G-ACh. The first 32 bits following the bottom of stack label then have a defined format called an associated channel header (ACH), which further defines the content of the packet. The ACH is therefore both a demultiplexer for G-ACh traffic on the PW, and a discriminator for the type of G-ACh traffic.

When the OAM, or a similar message is carried over an LSP, rather than over a pseudowire, it is necessary to provide an indication in the packet that the payload is something other than a user data packet. This is acheived by including a reserved label with a value of 13 in the label stack. This reserved label is referred to as the 'Generic Alert Label (GAL)', and is defined in [RFC5586] (Bocci, M., Vigoureux, M., and S. Bryant, “MPLS Generic Associated Channel,” June 2009.). When a GAL is found anywhere within the label stack it indicates that the payload begins with an ACH. The GAL is thus a demultiplexer for G-ACh traffic on the LSP, and the ACH is a discriminator for the type of traffic carried on the G-ACh. Note however that MPLS-TP forwarding follows the normal MPLS model, and that a GAL is invisible to an LSR unless it is the top label iin the label stack. The only other circumstance under which the label stack may be inspected for a GAL is when the TTL has expired. Any MPLS-TP component that intentionally performs this inspection must assume that it is asynchronous with respect to the forwarding of other packets. All operations on the label stack arein accordance with [RFC3031] (Rosen, E., Viswanathan, A., and R. Callon, “Multiprotocol Label Switching Architecture,” January 2001.) and [RFC3032] (Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, “MPLS Label Stack Encoding,” January 2001.).

In MPLS-TP, the 'Generic Alert Label (GAL)' always appears at the bottom of the label stack (i.e. S bit set to 1), however this does not preclude its use elsewhere in the label stack in other applications.

The G-ACH MUST only be used for channels that are an adjunct to the data service. Examples of these are OAM, APS, MCC and SCC, but the use is not resticted to those names services. The G-ACH MUST NOT be used to carry additional data for use in the forwarding path, i.e. it MUST NOT be used as an alternative to a PW control word, or to define a PW type.

Since the G-ACh traffic is indistinguishable from the user data traffic at the server layer, bandwidth and QoS commitments apply to the gross traffic on the LSP, PW or section. Protocols using the G-ACh must therefore take into consideration the impact they have on the user data that they are sharing resources with. In addition, protocols using the G-ACh MUST conform to the security and congestion considerations described in [RFC5586] (Bocci, M., Vigoureux, M., and S. Bryant, “MPLS Generic Associated Channel,” June 2009.). .

Figure 7 (PWE3 Protocol Stack Reference Model including the G-ACh ) shows the reference model depicting how the control channel is associated with the pseudowire protocol stack. This is based on the reference model for VCCV shown in Figure 2 of [RFC5085] (Nadeau, T. and C. Pignataro, “Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for Pseudowires,” December 2007.).

       +-------------+                                +-------------+
       |  Payload    |       < Service / FCAPS >      |  Payload    |
       +-------------+                                +-------------+
       |   Demux /   |       < CW / ACH for PWs >     |   Demux /   |
       |Discriminator|                                |Discriminator|
       +-------------+                                +-------------+
       |     PW      |             < PW >             |     PW      |
       +-------------+                                +-------------+
       |    PSN      |             < LSP >            |    PSN      |
       +-------------+                                +-------------+
       |  Physical   |                                |  Physical   |
       +-----+-------+                                +-----+-------+
             |                                              |
             |             ____     ___       ____          |
             |           _/    \___/   \    _/    \__       |
             |          /               \__/         \_     |
             |         /                               \    |
             +--------|      MPLS/MPLS-TP Network       |---+
                       \                               /
                        \   ___      ___     __      _/
                         \_/   \____/   \___/  \____/

PW associated channel messages are encapsulated using the PWE3 encapsulation, so that they are handled and processed in the same manner (or in some cases, an analogous manner) as the PW PDUs for which they provide a control channel.

Figure 8 (MPLS Protocol Stack Reference Model including the LSP Associated Control Channel ) shows the reference model depicting how the control channel is associated with the LSP protocol stack.

       +-------------+                                +-------------+
       |  Payload    |          < Service >           |   Payload   |
       +-------------+                                +-------------+
       |Discriminator|         < ACH on LSP >         |Discriminator|
       +-------------+                                +-------------+
       |Demultiplexer|         < GAL on LSP >         |Demultiplexer|
       +-------------+                                +-------------+
       |    PSN      |            < LSP >             |    PSN      |
       +-------------+                                +-------------+
       |  Physical   |                                |  Physical   |
       +-----+-------+                                +-----+-------+
             |                                              |
             |             ____     ___       ____          |
             |           _/    \___/   \    _/    \__       |
             |          /               \__/         \_     |
             |         /                               \    |
             +--------|      MPLS/MPLS-TP Network       |---+
                       \                               /
                        \   ___      ___     __      _/
                         \_/   \____/   \___/  \____/

3.8.  Control Plane

MPLS-TP should be capable of being operated with centralized Network Management Systems (NMS). The NMS may be supported by a distributed control plane, but MPLS-TP can operated in the absense of such a control plane. A distributed control plane may be used to enable dynamic service provisioning in multi-vendor and multi-domain environments using standardized protocols that guarantee interoperability. Where the requirements specified in [I‑D.ietf‑mpls‑tp‑requirements] (Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S. Ueno, “MPLS-TP Requirements,” August 2009.) can be met, the MPLS transport profile uses existing control plane protocols for LSPs and PWs.

Figure 9 (MPLS-TP Control Plane Architecture Context) illustrates the relationshop between the MPLS-TP control plane, the forwarding plane, the management plane, and OAM for point-to-point MPLS-TP LSPs or PWs.

 +------------------------------------------------------------------------+
 |                                                                        |
 |                   Network Management System and/or                     |
 |                                                                        |
 |           Control Plane for Point to Point Connections                 |
 |                                                                        |
 +------------------------------------------------------------------------+
              |      |           |       |          |    |
  ............|......|.....  ....|.......|....  ....|....|...............
            +---+    |    :  : +---+     |   :  : +---+  |              :
  :         |OAM|    |    :  : |OAM|     |   :  : |OAM|  |              :
  :         +---+    |    :  : +---+     |   :  : +---+  |              :
  :           |      |    :  :   |       |   :  :   |    |              :
 \: +----+   +----------+ :  : +----------+  :  : +----------+   +----+ :/
--+-|Edge|<->|Forwarding|<---->|Forwarding|<----->|Forwarding|<->|Edge|-+--
 /: +----+   |          | :  : |          |  :  : |          |   +----+ :\
  :          +----------+ :  : +----------+  :  : +----------+          :
  '''''''''''''''''''''''''  '''''''''''''''''   ''''''''''''''''''''''''

Note:
   1) NMS may be centralised or distributed. Control plane is distributed
   2) 'Edge' functions refers to those functions present at the edge of
      a PSN domain, e.g. NSP or classification.

The MPLS-TP control plane is based on a combination of the LDP-based control plane for pseudowires [RFC4447] (Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G. Heron, “Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP),” April 2006.) and the RSVP-TE based control plane for MPLS-TP LSPs [RFC3471] (Berger, L., “Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description,” January 2003.). Some of the RSVP-TE functions that are required for LSP signaling for MPLS-TP are based on GMPLS.

The distributed MPLS-TP control plane provides the following functions:

• Signaling
• Routing
• Traffic engineering and constraint-based path computation

In a multi-domain environment, the MPLS-TP control plane supports different types of interfaces at domain boundaries or within the domains. These include the User-Network Interface (UNI), Internal Network Node Interface (I-NNI), and External Network Node Interface (E-NNI). Note that different policies may be defined that control the information exchanged across these interface types.

The MPLS-TP control plane is capable of activating MPLS-TP OAM functions as described in the OAM section of this document Section 3.6 (Operations, Administration and Maintenance (OAM)) e.g. for fault detection and localization in the event of a failure in order to efficiently restore failed transport paths.

The MPLS-TP control plane supports all MPLS-TP data plane connectivity patterns that are needed for establishing transport paths including protected paths as described in the survivability section Section 3.10 (Survivability) of this document. Examples of the MPLS-TP data plane connectivity patterns are LSPs utilizing the fast reroute backup methods as defined in [RFC4090] (Pan, P., Swallow, G., and A. Atlas, “Fast Reroute Extensions to RSVP-TE for LSP Tunnels,” May 2005.) and ingress-to-egress 1+1 or 1:1 protected LSPs.

The MPLS-TP control plane provides functions to ensure its own survivability and to enable it to recover gracefully from failures and degredations. These include graceful restart and hot redundant configurations. Depending on how the control plane is transported, varying degrees of decoupling between the control plane and data plane may be achieved.

3.8.1.  PW Control Plane

An MPLS-TP network provides many of its transport services using single-segment or multi-segment pseudowires, in compliance with the PWE3 architecture ([RFC3985] (Bryant, S. and P. Pate, “Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture,” March 2005.) and [I‑D.ietf‑pwe3‑ms‑pw‑arch] (Bocci, M. and S. Bryant, “An Architecture for Multi-Segment Pseudowire Emulation Edge-to-Edge,” July 2009.) ). The setup and maintenance of single-segment or multi- segment pseudowires uses the Label Distribution Protocol (LDP) as per [RFC4447] (Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G. Heron, “Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP),” April 2006.) and extensions for MS-PWs [I‑D.ietf‑pwe3‑segmented‑pw] (Martini, L., Nadeau, T., Metz, C., Bocci, M., Aissaoui, M., Balus, F., and M. Duckett, “Segmented Pseudowire,” April 2010.) and [I‑D.ietf‑pwe3‑dynamic‑ms‑pw] (Martini, L., Bocci, M., Balus, F., Bitar, N., Shah, H., Aissaoui, M., Rusmisel, J., Serbest, Y., Malis, A., Metz, C., McDysan, D., Sugimoto, J., Duckett, M., Loomis, M., Doolan, P., Pan, P., Pate, P., Radoaca, V., Wada, Y., and Y. Seo, “Dynamic Placement of Multi Segment Pseudo Wires,” October 2009.).

3.8.2.  LSP Control Plane

MPLS-TP provider edge nodes aggregate multiple pseudowires and carry them across the MPLS-TP network through MPLS-TP tunnels (MPLS-TP LSPs). Applicable functions from the Generalized MPLS (GMPLS) protocol suite supporting packet-switched capable (PSC) technologies are used as the control plane for MPLS-TP transport paths (LSPs).

The LSP control plane includes:

• RSVP-TE for signalling
• OSPF-TE or ISIS-TE for routing

RSVP-TE signaling in support of GMPLS, as defined in [RFC4872] (Lang, J., Rekhter, Y., and D. Papadimitriou, “RSVP-TE Extensions in Support of End-to-End Generalized Multi-Protocol Label Switching (GMPLS) Recovery,” May 2007.), is used for the setup, modification, and release of MPLS-TP transport paths and protection paths. It supports unidirectional, bi-directional and multicast types of LSPs. The route of a transport path is typically calculated in the ingress node of a domain and the RSVP explicit route object (ERO) is utilized for the setup of the transport path exactly following the given route. GMPLS based MPLS-TP LSPs must be able to interoperate with RSVP-TE based MPLS-TE LSPs, as per [RFC5146] (Kumaki, K., “Interworking Requirements to Support Operation of MPLS-TE over GMPLS Networks,” March 2008.)

OSPF-TE routing in support of GMPLS as defined in [RFC4203] (Kompella, K. and Y. Rekhter, “OSPF Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS),” October 2005.) is used for carrying link state information in a MPLS-TP network. ISIS-TE routing in support of GMPLS as defined in [RFC5307] (Kompella, K. and Y. Rekhter, “IS-IS Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS),” October 2008.) is used for carrying link state information in a MPLS-TP network.

3.9.  Static Operation of LSPs and PWs

A PW or LSP may be statically configured without the support of a dynamic control plane. This may be either by direct configuration of the PEs/LSRs, or via a network management system. The colateral damage that loops can cause during the time taken to detect the failure may be severe. When static configuration mechanisms are used, care must be taken to ensure that loops to not form.

3.10.  Survivability

Survivability requirements for MPLS-TP are specified in [I‑D.ietf‑mpls‑tp‑survive‑fwk] (Sprecher, N. and A. Farrel, “Multiprotocol Label Switching Transport Profile Survivability Framework,” April 2010.).

A wide variety of resiliency schemes have been developed to meet the various network and service survivability objectives. For example, as part of the MPLS/PW paradigms, MPLS provides methods for local repair using back-up LSP tunnels ([RFC4090] (Pan, P., Swallow, G., and A. Atlas, “Fast Reroute Extensions to RSVP-TE for LSP Tunnels,” May 2005.)), while pseudowire redundancy [I‑D.ietf‑pwe3‑redundancy] (Muley, P. and V. Place, “Pseudowire (PW) Redundancy,” October 2009.) supports scenarios where the protection for the PW can not be fully provided by the PSN layer (i.e. where the backup PW terminates on a different target PE node than the working PW). Additionally, GMPLS provides a well known set of control plane driven protection and restoration mechanisms [RFC4872] (Lang, J., Rekhter, Y., and D. Papadimitriou, “RSVP-TE Extensions in Support of End-to-End Generalized Multi-Protocol Label Switching (GMPLS) Recovery,” May 2007.). MPLS-TP provides additional protection mechansisms that are optimised for both linear topologies and ring topologies, and that operate in the absense of a dynamic control plane. These are specified in [I‑D.ietf‑mpls‑tp‑survive‑fwk] (Sprecher, N. and A. Farrel, “Multiprotocol Label Switching Transport Profile Survivability Framework,” April 2010.).

Different protection schemes apply to different deployment topologies and operational considerations. Such protection schemes may provide different levels of resiliency. For example, two concurrent traffic paths (1+1), one active and one standby path with guaranteed bandwidth on both paths (1:1) or one active path and a standby path that is shared by one or more other active paths (shared protection). The applicability of any given scheme to meet specific requirements is outside the current scope of this document.

The characteristics of MPLS-TP resiliency mechanisms are listed below.

• Optimised for linear, ring or meshed topologies.
• Use OAM mechanisms to detect and localize network faults or service degenerations.
• Include protection mechanisms to coordinate and trigger protection switching actions in the absense of a dynamic control plane. This is known as an Automatic Protection Switching (APS) mechanism.
• MPLS-TP recovery schemes are applicable to all levels in the MPLS-TP domain (i.e. MPLS section, LSP and PW), providing segment and end-to- end recovery.
• MPLS-TP recovery mechanisms support the coordination of protection switching at multiple levels to prevent race conditions occuring between a client and its server layer.
• MPLS-TP recovery mechanisms can be data plane, control plane or management plane based.
• MPLS-TP supports revertive and non-revertive behavior.

3.11.  Network Management

The network management architecture and requirements for MPLS-TP are specified in [I‑D.ietf‑mpls‑tp‑nm‑req] (Mansfield, S. and K. Lam, “MPLS TP Network Management Requirements,” October 2009.). It derives from the generic specifications described in ITU-T G.7710/Y.1701 [G.7710] (, “ITU-T Recommendation G.7710/Y.1701 (07/07), "Common equipment management function requirements",” 2005.) for transport technologies. It also incorporates the OAM requirements for MPLS Networks [RFC4377] (Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S. Matsushima, “Operations and Management (OAM) Requirements for Multi-Protocol Label Switched (MPLS) Networks,” February 2006.) and MPLS-TP Networks [I‑D.ietf‑mpls‑tp‑oam‑requirements] (Vigoureux, M. and D. Ward, “Requirements for OAM in MPLS Transport Networks,” March 2010.) and expands on those requirements to cover the modifications necessary for fault, configuration, performance, and security in a transport network.

The Equipment Management Function (EMF) of a MPLS-TP Network Element (NE) (i.e. LSR, LER, PE, S-PE or T-PE) provides the means through which a management system manages the NE. The Management Communication Channel (MCC), realized by the G-ACh, provides a logical operations channel between NEs for transferring Management information. For the management interface from a management system to a MPLS-TP NE, there is no restriction on which management protocol should be used. It is used to provision and manage an end-to-end connection across a network where some segments are create/managed, for examples by Netconf or SNMP and other segments by XML or CORBA interfaces. Maintenance operations are run on a connection (LSP or PW) in a manner that is independent of the provisioning mechanism. An MPLS-TP NE is not required to offer more than one standard management interface. In MPLS-TP, the EMF must be capable of statically provisioning LSPs for an LSR or LER, and PWs for a PE, as per Section 3.9 (Static Operation of LSPs and PWs ).

Fault Management (FM) functions within the EMF of an MPLS-TP NE enable the supervision, detection, validation, isolation, correction, and alarm handling of abnormal conditions in the MPLS-TP network and its environment. FM must provide for the supervision of transmission (such as continuity, connectivity, etc.), software processing, hardware, and environment. Alarm handling includes alarm severity assignment, alarm suppression/aggregation/correlation, alarm reporting control, and alarm reporting.

Configuration Management (CM) provides functions to control, identify, collect data from, and provide data to MPLS-TP NEs. In addition to general configuration for hardware, software protection switching, alarm reporting control, and date/time setting, the EMF of the MPLS-TP NE also supports the configuration of maintenance entity identifiers (such as MEP ID and MIP ID). The EMF also supports the configuration of OAM parameters as a part of connectivity management to meet specific operational requirements. These may specify whether the operational mode is one-time on-demand or is periodic at a specified frequency.

The Performance Management (PM) functions within the EMF of an MPLS- TP NE support the evaluation and reporting of the behaviour of the NEs and the network. One particular requirement for PM is to provide coherent and consistent interpretation of the network behaviour in a hybrid network that uses multiple transport technologies. Packet loss measurement and delay measurements may be collected and used to detect performance degradation. This is reported via fault management to enable corrective actions to be taken (e.g. protection switching), and via performance monitoring for Service Level Agreement (SLA) verification and billing. Collection mechanisms for performance data should be should be capable of operating on-demand or proactively.

4.  Security Considerations

The introduction of MPLS-TP into transport networks means that the security considerations applicable to both MPLS and PWE3 apply to those transport networks. Furthermore, when general MPLS networks that utilise functionality outside of the strict MPLS-TP profile are used to support packet transport services, the security considerations of that additional functionality also apply.

The security considerations of [RFC3985] (Bryant, S. and P. Pate, “Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture,” March 2005.) and [I‑D.ietf‑pwe3‑ms‑pw‑arch] (Bocci, M. and S. Bryant, “An Architecture for Multi-Segment Pseudowire Emulation Edge-to-Edge,” July 2009.) apply.

Each MPLS-TP solution must specify the addtional security considerations that apply.

5.  IANA Considerations

IANA considerations resulting from specific elements of MPLS-TP functionality will be detailed in the documents specifying that functionality.

This document introduces no additional IANA considerations in itself.

6.  Acknowledgements

The editors wish to thank the following for their contribution to this document:

• Dieter Beller
• Italo Busi
• Hing-Kam Lam
• Marc Lasserre
• Vincenzo Sestito
• Martin Vigoureux
• Malcolm Betts

7.  References

7.1. Normative References

7.2. Informative References

Authors' Addresses