MPLS Working Group                                 B. Niven-Jenkins, Ed.
Internet-Draft                                                        BT
Intended status: Informational Standards Track                        D. Brungard, Ed.
Expires: September 11, October 6, 2009                                            AT&T
                                                           M. Betts, Ed.
                                                         Nortel Networks
                                                             N. Sprecher
                                                  Nokia Siemens Networks
                                                                 S. Ueno
                                                                     NTT
                                                          March 10,
                                                           April 4, 2009

                          MPLS-TP Requirements
                   draft-ietf-mpls-tp-requirements-05
                   draft-ietf-mpls-tp-requirements-06

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Abstract

   This document specifies the requirements of an MPLS Transport Profile
   (MPLS-TP).  This document is a product of a joint International
   Telecommunications Union (ITU)-IETF effort to include an MPLS
   Transport Profile within the IETF MPLS and PWE3 architectures to
   support the capabilities and functionalities of a packet transport
   network as defined by International Telecommunications Union -
   Telecommunications Standardization Sector (ITU-T).

   This work is based on two sources of requirements; MPLS and PWE3
   architectures as defined by IETF, and packet transport networks as
   defined by ITU-T.

   The requirements expressed in this document are for the behavior of
   the protocol mechanisms and procedures that constitute building
   blocks out of which the MPLS transport profile is constructed.  The
   requirements are not implementation requirements.

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" are to be
   interpreted as described in RFC 2119 [RFC2119] and are to be
   interpreted as instructions to the protocol designers producing
   solutions that satisfy the requirements set out in this document.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  6
       1.1.1.  Abbreviations  . . . . . . . . . . . . . . . . . . . .  6
       1.1.2.  Definitions  . . . . . . . . . . . . . . . . . . . . .  8
     1.2.  Transport network overview . . . . . . . . . . . . . . . . 11
     1.3.  Layer network overview . . . . . . . . . . . . . . . . . . 12
   2.  MPLS-TP Requirements . . . . . . . . . . . . . . . . . . . . . 13
     2.1.  General requirements . . . . . . . . . . . . . . . . . . . 13
     2.2.  Layering requirements  . . . . . . . . . . . . . . . . . . 15 16
     2.3.  Data plane requirements  . . . . . . . . . . . . . . . . . 16 17
     2.4.  Control plane requirements . . . . . . . . . . . . . . . . 18
     2.5.  Network Management (NM) requirements . . . . . . . . . . . 19 20
     2.6.  Operation, Administration and Maintenance (OAM)
           requirements . . . . . . . . . . . . . . . . . . . . . . . 19 20
     2.7.  Network performance management (PM) requirements . . . . . 19 20
     2.8.  Recovery requirements  . . . . . . . . . . . . . . . . . . 19 20
       2.8.1.  Data plane behavior requirements . . . . . . . . . . . 20 21
         2.8.1.1.  Protection . . . . . . . . . . . . . . . . . . . . 20 21
         2.8.1.2.  Restoration  . . . . . . . . . . . . . . . . . . . 21 22
         2.8.1.3.  Sharing of protection resources  . . . . . . . . . 21 22
         2.8.1.4.  Reversion  . . . . . . . . . . . . . . . . . . . . 22 23
       2.8.2.  Triggers for protection, restoration, and reversion  . 22 23
       2.8.3.  Management plane operation of protection and
               restoration  . . . . . . . . . . . . . . . . . . . . . 22 23
       2.8.4.  Control plane and in-band OAM operation of recovery  . 23 24
       2.8.5.  Topology-specific recovery mechanisms  . . . . . . . . 24 25
         2.8.5.1.  Ring protection  . . . . . . . . . . . . . . . . . 24 25
     2.9.  QoS requirements . . . . . . . . . . . . . . . . . . . . . 27 28
     2.10. Security requirements  . . . . . . . . . . . . . . . . . . 27 28
   3.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 28 29
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 28 29
   5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28 29
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 29
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 28 29
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 30
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30 31

1.  Introduction

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

   o  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.,

   o  Applications with various bandwidth and QoS 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 Networ Network (OTN)) has
   provided carriers with a high benchmark for reliability and
   operational simplicity.

   With the movement towards packet based services, the transport
   network has to evolve to encompass the provision of packet aware
   capabilities while enabling carriers to leverage their installed, as
   well as planned, transport infrastructure investments.

   Carriers are in need of technologies capable of efficiently
   supporting packet based services and applications on their transport
   networks with guaranteed Service Level Agreements (SLAs).  The need
   to increase their revenue while remaining competitive forces
   operators to look for the lowest network Total Cost of Ownership
   (TCO).  Investment in equipment and facilities (Capital Expenditure
   (CAPEX)) and Operational Expenditure (OPEX) should be minimized.

   There are a number of technology options for carriers to meet the
   challenge of increased service sophistication and transport
   efficiency, with increasing usage of hybrid packet transport and
   circuit transport technology solutions.  To realize these goals, it
   is essential that packet transport technology be available that can
   support the same high benchmarks for reliability and operational
   simplicity set by SDH/SONET and OTN technologies.

   Furthermore for carriers it is important that operation of such
   packet transport networks should preserve the look-and-feel to which
   carriers have become accustomed in deploying their optical transport
   networks, while providing common, multi-layer operations, resiliency,
   control and multi-technology management.

   Transport carriers require control and deterministic usage of network
   resources.  They need end-to-end control to engineer network paths
   and to efficiently utilize network resources.  They require
   capabilities to support static (management plane based based) or dynamic
   (control plane based) provisioning of deterministic, protected and
   secured services and their associated resources.

   It is also important to ensure smooth interworking of the packet
   transport network with other existing/legacy packet networks, and
   provide mappings to enable packet transport carriage over a variety
   of transport network infrastructures.  The latter has been termed
   vertical interworking, and is also known as client/server or network
   interworking.  The former has been termed horizontal interworking,
   and is also known as peer-partition or service interworking.  For
   more details on interworking and some of the issues that may arise
   (especially with horizontal interworking) seeG.805 [ITU.G805.2000]
   and Y.1401 [ITU.Y1401.2008].

   MPLS

   Multi-Protocol Label Switching (MPLS) is a maturing packet technology
   and it is already playing an important role in transport networks and
   services.  However, 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.  There is therefore the need to define an MPLS
   Transport Profile (MPLS-TP) that supports the capabilities and
   functionalities needed for packet transport network services and
   operations through combining the packet experience of MPLS with the
   operational experience and practices of existing transport networks.

   MPLS-TP will enable the migration of transport networks to a packet-
   based network that will efficiently scale to support packet services
   in a simple and cost effective way.  MPLS-TP needs to combine the
   necessary existing capabilities of MPLS with additional minimal
   mechanisms in order that it can be used in a transport role.

   This document specifies the requirements of an MPLS Transport Profile
   (MPLS-TP).  The requirements are for the behavior of the protocol
   mechanisms and procedures that constitute building blocks out of
   which the MPLS transport profile is constructed.  That is, the
   requirements indicate what features are to be available in the MPLS
   toolkit for use by MPLS-TP.  The requirements in this document do not
   describe what functions an MPLS-TP implementation supports.  The
   purpose of this document is to identify the toolkit and any new
   protocol work that is required.

   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" are used as
   described in [RFC2119] and are to be interpreted as instructions to
   the protocol designers producing solutions that satisfy the
   requirements set out in this document.

   This document is a product of a joint ITU-T and IETF effort to
   include an MPLS Transport Profile within the IETF MPLS and PWE3
   architectures to support the capabilities and functionalities of a
   packet transport network as defined by ITU-T.

   This work is based on two sources of requirements, MPLS and PWE3
   architectures as defined by IETF and packet transport networks as
   defined by ITU-T.  The requirements of MPLS-TP are provided below.
   The relevant functions of MPLS and PWE3 are included in MPLS-TP,
   except where explicitly excluded.

   Although both static and dynamic configuration of MPLS-TP transport
   paths (including Operations, Administration and Maintenance (OAM) and
   protection capabilities) is required by this document, it MUST be
   possible for operators to be able to completely operate (including
   OAM and protection capabilities) an MPLS-TP network in the absence of
   any control plane protocols for dynamic configuration.

1.1.  Terminology

   Note: Mapping between the terms in this section and ITU-T terminology
   will be described in a subsequent document.

   The recovery requirements in this document use the recovery
   terminology defined in RFC 4427 [RFC4427], this is applied to both
   control plane and management plane based operations of MPLS-TP
   transport paths.

1.1.1.  Abbreviations

   ASON: Automatically Switched Optical Network

   ASTN: Automatic Switched Transport Network

   ATM: Asynchronous Transfer Mode

   CAPEX: Capital Expenditure

   CE: Customer Edge

   FR: Frame Relay
   GMPLS: Generalised Multi-Protocol Label Switching

   IGP: Interior Gateway Protocol

   IPTV: IP Television

   L2: Layer 2

   L3: Layer 3

   LSP: Label Switched Path

   LSR: Label Switching Router

   ME:

   MEP: Maintenance End Point

   MIP: Maintenance Entity Intermediate Point

   MPLS: Multi-Protocol Label Switching

   OAM: Operations, Adminstration Administration and Maintenance

   OPEX: Operational Expenditure

   OSI: Open Systems Interconnection

   OTN: Optical Transport Network

   P2MP: Point to Multi-Point

   P2P: Point to Point

   PDU: Protocol Data Unit

   PM: Performance Management

   PSC: Protection State Coordination

   PW: Pseudo Wire

   QoS: Quality of Service

   RAN: Radio Access Network

   SDH: Synchronous Digital Hierarchy

   SLA: Service Level Agreement
   SLS: Service Level Specification

   S-PE: Switching Provider Edge

   SONET: Synchronous Optical Network

   SRLG: Shared Risk Link Group

   TCO: Total Cost of Ownership

   T-PE: Terminating Provider Edge

   VoIP: Voice over IP

   VPN: Virtual Private Network

   WDM: Wavelength Division Multiplexing

1.1.2.  Definitions

   Note: The definition of segment in a GMPLS/ASON context (i.e. as
   defined in RFC4397 [RFC4397]) encompasses both segment and
   concatenated segment as defined in this document.

   Associated bidirectional path: A path that supports traffic flow in
   both directions but which is constructed from a pair of
   unidirectional paths (one for each direction) which are associated
   with one another at the path's ingress/egress points.  The forward
   and backward directions are setup, monitored and protected
   independently.  As a consequence they may or may not follow the same
   route (links and nodes) across the network.

   Client layer network: In a client/server relationship (see G.805
   [ITU.G805.2000]), the client layer network receives a (transport)
   service from the lower server layer network (usually the layer
   network under consideration).

   Concatenated Segment: A serial-compound link connection as defined in
   G.805 [ITU.G805.2000].  A concatenated segment is a contiguous part
   of an LSP or multi-segment PW that comprises a set of segments and
   their interconnecting nodes in sequence.  See also "Segment".

   Co-routed Bidirectional path: A path where the forward and backward
   directions follow the same route (links and nodes) across the
   network.  Both directions are setup, monitored and protected as a
   single entity.

   Domain: A domain represents a collection of entities (for example
   network elements) that are grouped for a particular purpose, examples
   of which are administrative and/or managerial responsibilities, trust
   relationships, addressing schemes, infrastructure capabilities,
   aggregation, survivability techniques, distributions of control
   functionality, etc.  Examples of such domains include IGP areas and
   Autonomous Systems.

   Layer network: Layer network is defined in G.805 [ITU.G805.2000].  A
   layer network provides for the transfer of client information and
   independent operation of the client OAM.  A Layer Network may be
   described in a service context as follows: one layer network may
   provide a (transport) service to higher client layer network and may,
   in turn, be a client to a lower layer network.  A layer network is a
   logical construction somewhat independent of arrangement or
   composition of physical network elements.  A particular physical
   network element may topologically belong to more than one layer
   network, depending on the actions it takes on the encapsulation
   associated with the logical layers (e.g. the label stack), and thus
   could be modeled as multiple logical elements.  A layer network may
   consist of one or more sublayers.  Section 1.3 provides a more
   detailed overview of what constitutes a layer network.  For
   additional explanation of how layer networks relate to the OSI
   concept of layering see Appendix I of Y.2611 [ITU.Y2611.2006].

   Link: A physical or logical connection between a pair of LSRs that
   are adjacent at the (sub)layer network under consideration.  A link
   may carry zero, one or more LSPs or PWs.  A packet entering a link
   will emerge with the same label stack entry values.

   MPLS-TP Logical Ring: An MPLS-TP logical ring is constructed from a
   set of LSRs and logical data links (such as MPLS-TP LSP tunnels or
   MPLS-TP pseudowires) and physical data links that form a ring
   topology.

   Path: See Transport Path.

   MPLS-TP Physical Ring: An MPLS-TP physical ring is constructed from a
   set of LSRs and physical data links that form a ring topology.

   MPLS-TP Ring Topology: In an MPLS-TP ring topology each LSR is
   connected to exactly two other LSRs, each via a single point-to-point
   bidirectional MPLS-TP capable link.  A ring may also be constructed
   from only two LSRs where there are also exactly two links.  Rings may
   be connected to other LSRs to form a larger network.  Traffic
   originating or terminating outside the ring may be carried over the
   ring.  Client network nodes (such as CEs) may be connected directly
   to an LSR in the ring.

   Section Layer Network: A section is a server layer (which may be
   MPLS-TP or a different technology) which provides for encapsulation
   and OAM of a client layer network.  A section layer may provide for
   aggregation of multiple MPLS-TP clients.  Note that G.805
   [ITU.G805.2000] defines the section layer as one of the two layer
   networks in a transmission media layer network.  The other layer
   network is the physical media layer network.

   Segment: A link connection as defined in G.805 [ITU.G805.2000].  A
   segment is the part of an LSP that traverses a single link or the
   part of a PW that traverses a single link (i.e. that connects a pair
   of adjacent {Switching|Terminating} Provider Edges).  See also
   "Concatenated Segment".

   Server Layer Network: In a client/server relationship (see G.805
   [ITU.G805.2000]), the server layer network provides a (transport)
   service to the higher client layer network (usually the layer network
   under consideration).

   Sublayer: Sublayer is defined in G.805 [ITU.G805.2000].  The
   distinction between a layer network and a sublayer is that a sublayer
   is not directly accessible to clients outside of its encapsulating
   layer network and offers no direct transport service for a higher
   layer (client) network.

   Switching Provider Edge (S-PE): See [I-D.ietf-pwe3-ms-pw-arch].

   Tandem Connection: A tandem connection is an arbitrary part of a
   transport path that can be monitored (via OAM) independently from the
   end-to-end monitoring (OAM).  It may be a monitored segment or a
   monitored concatenated segment of a transport path.  The tandem
   connection may also include the forwarding engine(s) of the node(s)
   at the edge(s) of the segment or concatenated segment.

   Terminating Provider Edge (T-PE): See [I-D.ietf-pwe3-ms-pw-arch].

   Transport Path: A network connection as defined in G.805
   [ITU.G805.2000].  In an MPLS-TP environment a transport path
   corresponds to an LSP or a PW.

   Transport Path Layer: A layer network that provides point-to-point or
   point-to-multipoint transport paths that may be used to carry a
   higher (client) layer network or aggregates of higher (client) layer
   networks, for example the transport service layer.  It provides
   independent (of the client) OAM when transporting its clients.

   Transport Service Layer: A layer network in which transport paths are
   used to carry a customer's (individual or bundled) service (may be
   point-to-point, point-to-multipoint or multipoint-to-multipoint
   services).

   Transmission Media Layer: A layer network, consisting of a section
   layer network and a physical layer network as defined in G.805
   [ITU.G805.2000], that provides sections (two-port point-to-point
   connections) to carry the aggregate of network transport path or
   network service layers on various physical media.

   Unidirectional Path: A path that supports traffic flow in only one
   direction.

1.2.  Transport network overview

   The connectivity service is the basic service provided by a transport
   network.  The purpose of a transport network is to carry its customer
   traffic (i.e. the stream of customer PDUs or customer bits, including
   overhead) between endpoints in the transport network (typically over
   several intermediate nodes).  The connectivity services offered to
   customers are typically aggregated into large transport paths with
   long-holding times and independent OAM (of the client OAM), which
   contribute to enabling the efficient and reliable operation of the
   transport network.  These transport paths are modified infrequently.

   Quality-of-service mechanisms are required in the packet transport
   network to ensure the prioritization of critical services, to
   guarantee bandwidth and to control jitter and delay.  A transport
   network must provide the means to commit quality of service
   objectives to clients.  This is achieved by providing a mechanism for
   client network service demarcation for the network path together with
   an associated network resiliency mechanism.

   Aggregation is beneficial for achieving scalability and security
   since:

   1.  It reduces the number of provisioning and forwarding states in
       the network core.

   2.  It reduces load and the cost of implementing service assurance
       and fault management.

   3.  Customer traffic is encapsulated and layer associated OAM
       overhead is added.  This allows complete isolation of customer
       traffic and its management from carrier operations.

   An important attribute of a transport network is that it is able to
   function regardless of which clients are using its connection service
   or over which transmission media it is running.  The client,
   transport network and server layers are from a functional and
   operations point of view independent layer networks.  Another key
   characteristic of transport networks is the capability to maintain
   the integrity of the client across the transport network.  A
   transport network must also provide a method of service monitoring in
   order to verify the delivery of an agreed quality of service.  This
   is enabled by means of carrier-grade OAM tools.

   Customer traffic is first encapsulated within the transport service
   layer network.  The transport service layer network signals may then
   be aggregated into a transport path layer network for transport
   through the network in order to optimize network management.
   Transport service layer network OAM is used to monitor the transport
   integrity of the customer traffic and transport path layer network
   OAM is used to monitor the transport integrity of the aggregates.  At
   any hop, the aggregated signals may be further aggregated in lower
   layer transport network paths for transport across intermediate
   shared links.  The transport service layer network signals are
   extracted at the edges of aggregation domains, and are either
   delivered to the customer or forwarded to another domain.  In the
   core of the network, only the transport path layer network signals
   are monitored at intermediate points; individual transport service
   layer network signals are monitored at the network boundary.
   Although the connectivity of the transport service layer network may
   be point-to-point, point-to-multipoint or multipoint-to-multipoint,
   the transport path layer network only provides point-to-point or
   point-to-multipoint transport paths which are used to carry
   aggregates of transport service layer network traffic.

1.3.  Layer network overview

   A layer network provides its clients with a transport service and the
   operation of the layer network is independent of whatever client
   happens to use the layer network.  Information that passes between
   any client to the layer network is common to all clients and is the
   minimum needed to be consistent with the definition of the transport
   service offered.  The client layer network can be connectionless,
   connection oriented packet switched, or circuit switched.  The
   transport service transfers a payload (individual packet payload for
   connectionless networks, a sequence of packets payloads in the case
   of connection oriented packet switched networks, and a deterministic
   schedule of payloads in the case of circuit switched networks) such
   that the client can populate the payload without affecting any
   operation within the serving layer network.

   The operations within a layer network that are independent of its
   clients include the control of forwarding, the control of resource
   reservation, the control of traffic demerging, and the OAM and
   recovery of the transport service.  All of these operations are
   internal to a layer network.  By definition, a layer network does not
   rely on any client information to perform these operations and
   therefore all information required to perform these operations is
   independent of whatever client is using the layer network.

   A layer network will have common consistent features in order to support the
   control of forwarding, resource reservation, OAM and recovery.  For
   example, a layer network will have a common addressing scheme for the
   end points of the transport service and a common set of transport
   descriptors for the transport service.  However, a client may use a
   different addressing scheme or different traffic descriptors
   (consistent with performance inheritance).

   It is sometimes useful to independently monitor a smaller domain
   within a layer network (or the transport services that traverse this
   smaller domain) but the control of forwarding or the control of
   resource reservation involved retain their common elements.  These
   smaller monitored domains are sublayers.

   It is sometimes useful to independently control forwarding in a
   smaller domain within a layer network but the control of resource
   reservation and OAM retain their common elements.  These smaller
   domains are partitions of the layer network.

2.  MPLS-TP Requirements

   This document specifies the requirements of an MPLS Transport Profile
   (MPLS-TP).  The requirements are for the behavior of the protocol
   mechanisms and procedures that constitute building blocks out of
   which the MPLS transport profile is constructed.  That is, the
   requirements indicate what features are to be available in the MPLS
   toolkit for use by MPLS-TP.  The requirements in this document do not
   describe what functions an MPLS-TP implementation supports.  The
   purpose of this document is to identify the toolkit and any new
   protocol work that is required.

2.1.  General requirements

   1   The MPLS-TP data plane MUST be a subset of the MPLS data plane as
       defined by the IETF.  When MPLS offers multiple options in this
       respect, MPLS-TP SHOULD select the minimum sub-set (necessary and
       sufficient subset) applicable to a transport network application.

   2   Any new functionality that is defined to fulfill the requirements
       for MPLS-TP MUST be agreed within the IETF through the IETF
       consensus process and MUST re-use (as far as practically
       possible) existing MPLS standards.

   3   Mechanisms and capabilities MUST be able to interoperate with
       existing IETF MPLS [RFC3031] and IETF PWE3 [RFC3985] control and
       data planes where appropriate.

       A.  Data plane interoperability MUST NOT require a gateway
           function.

   4   MPLS-TP and its interfaces, both internal and external, MUST be
       sufficiently well-defined that interworking equipment supplied by
       multiple vendors will be possible both within a single domain,
       and between domains.

   5   MPLS-TP MUST be a connection-oriented packet switching technology
       with traffic engineering capabilities that allow deterministic
       control of the use of network resources.

   6   MPLS-TP MUST support traffic engineered point to point (P2P) and
       point to multipoint (P2MP) transport paths.

   7   MPLS-TP MUST support the logical separation of the control and
       management planes from the data plane.

   8   MPLS-TP MUST support the physical separation of the control and
       management planes from the data plane.

   9   MPLS-TP MUST support static provisioning of transport paths via
       the management plane.

   10  Mechanisms in an MPLS-TP network that satisfy functional
       requirements that are common to general transport networks (i.e.,
       independent of technology) SHOULD be operable in a way that is
       similar to the way the equivalent mechanisms are operated in
       other transport networks.

   11  Static provisioning MUST NOT depend on the presence of any
       element of a control plane.

   12  MPLS-TP MUST support the capability for network operation
       (including OAM and recovery) via the management plane (without
       the use of any control plane protocols).

   13  A solution MUST be defined to support dynamic provisioning and
       restoration of MPLS-TP transport paths via a control plane.

   14  MPLS-TP MUST support the co-existence of statically and
       dynamically provisioned/managed MPLS-TP transport paths within
       the same layer network or domain.

   15  The MPLS-TP data plane MUST be capable of

       A.  forwarding data independent of the control or management
           plane used to configure and operate the MPLS-TP layer
           network.

       B.  taking recovery actions independent of the control plane used
           to configure the MPLS-TP layer network.  If the control plane
           does not restart, the data plane connections MUST be held and
           NOT time out.

   15

   16  MPLS-TP MUST support mechanisms to avoid or minimize traffic
       impact (e.g. packet delay, reordering and loss) during network
       reconfiguration.

   16

   17  MPLS-TP MUST support transport paths through multiple homogeneous
       domains.

   17

   18  MPLS-TP SHOULD support transport paths through multiple non-
       homogeneous domains.

   18

   19  MPLS-TP MUST NOT dictate the deployment of any particular network
       topology either physical or logical, however:

       A.  It MUST be possible to deploy MPLS-TP in rings.

       B.  It MUST be possible to deploy MPLS-TP in arbitrarily
           interconnected rings with one or two points of
           interconnection.

       C.  MPLS-TP MUST support rings of at least 16 nodes in order to
           support the upgrade of existing TDM rings to MPLS-TP.
           MPLS-TP SHOULD support rings with more than 16 nodes.

   19

   20  MPLS-TP MUST be able to scale at least as well as existing
       transport technologies with growing and increasingly complex
       network topologies as well as with increasing bandwidth demands,
       number of customers, and number of services.

   20

   21  MPLS-TP SHOULD support mechanisms to safeguard against the
       provisioning of transport paths which contain forwarding loops.

2.2.  Layering requirements

   21

   22  A generic and extensible solution MUST be provided to support the
       transport of one or more client layer networks (e.g.  MPLS-TP,
       IP, MPLS, Ethernet, ATM, FR, etc.) over an MPLS-TP layer network.

   22

   23  A generic and extensible solution MUST be provided to support the
       transport of MPLS-TP transport paths over one or more server
       layer networks (such as MPLS-TP, Ethernet, SONET/SDH, OTN, etc.).
       Requirements for bandwidth management within a server layer
       network are outside the scope of this document.

   23

   24  In an environment where an MPLS-TP layer network is supporting a
       client layer network, and the MPLS-TP layer network is supported
       by a server layer network then operation of the MPLS-TP layer
       network MUST be possible without any dependencies on the server
       or client layer network.

       A.  The server layer MUST guarantee that the traffic loading
           imposed by other clients does not cause the transport service
           provided to the MPLS-TP layer to fall bellow the agreed
           level.  Mechanisms to achieve this are outside the scope of
           these requirements.

   24

       B.  It MUST be possible to isolate the control and management
           planes of the MPLS-TP layer network from the control and
           management planes of the client and server layer networks.

   25  A solution MUST be provided to support the transport of a client
       MPLS or MPLS-TP layer network over a server MPLS or MPLS-TP layer
       network.

       A.  The level of co-ordination required between the client and
           server MPLS(-TP) layer networks MUST be minimised minimized (preferably
           no co-ordination will be required).

       B.  The MPLS(-TP) server layer network MUST be capable of
           transporting the complete set of packets generated by the
           client MPLS(-TP) layer network, which may contain packets
           that are not MPLS packets (e.g.  IP or CNLS packets used by
           the control/management plane of the client MPLS(-TP) layer
           network).

   25

   26  It MUST be possible to operate the layers of a multi-layer
       network that includes an MPLS-TP layer autonomously.

   The above are not only technology requirements, but also operational
   requirements.  Different administrative groups may be responsible for
   the same layer network or different layer networks.

   26

   27  It MUST be possible to hide MPLS-TP layer network addressing and
       other information (e.g. topology) from client layer networks.
       However, it SHOULD be possible, at the option of the operator, to
       leak a limited amount of summarized information (such as SRLGs or
       reachability) between layers.

2.3.  Data plane requirements
   27

   28  It MUST be possible for the end points of an MPLS-TP transport
       path that is carrying an aggregate of client transport paths to
       be be able to decompose the aggregate transport path into its
       component client transport paths.

   28

   29  A transport path on a link MUST be uniquely identifiable by a
       single label on that link.

   29

   30  A transport path's source MUST be identifiable at its destination
       within its layer network.

   30 network in coordination with the management
       plane or control plane.

   31  MPLS-TP MUST be capable of using P2MP server (sub-)layer
       capabilities as well as P2P server (sub-)layer capabilities when
       supporting P2MP MPLS-TP transport paths.

   31

   32  MPLS-TP MUST support unidirectional, co-routed bidirectional and
       associated bidirectional point-to-point transport paths.

   32

   33  The end points of a co-routed bidirectional transport path MUST
       be aware of the pairing relationship of the forward and reverse
       paths used to support the bidirectional service.

   34  The intermediate nodes (including MEPs, MIPs and other internal
       functions as appropriate) of a co-routed bidirectional transport
       path at each (sub-)layer MUST be aware about of the pairing
       relationship of the forward and the backward directions belonging to the same co-routed bidirectional of that
       transport path.

   33  MPLS-TP MUST support

   35  The end points of an associated bidirectional transport paths with
       asymmetric bandwidth requirements, i.e. path MUST
       be aware of the amount pairing relationship of reserved
       bandwidth differs between the forward and backward directions.

   34  MPLS-TP MUST reverse
       paths used to support unidirectional point-to-multipoint transport
       paths.

   35  MPLS-TP MUST be extensible in the bidirectional service.

   36  The intermediate nodes (including MEPs, MIPs and other internal
       functions as appropriate) of an associated bidirectional
       transport path at each (sub-)layer SHOULD NOT be aware of the
       pairing relationship of the forward and the backward directions
       of that transport path.

   37  MPLS-TP MUST support bidirectional transport paths with
       asymmetric bandwidth requirements, i.e. the amount of reserved
       bandwidth differs between the forward and backward directions.

   38  MPLS-TP MUST support unidirectional point-to-multipoint transport
       paths.

   39  MPLS-TP MUST be extensible in order to accommodate new types of
       client layer networks and services.

   36

   40  MPLS-TP SHOULD support mechanisms to enable the reserved
       bandwidth associated with a transport path to be increased
       without impacting the existing traffic on that transport path
       provided enough resources are available.

   37

   41  MPLS-TP SHOULD support mechanisms to enable the reserved
       bandwidth of a transport path to be decreased without impacting
       the existing traffic on that transport path, provided that the
       level of existing traffic is smaller than the reserved bandwidth
       following the decrease.

   38

   42  MPLS-TP MUST support mechanisms which ensure the integrity of the
       transported customer's service traffic as required by its
       associated SLA.  Loss of integrity may be defined as packet
       corruption, re-ordering or loss during normal network conditions.

   39

   43  MPLS-TP MUST support mechanisms to detect when loss of integrity
       of the transported customer's service traffic has occurred.

   40

   44  MPLS-TP MUST support an unambiguous and reliable means of
       distinguishing users' (client) packets from MPLS-TP control
       packets (e.g. control plane, management plane, OAM and protection
       switching packets).

2.4.  Control plane requirements

   This section defines the requirements that apply to an MPLS-TP
   control plane.  Note that it MUST be possible to operate an MPLS-TP
   network without using a control plane.

   The ITU-T has defined an architecture for Automatically Switched
   Optical and Transport Networks (ASON/ASTN) in G.8080 [ITU.G8080.2006]
   and G.8080 Amd1 [ITU.G8080.2008].  The control plane for MPLS-TP MUST
   fit within the ASON/ASTN architecture.

   An interpretation of the ASON/ASTN signaling and routing requirements
   in the context of GMPLS can be found in [RFC4139] and [RFC4258].

   Additionally:

   41

   45  It MUST be possible to operate and configure the MPLS-TP data
       plane without any IP forwarding capability in the MPLS-TP data
       plane.

   42

   46  The MPLS-TP control pane MUST support control plane topology and
       data plane topology independence.  As a consequence a failure of
       the control plane does not imply that there has also been a
       failure of the data plane.

   43

   47  The MPLS-TP control plane MUST be able to be operated independent
       of any particular client or server layer control plane.

   44

   48  MPLS-TP SHOULD define a solution to support an integrated control
       plane encompassing MPLS-TP together with its server and client
       layer networks when these layer networks belong to the same
       administrative domain.

   45

   49  The MPLS-TP control plane MUST support establishing all the
       connectivity patterns defined for the MPLS-TP data plane (e.g.,
       unidirectional and bidirectional P2P, unidirectional P2MP, etc.)
       including configuration of protection functions and any
       associated maintenance functions.

   46

   50  The MPLS-TP control plane MUST support the configuration and
       modification of OAM maintenance points as well as the activation/
       deactivation of OAM when the transport path or transport service
       is established or modified.

   47

   51  An MPLS-TP control plane MUST support operation of the recovery
       functions described in Section 2.8.

   48

   52  An MPLS-TP control plane MUST scale gracefully to support a large
       number of transport paths, nodes and links.

   49

   53  If a control plane is used for MPLS-TP, the control plane's
       graceful restart capabilities, if any, MUST be supported.

   54  An MPLS-TP control plane MUST provide a mechanism for dynamic
       ownership transfer of the control of MPLS-TP transport paths from
       the management plane to the control plane and vice versa.  The
       number of reconfigurations required in the data plane MUST be
       minimized (preferably no data plane reconfiguration will be
       required).

2.5.  Network Management (NM) requirements

   For requirements related to NM functionality (Management Plane in
   ITU-T terminology) for MPLS-TP, see the MPLS-TP NM requirements
   document [I-D.gray-mpls-tp-nm-req]. [I-D.ietf-mpls-tp-nm-req].

2.6.  Operation, Administration and Maintenance (OAM) requirements

   For requirements related to OAM functionality for MPLS-TP, see the
   MPLS-TP OAM requirements document
   [I-D.ietf-mpls-tp-oam-requirements].

2.7.  Network performance management (PM) requirements

   For requirements related to PM functionality for MPLS-TP, see the
   MPLS-TP OAM requirements document
   [I-D.ietf-mpls-tp-oam-requirements].

2.8.  Recovery requirements

   Network survivability plays a critical role in the delivery of
   reliable services.  Network availability is a significant contributor
   to revenue and profit.  Service guarantees in the form of SLAs
   require a resilient network that rapidly detects facility or node
   failures and restores network operation in accordance with the terms
   of the SLA.

   50

   55  MPLS-TP MUST provide protection and restoration mechanisms.

       A.  MPLS-TP recovery techniques SHOULD be identical (or as
           similar as possible) to those already used in existing
           transport networks to simplify implementation and operations.
           However, this MUST NOT override any other requirement.

       B.  Recovery techniques used for P2P and P2MP SHOULD be identical
           to simplify implementation and operation.  However, this MUST
           NOT override any other requirement.

   51

   56  MPLS-TP recovery mechanisms MUST be applicable at various levels
       throughout the network including support for link, transport
       path, segment, concatenated segment and end to end recovery.

   52

   57  MPLS-TP recovery paths MUST meet the SLA protection objectives of
       the service.

       A.  MPLS-TP MUST provide mechanisms to guarantee 50ms recovery
           times from the moment of fault detection in networks with
           spans less than 1200 km.

       B.  For protection it MUST be possible to require protection of
           100% of the traffic on the protected path.

       C.  Recovery objectives SHOULD be configurable per transport
           path, and SHOULD support objectives for bandwidth and QoS.

       D.  Recovery MUST meet SLA requirements over multiple domains.

   53

   58  The recovery mechanisms SHOULD be applicable to any topology.

   54

   59  The recovery mechanisms MUST support the means to operate in
       synergy with (including coordination of timing) the recovery
       mechanisms present in any client or server transport networks
       (for example, Ethernet, SDH, OTN, WDM) to avoid race conditions
       between the layers.

   55

   60  MPLS-TP recovery and reversion mechanisms MUST prevent frequent
       operation of recovery in the event of an intermittent defect.

2.8.1.  Data plane behavior requirements

   General protection and survivability requirements are expressed in
   terms of the behavior in the data plane.

2.8.1.1.  Protection

   56

   Note: Only nodes that are aware of the pairing relationship between
   the forward and backward directions of an associated bidirectional
   transport path can be used as end points to protect all or part of
   that transport path.

   61  MPLS-TP MUST support 1+1 protection.

       A.  Bidirectional 1+1 protection for P2P connectivity MUST be
           supported.

       B.  Unidirectional 1+1 protection for P2P connectivity MUST be
           supported.

       C.  Unidirectional 1+1 protection for P2MP connectivity MUST be
           supported.

   57

   62  MPLS-TP MUST support 1:n protection (including 1:1 protection).

       A.  MPLS-TP 1:n protection MUST include bidirectional protection
           switching for P2P connectivity, and this SHOULD be the
           default behavior for 1:n protection.

       B.  Unidirectional 1:n protection for P2MP connectivity MUST be
           supported.

       C.  Unidirectional 1:n protection for P2P connectivity is not
           required.
           required and MAY be omitted from the MPLS-TP specifications.

       D.  The action of protection switching MUST NOT cause user data
           to loop.  Backtracking is allowed.

   Note: Support for extra traffic (as defined in [RFC4427]) is not
   required in MPLS-TP. MPLS-TP and MAY be omitted from the MPLS-TP
   specifications.

2.8.1.2.  Restoration

   58

   63  The restoration transport path MUST be able to share resources
       with the transport path being replaced (sometimes known as soft
       rerouting).

   59

   64  Restoration priority MUST be supported so that an implementation
       can determine the order in which transport paths should be
       restored (to minimize service restoration time as well as to gain
       access to available spare capacity on the best paths).

   60

   65  Preemption priority MUST be supported to allow restoration to
       displace other transport paths in the event of resource
       constraint.

2.8.1.3.  Sharing of protection resources

   61

   66  MPLS-TP SHOULD support 1:n (including 1:1) shared mesh
       restoration.

   62

   67  MPLS-TP MUST support the definition of shared protection groups
       to allow the coordination of protection actions resulting from
       triggers caused by events at different locations in the network.

   63

   68  MPLS-TP MUST support sharing of protection resources such that
       protection paths that are known not to be required concurrently
       can share the same resources.

2.8.1.4.  Reversion

   64

   69  MPLS-TP protection mechanisms MUST support revertive and non-
       revertive behavior.  Reversion MUST be the default behavior.

   65

   70  MPLS-TP restoration mechanisms MUST support revertive and non-
       revertive behavior.

2.8.2.  Triggers for protection, restoration, and reversion

   Recovery actions may be triggered from different places as follows:

   66

   71  MPLS-TP MUST support physical layer fault indication triggers.

   67

   72  MPLS-TP MUST support OAM-based triggers.

   68

   73  MPLS-TP MUST support management plane triggers (e.g., forced
       switch, etc.).

   69

   74  There MUST be a mechanism to allow administrative recovery
       actions to be distinguished from recovery actions initiated by
       other triggers.

   70

   75  Where a control plane is present, MPLS-TP SHOULD support control
       plane triggers.

   71

   76  MPLS-TP protection mechanisms MUST support priority logic to
       negotiate and accommodate coexisting requests (i.e., multiple
       requests) for protection switching (e.g., administrative requests
       and requests due to link/node failures).

2.8.3.  Management plane operation of protection and restoration

   All functions described here are for control by the operator.

   72

   77  It MUST be possible to configure protection paths and protection-
       to-working path relationships (sometimes known as protection
       groups).

   73

   78  There MUST be support for pre-calculation of recovery paths.

   74

   79  There MUST be support for pre-provisioning of recovery paths.

   75

   80  The external controls as defined in [RFC4427] MUST be supported.

       A.  External controls overruled by higher priority requests
           (e.g., administrative requests and requests due to link/node
           failures) or unable to be signaled to the remote end (e.g.
           because of a protection state coordination fail) MUST be
           dropped.

   76

   81  There MUST be support for the configuration of timers used for
       recovery operation.

   77

   82  Restoration resources MAY be pre-planned and selected a priori,
       or computed after failure occurrence.

   78

   83  When preemption is supported for restoration purposes, it MUST be
       possible for the operator to configure it.

   79

   84  The management plane MUST provide indications of protection
       events and triggers.

   80

   85  The management plane MUST allow the current protection status of
       all transport paths to be determined.

2.8.4.  Control plane and in-band OAM operation of recovery

   81

   86  The MPLS-TP control plane (which is not mandatory in an MPLS-TP
       implementation) MUST be capable of supporting:

       A.  establishment and maintenance of all recovery entities and
           functions

       B.  signaling of administrative control

       C.  protection state coordination (PSC).  Since control plane
           network topology is independent from the data plane network
           topology, the PSC supported by the MPLS-TP control plane MAY
           run on resources different than the data plane resources
           handled within the recovery mechanism (e.g. backup).

   82

   87  In-band OAM MUST be capable of supporting:

       A.  signaling of administrative control
       B.  protection state coordination (PSC).  Since in-band OAM tools
           share the data plane with the carried transport service, in
           order to optimize the usage of network resources, the PSC
           supported by in-band OAM MUST run on protection resources.

2.8.5.  Topology-specific recovery mechanisms

   83

   88  MPLS-TP MAY support recovery mechanisms that are optimized for
       specific network topologies.  These mechanisms MUST be
       interoperable with the mechanisms defined for arbitrary topology
       (mesh) networks to enable protection of end-to-end transport
       paths.

2.8.5.1.  Ring protection

   Several service providers have expressed a high level of interest in
   operating MPLS-TP in ring topologies and require a high level of
   survivability function in these topologies.  The requirements listed
   below have been collected from these service providers and from the
   ITU-T.

   The main objective in considering a specific topology (such as a
   ring) is to determine whether it is possible to optimize any
   mechanisms such that the performance of those mechanisms within the
   topology is significantly better than the performance of the generic
   mechanisms in the same topology.  The benefits of such optimizations
   are traded against the costs of developing, implementing, deploying,
   and operating the additional optimized mechanisms noting that the
   generic mechanisms MUST continue to be supported.

   Within the context of recovery in MPLS-TP networks, the optimization
   criteria considered in ring topologies are as follows:

   a.  Minimize the number of OAM entities that are needed to trigger
       the recovery operation - less than are required by other recovery
       mechanisms.

   b.  Minimize the number of elements of recovery in the ring - less
       than are required by other recovery mechanisms.

   c.  Minimize the number of labels required for the protection paths
       across the ring - less than are required by other recovery
       mechanisms.

   d.  Minimize the amount of control and management plane transactions
       during a maintenance operation (e.g., ring upgrade) - less than
       are required by other recovery mechanisms.

   e.  When a control plane is supported, minimize the impact on
       signalling
       signaling and routing information exchange during protection -
       less than are required by other recovery mechanisms.

   It may be observed that the requirements in this section are fully
   compatible with the generic requirements expressed above, and that no
   requirements that are specific to ring topologies have been
   identified.

   84

   89   MPLS-TP MUST include recovery mechanisms that operate in any
        single ring supported in MPLS-TP, and continue to operate within
        the single rings even when the rings are interconnected.

   85

   90   When a network is constructed from interconnected rings, MPLS-TP
        MUST support recovery mechanisms that protect user data that
        traverses more than one ring.  This includes the possibility of
        failure of the ring-interconnect nodes and links.

   86

   91   MPLS-TP recovery in a ring MUST protect unidirectional and
        bidirectional P2P transport paths.

   87

   92   MPLS-TP recovery in a ring MUST protect unidirectional P2MP
        transport paths.

   88

   93   MPLS-TP 1+1 and 1:1 protection in a ring MUST support switching
        time within 50 ms from the moment of fault detection in a
        network with a 16 nodes ring with less than 1200 km of fiber.

   89

   94   The protection switching time in a ring MUST be independent of
        the number of LSPs crossing the ring.

   90

   95   Recovery actions in a ring MUST be data plane functions
        triggered by different elements of control.  The triggers are
        configured by management or control planes and are subject to
        configurable policy.

   91

   96   The configuration and operation of recovery mechanisms in a ring
        MUST scale well with:

        A.  the number of transport paths (must be better than linear
            scaling)

        B.  the number of nodes on the ring (must be at least as good as
            linear scaling)

        C.  the number of ring interconnects (must be at least as good
            as linear scaling)
   92
   97   Recovery techniques used in a ring MUST NOT prevent the ring
        from being connected to a general MPLS-TP network in any
        arbitrary way, and MUST NOT prevent the operation of recovery
        techniques in the rest of the network.

   93

   98   MPLS-TP Recovery mechanisms applicable to a ring MUST be equally
        applicable in physical and logical rings.

   94

   99   Recovery techniques in a ring SHOULD be identical (or as similar
        as possible) to those in general transport networks to simplify
        implementation and operations.  However, this MUST NOT override
        any other requirement.

   95

   100  Recovery techniques in logical and physical rings SHOULD be
        identical to simplify implementation and operation.  However,
        this MUST NOT override any other requirement.

   96

   101  The default recovery scheme in a ring MUST be bidirectional
        recovery in order to simplify the recovery operation.

   97

   102  The recovery mechanism in a ring MUST support revertive
        switching, which MUST be the default behaviour. behavior.  This allows
        optimization of the use of the ring resources, and restores the
        preferred quality conditions for normal traffic (e.g., delay)
        when the recovery mechanism is no longer needed.

   98

   103  The recovery mechanisms in a ring MUST support ways to allow
        administrative protection switching, to be distinguished from
        protection switching initiated by other triggers.

   99

   104  It MUST be possible to lockout (disable) protection mechanisms
        on selected links (spans) in a ring (depending on operator's
        need).  This may require lockout mechanisms to be applied to
        intermediate nodes within a transport path.

   100

   105  MPLS-TP recovery mechanisms in a ring:

        A.  MUST include a mechanism to allow an implementation to
            handle (including the coordination of) coexisting requests
            or triggers (i.e., multiple requests - not necessarily
            arriving simultaneously and located anywhere in the ring)
            for protection switching based on priority.  Note that such
            coordiantion
            coordination is the ring equivalent of the definition of
            shared protection groups.

        B.  MAY support multiple failures without reconfiguring the
            protection actions.

   101

   106  MPLS-TP recovery and reversion mechanisms in a ring MUST offer a
        way to prevent frequent operation of recovery in the event of an
        intermittent defect.

   102

   107  MPLS-TP MUST support the sharing of protection bandwidth in a
        ring by allowing best effort traffic.

   103

   108  MPLS-TP MUST support sharing of ring protection resources such
        that protection paths that are known not to be required
        concurrently can share the same resources.

2.9.  QoS requirements

   Carriers require advanced traffic management capabilities to enforce
   and guarantee the QoS parameters of customers' SLAs.

   Quality of service mechanisms are REQUIRED in an MPLS-TP network to
   ensure:

   104

   109  Support for differentiated services and different traffic types
        with traffic class separation associated with different traffic.

   105

   110  Enabling the provisioning and the guarantee of Service Level
        Specifications (SLS), with support for hard and relative end-to-
        end bandwidth guaranteed.

   106

   111  Support of services, which are sensitive to jitter and delay.

   107

   112  Guarantee of fair access, within a particular class, to shared
        resources.

   108

   113  Guaranteed resources for in-band control and management plane
        traffic regardless of the amount of data plane traffic.

   109

   114  Carriers are provided with the capability to efficiently support
        service demands over the MPLS-TP network.  This MUST include
        support for a flexible bandwidth allocation scheme.

2.10.  Security requirements

   For a description of the security threats relevant in the context of
   MPLS and GMPLS and the defensive techniques to combat those threats
   see the Security Framework for MPLS & GMPLS Networks
   [I-D.draft-ietf-mpls-mpls-and-gmpls-security-framework].
   [I-D.ietf-mpls-mpls-and-gmpls-security-framework].

3.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

4.  Security Considerations

   See Section 2.10.

5.  Acknowledgements

   The authors would like to thank all members of the teams (the Joint
   Working Team, the MPLS Interoperability Design Team in the IETF, and
   the T-MPLS Ad Hoc Group in the ITU-T) involved in the definition and
   specification of MPLS Transport Profile.

   The authors would also like to thank Loa Andersson, Dieter Beller,
   Lou Berger, Italo Busi, John Drake, Adrian Farrel, Annamaria
   Fulignoli, Pietro Grandi, Eric Gray, Neil Harrison, Huub van
   Helvoort, Enrique Hernandez-Valencia, Wataru Imajuku, Kam Lam, Andy
   Malis, Alan McGuire, Julien Meuric, Greg Mirsky, Tom Nadeau, Hiroshi
   Ohta, Tom Petch, Andy Reid, Vincenzo Sestito, George Swallow, Lubo
   Tancevski, Tomonori Takeda, Yuji Tochio, Alexander Vainshtein, Eve
   Varma and Maarten Vissers for their comments and enhancements to the
   text.

   An ad hoc discussion group consisting of Stewart Bryant, Italo Busi,
   Andrea Digiglio, Li Fang, Adrian Farrel, Jia He, Huub van Helvoort,
   Feng Huang, Harald Kullman, Han Li, Hao Long and Nurit Sprecher
   provided valuable input to the requirements for deployment and
   survivability in ring topologies.

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

   [RFC3985]  Bryant, S. and P. Pate, "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.

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

   [RFC4427]  Mannie, E. and D. Papadimitriou, "Recovery (Protection and
              Restoration) Terminology for Generalized Multi-Protocol
              Label Switching (GMPLS)", RFC 4427, March 2006.

   [I-D.ietf-pwe3-ms-pw-arch]
              Bocci, M.

   [I-D.ietf-mpls-mpls-and-gmpls-security-framework]
              Fang, L. and S. Bryant, "Requirements M. Behringer, "Security Framework for OAM in MPLS
              Transport
              and GMPLS Networks", draft-ietf-pwe3-ms-pw-arch-06
              draft-ietf-mpls-mpls-and-gmpls-security-framework-05 (work
              in progress), September November 2008.

   [I-D.gray-mpls-tp-nm-req]
              Lam, H., Mansfield, S., and E. Gray, "MPLS TP Network
              Management Requirements", draft-gray-mpls-tp-nm-req-03
              (work in progress), January 2009.

   [I-D.ietf-mpls-tp-oam-requirements]
              Vigoureux, M., Ward, D., and

   [I-D.ietf-pwe3-ms-pw-arch]
              Bocci, M. Betts, and S. Bryant, "Requirements for OAM in MPLS
              Transport Networks",
              draft-ietf-mpls-tp-oam-requirements-01 (work in progress),
              November 2008.

   [I-D.draft-ietf-mpls-mpls-and-gmpls-security-framework]
              Fang, L. and M. Behringer, "Security Framework for MPLS
              and GMPLS Networks",
              draft-ietf-mpls-mpls-and-gmpls-security-framework-04 draft-ietf-pwe3-ms-pw-arch-06 (work
              in progress), November September 2008.

   [ITU.G870.2008]

   [ITU.G805.2000]
              International Telecommunications Union, "Terms and
              definitions for optical "Generic
              functional architecture of transport networks (OTN)", networks", ITU-
              T Recommendation G.870, G.805, March 2008. 2000.

   [ITU.G8080.2006]
              International Telecommunications Union, "Architecture for
              the automatically switched optical network (ASON)", ITU-
              T Recommendation G.8080, June 2006.

   [ITU.G8080.2008]
              International Telecommunications Union, "Architecture for
              the automatically switched optical network (ASON)
              Amendment 1", ITU-T Recommendation G.8080 Amendment 1,
              March 2008.

6.2.  Informative References

   [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.

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

   [RFC4397]  Bryskin, I. and A. Farrel, "A Lexicography for the
              Interpretation of Generalized Multiprotocol Label
              Switching (GMPLS) Terminology within the Context of the
              ITU-T's Automatically Switched Optical Network (ASON)
              Architecture", RFC 4397, February 2006.

   [ITU.Y2611.2006]
              International Telecommunications Union, "High-level
              architecture of future packet-based networks", ITU-
              T Recommendation Y.2611, December 2006.

   [I-D.ietf-mpls-tp-nm-req]
              Lam, H., Mansfield, S., and E. Gray, "MPLS TP Network
              Management Requirements", draft-ietf-mpls-tp-nm-req-00
              (work in progress), January 2009.

   [I-D.ietf-mpls-tp-oam-requirements]
              Vigoureux, M., Ward, D., and M. Betts, "Requirements for
              OAM in MPLS Transport Networks",
              draft-ietf-mpls-tp-oam-requirements-01 (work in progress),
              November 2008.

   [ITU.Y1401.2008]
              International Telecommunications Union, "Principles of
              interworking", ITU-T Recommendation Y.1401, February 2008.

   [ITU.G805.2000]

   [ITU.Y2611.2006]
              International Telecommunications Union, "Generic
              functional "High-level
              architecture of transport future packet-based networks", ITU-
              T Recommendation G.805, March 2000. Y.2611, December 2006.

Authors' Addresses

   Ben Niven-Jenkins (editor)
   BT
   208 Callisto House, Adastral Park
   Ipswich, Suffolk  IP5 3RE
   UK

   Email: benjamin.niven-jenkins@bt.com

   Deborah Brungard (editor)
   AT&T
   Rm. D1-3C22 - 200 S. Laurel Ave.
   Middletown, NJ  07748
   USA

   Email: dbrungard@att.com
   Malcolm Betts (editor)
   Nortel Networks
   3500 Carling Avenue
   Ottawa, Ontario  K2H 8E9
   Canada

   Email: betts01@nortel.com

   Nurit Sprecher
   Nokia Siemens Networks
   3 Hanagar St. Neve Ne'eman B
   Hod Hasharon,   45241
   Israel

   Email: nurit.sprecher@nsn.com

   Satoshi Ueno
   NTT

   Email: satoshi.ueno@ntt.com