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Versions: (draft-jenkins-mpls-mpls-tp-requirements) 00 01 02 03 04 05 06 07 08 09 10 RFC 5654

Network Working Group                              B. Niven-Jenkins, Ed.
Internet-Draft                                                        BT
Intended status: Informational                          D. Brungard, Ed.
Expires: August 9, 2009                                             AT&T
                                                           M. Betts, Ed.
                                                         Nortel Networks
                                                             N. Sprecher
                                                  Nokia Siemens Networks
                                                                 S. Ueno
                                                                     NTT
                                                        February 5, 2009


                          MPLS-TP Requirements
                   draft-ietf-mpls-tp-requirements-04

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   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.

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 architecture 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 architecture
   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

   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 RFC 2119.
























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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  6
     1.2.  Transport network overview . . . . . . . . . . . . . . . .  8
     1.3.  Layer network overview . . . . . . . . . . . . . . . . . . 10
   2.  MPLS-TP Requirements . . . . . . . . . . . . . . . . . . . . . 10
     2.1.  General requirements . . . . . . . . . . . . . . . . . . . 11
     2.2.  Layering requirements  . . . . . . . . . . . . . . . . . . 12
     2.3.  Data plane requirements  . . . . . . . . . . . . . . . . . 13
     2.4.  Control plane requirements . . . . . . . . . . . . . . . . 15
     2.5.  Network Management (NM) requirements . . . . . . . . . . . 15
     2.6.  Operation, Administration and Maintenance (OAM)
           requirements . . . . . . . . . . . . . . . . . . . . . . . 15
     2.7.  Network performance management (PM) requirements . . . . . 16
     2.8.  Recovery & Survivability requirements  . . . . . . . . . . 16
       2.8.1.  Data plane behavior requirements . . . . . . . . . . . 17
       2.8.2.  Triggers for protection, restoration, and reversion  . 18
       2.8.3.  Management plane operation of protection and
               restoration  . . . . . . . . . . . . . . . . . . . . . 19
       2.8.4.  Control plane and in-band OAM operation of recovery  . 19
       2.8.5.  Topology-specific recovery mechanisms  . . . . . . . . 20
     2.9.  QoS requirements . . . . . . . . . . . . . . . . . . . . . 23
     2.10. Security requirements  . . . . . . . . . . . . . . . . . . 24
   3.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 24
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 24
   5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 25
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 25
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26




















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1.  Introduction

   For many years, transport networks (e.g.  Synchronous Optical
   Networking (SONET)/Synchronous Digital hierarchy (SDH)) have provided
   carriers with a high benchmark for reliability and operational
   simplicity.  With the accelerating growth and penetration of:

   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 requirements.

   Carriers are in need of technologies capable of efficiently
   supporting packet-based services and applications on their transport
   networks.  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.

   Carriers are considering migrating or evolving to packet transport
   networks in order to reduce their costs and to improve their ability
   to support services with guaranteed Service Level Agreements (SLAs).
   For carriers it is important that migrating from their existing
   transport networks to packet transport networks should not involve
   dramatic changes in network operation, should not necessitate
   extensive retraining, and should not require major changes to
   existing work practices.  The aim is to preserve the look-and-feel to
   which carriers have become accustomed in deploying their transport
   networks, while providing common, multi-layer operations, resiliency,
   control and management for packet, circuit and lambda transport
   networks.

   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 (Operations Support System (OSS)
   based) or dynamic (control plane) provisioning of deterministic,
   protected and secured services and their associated resources.

   Carriers will still need to cope with legacy networks (which are
   composed of many layers and technologies), thus the packet transport
   network should interwork as appropriate with other packet and
   transport networks (both horizontally and vertically).  Vertical
   interworking is also known as client/server or network interworking.
   Horizontal interworking is also known as peer-partition or service
   interworking.  For more details on each type of interworking and some



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   of the issues that may arise (especially with horizontal
   interworking) see Y.1401 [ITU.Y1401.2008].

   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 is therefore the need to
   define an MPLS Transport Profile (MPLS-TP) in order to support the
   capabilities and functionalities needed for packet transport network
   services and operations through combining the packet experience of
   MPLS with the operational experience 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 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-IETF effort to include an
   MPLS Transport Profile within the IETF MPLS architecture 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 architecture
   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 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



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   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.

   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 may or may not follow the same route (links
   and nodes) across the network.

   Bidirectional path: A path where the forward and backward directions
   follow the same route (links and nodes) across the network.

   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.

   Co-routed bidirectional path: A bidirectional path where the forward
   and backward directions follow the same route (links and nodes)
   across its layer network.

   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



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   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(s)
   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 zero or more sublayers.  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.

   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 MSPL-TP
   pseudowires) and physical data links that form a ring topology.

   Path: See Transport path.

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

   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 data 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: A section is a server layer (which may be MPLS-TP or a
   different technology) which provides for encapsulation and OAM of a
   MPLS-TP transport path client layer.  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 {S|T}-PEs).

   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



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   layer network and offers no direct transport service for a higher
   layer (client) network.

   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, a
   monitored concatenated segment or any other monitored ordered
   sequence of contiguous hops and/or segments (and their
   interconnecting nodes) of a transport path.

   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 which provides point-to-point
   or point-to-multipoint transport paths which are used to carry a
   higher (client) layer network or aggregates of higher (client) layer
   networks, for example the transport service layer.  It provides for
   independent OAM (of the client OAM) in the transport of the 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 which 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 connection (or transport path) service is the basic service
   provided by a transport network.  The purpose of a transport network
   is to carry its clients (i.e. the stream of client PDUs or client
   bits) between endpoints in the network (typically over several
   intermediate nodes).  These endpoints may be service switching points
   or service terminating points.  The connection services offered to
   customers are 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.

   Aggregation and hierarchy are beneficial for achieving scalability
   and security since:



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   1.  They reduce the number of provisioning and forwarding states in
       the network core.

   2.  They reduce load and the cost of implementing service assurance
       and fault management.

   3.  Clients are 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 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.  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.

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

   Quality-of-service mechanisms are required in the packet transport
   network to ensure the prioritization of critical services, to
   guarantee BW and to control jitter and delay.






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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 the
   clients include the control of forwarding, the control of resource
   reservation, the control of traffic demerging, and the OAM 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 features in order to support the
   control of forwarding, resource reservation, and OAM.  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 as the 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 within
   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





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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 fulfil 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, without
       a gateway function, with existing IETF MPLS [RFC3031] and IETF
       PWE3 [RFC3985] control and data planes where appropriate.

   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 network,
       and between networks.

   5   MPLS-TP MUST be a connection-oriented packet switching model 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 allow the physical separation of the control and
       management planes from the data plane.

   9   MPLS-TP MUST support static provisioning of transport paths via
       an OSS, i.e. 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.






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   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 provided to support dynamic provisioning of
       MPLS-TP transport paths via a control plane.

   14  The MPLS-TP data plane MUST be capable of forwarding data and
       taking recovery actions independently of the control or
       management plane used to operate the MPLS-TP layer network.  That
       is, the MPLS-TP data plane MUST continue to operate normally if
       the management plane or control plane that configured the
       transport paths fails.

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

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

   17  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.

   18  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.

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

2.2.  Layering requirements








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

   21  A 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.

   22  In an environment where an MPLS-TP layer network is supporting a
       client 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
       network.

   23  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.
   Different administrative groups may be responsible for the same layer
   network or different layer networks.

   24  It MUST be possible to hide MPLS-TP layer network addressing and
       other information (e.g. topology) from client layers.

2.3.  Data plane requirements

   25  The identification of each transport path within its aggregate
       MUST be supported.

   26  A label in a particular link MUST uniquely identify the transport
       path within that link.

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

   28  MPLS-TP MUST be capable of using P2MP server (sub-)layer
       capabilities when supporting P2MP MPLS-TP transport paths (for
       example context-specific labels [RFC5331]).

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







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

   31  The forward and backward directions of a co-routed bidirectional
       transport path MUST follow the same links and nodes within its
       (sub-)layer network.

   32  The intermediate nodes at each (sub-)layer MUST be aware about
       the pairing relationship of the forward and the backward
       directions belonging to the same bidirectional transport path.

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

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

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

   36  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

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

   40  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).








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2.4.  Control plane requirements

   This section defines the requirements that apply to MPLS-TP when a
   control plane is deployed.

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

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

   Additionally:

   41  The MPLS-TP control pane SHOULD support control plane topology
       and data plane topology independence.

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

   43  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.

   44  The MPLS-TP control pane 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.

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

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

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].

2.6.  Operation, Administration and Maintenance (OAM) requirements

   For requirements related to OAM functionality for MPLS-TP, see the
   MPLS-TP OAM requirements document



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   [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 & Survivability 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.

   The requirements in this section use the recovery terminology defined
   in RFC 4427 [RFC4427].

   47  MPLS-TP MUST provide protection and restoration mechanisms.

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

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

   49  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 include bandwidth and QoS.








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   50  The recovery mechanisms MUST all be applicable to any topology.

   51  The recovery mechanisms MUST operate in synergy with (including
       coordination of timing) the recovery mechanisms present in any
       underlying server transport network (for example, Ethernet, SDH,
       OTN, WDM) to avoid race conditions between the layers.

   52  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).

   53  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

   54  MPLS-TP MUST support 1+1 protection.

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

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

       C.  Unidirectional 1+1 protection for P2P connectivity is not
           required.

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

       A.  MPLS-TP 1:n support 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.

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



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   Note: Support for extra traffic (as defined in G.870 [ITU.G870.2008])
   is not required in MPLS-TP.

2.8.1.2.  Restoration

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

   57  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).

   58  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

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

   60  MPLS-TP MUST support the sharing of protection bandwidth by
       allowing best effort traffic.

   61  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.

   62  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

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

   64  MPLS-TP restoration mechanisms MAY 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:







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

   66  MPLS-TP MUST support OAM-based triggers.

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

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

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

2.8.3.  Management plane operation of protection and restoration

   All functions described here are for control by the operator.

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

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

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

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

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

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

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

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

   78  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







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   79  The MPLS-TP control plane (which is not mandatory in an MPLS-TP
       implementation) MUST support:

       A.  establishment and maintenance of all recovery entities and
           functions

       B.  signaling of administrative control

       C.  protection state coordination (PSC)

   80  In-band OAM MAY be used for:

       A.  signaling of administrative control

       B.  protection state coordination

2.8.5.  Topology-specific recovery mechanisms

   81  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.

   Note that topology-specific recovery mechanisms are subject to the
   development of requirements using the normal IETF process.

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:





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   a.  Minimize the number of OAM MEs 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 management plane transactions during a
       maintenance operation (e.g., ring upgrade) - 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.

   82  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.

   83  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.

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

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

   86  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.

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

   88  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.





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   89  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)

   90  MPLS-TP recovery in ring topologies MAY support multiple failures
       without reconfiguring the protection actions.

   91  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.

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

   93  Recovery techniques in a ring SHOULD be identical to those in
       general networks to simplify implementation.  However, this MUST
       NOT override any other requirement.

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

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

   96  The recovery mechanism in a ring MUST support revertive
       switching, which MUST be the default behaviour.  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.

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

   98  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.



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   99   MPLS-TP recovery mechanisms in a ring MUST include a mechanism
        to allow an implementation to handle coexisting requests (i.e.,
        multiple requests - not necessarily arriving simultaneously) for
        protection switching based on priority.

   100  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.

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

   102  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.

   103  MUST support the coordination of triggers caused by events at
        different locations in a ring.  Note that this is the ring
        equivalent of the definition of shared protection groups.

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

   105  Prioritization of critical services.

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

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

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

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







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   110  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].


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

   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].


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, Lou Berger, Italo
   Busi, John Drake, Adrian Farrel, Eric Gray, Neil Harrison, Huub van
   Helvoort, Wataru Imajuku, Julien Meuric, Tom Nadeau, Hiroshi Ohta,
   George Swallow, Tomonori Takeda 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.





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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.

   [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-02
              (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-00 (work in progress),
              November 2008.

6.2.  Informative References

   [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.

   [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.

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

   [RFC5331]  Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
              Label Assignment and Context-Specific Label Space",
              RFC 5331, August 2008.



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   [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 (work
              in progress), November 2008.

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

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

   [ITU.G805.2000]
              International Telecommunications Union, "Generic
              functional architecture of transport networks", ITU-
              T Recommendation G.805, March 2000.

   [ITU.G870.2008]
              International Telecommunications Union, "Terms and
              definitions for optical transport networks (OTN)", ITU-
              T Recommendation G.870, March 2008.

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


Authors' Addresses

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

   Email: benjamin.niven-jenkins@bt.com











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   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



















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