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RFC 5654

Requirements of an MPLS Transport Profile

Pages: 31
Proposed Standard
Errata

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Network Working Group                              B. Niven-Jenkins, Ed.
Request for Comments: 5654                                            BT
Category: Standards Track                               D. Brungard, Ed.
                                                                    AT&T
                                                           M. Betts, Ed.
                                                     Huawei Technologies
                                                             N. Sprecher
                                                  Nokia Siemens Networks
                                                                 S. Ueno
                                                      NTT Communications
                                                          September 2009


               Requirements of an MPLS Transport Profile

Abstract

This document specifies the requirements of an MPLS Transport Profile (MPLS-TP). This document is a product of a joint effort of the International Telecommunications Union (ITU) and IETF 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. Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright and License Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved.
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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 1.2.1. Abbreviations . . . . . . . . . . . . . . . . . . . . 6 1.2.2. Definitions . . . . . . . . . . . . . . . . . . . . . 7 1.3. Transport Network Overview . . . . . . . . . . . . . . . . 10 1.4. Layer Network Overview . . . . . . . . . . . . . . . . . . 11 2. MPLS-TP Requirements . . . . . . . . . . . . . . . . . . . . . 12 2.1. General Requirements . . . . . . . . . . . . . . . . . . . 13 2.2. Layering Requirements . . . . . . . . . . . . . . . . . . 16 2.3. Data Plane Requirements . . . . . . . . . . . . . . . . . 17 2.4. Control Plane Requirements . . . . . . . . . . . . . . . . 18 2.5. Recovery Requirements . . . . . . . . . . . . . . . . . . 19 2.5.1. Data-Plane Behavior Requirements . . . . . . . . . . . 20 2.5.1.1. Protection . . . . . . . . . . . . . . . . . . . . 20 2.5.1.2. Sharing of Protection Resources . . . . . . . . . 21 2.5.2. Restoration . . . . . . . . . . . . . . . . . . . . . 21 2.5.3. Triggers for Protection, Restoration, and Reversion . 22 2.5.4. Management-Plane Operation of Protection and Restoration . . . . . . . . . . . . . . . . . . . . . 22 2.5.5. Control Plane and In-Band OAM Operation of Recovery . 23 2.5.6. Topology-Specific Recovery Mechanisms . . . . . . . . 24 2.5.6.1. Ring Protection . . . . . . . . . . . . . . . . . 24 2.6. QoS Requirements . . . . . . . . . . . . . . . . . . . . . 27 3. Requirements Discussed in Other Documents . . . . . . . . . . 27 3.1. Network Management Requirements . . . . . . . . . . . . . 27 3.2. Operation, Administration, and Maintenance (OAM) Requirements . . . . . . . . . . . . . . . . . . . . . . . 27 3.3. Network Performance-Monitoring Requirements . . . . . . . 28 3.4. Security Requirements . . . . . . . . . . . . . . . . . . 28 4. Security Considerations . . . . . . . . . . . . . . . . . . . 28 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6.1. Normative References . . . . . . . . . . . . . . . . . . . 29 6.2. Informative References . . . . . . . . . . . . . . . . . . 29
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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 Quality of Service (QoS) requirements. This growth in demand has resulted in dramatic increases in access rates that are, in turn, driving dramatic increases in metro and core network bandwidth requirements. Over the past two decades, the evolving optical transport infrastructure (Synchronous Optical Networking (SONET) / Synchronous Digital Hierarchy (SDH), Optical Transport Network (OTN)) has provided carriers with a high benchmark for reliability and operational simplicity. 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.
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   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) 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), see G.805 [ITU.G805.2000]
   and Y.1401 [ITU.Y1401.2008].

   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.  Therefore, there is 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 deployment of packet-based transport networks
   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
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   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.

   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.  The document is a
   requirements specification, but is presented on the Standards Track
   so that it can be more easily cited as a normative reference from
   within the work of the 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.  Any new functionality that is
   defined to fulfill the requirements for MPLS-TP must be agreed within
   the IETF through the IETF consensus process as per [RFC4929].

   MPLS-TP transport paths may be established using static or dynamic
   configuration.  It should be noted that the MPLS-TP network and its
   transport paths can always be operated fully (including OAM and
   protection capabilities) in the absence of any control plane.

1.1. 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 [RFC2119]. Although this document is not a protocol specification, the use of this language clarifies the instructions to protocol designers producing solutions that satisfy the requirements set out in this document.

1.2. Terminology

Note: Mapping between the terms in this section and ITU-T terminology is described in [TP-TERMS]. 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.
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1.2.1. Abbreviations

ASON: Automatically Switched Optical Network ATM: Asynchronous Transfer Mode CAPEX: Capital Expenditure CE: Customer Edge FR: Frame Relay GMPLS: Generalized 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 MPLS: Multi-Protocol Label Switching OAM: Operations, Administration, and Maintenance OPEX: Operational Expenditure OSI: Open Systems Interconnection OTN: Optical Transport Network P2MP: Point to Multipoint P2P: Point to Point PDU: Protocol Data Unit PSC: Protection State Coordination PW: Pseudowire QoS: Quality of Service
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   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

1.2.2. 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 that is constructed from a pair of unidirectional paths (one for each direction) that 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".
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   Control Plane: Within the scope of this document, the control plane
   performs transport path control functions.  Through signalling, the
   control plane sets up, modifies and releases transport paths, and may
   recover a transport path in case of a failure.  The control plane
   also performs other functions in support of transport path control,
   such as routing information dissemination.

   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.  A transport network path is typically co-routed.

   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 a 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 1.4 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.
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   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 layer is a server layer (which may
   be MPLS-TP or a different technology) that provides for the transfer
   of the section-layer client information between adjacent nodes in the
   transport-path layer or transport-service 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 {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 [MS-PW-ARCH].

   Terminating Provider Edge (T-PE): See [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.
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   Transport Path Layer: A (sub)layer network that provides point-to-
   point or point-to-multipoint transport paths.  It provides OAM that
   is independent of the clients that it is transporting.

   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.

1.3. 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 end points 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 OAM that is independent (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 meet the quality-of-service objectives of its 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.
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   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.  From a functional
   and operational point of view, the client, transport network, and
   server layers are 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.

1.4. 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 such that the client can populate the payload without affecting any operation within the serving layer network. Here, payload means:
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   o  an individual packet payload (for connectionless networks),

   o  a sequence of packet payloads (for connection-oriented packet-
      switched networks), or

   o  a deterministic schedule of payloads (for circuit-switched
      networks).

   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 de-merging, 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 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

The MPLS-TP requirements set out in this section 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.
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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 subset (necessary and sufficient subset) applicable to a transport network application. 2 The MPLS-TP design SHOULD as far as reasonably possible reuse 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 unidirectional, co-routed bidirectional, and associated bidirectional point-to-point transport paths. 8 MPLS-TP MUST support unidirectional point-to-multipoint transport paths. 9 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. 10 All nodes on the path of a co-routed bidirectional transport path in the same (sub)layer as the path MUST be aware of the pairing relationship of the forward and the backward directions of the transport path. 11 The end points of an associated bidirectional transport path MUST be aware of the pairing relationship of the forward and reverse paths used to support the bidirectional service.
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   12  Nodes on the path of an associated bidirectional transport path
       where both the forward and backward directions transit the same
       node in the same (sub)layer as the path SHOULD be aware of the
       pairing relationship of the forward and the backward directions
       of the transport path.

   13  MPLS-TP MUST support bidirectional transport paths with symmetric
       bandwidth requirements, i.e., the amount of reserved bandwidth is
       the same between the forward and backward directions.

   14  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.

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

   16  MPLS-TP MUST support the physical separation of the control and
       management planes from the data plane.  That is, it must be
       possible to operate the control and management planes out-of-
       band, and no assumptions should be made about the state of the
       data-plane channels from information about the control or
       management-plane channels when they are running out-of-band.

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

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

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

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

   21  Mechanisms in an MPLS-TP layer network that satisfy functional
       requirements that are common to general transport-layer 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-layer technologies.

   22  MPLS-TP MUST support the capability for network operation via the
       management plane (without the use of any control-plane
       protocols).  This includes the configuration and control of OAM
       and recovery functions.
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   23  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 or
           management plane used to configure the MPLS-TP layer network.

       C.  operating normally (i.e., forwarding, OAM, and protection
           MUST continue to operate) if the management plane or control
           plane that configured the transport paths fails.

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

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

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

   27  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 Time-Division Multiplexing
           (TDM) rings to MPLS-TP.  MPLS-TP SHOULD support rings with
           more than 16 nodes.

   28  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 amounts of
       customers, services, and bandwidth demand.

   29  MPLS-TP SHOULD support mechanisms to safeguard against the
       provisioning of transport paths which contain forwarding loops.
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2.2. Layering Requirements

30 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. 31 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. 32 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 below the agreed level. Mechanisms to achieve this are outside the scope of these requirements. 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. 33 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 coordination required between the client and server MPLS(-TP) layer networks MUST be minimized (preferably no coordination 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 Connectionless Network Protocol (CNLP) packets used by the control/management plane of the client MPLS(-TP) layer network). 34 It MUST be possible to operate the layers of a multi-layer network that includes an MPLS-TP layer autonomously.
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   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.

   35  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

36 It MUST be possible to operate and configure the MPLS-TP data plane without any IP forwarding capability in the MPLS-TP data plane. That is, the data plane only operates on the MPLS label. 37 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 able to decompose the aggregate transport path into its component client transport paths. 38 A transport path on a link MUST be uniquely identifiable by a single label on that link. 39 A transport path's source MUST be identifiable at its destination within its layer network. 40 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. 41 MPLS-TP MUST be extensible in order to accommodate new types of client layer networks and services. 42 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. 43 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.
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   44  MPLS-TP MUST support mechanisms that 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, reordering, or loss during normal network conditions.

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

   46  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 Networks (ASONs) in G.8080 [ITU.G8080.2006] and G.8080 Amendment 1 [ITU.G8080.2008]. The control plane for MPLS-TP MUST fit within the ASON architecture. An interpretation of the ASON signaling and routing requirements in the context of GMPLS can be found in [RFC4139] and [RFC4258]. Additionally: 47 The MPLS-TP control plane 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. 48 The MPLS-TP control plane MUST be able to be operated independently of any particular client- or server-layer control plane. 49 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. 50 The MPLS-TP control plane MUST support establishing all the connectivity patterns defined for the MPLS-TP data plane (i.e., unidirectional P2P, associated bidirectional P2P, co-routed bidirectional P2P, unidirectional P2MP) including configuration of protection functions and any associated maintenance functions.
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   51  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.

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

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

   54  If a control plane is used for MPLS-TP, following a control-plane
       failure, the control plane MUST be capable of restarting and
       relearning its previous state without impacting forwarding.

   55  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. 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. 56 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. 57 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. 58 MPLS-TP recovery paths MUST meet the SLA protection objectives of the service.
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       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 MUST meet SLA requirements over multiple domains.

   59  Recovery objectives SHOULD be configurable per transport path.

   60  The recovery mechanisms SHOULD be applicable to any topology.

   61  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.

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

2.5.1. Data-Plane Behavior Requirements

General protection and survivability requirements are expressed in terms of the behavior in the data plane.
2.5.1.1. Protection
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. 63 It MUST be possible to provide protection for the MPLS-TP data plane without any IP forwarding capability in the MPLS-TP data plane. That is, the data plane only operates on the MPLS label. 64 MPLS-TP protection mechanisms MUST support revertive and non- revertive behavior. 65 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.
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       C.  Unidirectional 1+1 protection for P2MP connectivity MUST be
           supported.

   66  MPLS-TP MUST support the ability to share protection resources
       amongst a number of transport paths.

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

       A.  Bidirectional 1:n protection for P2P connectivity MUST be
           supported and 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 and MAY be omitted from the MPLS-TP specifications.

       D.  The action of protection-switching MUST NOT cause the user
           data to enter an uncontrolled loop.  The protection-switching
           system MAY cause traffic to pass over a given link more than
           once, but it must do so in a controlled way such that
           uncontrolled loops do not form.

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

2.5.1.2. Sharing of Protection Resources
68 MPLS-TP SHOULD support 1:n (including 1:1) shared mesh recovery. 69 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.

2.5.2. Restoration

70 The restoration transport path MUST be able to share resources with the transport path being replaced (sometimes known as soft rerouting). 71 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).
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   72  Preemption priority MUST be supported to allow restoration to
       displace other transport paths in the event of resource
       constraint.

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

2.5.3. Triggers for Protection, Restoration, and Reversion

Recovery actions may be triggered from different places as follows: 74 MPLS-TP MUST support fault indication triggers from lower layers. This includes faults detected and reported by lower-layer protocols, and faults reported directly by the physical medium (for example, loss of light). 75 MPLS-TP MUST support OAM-based triggers. 76 MPLS-TP MUST support management-plane triggers (e.g., forced switch, etc.). 77 There MUST be a mechanism to distinguish administrative recovery actions from recovery actions initiated by other triggers. 78 Where a control plane is present, MPLS-TP SHOULD support control- plane restoration triggers. 79 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).

2.5.4. Management-Plane Operation of Protection and Restoration

All functions described here are for control by the operator. 80 It MUST be possible to configure protection paths and protection- to-working path relationships (sometimes known as protection groups). 81 There MUST be support for pre-calculation of recovery paths. 82 There MUST be support for pre-provisioning of recovery paths.
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   83  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.,
           due to a coordination failure of the protection state) MUST
           be dropped.

   84  It MUST be possible to test and validate any protection/
       restoration mechanisms and protocols:

       A.  Including the integrity of the protection/recovery transport
           path.

       B.  Without triggering the actual protection/restoration.

       C.  While the working path is in service.

       D.  While the working path is out of service.

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

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

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

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

2.5.5. Control Plane and In-Band OAM Operation of Recovery

89 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).
Top   ToC   RFC5654 - Page 24
   90  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.

2.5.6. Topology-Specific Recovery Mechanisms

91 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.
2.5.6.1. 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, such that it is less than is required by other recovery mechanisms. b. Minimize the number of elements of recovery in the ring, such that it is less than is required by other recovery mechanisms. c. Minimize the number of labels required for the protection paths across the ring, such that it is less than is required by other recovery mechanisms.
Top   ToC   RFC5654 - Page 25
   d.  Minimize the amount of control and management-plane transactions
       during a maintenance operation (e.g., ring upgrade), such that it
       is less than the amount required by other recovery mechanisms.

   e.  When a control plane is supported, minimize the impact on
       signaling and routing information exchange during protection,
       such that it is less than the impact caused by other recovery
       mechanisms.

   It may be observed that the requirements in Section 2.5.6.1 are fully
   compatible with the generic requirements expressed in Section 2.5
   through Section 2.5.6 inclusive, and that no requirements that are
   specific to ring topologies have been identified.

   92   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.

   93   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.

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

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

   96   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-node ring with less than 1200 km of fiber.

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

   98   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)
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   99   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.

   100  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.

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

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

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

   104  The recovery mechanisms in a ring MUST support ways to
        distinguish administrative protection-switching from protection-
        switching initiated by other triggers.

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

   106  MPLS-TP recovery mechanisms in a ring:

        A.  MUST include a mechanism to allow an implementation to
            handle and coordinate coexisting requests or triggers for
            protection-switching based on priority.  (For example, this
            includes multiple requests that are not necessarily arriving
            simultaneously and that are located anywhere in the ring.)
            Note that such coordination of the ring is equivalent to the
            use of shared protection groups.

        B.  SHOULD protect against multiple failures

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

   109  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.

2.6. 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: 110 Support for differentiated services and different traffic types with traffic class separation associated with different traffic. 111 Enabling the provisioning and the guarantee of Service Level Specifications (SLSs), with support for hard and relative end- to-end bandwidth guaranteed. 112 Support of services, which are sensitive to jitter and delay. 113 Guarantee of fair access, within a particular class, to shared resources. 114 Guaranteed resources for in-band control and management-plane traffic, regardless of the amount of data-plane traffic. 115 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.

3. Requirements Discussed in Other Documents

3.1. Network Management Requirements

For requirements related to network management functionality (Management Plane in ITU-T terminology) for MPLS-TP, see the MPLS-TP Network Management requirements document [TP-NM-REQ].

3.2. Operation, Administration, and Maintenance (OAM) Requirements

For requirements related to OAM functionality for MPLS-TP, see the MPLS-TP OAM requirements document [TP-OAM-REQS].
Top   ToC   RFC5654 - Page 28

3.3. Network Performance-Monitoring Requirements

For requirements related to performance-monitoring functionality for MPLS-TP, see the MPLS-TP OAM requirements document [TP-OAM-REQS].

3.4. 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 "Security Framework for MPLS and GMPLS Networks" [G/MPLS-SEC]. For a description of additional security threats relevant in the context of MPLS-TP and the defensive techniques to combat those threats see "Security Framework for MPLS-TP" [TP-SEC-FMWK].

4. Security Considerations

See Section 3.4.

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 the 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, Jia He, 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.
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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. [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. [RFC4929] Andersson, L. and A. Farrel, "Change Process for Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Protocols and Procedures", BCP 129, RFC 4929, June 2007. [ITU.G805.2000] International Telecommunications Union, "Generic functional architecture of transport networks", ITU-T Recommendation G.805, March 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.
Top   ToC   RFC5654 - Page 30
   [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.

   [TP-SEC-FMWK]     Fang, L. and B. Niven-Jenkins, "Security Framework
                     for MPLS-TP", Work in Progress, July 2009.

   [G/MPLS-SEC]      Fang, L., Ed., "Security Framework for MPLS and
                     GMPLS Networks", Work in Progress, July 2009.

   [TP-NM-REQ]       Lam, H., Mansfield, S., and E. Gray, "MPLS TP
                     Network Management Requirements", Work in Progress,
                     June 2009.

   [TP-TERMS]        van Helvoort, H., Ed., Andersson, L., Ed., and N.
                     Sprecher, Ed., "A Thesaurus for the Terminology
                     used in Multiprotocol Label Switching Transport
                     Profile (MPLS-TP) drafts/RFCs and ITU-T's Transport
                     Network Recommendations", Work in Progress,
                     June 2009.

   [TP-OAM-REQS]     Vigoureux, M., Ed., Ward, D., Ed., and M. Betts,
                     Ed., "Requirements for OAM in MPLS Transport
                     Networks", Work in Progress, June 2009.

   [MS-PW-ARCH]      Bocci, M. and S. Bryant, "An Architecture for
                     Multi-Segment Pseudowire Emulation Edge-to-Edge",
                     Work in Progress, July 2009.

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

   [ITU.Y2611.2006]  International Telecommunications Union, "High-level
                     architecture of future packet-based networks",
                     ITU-T Recommendation Y.2611, December 2006.
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Authors' Addresses

Ben Niven-Jenkins (editor) BT PP8a, 1st Floor, Orion Building, 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) Huawei Technologies EMail: malcolm.betts@huawei.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 Communications EMail: satoshi.ueno@ntt.com