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Internet Engineering Task Force (IETF) H. van Helvoort, Ed.
Request for Comments: 7087 L. Andersson, Ed.
Category: Informational Huawei Technologies
ISSN: 2070-1721 N. Sprecher, Ed.
Nokia Solutions and Networks
December 2013
A Thesaurus for the Interpretation of Terminology Used
in MPLS Transport Profile (MPLS-TP) Internet-Drafts and RFCs
in the Context of the ITU-T's Transport Network Recommendations
Abstract
The MPLS Transport Profile (MPLS-TP) is based on a profile of the
MPLS and Pseudowire (PW) procedures as specified in the MPLS Traffic
Engineering (MPLS-TE), PW, and Multi-Segment Pseudowire (MS-PW)
architectures developed by the Internet Engineering Task Force
(IETF). The International Telecommunication Union Telecommunication
Standardization Sector (ITU-T) has specified a Transport Network
architecture.
This document provides a thesaurus for the interpretation of MPLS-TP
terminology within the context of the ITU-T Transport Network
Recommendations.
It is important to note that MPLS-TP is applicable in a wider set of
contexts than just Transport Networks. The definitions presented in
this document do not provide exclusive or complete interpretations of
MPLS-TP concepts. This document simply allows the MPLS-TP terms to
be applied within the Transport Network context.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7087.
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Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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 Simplified BSD License.
Table of Contents
1. Introduction ....................................................4
1.1. Abbreviations ..............................................4
2. Terminology .....................................................5
2.1. MPLS-TP Terminology Sources ................................5
2.2. ITU-T Transport Network Terminology Sources ................6
2.3. Common Terminology Sources .................................6
3. Thesaurus .......................................................6
3.1. Associated Bidirectional Path ..............................6
3.2. Bidirectional Path .........................................6
3.3. Client-Layer Network .......................................6
3.4. Communication Channel ......................................7
3.5. Concatenated Segment .......................................7
3.6. Control Plane ..............................................7
3.7. Co-Routed Bidirectional Path ...............................7
3.8. Data Communication Network (DCN) ...........................7
3.9. Defect .....................................................8
3.10. Domain ....................................................8
3.11. Embedded Communication Channel (ECC) ......................8
3.12. Equipment Management Function (EMF) .......................8
3.13. Failure ...................................................8
3.14. Fault .....................................................8
3.15. Layer Network .............................................9
3.16. Link ......................................................9
3.17. Maintenance Entity (ME) ...................................9
3.18. Maintenance Entity Group (MEG) ...........................10
3.19. Maintenance Entity Group End Point (MEP) .................10
3.20. Maintenance Entity Group Intermediate Point (MIP) ........11
3.21. Management Communication Channel (MCC) ...................11
3.22. Management Communication Network (MCN) ...................11
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3.23. Monitoring ...............................................11
3.23.1. Path Segment Tunnel (PST) .........................11
3.23.2. Sub-Path Maintenance Element (SPME) ...............12
3.23.3. Tandem Connection .................................12
3.24. MPLS Section .............................................12
3.25. MPLS Transport Profile (MPLS-TP) .........................12
3.26. MPLS-TP NE ...............................................13
3.27. MPLS-TP Network ..........................................13
3.28. MPLS-TP Recovery .........................................13
3.28.1. End-to-End Recovery ...............................13
3.28.2. Link Recovery .....................................13
3.28.3. Segment Recovery ..................................13
3.29. MPLS-TP Ring Topology ....................................13
3.29.1. MPLS-TP Logical Ring ..............................14
3.29.2. MPLS-TP Physical Ring .............................14
3.30. OAM Flow .................................................14
3.31. Operations Support System (OSS) ..........................14
3.32. Path .....................................................14
3.33. Protection Priority ......................................14
3.34. Section-Layer Network ....................................14
3.35. Segment ..................................................15
3.36. Server Layer .............................................15
3.37. Server MEPs ..............................................15
3.38. Signaling Communication Channel (SCC) ....................16
3.39. Signaling Communication Network (SCN) ....................16
3.40. Span .....................................................16
3.41. Sublayer .................................................16
3.42. Transport Entity .........................................16
3.42.1. Working Entity ....................................16
3.42.2. Protection Entity .................................16
3.42.3. Recovery Entity ...................................16
3.43. Transmission Media Layer .................................17
3.44. Transport Network ........................................17
3.45. Transport Path ...........................................17
3.46. Transport-Path Layer .....................................17
3.47. Transport-Service Layer ..................................17
3.48. Unidirectional Path ......................................17
4. Guidance on the Application of This Thesaurus ..................18
5. Management Considerations ......................................18
6. Security Considerations ........................................18
7. Acknowledgments ................................................18
8. Contributors ...................................................18
9. References .....................................................19
9.1. Normative References ......................................19
9.2. Informative References ....................................20
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1. Introduction
The MPLS Transport Profile (MPLS-TP) has been developed by the IETF
to facilitate the Operations, Administration, and Maintenance (OAM)
of Label Switched Paths (LSPs) to be used in a Transport Network
environment as defined by the ITU-T.
The ITU-T has specified a Transport Network architecture for the
transfer of signals from different technologies. This architecture
forms the basis of many Recommendations within the ITU-T.
Because of the difference in historic background of MPLS, and
inherently MPLS-TP (the Internet) and the Transport Network (ITU
Telecommunication Sector), the terminology used is different.
This document provides a thesaurus (the analogy to the Rosetta Stone
has been used within the working groups) for the interpretation of
MPLS-TP terminology within the context of the ITU-T Transport Network
Recommendations. This allows MPLS-TP documents to be generally
understood by those familiar with MPLS RFCs. The definitions
presented in this document do not provide exclusive or complete
interpretations of the ITU-T Transport Network concepts.
1.1. Abbreviations
CE Customer Edge
DCC Data Communication Channel
DCN Data Communication Network
ECC Embedded Communication Channel
EMF Equipment Management Function
EMS Element Management System
GAL Generic Associated Channel Label
LER Label Edge Router
LSR Label Switching Router
MCC Management Communication Channel
MCN Management Communication Network
ME Maintenance Entity
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MEG Maintenance Entity Group
MEP Maintenance Entity Group End Point
MIP Maintenance Entity Group Intermediate Point
MPLS Multiprotocol Label Switching
MPLS-TP MPLS Transport Profile
MS-PW Multi-Segment Pseudowire
NE Network Element
NEF Network Element Function
OAM Operations, Administration, and Maintenance
OSS Operations Support System
PM Performance Monitoring
PST Path Segment Tunnel
PW Pseudowire
S-PE Switching Provider Edge
SCC Signaling Communication Channel
SCN Signaling Communication Network
SPME Sub-Path Maintenance Element
T-PE Terminating Provider Edge
TCM Tandem Connection Monitoring
2. Terminology
This section provides an overview regarding terminology used in this
document.
2.1. MPLS-TP Terminology Sources
MPLS-TP terminology is principally defined in [RFC3031]. Other
documents, including [RFC4397], provide further key definitions.
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2.2. ITU-T Transport Network Terminology Sources
The ITU-T Transport Network is specified in a number of
Recommendations: generic functional architectures and requirements
are specified in [ITU-T_G.805], [ITU-T_G.806], and [ITU-T_G.872].
ITU-T Recommendation G.8101/Y.1355 [ITU-T_G.8101] contains an
overview of the terms and definitions for transport MPLS.
2.3. Common Terminology Sources
The work in this document builds on the shared view of MPLS
requirements. It is intended to provide a source for common MPLS-TP
terminology. In general, the original terminology is used.
The following sources are used:
o IETF framework and requirements RFCs: [RFC6371], [RFC6372],
[RFC5654], [RFC5921], [RFC5860], [RFC5951], [RFC3031], and
[RFC4397].
o ITU-T architecture and requirements Recommendations:
[ITU-T_G.8101], [ITU-T_G.805], [ITU-T_G.806], [ITU-T_G.872],
[ITU-T_G.7710], and [ITU-T_Y.2611].
3. Thesaurus
3.1. Associated Bidirectional Path
An associated bidirectional path is 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. An associated
bidirectional path need not be a single management and operational
entity. The forward and backward directions are set up, monitored,
and protected independently. As a consequence, they may or may not
follow the same route (links and nodes) across the network.
3.2. Bidirectional Path
A bidirectional path refers to a path that supports traffic flow in
two opposite directions, i.e., the forward and backward direction.
3.3. Client-Layer Network
In a client/server relationship (see [ITU-T_G.805]), the client-layer
network receives a (transport) service from the lower server-layer
network (usually the layer network under consideration).
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3.4. Communication Channel
A Communication Channel is a logical channel between network elements
(NEs) that can be used, e.g., for management-plane applications or
control-plane applications. The physical channel supporting the
Communication Channel is technology specific. See [RFC5951],
Appendix A.
3.5. Concatenated Segment
A concatenated segment is a serial-compound link connection as
defined in [ITU-T_G.805]. A concatenated segment is a contiguous
part of an LSP or MS-PW that comprises a set of segments and their
interconnecting nodes in sequence. See also "Segment"
(Section 3.35).
3.6. Control Plane
Within the scope of [RFC5654], the control plane performs transport
path control functions. Through signaling, 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. It is possible to operate an MPLS-TP
network without using a control plane.
3.7. Co-Routed Bidirectional Path
A co-routed bidirectional path is a path where the forward and
backward directions follow the same route (links and nodes) across
the network. A co-routed bidirectional path is managed and operated
as a single entity. Both directions are set up, monitored, and
protected as a single entity. A Transport Network path is typically
co-routed.
3.8. Data Communication Network (DCN)
A DCN is a network that supports Layer 1 (physical layer), Layer 2
(data-link layer), and Layer 3 (network layer) functionality for
distributed management communications related to the management
plane, for distributed routing and signaling communications related
to the control plane, and for other operations communications (e.g.,
order-wire/voice communications, software downloads, etc.).
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3.9. Defect
"Defect" refers to the situation for which the density of anomalies
has reached a level where the ability to perform a required function
has been interrupted. Defects are used as input for Performance
Monitoring (PM), the control of consequent actions, and the
determination of fault cause. See also [ITU-T_G.806].
3.10. 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.
3.11. Embedded Communication Channel (ECC)
An ECC is a logical operations channel between network elements (NEs)
that can be utilized by multiple applications (e.g., management-plane
applications, control-plane applications, etc.). The physical
channel supporting the ECC is technology specific. An example of a
physical channel supporting the ECC is a Data Communication Channel
(DCC) within the Synchronous Digital Hierarchy (SDH).
3.12. Equipment Management Function (EMF)
The equipment management function (EMF) provides the means through
which an element management system (EMS) and other managing entities
manage the network element function (NEF). See [ITU-T_G.7710].
3.13. Failure
A failure is a detected fault. A failure will be declared when the
fault cause persisted long enough to consider that a required
transport function cannot be performed. The item may be considered
as failed; a fault has now been detected. See also [ITU-T_G.806]. A
failure can be used as a trigger for corrective actions.
3.14. Fault
A fault is the inability of a transport function to perform a
required action. This does not include an inability due to
preventive maintenance, lack of external resources, or planned
actions. See also [ITU-T_G.806].
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3.15. Layer Network
"Layer network" is defined in [ITU-T_G.805]. 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. For additional explanation of how
layer networks relate to the OSI concept of layering, see Appendix I
of [ITU-T_Y.2611].
3.16. Link
A link as discussed in this document refers to a physical or logical
connection between a pair of Label Switching Routers (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.
A link as defined in [ITU-T_G.805] is used to describe a fixed
relationship between two ports.
3.17. Maintenance Entity (ME)
A Maintenance Entity (ME) can be viewed as the association of two (or
more) Maintenance Entity Group End Points (MEPs) that should be
configured and managed in order to bound the OAM responsibilities of
an OAM flow across a network or sub-network, i.e., a transport path
or segment in the specific layer network that is being monitored and
managed. See also Section 3.1 of [RFC6371] and Clause 6.1 of
[ITU-T_G.8113.1] and [ITU-T_G.8113.2].
A Maintenance Entity may be defined to monitor and manage
bidirectional or unidirectional point-to-point connectivity or point-
to-multipoint connectivity in an MPLS-TP layer network.
Therefore, in the context of an MPLS-TP LSP ME or PW ME, Label Edge
Routers (LERs) and PW Terminating Provider Edges (T-PEs) can be MEPs,
while LSRs and PW Switching Provider Edges (S-PEs) can be MIPs. In
the case of an ME for a tandem connection, LSRs and S-PEs can be
either MEPs or MIPs.
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The following properties apply to all MPLS-TP MEs:
- OAM entities can be nested but not overlapped.
- Each OAM flow is associated with a unique Maintenance Entity.
- OAM packets are subject to the same forwarding treatment as the
data traffic, but they are distinct from the data traffic by the
Generic Associated Channel Label (GAL).
3.18. Maintenance Entity Group (MEG)
A Maintenance Entity Group is defined, for the purpose of connection
monitoring, between a set of connection points within a connection.
This set of connection points may be located at the boundary of one
administrative domain or a protection domain or the boundaries of two
adjacent administrative domains. The MEG may consist of one or more
Maintenance Entities (MEs). See also Section 3.1 of [RFC6371] and
Clause 6.2 of [ITU-T_G.8113.1] and [ITU-T_G.8113.2].
In an MPLS-TP layer network, a MEG consists of only one ME.
3.19. Maintenance Entity Group End Point (MEP)
Maintenance Entity Group End Points (MEPs) are the end points of a
pre-configured (through the management or control planes) ME. MEPs
are responsible for activating and controlling all of the OAM
functionality for the ME. A source MEP may initiate an OAM packet to
be transferred to its corresponding peer MEP (called the sink MEP) or
to an intermediate MIP that is part of the ME. See also Section 3.3
of [RFC6371] and Clause 6.3 of [ITU-T_G.8113.1] and [ITU-T_G.8113.2].
A sink MEP terminates all the OAM packets that it receives
corresponding to its ME and does not forward them further along the
path.
All OAM packets coming into a source MEP are tunneled via label
stacking and are not processed within the ME as they belong either to
the client network layers or to a higher Tandem Connection Monitoring
(TCM) level.
A MEP in a tandem connection is not coincident with the termination
of the MPLS-TP transport path (LSP or PW), though it can monitor its
connectivity (e.g., counts packets). A MEP of an MPLS-TP network
transport path is coincident with transport path termination and
monitors its connectivity (e.g., counts packets).
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An MPLS-TP sink MEP can notify a fault condition to its MPLS-TP
client-layer network.
3.20. Maintenance Entity Group Intermediate Point (MIP)
A Maintenance Entity Group Intermediate Point (MIP) is a point
between the two MEPs in an ME and is capable of responding to some
OAM packets and forwarding all OAM packets while ensuring fate
sharing with data-plane packets. A MIP responds only to OAM packets
that are sent on the ME it belongs to and that are addressed to the
MIP; it does not initiate OAM messages. See also Section 3.4 of
[RFC6371] and Clause 6.4 of [ITU-T_G.8113.1] and [ITU-T_G.8113.2].
3.21. Management Communication Channel (MCC)
A Communication Channel dedicated to management-plane communications
is referred to as a Management Communication Channel (MCC).
3.22. Management Communication Network (MCN)
A DCN supporting management-plane communication is referred to as a
Management Communication Network (MCN).
3.23. Monitoring
Monitoring is applying OAM functionality to verify and to maintain
the performance and the quality guarantees of a transport path.
There is a need to not only monitor the whole transport path (e.g.,
LSP or MS-PW), but also arbitrary parts of transport paths. The
connection between any two arbitrary points along a transport path is
described in one of three ways:
- as a Path Segment Tunnel,
- as a Sub-Path Maintenance Element, or
- as a Tandem Connection.
3.23.1. Path Segment Tunnel (PST)
A path segment is either a segment or a concatenated segment. Path
Segment Tunnels (PSTs) are instantiated to provide monitoring of a
portion of a set of co-routed transport paths (LSPs or MS-PWs). PSTs
can also be employed to meet the requirement to provide Tandem
Connection Monitoring. See "Tandem Connection" (Section 3.23.3).
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3.23.2. Sub-Path Maintenance Element (SPME)
To monitor, protect, and manage a portion (i.e., segment or
concatenated segment) of an LSP, a hierarchical LSP [RFC3031] can be
instantiated. A hierarchical LSP instantiated for this purpose is
called a Sub-Path Maintenance Element (SPME). Note that by
definition, an SPME does not carry user traffic as a direct client.
An SPME is defined between the edges of the portion of the LSP that
needs to be monitored, protected, or managed. The SPME forms an
MPLS-TP Section that carries the original LSP over this portion of
the network as a client. OAM messages can be initiated at the edge
of the SPME and sent to the peer edge of the SPME or to a MIP along
the SPME. A P router only pushes or pops a label if it is at the end
of an SPME. In this mode, it is an LER for the SPME.
3.23.3. 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.
Tandem Connection Monitoring (TCM) for a given path segment of a
transport path is implemented by creating a Path Segment Tunnel that
has a 1:1 association with the path segment of the transport path
that is to be uniquely monitored. This means that the PST used to
provide TCM can carry one and only one transport path, thus allowing
direct correlation between all fault-management and performance-
monitoring information gathered for the PST and the monitored path
segment of the end-to-end transport path. The PST is monitored using
normal LSP monitoring. See also Section 3.2 of [RFC6371] and
Clause 6.2.1 of [ITU-T_G.8113.1] and [ITU-T_G.8113.2].
3.24. MPLS Section
An MPLS Section is a network segment between two LSRs that are
immediately adjacent at the MPLS layer.
3.25. MPLS Transport Profile (MPLS-TP)
An MPLS Transport Profile refers to the set of MPLS functions used to
support packet transport services and network operations.
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3.26. MPLS-TP NE
A network element (NE) that supports MPLS-TP functions is referred to
as an MPLS-TP NE.
3.27. MPLS-TP Network
An MPLS-TP network is a network in which MPLS-TP NEs are deployed.
3.28. MPLS-TP Recovery
3.28.1. End-to-End Recovery
MPLS-TP end-to-end recovery refers to the recovery of an entire LSP,
from its ingress to its egress node.
3.28.2. Link Recovery
MPLS-TP link recovery refers to the recovery of an individual link
(and hence all or a subset of the LSPs routed over the link) between
two MPLS-TP nodes. For example, link recovery may be provided by
server-layer recovery.
3.28.3. Segment Recovery
MPLS-TP segment recovery refers to the recovery of an LSP segment
(i.e., segment and concatenated segment) between two nodes and is
used to recover from the failure of one or more links or nodes.
An LSP segment comprises one or more contiguous hops on the path of
the LSP. [RFC5654] defines two terms: a "segment" is a single hop
along the path of an LSP, while a "concatenated segment" is more than
one hop along the path of an LSP.
3.29. 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 Customer Edges (CEs)) may be connected
directly to an LSR in the ring.
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3.29.1. 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.
3.29.2. 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.
3.30. OAM Flow
An OAM flow is the set of all OAM packets originating with a specific
source MEP that measure the performance of one direction of a MEG (or
possibly both in the special case of data-plane loopback).
3.31. Operations Support System (OSS)
An OSS is a system that performs the functions that support
processing of information related to Operations, Administration,
Maintenance, and Provisioning (OAM&P) for the networks, including
surveillance and testing functions to support customer access
maintenance.
3.32. Path
See "Transport Path" (Section 3.45).
3.33. Protection Priority
Fault conditions (e.g., signal failed), external commands (e.g,
forced switch, manual switch), and protection states (e.g., no
request) are defined to have a relative priority with respect to each
other. Priority is applied to these conditions/command/states
locally at each end point and between the two end points.
3.34. 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 [ITU-T_G.805]
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.
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Section-layer networks are concerned with all the functions that
provide for the transfer of information between locations in path-
layer networks.
Physical-media-layer networks are concerned with the actual fibers,
metallic wires, or radio frequency channels that support a section-
layer network.
3.35. Segment
A segment is a link connection as defined in [ITU-T_G.805]. 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-PEs and/or T-PEs). See also "Concatenated Segment"
(Section 3.5).
3.36. Server Layer
A server layer is 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).
In a client/server relationship (see [ITU-T_G.805]), the server-layer
network provides a (transport) service to the higher client-layer
network (usually the layer network under consideration).
3.37. Server MEPs
A server MEP is a MEP of an ME that is defined in a layer network
below the MPLS-TP layer network being referenced. A server MEP
coincides with either a MIP or a MEP in the client-layer (MPLS-TP)
network. See also Section 3.5 of [RFC6371] and Clause 6.5 of
[ITU-T_G.8113.1].
For example, a server MEP can be one of the following:
o A termination point of a physical link (e.g., IEEE 802.3), an SDH
Virtual Circuit (VC), or OTN Optical Data Unit (ODU) for the
MPLS-TP Section layer network, defined in [RFC6371], Section 4.1;
o An MPLS-TP Section MEP for MPLS-TP LSPs, defined in [RFC6371],
Section 4.2;
o An MPLS-TP LSP MEP for MPLS-TP PWs, defined in [RFC6371],
Section 4.3; or
o An MPLS-TP TCM MEP for higher-level TCMs, defined in [RFC6371],
Section 3.2.
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The server MEP can run appropriate OAM functions for fault detection
and notifies a fault indication to the MPLS-TP layer network.
3.38. Signaling Communication Channel (SCC)
A Signaling Communication Channel is a Communication Channel
dedicated to control-plane communications. The SCC may be used for
GMPLS / Automatically Switched Optical Network (ASON) signaling
and/or other control-plane messages (e.g., routing messages).
3.39. Signaling Communication Network (SCN)
A DCN supporting control-plane communication is referred to as a
Signaling Communication Network (SCN).
3.40. Span
A span is synonymous with a link.
3.41. Sublayer
"Sublayer" is defined in [ITU-T_G.805]. 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.
3.42. Transport Entity
A transport entity is a node, link, transport path segment,
concatenated transport path segment, or entire transport path.
3.42.1. Working Entity
A working entity is a transport entity that carries traffic during
normal network operation.
3.42.2. Protection Entity
A protection entity is a transport entity that is pre-allocated and
used to protect and transport traffic when the working entity fails.
3.42.3. Recovery Entity
A recovery entity is a transport entity that is used to recover and
transport traffic when the working entity fails.
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3.43. Transmission Media Layer
A transmission media layer is a layer network, consisting of a
section-layer network and a physical-layer network as defined in
[ITU-T_G.805], 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.
3.44. Transport Network
A Transport Network provides transmission of traffic between attached
client devices by establishing and maintaining point-to-point or
point-to-multipoint connections between such devices. A Transport
Network is independent of any higher-layer network that may exist
between clients, except to the extent required to supply this
transmission service. In addition to client traffic, a Transport
Network may carry traffic to facilitate its own operation, such as
that required to support connection control, network management, and
OAM functions.
3.45. Transport Path
A transport path is a network connection as defined in [ITU-T_G.805].
In an MPLS-TP environment, a transport path corresponds to an LSP or
a PW.
3.46. Transport-Path Layer
A transport-path layer is 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.
3.47. Transport-Service Layer
A transport-service layer is 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).
3.48. Unidirectional Path
A unidirectional path is a path that supports traffic flow in only
one direction.
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4. Guidance on the Application of This Thesaurus
As discussed in the introduction to this document, this thesaurus is
intended to bring the concepts and terms associated with MPLS-TP into
the context of the ITU-T's Transport Network architecture. Thus, it
should help those familiar with MPLS to see how they may use the
features and functions of the Transport Network in order to meet the
requirements of MPLS-TP.
5. Management Considerations
Networks based on MPLS-TP require management. The MPLS-TP
specifications described in [RFC5654], [RFC5860], [RFC5921],
[RFC5951], [RFC6371], [RFC6372], [ITU-T_G.8110.1], and [ITU-T_G.7710]
include considerable efforts to provide operator control and
monitoring as well as OAM functionality.
These concepts are, however, out of the scope of this document.
6. Security Considerations
Security is a significant requirement of MPLS-TP. See [RFC6941] for
more information.
However, this informational document is intended only to provide a
lexicography, and the security concerns are, therefore, out of the
scope of this document.
7. Acknowledgments
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 MPLS-TP Ad Hoc Group in the ITU-T) involved in the definition and
specification of the MPLS Transport Profile. We would in particular
like to acknowledge the contributions by Tom Petch to improve the
quality of this document. Abdussalam Baryun also reviewed this
document.
8. Contributors
The following individuals contributed to this document: Italo Busi,
Ben Niven-Jenkins, Enrique Hernandez-Valencia, Lieven Levrau, Dinesh
Mohan, Stewart Bryant, Dan Frost, Matthew Bocci, Vincenzo Sestito,
Martin Vigoureux, and Yaacov Weingarten.
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9. References
9.1. Normative References
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
Sprecher, N., and S. Ueno, "Requirements of an MPLS
Transport Profile", RFC 5654, September 2009.
[RFC5860] Vigoureux, M., Ed., Ward, D., Ed., and M. Betts, Ed.,
"Requirements for Operations, Administration, and
Maintenance (OAM) in MPLS Transport Networks", RFC 5860,
May 2010.
[RFC5921] Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
L., and L. Berger, "A Framework for MPLS in Transport
Networks", RFC 5921, July 2010.
[RFC5951] Lam, K., Mansfield, S., and E. Gray, "Network Management
Requirements for MPLS-based Transport Networks", RFC 5951,
September 2010.
[RFC6371] Busi, I., Ed., and D. Allan, Ed., "Operations,
Administration, and Maintenance Framework for MPLS-Based
Transport Networks", RFC 6371, September 2011.
[RFC6372] Sprecher, N., Ed., and A. Farrel, Ed., "MPLS Transport
Profile (MPLS-TP) Survivability Framework", RFC 6372,
September 2011.
[ITU-T_G.805]
ITU-T Recommendation G.805, "Generic functional
architecture of transport networks", March 2000,
<http://www.itu.int/rec/T-REC/>.
[ITU-T_G.806]
ITU-T Recommendation G.806, "Characteristics of transport
equipment - Description methodology and generic
functionality", March 2006,
<http://www.itu.int/rec/T-REC/>.
[ITU-T_G.872]
ITU-T Recommendation G.872, "Architecture of optical
transport networks", November 2001,
<http://www.itu.int/rec/T-REC/>.
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[ITU-T_G.7710]
ITU-T Recommendation G.7710, "Common equipment management
function requirements", July 2007,
<http://www.itu.int/rec/T-REC/>.
[ITU-T_G.8101]
ITU-T Recommendation G.8101/Y.1355, "Terms and definitions
for MPLS Transport Profile", September 2013,
<http://www.itu.int/rec/T-REC/>.
[ITU-T_G.8110.1]
ITU-T Recommendation G.8110.1/Y.1370.1, "Architecture of
the Multi-Protocol Label Switching transport profile layer
network", December 2011, <http://www.itu.int/rec/T-REC/>.
[ITU-T_G.8113.1]
ITU-T Recommendation G.8113.1/Y.1372.1, "Operations,
administration and maintenance mechanism for MPLS-TP in
packet transport network (PTN)", November 2012,
<http://www.itu.int/rec/T-REC/>.
[ITU-T_G.8113.2]
ITU-T Recommendation G.8113.2/Y.1372.2, "Operations,
administration and maintenance mechanisms for MPLS-TP
networks using the tools defined for MPLS", November 2012,
<http://www.itu.int/rec/T-REC/>.
[ITU-T_Y.2611]
ITU-T Recommendation Y.2611, "High-level architecture of
future packet-based networks", December 2006,
<http://www.itu.int/rec/T-REC/>.
9.2. Informative References
[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.
[RFC6941] Fang, L., Ed., Niven-Jenkins, B., Ed., Mansfield, S., Ed.,
and R. Graveman, Ed., "MPLS Transport Profile (MPLS-TP)
Security Framework", RFC 6941, April 2013.
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Authors' Addresses
Huub van Helvoort (editor)
Huawei Technologies Co., Ltd.
EMail: Huub.van.Helvoort@huawei.com
Loa Andersson (editor)
Huawei Technologies Co., Ltd.
EMail: loa@mail01.huawei.com
Nurit Sprecher (editor)
Nokia Solutions and Networks
EMail: nurit.sprecher@nsn.com
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