MPLS Working Group M. Bocci, Ed.
Internet-Draft Alcatel-Lucent
Intended status: Informational S. Bryant, Ed.
Expires: October 4, 2010 D. Frost, Ed.
Cisco Systems
L. Levrau
Alcatel-Lucent
L. Berger
LabN
April 02, 2010
A Framework for MPLS in Transport Networks
draft-ietf-mpls-tp-framework-11
Abstract
This document specifies an architectural framework for the
application of Multiprotocol Label Switching (MPLS) to the
construction of packet-switched transport networks. It describes a
common set of protocol functions - the MPLS Transport Profile
(MPLS-TP) - that supports the operational models and capabilities
typical of such networks, including signaled or explicitly
provisioned bi-directional connection-oriented paths, protection and
restoration mechanisms, comprehensive Operations, Administration and
Maintenance (OAM) functions, and network operation in the absence of
a dynamic control plane or IP forwarding support. Some of these
functions are defined in existing MPLS specifications, while others
require extensions to existing specifications to meet the
requirements of the MPLS-TP.
This document defines the subset of the MPLS-TP applicable in general
and to point-to-point transport paths. The remaining subset,
applicable specifically to point-to-multipoint transport paths, is
outside the scope of this document.
This document is a product of a joint Internet Engineering Task Force
(IETF) / International Telecommunications Union Telecommunications
Standardization Sector (ITU-T) 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 the ITU-T.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Motivation and Background . . . . . . . . . . . . . . . . 4
1.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.1. Transport Network . . . . . . . . . . . . . . . . . . 6
1.3.2. MPLS Transport Profile . . . . . . . . . . . . . . . . 7
1.3.3. MPLS-TP Section . . . . . . . . . . . . . . . . . . . 7
1.3.4. MPLS-TP Label Switched Path . . . . . . . . . . . . . 7
1.3.5. MPLS-TP Label Switching Router . . . . . . . . . . . . 8
1.3.6. Customer Edge (CE) . . . . . . . . . . . . . . . . . . 8
1.3.7. Edge-to-Edge LSP . . . . . . . . . . . . . . . . . . . 9
1.3.8. Service LSP . . . . . . . . . . . . . . . . . . . . . 9
1.3.9. Layer Network . . . . . . . . . . . . . . . . . . . . 9
1.3.10. Network Layer . . . . . . . . . . . . . . . . . . . . 9
1.3.11. Service Interface . . . . . . . . . . . . . . . . . . 9
1.3.12. Additional Definitions and Terminology . . . . . . . . 9
2. MPLS Transport Profile Requirements . . . . . . . . . . . . . 10
3. MPLS Transport Profile Overview . . . . . . . . . . . . . . . 10
3.1. Packet Transport Services . . . . . . . . . . . . . . . . 10
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3.2. Scope of the MPLS Transport Profile . . . . . . . . . . . 11
3.3. Architecture . . . . . . . . . . . . . . . . . . . . . . . 12
3.3.1. MPLS-TP Native Service Adaptation Functions . . . . . 13
3.3.2. MPLS-TP Forwarding Functions . . . . . . . . . . . . . 13
3.4. MPLS-TP Native Service Adaptation . . . . . . . . . . . . 14
3.4.1. MPLS-TP Client/Server Layer Relationship . . . . . . . 15
3.4.2. MPLS-TP Transport Layers . . . . . . . . . . . . . . . 16
3.4.3. MPLS-TP Transport Service Interfaces . . . . . . . . . 17
3.4.4. Pseudowire Adaptation . . . . . . . . . . . . . . . . 23
3.4.5. Network Layer Adaptation . . . . . . . . . . . . . . . 26
3.5. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 30
3.6. Generic Associated Channel (G-ACh) . . . . . . . . . . . . 30
3.7. Operations, Administration and Maintenance (OAM) . . . . . 32
3.8. Return Path . . . . . . . . . . . . . . . . . . . . . . . 34
3.8.1. Return Path Types . . . . . . . . . . . . . . . . . . 35
3.8.2. Point-to-Point Unidirectional LSPs . . . . . . . . . . 35
3.8.3. Point-to-Point Associated Bidirectional LSPs . . . . . 36
3.8.4. Point-to-Point Co-Routed Bidirectional LSPs . . . . . 36
3.9. Control Plane . . . . . . . . . . . . . . . . . . . . . . 36
3.10. Interdomain Connectivity . . . . . . . . . . . . . . . . . 39
3.11. Static Operation of LSPs and PWs . . . . . . . . . . . . . 39
3.12. Survivability . . . . . . . . . . . . . . . . . . . . . . 39
3.13. Path Segment Tunnels . . . . . . . . . . . . . . . . . . . 41
3.14. Pseudowire Segment Tunnels . . . . . . . . . . . . . . . . 42
3.15. Network Management . . . . . . . . . . . . . . . . . . . . 42
4. Security Considerations . . . . . . . . . . . . . . . . . . . 44
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 45
7.1. Normative References . . . . . . . . . . . . . . . . . . . 45
7.2. Informative References . . . . . . . . . . . . . . . . . . 48
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1. Introduction
1.1. Motivation and Background
This document describes an architectural framework for the
application of MPLS to the construction of packet-switched transport
networks. It specifies the common set of protocol functions that
meet the requirements in [RFC5654], and that together constitute the
MPLS Transport Profile (MPLS-TP) for point-to-point transport paths.
The remaining MPLS-TP functions, applicable specifically to point-to-
multipoint transport paths, are outside the scope of this document.
Historically the optical transport infrastructure - Synchronous
Optical Network/Synchronous Digital Hierarchy (SONET/SDH) and Optical
Transport Network (OTN) - has provided carriers with a high benchmark
for reliability and operational simplicity. To achieve this,
transport technologies have been designed with specific
characteristics:
o Strictly connection-oriented connectivity, which may be long-lived
and may be provisioned manually, for example by network management
systems or direct node configuration using a command line
interface.
o A high level of availability.
o Quality of service.
o Extensive OAM capabilities.
Carriers wish to evolve such transport networks to take advantage of
the flexibility and cost benefits of packet switching technology and
to support packet based services more efficiently. While MPLS is a
maturing packet technology that already plays an important role in
transport networks and services, not all MPLS capabilities and
mechanisms are needed in, or consistent with, the transport network
operational model. There are also transport technology
characteristics that are not currently reflected in MPLS.
There are thus two objectives for MPLS-TP:
1. To enable MPLS to be deployed in a transport network and operated
in a similar manner to existing transport technologies.
2. To enable MPLS to support packet transport services with a
similar degree of predictability to that found in existing
transport networks.
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In order to achieve these objectives, there is a need to define a
common set of MPLS protocol functions - an MPLS Transport Profile -
for the use of MPLS in transport networks and applications. Some of
the necessary functions are provided by existing MPLS specifications,
while others require additions to the MPLS tool-set. Such additions
should, wherever possible, be applicable to MPLS networks in general
as well as those that conform strictly to the transport network
model.
This document is a product of a joint Internet Engineering Task Force
(IETF) / International Telecommunications Union Telecommunications
Standardization Sector (ITU-T) 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 the ITU-T.
1.2. Scope
This document describes an architectural framework for the
application of MPLS to the construction of packet-switched transport
networks. It specifies the common set of protocol functions that
meet the requirements in [RFC5654], and that together constitute the
MPLS Transport Profile (MPLS-TP) for point-to-point MPLS-TP transport
paths. The remaining MPLS-TP functions, applicable specifically to
point-to-multipoint transport paths, are outside the scope of this
document.
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1.3. Terminology
Term Definition
---------- ----------------------------------------------------------
LSP Label Switched Path
MPLS-TP MPLS Transport Profile
SDH Synchronous Digital Hierarchy
ATM Asynchronous Transfer Mode
OTN Optical Transport Network
cl-ps Connectionless - Packet Switched
co-cs Connection Oriented - Circuit Switched
co-ps Connection Oriented - Packet Switched
OAM Operations, Administration and Maintenance
G-ACh Generic Associated Channel
GAL G-ACh Label
MEG Maintenance Entity Group
MEP Maintenance Entity Group End Point
MIP Maintenance Entity Group Intermediate Point
APS Automatic Protection Switching
SCC Signaling Communication Channel
MCC Management Communication Channel
EMF Equipment Management Function
FM Fault Management
CM Configuration Management
PM Performance Management
LSR Label Switching Router
MPLS-TP PE MPLS-TP Provider Edge LSR
MPLS-TP P MPLS-TP Provider LSR
PW Pseudowire
AC Attachment Circuit
Adaptation The mapping of client information into a format suitable
for transport by the server layer
Native The traffic belonging to the client of the MPLS-TP network
Service
T-PE PW Terminating Provider Edge
S-PE PW Switching provider Edge
PST Path Segment Tunnel
1.3.1. Transport Network
A Transport Network provides transparent transmission of client user
plane traffic between attached client devices by establishing and
maintaining point-to-point or point-to-multipoint connections between
such devices. The architecture of networks supporting point to
multipoint connections is outside the scope of this document. 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
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Network may carry traffic to facilitate its own operation, such as
that required to support connection control, network management, and
Operations, Administration and Maintenance (OAM) functions.
See also the definition of Packet Transport Service in Section 3.1.
1.3.2. MPLS Transport Profile
The MPLS Transport Profile (MPLS-TP) is the subset of MPLS functions
that meet the requirements in [RFC5654]. Note that MPLS is defined
to include any present and future MPLS capability specified by the
IETF, including those capabilities specifically added to support
transport network requirements [RFC5654].
1.3.3. MPLS-TP Section
MPLS-TP Sections are defined in [I-D.ietf-mpls-tp-data-plane]. See
also the definition of "section layer network" in Section 1.2.2 of
[RFC5654].
1.3.4. MPLS-TP Label Switched Path
An MPLS-TP Label Switched Path (MPLS-TP LSP) is an LSP that uses a
subset of the capabilities of an MPLS LSP in order to meet the
requirements of an MPLS transport network as set out in [RFC5654].
The characteristics of an MPLS-TP LSP are primarily that it:
1. Uses a subset of the MPLS OAM tools defined as described in
[I-D.ietf-mpls-tp-oam-framework].
2. Supports 1+1, 1:1, and 1:N protection functions.
3. Is traffic engineered.
4. May be established and maintained via the management plane, or
using GMPLS protocols when a control plane is used.
5. Is either point-to-point or point-to-multipoint. Multipoint-to-
point and multipoint-to-multipoint LSPs are not supported.
Note that an MPLS LSP is defined to include any present and future
MPLS capability, including those specifically added to support the
transport network requirements.
See [I-D.ietf-mpls-tp-data-plane] for further details on the types
and data-plane properties of MPLS-TP LSPs.
The lowest server layer provided by MPLS-TP is an MPLS-TP LSP. The
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client layers of an MPLS-TP LSP may be network layer protocols, MPLS
LSPs, or PWs. The relationship of an MPLS-TP LSP to its client
layers is described in detail in Section 3.4.
1.3.5. MPLS-TP Label Switching Router
An MPLS-TP Label Switching Router (LSR) is either an MPLS-TP Provider
Edge (PE) router or an MPLS-TP Provider (P) router for a given LSP,
as defined below. The terms MPLS-TP PE router and MPLS-TP P router
describe logical functions; a specific node may undertake only one of
these roles on a given LSP.
Note that the use of the term "router" in this context is historic
and neither requires nor precludes the ability to perform IP
forwarding.
1.3.5.1. Label Edge Router
An MPLS-TP Label Edge Router (LER) is an LSR that exists at the
endpoints of an LSP and therefore pushes or pops the LSP label, i.e.
does not perform a label swap on the particular LSP under
consideration.
1.3.5.2. MPLS-TP Provider Edge Router
An MPLS-TP Provider Edge (PE) router is an MPLS-TP LSR that adapts
client traffic and encapsulates it to be transported over an MPLS-TP
LSP. Encapsulation may be as simple as pushing a label, or it may
require the use of a pseudowire. An MPLS-TP PE exists at the
interface between a pair of layer networks. For an MS-PW, an MPLS-TP
PE may be either an S-PE or a T-PE, as defined in [RFC5659]. A PE
that pushes or pops a label is an LER.
1.3.5.3. MPLS-TP Provider Router
An MPLS-TP Provider router is an MPLS-TP LSR that does not provide
MPLS-TP PE functionality for a given LSP. An MPLS-TP P router
switches LSPs which carry client traffic, but does not adapt client
traffic and encapsulate it to be carried over an MPLS-TP LSP.
1.3.6. Customer Edge (CE)
A Customer Edge (CE) is the client function sourcing or sinking
native service traffic to or from the MPLS-TP network. CEs on either
side of the MPLS-TP network are peers and view the MPLS-TP network as
a single link.
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1.3.7. Edge-to-Edge LSP
An Edge-to-Edge LSP is an LSP between a pair of PEs that may transit
zero or more provider LSRs.
1.3.8. Service LSP
A service LSP is an LSP that carries a single client service.
1.3.9. Layer Network
A layer network is defined in [G.805] and described in [RFC5654].
1.3.10. Network Layer
This document uses the term Network Layer in the same sense as it is
used in [RFC3031] and [RFC3032].
1.3.11. Service Interface
The packet transport service provided by MPLS-TP is provided at a
service interface. Two types of service interfaces are defined (see
:
o User-Network Interface (UNI) (see Section 3.4.3.1).
o Network-Network Interface (NNI) (see Section 3.4.3.2).
A UNI service interface may be a layer 2 interface that carries only
network layer clients. MPLS-TP LSPs are both necessary and
sufficient to support this service interface as described in section
3.4.3. Alternatively, it may be a layer 2 interface that carries
both network layer and non-network layer clients. To support this
service interface, a PW is required to adapt the client traffic
received over the service interface. This PW in turn is a client of
the MPLS-TP server layer. This is described in section 3.4.2.
An NNI service interface may be to an MPLS LSP or a PW. To support
this case an MPLS-TP PE participates in the service interface
signaling.
1.3.12. Additional Definitions and Terminology
Detailed definitions and additional terminology may be found in
[RFC5654].
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2. MPLS Transport Profile Requirements
The requirements for MPLS-TP are specified in [RFC5654],
[I-D.ietf-mpls-tp-oam-requirements], and [I-D.ietf-mpls-tp-nm-req].
This section provides a brief reminder to guide the reader. It is
not normative or intended as a substitute for these documents.
MPLS-TP must not modify the MPLS forwarding architecture and must be
based on existing pseudowire and LSP constructs.
Point to point LSPs may be unidirectional or bi-directional, and it
must be possible to construct congruent Bi-directional LSPs.
MPLS-TP LSPs do not merge with other LSPs at an MPLS-TP LSR and it
must be possible to detect if a merged LSP has been created.
It must be possible to forward packets solely based on switching the
MPLS or PW label. It must also be possible to establish and maintain
LSPs and/or pseudowires both in the absence or presence of a dynamic
control plane. When static provisioning is used, there must be no
dependency on dynamic routing or signaling.
OAM, protection and forwarding of data packets must be able to
operate without IP forwarding support.
It must be possible to monitor LSPs and pseudowires through the use
of OAM in the absence of control plane or routing functions. In this
case information gained from the OAM functions is used to initiate
path recovery actions at either the PW or LSP layers.
3. MPLS Transport Profile Overview
3.1. Packet Transport Services
One objective of MPLS-TP is to enable MPLS networks to provide packet
transport services with a similar degree of predictability to that
found in existing transport networks. Such packet transport services
inherit a number of characteristics, defined in [RFC5654]:
o 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 either the
server or client layer network.
o The service provided by the MPLS-TP network to the client is
guaranteed not to fall below the agreed level regardless of other
client activity.
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o The control and management planes of any client network layer that
uses the service is isolated from the control and management
planes of the MPLS-TP layer network, where the client network
layer is considered to be the native service of the MPLS-TP
network.
o Where a client network makes use of an MPLS-TP server that
provides a packet transport service, the level of co-ordination
required between the client and server layer networks is minimal
(preferably no co-ordination will be required).
o The complete set of packets generated by a client MPLS(-TP) layer
network using the packet transport service, which may contain
packets that are not MPLS packets (e.g. IP or CLNS packets used
by the control/management plane of the client MPLS(-TP) layer
network), are transported by the MPLS-TP server layer network.
o The packet transport service enables the MPLS-TP layer network
addressing and other information (e.g. topology) to be hidden from
any client layer networks using that service, and vice-versa.
These characteristics imply that a packet transport service does not
support a connectionless packet-switched forwarding mode. However,
this does not preclude it carrying client traffic associated with a
connectionless service.
3.2. Scope of the MPLS Transport Profile
Figure 1 illustrates the scope of MPLS-TP. MPLS-TP solutions are
primarily intended for packet transport applications. MPLS-TP is a
strict subset of MPLS, and comprises only those functions that are
necessary to meet the requirements of [RFC5654]. This includes MPLS
functions that were defined prior to [RFC5654] but that meet the
requirements of [RFC5654], together with additional functions defined
to meet those requirements. Some MPLS functions defined before
[RFC5654] such as Equal Cost Multi-Path, LDP signaling used in such a
way that it creates multipoint-to-point LSPs, and IP forwarding in
the data plane are explicitly excluded from MPLS-TP by that
requirements specification.
Note that MPLS as a whole will continue to evolve to include
additional functions that do not conform to the MPLS Transport
Profile or its requirements, and thus fall outside the scope of
MPLS-TP.
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|<============================== MPLS ==============================>|
|<============= Pre-RFC5654 MPLS ================>|
{ ECMP }
{ LDP/non-TE LSPs }
{ IP fwd }
|<================ MPLS-TP ====================>|
{ Additional }
{ Transport }
{ Functions }
Figure 1: Scope of MPLS-TP
3.3. Architecture
MPLS-TP comprises the following architectural elements:
o A standard MPLS data plane [RFC3031] as profiled in
[I-D.ietf-mpls-tp-data-plane].
o Sections, LSPs and PWs that provide a packet transport service for
a client network.
o Proactive and on-demand Operations, Administration and Maintenance
(OAM) functions to monitor and diagnose the MPLS-TP network, as
outlined in [I-D.ietf-mpls-tp-oam-framework].
o Optional control planes for LSPs and PWs, as well as support for
static provisioning and configuration.
o Optional path protection mechanisms to ensure that the packet
transport service survives anticipated failures and degradations
of the MPLS-TP network, as outlined in
[I-D.ietf-mpls-tp-survive-fwk].
o Network management functions, as outlined in
[I-D.ietf-mpls-tp-nm-framework].
The MPLS-TP architecture for LSPs and PWs includes the following two
sets of functions:
o MPLS-TP native service adaptation
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o MPLS-TP forwarding
The adaptation functions interface the native service (i.e. the
client layer network service) to MPLS-TP. This includes the case
where the native service is an MPLS-TP LSP.
The forwarding functions comprise the mechanisms required for
forwarding the encapsulated native service traffic over an MPLS-TP
server layer network, for example PW and LSP labels.
3.3.1. MPLS-TP Native Service Adaptation Functions
The MPLS-TP native service adaptation functions interface the client
layer network service to MPLS-TP. For pseudowires, these adaptation
functions are the payload encapsulation described in Section 4.4 of
[RFC3985] and Section 6 of [RFC5659]. For network layer client
services, the adaptation function uses the MPLS encapsulation format
as defined in [RFC3032].
The purpose of this encapsulation is to abstract the client layer
network data plane from the MPLS-TP data plane, thus contributing to
the independent operation of the MPLS-TP network.
MPLS-TP is itself a client of an underlying server layer. MPLS-TP is
thus also bounded by a set of adaptation functions to this server
layer network, which may itself be MPLS-TP. These adaptation
functions provide encapsulation of the MPLS-TP frames and for the
transparent transport of those frames over the server layer network.
The MPLS-TP client inherits its Quality of Service (QoS) from the
MPLS-TP network, which in turn inherits its QoS from the server
layer. The server layer must therefore provide the necessary QoS to
ensure that the MPLS-TP client QoS commitments can be satisfied.
3.3.2. MPLS-TP Forwarding Functions
The forwarding functions comprise the mechanisms required for
forwarding the encapsulated native service traffic over an MPLS-TP
server layer network, for example PW and LSP labels.
MPLS-TP LSPs use the MPLS label switching operations and TTL
processing procedures defined in [RFC3031], [RFC3032] and [RFC3443],
as profiled in [I-D.ietf-mpls-tp-data-plane]. These operations are
highly optimised for performance and are not modified by the MPLS-TP
profile.
In addition, MPLS-TP PWs use the SS-PW and optionally the MS-PW
forwarding operations defined in [RFC3985] and [RFC5659].
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Per-platform label space is used for PWs. Either per-platform, per-
interface or other context-specific label space [RFC5331] may be used
for LSPs.
MPLS-TP forwarding is based on the label that identifies the
transport path (LSP or PW). The label value specifies the processing
operation to be performed by the next hop at that level of
encapsulation. A swap of this label is an atomic operation in which
the contents of the packet after the swapped label are opaque to the
forwarder. The only event that interrupts a swap operation is TTL
expiry. This is a fundamental architectural construct of MPLS to be
taken into account when designing protocol extensions (such as those
for OAM) that require packets to be sent to an intermediate LSR.
Further processing to determine the context of a packet occurs when a
swap operation is interrupted in this manner, or a pop operation
exposes a specific reserved label at the top of the stack, or the
packet is received with the GAL (Section 3.6) at the top of stack.
Otherwise the packet is forwarded according to the procedures in
[RFC3032].
MPLS-TP supports Quality of Service capabilities via the MPLS
Differentiated Services (DiffServ) architecture [RFC3270]. Both
E-LSP and L-LSP MPLS DiffServ modes are supported.
Further details of MPLS-TP forwarding can be found in
[I-D.ietf-mpls-tp-data-plane].
3.4. MPLS-TP Native Service Adaptation
This document describes the architecture for two native service
adaptation mechanisms, which provide encapsulation and demultiplexing
for native service traffic traversing an MPLS-TP network:
o A PW
o An MPLS Label
A PW provides any emulated service that the IETF has defined to be
provided by a PW, for example Ethernet, Frame Relay, or PPP/HDLC. A
list of PW types is maintained by IANA in the the "MPLS Pseudowire
Type" registry. When the native service adaptation is via a PW, the
mechanisms described in Section 3.4.4 are used.
An MPLS LSP Label can also be used as the adaptation, in which case
any native service traffic type supported by [RFC3031] and [RFC3032]
is allowed. Examples of such traffic types include IP, and MPLS-
labeled packets. Note that the latter case includes TE-LSPs
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[RFC3209] and LSP based applications such as PWs, Layer 2 VPNs
[RFC4664], and Layer 3 VPNs [RFC4364]. When the native service
adaptation is via an MPLS label, the mechanisms described in
Section 3.4.5 are used.
3.4.1. MPLS-TP Client/Server Layer Relationship
The relationship between the client layer network and the MPLS-TP
server layer network is defined by the MPLS-TP network boundary and
the label context. It is not explicitly indicated in the packet. In
terms of the MPLS label stack, when the native service traffic type
is itself MPLS-labeled, then the S bits of all the labels in the
MPLS-TP label stack carrying that client traffic are zero; otherwise
the bottom label of the MPLS-TP label stack has the S-bit set to 1.
In other words, there can be only one S-bit set in a label stack.
The data plane behaviour of MPLS-TP is the same as the best current
practise for MPLS. This includes the setting of the S-bit. In each
case, the S-bit is set to indicate the bottom (i.e. inner-most) label
in the label stack that is contiguous between the MPLS-TP server
layer and the client layer. Note that this best current practice
differs slightly from [RFC3032] which uses the S-bit to identify when
MPLS label processing stops and network layer processing starts.
The relationship of MPLS-TP to its clients is illustrated in
Figure 2. Note that the label stacks shown in the figure are divided
between those inside the MPLS-TP Network and those within the client
network when the client network is MPLS(-TP). They illustrate the
smallest number of labels possible. These label stacks could also
include more labels.
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PW-Based MPLS Labelled IP
Services Services Transport
|------------| |-----------------------------| |------------|
Emulated PW over LSP IP over LSP IP
Service
+------------+
| PW Payload |
+------------+ +------------+ (CLIENTS)
|PW Lbl(S=1) | | IP |
+------------+ +------------+ +------------+ +------------+
| PW Payload | |LSP Lbl(S=0)| |LSP Lbl(S=1)| | IP |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|PW Lbl (S=1)| |LSP Lbl(S=0)| |LSP Lbl(S=0)| |LSP Lbl(S=1)|
+------------+ +------------+ +------------+ +------------+
|LSP Lbl(S=0)| . . .
+------------+ . . . (MPLS-TP)
. . . .
.
.
~~~~~~~~~~~ denotes Client <-> MPLS-TP layer boundary
Figure 2: MPLS-TP - Client Relationship
3.4.2. MPLS-TP Transport Layers
An MPLS-TP network consists logically of two layers: the Transport
Service layer and the Transport Path layer.
The Transport Service layer provides the interface between Customer
Edge (CE) nodes and the MPLS-TP network. Each packet transmitted by
a CE node for transport over the MPLS-TP network is associated at the
receiving MPLS-TP Provider Edge (PE) node with a single logical
point-to-point connection at the Transport Service layer between this
(ingress) PE and the corresponding (egress) PE to which the peer CE
is attached. Such a connection is called an MPLS-TP Transport
Service Instance, and the set of client packets associated with such
an instance on a particular CE-PE link is called a client flow.
The Transport Path layer provides aggregation of Transport Service
Instances over MPLS-TP transport paths (LSPs), as well as aggregation
of transport paths (via LSP hierarchy).
Awareness of the Transport Service layer need exist only at PE nodes.
MPLS-TP Provider (P) nodes need have no awareness of this layer.
Both PE and P nodes participate in the Transport Path layer. A PE
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terminates (i.e., is an LER with respect to) the transport paths it
supports, and is responsible for multiplexing and demultiplexing of
Transport Service Instance traffic over such transport paths.
3.4.3. MPLS-TP Transport Service Interfaces
An MPLS-TP PE node can provide two types of interface to the
Transport Service layer. The MPLS-TP User-Network Interface (UNI)
provides the interface between a CE and the MPLS-TP network. The
MPLS-TP Network-Network Interface (NNI) provides the interface
between two MPLS-TP PEs in different administrative domains.
When providing a Virtual Private Wire Service (VPWS), Virtual Private
Local Area Network Service (VPLS), Virtual Private Multicast Service
(VPMS), or Internet Protocol Local Area Network Service (IPLS),
pseudowires must be used to carry the client service. VPWS, VLPS,
and IPLS are described in [RFC4664]. VPMS is described in
[I-D.ietf-l2vpn-vpms-frmwk-requirements].
When MPLS-TP is used to provide a transport service for e.g. IP
services that are a part of a Layer 3 VPN, then packets are
transported in the same manner as specified in [RFC4364].
3.4.3.1. User-Network Interface
The MPLS-TP User-Network interface (UNI) is illustrated in Figure 3.
The UNI for a particular client flow may or may not involve signaling
between the CE and PE, and if signaling is used, it may or may not
traverse the same data-link that supports the client flow.
: User-Network Interface : MPLS-TP
:<-------------------------------------->: Network <----->
: :
-:------------- --------------:------------------
: | | : Transport |
: | | Transport : Path |
: | | Service : Mux/Demux |
: | | Control : -- |
: | | Plane : | | Transport|
: ---------- | Signaling | ---------- : | | Path |
:|Signaling |_|___________|_|Signaling | : | | --------->
:|Controller| | | |Controller| : | | |
: ---------- | | ---------- : | | --------->
: :......|...........|......: : | | |
: | Control | : | | Transport|
: | Channel | : | | Path |
: | | : | | --------->
: | | : | | -+----------->TSI
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: | | Transport : | | | --------->
: | Client | Service : | | | |
: | Traffic | Data Plane : | | | |
: ---------- | Flows | -------------- | | |Transport|
:|Signaling |-|-----------|-|Client/Service|-| |- Path |
:|Controller|=|===========|=| Traffic | | | --------->
: ---------- | | | Processing |=| |===+===========>TSI
: | | | -------------- | | --------->
: |______|___________|______| : | | |
: | Data Link | : | | |
: | | : -- |
: | | : Transport |
: | | : Service |
: | | : Data Plane|
--------------- ---------------------------------
Customer Edge Node MPLS-TP Provider Edge Node
TSI = Transport Service Instance
Client/Service Traffic Processing Stages
:
--------------From UNI-------> :
-------------------------------------------:------------------
| | Client Traffic Unit : |
| Link-Layer-Specific | Link Decapsulation : Service Instance |
| Processing | & : Transport |
| | Service Instance : Encapsulation |
| | Identification : |
-------------------------------------------:------------------
:
:
-------------------------------------------:------------------
| | : Service Instance |
| | : Transport |
| Link-Layer-Specific | Client Traffic Unit : Decapsulation |
| Processing | Link Encapsulation : & |
| | : Service Instance |
| | : Identification |
-------------------------------------------:------------------
<-------------To UNI --------- :
Figure 3: MPLS-TP PE Containing a UNI
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The figure shows the logical processing steps involved in a PE both
for traffic flowing from the CE to the MPLS-TP network (left to
right), and from the network to the CE (right to left).
In the first case, when a packet from a client flow is received by
the PE from the CE over the data-link, the following steps occur:
1. Link-layer specific preprocessing, if any, is performed. An
example of such preprocessing is the PREP function illustrated in
Figure 3 of [RFC3985]. Such preprocessing is outside the scope
of MPLS-TP.
2. The packet is extracted from the data-link frame if necessary,
and associated with a Transport Service Instance. At this point,
UNI processing has completed.
3. A transport service encapsulation is associated with the packet,
if necessary, for transport over the MPLS-TP network.
4. The packet is mapped to a transport path based on its associated
Transport Service Instance, the transport path encapsulation is
added, if necessary, and the packet is transmitted over the
transport path.
In the second case, when a packet associated with a Transport Service
Instance arrives over a transport path, the following steps occur:
1. The transport path encapsulation is disposed of.
2. The transport service encapsulation is disposed of and the
Transport Service Instance and client flow identified.
3. At this point, UNI processing begins. A data-link encapsulation
is associated with the packet for delivery to the CE based on the
client flow.
4. Link-layer-specific postprocessing, if any, is performed. Such
postprocessing is outside the scope of MPLS-TP.
3.4.3.2. Network-Network Interface
The MPLS-TP NNI is illustrated in Figure 4. The NNI for a particular
transport service instance may or may not involve signaling between
the two PEs, and if signaling is used, it may or may not traverse the
same data-link that supports the service instance.
: Network-Network Interface :
:<--------------------------------->:
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: :
------------:------------- -------------:------------
| Transport : | | : Transport |
| Path : Transport | | Transport : Path |
| Mux/Demux : Service | | Service : Mux/Demux |
| -- : Control | | Control : -- |
| | | : Plane |Sig- | Plane : | | |
|TP | | : ---------- | naling| ---------- : | | TP|
<--- | | :|Signaling |_|_______|_|Signaling |: | | --->
TSI<-+- | | :|Controller| | | |Controller|: | | |
<--- | | | : ---------- | | ---------- : | | --->
| | | | : :......|.......|......: : | | |
| | | | : |Control| : | | |
|TP | | | : |Channel| : | | TP|
<--- | | | : | | : | | --->
| | | | : | | : | | -+->TSI
<--- | | | : Transport | | Transport : | | | --->
| | | | : Service |Service| Service : | | | |
| | | | : Data Plane |Traffic| Data Plane : | | | |
| | | | ------------- | Flows | ------------- | | | |
|TP -| |-| Service |-|-------|-| Service |-| |- TP|
<--- | | | Traffic | | | | Traffic | | | --->
TSI<=+===| |=| Processing |=|=======|=| Processing |=| |===+=>TSI
<--- | | ------------- | | ------------- | | --->
| | | : |______|_______|______| : | | |
| | | : | Data | : | | |
| -- : | Link | : -- |
| : | | : |
-------------------------- --------------------------
MPLS-TP Provider Edge Node MPLS-TP Provider Edge Node
TP = Transport Path
TSI = Transport Service Instance
Service Traffic Processing Stages
:
--------------From NNI-------> :
--------------------------------------------:------------------
| | Service Traffic Unit : |
| Link-Layer-Specific | Link Decapsulation : Service Instance |
| Processing | & : Encapsulation |
| | Service Instance : Normalisation |
| | Identification : |
--------------------------------------------:------------------
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:
:
--------------------------------------------:------------------
| | : Service Instance |
| | : Identification |
| Link-Layer-Specific | Service Traffic Unit : & |
| Processing | Link Encapsulation : Service Instance |
| | : Encapsulation |
| | : Normalisation |
--------------------------------------------:------------------
<-------------To NNI --------- :
Figure 4: MPLS-TP PE Containing an NNI
The figure shows the logical processing steps involved in a PE for
traffic flowing both from the peer PE (left to right) and to the peer
PE (right to left).
In the first case, when a packet from a transport service instance is
received by the PE from the peer PE over the data-link, the following
steps occur:
1. Link-layer specific preprocessing, if any, is performed. Such
preprocessing is outside the scope of MPLS-TP.
2. The packet is extracted from the data-link frame if necessary,
and associated with a Transport Service Instance. At this point,
NNI processing has completed.
3. The transport service encapsulation of the packet is normalised
for transport over the MPLS-TP network. This step allows a
different transport service encapsulation to be used over the NNI
than that used in the internal MPLS-TP network. An example of
such normalisation is a swap of a label identifying the Transport
Service Instance.
4. The packet is mapped to a transport path based on its associated
Transport Service Instance, the transport path encapsulation is
added, if necessary, and the packet is transmitted over the
transport path.
In the second case, when a packet associated with a Transport Service
Instance arrives over a transport path, the following steps occur:
1. The transport path encapsulation is disposed of.
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2. The Transport Service Instance is identified from the transport
service encapsulation, and this encapsulation is normalised for
delivery over the NNI (see Step 3 above).
3. At this point, NNI processing begins. A data-link encapsulation
is associated with the packet for delivery to the peer PE based
on the normalised Transport Service Instance.
4. Link-layer-specific postprocessing, if any, is performed. Such
postprocessing is outside the scope of MPLS-TP.
3.4.3.3. Example Interfaces
This section considers some special cases of UNI and NNI processing
for particular transport service types. These are illustrative, and
do not preclude other transport service types.
3.4.3.3.1. Layer 2 Transport Service
In this example the MPLS-TP network is providing a point-to-point
Layer 2 transport service between attached CE nodes. This service is
provided by a Transport Service Instance consisting of a PW
established between the associated PE nodes. The client flows
associated with this Transport Service Instance are the sets of all
Layer 2 frames transmitted and received over the attachment circuits.
The processing steps in this case for a frame received from the CE
are:
1. Link-layer specific preprocessing, if any, is performed,
corresponding to the PREP function illustrated in Figure 3 of
[RFC3985].
2. The frame is associated with a Transport Service Instance based
on the attachment circuit over which it was received.
3. A transport service encapsulation, consisting of the PW control
word and PW label, is associated with the frame.
4. The resulting packet is mapped to an LSP, the LSP label is
pushed, and the packet is transmitted over the outbound interface
associated with the LSP.
The steps in the reverse direction for PW packets received over the
LSP are analogous.
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3.4.3.4. IP Transport Service
In this example the MPLS-TP network is providing a point-to-point IP
transport service between CE1, CE2, and CE3, as follows. One point-
to-point transport service instance delivers IPv4 packets between CE1
and CE2, and another instance delivers IPv6 packets between CE1 and
CE3.
The processing steps in this case for an IP packet received from CE1
are:
A1. No link-layer-specific processing is performed.
A2. The IP packet is extracted from the link-layer frame and
associated with a Service LSP based on the source MAC address (CE1)
and the IP protocol version.
A3. A transport service encapsulation, consisting of the Service LSP
label, is associated with the packet.
A4. The resulting packet is mapped to a tunnel LSP, the tunnel LSP
label is pushed, and the packet is transmitted over the outbound
interface associated with the LSP.
The steps in the reverse direction, for packets received over a
tunnel LSP carrying the Service LSP label, are analogous.
3.4.4. Pseudowire Adaptation
If the MPLS-TP network provides a layer 2 interface, that can carry
both network layer and non-network layer traffic, as a service
interface, then a PW is required to support the service interface.
The PW is a client of the MPLS-TP LSP server layer. The architecture
for an MPLS-TP network that provides such services is based on the
MPLS [RFC3031] and pseudowire [RFC3985] architectures. Multi-segment
pseudowires may optionally be used to provide a packet transport
service, and their use is consistent with the MPLS-TP architecture.
The use of MS-PWs may be motivated by, for example, the requirements
specified in [RFC5254]. If MS-PWs are used, then the MS-PW
architecture [RFC5659] also applies.
Figure 5 shows the architecture for an MPLS-TP network using single-
segment PWs. Note that, in this document, the client layer is
equivalent to the emulated service described in [RFC3985], while the
Transport LSP is equivalent to the Packet Switched Network (PSN)
tunnel of [RFC3985].
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|<----------------- Client Layer ------------------->|
| |
| |<-------- Pseudowire -------->| |
| | encapsulated, packet | |
| | transport service | |
| | | |
| | Transport | |
| | |<------ LSP ------->| | |
| V V V V |
V AC +----+ +-----+ +----+ AC V
+-----+ | | PE1|=======\ /========| PE2| | +-----+
| |----------|.......PW1.| \ / |............|----------| |
| CE1 | | | | | X | | | | | CE2 |
| |----------|.......PW2.| / \ |............|----------| |
+-----+ ^ | | |=======/ \========| | | ^ +-----+
^ | +----+ ^ +-----+ +----+ | ^
| | Provider | ^ Provider | |
| | Edge 1 | | Edge 2 | |
Customer | | P Router | Customer
Edge 1 | TE LSP | Edge 2
| |
| |
Native service Native service
Figure 5: MPLS-TP Architecture (Single Segment PW)
Figure 6 shows the architecture for an MPLS-TP network when multi-
segment pseudowires are used. Note that as in the SS-PW case,
P-routers may also exist.
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|<--------------------- Client Layer ------------------------>|
| |
| Pseudowire encapsulated, |
| |<---------- Packet Transport Service ------------->| |
| | | |
| | Transport Transport | |
| AC | |<-------- LSP1 --------->| |<--LSP2-->| | AC |
| | V V V V V V | |
V | +----+ +-----+ +----+ +----+ | V
+---+ | |TPE1|===============\ /=====|SPE1|==========|TPE2| | +---+
| |----|......PW1-Seg1.... | \ / | ......X...PW1-Seg2......|----| |
|CE1| | | | | X | | | | | | |CE2|
| |----|......PW2-Seg1.... | / \ | ......X...PW2-Seg2......|----| |
+---+ ^ | |===============/ \=====| |==========| | | ^+---+
| +----+ ^ +-----+ +----+ ^ +----+ |
| | ^ | |
| TE LSP | TE LSP |
| P-router |
Native Service Native Service
PW1-segment1 and PW1-segment2 are segments of the same MS-PW,
while PW2-segment1 and PW2-segment2 are segments of another MS-PW
Figure 6: MPLS-TP Architecture (Multi-Segment PW)
The corresponding MPLS-TP protocol stacks including PWs are shown in
Figure 7. In this figure the Transport Service Layer [RFC5654] is
identified by the PW demultiplexer (Demux) label and the Transport
Path Layer [RFC5654] is identified by the LSP Demux Label.
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+-------------------+ /===================\ /===================\
| Client Layer | H OAM PDU H H OAM PDU H
/===================\ H-------------------H H-------------------H
H PW Encap H H GACh H H GACh H
H-------------------H H-------------------H H-------------------H
H PW Demux (S=1) H H PW Demux (S=1) H H GAL (S=1) H
H-------------------H H-------------------H H-------------------H
H Trans LSP Demux(s)H H Trans LSP Demux(s)H H Trans LSP Demux(s)H
\===================/ \===================/ \===================/
| Server Layer | | Server Layer | | Server Layer |
+-------------------+ +-------------------+ +-------------------+
User Traffic PW OAM LSP OAM
Note: H(ighlighted) indicates the part of the protocol stack considered
in this document.
Figure 7: MPLS-TP label stack using pseudowires
PWs and their associated labels may be configured or signaled. See
Section 3.11 for additional details related to configured service
types. See Section 3.9 for additional details related to signaled
service types.
3.4.5. Network Layer Adaptation
MPLS-TP LSPs can be used to transport network layer clients. This
document uses the term Network Layer in the same sense as it is used
in [RFC3031] and [RFC3032]. The network layer protocols supported by
[RFC3031] and [RFC3032] can be transported between service
interfaces. Examples are shown in Figure 5 above. Support for
network layer clients follows the MPLS architecture for support of
network layer protocols as specified in [RFC3031] and [RFC3032].
With network layer adaptation, the MPLS-TP domain provides either a
uni-directional or bidirectional point-to-point connection between
two PEs in order to deliver a packet transport service to attached
customer edge (CE) nodes. For example, a CE may be an IP, MPLS or
MPLS-TP node. As shown in Figure 8, there is an attachment circuit
between the CE node on the left and its corresponding provider edge
(PE) node which provides the service interface, a bidirectional LSP
across the MPLS-TP network to the corresponding PE node on the right,
and an attachment circuit between that PE node and the corresponding
CE node for this service.
The attachment circuits may be heterogeneous (e.g., any combination
of SDH, PPP, Frame Relay, etc.) and network layer protocol payloads
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arrive at the service interface encapsulated in the Layer1/Layer2
encoding defined for that access link type. It should be noted that
the set of network layer protocols includes MPLS and hence MPLS
encoded packets with an MPLS label stack (the client MPLS stack), may
appear at the service interface.
|<------------- Client Network Layer --------------->|
| |
| |<----------- Packet --------->| |
| | Transport Service | |
| | | |
| | | |
| | Transport | |
| | |<------ LSP ------->| | |
| V V V V |
V AC +----+ +-----+ +----+ AC V
+-----+ | | PE1|=======\ /========| PE2| | +-----+
| |----------|..Svc LSP1.| \ / |............|----------| |
| CE1 | | | | | X | | | | | CE2 |
| |----------|..Svc LSP2.| / \ |............|----------| |
+-----+ ^ | | |=======/ \========| | | ^ +-----+
^ | +----+ ^ +-----+ +----+ | | ^
| | Provider | ^ Provider | |
| | Edge 1 | | Edge 2 | |
Customer | | P Router | Customer
Edge 1 | TE LSP | Edge 2
| |
| |
Native service Native service
Figure 8: MPLS-TP Architecture for Network Layer Clients
At the ingress service interface the client packets are received.
The PE pushes one or more labels onto the client packets which are
then label switched over the transport network. Correspondingly the
egress PE pops any labels added by the MPLS-TP networks and transmits
the packet for delivery to the attached CE via the egress service
interface.
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/===================\
H OAM PDU H
+-------------------+ H-------------------H /===================\
| Client Layer | H GACh H H OAM PDU H
/===================\ H-------------------H H-------------------H
H Encap Label H H GAL (S=1) H H GACh H
H-------------------H H-------------------H H-------------------H
H SvcLSP Demux H H SvcLSP Demux (S=0)H H GAL (S=1) H
H-------------------H H-------------------H H-------------------H
H Trans LSP Demux(s)H H Trans LSP Demux(s)H H Trans LSP Demux(s)H
\===================/ \===================/ \===================/
| Server Layer | | Server Layer | | Server Layer |
+-------------------+ +-------------------+ +-------------------+
User Traffic Service LSP OAM LSP OAM
Note: H(ighlighted) indicates the part of the protocol stack considered
in this document.
Figure 9: MPLS-TP Label Stack for IP and LSP Clients
In this figure the Transport Service Layer [RFC5654] is identified by
the Service LSP (SvcLSP) demultiplexer (Demux) label and the
Transport Path Layer [RFC5654] is identified by the Transport (Trans)
LSP Demux Label. Note that the functions of the Encapsulation label
(Encap Label) and the Service Label (SvcLSP Demux) shown above may
alternatively be represented by a single label stack entry. Note
that the S-bit is always zero when the client layer is MPLS-labelled.
Within the MPLS-TP transport network, the network layer protocols are
carried over the MPLS-TP network using a logically separate MPLS
label stack (the server stack). The server stack is entirely under
the control of the nodes within the MPLS-TP transport network and it
is not visible outside that network. Figure 9 shows how a client
network protocol stack (which may be an MPLS label stack and payload)
is carried over a network layer client service over an MPLS-TP
transport network.
A label may be used to identify the network layer protocol payload
type. Therefore, when multiple protocol payload types are to be
carried over a single service LSP, a unique label stack entry must be
present for each payload type. Such labels are referred to as
"Encapsulation Labels", one of which is shown in Figure 9.
Encapsulation Label may be either configured or signaled.
Both an Encapsulation Label and a Service Label should be present in
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the label stack when a particular packet transport service is
supporting more than one network layer protocol payload type. For
example, if both IP and MPLS are to be carried, as shown in Figure 8,
then two Encapsulation Labels are mapped on to a common Service
Label.
Note: The Encapsulation Label may be omitted when the service LSP is
supporting only one network layer protocol payload type. For
example, if only MPLS labeled packets are carried over a service,
then the Service Label (stack entry) provides both the payload type
indication and service identification.
Service labels are typically carried over an MPLS-TP Transport LSP
edge-to-edge (or transport path layer). An MPLS-TP Transport LSP is
represented as an LSP Transport Demux label, as shown in Figure 9.
Transport LSP is commonly used when more than one service exists
between two PEs.
Note that, if only one service exists between two PEs, the functions
of the Transport LSP label and the Service LSP Label may be combined
into a single label stack entry. For example, if only one service is
carried between two PEs then a single label could be used to provide
both the service indication and the MPLS-TP transport LSP.
Alternatively, if multiple services exist between a pair of PEs then
a per-client Service Label would be mapped on to a common MPLS-TP
transport LSP.
As noted above, the layer 2 and layer 1 protocols used to carry the
network layer protocol over the attachment circuits are not
transported across the MPLS-TP network. This enables the use of
different layer 2 and layer 1 protocols on the two attachment
circuits.
At each service interface, Layer 2 addressing must be used to ensure
the proper delivery of a network layer packet to the adjacent node.
This is typically only an issue for LAN media technologies (e.g.,
Ethernet) which have Media Access Control (MAC) addresses. In cases
where a MAC address is needed, the sending node must set the
destination MAC address to an address that ensures delivery to the
adjacent node. That is the CE sets the destination MAC address to an
address that ensures delivery to the PE, and the PE sets the
destination MAC address to an address that ensures delivery to the
CE. The specific address used is technology type specific and is not
specified in this document. In some technologies the MAC address
will need to be configured.
Note that when two CEs, which peer with each other, operate over a
network layer transport service and run a routing protocol such as
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IS-IS or OSPF, some care should be taken to configure the routing
protocols to use point-to-point adjacencies. The specifics of such
configuration is outside the scope of this document. See [RFC5309]
for additional details.
The CE to CE service types and corresponding labels may be configured
or signaled .
3.5. Identifiers
Identifiers are used to uniquely distinguish entities in an MPLS-TP
network. These include operators, nodes, LSPs, pseudowires, and
their associated maintenance entities. MPLS-TP defined two type of
sets of identifiers: Those that are compatible with IP, and another
set that is compatibple with ITU-T transport-based operations. The
definition of these sets of identifiers is outside the scope of this
document and is provided by [I-D.ietf-mpls-tp-identifiers].
3.6. Generic Associated Channel (G-ACh)
For correct operation of OAM mechanisms it is important that OAM
packets fate-share with the data packets. In addition in MPLS-TP it
is necessary to discriminate between user data payloads and other
types of payload. For example, a packet may be associated with a
Signaling Communication Channel (SCC), or a channel used for
Protection State Coordination (PSC) data. This is achieved by
carrying such packets in either:
o A generic control channel associated to the LSP, PW or section,
with no IP encapsulation. e.g. in a similar manner to
Bidirectional Forwarding Detection for Virtual Circuit
Connectivity Verification (VCCV-BFD) with PW ACH encapsulation
[I-D.ietf-pwe3-vccv-bfd]).
o An IP encapsulation where IP capabilities are present. e.g. PW
ACH encapsulation with IP headers for VCCV-BFD
[I-D.ietf-pwe3-vccv-bfd], or IP encapsulation for MPLS BFD
[I-D.ietf-bfd-mpls].
MPLS-TP makes use of such a generic associated channel (G-ACh) to
support Fault, Configuration, Accounting, Performance and Security
(FCAPS) functions by carrying packets related to OAM, PSC, SCC, MCC
or other packet types in-band over LSPs, PWs or sections. The G-ACh
is defined in [RFC5586] and is similar to the Pseudowire Associated
Channel [RFC4385], which is used to carry OAM packets over
pseudowires. The G-ACh is indicated by an Associated Channel Header
(ACH), similar to the Pseudowire VCCV control word; this header is
present for all sections, LSPs and PWs making use of FCAPS functions
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supported by the G-ACh.
The G-ACh must only be used for channels that are an adjunct to the
data service. Examples of these are OAM, PSC, MCC and SCC, but the
use is not restricted to these services. The G-ACh must not be used
to carry additional data for use in the forwarding path, i.e. it must
not be used as an alternative to a PW control word, or to define a PW
type.
At the server layer, bandwidth and QoS commitments apply to the gross
traffic on the LSP, PW or section. Since the G-ACh traffic is
indistinguishable from the user data traffic, protocols using the
G-ACh must take into consideration the impact they have on the user
data with which they are sharing resources. Conversely, capacity
must be made available for important G-ACh uses such as protection
and OAM. In addition, protocols using the G-ACh must conform to the
security and congestion considerations described in [RFC5586].
Figure 10 shows the reference model depicting how the control channel
is associated with the pseudowire protocol stack. This is based on
the reference model for VCCV shown in Figure 2 of [RFC5085].
+-------------+ +-------------+
| Payload | < FCAPS > | Payload |
+-------------+ +-------------+
| Demux / | < ACH for PW > | Demux / |
|Discriminator| |Discriminator|
+-------------+ +-------------+
| PW | < PW > | PW |
+-------------+ +-------------+
| PSN | < LSP > | PSN |
+-------------+ +-------------+
| Physical | | Physical |
+-----+-------+ +-----+-------+
| |
| ____ ___ ____ |
| _/ \___/ \ _/ \__ |
| / \__/ \_ |
| / \ |
+--------| MPLS-TP Network |---+
\ /
\ ___ ___ __ _/
\_/ \____/ \___/ \____/
Figure 10: PWE3 Protocol Stack Reference Model showing the G-ACh
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PW associated channel messages are encapsulated using the PWE3
encapsulation, so that they are handled and processed in the same
manner (or in some cases, an analogous manner) as the PW PDUs for
which they provide a control channel.
Figure 11 shows the reference model depicting how the control channel
is associated with the LSP protocol stack.
+-------------+ +-------------+
| Payload | < FCAPS > | Payload |
+-------------+ +-------------+
|Discriminator| < ACH on LSP > |Discriminator|
+-------------+ +-------------+
|Demultiplexer| < GAL on LSP > |Demultiplexer|
+-------------+ +-------------+
| PSN | < LSP > | PSN |
+-------------+ +-------------+
| Physical | | Physical |
+-----+-------+ +-----+-------+
| |
| ____ ___ ____ |
| _/ \___/ \ _/ \__ |
| / \__/ \_ |
| / \ |
+--------| MPLS-TP Network |---+
\ /
\ ___ ___ __ _/
\_/ \____/ \___/ \____/
Figure 11: MPLS Protocol Stack Reference Model showing the LSP
Associated Control Channel
3.7. Operations, Administration and Maintenance (OAM)
The MPLS-TP OAM architecture supports a wide range of OAM functions
to check continuity, to verify connectivity, to monitor path
performance, and to generate, filter and manage local and remote
defect alarms. These functions are applicable to any layer defined
within MPLS-TP, i.e. to MPLS-TP sections, LSPs and PWs.
The MPLS-TP OAM tool-set must be able to operate without relying on a
dynamic control plane or IP functionality in the datapath. In the
case of an MPLS-TP deployment in a network in which IP functionality
is available, all existing IP/MPLS OAM functions, e.g. LSP-Ping, BFD
and VCCV, may be used. Since MPLS-TP must be able to operate in
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environments where IP is not used in the forwarding plane, the
default mechanism for OAM demultiplexing in MPLS-TP LSPs and PWs is
the Generic Associated Channel (Section 3.6). Forwarding based on IP
addresses for user or OAM packets is not required for MPLS-TP.
[RFC4379] and BFD for MPLS LSPs [I-D.ietf-bfd-mpls] have defined
alert mechanisms that enable an MPLS LSR to identify and process MPLS
OAM packets when the OAM packets are encapsulated in an IP header.
These alert mechanisms are based on TTL expiration and/or use an IP
destination address in the range 127/8 for IPv4 and that same range
embedded as IPv4 mapped IPv6 addresses for IPv6 [RFC4379]. When the
OAM packets are encapsulated in an IP header, these mechanisms are
the default mechanisms for MPLS networks in general for identifying
MPLS OAM packets, although the mechanisms defined in [RFC5586] can
also be used. MPLS-TP must be able to operate in environments where
IP forwarding is not supported, and thus the G-ACh/GAL is the default
mechanism to demultiplex OAM packets in MPLS-TP in these
environments.
MPLS-TP supports a comprehensive set of OAM capabilities for packet
transport applications, with equivalent capabilities to those
provided in SONET/SDH.
MPLS-TP requires [I-D.ietf-mpls-tp-oam-requirements] that a set of
OAM capabilities is available to perform fault management (e.g. fault
detection and localisation) and performance monitoring (e.g. packet
delay and loss measurement) of the LSP, PW or section. The framework
for OAM in MPLS-TP is specified in [I-D.ietf-mpls-tp-oam-framework].
MPLS-TP OAM packets share the same fate as their corresponding data
packets, and are identified through the Generic Associated Channel
mechanism [RFC5586]. This uses a combination of an Associated
Channel Header (ACH) and a G-ACh Label (GAL) to create a control
channel associated to an LSP, Section or PW.
OAM and monitoring in MPLS-TP is based on the concept of maintenance
entities, as described in [I-D.ietf-mpls-tp-oam-framework]. A
Maintenance Entity (ME) can be viewed as the association of two
Maintenance Entity Group End Points (MEPs). A Maintenance Entity
Group (MEG) is a collection of one or more MEs that belongs to the
same transport path and that are maintained and monitored as a group.
The MEPs that form an ME limit the OAM responsibilities of an OAM
flow to within the domain of a transport path or segment, in the
specific layer network that is being monitored and managed.
A MEG may also include a set of Maintenance Entity Group Intermediate
Points (MIPs). MEPs are capable of sourcing and sinking OAM flows,
while MIPs can both react to OAM flows received from within a MEG.
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Intermediate nodes can also originate notifications to the MEPs as a
result of specific network conditions.
A G-ACh packet may be directed to an individual MIP along the path of
an LSP or MS-PW by setting the appropriate TTL in the label for the
G-ACh packet, as per the traceroute mode of LSP Ping [RFC4379] and
the vccv-trace mode of [I-D.ietf-pwe3-segmented-pw]. Note that this
works when the location of MIPs along the LSP or PW path is known by
the MEP. There may be circumstances where this is not the case, e.g.
following restoration using a facility bypass LSP. In these cases,
tools to trace the path of the LSP may be used to determine the
appropriate setting for the TTL to reach a specific MIP.
Within an LSR or PE, MEPs and MIPs can only be placed where MPLS
layer processing is performed on a packet. The MPLS architecture
mandates that MPLS layer processing occurs at least once on an LSR.
Any node on an LSP can send an OAM packet on that LSP. Likewise, any
node on a PW can send OAM packets on a PW, including S-PEs.
An OAM packet can only be received to be processed at an LSP
endpoint, a PW endpoint (T-PE), or on the expiry of the TTL of the
LSP or PW label.
3.8. Return Path
Management, control and OAM protocol functions may require response
packets to be delivered from the receiver back to the originator of a
message exchange. This section provides a summary of the return path
options in MPLS-TP networks. Although this section describes the
case of an MPLS-TP LSP, it is also applicable to a PW.
In this description, U and D are LSRs that terminate MPLS-TP LSPs
(i.e. LERs) and that Y is an intermediate LSR along the LSP. In the
unidirectional case, U is the upstream LER and D is the downstream
LER with respect to the LSP. This reference model is shown in
Figure 12.
LSP LSP
U ========= Y ========= D
LER LSR LER
---------> Direction of pcket flow
Figure 12: Return Path reference Model
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The following cases are described for the various types of LSPs:
Case 1 Packet transmission from D to U
Case 2 Packet transmission from Y to U
Case 3 Packet transmission from D to Y
Note that a return path may not always exist, and that packet
transmission in one or more of the above cases may not be possible.
In general the existence and nature of return paths for MPLS-TP LSPs
is determined by operational provisioning.
3.8.1. Return Path Types
There are two types of return path that may be used for the delivery
of traffic from a downstream node D to an upstream node U. Either:
a. The LSP between U and D is bidirectional, and therefore D has a
path via the MPLS-TP LSP to return traffic back to U, or
b. D has some other unspecified means of directing traffic back to
U.
The first option is referred to as an "in-band" return path, the
second as an "out-of-band" return path.
There are various possibilities for "out-of-band" return paths. Such
a path may, for example, be based on ordinary IP routing. In this
case packets would be forwarded as usual to a destination IP address
associated with U. In an MPLS-TP network that is also an IP/MPLS
network, such a forwarding path may traverse the same physical links
or logical transport paths used by MPLS-TP. An out-of-band return
path may also be indirect, via a distinct Data Communication Network
(DCN) (provided, for example, by the method specified in [RFC5718]);
or it may be via one or more other MPLS-TP LSPs.
3.8.2. Point-to-Point Unidirectional LSPs
Case 1 In this situation, either an in-band or out-of-band return
path may be used to deliver traffic from D back to U.
It is recommended for reasons of operational simplicity that
point-to-point unidirectional LSPs be provisioned as
associated bidirectional LSPs (which may also be co-routed)
whenever return traffic from D to U is required. Note that
the two directions of such an LSP may have differing
bandwidth allocations and QoS characteristics. In the in-
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band case there is in essence an associated bidirectional LSP
between U and D, and the discussion for such LSPs below
applies.
Case 2 In this case only the out-of-band return path option is
available. However, an additional out-of-band possibility is
worthy of note here: if D is known to have a return path to
U, then Y can arrange to deliver return traffic to U by first
sending it to D along the original LSP. The mechanism by
which D recognises the need for and performs this forwarding
operation is protocol-specific.
Case 3 In this case only the out-of-band return path option is
available. However, if D has a return path to U, then in a
manner analogous to the previous case D can arrange to
deliver return traffic to Y by first sending it to U along
that return path. The mechanism by which U recognises the
need for and performs this forwarding operation is protocol-
specific.
3.8.3. Point-to-Point Associated Bidirectional LSPs
For Case 1, D has a natural in-band return path to U, the use of
which is typically preferred for return traffic, although out-of-band
return paths are also applicable.
For Cases 2 and 3, the considerations are the same as those for
point-to-point unidirectional LSPs.
3.8.4. Point-to-Point Co-Routed Bidirectional LSPs
For all of Cases 1, 2, and 3, a natural in-band return path exists in
the form of the LSP itself, and its use is preferred for return
traffic. Out-of-band return paths, however, are also applicable,
primarily as an alternative means of delivery in case the in-band
return path has failed.
3.9. Control Plane
A distributed dynamic control plane may be used to enable dynamic
service provisioning in an MPLS-TP network. Where the requirements
specified in [RFC5654] can be met, the MPLS Transport Profile uses
existing standard control plane protocols for LSPs and PWs.
Note that a dynamic control plane is not required in an MPLS-TP
network. See Section 3.11 for further details on statically
configured and provisioned MPLS-TP services.
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Figure 13 illustrates the relationship between the MPLS-TP control
plane, the forwarding plane, the management plane, and OAM for point-
to-point MPLS-TP LSPs or PWs.
+------------------------------------------------------------------+
| |
| Network Management System and/or |
| |
| Control Plane for Point to Point Connections |
| |
+------------------------------------------------------------------+
| | | | | |
.............|.....|... ....|.....|.... ....|.....|............
: +---+ | : : +---+ | : : +---+ | :
: |OAM| | : : |OAM| | : : |OAM| | :
: +---+ | : : +---+ | : : +---+ | :
: | | : : | | : : | | :
\: +----+ +--------+ : : +--------+ : : +--------+ +----+ :/
--+-|Edge|<->|Forward-|<---->|Forward-|<----->|Forward-|<->|Edge|-+--
/: +----+ |ing | : : |ing | : : |ing | +----+ :\
: +--------+ : : +--------+ : : +--------+ :
''''''''''''''''''''''' ''''''''''''''' '''''''''''''''''''''''
Note:
1) NMS may be centralised or distributed. Control plane is
distributed.
2) 'Edge' functions refers to those functions present at
the edge of a PSN domain, e.g. NSP or classification.
3) The control plane may be transported over the server
layer, an LSP or a G-ACh.
Figure 13: MPLS-TP Control Plane Architecture Context
The MPLS-TP control plane is based on existing MPLS and PW control
plane protocols, and is consistent with the Automatically Switched
Optical Networks (ASON) architecture [G.8080]. MPLS-TP uses
Generalized MPLS (GMPLS) signaling ([RFC3945], [RFC3471], [RFC3473])
for LSPs and Targeted LDP (T-LDP) [RFC4447]
[I-D.ietf-pwe3-segmented-pw][I-D.ietf-pwe3-dynamic-ms-pw] for
pseudowires.
MPLS-TP requires that any control plane traffic be capable of being
carried over an out-of-band signaling network or a signaling control
channel such as the one described in [RFC5718]. Note that while
T-LDP signaling is traditionally carried in-band in IP/MPLS networks,
this does not preclude its operation over out-of-band channels.
References to T-LDP in this document do not preclude the definition
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of alternative PW control protocols for use in MPLS-TP.
PW control (and maintenance) takes place separately from LSP tunnel
signaling. The main coordination between LSP and PW control will
occur within the nodes that terminate PWs. The control planes for
PWs and LSPs may be used independently, and one may be employed
without the other. This translates into the four possible scenarios:
(1) no control plane is employed; (2) a control plane is used for
both LSPs and PWs; (3) a control plane is used for LSPs, but not PWs;
(4) a control plane is used for PWs, but not LSPs. The PW and LSP
control planes, collectively, must satisfy the MPLS-TP control plane
requirements reviewed in the MPLS-TP Control Plane Framework
[I-D.ietf-ccamp-mpls-tp-cp-framework]. When client services are
provided directly via LSPs, all requirements must be satisfied by the
LSP control plane. When client services are provided via PWs, the PW
and LSP control planes operate in combination and some functions may
be satisfied via the PW control plane while others are provided to
PWs by the LSP control plane.
Note that if MPLS-TP is being used in a multi-layer network, a number
of control protocol types and instances may be used. This is
consistent with the MPLS architecture which permits each label in the
label stack to be allocated and signaled by its own control protocol.
The distributed MPLS-TP control plane may provide the following
functions:
o Signaling
o Routing
o Traffic engineering and constraint-based path computation
In a multi-domain environment, the MPLS-TP control plane supports
different types of interfaces at domain boundaries or within the
domains. These include the User-Network Interface (UNI), Internal
Network-Network Interface (I-NNI), and External Network-Network
Interface (E-NNI). Note that different policies may be defined that
control the information exchanged across these interface types.
The MPLS-TP control plane is capable of activating MPLS-TP OAM
functions as described in the OAM section of this document
Section 3.7, e.g. for fault detection and localisation in the event
of a failure in order to efficiently restore failed transport paths.
The MPLS-TP control plane supports all MPLS-TP data plane
connectivity patterns that are needed for establishing transport
paths, including protected paths as described in Section 3.12.
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Examples of the MPLS-TP data plane connectivity patterns are LSPs
utilising the fast reroute backup methods as defined in [RFC4090] and
ingress-to-egress 1+1 or 1:1 protected LSPs.
The MPLS-TP control plane provides functions to ensure its own
survivability and to enable it to recover gracefully from failures
and degradations. These include graceful restart and hot redundant
configurations. Depending on how the control plane is transported,
varying degrees of decoupling between the control plane and data
plane may be achieved. In all cases, however, the control plane is
logically decoupled from the data plane such that a control plane
failure does not imply a failure of the existing transport paths.
3.10. Interdomain Connectivity
A number of methods exist to support inter-domain operation of
MPLS-TP, including the data plane, OAM and configuration aspects, for
example:
o Inter-domain TE LSPs [RFC4216]
o Multi-segment Pseudowires [RFC5659]
o LSP stitching [RFC5150]
o back-to-back attachment circuits [RFC5659]
An important consideration in selecting an inter-domain connectivity
mechanism is the degree of layer network isolation and types of OAM
required by the operator. The selection of which technique to use in
a particular deployment scenario is outside the scope of this
document.
3.11. Static Operation of LSPs and PWs
A PW or LSP may be statically configured without the support of a
dynamic control plane. This may be either by direct configuration of
the PEs/LSRs, or via a network management system. Static operation
is independent for a specific PW or LSP instance. Thus it should be
possible for a PW to be statically configured, while the LSP
supporting it is set up by a dynamic control plane. When static
configuration mechanisms are used, care must be taken to ensure that
loops are not created.
3.12. Survivability
The survivability architecture for MPLS-TP is specified in
[I-D.ietf-mpls-tp-survive-fwk].
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A wide variety of resiliency schemes have been developed to meet the
various network and service survivability objectives. For example,
as part of the MPLS/PW paradigms, MPLS provides methods for local
repair using back-up LSP tunnels ([RFC4090]), while pseudowire
redundancy [I-D.ietf-pwe3-redundancy] supports scenarios where the
protection for the PW cannot be fully provided by the underlying LSP
(i.e. where the backup PW terminates on a different target PE node
than the working PW in dual homing scenarios, or where protection of
the S-PE is required). Additionally, GMPLS provides a well known set
of control plane driven protection and restoration mechanisms
[RFC4872]. MPLS-TP provides additional protection mechanisms that
are optimised for both linear topologies and ring topologies, and
that operate in the absence of a dynamic control plane. These are
specified in [I-D.ietf-mpls-tp-survive-fwk].
Different protection schemes apply to different deployment topologies
and operational considerations. Such protection schemes may provide
different levels of resiliency, for example:
o Two concurrent traffic paths (1+1).
o one active and one standby path with guaranteed bandwidth on both
paths (1:1).
o one active path and a standby path the resources of which are
shared by one or more other active paths (shared protection).
The applicability of any given scheme to meet specific requirements
is outside the scope of this document.
The characteristics of MPLS-TP resiliency mechanisms are as follows:
o Optimised for linear, ring or meshed topologies.
o Use OAM mechanisms to detect and localise network faults or
service degenerations.
o Include protection mechanisms to coordinate and trigger protection
switching actions in the absence of a dynamic control plane. This
is known as a Protection State Coordination (PSC) mechanism.
o MPLS-TP recovery schemes are applicable to all levels in the
MPLS-TP domain (i.e. section, LSP and PW), providing segment and
end-to-end recovery.
o MPLS-TP recovery mechanisms support the coordination of protection
switching at multiple levels to prevent race conditions occurring
between a client and its server layer.
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o MPLS-TP recovery mechanisms can be data plane, control plane or
management plane based.
o MPLS-TP supports revertive and non-revertive behaviour.
3.13. Path Segment Tunnels
In order to monitor, protect and manage a portion of an LSP, a new
architectural element is defined called the Path Segment Tunnel
(PST). A PST is a hierarchical LSP [RFC3031] which is defined and
used for the purposes of OAM monitoring, protection or management of
LSP segments or concatenated LSP segments.
A PST is defined between the edges of the portion of the LSP that
needs to be monitored, protected or managed. OAM messages can be
initiated at the edge of the PST and sent to the peer edge of the PST
or to a MIP along the PST by setting the TTL value at the PST level
accordingly. A P router only pushes or pops a label if it is at the
end of a PST. In this mode, it is an LER for the PST.
For example in Figure 14, two PSTs are configured to allow
monitoring, protection and management of the LSP concatenated
segments. One PST is defined between LER2 and LER3, and a second PST
is set up between LER4 and LER5. Each of these PSTs may be
monitored, protected, or managed independently.
======================== End to End LSP ===========================
|<---- Carrier 1 ---->| |<---- Carrier 2 ---->|
[LER1]---[LER2]---[LSR]---[LER3]-------[LER4]---[LSR]---[LER5]---[LER6]
|======= PST =========| |======= PST =========|
(Carrier 1) (Carrier 2)
Note: LER2, LER3, LER4 and LER5 are with respect to the PST
Figure 14: PSTs in inter-carrier network
The end-to-end traffic of the LSP, including data traffic and control
traffic (OAM, Protection Switching Control, management and signaling
messages) is tunneled within the PST by means of label stacking as
defined in [RFC3031].
The mapping between an LSP and a PST can be 1:1, in which case it is
similar to the ITU-T Tandem Connection element [G.805]. The mapping
can also be 1:N to allow aggregated monitoring, protection and
management of a set of LSP segments or concatenated LSP segments.
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Figure 15 shows a PST which is used to aggregate a set of
concatenated LSP segments for the LSP from LERx to LERt and the LSP
from LERa to LERd. Note that such a construct is useful, for
example, when the LSPs traverse a common portion of the network and
they have the same Traffic Class.
|LERx|--|LSRy|-+ +-|LSRz|--|LERt|
| |
| |<---------- Carrier 1 --------->| |
| +-----+ +---+ +---+ +-----+ |
+--| |---| |---| |----| |--+
|LER1 | |LSR| |LSR| |LER2 |
+--| |---| |---| |----| |--+
| +-----+ +---+ + P + +-----+ |
| |============= PST ==============| |
|LERa|--|LSRb|-+ (Carrier 1) +-|LSRc|--|LERd|
Figure 15: PST for a Set of Concatenated LSP Segments
PSTs can be provisioned either statically or using control plane
signaling procedures. The make-before-break procedures which are
supported by MPLS allow the creation of a PST on existing LSPs in-
service without traffic disruption. A PST can be defined
corresponding to one or more end-to-end tunneled LSPs. New end-to-
end LSPs which are tunneled within the PST can be set up. Traffic of
the existing LSPs is switched over to the new end-to-end tunneled
LSPs. The old end-to-end LSPs can then be torn down.
3.14. Pseudowire Segment Tunnels
Hierarchical label stacking, in a similar manner to that described
above, can be used to implement path segment tunnels on pseudowires.
3.15. Network Management
The network management architecture and requirements for MPLS-TP are
specified in [I-D.ietf-mpls-tp-nm-framework] and
[I-D.ietf-mpls-tp-nm-req]. These derive from the generic
specifications described in ITU-T G.7710/Y.1701 [G.7710] for
transport technologies. They also incorporate the OAM requirements
for MPLS Networks [RFC4377] and MPLS-TP Networks
[I-D.ietf-mpls-tp-oam-requirements] and expand on those requirements
to cover the modifications necessary for fault, configuration,
performance, and security in a transport network.
The Equipment Management Function (EMF) of an MPLS-TP Network Element
(NE) (i.e. LSR, LER, PE, S-PE or T-PE) provides the means through
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which a management system manages the NE. The Management
Communication Channel (MCC), realised by the G-ACh, provides a
logical operations channel between NEs for transferring Management
information. For the management interface from a management system
to an MPLS-TP NE, there is no restriction on which management
protocol is used. The Network Management System (NMS) is used to
provision and manage an end-to-end connection across a network where
some segments are created/managed by, for example, Netconf [RFC4741]
or SNMP [RFC3411] and other segments by XML or CORBA interfaces.
Maintenance operations are run on a connection (LSP or PW) in a
manner that is independent of the provisioning mechanism. An MPLS-TP
NE is not required to offer more than one standard management
interface. In MPLS-TP, the EMF must be capable of statically
provisioning LSPs for an LSR or LER, and PWs for a PE, as well as any
associated MEPs and MIPs, as per Section 3.11.
Fault Management (FM) functions within the EMF of an MPLS-TP NE
enable the supervision, detection, validation, isolation, correction,
and alarm handling of abnormal conditions in the MPLS-TP network and
its environment. FM must provide for the supervision of transmission
(such as continuity, connectivity, etc.), software processing,
hardware, and environment. Alarm handling includes alarm severity
assignment, alarm suppression/aggregation/correlation, alarm
reporting control, and alarm reporting.
Configuration Management (CM) provides functions to control,
identify, collect data from, and provide data to MPLS-TP NEs. In
addition to general configuration for hardware, software protection
switching, alarm reporting control, and date/time setting, the EMF of
the MPLS-TP NE also supports the configuration of maintenance entity
identifiers (such as Maintenance Entity Group Endpoint (MEP) ID and
MEG Intermediate Point (MIP) ID). The EMF also supports the
configuration of OAM parameters as a part of connectivity management
to meet specific operational requirements. These may specify whether
the operational mode is one-time on-demand or is periodic at a
specified frequency.
The Performance Management (PM) functions within the EMF of an
MPLS-TP NE support the evaluation and reporting of the behaviour of
the NEs and the network. One particular requirement for PM is to
provide coherent and consistent interpretation of the network
behaviour in a hybrid network that uses multiple transport
technologies. Packet loss measurement and delay measurements may be
collected and used to detect performance degradation. This is
reported via fault management to enable corrective actions to be
taken (e.g. protection switching), and via performance monitoring for
Service Level Agreement (SLA) verification and billing. Collection
mechanisms for performance data should be capable of operating on-
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demand or pro-actively.
4. Security Considerations
The introduction of MPLS-TP into transport networks means that the
security considerations applicable to both MPLS and PWE3 apply to
those transport networks. Furthermore, when general MPLS networks
that utilise functionality outside of the strict MPLS Transport
Profile are used to support packet transport services, the security
considerations of that additional functionality also apply.
For pseudowires, the security considerations of [RFC3985] and
[RFC5659] apply.
Each MPLS-TP solution must specify the additional security
considerations that apply. This is discussed further in
[I-D.fang-mpls-tp-security-framework].
The security considerations in
[I-D.ietf-mpls-mpls-and-gmpls-security-framework] apply.
5. IANA Considerations
IANA considerations resulting from specific elements of MPLS-TP
functionality will be detailed in the documents specifying that
functionality.
This document introduces no additional IANA considerations in itself.
6. Acknowledgements
The editors wish to thank the following for their contribution to
this document:
o Rahul Aggarwal
o Dieter Beller
o Malcolm Betts
o Italo Busi
o John E Drake
o Hing-Kam Lam
o Marc Lasserre
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o Vincenzo Sestito
o Nurit Sprecher
o Martin Vigoureux
o Yaacov Weingarten
o The participants of ITU-T SG15
7. References
7.1. Normative References
[G.7710] "ITU-T
Recommendation
G.7710/Y.1701
(07/07), "Common
equipment
management
function
requirements"",
2005.
[G.805] "ITU-T
Recommendation
G.805 (11/95),
"Generic
Functional
Architecture of
Transport
Networks"",
November 1995.
[RFC3031] Rosen, E.,
Viswanathan, A.,
and R. Callon,
"Multiprotocol
Label Switching
Architecture",
RFC 3031,
January 2001.
[RFC3032] Rosen, E., Tappan,
D., Fedorkow, G.,
Rekhter, Y.,
Farinacci, D., Li,
T., and A. Conta,
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"MPLS Label Stack
Encoding",
RFC 3032,
January 2001.
[RFC3270] Le Faucheur, F.,
Wu, L., Davie, B.,
Davari, S.,
Vaananen, P.,
Krishnan, R.,
Cheval, P., and J.
Heinanen, "Multi-
Protocol Label
Switching (MPLS)
Support of
Differentiated
Services",
RFC 3270,
May 2002.
[RFC3473] Berger, L.,
"Generalized
Multi-Protocol
Label Switching
(GMPLS) Signaling
Resource
ReserVation
Protocol-Traffic
Engineering
(RSVP-TE)
Extensions",
RFC 3473,
January 2003.
[RFC3985] Bryant, S. and P.
Pate, "Pseudo Wire
Emulation Edge-to-
Edge (PWE3)
Architecture",
RFC 3985,
March 2005.
[RFC4090] Pan, P., Swallow,
G., and A. Atlas,
"Fast Reroute
Extensions to
RSVP-TE for LSP
Tunnels",
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RFC 4090,
May 2005.
[RFC4385] Bryant, S.,
Swallow, G.,
Martini, L., and
D. McPherson,
"Pseudowire
Emulation Edge-to-
Edge (PWE3)
Control Word for
Use over an MPLS
PSN", RFC 4385,
February 2006.
[RFC4447] Martini, L.,
Rosen, E., El-
Aawar, N., Smith,
T., and G. Heron,
"Pseudowire Setup
and Maintenance
Using the Label
Distribution
Protocol (LDP)",
RFC 4447,
April 2006.
[RFC4872] Lang, J., Rekhter,
Y., and D.
Papadimitriou,
"RSVP-TE
Extensions in
Support of End-to-
End Generalized
Multi-Protocol
Label Switching
(GMPLS) Recovery",
RFC 4872,
May 2007.
[RFC5085] Nadeau, T. and C.
Pignataro,
"Pseudowire
Virtual Circuit
Connectivity
Verification
(VCCV): A Control
Channel for
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Pseudowires",
RFC 5085,
December 2007.
[RFC5586] Bocci, M.,
Vigoureux, M., and
S. Bryant, "MPLS
Generic Associated
Channel",
RFC 5586,
June 2009.
7.2. Informative References
[G.8080] "ITU-T
Recommendation
G.8080/Y.1304,
"Architecture for
the automatically
switched optical
network (ASON)"",
2005.
[I-D.fang-mpls-tp-security-framework] Fang, L. and B.
Niven-Jenkins,
"Security
Framework for
MPLS-TP", draft-
fang-mpls-tp-
security-
framework-01 (work
in progress),
March 2010.
[I-D.ietf-bfd-mpls] Aggarwal, R.,
Kompella, K.,
Nadeau, T., and G.
Swallow, "BFD For
MPLS LSPs", draft-
ietf-bfd-mpls-07
(work in
progress),
June 2008.
[I-D.ietf-ccamp-mpls-tp-cp-framework] Andersson, L.,
Berger, L., Fang,
L., Bitar, N.,
Takacs, A.,
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Vigoureux, M.,
Bellagamba, E.,
and E. Gray,
"MPLS-TP Control
Plane Framework",
draft-ietf-ccamp-
mpls-tp-cp-
framework-01 (work
in progress),
March 2010.
[I-D.ietf-l2vpn-vpms-frmwk-requirements] Kamite, Y.,
JOUNAY, F., Niven-
Jenkins, B.,
Brungard, D., and
L. Jin, "Framework
and Requirements
for Virtual
Private Multicast
Service (VPMS)", d
raft-ietf-l2vpn-
vpms-frmwk-
requirements-02
(work in
progress),
October 2009.
[I-D.ietf-mpls-mpls-and-gmpls-security-framework] Fang, L. and M.
Behringer,
"Security
Framework for MPLS
and GMPLS
Networks", draft-
ietf-mpls-mpls-
and-gmpls-
security-
framework-09 (work
in progress),
March 2010.
[I-D.ietf-mpls-tp-data-plane] Frost, D., Bryant,
S., and M. Bocci,
"MPLS Transport
Profile Data Plane
Architecture", dra
ft-ietf-mpls-tp-
data-plane-01
(work in
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progress),
March 2010.
[I-D.ietf-mpls-tp-identifiers] Bocci, M. and G.
Swallow, "MPLS-TP
Identifiers", draf
t-ietf-mpls-tp-
identifiers-01
(work in
progress),
March 2010.
[I-D.ietf-mpls-tp-nm-framework] Mansfield, S.,
Gray, E., and H.
Lam, "MPLS-TP
Network Management
Framework", draft-
ietf-mpls-tp-nm-
framework-05 (work
in progress),
February 2010.
[I-D.ietf-mpls-tp-nm-req] Mansfield, S. and
K. Lam, "MPLS TP
Network Management
Requirements", dra
ft-ietf-mpls-tp-
nm-req-06 (work in
progress),
October 2009.
[I-D.ietf-mpls-tp-oam-framework] Allan, D., Busi,
I., and B. Niven-
Jenkins, "MPLS-TP
OAM Framework", dr
aft-ietf-mpls-tp-
oam-framework-05
(work in
progress),
March 2010.
[I-D.ietf-mpls-tp-oam-requirements] Vigoureux, M. and
D. Ward,
"Requirements for
OAM in MPLS
Transport
Networks", draft-
ietf-mpls-tp-oam-
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requirements-06
(work in
progress),
March 2010.
[I-D.ietf-mpls-tp-survive-fwk] Sprecher, N. and
A. Farrel,
"Multiprotocol
Label Switching
Transport Profile
Survivability
Framework", draft-
ietf-mpls-tp-
survive-fwk-04
(work in
progress),
March 2010.
[I-D.ietf-pwe3-dynamic-ms-pw] Martini, L.,
Bocci, M., Balus,
F., Bitar, N.,
Shah, H.,
Aissaoui, M.,
Rusmisel, J.,
Serbest, Y.,
Malis, A., Metz,
C., McDysan, D.,
Sugimoto, J.,
Duckett, M.,
Loomis, M.,
Doolan, P., Pan,
P., Pate, P.,
Radoaca, V., Wada,
Y., and Y. Seo,
"Dynamic Placement
of Multi Segment
Pseudo Wires", dra
ft-ietf-pwe3-
dynamic-ms-pw-10
(work in
progress),
October 2009.
[I-D.ietf-pwe3-redundancy] Muley, P. and V.
Place, "Pseudowire
(PW) Redundancy",
draft-ietf-pwe3-
redundancy-02
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(work in
progress),
October 2009.
[I-D.ietf-pwe3-segmented-pw] Martini, L.,
Nadeau, T., Metz,
C., Duckett, M.,
Bocci, M., Balus,
F., and M.
Aissaoui,
"Segmented
Pseudowire", draft
-ietf-pwe3-
segmented-pw-13
(work in
progress),
August 2009.
[I-D.ietf-pwe3-vccv-bfd] Nadeau, T. and C.
Pignataro,
"Bidirectional
Forwarding
Detection (BFD)
for the Pseudowire
Virtual Circuit
Connectivity
Verification
(VCCV)", draft-
ietf-pwe3-vccv-
bfd-07 (work in
progress),
July 2009.
[RFC3209] Awduche, D.,
Berger, L., Gan,
D., Li, T.,
Srinivasan, V.,
and G. Swallow,
"RSVP-TE:
Extensions to RSVP
for LSP Tunnels",
RFC 3209,
December 2001.
[RFC3411] Harrington, D.,
Presuhn, R., and
B. Wijnen, "An
Architecture for
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Describing Simple
Network Management
Protocol (SNMP)
Management
Frameworks",
STD 62, RFC 3411,
December 2002.
[RFC3443] Agarwal, P. and B.
Akyol, "Time To
Live (TTL)
Processing in
Multi-Protocol
Label Switching
(MPLS) Networks",
RFC 3443,
January 2003.
[RFC3471] Berger, L.,
"Generalized
Multi-Protocol
Label Switching
(GMPLS) Signaling
Functional
Description",
RFC 3471,
January 2003.
[RFC3945] Mannie, E.,
"Generalized
Multi-Protocol
Label Switching
(GMPLS)
Architecture",
RFC 3945,
October 2004.
[RFC4216] Zhang, R. and J.
Vasseur, "MPLS
Inter-Autonomous
System (AS)
Traffic
Engineering (TE)
Requirements",
RFC 4216,
November 2005.
[RFC4364] Rosen, E. and Y.
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Rekhter, "BGP/MPLS
IP Virtual Private
Networks (VPNs)",
RFC 4364,
February 2006.
[RFC4377] Nadeau, T.,
Morrow, M.,
Swallow, G.,
Allan, D., and S.
Matsushima,
"Operations and
Management (OAM)
Requirements for
Multi-Protocol
Label Switched
(MPLS) Networks",
RFC 4377,
February 2006.
[RFC4379] Kompella, K. and
G. Swallow,
"Detecting Multi-
Protocol Label
Switched (MPLS)
Data Plane
Failures",
RFC 4379,
February 2006.
[RFC4664] Andersson, L. and
E. Rosen,
"Framework for
Layer 2 Virtual
Private Networks
(L2VPNs)",
RFC 4664,
September 2006.
[RFC4741] Enns, R., "NETCONF
Configuration
Protocol",
RFC 4741,
December 2006.
[RFC5150] Ayyangar, A.,
Kompella, K.,
Vasseur, JP., and
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A. Farrel, "Label
Switched Path
Stitching with
Generalized
Multiprotocol
Label Switching
Traffic
Engineering (GMPLS
TE)", RFC 5150,
February 2008.
[RFC5254] Bitar, N., Bocci,
M., and L.
Martini,
"Requirements for
Multi-Segment
Pseudowire
Emulation Edge-to-
Edge (PWE3)",
RFC 5254,
October 2008.
[RFC5309] Shen, N. and A.
Zinin, "Point-to-
Point Operation
over LAN in Link
State Routing
Protocols",
RFC 5309,
October 2008.
[RFC5331] Aggarwal, R.,
Rekhter, Y., and
E. Rosen, "MPLS
Upstream Label
Assignment and
Context-Specific
Label Space",
RFC 5331,
August 2008.
[RFC5654] Niven-Jenkins, B.,
Brungard, D.,
Betts, M.,
Sprecher, N., and
S. Ueno,
"Requirements of
an MPLS Transport
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Profile",
RFC 5654,
September 2009.
[RFC5659] Bocci, M. and S.
Bryant, "An
Architecture for
Multi-Segment
Pseudowire
Emulation Edge-to-
Edge", RFC 5659,
October 2009.
[RFC5718] Beller, D. and A.
Farrel, "An In-
Band Data
Communication
Network For the
MPLS Transport
Profile",
RFC 5718,
January 2010.
Authors' Addresses
Matthew Bocci (editor)
Alcatel-Lucent
Voyager Place, Shoppenhangers Road
Maidenhead, Berks SL6 2PJ
United Kingdom
Phone:
EMail: matthew.bocci@alcatel-lucent.com
Stewart Bryant (editor)
Cisco Systems
250 Longwater Ave
Reading RG2 6GB
United Kingdom
Phone:
EMail: stbryant@cisco.com
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Dan Frost (editor)
Cisco Systems
Phone:
Fax:
EMail: danfrost@cisco.com
URI:
Lieven Levrau
Alcatel-Lucent
7-9, Avenue Morane Sulnier
Velizy 78141
France
Phone:
EMail: lieven.levrau@alcatel-lucent.com
Lou Berger
LabN
Phone: +1-301-468-9228
Fax:
EMail: lberger@labn.net
URI:
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