Network Working Group B. Niven-Jenkins, Ed.
Internet-Draft BT
Intended status: Informational D. Brungard, Ed.
Expires: August 9, 2009 AT&T
M. Betts, Ed.
Nortel Networks
N. Sprecher
Nokia Siemens Networks
S. Ueno
NTT
February 5, 2009
MPLS-TP Requirements
draft-ietf-mpls-tp-requirements-04
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Abstract
This document specifies the requirements of an MPLS Transport Profile
(MPLS-TP). This document is a product of a joint International
Telecommunications Union (ITU)-IETF effort to include an MPLS
Transport Profile within the IETF MPLS architecture to support the
capabilities and functionalities of a packet transport network as
defined by International Telecommunications Union -
Telecommunications Standardization Sector (ITU-T).
This work is based on two sources of requirements; MPLS architecture
as defined by IETF, and packet transport networks as defined by
ITU-T.
The requirements expressed in this document are for the behavior of
the protocol mechanisms and procedures that constitute building
blocks out of which the MPLS transport profile is constructed. The
requirements are not implementation requirements.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
1.2. Transport network overview . . . . . . . . . . . . . . . . 8
1.3. Layer network overview . . . . . . . . . . . . . . . . . . 10
2. MPLS-TP Requirements . . . . . . . . . . . . . . . . . . . . . 10
2.1. General requirements . . . . . . . . . . . . . . . . . . . 11
2.2. Layering requirements . . . . . . . . . . . . . . . . . . 12
2.3. Data plane requirements . . . . . . . . . . . . . . . . . 13
2.4. Control plane requirements . . . . . . . . . . . . . . . . 15
2.5. Network Management (NM) requirements . . . . . . . . . . . 15
2.6. Operation, Administration and Maintenance (OAM)
requirements . . . . . . . . . . . . . . . . . . . . . . . 15
2.7. Network performance management (PM) requirements . . . . . 16
2.8. Recovery & Survivability requirements . . . . . . . . . . 16
2.8.1. Data plane behavior requirements . . . . . . . . . . . 17
2.8.2. Triggers for protection, restoration, and reversion . 18
2.8.3. Management plane operation of protection and
restoration . . . . . . . . . . . . . . . . . . . . . 19
2.8.4. Control plane and in-band OAM operation of recovery . 19
2.8.5. Topology-specific recovery mechanisms . . . . . . . . 20
2.9. QoS requirements . . . . . . . . . . . . . . . . . . . . . 23
2.10. Security requirements . . . . . . . . . . . . . . . . . . 24
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
4. Security Considerations . . . . . . . . . . . . . . . . . . . 24
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.1. Normative References . . . . . . . . . . . . . . . . . . . 25
6.2. Informative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
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1. Introduction
For many years, transport networks (e.g. Synchronous Optical
Networking (SONET)/Synchronous Digital hierarchy (SDH)) have provided
carriers with a high benchmark for reliability and operational
simplicity. With the accelerating growth and penetration of:
o Packet-based services such as Ethernet, Voice over IP (VoIP),
Layer 2 (L2)/Layer 3 (L3) Virtual Private Networks (VPNs), IP
Television (IPTV), Radio Access Network (RAN) backhauling, etc.
o Applications with various bandwidth and QoS requirements.
Carriers are in need of technologies capable of efficiently
supporting packet-based services and applications on their transport
networks. The need to increase their revenue while remaining
competitive forces operators to look for the lowest network Total
Cost of Ownership (TCO). Investment in equipment and facilities
(Capital Expenditure (CAPEX)) and Operational Expenditure (OPEX)
should be minimized.
Carriers are considering migrating or evolving to packet transport
networks in order to reduce their costs and to improve their ability
to support services with guaranteed Service Level Agreements (SLAs).
For carriers it is important that migrating from their existing
transport networks to packet transport networks should not involve
dramatic changes in network operation, should not necessitate
extensive retraining, and should not require major changes to
existing work practices. The aim is to preserve the look-and-feel to
which carriers have become accustomed in deploying their transport
networks, while providing common, multi-layer operations, resiliency,
control and management for packet, circuit and lambda transport
networks.
Transport carriers require control and deterministic usage of network
resources. They need end-to-end control to engineer network paths
and to efficiently utilize network resources. They require
capabilities to support static (Operations Support System (OSS)
based) or dynamic (control plane) provisioning of deterministic,
protected and secured services and their associated resources.
Carriers will still need to cope with legacy networks (which are
composed of many layers and technologies), thus the packet transport
network should interwork as appropriate with other packet and
transport networks (both horizontally and vertically). Vertical
interworking is also known as client/server or network interworking.
Horizontal interworking is also known as peer-partition or service
interworking. For more details on each type of interworking and some
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of the issues that may arise (especially with horizontal
interworking) see Y.1401 [ITU.Y1401.2008].
MPLS is a maturing packet technology and it is already playing an
important role in transport networks and services. However, not all
of MPLS's capabilities and mechanisms are needed and/or consistent
with transport network operations. There is therefore the need to
define an MPLS Transport Profile (MPLS-TP) in order to support the
capabilities and functionalities needed for packet transport network
services and operations through combining the packet experience of
MPLS with the operational experience of existing transport networks.
MPLS-TP will enable the migration of transport networks to a packet-
based network that will efficiently scale to support packet services
in a simple and cost effective way. MPLS-TP needs to combine the
necessary existing capabilities of MPLS with additional minimal
mechanisms in order that it can be used in a transport role.
This document specifies the requirements of an MPLS Transport Profile
(MPLS-TP). The requirements are for the the behavior of the protocol
mechanisms and procedures that constitute building blocks out of
which the MPLS transport profile is constructed. That is, the
requirements indicate what features are to be available in the MPLS
toolkit for use by MPLS-TP. The requirements in this document do not
describe what functions an MPLS-TP implementation supports. The
purpose of this document is to identify the toolkit and any new
protocol work that is required.
Although this document is not a protocol specification, the key words
"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are used as
described in [RFC2119] and are to be interpreted as instructions to
the protocol designers producing solutions that satisfy the
requirements set out in this document.
This document is a product of a joint ITU-IETF effort to include an
MPLS Transport Profile within the IETF MPLS architecture to support
the capabilities and functionalities of a packet transport network as
defined by ITU-T.
This work is based on two sources of requirements, MPLS architecture
as defined by IETF and packet transport networks as defined by ITU-T.
The requirements of MPLS-TP are provided below. The relevant
functions of MPLS are included in MPLS-TP, except where explicitly
excluded.
Although both static and dynamic configuration of MPLS-TP transport
paths (including Operations, Administration and Maintenance (OAM) and
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protection capabilities) is required by this document, it MUST be
possible for operators to be able to completely operate (including
OAM and protection capabilities) an MPLS-TP network in the absence of
any control plane protocols for dynamic configuration.
1.1. Terminology
Note: Mapping between the terms in this section and ITU-T terminology
will be described in a subsequent document.
Note: The definition of segment in a GMPLS/ASON context (i.e. as
defined in RFC4397 [RFC4397]) encompasses both segment and
concatenated segment as defined in this document.
Associated bidirectional path: A path that supports traffic flow in
both directions but which is constructed from a pair of
unidirectional paths (one for each direction) which are associated
with one another at the path's ingress/egress points. The forward
and backward directions may or may not follow the same route (links
and nodes) across the network.
Bidirectional path: A path where the forward and backward directions
follow the same route (links and nodes) across the network.
Concatenated Segment: A serial-compound link connection as defined in
G.805 [ITU.G805.2000]. A concatenated segment is a contiguous part
of an LSP or multi-segment PW that comprises a set of segments and
their interconnecting nodes in sequence.
Co-routed bidirectional path: A bidirectional path where the forward
and backward directions follow the same route (links and nodes)
across its layer network.
Domain: A domain represents a collection of entities (for example
network elements) that are grouped for a particular purpose, examples
of which are administrative and/or managerial responsibilities, trust
relationships, addressing schemes, infrastructure capabilities,
aggregation, survivability techniques, distributions of control
functionality, etc. Examples of such domains include IGP areas and
Autonomous Systems.
Layer network: Layer network is defined in G.805 [ITU.G805.2000]. A
layer network provides for the transfer of client information and
independent operation of the client OAM. A Layer Network may be
described in a service context as follows: one layer network may
provide a (transport) service to higher client layer network and may,
in turn, be a client to a lower layer network. A layer network is a
logical construction somewhat independent of arrangement or
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composition of physical network elements. A particular physical
network element may topologically belong to more than one layer
network, depending on the actions it takes on the encapsulation(s)
associated with the logical layers (e.g. the label stack), and thus
could be modeled as multiple logical elements. A layer network may
consist of zero or more sublayers. For additional explanation of how
layer networks relate to the OSI concept of layering see Appendix I
of Y.2611 [ITU.Y2611.2006].
Link: A physical or logical connection between a pair of LSRs that
are adjacent at the (sub)layer network under consideration. A link
may carry zero, one or more LSPs or PWs. A packet entering a link
will emerge with the same label stack entry values.
Logical Ring: An MPLS-TP logical ring is constructed from a set of
LSRs and logical data links (such as MPLS-TP LSP tunnels or MSPL-TP
pseudowires) and physical data links that form a ring topology.
Path: See Transport path.
Physical Ring: An MPLS-TP physical ring is constructed from a set of
LSRs and physical data links that form a ring topology.
Ring Topology: In an MPLS-TP ring topology each LSR is connected to
exactly two other LSRs, each via a single point-to-point
bidirectional MPLS-TP capable data link. A ring may also be
constructed from only two LSRs where there are also exactly two
links. Rings may be connected to other LSRs to form a larger
network. Traffic originating or terminating outside the ring may be
carried over the ring. Client network nodes (such as CEs) may be
connected directly to an LSR in the ring.
Section: A section is a server layer (which may be MPLS-TP or a
different technology) which provides for encapsulation and OAM of a
MPLS-TP transport path client layer. A section layer may provide for
aggregation of multiple MPLS-TP clients. Note that G.805
[ITU.G805.2000] defines the section layer as one of the two layer
networks in a transmission media layer network. The other layer
network is the physical media layer network.
Segment: A link connection as defined in G.805 [ITU.G805.2000]. A
segment is the part of an LSP that traverses a single link or the
part of a PW that traverses a single link (i.e. that connects a pair
of adjacent {S|T}-PEs).
Sublayer: Sublayer is defined in G.805 [ITU.G805.2000]. The
distinction between a layer network and a sublayer is that a sublayer
is not directly accessible to clients outside of its encapsulating
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layer network and offers no direct transport service for a higher
layer (client) network.
Tandem Connection: A tandem connection is an arbitrary part of a
transport path that can be monitored (via OAM) independently from the
end-to-end monitoring (OAM). It may be a monitored segment, a
monitored concatenated segment or any other monitored ordered
sequence of contiguous hops and/or segments (and their
interconnecting nodes) of a transport path.
Transport path: A network connection as defined in G.805
[ITU.G805.2000]. In an MPLS-TP environment a transport path
corresponds to an LSP or a PW.
Transport path layer: A layer network which provides point-to-point
or point-to-multipoint transport paths which are used to carry a
higher (client) layer network or aggregates of higher (client) layer
networks, for example the transport service layer. It provides for
independent OAM (of the client OAM) in the transport of the clients.
Transport service layer: A layer network in which transport paths are
used to carry a customer's (individual or bundled) service (may be
point-to-point, point-to-multipoint or multipoint-to-multipoint
services).
Transmission media layer: A layer network which provides sections
(two-port point-to-point connections) to carry the aggregate of
network transport path or network service layers on various physical
media.
Unidirectional path: A path that supports traffic flow in only one
direction.
1.2. Transport network overview
The connection (or transport path) service is the basic service
provided by a transport network. The purpose of a transport network
is to carry its clients (i.e. the stream of client PDUs or client
bits) between endpoints in the network (typically over several
intermediate nodes). These endpoints may be service switching points
or service terminating points. The connection services offered to
customers are aggregated into large transport paths with long-holding
times and independent OAM (of the client OAM), which contribute to
enabling the efficient and reliable operation of the transport
network. These transport paths are modified infrequently.
Aggregation and hierarchy are beneficial for achieving scalability
and security since:
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1. They reduce the number of provisioning and forwarding states in
the network core.
2. They reduce load and the cost of implementing service assurance
and fault management.
3. Clients are encapsulated and layer associated OAM overhead is
added. This allows complete isolation of customer traffic and
its management from carrier operations.
An important attribute of a transport network is that it is able to
function regardless of which clients are using its connection service
or over which transmission media it is running. The client,
transport network and server layers are from a functional and
operations point of view independent layer networks. Another key
characteristic of transport networks is the capability to maintain
the integrity of the client across the transport network. A
transport network must provide the means to commit quality of service
objectives to clients. This is achieved by providing a mechanism for
client network service demarcation for the network path together with
an associated network resiliency mechanism. A transport network must
also provide a method of service monitoring in order to verify the
delivery of an agreed quality of service. This is enabled by means
of carrier-grade OAM tools.
Clients are first encapsulated. These encapsulated client signals
may then be aggregated into a connection for transport through the
network in order to optimize network management. Server layer OAM is
used to monitor the transport integrity of the client layer or client
aggregate. At any hop, the aggregated signals may be further
aggregated in lower layer transport network paths for transport
across intermediate shared links. The encapsulated client signals
are extracted at the edges of aggregation domains, and are either
delivered to the client or forwarded to another domain. In the core
of the network, only the server layer aggregated signals are
monitored; individual client signals are monitored at the network
boundary in the client layer network. Although the connectivity of
the client of the transport path layer may be point-to-point, point-
to-multipoint or multipoint-to-multipoint, the transport path layer
itself only provides point-to-point or point-to-multipoint transport
paths which are used to carry the client.
Quality-of-service mechanisms are required in the packet transport
network to ensure the prioritization of critical services, to
guarantee BW and to control jitter and delay.
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1.3. Layer network overview
A layer network provides its clients with a transport service and the
operation of the layer network is independent of whatever client
happens to use the layer network. Information that passes between
any client to the layer network is common to all clients and is the
minimum needed to be consistent with the definition of the transport
service offered. The client layer network can be connectionless,
connection oriented packet switched, or circuit switched. The
transport service transfers a payload (individual packet payload for
connectionless networks, a sequence of packets payloads in the case
of connection oriented packet switched networks, and a deterministic
schedule of payloads in the case of circuit switched networks) such
that the client can populate the payload without affecting any
operation within the serving layer network.
The operations within a layer network that are independent of the
clients include the control of forwarding, the control of resource
reservation, the control of traffic demerging, and the OAM of the
transport service. All of these operations are internal to a layer
network. By definition, a layer network does not rely on any client
information to perform these operations and therefore all information
required to perform these operations is independent of whatever
client is using the layer network.
A layer network will have common features in order to support the
control of forwarding, resource reservation, and OAM. For example, a
layer network will have a common addressing scheme for the end points
of the transport service and a common set of transport descriptors
for the transport service. However, a client may use a different
addressing scheme or different traffic descriptors (consistent with
performance inheritance).
It is sometimes useful to independently monitor a smaller domain
within a layer network (or the transport services as the traverse
this smaller domain) but the control of forwarding or the control of
resource reservation involved retain their common elements. These
smaller monitored domains are sublayers.
It is sometimes useful to independently control forwarding within
smaller domain within a layer network but the control of resource
reservation and OAM retain their common elements. These smaller
domains are partitions of the layer network.
2. MPLS-TP Requirements
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2.1. General requirements
1 The MPLS-TP data plane MUST be a subset of the MPLS data plane as
defined by the IETF. When MPLS offers multiple options in this
respect, MPLS-TP SHOULD select the minimum sub-set (necessary and
sufficient subset) applicable to a transport network application.
2 Any new functionality that is defined to fulfil the requirements
for MPLS-TP MUST be agreed within the IETF through the IETF
consensus process and MUST re-use (as far as practically
possible) existing MPLS standards.
3 Mechanisms and capabilities MUST be able to interoperate, without
a gateway function, with existing IETF MPLS [RFC3031] and IETF
PWE3 [RFC3985] control and data planes where appropriate.
4 MPLS-TP and its interfaces, both internal and external, MUST be
sufficiently well-defined that interworking equipment supplied by
multiple vendors will be possible both within a single network,
and between networks.
5 MPLS-TP MUST be a connection-oriented packet switching model with
traffic engineering capabilities that allow deterministic control
of the use of network resources.
6 MPLS-TP MUST support traffic engineered point to point (P2P) and
point to multipoint (P2MP) transport paths.
7 MPLS-TP MUST support the logical separation of the control and
management planes from the data plane.
8 MPLS-TP MUST allow the physical separation of the control and
management planes from the data plane.
9 MPLS-TP MUST support static provisioning of transport paths via
an OSS, i.e. via the management plane.
10 Mechanisms in an MPLS-TP network that satisfy functional
requirements that are common to general transport networks (i.e.,
independent of technology) SHOULD be operable in a way that is
similar to the way the equivalent mechanisms are operated in
other transport networks.
11 Static provisioning MUST NOT depend on the presence of any
element of a control plane.
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12 MPLS-TP MUST support the capability for network operation
(including OAM and recovery) via the management plane (without
the use of any control plane protocols).
13 A solution MUST be provided to support dynamic provisioning of
MPLS-TP transport paths via a control plane.
14 The MPLS-TP data plane MUST be capable of forwarding data and
taking recovery actions independently of the control or
management plane used to operate the MPLS-TP layer network. That
is, the MPLS-TP data plane MUST continue to operate normally if
the management plane or control plane that configured the
transport paths fails.
15 MPLS-TP MUST support mechanisms to avoid or minimize traffic
impact (e.g. packet delay, reordering and loss) during network
reconfiguration.
16 MPLS-TP MUST support transport paths through multiple homogeneous
domains.
17 MPLS-TP MUST NOT dictate the deployment of any particular network
topology either physical or logical, however:
A. It MUST be possible to deploy MPLS-TP in rings.
B. It MUST be possible to deploy MPLS-TP in arbitrarily
interconnected rings with one or two points of
interconnection.
C. MPLS-TP MUST support rings of at least 16 nodes in order to
support the upgrade of existing TDM rings to MPLS-TP.
MPLS-TP SHOULD support rings with more than 16 nodes.
18 MPLS-TP MUST be able to scale at least as well as existing
transport technologies with growing and increasingly complex
network topologies as well as with increasing bandwidth demands,
number of customers, and number of services.
19 MPLS-TP SHOULD support mechanisms to safeguard against the
provisioning of transport paths which contain forwarding loops.
2.2. Layering requirements
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20 A generic and extensible solution MUST be provided to support the
transport of one or more client layer networks (e.g. MPLS-TP,
Ethernet, ATM, FR, etc.) over an MPLS-TP layer network.
21 A solution MUST be provided to support the transport of MPLS-TP
transport paths over one or more server layer networks (such as
MPLS-TP, Ethernet, SONET/SDH, OTN, etc.). Requirements for
bandwidth management within a server layer network are outside
the scope of this document.
22 In an environment where an MPLS-TP layer network is supporting a
client network, and the MPLS-TP layer network is supported by a
server layer network then operation of the MPLS-TP layer network
MUST be possible without any dependencies on the server or client
network.
23 It MUST be possible to operate the layers of a multi-layer
network that includes an MPLS-TP layer autonomously.
The above are not only technology requirements, but also operational.
Different administrative groups may be responsible for the same layer
network or different layer networks.
24 It MUST be possible to hide MPLS-TP layer network addressing and
other information (e.g. topology) from client layers.
2.3. Data plane requirements
25 The identification of each transport path within its aggregate
MUST be supported.
26 A label in a particular link MUST uniquely identify the transport
path within that link.
27 A transport path's source MUST be identifiable at its destination
within its layer network.
28 MPLS-TP MUST be capable of using P2MP server (sub-)layer
capabilities when supporting P2MP MPLS-TP transport paths (for
example context-specific labels [RFC5331]).
29 It MUST be possible to operate and configure the MPLS-TP data
(transport) plane without any IP forwarding capability in the
MPLS-TP data plane.
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30 MPLS-TP MUST support unidirectional, bidirectional and co-routed
bidirectional point-to-point transport paths.
31 The forward and backward directions of a co-routed bidirectional
transport path MUST follow the same links and nodes within its
(sub-)layer network.
32 The intermediate nodes at each (sub-)layer MUST be aware about
the pairing relationship of the forward and the backward
directions belonging to the same bidirectional transport path.
33 MPLS-TP MAY support transport paths with asymmetric bandwidth
requirements, i.e. the amount of reserved bandwidth differs
between the forward and backward directions.
34 MPLS-TP MUST support unidirectional point-to-multipoint transport
paths.
35 MPLS-TP MUST be extensible in order to accommodate new types of
client networks and services.
36 MPLS-TP SHOULD support mechanisms to enable the reserved
bandwidth associated with a transport path to be increased
without impacting the existing traffic on that transport path
37 MPLS-TP SHOULD support mechanisms to enable the reserved
bandwidth of a transport path to be decreased without impacting
the existing traffic on that transport path, provided that the
level of existing traffic is smaller than the reserved bandwidth
following the decrease.
38 MPLS-TP MUST support mechanisms which ensure the integrity of the
transported customer's service traffic as required by its
associated SLA. Loss of integrity may be defined as packet
corruption, re-ordering or loss during normal network conditions.
39 MPLS-TP MUST support mechanisms to detect when loss of integrity
of the transported customer's service traffic has occurred.
40 MPLS-TP MUST support an unambiguous and reliable means of
distinguishing users' (client) packets from MPLS-TP control
packets (e.g. control plane, management plane, OAM and protection
switching packets).
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2.4. Control plane requirements
This section defines the requirements that apply to MPLS-TP when a
control plane is deployed.
The ITU-T has defined an architecture for Automatically Switched
Optical and Transport Networks (ASON/ASTN) in G.8080
[ITU.G8080.2006]. The control plane for MPLS-TP MUST fit within the
ASON/ASTN architecture.
An interpretation of the ASON/ASTN control plane requirements in the
context of GMPLS can be found in [RFC4139] and [RFC4258].
Additionally:
41 The MPLS-TP control pane SHOULD support control plane topology
and data plane topology independence.
42 The MPLS-TP control plane MUST be able to be operated independent
of any particular client or server layer control plane.
43 The MPLS-TP control plane MUST support establishing all the
connectivity patterns defined for the MPLS-TP data plane (e.g.,
unidirectional and bidirectional P2P, unidirectional P2MP, etc.)
including configuration of protection functions and any
associated maintenance functions.
44 The MPLS-TP control pane MUST support the configuration and
modification of OAM maintenance points as well as the activation/
deactivation of OAM when the transport path or transport service
is established or modified.
45 An MPLS-TP control plane MUST support operation of the recovery
functions described in Section 2.8.
46 An MPLS-TP control plane MUST scale gracefully to support a large
number of transport paths, nodes and links.
2.5. Network Management (NM) requirements
For requirements related to NM functionality (Management Plane in
ITU-T terminology) for MPLS-TP, see the MPLS-TP NM requirements
document [I-D.gray-mpls-tp-nm-req].
2.6. Operation, Administration and Maintenance (OAM) requirements
For requirements related to OAM functionality for MPLS-TP, see the
MPLS-TP OAM requirements document
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[I-D.ietf-mpls-tp-oam-requirements].
2.7. Network performance management (PM) requirements
For requirements related to PM functionality for MPLS-TP, see the
MPLS-TP OAM requirements document
[I-D.ietf-mpls-tp-oam-requirements].
2.8. Recovery & Survivability requirements
Network survivability plays a critical role in the delivery of
reliable services. Network availability is a significant contributor
to revenue and profit. Service guarantees in the form of SLAs
require a resilient network that rapidly detects facility or node
failures and restores network operation in accordance with the terms
of the SLA.
The requirements in this section use the recovery terminology defined
in RFC 4427 [RFC4427].
47 MPLS-TP MUST provide protection and restoration mechanisms.
A. Recovery techniques used for P2P and P2MP SHOULD be identical
to simplify implementation and operation. However, this MUST
NOT override any other requirement.
48 MPLS-TP recovery mechanisms MUST be applicable at various levels
throughout the network including support for link, path segment
and end-to-end path, and pseudowire segment, and end-to-end
pseudowire recovery.
49 MPLS-TP recovery paths MUST meet the SLA protection objectives of
the service.
A. MPLS-TP MUST provide mechanisms to guarantee 50ms recovery
times from the moment of fault detection in networks with
spans less than 1200 km.
B. For protection it MUST be possible to require protection of
100% of the traffic on the protected path.
C. Recovery objectives SHOULD be configurable per transport
path, and SHOULD include bandwidth and QoS.
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50 The recovery mechanisms MUST all be applicable to any topology.
51 The recovery mechanisms MUST operate in synergy with (including
coordination of timing) the recovery mechanisms present in any
underlying server transport network (for example, Ethernet, SDH,
OTN, WDM) to avoid race conditions between the layers.
52 MPLS-TP protection mechanisms MUST support priority logic to
negotiate and accommodate coexisting requests (i.e., multiple
requests) for protection switching (e.g., administrative requests
and requests due to link/node failures).
53 MPLS-TP recovery and reversion mechanisms MUST prevent frequent
operation of recovery in the event of an intermittent defect.
2.8.1. Data plane behavior requirements
General protection and survivability requirements are expressed in
terms of the behavior in the data plane.
2.8.1.1. Protection
54 MPLS-TP MUST support 1+1 protection.
A. MPLS-TP 1+1 support MUST include bidirectional protection
switching for P2P connectivity, and this SHOULD be the
default behavior for 1+1 protection.
B. Unidirectional 1+1 protection for P2MP connectivity MUST be
supported.
C. Unidirectional 1+1 protection for P2P connectivity is not
required.
55 MPLS-TP MUST support 1:n protection (including 1:1 protection).
A. MPLS-TP 1:n support MUST include bidirectional protection
switching for P2P connectivity, and this SHOULD be the
default behavior for 1:n protection.
B. Unidirectional 1:n protection for P2MP connectivity MUST be
supported.
C. Unidirectional 1:n protection for P2P connectivity is not
required.
D. The action of protection switching MUST NOT cause user data
to loop. Backtracking is allowed.
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Note: Support for extra traffic (as defined in G.870 [ITU.G870.2008])
is not required in MPLS-TP.
2.8.1.2. Restoration
56 The restoration LSP MUST be able to share resources with the LSP
being replaced (sometimes known as soft rerouting).
57 Restoration priority MUST be supported so that an implementation
can determine the order in which transport paths should be
restored (to minimize service restoration time as well as to gain
access to available spare capacity on the best paths).
58 Preemption priority MUST be supported to allow restoration to
displace other transport paths in the event of resource
constraint.
2.8.1.3. Sharing of protection resources
59 MPLS-TP SHOULD support 1:n (including 1:1) shared mesh
restoration.
60 MPLS-TP MUST support the sharing of protection bandwidth by
allowing best effort traffic.
61 MPLS-TP MUST support the definition of shared protection groups
to allow the coordination of protection actions resulting from
triggers caused by events at different locations in the network.
62 MPLS-TP MUST support sharing of protection resources such that
protection paths that are known not to be required concurrently
can share the same resources.
2.8.1.4. Reversion
63 MPLS-TP protection mechanisms MUST support revertive and non-
revertive behavior. Reversion MUST be the default behavior.
64 MPLS-TP restoration mechanisms MAY support revertive and non-
revertive behavior.
2.8.2. Triggers for protection, restoration, and reversion
Recovery actions may be triggered from different places as follows:
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65 MPLS-TP MUST support physical layer fault indication triggers.
66 MPLS-TP MUST support OAM-based triggers.
67 MPLS-TP MUST support management plane triggers (e.g., forced
switch, etc.).
68 There MUST be a mechanism to allow administrative recovery
actions to be distinguished from recovery actions initiated by
other triggers.
69 Where a control plane is present, MPLS-TP SHOULD support control
plane triggers.
2.8.3. Management plane operation of protection and restoration
All functions described here are for control by the operator.
70 It MUST be possible to configure of protection paths and
protection-to-working path relationships (sometimes known as
protection groups).
71 There MUST be support for pre-calculation of recovery paths.
72 There MUST be support for pre-provisioning of recovery paths.
73 The external controls as defined in [RFC4427] MUST be supported.
74 There MUST be support for the configuration of timers used for
recovery operation.
75 Restoration resources MAY be pre-planned and selected a priori,
or computed after failure occurrence.
76 When preemption is supported for recovery purposes, it MUST be
possible for the operator to configure it.
77 The management plane MUST provide indications of protection
events and triggers.
78 The management plane MUST allow the current protection status of
all transport paths to be determined.
2.8.4. Control plane and in-band OAM operation of recovery
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79 The MPLS-TP control plane (which is not mandatory in an MPLS-TP
implementation) MUST support:
A. establishment and maintenance of all recovery entities and
functions
B. signaling of administrative control
C. protection state coordination (PSC)
80 In-band OAM MAY be used for:
A. signaling of administrative control
B. protection state coordination
2.8.5. Topology-specific recovery mechanisms
81 MPLS-TP MAY support recovery mechanisms that are optimized for
specific network topologies. These mechanisms MUST be
interoperable with the mechanisms defined for arbitrary topology
(mesh) networks to enable protection of end-to-end transport
paths.
Note that topology-specific recovery mechanisms are subject to the
development of requirements using the normal IETF process.
2.8.5.1. Ring protection
Several service providers have expressed a high level of interest in
operating MPLS-TP in ring topologies and require a high level of
survivability function in these topologies. The requirements listed
below have been collected from these service providers and from the
ITU-T.
The main objective in considering a specific topology (such as a
ring) is to determine whether it is possible to optimize any
mechanisms such that the performance of those mechanisms within the
topology is significantly better than the performance of the generic
mechanisms in the same topology. The benefits of such optimizations
are traded against the costs of developing, implementing, deploying,
and operating the additional optimized mechanisms noting that the
generic mechanisms MUST continue to be supported.
Within the context of recovery in MPLS-TP networks, the optimization
criteria considered in ring topologies are as follows:
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a. Minimize the number of OAM MEs that are needed to trigger the
recovery operation - less than are required by other recovery
mechanisms.
b. Minimize the number of elements of recovery in the ring - less
than are required by other recovery mechanisms.
c. Minimize the number of labels required for the protection paths
across the ring - less than are required by other recovery
mechanisms.
d. Minimize the amount of management plane transactions during a
maintenance operation (e.g., ring upgrade) - less than are
required by other recovery mechanisms.
It may be observed that the requirements in this section are fully
compatible with the generic requirements expressed above, and that no
requirements that are specific to ring topologies have been
identified.
82 MPLS-TP MUST include recovery mechanisms that operate in any
single ring supported in MPLS-TP, and continue to operate within
the single rings even when the rings are interconnected.
83 When a network is constructed from interconnected rings, MPLS-TP
MUST support recovery mechanisms that protect user data that
traverses more than one ring. This includes the possibility of
failure of the ring-interconnect nodes and links.
84 MPLS-TP recovery in a ring MUST protect unidirectional and
bidirectional P2P transport paths.
85 MPLS-TP recovery in a ring MUST protect unidirectional P2MP
transport paths.
86 MPLS-TP 1+1 and 1:1 protection in a ring MUST support switching
time within 50 ms from the moment of fault detection in a network
with a 16 nodes ring with less than 1200 km of fiber.
87 The protection switching time in a ring MUST be independent of
the number of LSPs crossing the ring.
88 Recovery actions in a ring MUST be data plane functions triggered
by different elements of control. The triggers are configured by
management or control planes and are subject to configurable
policy.
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89 The configuration and operation of recovery mechanisms in a ring
MUST scale well with:
A. the number of transport paths (must be better than linear
scaling)
B. the number of nodes on the ring (must be at least as good as
linear scaling)
C. the number of ring interconnects (must be at least as good as
linear scaling)
90 MPLS-TP recovery in ring topologies MAY support multiple failures
without reconfiguring the protection actions.
91 Recovery techniques used in a ring MUST NOT prevent the ring from
being connected to a general MPLS-TP network in any arbitrary
way, and MUST NOT prevent the operation of recovery techniques in
the rest of the network.
92 MPLS-TP Recovery mechanisms applicable to a ring MUST be equally
applicable in physical and logical rings.
93 Recovery techniques in a ring SHOULD be identical to those in
general networks to simplify implementation. However, this MUST
NOT override any other requirement.
94 Recovery techniques in logical and physical rings SHOULD be
identical to simplify implementation and operation. However,
this MUST NOT override any other requirement.
95 The default recovery scheme in a ring MUST be bidirectional
recovery in order to simplify the recovery operation.
96 The recovery mechanism in a ring MUST support revertive
switching, which MUST be the default behaviour. This allows
optimization of the use of the ring resources, and restores the
preferred quality conditions for normal traffic (e.g., delay)
when the recovery mechanism is no longer needed.
97 The recovery mechanisms in a ring MUST support ways to allow
administrative protection switching, to be distinguished from
protection switching initiated by other triggers.
98 It MUST be possible to lockout (disable) protection mechanisms on
selected links (spans) in a ring (depending on operator's need).
This may require lockout mechanisms to be applied to intermediate
nodes within a transport path.
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99 MPLS-TP recovery mechanisms in a ring MUST include a mechanism
to allow an implementation to handle coexisting requests (i.e.,
multiple requests - not necessarily arriving simultaneously) for
protection switching based on priority.
100 MPLS-TP recovery and reversion mechanisms in a ring MUST offer a
way to prevent frequent operation of recovery in the event of an
intermittent defect.
101 MPLS-TP MUST support the sharing of protection bandwidth in a
ring by allowing best effort traffic.
102 MPLS-TP MUST support sharing of ring protection resources such
that protection paths that are known not to be required
concurrently can share the same resources.
103 MUST support the coordination of triggers caused by events at
different locations in a ring. Note that this is the ring
equivalent of the definition of shared protection groups.
2.9. QoS requirements
Carriers require advanced traffic management capabilities to enforce
and guarantee the QoS parameters of customers' SLAs.
Quality of service mechanisms are REQUIRED in an MPLS-TP network to
ensure:
104 Support for differentiated services and different traffic types
with traffic class separation associated with different traffic.
105 Prioritization of critical services.
106 Enabling the provisioning and the guarantee of Service Level
Specifications (SLS), with support for hard and relative end-to-
end bandwidth guaranteed.
107 Support of services, which are sensitive to jitter and delay.
108 Guarantee of fair access, within a particular class, to shared
resources.
109 Guaranteed resources for in-band control and management plane
traffic regardless of the amount of data plane traffic.
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110 Carriers are provided with the capability to efficiently support
service demands over the MPLS-TP network. This MUST include
support for a flexible bandwidth allocation scheme.
2.10. Security requirements
For a description of the security threats relevant in the context of
MPLS and GMPLS and the defensive techniques to combat those threats
see the Security Framework for MPLS & GMPLS Networks
[I-D.draft-ietf-mpls-mpls-and-gmpls-security-framework].
3. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
4. Security Considerations
For a description of the security threats relevant in the context of
MPLS and GMPLS and the defensive techniques to combat those threats
see the Security Framework for MPLS & GMPLS Networks
[I-D.draft-ietf-mpls-mpls-and-gmpls-security-framework].
5. Acknowledgements
The authors would like to thank all members of the teams (the Joint
Working Team, the MPLS Interoperability Design Team in the IETF, and
the T-MPLS Ad Hoc Group in the ITU-T) involved in the definition and
specification of MPLS Transport Profile.
The authors would also like to thank Loa Andersson, Lou Berger, Italo
Busi, John Drake, Adrian Farrel, Eric Gray, Neil Harrison, Huub van
Helvoort, Wataru Imajuku, Julien Meuric, Tom Nadeau, Hiroshi Ohta,
George Swallow, Tomonori Takeda and Maarten Vissers for their
comments and enhancements to the text.
An ad hoc discussion group consisting of Stewart Bryant, Italo Busi,
Andrea Digiglio, Li Fang, Adrian Farrel, Jia He, Huub van Helvoort,
Feng Huang, Harald Kullman, Han Li, Hao Long and Nurit Sprecher
provided valuable input to the requirements for deployment and
survivability in ring topologies.
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6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[I-D.gray-mpls-tp-nm-req]
Lam, H., Mansfield, S., and E. Gray, "MPLS TP Network
Management Requirements", draft-gray-mpls-tp-nm-req-02
(work in progress), January 2009.
[I-D.ietf-mpls-tp-oam-requirements]
Vigoureux, M., Ward, D., and M. Betts, "Requirements for
OAM in MPLS Transport Networks",
draft-ietf-mpls-tp-oam-requirements-00 (work in progress),
November 2008.
6.2. Informative References
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC4139] Papadimitriou, D., Drake, J., Ash, J., Farrel, A., and L.
Ong, "Requirements for Generalized MPLS (GMPLS) Signaling
Usage and Extensions for Automatically Switched Optical
Network (ASON)", RFC 4139, July 2005.
[RFC4258] Brungard, D., "Requirements for Generalized Multi-Protocol
Label Switching (GMPLS) Routing for the Automatically
Switched Optical Network (ASON)", RFC 4258, November 2005.
[RFC4397] Bryskin, I. and A. Farrel, "A Lexicography for the
Interpretation of Generalized Multiprotocol Label
Switching (GMPLS) Terminology within the Context of the
ITU-T's Automatically Switched Optical Network (ASON)
Architecture", RFC 4397, February 2006.
[RFC4427] Mannie, E. and D. Papadimitriou, "Recovery (Protection and
Restoration) Terminology for Generalized Multi-Protocol
Label Switching (GMPLS)", RFC 4427, March 2006.
[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space",
RFC 5331, August 2008.
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[I-D.draft-ietf-mpls-mpls-and-gmpls-security-framework]
Fang, L. and M. Behringer, "Security Framework for MPLS
and GMPLS Networks",
draft-ietf-mpls-mpls-and-gmpls-security-framework-04 (work
in progress), November 2008.
[ITU.Y2611.2006]
International Telecommunications Union, "High-level
architecture of future packet-based networks", ITU-
T Recommendation Y.2611, December 2006.
[ITU.Y1401.2008]
International Telecommunications Union, "Principles of
interworking", ITU-T Recommendation Y.1401, February 2008.
[ITU.G805.2000]
International Telecommunications Union, "Generic
functional architecture of transport networks", ITU-
T Recommendation G.805, March 2000.
[ITU.G870.2008]
International Telecommunications Union, "Terms and
definitions for optical transport networks (OTN)", ITU-
T Recommendation G.870, March 2008.
[ITU.G8080.2006]
International Telecommunications Union, "Architecture for
the automatically switched optical network (ASON)", ITU-
T Recommendation G.8080, June 2006.
Authors' Addresses
Ben Niven-Jenkins (editor)
BT
208 Callisto House, Adastral Park
Ipswich, Suffolk IP5 3RE
UK
Email: benjamin.niven-jenkins@bt.com
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Deborah Brungard (editor)
AT&T
Rm. D1-3C22 - 200 S. Laurel Ave.
Middletown, NJ 07748
USA
Email: dbrungard@att.com
Malcolm Betts (editor)
Nortel Networks
3500 Carling Avenue
Ottawa, Ontario K2H 8E9
Canada
Email: betts01@nortel.com
Nurit Sprecher
Nokia Siemens Networks
3 Hanagar St. Neve Ne'eman B
Hod Hasharon, 45241
Israel
Email: nurit.sprecher@nsn.com
Satoshi Ueno
NTT
Email: satoshi.ueno@ntt.com
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