One document matched: draft-ietf-pce-inter-layer-req-06.txt
Differences from draft-ietf-pce-inter-layer-req-05.txt
Network Working Group Eiji Oki (Editor)
Internet Draft NTT
Category: Informational
Expires: May 2008
November 2007
PCC-PCE Communication and PCE Discovery Requirements for Inter-
Layer Traffic Engineering
draft-ietf-pce-inter-layer-req-06.txt
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Abstract
The Path Computation Element (PCE) provides functions of path
computation in support of traffic engineering in Multi-Protocol
Label Switching (MPLS) and Generalized MPLS (GMPLS) networks.
MPLS and GMPLS networks may be constructed from layered
client/server networks. It is advantageous for overall network
efficiency to provide end-to-end traffic engineering across
multiple network layers. PCE is a candidate solution for such
requirements.
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Generic requirements for a communication protocol between Path
Computation Clients (PCCs) and PCEs are presented in 撤CE
Communication Protocol Generic Requirements". Generic requirements
for PCE discovery protocol are presented in 迭equirements for Path
Computation Element (PCE) Discovery・
This document complements the generic requirements and presents
detailed sets of PCC-PCE communication protocol requirements and
PCE discovery protocol requirements for inter-layer traffic
engineering.
Table of Contents
1. Introduction.................................................3
1.1. Terminology...............................................4
2. Motivation for PCE-Based Inter-Layer Path Computation........4
3. PCC-PCE Communication and Discovery Requirements for Inter-
Layer Traffic Engineering........................................5
3.1. PCC-PCE Communication.....................................5
3.1.1. Control of Inter-Layer Path Computation.................5
3.1.2. Control of The Type of Path to be Computed..............6
3.1.3. Communication of Inter-Layer Constraints................7
3.1.4. Adaptation Capability...................................7
3.1.5. Cooperation Between PCEs................................7
3.1.6. Inter-Layer Diverse paths...............................7
3.2. Capabilities Advertisements for PCE Discovery.............8
3.3. Supported Network Models..................................8
4. Manageability considerations.................................8
4.1. Control of Function and Policy............................8
4.2. Information and Data Models...............................9
4.3. Liveness Detection and Monitoring.........................9
4.4. Verifying Correct Operation...............................9
4.5. Requirements on Other Protocols and Functional Components 10
4.6. Impact on Network Operation..............................10
5. Security Considerations.....................................10
6. Acknowledgments.............................................11
7. References..................................................11
7.1. Normative Reference......................................11
7.2. Informative Reference....................................11
8. Authors・Addresses..........................................12
9. Intellectual Property Statement.............................12
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1. Introduction
The Path Computation Element (PCE) defined in [RFC4655] is an
entity that is capable of computing a network path or route based
on a network graph, and applying computational constraints.
A network may comprise multiple layers. These layers may represent
separations of technologies (e.g., packet switch capable (PSC),
time division multiplex (TDM), lambda switch capable (LSC))
[RFC3945], separation of data plane switching granularity levels
(e.g., PSC-1 and PSC-2, or VC4 and VC12) [MLN-REQ], or a
distinction between client and server networking roles (e.g.,
commercial or administrative separation of client and server
networks). In this multi-layer network, LSP in lower layers are
used to carry upper-layer LSPs. The network topology formed by
lower-layer LSPs and advertised to the higher layer is called a
Virtual Network Topology (VNT) [MLN-REQ].
It is important to optimize network resource utilization globally,
i.e. taking into account all layers, rather than optimizing
resource utilization at each layer independently. This allows
achieving better network efficiency. This is what we call Inter-
layer traffic engineering. This includes mechanisms allowing to
compute end-to-end paths across layers, as known as inter-layer
path computation, and mechanisms for control and management of the
VNT by setting up and releasing LSPs in the lower layers [MLN-REQ].
Inter-layer traffic engineering is included in the scope of the
PCE architecture [RFC4655], and PCE can provide a suitable
mechanism for resolving inter-layer path computation issues. The
applicability of the PCE-based path computation architecture to
inter-layer traffic engineering is described in [PCE-INTER-LAYER-
FRWK].
This document presents sets of PCC-PCE communication protocol
(PCECP) and PCE Discovery protocol requirements for inter-layer
traffic engineering. It supplements the generic requirements
documented in [RFC4657] and [RFC4674].
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1.1. Terminology
LSP: Label Switched Path.
LSR: Label Switching Router.
PCC: Path Computation Client: any client application requesting a
path computation to be performed by a Path Computation Element.
PCE: Path Computation Element: an entity (component, application
or network node) that is capable of computing a network path or
route based on a network graph and applying computational
constraints.
PCECP: PCE Communication Protocol, a protocol for communication
between PCCs and PCEs.
TED: Traffic Engineering Database which contains the topology and
resource information of the domain. The TED may be fed by IGP
extensions or potentially by other means.
TE LSP: Traffic Engineering Label Switched Path.
TE LSP head-end: head/source/ingress of the TE LSP.
TE LSP tail-end: tail/destination/egress of the TE LSP.
Although this requirements document is an informational document
not a protocol specification, the key words "MUST", "MUST NOT",
"REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in RFC 2119 [RFC2119] for clarity of
requirement specification.
2. Motivation for PCE-Based Inter-Layer Path Computation
[RFC4206] defines a way to signal a Multiprotocol Label Switching
(MPLS) or Generalized MPLS (GMPLS) LSP with an explicit route in a
higher layer of a network that includes hops traversed by LSPs in
lower layers of the network. The computation of end-to-end paths
across layers is called Inter-Layer Path Computation.
An LSR in the higher-layer might not have information on the
topology of lower-layers, particularly in an overlay or augmented
model, and hence might not be able to compute an end-to-end path
across layers.
PCE-based inter-layer path computation, consists of relying on one
or more PCEs to compute an end-to-end path across layers. This
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could rely on a single PCE path computation where the PCE has
topology information about multiple layers and can directly
compute an end-to-end path across layers considering the topology
of all of the layers. Alternatively, the inter-layer path
computation could be performed as a multiple PCE computation where
each member of a set of PCEs has information about the topology of
one or more layers, but not all layers, and collaborate to compute
an end-to-end path.
Consider a two-layer network where the higher-layer network is a
packet-based IP/MPLS or GMPLS network and the lower-layer network
is a GMPLS optical network. An ingress LSR in the higher-layer
network tries to set up an LSP to an egress LSR also in the
higher-layer network across the lower-layer network, and needs a
path in the higher-layer network. However, suppose that there is
no TE link between border LSRs, which are located on the boundary
between the higher-layer and lower-layer networks, and that the
ingress LSR does not have topology visibility in the lower layer.
If a single-layer path computation is applied for the higher-layer,
the path computation fails. On the other hand, inter-layer path
computation is able to provide a route in the higher-layer and a
suggestion that a lower-layer LSP be setup between border LSRs,
considering both layers・TE topologies.
Further discussion of the application of PCE to inter-layer path
computation can be found in [PCE-INTER-LAYER-FRWK].
3. PCC-PCE Communication and Discovery Requirements for Inter-Layer
Traffic Engineering
This section sets out additional requirements specific to the
problems of multi-layer TE that are not covered in [RFC4657] or
[RFC4674].
3.1. PCC-PCE Communication
The PCC-PCE communication protocol MUST allow requests and replies
for inter-layer path computation.
This requires no additional messages, but implies the following
additional constraints to be added to the PCC-PCE communication
protocol.
3.1.1.
Control of Inter-Layer Path Computation
A request from a PCC to a PCE SHOULD indicate whether inter-layer
path computation is allowed. In the absence of such an indication,
the default is that inter-layer path computation is not allowed.
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Therefore, a request from a PCC to a PCE MUST support the
inclusion of such an indication.
3.1.2.
Control of The Type of Path to be Computed
The PCE computes and returns a path to the PCC that the PCC can
use to build a higher-layer or lower-layer LSP once converted to
an Explicit Route Object (ERO) for use in RSVP-TE signaling. There
are two options [PCE-INTER-LAYER-FRWK].
- Option 1: Mono-layer path. The PCE computes a "mono layer" path,
i.e. a path that includes only TE-links from the same layer.
- Option 2: Multi-layer path. The PCE computes a "multi-layer"
path, i.e. a path that includes TE links from distinct layers
[RFC4206].
It may be necessary or desirable for a PCC to control the type of
path that is produced by a PCE. For example, a PCC may know that
it is not possible for technological or policy reasons to signal a
multi-layer path and that a mono-layer path is required, or the
PCC may know that it does not wish the layer border node to have
control of path computation. In order to make this level of
control possible, the PCECP MUST allow the PCC to select the path
types that may be returned by choosing one or more from the
following list:
- A mono-layer path that is specified by strict hop(s). The path
may include virtual TE link(s).
- A mono-layer path that includes loose hop(s).
- A multi-layer path that can include the path (as strict or loose
hops) of one or more lower-layer LSPs not yet established.
The path computation response from a PCE to a PCC MUST report the
type of path computed, and where a multi-layer path is returned,
PCECP MUST support the inclusion, as part of end-to-end path, of
the path of the lower-layer LSPs to be established.
If a response message from a PCE to PCC carries a mono-layer path
that is specified by strict hops but includes virtual TE link(s),
or includes loose hop(s), or carries a multi-layer path that can
include the complete path of one or more lower-layer LSPs not yet
established, the signaling of the higher-layer LSP may trigger the
establishment of the lower-layer LSPs (nested signaling). The
nested signaling may increase the higher-layer connection setup
latency. An ingress LSR for the higher-layer LSP, or a PCC, needs
to know whether nested signaling is required or not.
A request from a PCC to a PCE MUST allow indicating whether nested
signaling is acceptable or not.
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A response from a PCE to a PCC MUST allow indicating whether the
computed path triggers nested signaling or not.
3.1.3.
Communication of Inter-Layer Constraints
A request from a PCC to a PCE MUST support the inclusion of
constraints for a multi-layer path. This includes control over
which network layers may, must, or must not be included in the
computed path. Such control may be expressed in terms of the
switching types of the layer networks.
The path computation request MUST also allow for different
objective functions to be applied within different network layers.
For example, the path in a packet-network may need to be optimized
for least delay using the IGP metric as a measure of delay, while
the path in an under-lying TDM network might be optimized for
fewest hops.
3.1.4.
Adaptation Capability
It MUST be possible for the path computation request to indicate
the desired adaptation function at the end points of the lower-
layer LSP that is being computed. This will be particularly
important where the ingress and egress LSR participate in more
than one layer network but may not be capable of all associated
adaptations.
3.1.5.
Cooperation Between PCEs
When each layer is controlled by a PCE, which only has access to
the topology information of its layer, the PCEs of each layer need
to cooperate to perform inter-layer path computation. In this case,
communication between PCEs is required for inter-layer path
computation. A PCE that behaves as a client is defined as a PCC
[RFC4655].
The PCC-PCE communication protocol MUST allow requests and replies
for multiple PCE inter-layer path computation.
3.1.6.
Inter-Layer Diverse paths
The PCE communication protocol MUST allow for the computation of
diverse inter-Layer paths. A request from a PCC to a PCE MUST
support the inclusion of multiple path requests, with the desired
level of diversity at each layer (link, node, SRLG).
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3.2. Capabilities Advertisements for PCE Discovery
In the case where there are several PCEs with distinct
capabilities available, a PCC has to select one or more
appropriate PCEs.
For that purpose, the PCE discovery mechanism MAY support the
disclosure of some detailed PCE capabilities.
A PCE MAY (to be consistent with the above text and RFC4674) be
able to advise the following inter-layer-path-computation-related
PCE capabilities:
- Support for inter-layer path computation
- Support for mono-layer/multi-layer paths
- Support for Adaptation Capability
- Support for Inter-PCE communication
- Support for inter-layer diverse path computation
3.3. Supported Network Models
The PCC-PCE communication protocol SHOULD allow several
architectural alternatives for interworking between MPLS and GMPLS
networks: overlay, integrated and augmented models
[RFC3945][INTWORK-FRWK][INTWORK-REQ].
4. Manageability considerations
4.1. Control of Function and Policy
An individual PCE MAY elect to support inter-layer computations
and advertise its capabilities as described in the previous
sections. PCE implementations MAY provide a configuration switch
to allow support of inter-layer path computations to be enabled or
disabled. When the level of support is changed, this SHOULD be re-
advertised.
However, a PCE MAY also elect to support inter-layer computations,
but not to advertise the fact, so that only those PCCs configured
to know of the PCE and its capabilities can use it.
Support for, and advertisement of support for, inter-layer path
computation MAY be subject to policy and a PCE MAY hide its inter-
layer capabilities from certain PCCs by not advertising them
through the discovery protocol, and not reporting them to the
specific PCCs in any PCECP capabilities exchange. Further, a PCE
MAY be directed by policy to refuse an inter-layer path
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computation request for any reason including, but not limited to,
the identity of the PCC that makes the request.
4.2. Information and Data Models
PCECP protocol extensions to support inter-layer computations MUST
be accompanied by MIB objects for the control and monitoring of
the protocol and of the PCE that performs the computations. The
MIB objects MAY be provided in the same MIB module as used for
general PCECP control and monitoring [PCEP-MIB] or MAY be
provided in a new MIB module.
The MIB objects MUST provide the ability to control and monitor
all aspects of PCECP relevant to inter-layer path computation.
4.3. Liveness Detection and Monitoring
No changes are necessary to the liveness detection and monitoring
requirements as already embodied in [RFC4657]. It should be noted,
however, that inter-layer path computations might require extended
cooperation between PCEs (as is also the case for inter-AS and
inter-area computations) and so the liveness detection and
monitoring SHOULD be applied to each PCECP communication and
aggregated to report the behavior of an individual PCECP request
to the originating PCC.
In particular, where a request is forwarded between multiple PCEs
neither the PCC not the first PCE can monitor the liveness of all
inter-PCE-PCE connections or of the PCEs themselves. In this case,
suitable performance of the original PCECP request relies on each
PCE operating correct monitoring procedures and correlating any
failures back to the PCECP requests that are outstanding. These
requirements are no different from those for any cooperative PCE
usage, and are expected to be already covered by general, and by
inter-AS and inter-area implementations.
4.4. Verifying Correct Operation
There are no additional requirements beyond those expressed in
[RFC4657] for verifying the correct operation of the PCECP. Note
that verification of the correct operation of the PCE and its
algorithms is out of scope for the protocol requirements, but a
PCC MAY send the same request to more than one PCE and compare the
results.
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4.5. Requirements on Other Protocols and Functional Components
A PCE operates on a topology graph that may be built using
information distributed by TE extensions to the routing protocol
operating within the network. In order that the PCE can select a
suitable path for the signaling protocol to use to install the
inter-layer LSP, the topology graph must include information about
the inter-layer signaling and forwarding (i.e. adaptation)
capabilities of each LSR in the network.
Whatever means is used to collect the information to build the
topology graph MUST include the requisite information. If the TE
extensions to the routing protocol are used, these SHOULD satisfy
the requirements as described in [MLN-REQ].
4.6. Impact on Network Operation
The use of a PCE to compute inter-layer paths is not expected to
have significant impact on network operations. But it should be
noted that the introduction of inter-layer support to a PCE that
already provides mono-layer path computation might change the
loading of the PCE and that might have an impact on the network
behavior especially during recovery periods immediately after a
network failure.
On the other hand, it is envisioned that the use of inter-layer
path computation will have significant benefits to the operation
of a multi-layer network including improving the network resource
usage and enabling a greater number of higher-layer LSPs to be
supported.
5. Security Considerations
Inter-layer traffic engineering with PCE may raise new security
issues when PCE-PCE communication is done between different layer
networks for inter-layer path computation. Security issues may
also exist when a single PCE is granted full visibility of TE
information that applies to multiple layers.
The formal introduction of a VNT Manager component as described in
[PCE-INTER-LAYER-FRWK] provides the basis for the application of
inter-layer security and policy.
It is expected that solutions for inter-layer protocol extensions
will address these issues in detail.
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6. Acknowledgments
We would like to thank Kohei Shiomoto, Ichiro Inoue, and Dean
Cheng for their useful comments.
7. References
7.1. Normative Reference
[RFC2119] Bradner, S., "Key words for use in RFCs to indicate
requirements levels", RFC 2119, March 1997.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
Architecture", RFC 3945, October 2004.
[RFC4206] Kompella, K., and Rekhter, Y., "Label Switched Paths
(LSP) Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
7.2. Informative Reference
[RFC4655] A. Farrel, JP. Vasseur and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, September 2006.
[RFC4657] J. Ash, J.L Le Roux et al., " Path Computation Element
(PCE) Communication Protocol Generic Requirements", RFC 4657,
September 2006.
[RFC4674] JL Le Roux et al., "Requirements for Path Computation
Element (PCE) Discovery", RFC 4674, September 2006.
[MLN-REQ] K. Shiomoto et al., "Requirements for GMPLS-based multi-
region and multi-layer networks (MRN/MLN)", draft-ietf-ccamp-
gmpls-mln-reqs (work in progress).
[PCE-INTER-LAYER-FRWK] E. Oki et al., "Framework for PCE-Based
Inter-Layer MPLS and GMPLS Traffic Engineering", draft-ietf-pce-
inter-layer-frwk (work in progress).
[PCEP-MIB] A. Koushik, and E. Stephan, "PCE communication
protocol(PCEP) Management Information Base", draft-kkoushik-pce-
pcep-mib (work in progress).
[INTWORK-FRWK] K. Shiomoto, 擢ramework for MPLS-TE to GMPLS
migration,・draft-ietf-ccamp-mpls-gmpls-interwork-fmwk (work in
progress).
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[INTWORK-REQ] K. Kumaki et al., 的nterworking Requirements to
Support operation of MPLS-TE over GMPLS Networks,・draft-ietf-
ccamp-mpls-gmpls-interwork-reqts (work in progress).
8. Authors・Addresses
Eiji Oki
NTT
3-9-11 Midori-cho,
Musashino-shi, Tokyo 180-8585, Japan
Email: oki.eiji@lab.ntt.co.jp
Jean-Louis Le Roux
France Telecom R&D,
Av Pierre Marzin,
22300 Lannion, France
Email: jeanlouis.leroux@orange-ftgroup.com
Kenji Kumaki
KDDI Corporation
Garden Air Tower
Iidabashi, Chiyoda-ku,
Tokyo 102-8460, JAPAN
Phone: +81-3-6678-3103
Email: ke-kumaki@kddi.com
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
9. Intellectual Property Statement
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Intellectual Property Rights or other rights that might be claimed
to pertain to the implementation or use of the technology
described in this document or the extent to which any license
under such rights might or might not be available; nor does it
represent that it has made any independent effort to identify any
such rights. Information on the procedures with respect to rights
in RFC documents can be found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use
of such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository
at http://www.ietf.org/ipr.
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The IETF invites any interested party to bring to its attention
any copyrights, patents or patent applications, or other
proprietary rights that may cover technology that may be required
to implement this standard. Please address the information to the
IETF at ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on
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REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
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WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE
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FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
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