Network Working Group Eiji Oki (Editor)
Internet Draft NTT
Category: Informational
Expires: April 2007
October 2006
PCC-PCE Communication Requirements for Inter-Layer Traffic
Engineering
draft-ietf-pce-inter-layer-req-03.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 service
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.
Generic requirements for a communication protocol between Path
Computation Clients (PCCs) and PCEs are presented in "PCE
Communication Protocol Generic Requirements". This document
complements the generic requirements and presents a detailed set of
PCC-PCE communication protocol requirements for inter-layer traffic
engineering.
Conventions used in this document
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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].
Table of Contents
1. Contributors....................................................2
2. Terminology.....................................................2
3. Introduction....................................................3
4. Motivation for PCE-Based Inter-Layer Path Computation...........4
5. PCC-PCE Communication Requirements for Inter-Layer Traffic
Engineering.........................................................4
5.1. PCC-PCE Communication........................................4
5.1.1. Control of Inter-Layer Path Computation....................5
5.1.2. Control of The Type of Path to be Computed.................5
5.1.3. Communication of Inter-Layer Constraints...................6
5.1.4. Cooperation Between PCEs...................................6
5.1.5. Inter-Layer Diverse paths..................................6
5.2. Supportive Network Models....................................6
6. Manageability considerations....................................6
7. Security Considerations.........................................6
8. Acknowledgments.................................................7
9. References......................................................7
9.1. Normative Reference..........................................7
9.2. Informative Reference........................................7
10. Authors' Addresses............................................7
11. Intellectual Property Statement...............................8
1. Contributors
The following are the authors that contributed to the present
document:
Eiji Oki (NTT)
Jean-Louis Le Roux (France Telecom)
Kenji Kumaki (KDDI)
Adrian Farrel (Old Dog Consulting)
2. 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.
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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.
3. 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 of 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) [MRN-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 [MRN-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 a set of PCC-PCE communication protocol
(PCECP) requirements for inter-layer traffic engineering. It
supplements the generic requirements documented in [RFC4657].
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4. Motivation for PCE-Based Inter-Layer Path Computation
[RFC4206] defines a way to signal a higher-layer LSP, whose explicit
route includes hops traversed by LSPs in lower layers. 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 lower-
layer topology, 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 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].
5. PCC-PCE Communication Requirements for Inter-Layer Traffic
Engineering
This section sets out additional requirements not covered in
[RFC4657] specific to the problems of multi-layer TE.
5.1. PCC-PCE Communication
The PCC-PCE communication protocol MUST allow requests and replies
for inter-layer path computation.
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This requires no additional messages, but implies the following
additional constraints to be added to the PCC-PCE communication
protocol.
5.1.1. 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.
Therefore, a request from a PCC to a PCE MUST support the inclusion
of such an indication.
5.1.2. 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].
A request from a PCC to a PCE MUST allow control of the type of the
path to be computed by selection 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 complete path of one or
more lower-layer LSPs not yet established.
When multi-layer path computation is requested, a response from a PCE
to a PCC 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.
A response from a PCE to a PCC MUST allow indicating whether the
computed path triggers nested signaling or not.
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5.1.3. Communication of Inter-Layer Constraints
A request from a PCC to a PCE MUST support the inclusion of
constraints for multiple layers. This includes the switching type(s)
and encoding type(s) that can, must, or must not be used in the
computed path.
5.1.4. 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.
5.1.5. 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 request, with the desired level of
diversity at each layer (link, node, SRLG).
5.2. Supportive 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].
6. Manageability considerations
Manageability of inter-layer traffic engineering with PCE must
address the following consideration for section 5.1.
- need for a MIB module for control and monitoring
- need for built-in diagnostic tools
- configuration implication for the protocol
7. 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.
It is expected that solutions for inter-layer protocol extensions
will address these issues in detail using security techniques such as
authentication.
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8. Acknowledgments
We would like to thank Kohei Shiomoto, Ichiro Inoue, and Dean Cheng
for their useful comments.
9. References
9.1. 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.
9.2. 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.
[MRN-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-oki-pce-inter-layer-
frwk (work in progress)
10. 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
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Email: jeanlouis.leroux@francetelecom.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
11. Intellectual Property Statement
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except as set forth therein, the authors retain all their rights.
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