Network Working Group Eiji Oki (Editor)
Internet Draft NTT
Category: Informational
Expires: August 2006
February 2006
PCC-PCE Communication Requirements for Inter-Layer Traffic
Engineering
draft-ietf-pce-inter-layer-req-01.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.
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Conventions used in this document
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.................5
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...............................................6
9. References....................................................7
9.1. Normative Reference........................................7
9.2. Informative Reference......................................7
10. AuthorsÂEAddresses..........................................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 [PCE-ARCH] 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 [PCE-ARCH], 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-
APP].
This document presents a set of PCC-PCE communication protocol
(PCECP) requirements for inter-layer traffic engineering. It
supplements the generic requirements documented in [PCE-COM-REQ].
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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-APP].
5. PCC-PCE Communication Requirements for Inter-Layer Traffic
Engineering
This section sets out additional requirements not covered in [PCE-
COM-REQ] 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-APP].
- 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 includes already established lower-layer
LSPs
- 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 includes loose hop(s), or 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.
5.1.3. Communication of Inter-Layer Constraints
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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
[PCE-ARCH].
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.
8. Acknowledgments
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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
[PCE-ARCH] A. Farrel, JP. Vasseur and J. Ash, "Path Computation
Element (PCE) Architecture", draft-ietf-pce-architecture (work in
progress).
[PCE-COM-REQ] J. Ash, J.L Le Roux et al., "PCE Communication
Protocol Generic Requirements", draft-ietf-pce-comm-protocol-gen-
reqs (work in progress).
[PCE-DISC-REQ] JL Le Roux et al., "Requirements for Path
Computation Element (PCE) Discovery", draft-ietf-pce-discovery-reqs
(work in progress).
[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-APP] E. Oki et al., "PCE Applicability for Inter-
Layer MPLS and GMPLS Traffic Engineering", draft-oki-pce-inter-
layer-app (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
Email: jeanlouis.leroux@francetelecom.com
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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
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