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Network Working Group E. Oki
Internet Draft NTT
Category: Standards Track J-L Le Roux
Expires: April 2008 France Telecom
A. Farrel
Old Dog Consulting
October 2007
Extensions to the Path Computation Element communication Protocol
(PCEP) for Inter-Layer MPLS and GMPLS Traffic Engineering
draft-oki-pce-inter-layer-ext-00.txt
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Abstract
The Path Computation Element (PCE) provides path computation
functions 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 through a process called inter-layer traffic engineering.
PCE is a candidate solution for such requirements.
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The PCE communication Protocol (PCEP) is designed as a
communication protocol between Path Computation Clients (PCCs) and
PCEs. This document presents PCEP extensions for inter-layer
traffic engineering.
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. Introduction.................................................2
2. Overview of PCE-Based Inter-Layer Path Computation...........3
3. Protocol Extensions..........................................4
3.1. INTER-LAYER Object........................................4
3.2. SWITCH-LAYER Object.......................................5
3.2.1. REQ-ADAP-CAP Object......................................7
4. Procedure....................................................7
4.1. Path Computation Request..................................7
4.2. Path Computation Reply....................................8
5. Updated Format of PCEP Messages..............................8
6. Manageability considerations.................................9
7. IANA considerations.........................................10
8. Security Considerations.....................................10
9. Acknowledgments.............................................10
10. References.................................................10
10.1. Normative Reference......................................10
10.2. Informative Reference....................................11
11. Authors' Addresses.........................................11
12. Intellectual Property Statement............................11
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 Path
Computation Client (PCC) may make requests to a PCE for paths to be
computed.
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))
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[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, Label Switched Paths (LSPs)
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
better network efficiency to be achieved. This is what we call
inter-layer traffic engineering. This includes mechanisms allowing
the computation of end-to-end paths across layers (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].
PCE can provide a suitable mechanism for resolving inter-layer path
computation issues. The framework for applying the PCE-based path
computation architecture to inter-layer traffic engineering is
described in [PCE-INTER-LAYER-FRWK].
The PCE communication protocol (PCEP) is designed as a
communication protocol between PCCs and PCEs and is defined in
[PCEP]. A set of requirements for PCEP extensions to support inter-
layer traffic engineering is described in [PCE-INTER-LAYER-REQ].
This document presents PCEP extensions for inter-layer traffic
engineering that satisfy the requirements described in [PCE-INTER-
LAYER-REQ].
2. Overview of PCE-Based Inter-Layer Path Computation
[RFC4206] defines a way to signal a higher-layer LSP which has an
explicit route that includes hops traversed by LSPs in lower layers.
The computation of end-to-end paths across layers is called Inter-
Layer Path Computation.
A Label Switching Router (LSR) in the higher-layer might not have
information on the lower-layer topology, particularly in an overlay
or augmented model [RFC3945], and hence may not be able to compute
an end-to-end path across layers.
PCE-based inter-layer path computation consists of using one or
more PCEs to compute an end-to-end path across layers. This could
be achieved by relying on a single PCE that has topology
information about multiple layers and can directly compute an end-
to-end path across layers considering the topology of all of the
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layers. Alternatively, the inter-layer path computation could be
performed using multiple cooperating PCEs where each PCE has
information about the topology of one or more layers (but not all
layers) and where the PCEs collaborate to compute an end-to-end
path.
[PCE-INTER-LAYER-FRWK] describes models for inter-layer path
computation in more detail.
3. Protocol Extensions
This section describes PCEP extensions for inter-layer path
computation. Three new objects are defined: the INTER-LAYER object,
the SWITCH-LAYER object, and the REQ-ADAP-CAP object.
3.1. INTER-LAYER Object
The INTER-LAYER object is optional and can be used in PCReq and
PCRep messages.
In a PCReq message, the INTER-LAYER object indicates whether inter-
layer path computation is allowed, the type of path to be computed,
and whether nested signaling is allowed. When the INTER-LAYER
object is absent from a PCReq message, the receiving PCE SHOULD
process as though inter-layer path computation had been explicitly
disallowed (I-bit set to zero - see below).
In a PCRep message, the INTER-LAYER object indicates whether inter-
layer path computation has been performed, the type of path that
has been computed, and whether nested signaling is used.
When a PCReq message includes more than one request, an INTER-LAYER
object is used per request. When a PCRep message includes more than
one path per request, an INTER-LAYER object is used per path.
INTER-LAYER Object-Class is to be assigned by IANA (recommended
value=18)
INTER-LAYER Object-Type is to be assigned by IANA (recommended
value=1)
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The format of the INTER-LAYER object body is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |N|I|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
I flag (1 bit): the I flag is used by a PCC in a PCReq message to
indicate to a PCE whether an inter-layer path is allowed. When the
I flag is set (one), the PCE MAY perform inter-layer path
computation and return an inter-layer path. When the flag is clear
(zero), the path that is returned MUST NOT be an inter-layer path.
The I flag is used by a PCE in a PCRep message to indicate to a PCC
whether the path returned is an inter-layer path. When the I flag
is set (one), the path is an inter-layer path. When it is clear
(zero), the path is contained within a single layer either because
inter-layer path computation was not performed or because a mono-
layer path was found notwithstanding the use of inter-layer path
computation.
N flag (1 bit): the N flag is used by a PCC in a PCReq message to
indicate to a PCE whether nested signaling is allowed. When the N
flag is set (one), nested signaling is allowed. When it is clear
(zero), nested signaling is not allowed.
The N flag is used by a PCE in a PCRep message to indicate to a PCC
whether nested signaling is required to support the returned path.
When the N flag is set (one), nested signaling is required. When it
is clear (zero), nested signaling is not required.
Note that nested signaling is used to support hierarchical
[RFC4206] or stitched [LSP-STITCH] LSPs according to the physical
attributes of the network layers.
If the I flag is clear (zero), the N flag has no meaning and MUST
be ignored.
Reserved bits of the INTER-LAYER object SHOULD be transmitted as
zero and SHOULD be ignored on receipt. A PCE that forwards a path
computation request to other PCEs SHOULD preserve the settings of
reserved bits in the PCReq messages it sends and in the PCRep
messages it forwards to PCCs.
3.2. SWITCH-LAYER Object
The SWITCH-LAYER object is optional on a PCReq message and
specifies switching layers in which a path MUST, or MUST NOT be
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established. A switching layer is expressed as a switching type and
encoding type. The SWITCH-LAYER object MUST NOT be used on a PCRep
unless an INTER-LAYER object is also present on the PCReq message.
The SWITCH-LAYER object is optional on a PCRep message, where it is
used with the NO-PATH object in the case of unsuccessful path
computation to indicate the set of constraints that could not be
satisfied.
SWTICH-LAYER Object-Class is to be assigned by IANA (recommended
value=19)
SWTICH-LAYER Object-Type is to be assigned by IANA (recommended
value=1)
The format of the SWTICH-LAYER object body is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP Enc. Type |Switching Type | Reserved |I|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
// . //
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP Enc. Type |Switching Type | Reserved |I|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Each row indicates the switching type and encoding type that MUST,
or MUST NOT be used for specified layer(s) in the computed path.
LSP Encoding Type (8 bits): see [RFC3471] for a description of
parameters.
Switching Type (8 bits): see [RFC3471] for a description of
parameters.
I flag (1 bit): the I flag indicates whether or NOT a layer with
the specified switching type and encoding type MUST be used by the
computed path. When the I flag is set (one), the computed path MUST
traverse a layer with the specified switching type and encoding
type. When the I flag is clear (zero), the computed path MUST NOT
enter or traverse any layer with the specified switching type and
encoding type.
A PCC may want to specify only a Switching Type and not an LSP
Encoding Type. In this case, the LSP Encoding Type is set to zero.
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3.2.1.
REQ-ADAP-CAP Object
The REQ-ADAP-CAP object is optional and is used to specify a
requested adaptation capability for both ends of the lower layer
LSP. The REQ-ADAP-CAP object is used in inter-PCE communication,
where the PCE that is responsible for computing higher layer paths
acts as a PCC to request a path computation from a PCE that is
responsible for computing lower layer paths.
The REQ-ADAP-CAP object can be carried within a PCReq message and a
PCRep message. It is used in a PCRep message in case of
unsuccessful path computation (in this case, the PCRep message also
contains a NO-PATH object and the REQ-ADAP-CAP object is used to
indicate the set of constraints that could not be satisfied).
The REQ-ADAP-CAP object MAY be used in a mono-layer network to
specify a requested adaptation capability for both ends of the LSP.
In this case, it MAY be carried without INTER-LAYER Object.
REQ-ADAP-CAP Object-Class is to be assigned by IANA (recommended
value=20)
REQ-ADAP-CAP Object-Type is to be assigned by IANA (recommended
value=1)
The format of the REQ-ADAP-CAP object body is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Switching Cap | Encoding | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Switching Capability (8 bits): see [RFC4203] for a description of
parameters.
Encoding (8 bits): see [RFC3471] for a description of parameters.
A PCC may want to specify a Switching Capability, but not an
Encoding. In this case, the Encoding MUST be set zero.
4. Procedure
4.1. Path Computation Request
A PCC requests inter-layer path computation in a PCReq message by
including the INTER-LAYER object with the I flag set. The INTER-
LAYER object indicates whether inter-layer path computation is
allowed and whether nested signaling is allowed.
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The SWITCH-LAYER object, which MUST NOT be present unless the
INTER-LAYER object is also present, is optionally used to specify
the switching types and encoding types that define layers that MUST,
or MUST NOT, be used in the computed path.
The REQ-ADAP-CAP object is optionally used to specify the interface
switching capability of both ends of the lower layer LSP. The REQ-
ADAP-CAP object is used in inter-PCE communication, where the PCE
that is responsible for computing higher layer paths makes a
request as a PCC to a PCE that is responsible for computing lower
layer paths.
4.2. Path Computation Reply
The requested PCE replies to the requesting PCC for the inter-layer
path computation result in a PCRep message including the INTER-
LAYER object.
In the case of unsuccessful path computation, the PCRep message
also contains a NO-PATH object, and the SWITCH-TYPE object and/or
the REQ-ADAP-CAP MAY be used to indicate the set of constraints
that could not be satisfied.
5. Updated Format of PCEP Messages
The format of the PCReq message is updated as follows:
<PCReq Message>::= <Common Header>
[<SVEC-list>]
<request-list>
where:
<svec-list>::=<SVEC>
[<svec-list>]
<request-list>::=<request>[<request-list>]
<request>::= <RP>
<END-POINTS>
[<OF>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<RRO>]
[<IRO>]
[<LOAD-BALANCING>]
[<INTER-LAYER>]
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[<SWITCH-LAYER>]
[<REQ-ADAP-CAP>]
where:
<metric-list>::=<METRIC>[<metric-list>]
The format of the PCRep message is updated as follows:
<PCRep Message> ::= <Common Header>
<response-list>
where:
<response-list>::=<response>[<response-list>]
<response>::=<RP>
[<NO-PATH>]
[<path-list>]
<path-list>::=<path>[<path-list>]
<path>::= <ERO>
[<OF>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
[<INTER-LAYER>]
[<SWITCH-LAYER>]
[<REQ-ADAP-CAP>]
where:
<metric-list>::=<METRIC>[<metric-list>]
6. Manageability considerations
TBD
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
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- configuration implication for the protocol
7. IANA considerations
TBD
8. Security Considerations
TBD
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.
9. Acknowledgments
10. References
10.1. Normative Reference
[RFC2119] S. Bradner, "Key words for use in RFCs to indicate
requirements levels", RFC 2119, March 1997.
[RFC3471] L. Burger, "Generalized Multi-Protocol Label Switching
(GMPLS)E RFC 3471, January 2003.
[RFC3945] E. Mannie, "Generalized Multi-Protocol Label Switching
Architecture", RFC 3945, October 2004.
[RFC4203] K. Kompella and Y. Rekhter, "OSPF Extensions in Support
of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4203,
October 2005.
[RFC4206] K. Kompella, and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS)
Traffic Engineering (TE)", RFC 4206, October 2005.
[PCEP] JP. Vasseur et al, "Path Computation Element (PCE)
communication Protocol (PCEP) - Version 1 -" draft-ietf-pce-pcep
(work in progress).
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[PCE-INTER-LAYER-REQ] E. Oki et al., "PCC-PCE Communication
Requirements for Inter-Layer Traffic Engineering", draft-ietf-pce-
inter-layer-req (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)
10.2. Informative Reference
[RFC4655] A. Farrel, JP. Vasseur and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, 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).
[LSP-STITCH] A. Ayyangar et al., "Label Switched Path Stitching
with Generalized Multiprotocol Label Switching Traffic Engineering
(GMPLS TE) ", draft-ietf-ccamp-lsp-stitching (work in progress).
11. 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
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
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PCEP Extensions for Inter-Layer TE October 2007
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This document is subject to the rights, licenses and restrictions
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