Network Working Group E. Crabbe
Internet-Draft Google, Inc.
Intended status: Standards Track I. Minei
Expires: October 12, 2013 Juniper Networks, Inc.
S. Sivabalan
Cisco Systems, Inc.
R. Varga
Pantheon Technologies SRO
April 10, 2013
PCEP Extensions for PCE-initiated LSP Setup in a Stateful PCE Model
draft-crabbe-pce-pce-initiated-lsp-01
Abstract
The Path Computation Element Communication Protocol (PCEP) provides
mechanisms for Path Computation Elements (PCEs) to perform path
computations in response to Path Computation Clients (PCCs) requests.
The extensions described in [I-D.ietf-pce-stateful-pce] provide
stateful control of Multiprotocol Label Switching (MPLS) Traffic
Engineering Label Switched Paths (TE LSP) via PCEP, for a model where
the PCC delegates control over one or more locally configured LSPs to
the PCE. This document describes the creation and deletion of PCE-
initiated LSPs under the stateful PCE model.
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 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on October 12, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Architectural Overview . . . . . . . . . . . . . . . . . . . . 4
3.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Operation overview . . . . . . . . . . . . . . . . . . . . 5
4. Support of PCE-initiated LSPs . . . . . . . . . . . . . . . . 6
4.1. Stateful PCE Capability TLV . . . . . . . . . . . . . . . 6
5. PCE-initiated LSP creation . . . . . . . . . . . . . . . . . . 7
5.1. The LSP Create Message . . . . . . . . . . . . . . . . . . 7
6. LSP delegation and cleanup . . . . . . . . . . . . . . . . . . 9
6.1. LSP delegation procedures . . . . . . . . . . . . . . . . 9
6.2. LSP cleanup procedures . . . . . . . . . . . . . . . . . . 9
6.2.1. LSP-CLEANUP TLV . . . . . . . . . . . . . . . . . . . 10
7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 11
7.1. PCEP Messages . . . . . . . . . . . . . . . . . . . . . . 11
7.2. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 11
7.3. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8.1. Malicious PCE . . . . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
[RFC5440] describes the Path Computation Element Protocol PCEP. PCEP
defines the communication between a Path Computation Client (PCC) and
a Path Control Element (PCE), or between PCE and PCE, enabling
computation of Multiprotocol Label Switching (MPLS) for Traffic
Engineering Label Switched Path (TE LSP) characteristics.
Stateful pce [I-D.ietf-pce-stateful-pce] specifies a set of
extensions to PCEP to enable stateful control of TE LSPs between and
across PCEP sessions in compliance with [RFC4657]. It includes
mechanisms to effect LSP state synchronization between PCCs and PCEs,
delegation of control of LSPs to PCEs, and PCE control of timing and
sequence of path computations within and across PCEP sessions and
focuses on a model where LSPs are configured on the PCC and control
over them is delegated to the PCE.
This document describes the setup and teardown of PCE-initiated LSPs
under the stateful PCE model, without the need for local
configuration on the PCC, thus allowing for a dynamic network that is
centrally controlled and deployed.
2. Terminology
This document uses the following terms defined in [RFC5440]: PCC,
PCE, PCEP Peer.
This document uses the following terms defined in
[I-D.ietf-pce-stateful-pce]: Stateful PCE, Delegation, Delegation
Timeout Interval, LSP State Report, LSP Update Request.
The following terms are defined in this document:
PCE-initiated LSP: LSP that is instantiated as a result of a request
from the PCE.
LSP cleanup timer: PCE-defined timer for cleanup of PCE-initiated
LSPs that are no longer delegated to a PCE.
The message formats in this document are specified using Routing
Backus-Naur Format (RBNF) encoding as specified in [RFC5511].
3. Architectural Overview
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3.1. Motivation
[I-D.ietf-pce-stateful-pce] provides stateful control over LSPs that
are locally configured on the PCC. This model relies on the LER
taking an active role in delegating locally configured LSPs to the
PCE, and is well suited in environments where the LSP placement is
fairly static. However, in environments where the LSP placement
needs to change in response to application demands, it is useful to
support dynamic creation and tear down of LSPs. The ability for a
PCE to trigger the creation of LSPs on demand can make possible agile
software-driven network operation, and can be seamlessly integrated
into a controller-based network architecture, where intelligence in
the controller can determine when and where to set up paths.
A possible use case is one of a software-driven network, where
applications request network resources and paths from the network
infrastructure. For example, an application can request a path with
certain constraints between two LSRs by contacting the PCE. The PCE
can compute a path satisfying the constraints, and instruct the head
end LSR to create and signal it. When the path is no longer required
by the application, the PCE can request its teardown.
Another use case is that of demand engineering, where a PCE with
visibility into both the network state and the demand matrix can
anticipate and optimize how traffic is distributed across the
infrastructure. Such optimizations may require creating new paths
across the infrastructure.
3.2. Operation overview
A PCC indicates its ability to support PCE provisioned dynamic LSPs
during the PCEP Initialization Phase via a new flag in the STATEFUL-
PCE-CAPABILITY TLV (see details in Section 4.1).
The decision when to create a PCE-initiated LSP is out of the scope
of this document. To instantiate an LSP, the PCE sends a new
message, the LSP Create Request (PCCreate) message to the PCC. The
LSP Create Request MUST include the END-POINTS and LSPA objects, and
the LSPA object MUST include the SYMBOLIC-PATH-NAME TLV. The PCC
creates the LSP using the attributes communicated by the PCE, and
local values for the unspecified parameters. It assigns a unique
LSP-ID for the LSP and automatically delegates the LSP to the PCE.
It then generates an LSP State Report (PCRpt) for the LSP, carrying
the LSP-ID and the delegation bit. The PCE may update the attributes
of the LSP via subsequent PCUpd messages.
Subsequent LSP State Report and LSP Update Request for the LSP will
carry the PCC-assigned LSP-ID, which uniquely identifies the LSP.
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The LSPA Object included in these messages MUST carry the SYMBOLIC-
PATH-NAME TLV which will be used to correlate between the PCC-
assigned LSP-ID and the LSP. See details in Section 5.
Removal of PCE-initiated LSPs is done by the PCE by setting the R
flag in the LSP Object in the PCUpd message. Upon receiving the
PCUpd message with the R Flag set, the PCC deletes the LSP. See
details in Section 5.
Once instantiated, a PCRpt is generated for the LSP, with the
delegation bit set. After this, the delegation procedures for PCE-
initiated LSPs are the same as for PCC initiated LSPs. Upon session
failure, PCE-initiated LSPs are not immediately removed, in order to
avoid LSP flap and service interruption. However, to allow for
network cleanup without manual intervention, such "orphan" PCE-
initiated LSPs must be either adopted by a different PCE or cleaned
up within a time interval. This time is negotiated between PCE and
PCC at session initialization time. See details in Section 6.
4. Support of PCE-initiated LSPs
A PCC indicates its ability to support PCE provisioned dynamic LSPs
during the PCEP Initialization Phase. The Open Object in the Open
message contains the "Stateful PCE Capability" TLV, defined in
[I-D.ietf-pce-stateful-pce].
A new flag, the I (LSP-INSTANTIATION-CAPABILITY) flag is introduced
to indicate support for instantiation of PCE-initiated LSPs. A PCE
wishing to initiate LSPs, can do so only for PCCs that advertised
this capability and a PCC will follow the procedures described in
this document only on sessions where the PCE advertised the I flag.
A PCE or PCC that advertise support of LSP initiation MUST also
advertise a cleanup time for the removal of such LSPs. The cleanup
time is advertised via a new TLV in the Open Object, the LSP-CLEANUP
TLV, discussed in Section 6, and the value is negotiated to the lower
one advertised on a session.
4.1. Stateful PCE Capability TLV
The format of the STATEFUL-PCE-CAPABILITY TLV is shown in the
following figure:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=16 | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |I|S|U|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+
Figure 1: STATEFUL-PCE-CAPABILITY TLV format
The type of the TLV is defined in [I-D.ietf-pce-stateful-pce] and it
has a fixed length of 4 octets.
The value comprises a single field - Flags (32 bits). The U and S
bits are defined in [I-D.ietf-pce-stateful-pce].
If set to 1 by a PCC, the I Flag indicates that the PCC allows
instantiation of an LSP by a PCE. If set to 1 by a PCE, the I flag
indicates that the PCE will attempt to instantiate LSPs. The LSP-
INSTANTIATION-CAPABILITY flag must be set by both PCC and PCE in
order to support PCE-initiated LSP instantiation.
Unassigned bits are considered reserved. They MUST be set to 0 on
transmission and MUST be ignored on receipt.
5. PCE-initiated LSP creation
To create a PCE-initiated LSP, a PCE sends a PCCreate message to a
PCC, which include a set of objects and TLVs describing the LSP to be
instantiated. The message format, the objects and TLVs are discussed
separately below.
5.1. The LSP Create Message
A Path Computation LSP Create message (also referred to as PCCreate
message) is a PCEP message sent by a PCE to a PCC to trigger an LSP
instantiation. The Message-Type field of the PCEP common header for
the PCCreate message is set to [TBD].
The PCCreate message MUST include the END-POINTS and the LSPA
objects. In the LSPA object, it MUST include the SYMBOLIC-PATH-NAME
TLV for the LSP. The PCCreate message MAY include other attributes
for the LSP. If specified, the PCC MUST use them for the LSP
instantiation, otherwise it MUST use its locally configured values.
The error messages will be specified in a future version of this
document.
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The format of a PCCreate message is as follows:
<PCCreate Message> ::= <Common Header>
<lsp-instantiation-list>
Where:
<lsp-instantiation-list> ::= <lsp-instantiation-request>[<lsp-instantiation-list>]
<lsp-instantiation-request> ::= <END-POINTS>
<LSPA>
[<ERO>]
[<BANDWIDTH>]
[<metric-list>]
Where:
<metric-list>::=<METRIC>[<metric-list>]
The END-POINTS Object contains the source and destination addresses
for provisioning the PCE-initiated LSP. If the END-POINTS Object is
missing, the PCC MUST send a PCErr message with Error-type=6
(Mandatory Object missing) and Error-value=3 (END-POINTS Object
missing).
The LSPA Object MUST include the SYMBOLIC-PATH-NAME TLV, which will
be used to correlate between the PCC-assigned LSP-ID and the LSP. If
the TLV is missing, the PCC MUST send a PCErr message with Error-
type=6(Mandatory object missing) and Error-value=14 (SYMBOLIC-PATH-
NAME TLV missing). The symbolic name used for provisioning PCE-
initiated LSPs must not have conflict with the LSP name of any
existing LSP in the PCC. (Existing LSPs may be either statically
configured, or initiated by another PCE). If there is conflict with
the LSP name, the PCC MUST send a PCErr message with Error-type=23
(Bad Parameter value) and Error-value=1 (SYMBOLIC-PATH-NAME in use).
The only exception to this rule is for LSPs for which the LSP-cleanup
timer is running (see Section 6).
PCE-initiated removal of a PCE-initiated LSP is done by setting the R
(remove) flag in the LSP Object in the PCUpd request from the PCE.
The definition of the R bit is updated as follows:
R (Remove - 1 bit): On PCRpt messages the R Flag indicates that the
LSP has been removed from the PCC. Upon receiving a PCRpt message
with the R Flag set to 1, the PCE SHOULD remove all state related to
the LSP from its database. In PCUpd messages the R flag indicates
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that the PCE wishes to disable the LSP. Upon receiving the PCUpd
message with the R Flag set for a PCE-initiated LSP, the PCC tears
down the LSP and removes its state.
A PCC SHOULD be able to place a limit on either the number of LSPs or
the percentage of resources that are allocated to honor PCE-initiated
LSP requests. As soon as that limit is reached, the PCC MUST send a
PCErr message of type 19 (Invalid Operation) and value TBD "PCE-
initiated limit reached" and is free to drop any incoming PCCreate
messages without additional processing.
A PCC SHOULD relay to the PCE errors it encounters in the setup of
PCE-initiated LSP. The error codes and error processing will be
detailed in a future version of this document.
6. LSP delegation and cleanup
6.1. LSP delegation procedures
PCE-initiated LSPs are automatically delegated by the PCC to the PCE
upon instantiation. The PCC MUST delegate the LSP to the PCE by
setting the delegation bit to 1 in the PCRpt that includes the
assigned LSP-Id. All subsequent messages from the PCC must have the
delegation bit set to 1. The PCC cannot revoke the delegation for
PCE-initiated LSPs for an active PCEP session. Sending a PCRpt
message with the delegation bit set to 0 results in a PCErr message
of type 19 (Invalid Operation) and value TBD "Delegation for PCE-
initiated LSP cannot be revoked".
A PCE MAY return a delegation to the PCC, to allow for LSP transfer
between PCEs. Doing so MUST trigger the LSP cleanup timer described
in Section 6.2.
Control over PCE-initiated LSPs reverts to the PCC at the expiration
of the delegation timeout. To obtain control of a PCE-initiated LSP,
a PCE (either the original or one of its backups) sends a PCCreate
message specifying the endpoints and symbolic name (the same process
used when initiating an LSP from the PCE). See more in the next
section.
6.2. LSP cleanup procedures
The LSP cleanup timer ensures that a PCE crash does not result in
automatic and immediate disruption for the services using PCE-
initiated LSPs. PCE-initiated LSPs are not be removed immediately
upon PCE failure. Instead, they are cleaned up on the expiration of
this timer. This allows for network cleanup without manual
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intervention. The LSP cleanup timer is advertised in the session
open message via a mandatory TLV for sessions where PCE-initiated
LSPs are supported. The timer is started upon PCEP session failure
and is stopped when the LSP is delegated to a PCE. Both PCE and PCC
advertise a value for this timer, and the timer value is negotiated
to the lower value of the two.
6.2.1. LSP-CLEANUP TLV
The LSP-CLEANUP TLV is advertised in the Open Object and is mandatory
when the I flag is set in the STATEFUL-PCE-CAPABILITY TLV. The LSP-
CLEANUP TLV contains the time in seconds that the PCC has to wait
before cleaning up any PCE-initiated LSPs belonging to a particular
PCEP session when a PCEP session terminates. Both PCE and PCC
advertise a value for the cleanup time, and the cleanup timer is set
to the lower of the two. The timer is triggered on PCEP session
failure and reset when the LSP is delegated to a PCE.
Failure to include the mandatory LSP-CLEANUP TLV in the Open Object
when the I flag is set MUST trigger PCErr of type 6 (Mandatory Object
missing) and value 13 (LSP-CLEANUP TLV missing).
The format of the LSP-CLEANUP TLV is shown in the following figure:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=TBD | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP cleanup timeout value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+
Figure 2: LSP-CLEANUP TLV format
The type of the TLV is TBD and it has a fixed length of 4 octets.
The value comprises a single field, the LSP cleanup timeout value.
The time in seconds to wait before cleaning up PCE-initiated LSPs.
Zero means immediate removal. The value OXFFFFFFFF is reserved.
A PCE may take control of the dynamic LSPs for which the LSP cleanup
timer is running by sending an PCCreate request for the LSP. In this
case, the "Bad Symbolic Path Name" error MUST NOT be generated, the
LSP MUST be delegated and the cleanup timer MUST be stopped.
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7. IANA considerations
7.1. PCEP Messages
This document defines the following new PCEP messages:
Value Meaning Reference
12 Create This document
7.2. PCEP-Error Object
This document defines new Error-Type and Error-Value for the
following new error conditions:
Error-Type Meaning
6 Mandatory Object missing
Error-value=13: LSP cleanup TLV missing
Error-value=14: SYMBOLIC-PATH-NAME TLV missing
19 Invalid operation
Error-value=3: PCE-initiated LSP limit reached
Error-value=4: Delegation for PCE-initiated LSP cannot
be revoked
23 Bad parameter value
Error-value=1: SYMBOLIC-PATH-NAME in use
7.3. PCEP TLV Type Indicators
This document defines the following new PCEP TLVs:
Value Meaning Reference
26 LSP cleanup This document
8. Security Considerations
The security considerations described in [I-D.ietf-pce-stateful-pce]
apply to the extensions described in this document. Additional
considerations related to a malicious PCE are introduced.
8.1. Malicious PCE
The LSP instantiation mechanism described in this document allows a
PCE to generate state on the PCC and throughout the network. As a
result, it introduces a new attack vector: an attacker may flood the
PCC with LSP instantiation requests and consume network and LSR
resources, either by spoofing messages or by compromising the PCE
itself.
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A PCC can protect itself from such an attack by imposing a limit on
either the number of LSPs or the percentage of resources that are
allocated to honor PCE-initiated LSP requests. As soon as that limit
is reached, the PCC MUST send a PCErr message of type 19 (Invalid
Operation) and value 3 "PCE-initiated LSP limit reached" and is free
to drop any incoming PCCreate messages without additional processing.
Rapid flaps triggered by the PCE can also be an attack vector. This
will be discussed in a future version of this document.
9. Acknowledgements
We would like to thank Jan Medved, Ambrose Kwong and Raveendra Trovi
for their contributions to this document.
10. References
10.1. Normative References
[I-D.ietf-pce-stateful-pce]
Crabbe, E., Medved, J., Minei, I., and R. Varga, "PCEP
Extensions for Stateful PCE",
draft-ietf-pce-stateful-pce-03 (work in progress),
March 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
May 2005.
[RFC5088] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
"OSPF Protocol Extensions for Path Computation Element
(PCE) Discovery", RFC 5088, January 2008.
[RFC5089] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
"IS-IS Protocol Extensions for Path Computation Element
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(PCE) Discovery", RFC 5089, January 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element
(PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
[RFC5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
Used to Form Encoding Rules in Various Routing Protocol
Specifications", RFC 5511, April 2009.
10.2. Informative References
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS",
RFC 2702, September 1999.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[RFC3346] Boyle, J., Gill, V., Hannan, A., Cooper, D., Awduche, D.,
Christian, B., and W. Lai, "Applicability Statement for
Traffic Engineering with MPLS", RFC 3346, August 2002.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
September 2003.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC4657] Ash, J. and J. Le Roux, "Path Computation Element (PCE)
Communication Protocol Generic Requirements", RFC 4657,
September 2006.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
[RFC5394] Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash,
"Policy-Enabled Path Computation Framework", RFC 5394,
December 2008.
[RFC5557] Lee, Y., Le Roux, JL., King, D., and E. Oki, "Path
Computation Element Communication Protocol (PCEP)
Requirements and Protocol Extensions in Support of Global
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Concurrent Optimization", RFC 5557, July 2009.
Authors' Addresses
Edward Crabbe
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: edc@google.com
Ina Minei
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: ina@juniper.net
Siva Sivabalan
Cisco Systems, Inc.
170 West Tasman Dr.
San Jose, CA 95134
US
Email: msiva@cisco.com
Robert Varga
Pantheon Technologies SRO
Mlynske Nivy 56
Bratislava 821 05
Slovakia
Email: robert.varga@pantheon.sk
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