Internet DRAFT - draft-he-pce-pcep-associated-lsp-extensions
draft-he-pce-pcep-associated-lsp-extensions
PCE Working Group WJ. He, Ed.
Internet-Draft ZTE
Intended status: Standards Track November 14, 2011
Expires: May 17, 2012
Extensions to the Path Computation Element Communication Protocol (PCEP)
for Associated Bidirectional LSP
draft-he-pce-pcep-associated-lsp-extensions-01
Abstract
The MPLS Transport Profile (MPLS-TP) requirements document[RFC5654],
describes that MPLS-TP MUST support associated bidirectional point-
to-point LSPs. Path Computation Element (PCE), see [RFC4655], may be
used for path computation of an associated bidirectional LSP. This
document defines the Path Computation Element Protocol (PCEP)-based
[RFC5440] extensions for associated bidirectional LSP.
Status of this Memo
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This Internet-Draft will expire on May 17, 2012.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . . 3
3. Processing . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Concurrent Computation . . . . . . . . . . . . . . . . . . 4
3.2. Successive Computation . . . . . . . . . . . . . . . . . . 4
4. PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Extended ASSOCIATION Object . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
The MPLS Transport Profile (MPLS-TP) requirements [RFC5654] and
control plane framework documents[RFC6373]describe that MPLS-TP MUST
support associated bidirectional point-to-point LSPs. Path
Computation Element (PCE), see [RFC4655], may be used for path
computation of a GMPLS LSP, see
[I-D.ietf-pce-gmpls-pcep-extensions],and consequently an associated
bidirectional LSP, across domains and in a single domain.
Dependent path computations are requests that need to be synchronized
in order to meet specific objectives, see [RFC6007]. For associated
bidirectional LSP, if the forward LSP and the backward LSP are
computed concurrently, the PCE can find the optimum path.
This document defines the Path Computation Element Protocol (PCEP)-
based [RFC5440] extensions for associated bidirectional LSP.
2. 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 [RFC2119].
3. Processing
Consider the topology described in Figure 1. (An example of
associated bidirectional LSP). The LSP1 [via nodes A,D,B] (from A to
B) and LSP2 [via nodes B,D,C,A] (from B to A) need to be established,
which can form an associated bidirectional LSP deployed by Single
Sided Provisioning model or Double Sided Provisioning
model[I-D.ietf-ccamp-mpls-tp-rsvpte-ext-associated-lsp]. Node A, the
ingress LSR of LSP1, can play the role of a PCC and request the PCE
to compute the LSP1 or the associated bidirectional LSP.
A-------D-------B
\ /
\ /
\ /
C
Figure 1 : An example of associated bidirectional LSP
The path computation for associated bidirectional LSP can be realized
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by the concurrent or successive computation. The concurrent
computation means that the head-end submits the computation request
for both two directional LSPs concurrently, which is applicable to
the Single Sided Provisioning model. As to the successive
computation, the head-end and the tail-end send the forward LSP and
backward LSP computation requests separately, which is applicable to
both the Single Sided Provisioning model and the Double Sided
Provisioning model.
3.1. Concurrent Computation
The PCC sends the PCReq message to PCE for computing an associated
bidirectional LSP, whose forward and backward paths are computed
concurrently. Concurrent computation can ensure that the paths for
the associated bidirectional LSP is optimal [RFC5557].
The SVEC object described in [RFC6007] can be used to synchronize the
requests about the forward and backward LSPs, and get the optimal
path for the associated bidirectional LSP.
3.2. Successive Computation
For the Successive computation, the PCCs submit the path computation
request for the forward LSP and the backward LSP separately, then,
the path for the associated bidirectional LSP may be not optimal. So
that the two reverse LSPs should be associated, the ASSOCIATION
object [I-D.ietf-ccamp-assoc-ext]may be useful. The stateful PCE
[RFC4655] can coordinate the two reverse LSPs to get the optimal path
for the associated bidirectional LSP through the ASSOCIATION object,
if both the head-end and the tail-end PCCs delegate their respective
LSPs (forward and backward) to the PCE .
When the PCC submits the path computation request for the forward LSP
or the backward LSP, the PCReq message may carry Extended ASSOCIATION
object to indicate there is a reverse LSP to be associated, see
[I-D.ietf-ccamp-mpls-tp-rsvpte-ext-associated-lsp]. At the same
time, both the head-end and the tail-end PCCs delegate their
respective LSPs (forward and backward) to the PCE using PCRpt
messages[I-D.crabbe-pce-stateful-pce].
Upon receipt of the PCReq message,the PCE will locate the reverse LSP
with the same association information. If there is no matched
reverse LSP, the PCE will compute the LSP independently. Otherwise,
the PCE will coordinate the two reverse LSPs and compute path for the
associated bidirectional LSP. After the successful computation, the
PCE will trigger the head-end to setup the forward LSP and the tail-
end to setup the backward LSP using PCUpd messages. The PCC will use
make-before-break whenever possible in the re-signaling
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operation,[I-D.crabbe-pce-stateful-pce].
4. PCEP Extensions
4.1. Extended ASSOCIATION Object
The Extended ASSOCIATION Object is used to associate the two reverse
LSPs, which form an associated bidirectional LSP. The Extended
ASSOCIATION Object is carried within a PCRep message to locate the
reverse LSP, and the PCE will coordinate the forward LSP and the
backward LSP to get the optimal path for the associated bidirectional
LSP.
The contents of this object are identical in encoding to the contents
of the RSVP-TE Extended ASSOCIATION Object defined in
[I-D.ietf-ccamp-assoc-ext] and
[I-D.ietf-ccamp-mpls-tp-rsvpte-ext-associated-lsp].
PCEP Extended ASSOCIATION object types correspond to RSVP-TE Extended
ASSOCIATION object types.
Extended ASSOCIATION Object-Class is TBD.
Extended ASSOCIATION Object-Type is TBD.
5. IANA Considerations
TBD
6. Security Considerations
TBD
7. Acknowledgement
The author would like to thank Jan Medved for his valuable comments
on the double sided provisioning, Cyril for the discussion of the
concurrent computation. At the same time, the author would also like
to acknowledge the contributions of Fei Zhang for the discussions.
8. References
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8.1. Normative References
[I-D.crabbe-pce-stateful-pce]
Crabbe, E., Medved, J., and R. Varga, "PCEP Extensions for
Stateful PCE", draft-crabbe-pce-stateful-pce-01 (work in
progress), October 2011.
[I-D.ietf-ccamp-assoc-ext]
Berger, L., Faucheur, F., and A. Narayanan, "RSVP
Association Object Extensions",
draft-ietf-ccamp-assoc-ext-01 (work in progress),
October 2011.
[I-D.ietf-ccamp-mpls-tp-rsvpte-ext-associated-lsp]
Zhang, F. and R. Jing, "RSVP-TE Extensions for Associated
Bidirectional LSPs",
draft-ietf-ccamp-mpls-tp-rsvpte-ext-associated-lsp-02
(work in progress), October 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element
(PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
8.2. Informative References
[I-D.ietf-pce-gmpls-pcep-extensions]
Margaria, C., Dios, O., and F. Zhang, "PCEP extensions for
GMPLS", draft-ietf-pce-gmpls-pcep-extensions-04 (work in
progress), October 2011.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[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
Concurrent Optimization", RFC 5557, July 2009.
[RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N.,
and S. Ueno, "Requirements of an MPLS Transport Profile",
RFC 5654, September 2009.
[RFC6007] Nishioka, I. and D. King, "Use of the Synchronization
VECtor (SVEC) List for Synchronized Dependent Path
Computations", RFC 6007, September 2010.
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[RFC6373] Andersson, L., Berger, L., Fang, L., Bitar, N., and E.
Gray, "MPLS Transport Profile (MPLS-TP) Control Plane
Framework", RFC 6373, September 2011.
Author's Address
Wenjuan He (editor)
ZTE
Email: he.wenjuan1@zte.com.cn
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