One document matched: draft-bernstein-pce-wson-evaluation-00.txt
Network Working Group G. Bernstein (ed.)
Internet Draft Grotto Networking
Young Lee (ed.)
Huawei
Intended status: Informational June 30, 2008
Expires: December 2008
Performance Evaluation of PCE Architectures for Wavelength Switched
Optical Networks
draft-bernstein-pce-wson-evaluation-00.txt
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Bernstein Expires December 30, 2008 [Page 1]
Internet-Draft PCE WSON Performance Evaluation June 2008
Abstract
In this note a number of PCE architectural and computational options
are evaluated against a medium sized wavelength switched optical
network. The key performance measures of overall and backward
blocking are reported under different dynamic traffic scenarios. The
corresponding reduction in connection blocking probabilities and
computational advantages enabled by these architectural alternatives
strongly warrant their inclusion in continuing PCE WSON work.
Table of Contents
1. Introduction...................................................2
2. Simulated PCE Architectures and Variations.....................4
2.1. Routing with Distributed RWA..............................4
2.2. Separate Routing from Wavelength Assignment...............5
2.3. Combined Routing and Wavelength Assignment................5
3. Simulation Runs and Results....................................5
4. Interpretation of results and Conclusions......................7
5. Security Considerations........................................8
6. IANA Considerations............................................8
7. Acknowledgments................................................8
7.1. Informative References....................................9
Author's Addresses...............................................10
Intellectual Property Statement..................................10
Disclaimer of Validity...........................................11
1. Introduction
Path computation in Wavelength Switched Optical Networks (WSON) is
typically subject to a wavelength continuity constraint. The nature
of this constraint has lead to a number of different practical
schemes for path computation in WSONs. The general class of these
computational problems is typically referred to as Routing and
Wavelength Assignment (RWA) problems. It must be emphasized that the
wavelength assignment (WA) mentioned here is an integral part of path
computation and not a part of network planning or static
configuration problem and hence falls within the scope of the path
computation element (PCE) architecture.
In the WSON Framework draft [Frame] three basic computational
architectures were described:
o Combined RWA --- Both routing and wavelength assignment are
performed at a single computational entity.
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o Separate Routing and WA --- Separate entities perform routing and
wavelength assignment. The path obtained from the routing
computational entity must be furnished to the entity performing
wavelength assignment.
o Routing with Distributed WA --- Routing is performed at a
computational entity while wavelength assignment is performed in a
distributed fashion across nodes along the path.
The implications to the control plane of these three approaches are
described in [Frame] and [WSON-PCE]. In reference [ECOC-08] initial
simulations are reported on the performance of these different
approaches along with various computational options. Here we will
review those aspects of [ECOC-08] relevant to WSON PCE
standardization efforts and discuss further simulations under
different traffic load and network sizing parameters. Note that these
results are expressed in the form of graphs that do not appear in the
text version of this draft.
In circuit switching networks such as WSON a key performance measure
used to evaluate network performance under dynamic loads is the
probability that a connection request will be blocked. For GMPLS
based network there can be a portion of the overall blocking, termed
"backward blocking" in [ECOC-08] due to resource contention during
the signaling phase of lightpath set up, i.e. when two different
RSVP-TE instances try to reserve the same wavelength on the same
link. In this note we will primarily be concerned with the overall
blocking performance of the various PCE computation architectures for
WSON.
The simulations were carried out on a Pan European network topology
with 27 optical nodes and 55 WDM links [Should we reference Alessio's
OFC paper?] as shown in Figure 1. Each link carries either 32 or 80
wavelengths depending upon the simulation run. The traffic is
uniformly distributed among all node pairs, lightpath requests arrive
following a Poisson process with an exponentially distributed inter-
arrival time (with average 1/u seconds) and holding time (with
average 1/lambda=60s seconds or 6000s depending on simulation run).
The load offered to the network is thus expressed in Erlang as
lambda/u and it is varied by controlling the inter-arrival time. In
all the figures, each simulation point is plotted with the confidence
interval at 90% of confidence level.
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Figure 1 is shown here in the PDF.
Figure 1
2. Simulated PCE Architectures and Variations
2.1. Routing with Distributed RWA
The following variants were studied:
1. In the "Fully Distributed" (FD) case the PCE was assumed to reside
on the originating node for the light path and only had aggregate
wavelength usage (bandwidth) information. In this case a least
congested route (LCR) path selection algorithm was used.
2. In the "R-" case a centralized PCE was assumed to compute paths
(but not wavelength assignment) based on the same LCR algorithm as
above. Then distributed wavelength assignment via signaling was
utilized. For the purposes of blocking probability calculation
this leads to similar results as the previous case.
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3. In the "R+" case a centralized PCE was assumed to compute paths
(but not wavelength assignment) based on detailed link wavelength
utilization/availability. A variant of the LCR algorithm that
understood the wavelength continuity constraint was employed.
2.2. Separate Routing from Wavelength Assignment
In this case it was assumed that routing (but not wavelength
assignment) was performed at the ingress node based only on aggregate
wavelength utilization (bandwidth). The results of this computation
are then passed to a separate PCE server for wavelength assignment
(WA). It was assumed that this separate WA PCE had detailed knowledge
of link wavelength utilization.
An important variation of the above is when the first route
computation element (in this case on the ingress node) calculates K
alternative paths which are then fed to the WA PCE which will then
choose one of the paths and a viable wavelength (where possible).
This scenario is denoted by "WA-k" on the various graphs and
simulations were performed for k = 2 and k = 3.
2.3. Combined Routing and Wavelength Assignment
In this case in the simulations a central PCE was responsible for
both routing and wavelength assignment. This requires the PCE to run
a reasonably sophisticated algorithm and have detailed link
wavelength utilization information. This is denoted by "R+WA" in the
simulation results.
3. Simulation Runs and Results
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Figure 2 is shown here in the PDF
Figure 2 shows the following inferences:
o R+WA (Combined Routing and Wavelength Assignment) performs the
best due to the absence of backward blocking while FD suffers a
highest blocking.
o In the heavy network load, R+ is as good as R+WA due to
wavelength-continuity aware routing scheme (WC-LCR) employed by R+
scheme in which case there is virtually no backward blocking
similar to R+WA.
o R- and FD suffer the worst blocking performance due to the routing
scheme employed that is not wavelength continuity aware.
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Figure 3 is shown her in the PDF.
Figure 3. WA, WA-2, WA-3 and R+WA scenarios with 32 wavelengths
per link, 1/u = 60s.
Figure 3 shows the following inferences:
o For the medium and heavy loads, WA and FD show high blocking
probability due to the routing schemes that is based on aggregated
bandwidth information.
o WA-k (k=3) significantly improves the WA assignment performance.
Simulation results with a longer holding time (100x) maintain the
similar inferences obtained for the case of a shorter holding time.
4. Interpretation of results and Conclusions
(a) Importance of accurate wavelength usage information, e.g., FD and
R- compared to R+, WA
(b) Reduction (elimination) of backward blocking in the R+WA, WA, and
WA-K situations
(c) The usefulness of WA-k in reducing blocking compared to R+, WA
and the simplification compared to R+WA
In terms of the PCE architecture options, centralized wavelength
assignment shows a clear performance benefit over distributed
wavelength assignment.
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In regards to routing, separating routing from wavelength assignment
could be a viable option to consider. In this case, the number of
routes fed to a central WA PCE affects the overall performance.
5. Security Considerations
This draft in showing the advantages of the PCE R+WA and WA-k
architectures in WSON networks, makes clear the need for securing the
PCE architecture in general but does not add any new security
requirements. It should be noted that WSON light paths and link
resources are relatively scarce and expensive resources and hence a
potentially higher value target for attacks.
6. IANA Considerations
This draft does not require IANA services.
7. Acknowledgments
This document was prepared using 2-Word-v2.0.template.dot.
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References
7.1. Informative References
[Frame] G. Bernstein, Y. Lee, W. Imajuku, "Framework for GMPLS and
PCE Control of Wavelength Switched Optical Networks", work
in progress: draft-ietf-ccamp-wavelength-switched-00.txt,
May 2008.
[ECOC-08] A. Giorgetti, F. Paolucci, F. Cugini, L. Valcarenghi, P.
Castoldi, G. Bernstein, "Routing and Wavelength Assignment
in PCE-based Wavelength Switched Optical Networks (WSONs)",
To Appear ECOC 2008.
[WSON-PCE] Y. Lee and G. Bernstein, "PCEP Requirements and
Extensions for WSON Routing and Wavelength Assignment",
work in progress: draft-lee-pce-wson-routing-wavelength-
02.txt.
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Author's Addresses
Aessio Giorgetti
Scuola Superiore Sant'Anna, Pisa, Italy
Email: a.giorgetti@sssup.it
F. Paolucci
Scuola Superiore Sant'Anna, Pisa, Italy
Email: fr.paolucci@sssup.it
Filippo Cugini
CNIT, Pisa, Italy
Email: filippo.cugini@cnit.it
L. Valcarenghi
Scuola Superiore Sant'Anna, Pisa, Italy
Email: valcarenghi@sssup.it
P. Castoldi
Scuola Superiore Sant'Anna, Pisa, Italy
Email: castoldi@sssup.it
Greg Bernstein (Ed.)
Grotto Networking
Fremont California, U.S.A.
Phone: (510) 573-2237
Email: gregb@grotto-networking.com
Young Lee (Ed.)
Huawei Technologies
1700 Alma Drive, Suite 100
Plano, TX 75075, USA
Phone: (972) 509-5599 (x2240)
Email: ylee@huawei.com
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