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 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. This document may not be modified, and derivative works of it may not be created, except to publish it as an RFC and to translate it into languages other than English. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on December 30, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). 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. Bernstein & Lee Expires December 30, 2008 [Page 2] Internet-Draft PCE WSON Performance Evaluation June 2008 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. Bernstein & Lee Expires December 30, 2008 [Page 3] Internet-Draft PCE WSON Performance Evaluation June 2008 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. Bernstein & Lee Expires December 30, 2008 [Page 4] Internet-Draft PCE WSON Performance Evaluation June 2008 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 Bernstein & Lee Expires December 30, 2008 [Page 5] Internet-Draft PCE WSON Performance Evaluation June 2008 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. Bernstein & Lee Expires December 30, 2008 [Page 6] Internet-Draft PCE WSON Performance Evaluation June 2008 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. Bernstein & Lee Expires December 30, 2008 [Page 7] Internet-Draft PCE WSON Performance Evaluation June 2008 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. Bernstein & Lee Expires December 30, 2008 [Page 8] Internet-Draft PCE WSON Performance Evaluation June 2008 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. Bernstein & Lee Expires December 30, 2008 [Page 9] Internet-Draft PCE WSON Performance Evaluation June 2008 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 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information Bernstein & Lee Expires December 30, 2008 [Page 10] Internet-Draft PCE WSON Performance Evaluation June 2008 on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Bernstein & Lee Expires December 30, 2008 [Page 11]