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Bernstein (ed.) 2 Internet Draft Grotto Networking 3 Young Lee (ed.) 4 Huawei 5 Intended status: Informational June 30, 2008 6 Expires: December 2008 8 Performance Evaluation of PCE Architectures for Wavelength Switched 9 Optical Networks 10 draft-bernstein-pce-wson-evaluation-00.txt 12 Status of this Memo 14 By submitting this Internet-Draft, each author represents that 15 any applicable patent or other IPR claims of which he or she is 16 aware have been or will be disclosed, and any of which he or she 17 becomes aware will be disclosed, in accordance with Section 6 of 18 BCP 79. 20 This document may not be modified, and derivative works of it may not 21 be created, except to publish it as an RFC and to translate it into 22 languages other than English. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF), its areas, and its working groups. Note that 26 other groups may also distribute working documents as Internet- 27 Drafts. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 The list of current Internet-Drafts can be accessed at 35 http://www.ietf.org/ietf/1id-abstracts.txt 37 The list of Internet-Draft Shadow Directories can be accessed at 38 http://www.ietf.org/shadow.html 40 This Internet-Draft will expire on December 30, 2008. 42 Copyright Notice 44 Copyright (C) The IETF Trust (2008). 46 Abstract 48 In this note a number of PCE architectural and computational options 49 are evaluated against a medium sized wavelength switched optical 50 network. The key performance measures of overall and backward 51 blocking are reported under different dynamic traffic scenarios. The 52 corresponding reduction in connection blocking probabilities and 53 computational advantages enabled by these architectural alternatives 54 strongly warrant their inclusion in continuing PCE WSON work. 56 Table of Contents 58 1. Introduction...................................................2 59 2. Simulated PCE Architectures and Variations.....................4 60 2.1. Routing with Distributed RWA..............................4 61 2.2. Separate Routing from Wavelength Assignment...............5 62 2.3. Combined Routing and Wavelength Assignment................5 63 3. Simulation Runs and Results....................................5 64 4. Interpretation of results and Conclusions......................7 65 5. Security Considerations........................................8 66 6. IANA Considerations............................................8 67 7. Acknowledgments................................................8 68 7.1. Informative References....................................9 69 Author's Addresses...............................................10 70 Intellectual Property Statement..................................10 71 Disclaimer of Validity...........................................11 73 1. Introduction 75 Path computation in Wavelength Switched Optical Networks (WSON) is 76 typically subject to a wavelength continuity constraint. The nature 77 of this constraint has lead to a number of different practical 78 schemes for path computation in WSONs. The general class of these 79 computational problems is typically referred to as Routing and 80 Wavelength Assignment (RWA) problems. It must be emphasized that the 81 wavelength assignment (WA) mentioned here is an integral part of path 82 computation and not a part of network planning or static 83 configuration problem and hence falls within the scope of the path 84 computation element (PCE) architecture. 86 In the WSON Framework draft [Frame] three basic computational 87 architectures were described: 89 o Combined RWA --- Both routing and wavelength assignment are 90 performed at a single computational entity. 92 o Separate Routing and WA --- Separate entities perform routing and 93 wavelength assignment. The path obtained from the routing 94 computational entity must be furnished to the entity performing 95 wavelength assignment. 97 o Routing with Distributed WA --- Routing is performed at a 98 computational entity while wavelength assignment is performed in a 99 distributed fashion across nodes along the path. 101 The implications to the control plane of these three approaches are 102 described in [Frame] and [WSON-PCE]. In reference [ECOC-08] initial 103 simulations are reported on the performance of these different 104 approaches along with various computational options. Here we will 105 review those aspects of [ECOC-08] relevant to WSON PCE 106 standardization efforts and discuss further simulations under 107 different traffic load and network sizing parameters. Note that these 108 results are expressed in the form of graphs that do not appear in the 109 text version of this draft. 111 In circuit switching networks such as WSON a key performance measure 112 used to evaluate network performance under dynamic loads is the 113 probability that a connection request will be blocked. For GMPLS 114 based network there can be a portion of the overall blocking, termed 115 "backward blocking" in [ECOC-08] due to resource contention during 116 the signaling phase of lightpath set up, i.e. when two different 117 RSVP-TE instances try to reserve the same wavelength on the same 118 link. In this note we will primarily be concerned with the overall 119 blocking performance of the various PCE computation architectures for 120 WSON. 122 The simulations were carried out on a Pan European network topology 123 with 27 optical nodes and 55 WDM links [Should we reference Alessio's 124 OFC paper?] as shown in Figure 1. Each link carries either 32 or 80 125 wavelengths depending upon the simulation run. The traffic is 126 uniformly distributed among all node pairs, lightpath requests arrive 127 following a Poisson process with an exponentially distributed inter- 128 arrival time (with average 1/u seconds) and holding time (with 129 average 1/lambda=60s seconds or 6000s depending on simulation run). 130 The load offered to the network is thus expressed in Erlang as 131 lambda/u and it is varied by controlling the inter-arrival time. In 132 all the figures, each simulation point is plotted with the confidence 133 interval at 90% of confidence level. 135 Figure 1 is shown here in the PDF. 137 Figure 1 139 2. Simulated PCE Architectures and Variations 141 2.1. Routing with Distributed RWA 143 The following variants were studied: 145 1. In the "Fully Distributed" (FD) case the PCE was assumed to reside 146 on the originating node for the light path and only had aggregate 147 wavelength usage (bandwidth) information. In this case a least 148 congested route (LCR) path selection algorithm was used. 150 2. In the "R-" case a centralized PCE was assumed to compute paths 151 (but not wavelength assignment) based on the same LCR algorithm as 152 above. Then distributed wavelength assignment via signaling was 153 utilized. For the purposes of blocking probability calculation 154 this leads to similar results as the previous case. 156 3. In the "R+" case a centralized PCE was assumed to compute paths 157 (but not wavelength assignment) based on detailed link wavelength 158 utilization/availability. A variant of the LCR algorithm that 159 understood the wavelength continuity constraint was employed. 161 2.2. Separate Routing from Wavelength Assignment 163 In this case it was assumed that routing (but not wavelength 164 assignment) was performed at the ingress node based only on aggregate 165 wavelength utilization (bandwidth). The results of this computation 166 are then passed to a separate PCE server for wavelength assignment 167 (WA). It was assumed that this separate WA PCE had detailed knowledge 168 of link wavelength utilization. 170 An important variation of the above is when the first route 171 computation element (in this case on the ingress node) calculates K 172 alternative paths which are then fed to the WA PCE which will then 173 choose one of the paths and a viable wavelength (where possible). 174 This scenario is denoted by "WA-k" on the various graphs and 175 simulations were performed for k = 2 and k = 3. 177 2.3. Combined Routing and Wavelength Assignment 179 In this case in the simulations a central PCE was responsible for 180 both routing and wavelength assignment. This requires the PCE to run 181 a reasonably sophisticated algorithm and have detailed link 182 wavelength utilization information. This is denoted by "R+WA" in the 183 simulation results. 185 3. Simulation Runs and Results 186 Figure 2 is shown here in the PDF 188 Figure 2 shows the following inferences: 190 o R+WA (Combined Routing and Wavelength Assignment) performs the 191 best due to the absence of backward blocking while FD suffers a 192 highest blocking. 194 o In the heavy network load, R+ is as good as R+WA due to 195 wavelength-continuity aware routing scheme (WC-LCR) employed by R+ 196 scheme in which case there is virtually no backward blocking 197 similar to R+WA. 199 o R- and FD suffer the worst blocking performance due to the routing 200 scheme employed that is not wavelength continuity aware. 202 Figure 3 is shown her in the PDF. 204 Figure 3. WA, WA-2, WA-3 and R+WA scenarios with 32 wavelengths 205 per link, 1/u = 60s. 207 Figure 3 shows the following inferences: 209 o For the medium and heavy loads, WA and FD show high blocking 210 probability due to the routing schemes that is based on aggregated 211 bandwidth information. 213 o WA-k (k=3) significantly improves the WA assignment performance. 215 Simulation results with a longer holding time (100x) maintain the 216 similar inferences obtained for the case of a shorter holding time. 218 4. Interpretation of results and Conclusions 220 (a) Importance of accurate wavelength usage information, e.g., FD and 221 R- compared to R+, WA 222 (b) Reduction (elimination) of backward blocking in the R+WA, WA, and 223 WA-K situations 224 (c) The usefulness of WA-k in reducing blocking compared to R+, WA 225 and the simplification compared to R+WA 227 In terms of the PCE architecture options, centralized wavelength 228 assignment shows a clear performance benefit over distributed 229 wavelength assignment. 231 In regards to routing, separating routing from wavelength assignment 232 could be a viable option to consider. In this case, the number of 233 routes fed to a central WA PCE affects the overall performance. 235 5. Security Considerations 237 This draft in showing the advantages of the PCE R+WA and WA-k 238 architectures in WSON networks, makes clear the need for securing the 239 PCE architecture in general but does not add any new security 240 requirements. It should be noted that WSON light paths and link 241 resources are relatively scarce and expensive resources and hence a 242 potentially higher value target for attacks. 244 6. IANA Considerations 246 This draft does not require IANA services. 248 7. Acknowledgments 250 This document was prepared using 2-Word-v2.0.template.dot. 252 References 254 7.1. Informative References 256 [Frame] G. Bernstein, Y. Lee, W. Imajuku, "Framework for GMPLS and 257 PCE Control of Wavelength Switched Optical Networks", work 258 in progress: draft-ietf-ccamp-wavelength-switched-00.txt, 259 May 2008. 261 [ECOC-08] A. Giorgetti, F. Paolucci, F. Cugini, L. Valcarenghi, P. 262 Castoldi, G. Bernstein, "Routing and Wavelength Assignment 263 in PCE-based Wavelength Switched Optical Networks (WSONs)", 264 To Appear ECOC 2008. 266 [WSON-PCE] Y. Lee and G. Bernstein, "PCEP Requirements and 267 Extensions for WSON Routing and Wavelength Assignment", 268 work in progress: draft-lee-pce-wson-routing-wavelength- 269 02.txt. 271 Author's Addresses 273 Aessio Giorgetti 274 Scuola Superiore Sant'Anna, Pisa, Italy 275 Email: a.giorgetti@sssup.it 277 F. Paolucci 278 Scuola Superiore Sant'Anna, Pisa, Italy 279 Email: fr.paolucci@sssup.it 281 Filippo Cugini 282 CNIT, Pisa, Italy 283 Email: filippo.cugini@cnit.it 285 L. Valcarenghi 286 Scuola Superiore Sant'Anna, Pisa, Italy 287 Email: valcarenghi@sssup.it 289 P. Castoldi 290 Scuola Superiore Sant'Anna, Pisa, Italy 291 Email: castoldi@sssup.it 293 Greg Bernstein (Ed.) 294 Grotto Networking 295 Fremont California, U.S.A. 297 Phone: (510) 573-2237 298 Email: gregb@grotto-networking.com 300 Young Lee (Ed.) 301 Huawei Technologies 302 1700 Alma Drive, Suite 100 303 Plano, TX 75075, USA 305 Phone: (972) 509-5599 (x2240) 306 Email: ylee@huawei.com 308 Intellectual Property Statement 310 The IETF takes no position regarding the validity or scope of any 311 Intellectual Property Rights or other rights that might be claimed to 312 pertain to the implementation or use of the technology described in 313 this document or the extent to which any license under such rights 314 might or might not be available; nor does it represent that it has 315 made any independent effort to identify any such rights. 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