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'2') (Obsoleted by RFC 4234) -- Duplicate reference: RFC2119, mentioned in 'RFC2119', was also mentioned in '1'. -- Duplicate reference: RFC2234, mentioned in 'RFC2234', was also mentioned in '2'. ** Obsolete normative reference: RFC 2234 (Obsoleted by RFC 4234) Summary: 3 errors (**), 0 flaws (~~), 6 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Networking Group Sh.G. Huang 2 Internet Draft S. Yin 3 Intended status: Informational BUPT 4 Expires: November 2020 Ch.G Wang 5 S. Zhou 6 BUPT 7 May 23, 2020 9 RSCA method with Dividing Frequency Slots Area in Space Division 10 Multiplexing Elastic Optical Networks 11 draft-huang-rsca-sdm-eon-04 13 Status of this Memo 15 This Internet-Draft is submitted in full conformance with the 16 provisions of BCP 78 and BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet-Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html 33 This Internet-Draft will expire on November 23, 2020. 35 Copyright Notice 37 Copyright (c) 2018 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents carefully, 44 as they describe your rights and restrictions with respect to this 45 document. Code Components extracted from this document must include 46 Simplified BSD License text as described in Section 4.e of the Trust 47 Legal Provisions and are provided without warranty as described in 48 the Simplified BSD License. 50 Abstract 52 This documentary provides a routing, spectrum and core assignment 53 method with the dividing frequency slots area for space division 54 multiplexing elastic optical networks. This effective RSCA method to 55 solve this problem better. The proposed method utilizes the Frequency 56 Slots Area (FSA) concept and first-last fit policy of frequency slots 57 assignment to have less spectrum fragments, lower crosstalk, smaller 58 traffic blocking probability and higher spectrum resource utilization. 60 Table of Contents 62 1. Introduction ................................................ 2 63 1.1. Terminology ............................................ 3 64 2. Conventions used in this document ............................ 3 65 3. Overview ...................................................... 4 66 3.1. Elastic Optical Networks ................................ 4 67 3.2. Multi-Core Fiber ........................................ 4 68 4. RSCA ........................................................ 5 69 5. The proposed spectrum and core assignment method ............. 5 70 6. Formal Syntax ............................................... 7 71 7. Security Considerations ...................................... 7 72 8. IANA Considerations ......................................... 7 73 9. Conclusions ................................................. 7 74 10. References ................................................. 7 75 10.1. Normative References ................................... 7 76 10.2. Informative References ................................. 8 77 11. Acknowledgments ............................................ 8 79 1. Introduction 81 With the rapid development of Internet technology and the emergence 82 of new applications such as intense social networking, real-time 83 gaming, High Definition audio-video streaming and cloud computing, 84 the demand for network capacity has increased greatly. The capacity 85 of traditional single-mode fiber is close to its physical capacity 86 limit, so the SDM technology that can greatly improve the network 87 capacity has received more and more attention. In SDM technology, MCF 88 is one of the most promising technology. On the other hand, for the 89 sake of flexible and effective use of spectrum resources, EON has 90 been widely accepted as the next generation high-speed network. In 91 the elastic optical network, the spectrum resources are divided into 92 finer frequency slots, which can be more flexible and effective used 93 by traffic requests. In elastic optical networks, spectrum resources 94 are assigned flexibly according to connections' requirements. This 95 flexibility based on fine-grained resource provisioning can reduce 96 the amount of spectrum resources wasted, compared with traditional 97 rigid spectrum assignments. At the network level, the RSA problem is 98 the most important problem concerning elastic optical networks. There 99 are two continuity constraints for an assigned spectrum in the RSA 100 problem. These constraints require the same and continuous spectrum 101 to be assigned for all links on the selected transmission route if 102 there is no wavelength converter. Because it is necessary to satisfy 103 the spectral constraints of the RSA problem according to traffic 104 demands, which change dynamically, dynamic resource allocation can 105 effectively improve the performance of optical networks. 107 The advantage of SDM-EONs is that it greatly improves the capacity of 108 the network, allowing for more flexible and efficient use of spectrum 109 resources. However, it brings the RSCA problem with serious crosstalk 110 and high computing complexity. Crosstalk refers to the mutual 111 interference generated by the transmission of signals on the same 112 frequency between adjacent cores. With the increasing number of cores 113 in the fiber, the core-pitch is getting smaller and smaller, and the 114 crosstalk between adjacent cores is becoming more and more serious. 115 At the same time, compared to the traditional EONs, the new core 116 dimension in MCF-EONs makes its computational complexity higher. 117 However, in the RSCA problem, the impact of inter-core crosstalk can 118 be alleviated by properly assigning the core and spectrum resources 119 to requests. Therefore, how to solve the RSCA problem effectively in 120 SDM-EON is a challenge cannot be ignored. 122 1.1. Terminology 124 SDM: Space Division multiplexing. 126 EON: Elastic Optical Network. 128 RSA: Routing and spectrum assignment problem. 130 RSCA: Routing, Spectrum and Core Assignment problem. 132 FSA: Frequency Slots Area. 134 2. Conventions used in this document 136 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 137 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 138 document are to be interpreted as described in RFC 2119 [RFC2119]. 140 3. Overview 142 In elastic optical network, the traffic requests are constantly 143 changing with time, so it is very important to choose a dynamic 144 solution to the RSCA problem. However, with the continuous 145 establishment and release of the traffic requests, there will be 146 fragments between the frequency slots. In order to improve the 147 utilization of spectrum resources in SDM-EON, it is essential to 148 solve the problem of spectrum fragmentation. 150 3.1. Elastic Optical Networks 152 Elastic optical network is different with traditional wavelength- 153 division multiplexing (WDM) network because of the flexible use of 154 spectrum resource. In traditional WDM networks, different traffic 155 requests are assigned with the same fixed spectrum grid. Therefore, 156 if the transmission distance of the request is short and demands less 157 spectrum resource, there will be a lot of spectrum resource wasted in 158 the fixed grid. In elastic optical network, the spectrum resource is 159 allocated to the traffic request by flexible grid. That is to say, 160 the network can choose the modulation format flexibly according to 161 the length of the optical transmission route to save the spectrum 162 resource. For example, when the transmission distance of the traffic 163 is short, the network can choose the modulation formats with high 164 spectrum utilization, such as 16-quadrature amplitude modulation (QAM) 165 and 64-QAM, so that the resource utilization of the network can be 166 improved. On the other hand, if the requested transmission distance 167 of the traffic is long, the network can choose a modulation format 168 with lower spectrum resource utilization, such as quadrature phase- 169 shift keying (QPSK). 171 3.2. Multi-Core Fiber 173 Because the transmission capacity of single-mode optical fiber is 174 close to its physical limit, in order to improve the network capacity 175 further, SDM has been widely concerned recently. MCF is one of the 176 most promising transmission technology in SDM system. MCF using 177 single-mode optical fibers is considered to greatly improve the 178 transmission capacity of the network. However, one of the major 179 problems with MCF is the physical impairment of transmitted signals 180 due to crosstalk between cores during transmission. Large crosstalk 181 occurs when the signals are transmitted in the same frequency on 182 adjacent cores. The smaller the distance of the cores, the more 183 serious the crosstalk will be. As shown in Fig.1, since 1 is used in 184 both the adjacent core one and core two, large crosstalk occurs 185 between the core one and core two. Since core one is not adjacent to 186 core three, even if they both use 2, the crosstalk between them is 187 much lower than the crosstalk between cores one and three. Normally, 188 we can ignore the effects of these low crosstalk. 190 4. RSCA 192 The RSA problem is the most important part of the elastic optical 193 network. In the same way, RSCA is the most important part of EDM-EON. 194 In the traditional WDM network, wavelength channel is the basic unit 195 of resource allocation. Nevertheless, in the elastic optical network 196 basic unit of resource allocation is the frequency slot. The RSA 197 problem in EON is equivalent to the Routing and Wavelength Assignment 198 (RWA) problem in the traditional WDM network. However, due to the 199 flexible resource allocation method of elastic optical network and 200 the application of SDM technology, the RSCA problem in SDM-EON 201 becomes more complex and challenging. 203 In the traditional WDM network, there is a wavelength continuity 204 constraint, that is, the network must select the same wavelength 205 channel for each link in the transmission route. In elastic optical 206 network, there is a similar continuity constraint for frequency slot. 207 In addition, there is a spectrum contiguity constraint. Spectrum 208 contiguity constraint ensures that the assigned frequency slots have 209 to be consecutive in the spectrum resources of the fiber. Spectrum 210 continuity constraint refers to the frequency slots used by each link 211 on the selected routing path have to be same. According to the 212 transmission distance of traffic requests, the elastic optical 213 network selects different modulation formats to utilize spectrum 214 resources effectively, and determines the number of consecutive 215 frequency slots needed for transmission. 217 In elastic optical network, the traffic requests are constantly 218 changing with time, so it is very important to choose a dynamic 219 solution to the RSCA problem. However, with the continuous 220 establishment and release of the traffic requests, there will be 221 fragments between the frequency slots. In order to improve the 222 utilization of spectrum resources in SDM-EON, it is essential to 223 solve the problem of spectrum fragmentation. 225 5. The proposed spectrum and core assignment method 227 Through routing algorithm and wavelength assignment algorithm, we 228 calculate the K feasible routing of a specific business wavelength. K 229 feasible routing pathes are arranged according to preset priority, 230 among them, the ith routing is recorded as Ri , i=1,2,3 We choose 231 the first reachable optical path and calculate the output power and 232 OSNR value of the first path, and do the following operations 233 In this draft, we use a k-shortest path algorithm based on Yen's 234 ranking loopless paths algorithm to solve the routing problem .When a 235 traffic request arrives, we use the routing algorithm to calculate k- 236 shortest end-to-end routing paths for it. Then we select the path in 237 order and process the spectrum and core assignment method. If no one 238 path can meet the two constraints, the traffic request will be 239 blocked. In SDM-EONs, it is more difficult to provision huger demands 240 with satisfying continuity constraints due to fragmentation issue . 241 To deal with it, we propose that the spectrum resource of the 7-core 242 MCFs can be divided into several Frequency Slots Areas. This division 243 reduces the blocking probability. Fig. 1 shows the flowchart of the 244 proposed method. 246 The 7-core MCF can be divided into several different areas according 247 to the number of slots required for traffic requests. In the example, 248 the number of slots required for traffic requests is three, four and 249 five respectively. The first half of the core one, core two and the 250 second half of them are divided into Frequency Slots Area of three 251 (FSA-3) and Frequency Slots Area of five (FSA-5), respectively. The 252 first half of the core five, core six is FSA-5, and the second half 253 is divided into FSA-3.Then we divide the first half and second half 254 of core three and core four into two different Frequency Slots Areas 255 of four (FSA-4). In the last, the remaining entire core seven can be 256 utilized by all the traffic with different frequency slots demand as 257 a common area. When the traffic request needs three frequency slots, 258 only the available frequency slots in FSA-3 and common area will be 259 utilized. In our proposed method, we use first-last fit policy to 260 find the available frequency slots. In other words, when the first 261 three-slot traffic request arrives, we use first fit policy to search 262 for the three available and consecutive frequency slots in FSA-3 and 263 common area. This means that we will first search FSA-3 of core one 264 and core two, then search FSA-3 of core four and core five until 265 there is no available frequency slots and we will search the common 266 area. When the second three-slot traffic request arrives, the last 267 fit policy is applied to find required slots in FSA-3 and common area. 268 That is to say, we take turns using the first fit policy and the last 269 fit policy in FSA and common area for the traffic requests that 270 demand the same number of slots. Because of the first-last fit policy, 271 we can make the distribution of traffic requests with same number of 272 frequency slots more balanced, while bringing fewer fragments. As a 273 result of the use of such frequency slots area concept and special 274 core selected policy, in dealing with a large number of traffic 275 requests with the same frequency slots number demanded the crosstalk 276 will be smaller. 278 6. Formal Syntax 280 The following syntax specification uses the augmented Backus-Naur 281 Form (BNF) as described in RFC-2234 [RFC2234]. 283 7. Security Considerations 285 This kind of information includes network topology, link state and 286 current utilization, as well as the capabilities of switches and 287 routers within the network, which is owing to that the information 288 should be protected from disclosure to unintended recipients. In 289 addition, the intentional modification of this information can 290 significantly affect network operations, particularly due to the 291 large capacity of the optical infrastructure has been controlled. 293 8. IANA Considerations 295 This informational document does not make any requests for IANA 296 action. 298 9. Conclusions 300 This document discussed a routing, spectrum and core assignment 301 method with dividing frequency slots area in SDM-EONs with 7-core MFC. 302 The simulation results suggest that the proposed method is effective 303 in reducing the path blocking probability and enhancing the spectrum 304 resource utilization. 306 10. References 308 10.1. Normative References 310 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 311 Levels", BCP 14, RFC 2119, March 1997. 313 [2] Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax 314 Specifications: ABNF", RFC 2234, Internet Mail Consortium and 315 Demon Internet Ltd., November 1997. 317 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 318 Requirement Levels", BCP 14, RFC 2119, March 1997. 320 [RFC2234] Crocker, D. and Overell, P.(Editors), "Augmented BNF for 321 Syntax Specifications: ABNF", RFC 2234, Internet Mail 322 Consortium and Demon Internet Ltd., November 1997. 324 10.2. Informative References 326 [3] Faber, T., Touch, J. and W. Yue, "The TIME-WAIT state in TCP 327 and Its Effect on Busy Servers", Proc. Infocom 1999 pp. 1573- 328 1583. 330 [Fab1999] Faber, T., Touch, J. and W. Yue, "The TIME-WAIT state in 331 TCP and Its Effect on Busy Servers", Proc. Infocom 1999 pp. 332 1573-1583. 334 11. Acknowledgments 336 This document is supported in part by the National Natural Science 337 Foundation of China (Nos.61601054, 61331008, 61701039 and 61571058), 338 the National Science Foundation for Outstanding Youth Scholars of 339 China (No.61622102) and Youth research and innovation program of 340 BUPT(2017RC14). 342 Authors' Addresses 344 Shanguo Huang 345 BUPT 346 No.10, Xitucheng Road,Haidian District 347 Beijing 100876 348 P.R.China 349 Phone: +8613693578265 350 Email: shghuang@bupt.edu.cn 352 Shan Yin 353 BUPT 354 No.10, Xitucheng Road,Haidian District 355 Beijing 100876 356 P.R.China 357 Phone: +8613488795778 358 Email: yinshan@bupt.edu.cn 360 Chenge Wang 361 BUPT 362 No.10, Xitucheng Road,Haidian District 363 Beijing 100876 364 P.R.China 365 Phone: +8618800122360 366 Email: wangchenge@bupt.edu.cn 368 Shuang Zhou 369 BUPT 370 No.10, Xitucheng Road,Haidian District 371 Beijing 100876 372 P.R.China 373 Phone: +8618101053965 374 Email: zs_yolanda@163.com