Networking Group Sh.G. Huang Internet Draft S. Yin Intended status: Informational BUPT Expires: November 2018 Ch.G Wang S. Zhou BUPT May 20, 2018 RSCA method with Dividing Frequency Slots Area in Space Division Multiplexing Elastic Optical Networks draft-huang-rsca-sdm-eon-00 Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. 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 November 21, 2018. Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Huang, et al. Expires November 21, 2018 [Page 1] Internet-Draft rsca-sdm-eon Problem May 2018 Legal Provisions and are provided without warranty as described in the Simplified BSD License. Abstract This documentary provides a routing, spectrum and core assignment method with the dividing frequency slots area for space division multiplexing elastic optical networks. This effective RSCA method to solve this problem better. The proposed method utilizes the Frequency Slots Area (FSA) concept and first-last fit policy of frequency slots assignment to have less spectrum fragments, lower crosstalk, smaller traffic blocking probability and higher spectrum resource utilization. Table of Contents 1. Introduction ................................................ 2 1.1. Terminology ............................................ 3 2. Conventions used in this document ............................ 3 3. Overview ...................................................... 4 3.1. Elastic Optical Networks ................................ 4 3.2. Multi-Core Fiber ........................................ 4 4. RSCA ........................................................ 5 5. The proposed spectrum and core assignment method ............. 5 6. Formal Syntax ............................................... 7 7. Security Considerations ...................................... 7 8. IANA Considerations ......................................... 7 9. Conclusions ................................................. 7 10. References ................................................. 7 10.1. Normative References ................................... 7 10.2. Informative References ................................. 8 11. Acknowledgments ............................................ 8 1. Introduction With the rapid development of Internet technology and the emergence of new applications such as intense social networking, real-time gaming, High Definition audio-video streaming and cloud computing, the demand for network capacity has increased greatly. The capacity of traditional single-mode fiber is close to its physical capacity limit, so the SDM technology that can greatly improve the network capacity has received more and more attention. In SDM technology, MCF is one of the most promising technology. On the other hand, for the sake of flexible and effective use of spectrum resources, EON has been widely accepted as the next generation high-speed network. In the elastic optical network, the spectrum resources are divided into finer frequency slots, which can be more flexible and effective used Huang, et al. Expires November 21, 2018 [Page 2] Internet-Draft rsca-sdm-eon Problem May 2018 by traffic requests. In elastic optical networks, spectrum resources are assigned flexibly according to connections' requirements. This flexibility based on fine-grained resource provisioning can reduce the amount of spectrum resources wasted, compared with traditional rigid spectrum assignments. At the network level, the RSA problem is the most important problem concerning elastic optical networks. There are two continuity constraints for an assigned spectrum in the RSA problem. These constraints require the same and continuous spectrum to be assigned for all links on the selected transmission route if there is no wavelength converter. Because it is necessary to satisfy the spectral constraints of the RSA problem according to traffic demands, which change dynamically, dynamic resource allocation can effectively improve the performance of optical networks. The advantage of SDM-EONs is that it greatly improves the capacity of the network, allowing for more flexible and efficient use of spectrum resources. However, it brings the RSCA problem with serious crosstalk and high computing complexity. Crosstalk refers to the mutual interference generated by the transmission of signals on the same frequency between adjacent cores. With the increasing number of cores in the fiber, the core-pitch is getting smaller and smaller, and the crosstalk between adjacent cores is becoming more and more serious. At the same time, compared to the traditional EONs, the new core dimension in MCF-EONs makes its computational complexity higher. However, in the RSCA problem, the impact of inter-core crosstalk can be alleviated by properly assigning the core and spectrum resources to requests. Therefore, how to solve the RSCA problem effectively in SDM-EON is a challenge cannot be ignored. 1.1. Terminology SDM: Space Division multiplexing. EON: Elastic Optical Network. RSA: Routing and spectrum assignment problem. RSCA: Routing, Spectrum and Core Assignment problem. FSA: Frequency Slots Area. 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 RFC 2119 [RFC2119]. Huang, et al. Expires November 21, 2018 [Page 3] Internet-Draft rsca-sdm-eon Problem May 2018 3. Overview In elastic optical network, the traffic requests are constantly changing with time, so it is very important to choose a dynamic solution to the RSCA problem. However, with the continuous establishment and release of the traffic requests, there will be fragments between the frequency slots. In order to improve the utilization of spectrum resources in SDM-EON, it is essential to solve the problem of spectrum fragmentation. 3.1. Elastic Optical Networks Elastic optical network is different with traditional wavelength- division multiplexing (WDM) network because of the flexible use of spectrum resource. In traditional WDM networks, different traffic requests are assigned with the same fixed spectrum grid. Therefore, if the transmission distance of the request is short and demands less spectrum resource, there will be a lot of spectrum resource wasted in the fixed grid. In elastic optical network, the spectrum resource is allocated to the traffic request by flexible grid. That is to say, the network can choose the modulation format flexibly according to the length of the optical transmission route to save the spectrum resource. For example, when the transmission distance of the traffic is short, the network can choose the modulation formats with high spectrum utilization, such as 16-quadrature amplitude modulation (QAM) and 64-QAM, so that the resource utilization of the network can be improved. On the other hand, if the requested transmission distance of the traffic is long, the network can choose a modulation format with lower spectrum resource utilization, such as quadrature phase- shift keying (QPSK). 3.2. Multi-Core Fiber Because the transmission capacity of single-mode optical fiber is close to its physical limit, in order to improve the network capacity further, SDM has been widely concerned recently. MCF is one of the most promising transmission technology in SDM system. MCF using single-mode optical fibers is considered to greatly improve the transmission capacity of the network. However, one of the major problems with MCF is the physical impairment of transmitted signals due to crosstalk between cores during transmission. Large crosstalk occurs when the signals are transmitted in the same frequency on adjacent cores. The smaller the distance of the cores, the more serious the crosstalk will be. As shown in Fig.1, since 1 is used in both the adjacent core one and core two, large crosstalk occurs between the core one and core two. Since core one is not adjacent to core three, even if they both use 2, the crosstalk between them is Huang, et al. Expires November 21, 2018 [Page 4] Internet-Draft rsca-sdm-eon Problem May 2018 much lower than the crosstalk between cores one and three. Normally, we can ignore the effects of these low crosstalk. 4. RSCA The RSA problem is the most important part of the elastic optical network. In the same way, RSCA is the most important part of EDM-EON. In the traditional WDM network, wavelength channel is the basic unit of resource allocation. Nevertheless, in the elastic optical network basic unit of resource allocation is the frequency slot. The RSA problem in EON is equivalent to the Routing and Wavelength Assignment (RWA) problem in the traditional WDM network. However, due to the flexible resource allocation method of elastic optical network and the application of SDM technology, the RSCA problem in SDM-EON becomes more complex and challenging. In the traditional WDM network, there is a wavelength continuity constraint, that is, the network must select the same wavelength channel for each link in the transmission route. In elastic optical network, there is a similar continuity constraint for frequency slot. In addition, there is a spectrum contiguity constraint. Spectrum contiguity constraint ensures that the assigned frequency slots have to be consecutive in the spectrum resources of the fiber. Spectrum continuity constraint refers to the frequency slots used by each link on the selected routing path have to be same. According to the transmission distance of traffic requests, the elastic optical network selects different modulation formats to utilize spectrum resources effectively, and determines the number of consecutive frequency slots needed for transmission. In elastic optical network, the traffic requests are constantly changing with time, so it is very important to choose a dynamic solution to the RSCA problem. However, with the continuous establishment and release of the traffic requests, there will be fragments between the frequency slots. In order to improve the utilization of spectrum resources in SDM-EON, it is essential to solve the problem of spectrum fragmentation. 5. The proposed spectrum and core assignment method Through routing algorithm and wavelength assignment algorithm, we calculate the K feasible routing of a specific business wavelength. K feasible routing pathes are arranged according to preset priority, among them, the ith routing is recorded as Ri , i=1,2,3 We choose the first reachable optical path and calculate the output power and OSNR value of the first path, and do the following operations Huang, et al. Expires November 21, 2018 [Page 5] Internet-Draft rsca-sdm-eon Problem May 2018 In this draft, we use a k-shortest path algorithm based on Yen's ranking loopless paths algorithm to solve the routing problem .When a traffic request arrives, we use the routing algorithm to calculate k- shortest end-to-end routing paths for it. Then we select the path in order and process the spectrum and core assignment method. If no one path can meet the two constraints, the traffic request will be blocked. In SDM-EONs, it is more difficult to provision huger demands with satisfying continuity constraints due to fragmentation issue . To deal with it, we propose that the spectrum resource of the 7-core MCFs can be divided into several Frequency Slots Areas. This division reduces the blocking probability. Fig. 1 shows the flowchart of the proposed method. The 7-core MCF can be divided into several different areas according to the number of slots required for traffic requests. In the example, the number of slots required for traffic requests is three, four and five respectively. The first half of the core one, core two and the second half of them are divided into Frequency Slots Area of three (FSA-3) and Frequency Slots Area of five (FSA-5), respectively. The first half of the core five, core six is FSA-5, and the second half is divided into FSA-3.Then we divide the first half and second half of core three and core four into two different Frequency Slots Areas of four (FSA-4). In the last, the remaining entire core seven can be utilized by all the traffic with different frequency slots demand as a common area. When the traffic request needs three frequency slots, only the available frequency slots in FSA-3 and common area will be utilized. In our proposed method, we use first-last fit policy to find the available frequency slots. In other words, when the first three-slot traffic request arrives, we use first fit policy to search for the three available and consecutive frequency slots in FSA-3 and common area. This means that we will first search FSA-3 of core one and core two, then search FSA-3 of core four and core five until there is no available frequency slots and we will search the common area. When the second three-slot traffic request arrives, the last fit policy is applied to find required slots in FSA-3 and common area. That is to say, we take turns using the first fit policy and the last fit policy in FSA and common area for the traffic requests that demand the same number of slots. Because of the first-last fit policy, we can make the distribution of traffic requests with same number of frequency slots more balanced, while bringing fewer fragments. As a result of the use of such frequency slots area concept and special core selected policy, in dealing with a large number of traffic requests with the same frequency slots number demanded the crosstalk will be smaller. Huang, et al. Expires November 21, 2018 [Page 6] Internet-Draft rsca-sdm-eon Problem May 2018 6. Formal Syntax The following syntax specification uses the augmented Backus-Naur Form (BNF) as described in RFC-2234 [RFC2234]. 7. Security Considerations This kind of information includes network topology, link state and current utilization, as well as the capabilities of switches and routers within the network, which is owing to that the information should be protected from disclosure to unintended recipients. In addition, the intentional modification of this information can significantly affect network operations, particularly due to the large capacity of the optical infrastructure has been controlled. 8. IANA Considerations This informational document does not make any requests for IANA action. 9. Conclusions This document discussed a routing, spectrum and core assignment method with dividing frequency slots area in SDM-EONs with 7-core MFC. The simulation results suggest that the proposed method is effective in reducing the path blocking probability and enhancing the spectrum resource utilization. 10. References 10.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, Internet Mail Consortium and Demon Internet Ltd., November 1997. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2234] Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, Internet Mail Consortium and Demon Internet Ltd., November 1997. Huang, et al. Expires November 21, 2018 [Page 7] Internet-Draft rsca-sdm-eon Problem May 2018 10.2. Informative References [3] Faber, T., Touch, J. and W. Yue, "The TIME-WAIT state in TCP and Its Effect on Busy Servers", Proc. Infocom 1999 pp. 1573- 1583. [Fab1999] Faber, T., Touch, J. and W. Yue, "The TIME-WAIT state in TCP and Its Effect on Busy Servers", Proc. Infocom 1999 pp. 1573-1583. 11. Acknowledgments This document is supported in part by the National Natural Science Foundation of China (Nos.61601054, 61331008, 61701039 and 61571058), the National Science Foundation for Outstanding Youth Scholars of China (No.61622102) and Youth research and innovation program of BUPT(2017RC14). Huang, et al. Expires November 21, 2018 [Page 8] Internet-Draft rsca-sdm-eon Problem May 2018 Authors' Addresses Shanguo Huang BUPT No.10, Xitucheng Road,Haidian District Beijing 100876 P.R.China Phone: +8613693578265 Email: shghuang@bupt.edu.cn Shan Yin BUPT No.10, Xitucheng Road,Haidian District Beijing 100876 P.R.China Phone: +8613488795778 Email: yinshan@bupt.edu.cn Chenge Wang BUPT No.10, Xitucheng Road,Haidian District Beijing 100876 P.R.China Phone: +8618800122360 Email: wangchenge@bupt.edu.cn Shuang Zhou BUPT No.10, Xitucheng Road,Haidian District Beijing 100876 P.R.China Phone: +8618101053965 Email: zs_yolanda@163.com Huang, et al. Expires November 21, 2018 [Page 9]