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Networking Group                                             Sh.G. Huang
Internet Draft                                                    S. Yin
Intended status: Informational                                      BUPT
Expires: November 2019                                         Ch.G Wang
                                                                 S. Zhou
                                                                    BUPT
                                                            May 23, 2019


      RSCA method with Dividing Frequency Slots Area in Space Division
                   Multiplexing Elastic Optical Networks
                        draft-huang-rsca-sdm-eon-02


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   Legal Provisions and are provided without warranty as described in
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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


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   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].



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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


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   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



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   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.





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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.




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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).































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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












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