75 research outputs found

    Spectrum Allocation Suppressing Fragmentation Proactively in Elastic Optical Networks

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    エラスティック光ネットワーク(EON: Elastic Optical Network) において,帯域フラグメンテーションは,サブキャリアスロットのセットにおける未使用である未整列・非連続のサブキャリアの存在によって生じる。コネクションが使用する波長は,連続したサブキャリアスロットに割り当てられなければならないので,これらの未整列・非連続サブキャリアスロットは,帯域ブロッキングの原因となる。本論文はエラスティック光ネットワークにおけるスペクトル分断を抑制するスペクトル割り当てを提案する。2つ方式、サブキャリアスロット分割方式とfirst-last-exact fit 割り当てポリシー、が提示された。1つ目の方式には、1 つの同一のリンクを共有していないコネクションは同じパティションに割り当てられて、同一のリンクを使用するコネクションは別のパティションに割り当てられた。こうしてより多くの整列サブキャリアスロットを生成し。また、奇数インデックスのパティションはfirst fit波長割り当てポリシーを採用して、偶数インデックスのパティションはlast-fit波長割り当てポリシーを採用した。こうしてより多くの連続したサブキャリアスロットを生成し。2つ目の方式には、1 つの同一のリンクを共有していないコネクションはfirst-exact fit波長割り当てポリシーを採用して、同一のリンクを使用するコネクションはlast-exact fit波長割り当てポリシーを採用した。こうしてもより多くの整列・連続したサブキャリアスロットを生成し。提案方式は,より多くの整列・連続したサブキャリアスロットを生成し,帯域ブロッキングを削減する。シミュレーション結果により従来方式と比べ,帯域ブロッキングを削減することが定量的に示されている。電気通信大学201

    Optical Network Virtualisation using Multi-technology Monitoring and SDN-enabled Optical Transceiver

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    We introduce the real-time multi-technology transport layer monitoring to facilitate the coordinated virtualisation of optical and Ethernet networks supported by optical virtualise-able transceivers (V-BVT). A monitoring and network resource configuration scheme is proposed to include the hardware monitoring in both Ethernet and Optical layers. The scheme depicts the data and control interactions among multiple network layers under the software defined network (SDN) background, as well as the application that analyses the monitored data obtained from the database. We also present a re-configuration algorithm to adaptively modify the composition of virtual optical networks based on two criteria. The proposed monitoring scheme is experimentally demonstrated with OpenFlow (OF) extensions for a holistic (re-)configuration across both layers in Ethernet switches and V-BVTs

    Routing, Modulation and Spectrum Assignment Algorithm Using Multi-Path Routing and Best-Fit

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    Producción CientíficaElastic Optical Networks (EONs) are a promising optical technology to deal with the ever-increasing traffic and the vast number of connected devices of the next generation of the Internet, associated to paradigms like the Internet of Things (IoT), the Tactile Internet or the Industry 4.0, to name just a few. In this kind of optical network, each optical circuit or lightpath is provisioned by means of superchannels of variable bandwidth. In this manner, only the necessary bandwidth to accommodate the demand is allocated, improving the spectrum usage. When establishing a connection, the EON control layer determines the modulation format to be used and allocates a portion of the spectrum in a sequence of fibers from the source to the destination node providing the user-demanded bandwidth. This is known as the routing, modulation level and spectrum assignment (RMSA) problem. In this work, we firstly review the most important contributions in that area, and then, we propose a novel RMSA algorithm, multi-path best-fit (MP-BF), which uses a split spectrum multi-path strategy together with a spectrum assignment technique (best-fit), and which jointly exploit the flexibility of EONs. A simulation study has been conducted comparing the performance of EONs when using MP-BF with other proposals from the literature. The results of this study show that, by using MP-BF, the network can increase its performance in terms of lightpath request blocking ratio and supported traffic load, without affecting the energy per bit or the computation time required to find a solution

    Real-time DSP-enabled digital subcarrier cross-connect (DSXC) for optical communication networks

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    Elastic optical networking (EON) is intended to offer flexible channel wavelength granularity to meet the requirement of high spectral efficiency (SE) in today’s optical networks. However, optical cross-connects (OXC) and switches based on optical wavelength division multiplexing (WDM) are not flexible enough due to the coarse bandwidth granularity imposed by optical filtering. Thus, OXC may not meet the requirements of many applications which require finer bandwidth granularities than that carried by an entire wavelength channel. In order to achieve highly flexible and fine enough bandwidth granularities, electrical digital subcarrier cross-connect (DSXC) can be utilized in EON. As presented in this dissertation, my research work focuses on the investigation and implementation of real-time digital signal processing (DSP) enabled DSXC which can dynamically assign both bandwidth and power to each individual sub-wavelength channel, known as subcarrier. This DSXC is based on digital subcarrier multiplexing (DSCM), which is a frequency division multiplexing (FDM) technique that multiplexes a large number of digitally created subcarriers on each optical wavelength. Compared with OXC based on optical WDM, DSXC based on DSCM has much finer bandwidth granularities and flexibilities for dynamic bandwidth allocation. Based on a field programmable gate array (FPGA) hardware platform, we have designed and implemented a real-time DSP-enabled DSXC which uses Nyquist FDM as the multiplexing scheme. For the first time, we demonstrated real-time DSP enabled real-time DSXC which uses resampling filters for channel selection and frequency translation. This circuit-based DSXC supports flexible and fine data-rate subcarrier channel granularities, offering a low latency data plane, transparency to modulation formats, and the capability of compensating transmission impairments in the digital domain. The experimentally demonstrated 8×8 DSXC makes use of a Virtex-7 FPGA platform, which supports any-to-any switching of eight subcarrier channels with mixed modulation formats and data rates. Digital resampling filters, which enable frequency selections and translations of multiple subcarrier channels, have much lower DSP complexity and reduced FPGA resources requirements (DSP slices used in FPGA) in comparison to the traditional technique based on I/Q mixing and filtering. We have also investigated the feasibility of using distributed arithmetic (DA) for real-time DSXC to completely eliminate the usage of DSP slices in FPGA implementation. For the first time, we experimentally demonstrated the implementation of real-time frequency translation and channel selection based on the DA architecture in the same FPGA platform. Compared with resampling filters that leverage multipliers, the DA-based approach eliminates the need of DSP slices in the FPGA implementation and significantly reduces the hardware cost. In addition, with a processing latency that equals to a few clock cycles, a DA-based resampling filter is significantly faster when compared to a conventional direct-structured FIR filter whose overall latency is proportional to the filter order. The DA-based DSXC is, therefore, able to achieve not only the improved spectral efficiency, programmability of multiple orthogonal subcarrier channels, and low hardware resources requirements, but also much reduced cross-connect switching latency when implemented in a real-time DSP hardware platform. This reduced latency can be critically important for time-sensitive applications such as 5G mobile fronthaul, cloud radio access network (C-RAN), cloud-based robot control, tele-surgery and network gaming

    エラスティック光ネットワークにおけるトラヒック収容性を向上させるための無瞬断デフラグメンテーション

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    In elastic optical networks (EONs), a major obstacle to using the spectrum resources efficiently is spectrum fragmentation. Much of the research activities in EONs focuses on finding defragmentation methods which remove the spectrum fragmentation. Among the defragmentation methods presented in the literature, hitless defragmentation has been introduced as an approach to limit the spectrum fragmentation in elastic optical networks without traffic disruption. It facilitates the accommodation of new request by creating large spectrum blocks, as it moves active lightpaths (retuning) to fill in gaps left in the spectrum by expired ones. Nevertheless, hitless defragmentation witnesses limitations for gradual retuning with the conventionally used first fit allocation. The first fit allocation stacks all lightpaths to the lower end of the spectrum. This leads to a large number of lightpaths that need to be retuned and are subject to interfere with each other\u27s retuning. This thesis presents two schemes, which are based on hitless defragmentation, to increase the admissible traffic in EONs. Firstly, a route partitioning scheme for hitless defragmentation in default EONs is presented. The proposed scheme uses route partitioning with the first-last fit allocation to increase the possibilities of lightpath retuning by avoiding the retuning interference among lightpaths. The first-last fit allocation is used to set a bipartition with one partition allocated with the first fit and the second with the last fit. Lightpaths that are allocated on different partitions cannot interfere with each other. Thus the route partitioning avoids the interferences among lightpaths when retuning. The route partitioning problem is defined as an optimization problem to minimize the total interferences. Secondly, this thesis presents a defragmentation scheme using path exchanging in 1+1 path protected EONs. For 1+1 path protection, conventional defragmentation approaches consider designated primary and backup paths. This exposes the spectrum to fragmentations induced by the primary lightpaths, which are not to be disturbed in order to achieve hitless defragmentation. The presented path exchanging scheme exchanges the path function of the 1+1 protection with the primary toggling to the backup state while the backup becomes the primary. This allows both lightpaths to be reallocated during the defragmentation process while they work as backup, offering hitless defragmentation. Considering path exchanging, a static spectrum reallocation optimization problem that minimizes the spectrum fragmentation while limiting the number of path exchanging and reallocation operations is defined. For each of the presented schemes, after the problem is defined as an optimization problem, it is then formulated as an integer linear programming problem (ILP). A decision version of each defined problem is proven NP-complete. A heuristic algorithm is then introduced for large networks, where the ILP used to represent the problem is not tractable. The simulation results show that the proposed schemes outperform the conventional ones and improve the total admissible traffic.電気通信大学201

    エラスティック光ネットワークにおけるトラヒック収容性を向上させるための無瞬断デフラグメンテーション

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    In elastic optical networks (EONs), a major obstacle to using the spectrum resources efficiently is spectrum fragmentation. Much of the research activities in EONs focuses on finding defragmentation methods which remove the spectrum fragmentation. Among the defragmentation methods presented in the literature, hitless defragmentation has been introduced as an approach to limit the spectrum fragmentation in elastic optical networks without traffic disruption. It facilitates the accommodation of new request by creating large spectrum blocks, as it moves active lightpaths (retuning) to fill in gaps left in the spectrum by expired ones. Nevertheless, hitless defragmentation witnesses limitations for gradual retuning with the conventionally used first fit allocation. The first fit allocation stacks all lightpaths to the lower end of the spectrum. This leads to a large number of lightpaths that need to be retuned and are subject to interfere with each other\u27s retuning. This thesis presents two schemes, which are based on hitless defragmentation, to increase the admissible traffic in EONs. Firstly, a route partitioning scheme for hitless defragmentation in default EONs is presented. The proposed scheme uses route partitioning with the first-last fit allocation to increase the possibilities of lightpath retuning by avoiding the retuning interference among lightpaths. The first-last fit allocation is used to set a bipartition with one partition allocated with the first fit and the second with the last fit. Lightpaths that are allocated on different partitions cannot interfere with each other. Thus the route partitioning avoids the interferences among lightpaths when retuning. The route partitioning problem is defined as an optimization problem to minimize the total interferences. Secondly, this thesis presents a defragmentation scheme using path exchanging in 1+1 path protected EONs. For 1+1 path protection, conventional defragmentation approaches consider designated primary and backup paths. This exposes the spectrum to fragmentations induced by the primary lightpaths, which are not to be disturbed in order to achieve hitless defragmentation. The presented path exchanging scheme exchanges the path function of the 1+1 protection with the primary toggling to the backup state while the backup becomes the primary. This allows both lightpaths to be reallocated during the defragmentation process while they work as backup, offering hitless defragmentation. Considering path exchanging, a static spectrum reallocation optimization problem that minimizes the spectrum fragmentation while limiting the number of path exchanging and reallocation operations is defined. For each of the presented schemes, after the problem is defined as an optimization problem, it is then formulated as an integer linear programming problem (ILP). A decision version of each defined problem is proven NP-complete. A heuristic algorithm is then introduced for large networks, where the ILP used to represent the problem is not tractable. The simulation results show that the proposed schemes outperform the conventional ones and improve the total admissible traffic.電気通信大学201

    Efficient Spectrum Utilization in Large-Scale RWA and RSA Problems

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    While the Routing and Wavelength Assignment (RWA) problem has been widely studied, very few studies attempt to solve realistic size instances, namely, with 100 wavelengths per fiber and a few hundred nodes. Indeed, state of the art is closer to around 20 nodes and 30 wavelengths. In this study, we are interested in reducing the gap between realistic data sets and testbed instances, using exact methods. We propose different algorithms that lead to solve exactly or near exactly much larger instances than in the literature, with up to 150 wavelengths and 90 nodes. Extensive numerical experiences are conducted on both the static and the dynamic cases. For the latter, we investigate how much bandwidth is wasted when no lightpath re-arrangement is allowed, and compare it with the number of lightpath re-arrangement it requires in order to fully maximize the grade of service. Results show that the amount of lightpath re-arrangement remains very small in comparison to the amount of wasted bandwidth if not done. The Routing and Spectrum Assignment (RSA) problem is a much more difficult problem than RWA, considered in elastic optical networks. Although investigated extensively, there is still a gap between the size of the instances that can be solved using the current heuristic or exact algorithms, and the size of the instances arising in the industry. As the second objective of this study, we aim to reduce the gap between the two, using a new mathematical modeling, and compare its performance with the best previous algorithms/models on realistic data instances
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