SimEON: an open-source elastic optical network simulator for academic and industrial purposes

In comparison with wavelength division multiplexing optical networks, elastic optical networks are much more flexible, presenting an efficient alternative to use the frequency spectrum to establish call requests in a scenario with different transmission bit rates and modulation schemes. Due to the variety of optical devices, node architectures and physical topologies, it is difficult to implement optical network prototypes to analyze operational scenarios in terms of blocking probability of call requests, the impact of capital and operational expenditures and energy consumption, for example. To our knowledge, there is no available open-source simulation tool exclusively for elastic optical networks in the literature. There are a few simulation tools that were used to obtain results for optical networks but most of their source codes are unavailable. The state of the art of these simulators and our developed simulation tool called Simulator for Elastic Optical Networks (SimEON) are presented. SimEON is an open-source software. It is developed under the GNU Lesser General Public License and takes into account principles of software engineering. In this article, we present the characteristics of our simulator, its architecture and considered parameters, along with some examples of the simulations that can be executed on it.     

Exact performance analytical model for spectrum allocation in flexible grid optical networks

Dynamic flexible grid optical networks have gained much attention because of the advantages of high spectrum efficiency and flexibility, while the performance analysis will be more complex compared with fixed grid optical networks. An analytical Markov model is first presented in the paper, which can exactly describe the stochastic characteristics of the spectrum allocation in flexible grid optical networks considering both random-fit and first-fit resource assignment policies. We focus on the effect of spectrum contiguous constraint which has not been systematically studied in respect of mathematical modeling, and three major properties of the model are presented and analyzed. The model can expose key performance features and act as the foundation of modeling the Routing and Spectrum Assignment (RSA) problem with diverse topologies. Two heuristic algorithms are also proposed to make it more tractable. Finally, several key parameters, such as blocking probability, resource utilization rate and fragmentation rate are presented and computed, and the corresponding Monte Carlo simulation results match closely with analytical results, which prove the correctness of this mathematical model.     

可变带宽光网络中多项式复杂度的频谱扫描路由算法

Optical Orthogonal Frequency Division Multiplexing (OOFDM) has been proposed as a highly spectrum-efficient modulation technique, which can provide flexible spectrum assignment with fine granularity. In OOFDM-based flexible optical networks, Routing and Spectrum Assignment (RSA) has become a key problem. However, widely used dynamic RSA schemes, such as Fixed Routing (FR) and K-shortest Paths (KSP) routing schemes, are not able to realize route computation based on the link state in-formation, thus leading to poor blocking performance and inefficient resource utilization. To solve this problem, Adaptive Routing (AR) schemes, e.g., the Entire Path Searching (EPS) scheme, have been proposed recently. These schemes have low blocking probability; however, since their computational complexities are factorial, they are not suitable for use in real networks. In this paper, we propose a novel Spectrum-Scan Routing (SSR) scheme in dynamic flexible optical networks. To the best of our knowledge, SSR is the first polynomial-time AR scheme that can realize adaptive shortest-route computation. Simulation results show that our proposed SSR scheme has lower blocking probability and higher resource utilization compared with FR and EPS. Moreover, the worst-case computational complexity of SSR increases linearly with the network scale of the torus topologies, making it applicable to real networks.     

弹性光网络基于区分降级服务和自适应调制的动态路由与频谱分配算法

面对高速发展的互联网应用,传统的路由与频谱分配(RSA)问题迎来新的挑战。融合降级服务(DS)技术的弹性光网络无疑为降低业务阻塞率,提高用户体验质量(QoE)提供了新方向。该文首先针对频谱资源的低效利用和DS导致的业务收益下降问题,建立以最小化频谱消耗和最小化DS等级、频次为联合优化目标的RSA问题的混合整数线性规划模型。随后,提出一种基于区分DS和自适应调制的动态RSA算法。该算法考虑业务等级的差异化,并整合自适应调制和DS技术。同时,设计区分业务等级的DS损失函数及DS窗口选择策略,为即将受阻业务分配理想的频谱位置和资源。此外,设计考虑频谱与收益均衡关系的网络收益函数,达到频谱资源高效利用,减少降级影响,提升网络收益的目的。最后,仿真验证了所提算法在业务阻塞率和网络收益等方面的优势。     

基于光森林的弹性光网络能效组播路由频谱分配策略

在弹性光网络中,光树传输组播可以节省链路代价,但较长的光树需要选择更低的调制等级,消耗更多的频谱资源和发射机功耗.提出一种基于遗传算法的光森林组播和光树重配置(GAMF-TR)优化组播的能效路由、调制格式和频谱分配(RMSA)策略.GAMF-TR策略设计染色体编码表示光森林的组播目的节点划分和光路径组合,通过染色体的基因位概率交叉和变异得到更多的光森林RMSA策略,设计了一个频谱分配效率和发射机功耗折中的适应度函数选择能效最高的光森林RMSA策略,并设计在网络资源充足时将组播从光森林重配置到光树传输,进一步减少发射机功耗的消耗.仿真结果表明:提出的GAMF-TR策略获得了组播的最低带宽阻塞率和最高能效性能.     

Exploiting IP‐layer traffic prediction analytics to allocate spectrum resources using swarm intelligence

Elastic optical networks emerge as a reliable backbone platform covering the next‐generation connectivity requirements. It consists of advanced enabling components that provide the ability for extensive configuration leading to performance improvement in many areas of interest. Higher layer analytics like data from IP traffic prediction can assist in the process of allocating resources at the optical layer. This way, light connections are established more efficiently while targeting specific performance goals. For that purpose, an algorithm is designed and evaluated that exploits traffic prediction of data transfers between nodes of an optical metro or backbone network. Next, it utilizes adaptive functionality based on particle swarm optimization to find paths with available spectrum resources. These resources can facilitate more efficiently the future traffic demand, since traffic prediction data are considered when finding the related paths. The innovative resource allocation method is evaluated using small and very large real topologies. It scales (in execution time and resource usage) according to node increase, executes in feasible time frames, and reduces transponder utilization resulting to increased energy efficiency.     

A novel partition-plane impairment aware routing and spectrum assignment algorithm in mixed line rates elastic optical networks

In mixed line rates elastic optical networks, different line rate signals can coexist on the same fiber. As different line rates coexist in the same fiber, the impairments, especially the cross-phase modulation (XPM), become more and more serious affecting the quality of transmission of signals. Moreover, the spectrum constraints limit the efficient allocation of spectrum resources. In this paper, we propose a novel spectrum Partition-topology Plane impairments aware routing and spectrum assignment algorithm to set up lightpaths for connection requests, therefore decreasing the XPM impairments and increasing spectrum utilization. The proposed algorithm can satisfy the spectrum constraints restriction and avoid the XPM impairment together. The simulation results show that the proposed algorithm can significantly improve the performance of networks in blocking probability and the spectrum efficiency.     

Dynamic RWA with FWM-induced crosstalk awareness and modulation format conversion in wavelength-routed optical networks

The constraint of signal transmission quality and network resources utilization in transparent optical networks are herein addressed through a representative cost function based upon an impairment-constraint-base routing (ICBR) approach, taking into account link capacity utilization and the nonlinear physical effect, in the primary instance due to Four-Wave Mixing (FWM)-induced crosstalk. The FWM effect is considered one of the most severe physical impairments for the future photonic networks since the accumulation of FWM crosstalk may cause a fatal degradation in the teletraffic network performance. This paper presents an added functionality to the network model design based on all-optical modulation format conversion from conventional on-off keying (OOK) to quadrature phase-shift keying (QPSK) sending more data within the same bandwidth while minimizing the blocking probability. The joint effect of physical impairment (i.e., FWM-induced crosstalk) awareness and two different modulation formats is considered through numerical simulations. The proposed scheme is expected to realize an all-optical transparent interconnection between networks that employ diverse modulation formats. Results show that the proposed FWM-aware Routing and Wavelength Assignment (RWA) algorithm leads to a more realistic system performance while giving a significant improvement on the network performance.     

Survivable elastic optical networks: survey and perspective (invited)

Elastic optical networks (EONs) have been receiving extensive attention because of their inherent flexibility and the efficiency with which they allocate fiber-bandwidth. For an EON, survivability is of crucial importance because of the very high bandwidth that it carries on each optical channel. In this article, we review the current state of the art of survivable EONs which reviews the literature to summarize the following aspects: (a) spectrum resource sharing among backup lightpaths, (b) sharing of high-speed optical transponders, (c) effect of spectrum conversion, (d) bandwidth squeezed restoration (BSR), (e) joint restoration by multiple sub-band optical channels, (f) multi-layer survivability, and (g) energy efficiency. Apart from a summary on the current research status, we also discuss open research issues which are important to survivable EONs from the perspectives of (a) impact of spectrum conversion, (b) impact of elastic optical transponder configuration, (c) impact of physical layer impairments and limitations, (d) protection-path-based spectrum defragmentation, and (e) network availability.     

节点中介性和频谱离散度感知虚拟光网络生存性协同映射

虚拟网络的映射策略影响弹性光网络(EON)资源可用性和网络生存性。该文提出一种基于节点间距离和频谱离散度感知的虚拟光网络生存性协同映射(CM-DSDA)算法,研究节点计算资源和拓扑位置中介性的光节点排序策略,设计频谱离散度方法评价链路频谱碎片化程度。在虚拟链路的生存性映射中,选择邻接已映射节点中消耗频隙数少且频谱离散度低的工作光路和保护光路协同映射虚拟网络。仿真结果表明所提算法能有效地提高EON的频谱占用率和减少带宽阻塞率。     

An effective method for blocking performance analysis of WDM all-optical networks

We propose a rational approximation (RA)-based algorithm to perform the blocking analysis of circuit-switched all-optical networks. Our algorithm can be applied to large networks with various topologies and routing and wavelength assignment algorithms. It can be applied to optical networks with either full, sparse, or no wavelength conversion. We also propose fixed-path wavelength assignment algorithms for networks with balanced and unbalanced traffic.     

Adaptive multilevel modulation for grooming in elastic cloud optical networks

In order to mitigate the mismatch of granularities between fixed grid and client traffic, the elastic optical network (EON) was proposed by using orthogonal frequency division multiplexing. In EONs, the bandwidth variable transponder adjusts the number of bits per symbol, so that an optical signal generates by using just enough sub-carriers each with appropriate modulation level. Owing to the advantage of line-rate adaption above, the application of cloud computing has witnessed rapid growth in EONs. However, bandwidth variable transponders consume more power compared with ordinary ones, which will lead to a power-thirsty EON if no effective measure is taken. As a result, the green grooming was proposed for EONs. Unfortunately, the adaptive multilevel modulation was neglected in the current works focusing on green grooming. Thus, in this paper, we design a novel modulation adaptive grooming with guaranteeing transmission performances in green EONs. The distance-adaptive spectrum resource allocation is applied to the green grooming algorithm previously designed by us for EONs. The simulation results show that the adaptive multilevel modulation plays an important role on saving spectrum and power consumption for the green grooming in EONs, because the spectral bandwidth can be saved by increasing the number of bits per symbol to transmit the same data rate.     

串扰感知的空分弹性光网络频谱转换器稀疏配置和资源分配方法

针对大容量多芯光纤空分复用弹性光网络(SDM-EON)中芯间串扰导致业务传输质量下降和阻塞率上升的问题,该文提出了节点稀疏配置频谱转换器降低芯间串扰的路由纤芯频谱分配方法。该方法根据网络中节点中介中心性稀疏配置频谱转换器。在业务路由阶段,设计综合考虑光路负载和节点频谱转换能力的光路选择的权重方法;为了降低串扰,在纤芯频谱分配阶段,设计纤芯分组和频谱分区分配方法;最后,针对串扰较大的业务,采用频谱转换以降低业务串扰和改善带宽阻塞率。仿真结果表明,所提算法能有效地提高频谱利用率,降低因芯间串扰导致的带宽阻塞率。     

All-optical networks with sparse wavelength conversion

Unlike broadcast-and-select networks, wavelength-routing networks offer the advantages of wavelength reuse and scalability and are thus suitable for wide-area networks (WANs) We study the effects of topological connectivity and wavelength conversion in circuit-switched all-optical wavelength-routing networks. A blocking analysis of such networks is given. We first propose an analytical framework for accurate analysis of networks with arbitrary topology. We then introduce a model for networks with a variable number of converters and analyze the effect of wavelength converter density on the blocking probability. This framework is applied to three regular network topologies that have varying levels of connectivity: the ring, the mesh-torus, and the hypercube. The results show that either a relatively small number of converters is sufficient for a certain level of performance or that conversion does not offer a significant advantage. The benefits of conversion are largely dependent on the network load, the number of available wavelengths, and the connectivity of the network. Finally, the tradeoff between physical connectivity, wavelength conversion, and the number of available wavelengths is studied through networks with random topologies     

The Role of Network Topologies in the Optical Core of IP-over-WDM Networks with Static Wavelength Routing

In this paper, we present a performance analysis of network topologies for the optical core of IP-over-WDM networks with static wavelength routing. The performance analysis is focused on regular degree four topologies, and, for comparison purposes, degree three topologies are also considered. It is shown that the increase of the nodal degree from three (degree three topology with smallest diameter) to four (degree four topology with smallest diameter) improves the network performance if a larger number of wavelengths per link is available. However, the influence of wavelength interchange on the nodal degree gain is small. The performance of regular degree four topologies with smallest diameter is also compared with the performance of mesh–torus topologies (which are also degree four topologies), and it is shown that the blocking probability of degree four topologies with smallest diameter is about two orders of magnitude lower than the blocking probability of mesh–torus topologies. It is also presented a performance comparison of WDM-based networks with nodal degrees ranging from two to five and it is shown that the increase of the nodal degree from two to three leads to high nodal degree gains, while de increase of the nodal degree from four to five leads to low nodal degree gains. These results show that degree three and degree four topologies are very attractive for use in the optical core of IP-over-WDM networks.     

An efficient network‐side path protection scheme in OFDM‐based elastic optical networks

Elastic optical networks (EONs) based on orthogonal frequency division multiplexing (OFDM) technologies are seen as a promising solution for next‐generation optical transport networks to support the rapidly growing and heterogeneous traffic. In EONs, the elastic bandwidth allocation and modulation format agilities combined with reconfiguration capabilities pave the new way for leveraging the network efficiency. In this paper, we recast the network‐side path protection in EONs considering the opportunities and challenges enabled by the flexible operation of OFDM technologies. For the first time, we propose to take advantages of the reconfiguration capabilities of OFDM transponders for adapting to transmission condition variations when switching from the working to protection path in network‐side protection. The idea is inspired by the observation that in reach‐diverse networks, the transmission margin between the working path and protection path of a connection might be large enough, and thus, the most spectrum‐efficient modulation format for each path could be separately tailored, rather than imposed by a common one based on the worse condition as with current fixed transmission technologies. We formulate survivable transparent network designs for both dedicated and shared path protection in the form of integer linear programming model taking into account our proposal for enabling different transmission operations between working and protection mode. Numerical results based on extensive simulations on a realistic network topology, COST239, are presented to highlight the benefits of our proposal compared to conventional approaches in terms of spectrum efficiency for un‐capacitated scenarios and improvements in blocking ratio for capacitated scenarios.     

ACO-based routing and spectrum allocation in flexible bandwidth networks

Optical networks with flexible bandwidth provisioning are a very promising networking architecture. It enables efficient resource utilization and supports heterogeneous bandwidth demands. In this paper, we focus on the dynamic routing and spectrum allocation (RSA) problem which emerges in such networks and propose a novel dynamic RSA algorithm by means of ant colony optimization (ACO). In our proposed algorithm, ants are launched to modify the routing table according to the length and the spectrum fragmentation information along the path. A simulation study is performed considering five algorithms in terms of blocking probability: WDM-based RWA approach, KSP-based RSA approach, Slot-based RSA algorithm, and our proposed ACO-based RSA approach. We then compare the deterioration degree of blocking probability by adding more types of line rate. Simulation results indicate that our proposed ACO-based RSA approach achieves lower blocking probability, complexity, and higher adaptability to more line rates mixture.     

An efficient hybrid protection scheme with shared/dedicated backup paths on elastic optical networks

Fast recovery and minimum utilization of resources are the two main criteria for determining the protection scheme quality. We address the problem of providing a hybrid protection approach on elastic optical networks under contiguity and continuity of available spectrum constraints. Two main hypotheses are used in this paper for backup paths computation. In the first case, it is assumed that backup paths resources are dedicated. In the second case, the assumption is that backup paths resources are available shared resources. The objective of the study is to minimize spectrum utilization to reduce blocking probability on a network. For this purpose, an efficient survivable Hybrid Protection Lightpath (HybPL) algorithm is proposed for providing shared or dedicated backup path protection based on the efficient energy calculation and resource availability. Traditional First-Fit and Best-Fit schemes are employed to search and assign the available spectrum resources. The simulation results show that HybPL presents better performance in terms of blocking probability, compared with the Minimum Resources Utilization Dedicated Protection (MRU-DP) algorithm which offers better performance than the Dedicated Protection (DP) algorithm.     

光树分割和共享光路合并优化任多播阻塞率

针对弹性光互联数据中心网络中任多播业务的频谱利用率低和带宽阻塞率高等问题,论文提出了一种基于光树分割和共享光路合并算法.该算法选择对光树最大长度和调制等级影响较小的树枝加入光树,使生成光树频谱代价最小.当光树传输所需频谱资源不足时,该算法将光树分割为可选较高调制等级的多子光树传输,提高频谱利用率.当网络中有足够资源时,设计一种基于链路共享度的将满足条件的子光树合并到光树上传输的机制以降低频谱消耗.仿真结果表明：论文所提算法具有较低的带宽阻塞率和较高的频谱利用率.     

Blocking in Wavelength-Routed Optical Networks With Heterogeneous Traffic

In this paper, we present a new analytical model that can give an accurate estimation of the blocking probabilities in wavelength-routed optical networks with heterogeneous traffic. By heterogeneous, we mean that each session offered to the network has its own traffic intensity and burstiness. In such cases, the blocking probability of a session is determined by the busy-wavelength distributions of the links seen at the arrival points of its calls. Thus, we first present two single-link models to estimate the arrival-point busy-wavelength distribution of a link with heterogeneous traffic: the full-population (FP) model and the reduced-population (RP) model. Both models are based on the BPP/M/W/W model, where the first two moments of an arbitrary session are matched by those of a birth–death process whose arrival rate linearly varies with the average number of busy wavelengths occupied by its own calls. We show that different sessions have different arrival-point busy-wavelength distributions depending on the burstiness of their traffic, i.e., a bursty session observes the link more congested than a smooth session. Next, we provide two extensions of the single-link models, the FP-full-load link-correlation model and the RP-reduced-load link-correlation model, to estimate the blocking probabilities of optical networks with heterogeneous traffic and sparse wavelength conversion. Both models employ the existing link-correlation models to take into account the occupied-wavelength-index correlation between two adjacent links. By comparing the results from the models with simulation results, we demonstrate that both models well approximate the blocking probabilities of individual sessions, as well as the network-wide blocking probability, for a wide range of traffic intensity, burstiness, and heterogeneity.