Optical Switching and Networking最新文献

The advent of Elastic Optical Networks (EON) has led to significant improvements in optical network spectrum utilization when compared to Wavelength Division Multiplexing Optical Networks. However, the EON brought challenges to be explored, notably the Power, Routing, Modulation Level and Spectrum Assignment (PRMLSA) problem. This article aims to explore techniques for the PRMLSA problem, being developed two strategies named Shortest and Least Allocated (SLA) Path and Route-Based Spectrum Assignment (RBSA), which, respectively, include the link power spectral density inspection dynamic for routing and a physical layer factor (distance traveled) for Spectrum Assignment. Furthermore, a simplified version of the Adaptive Power Assignment (APA) [1] algorithm is presented, in which a power value between the minimum necessary and the maximum allowed is assigned to the signal. The simultaneous use of the SLA and RBSA algorithms resulted in locks of up to 0.00132%, being more than 10 times lower than the 0.0164% of the Shortest-Path and First-Fit algorithms. While the simplification of the APA resulted in 18.38% of the execution time of its respective original version, but with an increase in the blocking probability, which went from 0.016% to 0.031%, despite still being below conventional techniques, as the Constant Power Assignment strategy.

This paper proposes a novel joint resource allocation technique for flexible-grid systems by utilizing non-dominant sort genetic algorithm (NSGA-II) in a multi-objective optimization framework. It pioneers the implementation of an evolutionary mechanism to optimize resources as means of mitigation of physical layer impairments. This investigation initially introduces a proposal in which bandwidth reduction, maximization of the minimum signal-to-noise ratio (SNR) margin, and minimization/maximization of the sum of SNR margins are studied under dual-objective Pareto analysis in the link-level scenario. Later, the technique extends existing provisioning strategies for network planning by targeting the reduction of blocking and spectral utilization of optical connections.

In this work, we present a co-evolutionary genetic (CEGA) algorithm to adapt the optical launch powers and optimize the signal-to-noise ratio (SNR) values based on maximizing the minimum SNR margin. The introduced co-evolutionary algorithm provides lower computational complexity rather than convex optimization and linear programming techniques, applicable for both static and time-critical dynamic networking. The enhanced Gaussian noise nonlinear model is exploited to take the physical-layer impairments into account, considering networks with partial spectrum utilization. To optimize the minimum SNR margin, we formulate the power allocation problem as a minimax optimization problem. To this end, a two-space genetic algorithm (GA) is proposed to reduce the computational complexity. The obtained results demonstrate that the introduced co-evolutionary algorithm outperforms the common optimization methods in terms of run time. It is shown that the computational complexity of proposed co-evolutionary algorithm is significantly lower than convex and single-space evolutionary approaches by several orders of magnitude. Moreover, the minimum SNR margin is improved by about 2.4 dB compared to a flat launch power optimization.

Space-division multiplexing (SDM) is regarded as one of the most promising technologies to satisfy the explosively growing internet traffic. Elastic optical networks with SDM is one of the newest network architectures for network planning in the future. However, the resource allocation problem in these networks becomes more complicated due to the expansion of spatial dimensions. In this paper, we propose a novel channel-based integer linear programming (ILP) model for the problem of routing, space, and spectrum assignment (RSSA) in consideration of space lane change in SDM-EON. To evaluate our model, we make a comparison with the slot-based model [15] via simulation experiments. Different spatial switching granularities are considered in our performance evaluation because they will greatly change the detailed results of allocation. By the numerical results, we find that our novel model has an overwhelming advantage over the previous slot-based one in computing time for the optimization process.

Inter-core crosstalk causes severe signal impairment in Space Division Multiplexing Elastic Optical Networks (SDM-EON) with multi-core fibre (MCF). In order to mitigate the influence of crosstalk between cores, bidirectional MCF is used. SDM-EON has dramatically increased the network bandwidth and is the mainstream trend of future communications, but the overall cost of such an SDM-EON will increase with traditional hard-connected node structures. On-demand architecture node (AoD) in SDM-EON can dynamically select modes based on incoming services with less cost than traditional node. Although bidirectional multi-core optical fibres can mitigate the impact of crosstalk between adjacent cores, it is still necessary to develop appropriate routing, spectrum, and core assignment strategies to reduce the impact of crosstalk. In addition, the resource allocation strategy will affect the type of on-demand architecture node. This paper develops a core selection method for classified services on a multi-dimensional optical network with bidirectional multi-core fibres. It also proposes an on-demand architecture node suitable for this services classification scheme. According to the proposed core classification method, a routing and resource allocation algorithm that considers the impact of spectrum fragmentation and crosstalk between cores is proposed. The final simulation results prove that the algorithm is beneficial to improve network performance.

The Internet is a collection of interconnected Autonomous Systems (ASes) that use the Border Gateway Protocol (BGP) to exchange reachability information. In this regard, BGP stability and scalability in the inter-domain scope have been matters of major concern for many years, and network engineers have been applying several techniques to cope with these issues. BGP is also used intra-domain (internal BGP - iBGP), to disseminate reachability information inside each AS, and works together with the Interior Gateway Protocols (IGPs) such as OSPF or IS-IS, to build routing tables. Route reflection is a widely adopted technique to tackle BGP scalability in the intra-domain scope, and choosing which routers will play the reflector role and which BGP sessions will be established among reflectors and clients (i.e. the routers which are not elected as reflectors), building an overlay of iBGP sessions, is known as the iBGP overlay design problem. The design of an optimal iBGP overlay is known to be a NP-Hard problem, and we proposed solutions for pure IP networks (i.e. best effort traffic forwarding) in our previous work. However, most Internet providers implement their backbones by combining IP routing with MPLS (Multiprotocol Label Switching) for QoS-aware traffic forwarding. MPLS forwarding incorporates traffic engineering and more efficient failover mechanisms; under this traffic forwarding paradigm, the design of traffic-engineered Label Switched Paths (LSPs, also referred as MPLS tunnels) shall be combined with the aforementioned iBGP overlay design. The present work introduces a coordinated design of both the iBGP overlay and the IP/MPLS substrates. Our contribution is the proposal of an optimal and resilient topology design for an IP/MPLS Internet backbone, which takes advantage of traffic engineering features to optimize the demands, while guaranteeing iBGP overlay optimality. We present a complete solution for a real world scenario, and we study the scalability of the solution for synthetic topologies, achieving encouraging results.

This work considers the joint problem of securing confidential demands against eavesdropping attacks and protecting the network against link failures in elastic optical networks (EONs). Network coding is used to provide security for confidential connections by encrypting the data through XOR operations at the physical layer with other established connections in the network. Backup paths are also computed for protecting the primary path of the confidential connections, while ensuring that the level of security for the confidential demands is preserved in case of a link failure on the primary path or on any of the paths involved in the XOR process. A realistic network scenario is modeled, where four different classes of connections are considered with respect to their protection and security requirements, while a combination of novel integer linear programming (ILP) and heuristic algorithms are used to establish each class of demands in the network. The proposed algorithms are evaluated in terms of spectrum utilization, network blocking, and level of security provided. From the results obtained it is evident that confidential connections can be transmitted in a secure manner, while for the classes that require both security and protection, the connections retain their required level of security in the event of any single link failure in the network.

For several decades, optical networks, due to their high capacity and long-distance transmission range, have been used as the major communication technology to serve network traffic, especially in the core and metro segments of communication networks. Unfortunately, our society has often experienced how the correct functioning of these critical infrastructures can be substantially hindered by massive failures triggered by natural disasters, weather-related disruptions and malicious human activities.

In this position paper, we discuss the impact on optical networks of all major classes of disaster events mentioned above, and we overview recent relevant techniques that have been proposed to increase the disaster resilience of optical networks against the various classes of disaster events. We start by presenting some proactive methods to be applied before the occurrence of a disaster. Then we move our focus also on other preparedness methods that can be executed in the (typically short) time frame between the occurrence of an early alert of an incoming disaster and the time a disaster actually hits the network. Finally, we discuss reactive procedures that allow performing post-disaster recovery operations effectively. The analysis of disaster resilience mechanisms provided in this paper covers both wired and optical wireless communication infrastructures and also contains explicit remarks covering the role of emerging technologies (e.g., fixed-mobile convergence in the 5G era and beyond) in disaster resilience.

This work deals with dimensioning of wireless mesh networks (WMN) composed of FSO (free space optics) links. Although FSO links realize broadband transmission at low cost, their drawback is sensitivity to adverse weather conditions causing transmission degradation on multiple links. Hence, designing such FSO networks requires an optimization model to find the cheapest configuration of link capacities that will be able to carry an acceptable level of the demanded traffic in all weather states that can be foreseen in network operation. Such a model can be achieved using robust optimization techniques, and for that it is important to find a tractable way of characterizing possible link (capacity) degradation states corresponding to weather conditions not known in advance. In the paper we show how the set of link degradation states may be represented mathematically in a compact and tractable way to be exploited in optimization. To solve this task we will make use of a generalization of a combinatorial problem of finding a minimum hitting set to deduce a compact set approximating a given set of link degradation states, (called uncertainty set). Finally, we provide a mathematical model with respect to a general form of uncertainty sets and illustrate the effectiveness of our model by means of a numerical study.

In this paper, we propose the design of a survivable energy-efficient and crosstalk-aware routing, spectrum, and core allocation (RSCA) scheme for online multiclass traffic in both spectral and temporal domains in SDM-EON. Multipath based protection scheme is applied to ensure survivability against single link failure. Advanced reservation (AR) connections being a part of multiclass traffic may withstand some delay in its service from its arrival. Six heuristic algorithms are developed by using three resource allocation schemes associated with both core-classified and non-core classified approaches which are presented in this paper. Extensive simulation experiments are conducted using three well-known network topologies and the performances of the heuristics are evaluated in terms of bandwidth blocking ratio, total energy consumption, and resource occupation rate versus traffic load as well as percentage of AR connections in multiclass traffic.