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.     

An experimental switching-aware GMPLS-based lightpath provisioning protocol in wavelength-routed networks

In wavelength-routed optical networks, the high-delay introduced by the optical switching fabric for resource reservation increases critically the lightpath setup delay. In order to minimize the setup delay, Generalized Multi-protocol Label Switching (GMPLS) introduced the concept of Suggested Label Object (SL), which allows to start reserving and configuring the hardware with a proposed wavelength from the source node to the destination node. This solution is not optimal in wavelength selective networks (WSN) (i.e., without wavelengths converters). The need of guaranteeing the wavelength continuity constraint for end-to-end optical connections, combined with the lack of global wavelength-based link information (the source node is not aware of which wavelengths are available on each link), makes that the likelihood of establishing a lightpath using the proposed suggested label may be minimum. In this article, we propose an enhancement to the current GMPLS RSVP-TE signaling protocol with offset time-based provisioning that minimizes the lightpath setup, improving the overall network performance in terms of blocking probability and setup delay. Experimental performance evaluation has been carried out in ADRENALINE testbed, a GMPLS-based intelligent all-optical transport network.     

WDM光网络中基于业务等级的动态RWA算法研究

在WDM光网络中,将波长路由算法(Routing and Wavelength Assignment,RWA)与服务等级约定(Service Level Agreement,SLA)结合在一起研究,以此来确保高等级业务在传输时具有更好的可靠性和低阻塞率,并对实验数据进行仿真分析.     

A dynamic hop count shifting RWA algorithm for wavelength routed optical networks

In this article, we find that the limiting hop count in a lightpath impacts on the performance of optical networks. Based on this observation, we propose a dynamic hop count shifting (DYHOS) algorithm that limits the hop count of lightpaths dynamically, depending on the traffic load. The proposed algorithm searches an available route, while minimizing the waste of network resources and limiting excessive traffic on the network. Hence, the proposed algorithm increases the network throughput and reduces the blocking probability. Comparing with shortest path routing and adaptive path routing algorithms, we show the performance of the proposed algorithm has the lowest blocking probability influenced by the hop count of lightpaths for a given routing algorithm.

An Ant-Based Approach for Dynamic RWA in Optical WDM Networks

In this paper, we propose a new ant-based algorithm for the dynamic routing and wavelength assignment (RWA) problem in optical WDM networks under the wavelength continuity constraint. Unlike conventional approaches, which usually require centralized global network information, our new RWA algorithm constructs the routing solution in a distributed manner by means of cooperative ants. To facilitate the ants’ foraging task, we adopt in our algorithm a probabilistic routing table structure for route selection. The new algorithm is highly adaptive in that it always keeps a suitable number of ants in the network to cooperatively explore the network states and continuously update the routing tables, so that the route for a connection request can be determined promptly by the current states of routing tables with only a small setup delay. Some new schemes for path scoring and path searching are also proposed to enhance the performance of our ant-based algorithm. Extensive simulation results upon three typical network topologies indicate that the proposed algorithm has a very good adaptability to traffic variations and it outperforms both the fixed routing algorithm and the promising fixed–alternate routing algorithm in terms of blocking probability. The ability to guarantee both a low blocking probability and a small setup delay makes the new ant-based routing algorithm very attractive for both the optical circuit switching networks and future optical burst switching networks     

路由与波长分配的RWA算法应用于光通信网络

随着科学技术的不断发展,光通信网络成为了网络技术的主要发展趋势,逐渐在通信网络中发挥出显著作用.现阶段,光通信网络中的光网络主要采用基于密集波分复用技术组成,一旦波分数量增加,光网络中的路由选择与波长分配问题就难以解决.本文详细阐述了分层图模型的概念,提出波长可变光网络中的动态RWA算法,并在此基础上分析了动态RWA算法的数值模拟,以在提高波长资源利用率的同时,降低网络阻塞率.     

A dynamic and quasi-centralized RWA method for optical fast circuit switching networks employing route pre-prioritization

We propose a new dynamic RWA algorithm for optical fast circuit switching networks, agile optical networks that can accommodate changing broadband demands. The algorithm utilizes pre-computed prioritized route candidates that reflect statistical information such as traffic distribution characteristics to attain better load balancing. The route priority is periodically distributed over a network and RWA for each path connection demand is processed in a distributed manner. Numerical experiments demonstrate that the algorithm matches the performance of a centralized RWA algorithm that uses all the necessary information on a network.     

On the performance of distributed lightpath provisioning with dynamic routing and wavelength assignment

Distributed lightpath provisioning in wavelength-division multiplexing (WDM) networks has gained wide research interests. In this article, we study the performance of distributed lightpath provisioning in WDM networks with dynamic routing and wavelength assignment (RWA). Specifically, we consider the case where routing of each lightpath is calculated based on globally flooded link-state information, and wavelength assignment is decided through local information exchanges. Simulation results show that such schemes steadily outperform those schemes with only global flooding or only local information exchanges. More significantly, the impacts of various factors on the proposed scheme, including RWA algorithm, network topology, number of wavelengths per fiber, global flooding interval, and traffic load, have been evaluated. Such evaluations help to achieve some insights useful for the future developments of efficient lightpath provisioning schemes.

具有容错能力的波长路由光网络的拓扑设计

研究了具有容错能力的波长路由光网络的拓扑设计问题.提出了一种基于业务流的初始物理拓扑产生算法,与随机拓扑生成算法相比,该算法产生的物理拓扑更接近于最优拓扑.另外,还提出了一种新的链路拥塞计算方法,它能够更好地反应链路的实际状态.数值结果显示文章提出的物理拓扑设计策略具有更快的收敛速度.     

波长路由光网络中RWA算法的设计分析

文章通过对波长路由光网络中路由与波长分配(RWA)问题的研究,介绍了求解路由子问题和波长分配子问题的常用方法,总结了3种类型的RWA问题的优化解决方法,最后对目前RWA算法设计中存在的问题进行了分析并阐述了解决此类问题的重要性.     

Reducing vulnerability of shared-path protection subject to double-link failures in WDM mesh networks

Shared-path protection (SPP) is a capacity- efficient mechanism to provide 100% single-link failure protection in WDM mesh networks. After the first link failure, however, if reconfiguration is unavailable, a second link failure may lead to tremendous service interruption. Vulnerability of a link is the percentage of links that are vulnerable to the arbitrary second link failure after the link failed and network vulnerability is defined as the average vulnerability of links in the network. In this article, we present three policies that can reduce network vulnerability by reducing backup sharing in shared-path protection. The first policy tries to restrict the times of sharing a wavelength-link by connections. The second policy tries to avoid backup sharing on highly vulnerable links. The third policy tries to avoid backup sharing on highly vulnerable wavelength-links. Algorithms to implement these policies based on a similar framework are presented. Numerical results suggest that there is a trade-off between capacity efficiency and network vulnerability in all the three policies. The third policy can deliver a better performance in terms of blocking probability and network vulnerability.

OSNR model to consider physical layer impairments in transparent optical networks

We propose a model that considers several physical impairments in all-optical networks based on optical signal-to-noise degradation. Our model considers the gain saturation effect and amplified spontaneous emission depletion in optical amplifiers, coherent crosstalk in optical switches, and four-wave mixing in transmission fibers. We apply our model to investigate the impact of different physical impairments on the performance of all-optical networks. The simulation results show the impact of each impairment on network performance in terms of blocking probability as a function of device parameters. We also apply the model as a metric for impairment-constraint routing in all-optical networks. We show that our proposed routing and wavelength assignment algorithm outperforms two common approaches.

光网络中一种考虑信号损伤限制和服务质量区分的动态RWA算法

在光网络中,光信号沿着路由与波长分配(RWA)算法选定的光通路传输的过程中会受到各种信号损伤的影响而导致信号质量的不断下降,严重影响着业务的服务质量(QoS).而光网络中多样化的客户层业务往往有着不同的QoS的需求,因此有必要根据不同的业务QoS需求对光信号损伤的影响进行不同程度的控制.针对这一问题,提出了一种能同时考虑信号损伤限制和服务质量区分的动态RWA算法,并通过计算机仿真的方法对其性能进行了分析和验证.结果表明:该算法既能克服光网络中信号损伤的影响又能为不同级别的业务提供不同的QoS保证,更贴近实际需求.     

一种提高光网络攻击容忍性的RWA算法研究

通过研究光网络中带内串扰攻击及其传播原理,在基于串扰攻击有限传播的模型之上,提出了一种限制串扰攻击传播的波长路由分配(Routing and Wavelength Assignment,RWA)算法.该算法把分配后能产生最小串扰攻击传播最大值(Crosstalk Attack Propagation Maximum,CAPM)的波长路由分配给新的光路请求,从而减少全网的潜在的攻击传播范围.仿真结果显示,与常用的首次命中(Fist-fit)RWA算法相比,该算法能显著降低全网的串扰攻击传播最大值,从而提高光网络的攻击容忍性.     

多域光网络中的动态RWA算法研究

随着光网络规模的不断增大,下一代智能光网络将被划分为多个路由域进行分布式管理.由于在这种具有分布式特点的多域光网络中,每个路由域只了解本地子网内的拓扑和资源信息,因此以往光网络中已有的基于全网信息的动态RWA算法将不在有效.文章首先分析了多域光网络中的动态RWA问题,然后针对多域网的特点对已有的RWA算法进行了修改,并在给定的多域光网络模型中对该算法进行了仿真研究.结果表明:在多域网络环境下,以往的动态RWA算法急需改进.     

A new approach for routing and wavelength assignment for permanent and reliable wavelength paths in wide all-optical WDM networks

This article proposes a new approach for routing and wavelength assignment (RWA) for permanent and reliable wavelength paths (WP) in wide all-optical WDM networks with wavelength continuity constraint. Given a number of available wavelengths on each optical fiber, for each simple link failure of the network, we seek to maximize the number of satisfied requests for connections. This is known as RWAP problem. In our algorithm, called RWA with Minimum Loaded Link for Permanent and Reliable wavelength paths (MLL-PR), routing is based on the search for the optimal path while trying to minimize the maximum load on the links of the network in order to minimize the maximum link capacity and then minimize the number of dropped lightpaths after any link failure. The wavelength assignment is based on a graph coloring method using tabu-search. A series of experiments using two well-known networks (ARPANET and NSFNET) have been carried out in order to evaluate the performance of our approach, in terms of the number of blocked demands, for different failure scenarios. Generally, our results are better than those provided by the current solving approaches taken as reference.

A tabu search heuristic for the routing and wavelength assignment problem in multigranular optical networks

This paper proposes a tabu search heuristic for solving the routing and wavelength assignment problem in multigranular optical networks, considering the wavelength-continuity constraint and a set of connections to satisfy. For a number of fibers per link, a number of wavebands per fiber, and a number of wavelengths per waveband, this algorithm attempts to minimize the total number of ports used in the network by efficiently grouping lightpaths into bands and fibers, and switching the whole bands and fibers. The algorithm has been implemented and tested on the NSFNET network, and comparisons have been made with the Balanced Path Routing and Heavy Traffic First (BPHT) algorithm in terms of number of ports. Generally, the results obtained with our tabu search heuristic are better than those provided by this algorithm.

Energy-efficient dynamic wavelength and bandwidth allocation algorithm with delay constraint for time and wavelength division multiplexed passive optical networks

Based on offline scheduling and node modular design,an energy-efficient dynamic wavelength and bandwidth allocation algorithm with the delay constraint (EE-DWBA-DC) was proposed.Optical line terminal (OLT) and optical network units (ONU) were considered to save energy.Under the constraint of packet delay,the number of active wavelengths could be reduced as much as possible and the length of polling cycle was increased.At the same time,the uplink and downlink transmission time of OLT and ONU were concentrated to reduce the state conversion times and extend its low-power duration.In addition,the high energy consumption voids of channels were attempted to be minimized.The simulation results verify that the proposed algorithm can reduce the energy consumption of OLT and ONU and the total energy consumption of the whole network under the premise of guaranteeing packet delay constraints.     

Routing and wavelength assignment in optical WDM networks with maximum quantity of edge disjoint paths

In the present paper, routing and wavelength assignment (RWA) in optical WDM networks is discussed. Previous techniques based on the combination of integer linear programming based lpsolver and graph coloring are complex and require extensive use of heuristics such as rounding heuristic which makes them slow and sometimes practically not reasonable. Another method employs the greedy approach in graph theory for obtaining available edge disjoint paths. Even though it is fast, it produces a solution for any connection request which is far from the optimal utilization of wavelengths. We propose a novel algorithm, which is based on the maximum flow to have the maximum quantity of edge disjoint paths. Here, we compare the offered method with previous edge disjoint paths algorithms applied to the RWA. Comprehensive computer simulation shows that the proposed method outperforms previous ones significantly in terms of running time. Furthermore, the new method shows compatible or better performance comparing to others in number of wavelengths used.The earlier version was published in ICCS 2004, Poland (Krakow). This research was supported by the Ministry of Information and Communication, Korea under the Information Technology Research Center support program supervised by the Institute of Information Technology Assessment, IITA-2005-(C1090-0501-0019).