波分复用波长路由节点的阻塞特性分析

利用概率统计理论的方法，从节点层次上定量分析了节点规模、复用波长数目以及波长转换对波分复用(WDM)波长路由网络中波长路由节点的影响。提出了基于概率统计的节点阻塞模型。数值结果突出表明波长转换能力越强的全光节点，其性能越优。为了提高网络资源的使用效率并增强全光网络的灵活性，必须实现全光网络中的虚波长路由波长转换器。通过数值计算找到了阻塞性能和代价的折中，研究中发现配置较低波长转换能力波长转换器的波长路由节点将会具备更强的性价比优势，当前在构建光通信系统时使用弱波长转换能力的光节点更可行。     

基于连通支配集的OBS网络多粒度业务疏导机制

针对目前光网络核心节点的交换速度无法匹配单波长的传输速度难以满足大量的业务请求而拥塞,为了提高核心节点交换效率使其具有大容量数据交换的能力,本文提出了一种基于连通支配集(CDS)的光突发交换(OBS)网络稀疏节点疏导机制(CDS-TG).主要思路是:首先在OBS核心网络中根据改进的连通支配集算法选取疏导节点;其次在疏导...     

基于历史连接数据的机会网络关键节点预测

鉴于无线传感网络关键节点探测算法的研究基础,设计了一种基于历史连接数据预测机会网络关键节点的算法(HDPA)。考虑到节点间连接时长与频率对连通概率的影响,提出了一种连通概率的计算方法。将研究时间切分成若干个周期,利用历史连接数据对各周期的连通概率进行计算。将所得时序周期的连通概率进行趋势分析,根据其走势应用相应的指数平滑法预测未来周期内的连通概率,从而得到一个概率连通图。将疑似节点从图中删除,计算概率连通子图的连通概率即可得到该节点成为关键节点的概率。最终将节点概率大于0.5的节点预测为关键节点。实验结果表明,HDPA具有较高准确度和较好扩展性。     

时隙光突发交换技术及其网络阻塞性能分析

介绍光突发交换技术及其网络工作原理,并提出基于多波长多光纤的网络阻塞分析模型。应用该模型,可计算光突发交换网络中存在多类业务时的阻塞概率,仿真结果表明该模型不仅准确反映了网络阻塞特性,而且说明在不使用波长转换器件时,时隙化突发交换网络仍有较好的阻塞性能,本文工作对于评估其网络性能和设计实现参数具有重要意义。     

多波长光标记分组交换及相关技术综述

光分组交换能有效地改进光网络节点的处理能力。介绍了光分组交换中的一种:多波长光标记分组交换。介绍了多波长光标记分组交换的基本原理,探讨了实现多波长光标记分组交换的一些关键技术。     

一种光交换核心节点调度算法研究

光交换核心节点是光交换网络的核心设备,其性能的优劣直接影响网络的吞吐量、时延等重要指标。文章提出一种SWC-MSD(基于波长变换器的多播空分交换)模块的严格无阻塞光交换核心节点,在此基础上提出了三种调度算法,通过数学分析和实验仿真验证了算法的正确性。考察了这种核心节点在有无波长变换以及业务优先级不同的场景下阻塞率的变化情况,结果表明所提出的严格无阻塞光交换核心节点具有较低的阻塞率。     

基于时空冲突图的卫星光网络波长资源特性研究

针对动态卫星光网络中的波长资源紧缺问题，研究了其波长数与网络物理连通度的关系，提出了一种基于时空冲突图的波长资源特性分析方法。利用随机生成网络拓扑连接的方式，将卫星光网络的动态拓扑离散为空间和时间冲突图，分别表示网络的物理连通度和有效窗口。基于时空冲突图理论，建立空间冲突避免的路径选择概率和时间存储的有效窗口业务概率，两者相乘得到时空冲突概率，进而计算网络所需波长数。研究结果表明，波长需求与网络物理连通度、链路最大跳数和转发器数目有着密切关系，在业务重叠因子较大的情况下应该给卫星光网络分配更多的波长资源。     

基于FDLs的光突发交换突发包丢失率的分析模型

对采用光纤延迟线（FDL）解决竞争问题的光突发交换网络节点，本文提出了一种新的数学分析模型计算OBS节点的突发包丢失率。模型基于Markovian链及光纤延迟线，推导了状态方程，并通过数值求解各状态的概率来得出交换节点总的突发包丢失率。与此同时用C＋＋语言对节点的交换过程进行了仿真模拟。分析模型与仿真结果的比较表明，两者的一致性相当好。     

利用GMPLS实现光突发交换

DWDM技术虽然可以实现较大的传输容量，但是在对信息进行处理的过程中，却存在着电子瓶颈，传统网络仍然需要在交换节点处对数据进行电的交换处理，从而降低了网络的交换处理速度。为了实现在光网络上直接传送数据业务，人们提出三种IP over DWDM网络方案：波长路由交换光网络、突发交换光网络和分组交换光网络。     

OBS节点的偏射路由研究

研究了光突发交换（optical bursts witching，OBS）网络中的一种竞争解决策略——偏射路由并且提出了有波长变换和无波长变换的单个OBS节点的突发丢失分析的近似模型和精确模型。     

Routing and wavelength assignment strategies in optical networks

We consider the routing and wavelength assignment (RWA) problem on wavelength division multiplexing (WDM) networks without wavelength conversion. When the physical network and required connections are given, RWA is the problem to select a suitable path and wavelength among the many possible choices for each connection such that no two paths using the same wavelength pass through the same link. In WDM optical networks, there is need to maximize the number of connections established and to minimize the blocking probability using limited resources. This paper presents efficient RWA strategies, which minimizes the blocking probability. Simulation results show that the performance of the proposed strategies is much better than the existing strategy.     

The effects of polarization mode dispersion on 2D wavelength-hopping time spreading code routed networks

In this study, we investigate the effects of multiple access interference (MAI) and polarization mode dispersion (PMD) in 2D wavelength-hopping time spreading optical code paths. The main results show the MAI effects and PMD constraint at the outage probability. The contribution of these sources of interference is analysed to choose the better design of code parameters in order to increase the performance of networks based on optical code paths. These results could be applied to determine the parameters design in code/wavelength routed networks.     

光网络中基于SRLG约束的动态RWA算法

在IPoverWDM光网络中,需要为每条工作光路提供光通路保护,即提供一条保护光路。光网络中引入了共享风险链路组(SRLG)的概念,要求工作光路与保护光路不共享风险链路组。不考虑波长分配提出一种新的启发式算法,该算法同时计算两条SRLG分离且总费用低;在此算法基础上利用分层图的思想,提出WDM网络中的一种在SRLG约束条件下的动态选路波长分配算法。     

光因特网中动态综合考虑的资源分配算法

该文研究了光因特网络中的动态资源分配问题，提出了基于分层图模型的路由选择和波长分配算法。对于动态变化的业务到达请求，如果在已有的基于IP级的逻辑拓扑上不能有效建立，则需要为该请求按算法分配资源，即解决路由选择和波长分配问题。由于该文算法将IP层和光层综合进行考虑，所以能大大提高资源利用的有效性，取得较好的阻塞性能。仿真结果表明，该算法既能选择比较短的路由，又能使网络取得较低的阻塞率。     

一种改进遗传算法在WDM光网络中的应用

在波长路由光网(WRON)中,波长转换对提高网络性能、减少阻塞率起着重要的作用.但由于目前全光波长转换器非常昂贵,因而如何最优利用波长转换是配置光网络的一个重要问题.文中利用遗传算法很好地解决了这一问题,并且利用数值模拟的方法,计算了美国自然科学基金网(NSFnet)网络中最优配置下网络的阻塞情况.然后针对普通遗传算法的缺点,提出了一种改进遗传算法.最后利用数值模拟的方法,比较了两种算法的性能.     

Effects of wavelength routing and selection algorithms onwavelength conversion gain in WDM optical networks

Wavelength-division multiplexing (WDM) technology is emerging as the transmission and switching mechanism for future optical mesh networks. In these networks it is desired that a wavelength can be routed without electrical conversions. Two technologies are possible for this purpose: wavelength selective cross-connects (WSXC) and wavelength interchanging cross-connects (WIXC), which involve wavelength conversion. It is believed that wavelength converters may improve the blocking performance, but there is a mix of results in the literature on the amount of this performance enhancement. We use two metrics to quantify the wavelength conversion gain: the reduction in blocking probability and the increase in maximum utilization, compared to a network without converters. We study the effects of wavelength routing and selection algorithms on these measures for mesh networks. We use the overflow model to analyze the blocking probability for wavelength-selective (WS) mesh networks using the first-fit wavelength assignment algorithm. We propose a dynamic routing and wavelength selection algorithm, the least-loaded routing (LLR) algorithm, which jointly selects the least-loaded route-wavelength pair. In networks both with and without wavelength converters the LLR algorithm achieves much better blocking performance compared to the fixed shortest path routing algorithm. The LLR produces larger wavelength conversion gains; however, these large gains are not realized in sufficiently wide utilization regions and are diminished with the increased number of fibers     

Design-dimensioning model for transparent WDM packet-switchedirregular networks

A detailed analytical traffic model for all-optical wavelength division multiplexing (WDM) photonic packet-switched networks is presented and the requirements for buffer size and link dimensions are analyzed. This paper shows that due to the topology, packets may generate traffic bottlenecks produced by a tendency of the routing scheme to send packets with different destinations through preferred paths. This effect increases the traffic load and, hence, the probability of blocking at the output links of specific routers in the network and, therefore, a large buffer depth or an increment in the number of fibers per link is required. Three router architectures are analyzed and it is shown that WDM all-optical router architectures with shared contention resolution resources are the best candidates to reduce hardware volume and cost of all-optical networks. It is shown that routers with a bank of completely shared wavelength converters (WCs) require a fraction of WCs compared to router architectures that use a WC per wavelength. This fraction depends on the location of the router, the network topology, and the traffic load in the network. However, in general terms, about 50% to 90% of WCs can be saved by architectures with shared wavelength-conversion resources. Also, it is shown that limited wavelength conversion degrees d=8 and d=10 in packet-switching routers with 16 and 32 wavelengths give the same probability of packet loss performance as full wavelength conversion     

An optical IM/FSK coding technique for the implementation of a label-controlled arrayed waveguide packet router

In this paper, we present a new concept of optical packet/burst switching suitable for generalized multiprotocol label switched (GMPLS)-based optical networks. In such networks, optical labeled switched paths are being established in a similar way as label-switched paths in MPLS. We use a wavelength label as well as an orthogonally modulated label, with respect to the payload modulation format, and which is encoded using either frequency-shift keying (FSK) or differential phase-shift keying (DPSK). Wavelength is used for switching in the node, whereas the orthogonal label defines the label-switched path. We present both simulation and experimental results to assess transmission performance of the proposed combined modulation scheme. In addition, we propose a suitable optical node architecture that can take advantage of this stacked label concept. Toward this, we use widely tunable wavelength converters to efficiently route IM/FSK (or IM/DPSK) optically labeled packets in an arrayed-waveguide grating (AWG)-based node structure. We present performance simulation results in terms of packet loss ratio and internal block probability. Internal blocking is an inherent problem of AWG optical routers, and a specific wavelength assignment algorithm has been developed to minimize it. Finally, the feasibility of IM/FSK transmission is experimentally demonstrated over an 88-km single-mode fiber span, and novel aspects of FSK generation and detection techniques are presented.     

Link-State-Based Algorithms for Dynamic Routing in All-Optical Networks with Ring Topologies

The increased usage of large bandwidth in optical networks raises the problems of efficient routing to allow these networks to deliver fast data transmission with low blocking probabilities. Due to limited optical buffering in optical switches and constraints of high switching speeds, data transmitted over optical networks must be routed without waiting queues along a path from source to destination. Moreover, in optical networks deprived of wavelength converters, it is necessary for each established path to transfer data from source to destination by using only one wavelength. To solve this NP-hard problem, many algorithms have been proposed for dynamic optical routing like Fixed-Paths Least Congested (FPLC) routing or Least Loaded Path Routing (LLR). This paper proposes two heuristic algorithms based on former algorithms to improve network throughput and reduce blocking probabilities of data transmitted in all-optical networks with regard to connection costs. We also introduce new criteria to estimate network congestion and choose better routing paths. Experimental results in ring networks show that both new algorithms achieve promising performance.     

On service provisioning using light-trails in WDM optical networks with waveband switching

As the number of wavelengths in a single optical fiber increases, so does the number of ports needed for wavelength switching in optical cross-connects (OXCs), which may significantly increase the cost and difficulty associated with controlling large OXCs. Waveband switching (WBS) treats several wavelengths as a bundle that is switched through a single port if they share the same switch route, so that the number of ports needed can be reduced. On the other hand, light-trails in wavelength division multiplexing (WDM) optical networks allow intermediate nodes on established optical paths to access the data paths whereas light-paths only allow two end nodes to access the data paths. Therefore, light-trails offer significantly better flexibility for service provisioning and traffic grooming. In this article, we study service provisioning using light-trails in WDM optical networks with the WBS capability under a static traffic model. For comparison, integer linear programs are formulated for establishing light-trails with and without WBS. Numerical studies show that in certain cases, service provisioning with WBS in light-trail networks can reduce the number of ports needed while providing a more flexible sub-wavelength service provisioning capability. However, contrary to intuition, in most cases applying the WBS technique requires more ports in OXCs in light-trail networks. This study provides insights into the network design problem that applies the WBS technology to light-trail based optical networks.