树形全光网络中波长转换器配置算法

配置有限数量的波长转换器使网络阻塞率最低,是全光网络中需要解决的一个关键问题.通过考虑网络的直径、中心以及节点和链路的通信量,采用网络分解和迭代的方法,提出树形网络中基于赋权直径的波长转换器配置算法、基于节点加权中心的波长转换器配置算法,以及基于光路加权中心的波长转换器配置算法.算法演示表明,提出的3个算法总是将波长转换器放置在阻塞率较高的节点上,从而大大降低网络整体阻塞率.     

全光网络中波长转换器配置问题的蚁群算法

研究提高网络的利用率,在全光网络中放置波长转换器是打破波长一致性约束,为了降低网络阻塞率,提高网络通信能力的有效途径。但限于波长转换器的高昂成本,不可能为网络中的每个节点都配置波长转换器,所以波长转换器应以最优方案放置在网络中的个别关键节点上。提出了一种基于蚁群算法的波长转换器配置方法,通过蚁群算法寻找给定网络中任意源、目的节点之间的最优路径,并利用蚂蚁对最优路径的记录,统计路径在节点处发生波长转换的次数,将具有较高波长转换次数的节点作为网络中波长转换器放置节点。最后通过对一个5节点的网络进行算法演示和仿真分析,结果表明该算法能求得波长转换器的合理配置,得到较好的通信效果。     

全光网波长转换器配置问题的一种启发式算法

波长转换技术可以消除全光网络中的波长一致性限制,降低网络阻塞率,因此在具有波长转换器的全光网中,如何通过合理配置、使用数量有限的波长转换器来最大程度的降低网络的阻塞率,这是全光网络需要解决的一个关键问题。因此对网络中通过节点的路由数量、通信量、路由长度及节点处于路由的中心距离进行分析,并给上述四个参数赋予一定的权重进行加权处理,提出了一种基于节点权的全光网络波长转换器配置算法,并针对一般拓扑网络进行了算法演示和分析。     

有固定波长转换器的全光环网波长分配算法

采用波分复用技术的全光网是目前宽带网络研究的方向之一,波长分配是其中主要的算法问题,具有重要的理论和应用价值.研究了具有任意固定波长转换器的环形光网上的波长分配问题.首先,提出了两个对环网上的请求集合预处理的算法,这两个算法可以将请求集合分解成一些连续的循环序列;然后,采用置换群来描述具有固定波长转换器的光环网,基于这种数学表示,提出了对环网上的波长信道进行分解的算法;基于这些算法,进一步提出了一个波长分配算法,该算法对于环形光网上的任意固定转换模式都能给出一个较好的波长分配方案.     

改进遗传算法应用于全光网中静态路由与波长分配的优化

文章对静态情况下光网络的路由和波长分配问题进行了深入研究,创新性地提出了两条规则调整波长关系图,使得波长关系图中的连通度比较均衡,减少了波长使用数量1/3。文章同时改进了遗传算法,提出了一种新的可以自我调节变异和交叉因子的值的算法(VMCR-GA),通过交叉算子的操作,形成了一种正反馈机制,可以大大加速遗传算法的解空间搜索速度和收敛速度。通过对CERNET网络的仿真计算,发现无论在最短路径还是在优化路由算法中,改进的遗传算法和波长分配方法的性能都比基本遗传算法的性能有很大的提高,证明这种改进的算法和方法是非常有效的。     

WDM全光网络中的路由及波长分配

在全光网络中,光信号在全光域内传输,避免了光-电转换带来的延迟,因此,全光网支持高数据率传输并提供巨大的网络容量。WDM(波分多路复用)技术的采用使得高速光传输线路与低速终端处理设备之间能够相互兼容。论文探讨了WDM全光网中的路由及波长分配问题,对各种常用算法进行了详细的分析,并提出了对一种新型的用于WDM网络上的实时组播请求的分布式RWA算法进行改进的意见。     

不同通信模型下的全光树环网波长分配算法

研究了波分复用全光树环网在不同通信模型下的波长分配算法及其最坏性能分析.对于静态模型,证明了5L/2是树环网所需波长数的紧界.对于动态模型,提出了一种近似比为∑_i=1^hmax_r∈Ri[log|V(r)|]+h的波长分配算法,其中h为树环网的基树的层数,R_i为树环网中处于第i层的环的集合,|V(r)|为环r上的节点数.对于增量模型,提出了一种近似度为O[log₂(t+1)]的波长分配算法,其中t为树环网中的环数.     

波分复用光传输网中波长路由算法的研究进展

光纤正迅速成为主干通信网的标准传介媒质．随着光学器件的发展，使得信号在传输过程中，除了在源、汇节点需要光电转换外，中间节点可保持光传输，这种通信网络叫光传送网．光传送网中的波分复用技术是将整个光纤的带宽分成多个信道，不同的信道可使用不同的波长来同时进行信息传输，从而增加了整个网络的带宽．在光传送网中，实现一个通信请求需要建立一条通信路径，并为该通信路径所经过的每条链上分配一个波长，即所谓波长路由．该文详细介绍了波分复用光传送网中波长路由算法的研究进展，内容包括波长分配算法、网络的信元阻塞率分析、容错和QoS波长路由、多播波长路由、最小化ADM数路由以及基于光或光电连接的并行机模型等．     

光网络中波长转换器的优化放置问题求解

基于分层图模型,提出了一种的简化的计算具有波长转换器光网络中光链路阻塞率的数学模型和公式,并应用于遗传算法的迭代函数,通过遗传算法对波长转换器在光网络中的优化放置问题进行求解,分析了波长转换器的最优放置和波长转换器的最小使用数量。通过在美国自然科学基金网(NSFNet)的仿真模拟,得出了使用部分和全部波长转换时的网络阻塞特性。     

光通信网络中路由与波长分配的算法研究

光通信网络作为下一代网络的主要网络之一,在整个通信网中起着至关重要的作用。目前光通信中主要是采用基于DWDM(密集波分复用)技术组成的光网络,随着波分数量的增加,DWDM网络中的路由与波长分配问题显得十分重要,需要有一种有效的算法来使有限的波长资源得到充分地利用。本文根据原有的数学分析模型,提出了一种分层图模型,并根据此模型提出了一种用来解决DWDM网络中出现的波长分配问题的一种算法,并通过计算机仿真来表明此算法提高了波长资源的利用率,降低了网络的阻塞率。     

Optimal bandwidth utilization of all-optical ring with a converter of degree 4

In many models of all-optical routing,a set of communication paths in a network is given,and a wavelength is to be assigned to each path so that paths sharing an edge receive different wavelengths .The goal is to assign as few wavelengths as possible,in order to use the optical bandwidth efficiently.If a node of a network contains a wavelength converter,any path that passes through this node may change its wavelength .Having converters at some of the nodes can reduce the mumber of wavelengths required for routing,This paper presents a wavelength converter with degree 4and gives a routing algorithm which shows that any routing with load L can be realized with L wavelengths when a node of an all-optical ring hosts such a wavelength converter.It is also proved that 4 is the minimum degree of the converter to reach the full utilization of the available wavelengths if only one mode of an all-optical ring hosts a converter.     

树形网络中的副本更新策略及算法

树形网络中的副本放置和更新是网络通讯中值得研究的重要问题之一。面对网络中数据访问需求的动态变化,好的副本放置和更新策略可以在保证服务质量的前提下有效减少网络运行及副本更新成本。针对此问题提出了两种贪心的动态副本更新策略,最大重用策略和请求覆盖策略。通过算法复杂度分析和仿真实验可以看出,所提出的两种算法的最坏时间复杂度为O(nlog n),远低于现有的使用动态规划求最优解的最坏时间复杂度O(n5),而网络运行及副本更新成本与最优解相差不超过11%。在极大地缩短了运算时间的同时,保持了尽可能低的网络运行及副本更新成本。     

基于塑料光纤的全光系统成套设备核心技术研究

提出采用塑料光纤接入技术实现室内100m全光网络光纤到桌面的一种可行方案,针对全光系统中的全塑料光口接入的ONU端口和全塑料光口的交换机两个部分进行了重点讨论与研究。该塑料全光系统相对石英光纤接续方便、便于敷设;相对网线抗干扰性强,成本较低,具有较强的先进性和实用性。     

Co-evolutionary algorithms to solve hierarchized Steiner tree problems in telecommunication networks

This study investigates a hierarchized Steiner tree problem in telecommunication networks. In such networks, users must be connected to capacitated hubs. Additionally, selected hubs must be connected to each other and to extra hubs, if necessary, by considering the latency of the resultant network. A connection between hubs can be considered to be a Steiner tree. This Steiner tree problem is modeled as a bi-level mathematical programming problem that considers two decision levels. In the upper-level, the allocation of users to hubs is performed to minimize the total network connection cost. The lower-level minimizes the user latency concerning the information that flows through the capacitated hubs. Further, two co-evolutionary schemes are developed to solve this bi-level model. The first scheme is an individual–population approach, whereas the second scheme is the traditional population–population approach. The first proposed algorithm exploits the structure of the problem by employing parallel computing in one of the populations. Numerical results depict the effectiveness of the proposed algorithms when the lower-level problem cannot be optimally solved efficiently. Furthermore, the advantages of the proposed schemes over an evolutionary one are exhibited. Finally, the hybridization of both co-evolutionary schemes is implemented to improve the semi-feasible solutions obtained by the second scheme, showing its effectiveness to solve the problem.     

Relay node placement in structurally damaged wireless sensor networks via triangular steiner tree approximation

Wireless sensor networks (WSNs) have many applications which operate in hostile environments. Due to the harsh surroundings, WSNs may suffer from a large scale damage that causes many nodes to fail simultaneously and the network to get partitioned into multiple disjoint segments. In such a case, restoring the network connectivity is very important in order to avoid negative effects on the applications. In this paper, we pursue the placement of the least number of relay nodes to re-establish a strongly connected network topology. The problem of finding the minimum count and the position of relay nodes is NP-hard and hence we pursue heuristics. We present a novel three-step algorithm called FeSTA which is based on steinerizing appropriate triangles. Each segment is represented by a terminal. Each subset of 3 terminals forms a triangle. Finding the optimal solution for a triangle (i.e. connecting 3 segments) is a relatively easier problem. In the first step, FeSTA finds the best triangles and form islands of segments by establishing intra-triangle connectivity. Then in the second, disjoint islands of segment are federated. In the final step, the steinerized edges are optimized. The performance of FeSTA is validated through simulation.     

Parallel algorithms for tree traversals

Three commonly used traversal methods for binary trees (forsets) are pre-order, in-order and post-order. It is well known that sequential algorithms for these traversals takes order O(N) time where N is the total number of nodes. This paper establishes a one-to-one correspondence between the set of nodes that possess right sibling and the set of leaf nodes for any forest. For the case of pre-order traversal, this result is shown to provide an alternate characterization that leads to a simple and elegant parallel algorithm of time complexity O(log N) with or without read-conflicts on an N processor SIMD shared memory model, where N is the total number of nodes in a forest.     

动态虚拟盘阵数据分布算法

尽管当今的磁盘等外存储设备容量增加得很快,但还是无法满足用户应用程序的需要;在性能上,外存储设备已经成为计算机系统的瓶颈;为此,在集群环境下,将分布式的外设构成动态虚拟盘阵系统是一种较好的解决方案,而数据分布算法是动态虚拟研究的一项重要内容。也就是说,采用优化的数据分布算法,使得盘阵的性能和容量随盘阵的扩展而扩展。研究的主要工作是综述以往对动态盘阵数据分布算法,并对以往SCADDAR算法进行了扩充,提出了D／H(Double／Halve)数据分布算法。     

Resource placement in Cartesian product of networks

The utilization of the limited resources of a multiprocessor or multicomputer system is a primary performance issue which is crucial for the design of many scheduling algorithms. While many of the existing parallel machines benefit from a regular product network topology, almost none of the previous resource placement techniques have come to recognize and exploit this inherent regularity. This paper introduces several novel algorithms for deriving resource placement schemes in product networks based on the assumption of perfect resource placement in their underling basic graphs. Our techniques use known schemes for the basic networks as their building blocks for deploying the resource placement scheme in the product network. This seriously cuts down the expenses required for deploying and rescaling the network. In particular, we propose some efficient algorithms for adjacency placement in a product of k$k$ heterogeneous graphs. Furthermore, we extend our approach and present algorithms for distant resource placement in product networks.     

On approximation algorithms for the terminal Steiner tree problem

The terminal Steiner tree problem is a special version of the Steiner tree problem, where a Steiner minimum tree has to be found in which all terminals are leaves. We prove that no polynomial time approximation algorithm for the terminal Steiner tree problem can achieve an approximation ratio less than (1−o(1))lnn unless NP has slightly superpolynomial time algorithms. Moreover, we present a polynomial time approximation algorithm for the metric version of this problem with a performance ratio of 2ρ, where ρ denotes the best known approximation ratio for the Steiner tree problem. This improves the previously best known approximation ratio for the metric terminal Steiner tree problem of ρ+2.