全光波长变换技术及其在DWDM网络中的应用

全光波长变换技术是DWDM系统中的一项关键技术。它不仅可以充分利用波长资源,提供操作上的透明性和空闲波长调度的灵活性,还可以满足未来的动态路由分配需求。本文首先介绍了几种主要的全光波长变换技术的主要原理,继而阐述了其在DWDM网络中的应用。     

一种稀疏波长转换光网络中的波长分配算法

研究了具有波长转换功能的WDM光网络的分类以及已有的几种波长分配算法,分析了波长分配算法的一般流程。文中以波长变换次数最少做为所提出的波长分配算法的主要优化目标,根据WDM光网络中的节点是否具有波长转换的功能,结合等价光路由替换的思想,提出了在稀疏有限波长转换光网络中的一种启发式的波长分配算法。仿真实验表明,当光网络中的连接请求量较大时,该算法的阻塞率低于已有的一些波长分配算法,连接能力有了较大提高。     

一种稀疏波长转换光网络中的波长分配算法

研究了具有波长转换功能的WDM光网络的分类以及已有的几种波长分配算法，分析了波长分配算法的一般流程。文中以波长变换次数最少做为所提出的波长分配算法的主要优化目标，根据WDM光网络中的节点是否具有波长转换的功能，结合等价光路由替换的思想，提出了在稀疏有限波长转换光网络中的一种启发式的波长分配算法。仿真实验表明，当光网络中的连接请求量较大时，该算法的阻塞率低于已有的一些波长分配算法，连接能力有了较大提高。     

WDM光网络动态路由和波长分配算法

研究了WDM光网络中的路由和波长分配问题,比较了目前提出的算法,并结合分层图模型提出了一种新的动态路由和波长分配算法。对算法的时间复杂度进行了分析和仿真。     

DWDM光网络中RWA问题的遗传求解方法

针对密集波分复用(dense wavelength-division multiplexing,DWDM)光网络通信中的动态路由与波长分配(routing and wavelength assignment,RWA)问题,提出了一种基于遗传算法的动态RWA方法.将遗传算法与分层图模型相结合,实现了RWA的方便计算.通过扩展适应值函数,能够有效地处理带时延约束的通信量请求.实验结果表明,与已有最短路径算法(Dijks-tra)相比,该算法能够提供多条候选路由方案,更适应较差环境下的网络通信.     

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.     

IP／DWDM光因特网中一种基于人工免疫算法的QOS组播路由算法

本文提出了一种IP／DWDM光因特网中基于人工免疫算法的QoS组播路由算法，当QoS组播请求和需求区间给定时，能够找到一棵基于QoS的柔性费用近优组播路由树。该算法基于人工免疫算法构造QoS组播路由树，并基于波长图对树进行波长分配，将路由和波长分配集成到一个过程中，同时考虑了负载平衡。仿真结果表明，算法为IP／DWDM光因特网中的组播应用构造的QoS组播路由树是可行和有效的。     

WDM网络中备用路由下支持优先级的一种新的波长分配算法

文章研究了WDM光网络中动态业务下的波长分配问题,提出了一种改进的动态门限算法。该算法不仅能保证高优先级的请求有较低的阻塞率,同时还能优化低优先级请求的阻塞率,从而改善全网的平均阻塞率。此外,该算法利用相对最小影响算法,能更加精确地描述波长分配对全网状态的影响,从而更加有效地利用了网络资源。计算机仿真表明,该算法性能较好。     

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．     

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。     

IP／DWDM光Internet中基于软计算的智能多约束波长分配算法的研究

波长分配问题是影响IP／DwDM光Internet中网络资源利用的关键问题之一。本文提出了两种基于软计算的多限制的波长分配算法，使得波长源分配适应实际的网络特征。事实上，由于考虑到多种限制问题，包括成本，功率和网络性能等，因此采用分层解决方案。因为每一层都是NP完全问题，所以采用软计算和启发式相结合的方法进行求解，设计并实现了一个仿真软件，仿真表明该算法既是可行的又是有效的。     

QoS multicast tree construction in IP/DWDM optical internet by bio-inspired algorithms

In this paper, two bio-inspired Quality of Service (QoS) multicast algorithms are proposed in IP over dense wavelength division multiplexing (DWDM) optical Internet. Given a QoS multicast request and the delay interval required by the application, both algorithms are able to find a flexible QoS-based cost suboptimal routing tree. They first construct the multicast trees based on ant colony optimization and artificial immune algorithm, respectively. Then a dedicated wavelength assignment algorithm is proposed to assign wavelengths to the trees aiming to minimize the delay of the wavelength conversion. In both algorithms, multicast routing and wavelength assignment are integrated into a single process. Therefore, they can find the multicast trees on which the least wavelength conversion delay is achieved. Load balance is also considered in both algorithms. Simulation results show that these two bio-inspired algorithms can construct high performance QoS routing trees for multicast applications in IP/DWDM optical Internet.     

Efficient fault-tolerant routing in multihop optical WDM networks

This paper addresses the problem of efficient routing in unreliable multihop optical networks supported by Wavelength Division Multiplexing (WDM). We first define a new cost model for routing in (optical) WDM networks that is more general than the existing models. Our model takes into consideration not only the cost of wavelength access and conversion but also the delay for queuing signals arriving at different input channels that share the same output channel at the same node. We then propose a set of efficient algorithms in a reliable WDM network on the new cost model for each of the three most important communication patterns-multiple point-to-point routing, multicast, and multiple multicast. Finally, we show how to obtain a set of efficient algorithms in an unreliable WDM network with up to f faulty optical channels and wavelength conversion gates. Our strategy is to first enhance the physical paths constructed by the algorithms for reliable networks to ensure success of fault-tolerant routing, and then to route among the enhanced paths to establish a set of fault-free physical routes to complete the corresponding routing request for each of the communication patterns     

Optimal switch location in mobile communication networks using hybrid genetic algorithms

The optimal positioning of switches in a mobile communication network is an important task, which can save costs and improve the performance of the network. In this paper we propose a model for establishing which are the best nodes of the network for allocating the available switches, and several hybrid genetic algorithms to solve the problem. The proposed model is based on the so-called capacitated p-median problem, which have been previously tackled in the literature. This problem can be split in two subproblems: the selection of the best set of switches, and a terminal assignment problem to evaluate each selection of switches. The hybrid genetic algorithms for solving the problem are formed by a conventional genetic algorithm, with a restricted search, and several local search heuristics. In this work we also develop novel heuristics for solving the terminal assignment problem in a fast and accurate way. Finally, we show that our novel approaches, hybridized with the genetic algorithm, outperform existing algorithms in the literature for the p-median problem.     

Routing and wavelength assignment for hypercube in array-based WDM optical networks

Hypercube is one of the most versatile and efficient communication patterns shared by a large number of computational problems. As the number of edges in hypercube grows logarithmically with the size of networks, the complexity of network topologies can be significantly reduced to realize hypercube in optical networks by taking advantage of the parallel transmission characteristic of optical fibers. In this paper, we study the routing and wavelength assignment for realizing hypercube on WDM optical networks including linear arrays and rings with the consideration of communication directions. Specifically, we analyze this problem for both bidirectional and unidirectional hypercubes. For each case, we identify a lower bound on the number of wavelengths required, and design the embedding scheme and wavelength assignment algorithm that uses a provably near-optimal number of wavelengths. In addition, we extend the results to meshes and tori. By our embedding schemes, many algorithms, originally designed based on hypercubes, can be applied to optical networks, and the wavelength requirements can be easily derived using our obtained results.     

Efficient Multiple Multicast on Heterogeneous Network of Workstations

In recent years, network of workstations/PCs (so called NOW) are becoming appealing vehicles for cost-effective parallel computing. Due to the commodity nature of workstations and networking equipment, LAN environments are gradually becoming heterogeneous. The diverse sources of heterogeneity in NOW systems pose a challenge on the design of efficient communication algorithms for this class of systems. In this paper, we propose efficient algorithms for multiple multicast on heterogeneous NOW systems, focusing on heterogeneity in processing speeds of workstations/PCs. Multiple multicast is an important operation in many scientific and industrial applications. Multicast on heterogeneous systems has not been investigated until recently. Our work distinguishes itself from others in two aspects: (1) In contrast to the blocking communication model used in prior works, we model communication in a heterogeneous cluster more accurately by a non-blocking communication model, and design multicast algorithms that can fully take advantage of non-blocking communication. (2) While prior works focus on single multicast problem, we propose efficient algorithms for general, multiple multicast (in which single multicast is a special case) on heterogeneous NOW systems. To our knowledge, our work is the earliest effort that addresses multiple multicast for heterogeneous NOW systems. These algorithms are evaluated using a network simulator for heterogeneous NOW systems. Our experimental results on a system of up to 64 nodes show that some of the algorithms outperform others in many cases. The best algorithm achieves completion time that is within 2.5 times of the lower bound.     

COMPARATIVE ANALYSIS OF A HYBRID DE ALGORITHM WITH THE VNS ALGORITHM AND ITS VARIATION SVNS TO SOLVE A REAL-WORLD FREQUENCY ASSIGNMENT PROBLEM

The Frequency Assignment is a very important task in the planning of the GSM networks, and it still continues to be a critical task for current (and future) mobile communication operators. In this work, we compare a hybrid Differential Evolution algorithm with the Variable Neighbourhood Search algorithm and also its variant Skewed Variable Neighbourhood Search to solve a real-world Frequency Assignment problem (FAP) in GSM Networks. The results that are shown use accurate interference information. That information was also adopted by other researchers and it represents a real GSM network, granting, therefore, an really important applicability. Furthermore, we have analyzed and compared our approach with other algorithms proposed so far to this problem. Hence, our approach using the SVNS algorithm has proven to be efficient in solving this problem, and permitted us to obtain good results. In fact, with this work we have contributed to the FAP problem with an additional comparison between approaches using metaheuristics based on trajectory (VNS and SVNS) and others based on population (DE).     

一种基于种族分类进化的QoS异构组播路由机制

随着新型网络应用的大量涌现,传统的网络技术已无法满足当前应用在带宽、延迟及出错率等方面的需求,IP over DWDM光互联网以其独特性能优势成为研究热点。基于种族分类进化算法,提出了一种IP over DWDM光互联网服务质量QoS异构组播路由机制。具体地,利用概率论方法处理网络状态参数信息的不确定性;引入模糊数学方法,确定用户对QoS的需求并提供柔性QoS支持;综合考虑网络提供方和用户方的利益,设计公平的带宽定价方法。仿真结果表明,该路由机制获得了良好的综合性能指标,可以有效地解决IP over DWDM光互联网中的柔性QoS异构组播路由选择问题。     

Optimal total exchange in Cayley graphs

Consider an interconnection network and the following situation: Every node needs to send a different message to every other node. This is the total exchange or all-to-all personalized communication problem, one of a number of information dissemination problems known as collective communications. Under the assumption that a node can send and receive only one message at each step (single-port model), it is seen that the minimum time required to solve the problem is governed by the status (or total distance) of the nodes in the network. We present a time-optimal solution for any Cayley network. Rings, hypercubes, cube-connected cycles, and butterflies are some well-known Cayley networks which can take advantage of our method. The solution is based on a class of algorithms which we call node-invariant algorithms and which behave uniformly across the network     

A framework for adaptive collective communications for heterogeneous hierarchical computing systems

Collective communication operations are widely used in MPI applications and play an important role in their performance. However, the network heterogeneity inherent to grid environments represent a great challenge to develop efficient high performance computing applications. In this work we propose a generic framework based on communication models and adaptive techniques for dealing with collective communication patterns on grid platforms. Toward this goal, we address the hierarchical organization of the grid, selecting the most efficient communication algorithms at each network level. Our framework is also adaptive to grid load dynamics since it considers transient network characteristics for dividing the nodes into clusters. Our experiments with the broadcast operation on a real-grid setup indicate that an adaptive framework allows significant performance improvements on MPI collective communications.