SPC、SPL和SPN波长转换竞争解决的研究

对光分组交换中波长共享(SPC)、链路共享(SPL)和节点共享(SPN)的结构进行了理论分析,推导出三种结构的丢包率公式,并对其系统丢包率与负载、输入光纤端口数和每纤波长数的关系进行了数值计算。结果表明:在相同的波长转换器数目(没有达到极限值)时,SPN结构的丢包率低于SPL的丢包率,并且在接近极限值时,SPN结构所需要的波长转换器数目也小于SPL结构所需要的波长转换器数目。     

基于优先级的OBS核心节点性能研究

设计了基于业务优先级的光突发交换核心节点模型,采用多级光纤延迟线的光缓存来提高交换网络的性能.交换节点在4个端口8条波长(4×8核心交换结构)的情况下,当光纤延迟线基本延迟单元为50μs、级数为8,负载为0.8时,丢包率小于0.01;为了满足不同业务服务质量的要求,将数据包按优先级划分,采用基于优先级的插空算法(VFPP),在相同缓存配置条件下使高优先级数据的丢包率降低到以下,在高负载下平均时延小于不区分优先级的情况.     

SPL波长转换竞争解决的研究

对光分组交换中每条链路共享波长转换器(SPL,share-per-link)的结构进行了理论分析,推导出SPL系统的丢包率公式,并对系统丢包率与负载、输入光纤端口数和每纤波长数的关系进行了数值计算.结果表明:SPL的丢包率极限是随着波长数的增加而减小,在SPL结构中当波长转换器数目较小且一定时,波长数大的系统的丢包率比波长数小的系统要大.     

SPN波长转换竞争解决的研究

对光分组交换中节点共享(SPN)的结构进行了理论分析,推导出SPN系统的丢包率公式,并对系统丢包率与负载、输入光纤端口数和每纤波长数的关系进行了数值计算。结果表明:当共享波长转换器的数目从0开始增加时,首先改善的是低负载的丢包率,当低负载的丢包率接近极限后,开始明显改善中负载的丢包率,最后改善高负载的丢包率。     

可用于光分组交换网的一种新型2×1节点接收机

提出了一种可用于光分组交换的2×1节点接收机,其特征在于,缓存是由前馈和反馈形式的光纤延迟线(FDLs)组合实现的。理论分析和仿真结果表明:当前馈和反馈形式的FDLs均可使用时,尽量使用前馈FDL的BCS控制策略更有利于改善接收机的分组丢弃性能,结构能很好地应用于突发业务和非突发业务环境,而且控制复杂度也较低。     

一种新的突发分配业务模型以及在OBS中的应用

文章提出了一种新的突发分配业务模型,给出了这种业务模型的详细定义,并应用此模型和传统的非突发分配模型对光突发交换(OBS)中的交换机构进行了性能分析和对比.计算结果表明,当交换机构扇出比F=1、突发强度B1=2时,突发分配模式下的丢包率比非突发分配模式下的丢包率增加大约一个数量级.也许该突发业务模型并不能真实地反映现实世界的业务流,但其能提供一种逼近现实世界业务流的分析方法.     

基于光波长转换的光分组交换系统的性能分析与仿真

提出并分析了一种具有波分复用的光分组交换架构中置入波长转换器的模型,在该结构中每个输入线都共享波长转换器,讨论了在均衡和非均衡条件下,网络丢包率和波长转换器数目的关系,仿真结果表明该模型能在降低丢包率的同时又能减少波长转换器的数目.     

光分组交换中的波长变换器配置研究

首先对波长变换器的功能及分类进行详细的论述,然后,对波长变换器的配置进行分析,总结出两种波长变换器配置方法,即独占式配置方法和共享式配置方法.针对独占式配置方法,本文使用仿真实验的方法研究了在不同类型的波长变换器下交换节点丢包性能的差异.本文还对独占式配置方法和共享式配置方法进行对比研究.     

一种基于负载选择的光分组交换缓存结构

提出了一种基于业务负载选择的光分组交换(OPS)网络的光缓存结构,根据业务负载大小灵活选择缓存方式。输出缓存光纤延迟线(FDL)采用分段式共享机制配置,输出/反馈共享缓存模块采用简并式配置,以提高有限数目FDL的利用率。分析和仿真表明,这种可选择的缓存结构可以有效降低丢包率和OPS节点需求的FDL数目。     

基于时频二维竞争解决机制的光数据包交换节点性能分析

针对光数据包交换的应用需求,提出了基于时频二维竞争解决机制的光数据包交换节点结构,建立了该节点基于排队论的丢包率分析模型,分析讨论了光交换节点竞争解决机制对丢包率的影响。输出端口归一化负载为0.8时,时频二维竞争解决机制在8波复用和8根延迟线结构下使丢包率降低至约10-7。数值分析结果表明,高端口负载下增加复用波长个数对减小端口丢包率比较有效,低端口负载下增加FDL延迟线数量对减小端口丢包率比较有效。     

一种FDL和LRWC相结合的光分组交换网络的性能分析

研究了FDL和有限长波长转换器(LRWC)相结合的方法来解决异步变长的分组交换网中的冲突问题,对这种冲突解决方案建立了数学模型并进行了理论分析,提出了一个用于修正最佳延迟单元的公式,即在负载较大的情况下,我们要求延迟单元较小,这样可显著的降低在此交换网中的分组丢失率;对系统丢包率与负载、FDL数目和最佳延迟单元的关系进行了研究和讨论,结果表明:在同样的输入负载情况下,有限长波长转换器(LRWC)的引入可以降低缓存的数量;对延迟单元的修正可以大大降低丢包率,同时系统的性能较之单独使用FDL时有较大的改善。     

Contention resolution and QoS provisioning using sparse fiber delay lines in WDM networks

In this paper, we combine fiber delay lines (FDL) and optical wavelength conversion (OWC) as the solution for the burst contention problem in optical burst switching (OBS). We present a placement algorithm, k-WDS, for the sparse placement of FDLs at a set of selected nodes in the network. The algorithm can handle both uniform and non-uniform traffic patterns. Our extensive performance tests show that k-WDS provides more efficient placement of optical fiber delay lines than the well-known approach of placing the resources at nodes with the highest experienced burst loss. Performance results are also given to compare the benefit of using FDLs alone, OWCs alone, as well as a mixture of both FDLs and OWCs. A new algorithm, A-WDS, for the placement of an arbitrary numbers of FDLs and OWCs is presented and evaluated under different uniform and non-uniform traffic loads using network simulation of the NSFNET topology and randomly generated graphs. The paper is concluded by presenting the design of a cost-effective optical switch equipped with variable-delay FDL bank. Based on the switch design, a scheme to provide differentiated services for multiple classes of traffic is presented and evaluated.     

A Totally Shared Optical Packet Switch: Dimensioning, Control Algorithm and Performance

In this paper, a novel optical packet switch is proposed, which uses a set of shared fiber delay lines (FDLs) and a set of shared tunable wavelength converters (TWCs) to resolve optical packet contentions. In addition, two control algorithms, i.e., Fiber-First (FF) and Wavelength-First (WF), are proposed to schedule optical packets. Performance of the novel switch is evaluated by means of simulation experiments. Simulation results show that based on either of these two control algorithms, the switch can achieve super performance without employing a lot of FDLs and TWCs. Moreover, the performance of FF and WF is compared. Detail analyses are also given in this paper.     

A framework for fiber delay‐line buffers in packet‐based asynchronous multifiber optical networks (PAMFONET)

A major challenge in packet‐based optical networks is packet contention, which occurs when two or more packets are heading to the same output at the same time. To resolve contention in the optical domain, a fundamental approach is fiber delay‐line (FDL) buffering, in which packets can be delayed for a fixed amount of time. In the literature, the performance of FDL buffering has been studied extensively. However, most existing works are based on an assumption that there is only one fiber per link in the network. In this paper, we address the architecture and performance of FDL buffers in packet‐based asynchronous multifiber optical networks (PAMFONET), in which each link in the network may consist of multiple optical fibers. We propose a framework for FDL buffers in PAMFONET, in which we provide three essential architectures and corresponding packet scheduling policies. Extensive simulation results show that, with appropriate settings, the same number of FDLs can lead to better performance in multifiber networks than in single‐fiber networks. Copyright © 2011 John Wiley & Sons, Ltd.     

Burst loss and delay in optical buffers with offset-time management

In this paper, we study the loss and delay of data bursts in an optical buffer. We assume that this buffer consists of a number of fiber delay lines (FDLs). In order to guarantee quality of service (QoS) differentiation in such a buffer, we investigate analytically an offset-time based scheduling mechanism. We consider a system with C QoS classes, where the high-priority QoS classes have a larger offset time than the low-priority QoS classes. For this system, we calculate the total burst loss probability and the burst loss probability within each QoS class. Furthermore, we study the delay of an arbitrary arriving data burst, as well as the delay of an arriving data burst of a certain QoS class. MACS: Stochastic Modeling and Analysis of Communication Systems     

Buffered time-wavelength cross-connects: Architectures and performance evaluation

An all-optical approach to reduce the speed mismatch between electronic sources and high-speed wavelength channels is to time-division multiplex low-capacity circuits onto each wavelength. In such a Time-Wavelength-Switched Network (TWSN), the optical crossconnects (OXCs) are configured to switch time-wavelength-slots within the network. The OXCs can be deployed with a bank of fiber delay lines (FDLs) to improve the connection slot scheduling and decrease the connection blocking probability. In this paper, we consider the two broad scenarios of sharing a bank of FDLs: shared per output link (SPL) and shared per crossconnect (SPC). We present several OXC architectures and develop graph formulations that can be used to optimally solve the scheduling problem. We also incorporate wavelength conversion and feedback in these architectures and study the impact of various FDL configurations on a crossconnect’s performance. Results using numerical simulations show that the FDL configuration does in fact affect the performance of the OXC. We also evaluate the performance of an OXC equipped with an FDL bank for both the SPL and SPC scenarios by considering sparse wavelength converters (limited number of full range wavelength converters). Results show that using sparse converters along with FDLs could provide significant benefits.     

Performance modeling of optical-burst switching with fiber delay lines

We develop analytical models to evaluate the performance of optical-burst switch (OBS) architectures employing fiber delay lines (FDLs) as optical buffers to reduce burst-loss probability. The performance of such architectures cannot be captured accurately using traditional queueing models, since FDLs behave fundamentally differently from conventional electronic buffers. We formulate a Markovian model to evaluate the system performance when the burst-arrival process is Poisson and the burst lengths are exponentially distributed under an idealized model of FDL behavior. The model accurately captures both the balking and deterministic delay properties of FDLs, but the complexity of the model makes it infeasible for solving problems of practical interest. By considering approximations of the model in the regimes of short and long FDLs, we develop relatively simple closed-form expressions that can be used for dimensioning OBS architectures. We also extend the approximate model to include the impact of FDL delay granularity. We present numerical results that validate our modeling approach and demonstrate that significant performance gains in optical-burst switching are achievable when FDLs are employed as optical buffers.     

光分组交换网络的冲突解决：用光纤延迟线还是波长转换器

该文研究了光分组网络的冲突处理问题,提出了两种异于传统设计方法的交换结构。研究表明:对于非突发性业务,非简并排列方式的光纤延迟线是成本最低的解决手段;而对于突发业务,将波长转换器和延迟线结合使用是兼顾分组丢弃性能,系统体积和成本的较好策略,文中基于此给出了系统设计原则,该原则可确保系统节约大量的波长转换器和延迟线,对改善系统的整体性能十分有利。     

在光缓存器中节省光延迟线的技术

使用光纤延迟线(FDL)是构造全光缓存器的基本手段.但在当前提出的全光缓存器设计中,FDL利用率即缓存容量与所使用的FDL总长度之比是相当低的(通常为2/N,其中N为输入端口数).为了解决这个问题,提出了两种新的FDL组织形式:线性结构和树状结构,用于代替传统设计方法中功能相同的FDL模块.这种方法可以应用在多种光缓存器设计中,将FDL利用率提升至一个与N无关的常量或是1/log2N,节省效果是十分显著的.     

光纤局域网中一种新的光缓存器级联结构

采用光分路器级联光纤延迟线作为波分复用星形网的光接收机缓存可以提高网络的性能.光纤延迟线的个数影响网络的性能,它们之间级联的方式影响整个网络的性价比.对网络性能模拟的结果表明当光纤延迟线的个数增加到一定数量之后再继续增加,网络性能的提高很小.在此基础上,提出了一种新的光纤延迟线级联结构,这种结构具有无源、可模块化、高可靠性和高性价比的突出优点.