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。     

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。     

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.     

共享有限范围多波长和全单波长转换器的光组播冲突解决方案

研究了一种有限范围多波长转换器(LMWC)反馈共享连接和全单波长转换器(FRWC)输出共享连接相结合的解决全光组播波长资源竞争的解决方案,并提出有限范围多波长转换器优先的波长变换调度算法,以最大双向匹配最小边长权重方法选择多波长转换器解决冲突光组播波长变换。仿真结果表明:所提的结构与输出共享全多波长转换器(FMWC)节点结构或输出共享FRWC节点结构相比,都能够明显降低光组播节点的分组丢包率(PLP),减少系统需求LM-WC多波长转换器的数目,提高多波长转换器的利用率;LMWC具有不同波长转换范围对光分组冲突解决性能也有影响。     

基于共享有限波长和参量波长转换器的冲突解决方案

研究了一种共享有限波长转换器(LRWC)和参量波长转换器(PWC)相结合的解决全光分组波长资源竞争的方案,并提出了PWC优先算法作为光分组交换中的波长竞争解决方案。仿真结果表明:本文结构与共享LRWC节点结构相比,减少了波长转换器的数目,并且能够明显降低光分组交换节点的分组丢包率(PLP),提高波长转换器的利用率。研究还发现,不同波长转换器配置方案对系统性能有影响。     

波长转换能力受限网络的路由算法研究

波长转换器的应用有效地提高了光网络的网络性能.把整数线性算法(ILP)做了相应改动并应用到所有节点均配有波长转换能力受限的波长转换器的OBS网络中,与通常采用的最短路径算法(SP)的性能进行了比较分析,同时在典型拓扑上进行了仿真.结果表明ILP算法比SP算法更有效地降低了全网丢包率.     

一种新颖的全光分组交换节点结构及其性能分析

本文提出了一种共享波长转换器和光纤延迟线的全光分组交换结构,与传统的设计方法和实验报道相比,该结构提供了更灵活的冲突解决措施.为了获得与在交换系统输入级分别为每个波长信道提供波长转换器相等价的性能,本文给出了交换结构最多所需的转换器数量.仿真结果表明,本文结构是兼顾交换系统体积、成本和性能等三方面较理想的折衷方案.研究还表明,光纤数与每纤的波长数量之积愈大,本文结构所节约的转换器和延迟线数量将愈加可观.     

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。     

慢光缓存器及其在光分组交换中的应用

将一种新的光缓存技术--慢光可变延时缓存器,与可调波长转换器结合,构成光分组交换模型.简要分析了慢光缓存器的时延特性,并对其解决信息网络交换拥塞进行了应用设计与仿真,分析结果表明,慢光缓存器与光纤延迟线缓存相比较,不仅能更有效地降低丢包率,而且还可以简化光分组交换的结构,其体积更小,使用更灵活.     

基于级联倍频+差频效应的宽带波长转换过程

利用阶梯分段准相位匹配结构实现了基于级联倍频+差频效应的单通/双通宽带波长转换.对于固定的晶体长度,通过增加阶梯段数并合理设计准相位匹配结构参数,可以同时获得高转换效率、大转换带宽和高平坦性.当晶体长度为3 cm时,在保证平坦度低于0.2 dB的前提下,单通构型波长转换器的转换带宽和最大转换效率可分别达到177 nm和-9.94 dB,而双通构型的分别为170 nm和-4.15 dB.最后对基于阶梯分段准相位匹配结构的波长转换器与基于正弦啁啾光学超晶格和分段光栅结构的波长转换器的特性进行了对比分析,结果显示阶梯分段结构具有良好的综合特性.     

采用部分共享光缓存和共享波长转换器的光分组交换节点性能分析

本文研究了采用部分共享缓存(PSB)和共享波长转换器(SWC)的光分组交换节点在自相似流量下分组丢失率和时延与输出光缓存深度、循环共享光缓存的深度和组数以及波长转换器数量之间的关系,并讨论了相关的尺度和规模问题.结果表明,部分共享光缓存和共享波长转换器的光分组交换节点交换结构可以达到很高的性能;采用共享方式可显著减少波长转换器的数量;在保持共享缓存总的深度不变的情况下,适当增加循环共享光缓存组数可以使交换达到更好的性能.     

Resources sharing in optical packet switches with limited-range wavelength converters

This paper compares selected optical packet switching architectures that use the wavelength conversion technique to solve the packet contention problem. The architectures are equipped with shared and limited-range wavelength converters (LRWCs). This paper focuses on two architectures: the shared per node (SPN) and the shared per output fiber (SPOF) architectures, in which the wavelength converters are SPN and output fiber, respectively. Packet loss probability is expressed as a function of the number of wavelength converters used, by means of analytical models validated by simulations. The analytical results show how the use of a reduced number of LRWCs with small range allows the switch to obtain the same performances of an architecture equipped with all of the wavelength converters and using a full wavelength conversion.     

Dimensioning of the Wavelength Converters in a WDM Optical Packet Switch

This paper analyzes the performances of a WDM optical packet switch making use of fiber delay lines to resolve output packet contentions; the optical packet switch is equipped with tunable wavelength converters which can shift optical packets to any wavelength of the output link which they are directed to. As not all packets need conversion, we propose a dimensioning technique allowing to reduce the number of converters and to improve the signal quality by reducing unnecessary conversions. The obtained results show that a remarkable reduction of the number of converters is obtained with respect to that needed by other switches described in literature. Such a saving is achieved by maintaining the packet loss probability below a prefixed threshold.     

An optical packet contention resolution supporting QoS differentiation with LRWC wavelength converters for OPS

The wavelength conversion is regarded as an effective way to resolve the optical packet contention in the wavelength domain for optical packet switching. An optical packet switching node, based on shared-per-node equipped with limited range wavelength converters and parametric wavelength converters (SPN-LP), is designed to further reduce optical packet loss probability. A novel optical packet contention resolution with priority differentiation wavelength scheduling algorithm to support quality of service (QoS) for the SPN-LP architecture is put forward in the article. The simulation results show that proposed optical packet resolution enables a good QoS differentiation, namely the high priority contending optical packet has the sufficient low packet loss probability.     

Packet loss and delay performance of feedback and feed-forwardarrayed-waveguide gratings-based optical packet switches with WDMinputs-outputs

This paper analyzes the packet loss and delay performance of an arrayed-waveguide-grating-based (AWG) optical packet switch developed within the EPSRC-funded project WASPNET (wavelength switched packet network). Two node designs are proposed based on feedback and feed-forward strategies, using sharing among multiple wavelengths to assist in contention resolution. The feedback configuration allows packet priority routing at the expense of using a larger AWG. An analytical framework has been established to compute the packet loss probability and delay under Bernoulli traffic, justified by simulation. A packet loss probability of less than 10^-9 was obtained with a buffer depth per wavelength of 10 for a switch size of 16 inputs-outputs, four wavelengths per input at a uniform Bernoulli traffic load of 0.8 per wavelength. The mean delay is less than 0.5 timeslots at the same buffer depth per wavelength     

Exploitation of DWDM for optical packet switching with quality ofservice guarantees

This paper addresses the problem of building optical packet switches that are able to effectively cope with variable length packet traffic and quality of service management, therefore able to support IP traffic. The paper aims at showing that the availability of dense wavelength division multiplexing is crucial. By suitably exploiting the wavelength dimension a multistage fiber delay line buffer can be implemented, with fine granularity and long delay with an architecture of limited complexity. This is necessary to fulfill the buffering requirements of variable length packets. Furthermore, the wavelength domain is proved to be more effective than the time domain to manage different levels of quality of service. Algorithms are presented that are peculiarly designed for this environment showing that they can effectively differentiate the packet loss probability between three priority classes     

Cost Evaluation of Optical Packet Switches Equipped With Limited-Range and Full-Range Converters for Contention Resolution

Two architectures are proposed for a wavelength-division multiplexed optical packet switch equipped with both limited-range wavelength converters (LRWCs) and shared full-range wavelength converters (FRWCs). The FRWCs are used to overcome the performance degradation in terms of packet loss probability due to the use of LRWCs only. Two different sharing strategies of the FRWCs are considered. In the first architecture, a pool of FRWCs is shared among the arriving packets. In the second one, the sharing is only partial and the packets directed to the same output share a same pool of FRWCs. A probabilistic model is proposed to dimension the number of shared FRWCs so that the same packet loss probability of a switch equipped with only shared FRWCs is guaranteed. After introducing a cost model of the converters depending on the conversion range, we show that the architectures may allow a conversion cost savings on the order of 90%.     

Performance of fiber delay‐line buffers in asynchronous packet‐based optical switching networks with wavelength conversion

A major challenge in asynchronous packet‐based optical networks is packet contention, which occurs when two or more packets head to the same output at the same time. To resolve contention in the optical domain, two primary approaches are wavelength conversion and fiber delay line (FDL) buffering. In wavelength conversion, a contending packet can be converted from one wavelength to another in order to avoid conflict. In FDL buffering, contending packets can be delayed for a fixed amount of time. While the performance of wavelength conversion and FDL buffering has been evaluated extensively in synchronous networks with fixed‐sized packets, in this paper, we study the performance of FDL buffers in asynchronous packet‐based optical networks with wavelength conversion. An analytical model is proposed to evaluate the performance in terms of packet loss probability and average delay. Extensive simulation and analytical results show that, with appropriate settings, FDL buffers can perform much better in switches with wavelength conversion than in switches with no conversion. Copyright © 2014 John Wiley & Sons, Ltd.