共享式光缓存中的控制策略

在光分组交换（0PS）节点结构中,由光纤延迟线（FDL）所构成的光缓存是解决光分组冲突的一种非常有效的方法。对于共享式FDL光缓存,由于FDL竞争的出现会导致光缓存性能的恶化。为了有效利用光缓存,需要对光缓存资源的分配进行有效的控制。为此,针对共事式FDL光缓存,提出一种有效的光缓存控制策略,即有限贪婪模式（limited greedy mode,LGM）缓存控制策略。使用仿真实验的方法对LGM的性能进行了评估。     

光缓存配置研究

首先讨论了FDL光缓存的分类及常用的配置方法,然后以共享式FDL光缓存为研究目标,分别针对简并式、双简并式和递增简并式等三种光缓存配置方法展开对比研究。最后,使用仿真实验的方法对这三种光缓存配置方法的性能进行评估。     

Scheduling Algorithms for a Slotted Packet Switch with either Fixed or Variable Length Packets

We address the problem of congestion resolution in optical packet switching (OPS). We consider a fairly generic all-optical packet switch architecture with a feedback optical buffer constituted of fiber delay lines (FDL). Two alternatives of switching granularity are addressed for a switch operating in a slotted transfer mode: switching at the slot level (i.e., fixed length packets of a single slot) or at the burst level (variable length packets that are integer multiples of the slot length). For both cases, we show that in spite of the limited queuing resources, acceptable performance in terms of packet loss can be achieved for reasonable hardware resources with an appropriate design of the time/wavelength scheduling algorithms. Depending on the switching units (slots or bursts), an adapted scheduling algorithm needs to be deployed to exploit the bandwidth and buffer resources most efficiently.     

光分组交换网络中光纤延迟线缓存技术

光分组交换网是全光网络发展的必然趋势.然而,光分组交换网络发展的瓶颈是光缓存技术.目前,在光域比较现实的还是采用光纤延迟线(FDL)作光缓存.重点研究了光纤延迟线光缓存技术,对FDL光缓存技术进行了深入的分析和归纳,并对每一种光纤延迟线光缓存调度策略的优缺点都进行了细致的分析.最后指出了光纤延迟线光缓存技术的未来研究重点和发展方向.     

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.     

一种新型的输出缓存式光分组交换节点性能分析

光缓存和波长变换是解决光分组竞争的有效方法.提出一种称为FCOB的新型光分组交换节点结构,它使用固定波长变换器和输出式光缓存来解决光分组的竞争.针对FCOB交换结构,还提出一种有效的竞争控制算法.最后,使用仿真实验对FCOB的性能进行了评估.仿真结果表明,虽然使用的是固定波长变换器,但FCOB交换结构仍具有良好的性能.     

基于光纤环的光缓存器

提出了一种基于光纤环的光缓存器的结构,对结合半导体光放大器作光开关的此结构的物理模型进行了详细描述,并根据此模型分析了其增益、噪声、信噪比等方面的特性.     

不同长度分布下的光分组交换性能研究

通过分析不同分组长度分布(PLD)对光分组交换(OPS)性能的影响,以便为OPS在不同长度业务下配置不同的冲突解决方案.研究了光分组在固定长度分布、指数分布和因特网经验长度分布下分别对没有光纤延迟线(FDL)和有FDL下的OPS的性能影响.分析和仿真表明,因特网经验长度分布的业务在没有FDL缓存的条件下,获得最低的分组丢失率(PLR)性能;而固定长度分布的业务,仅在OPS配置有FDL时才可以获得最低的PLR性能.     

具有反馈式光缓存的OPS节点结构性能研究

对反馈式光分组交换节点的性能进行深入分析,并针对现有反馈式光分组交换节点结构的不足,提出一种改进的反馈式光分组交换节点结构,即SMOP-TWC交换结构.最后,本文使用仿真实验的方法对SMOP-TWC交换结构的性能进行深入研究.     

Optimized Combination of Converter Pools and FDL Buffers for Contention Resolution in Optical Burst Switching

Optical burst switching (OBS) has attracted interest as a transport network architecture for the future optical Internet. As OBS relies on statistical multiplexing efficient contention resolution is a key issue in order to achieve a low burst loss probability. First, this paper discusses options and key design parameters for contention resolution in OBS. Then, it evaluates the performance of OBS nodes which employ shared wavelength converter pools and simple fiber delay line (FDL) buffers. Finally, optimized strategies for the order of probing a wavelength converter pool and an FDL buffer for contention resolution are presented and compared. It is shown that these strategies can be used to optimize performance for a given, for example, minimal cost, dimensioning of the wavelength converter pool and the FDL buffer.     

FDL结构竞争解决的研究

使用光纤延时线（FDL）来解决光分组交换中的竞争问题,研究系统丢包率、时延与输入端口数、输出端口数、FDL数之间的关系,并比较输入端口优先、FDL优先、输入端口和FDL优先级的三种光分组调度策略。结果表明：适当减少端口数,增大FDL数目可以使丢包率趋近于零;而适当增大端口数,减小FDL数目又可以使时延减小。因此,在使用FDL解决竞争冲突时,端口数和FDL数目的选择很重要,它们之间的关系大小直接影响到丢包率和时延的大小。     

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。     

Analytical MMAP-Based Bounds for Packet Loss in Optical Packet Switching with Recirculating FDL Buffers

The major goal of optical packet switching (OPS) is to match switching technology to the huge capacities provided by (D)WDM. A crucial issue in packet switched networks is the avoidance of packet losses stemming from contention. In OPS, contention can be solved using a combination of exploitation of the wavelength domain (through wavelength conversion) and buffering. To provide optical buffering, fiber delay lines (FDLs) are used. In this paper, we focus on an optical packet switch with recirculating FDL buffers and wavelength converters. We introduce the Markovian arrival process with marked transitions (MMAP), which has very desirable properties as a traffic model for OPS performance assessment. Using this model, we determine lower and upper bounds for the packet loss rate (PLR) achieved by the aforementioned switch. The calculation of the PLR bounds through matrix analytical methods is repeated for a wide range of traffic conditions, including highly non-uniform traffic, both in space (i.e., packet destinations) and time (bursty traffic). The quality of these bounds is verified through comparison with simulation results.     

End-to-End Delay Evaluation for an Optical Transparent Packet Network

In this paper an all optical packet switching network is considered to provide transparent transport of information. To this end the evaluation of the end-to-end packet delay is performed by means of analytical tools. Bounds are proposed for the maximum packet delay and calculated by means of a simple additive formula that can be used for approximate end-to-end delay evaluation. Packetization and multiplexing delay at the access interface and queuing delay inside the nodes are considered as contributions to the whole packet delay. The obtained results shown that time transparency can be reached within suitable network design.     

Routing Strategies to Minimize Packet Loss in an Optical Packet Switched Network with Recirculating FDL Buffers

The major goal of optical packet switching (OPS) is to match switching technology to the huge capacities provided by (D)WDM. We study optical packet switches with recirculating fiber delay line (FDL) buffers. Through simulation, we have assessed the logical performance of a single optical packet router (OPR), focusing on packet loss rate (PLR). By verifying that our scheduling algorithm does not alter the traffic profile characteristics from in- to output, we illustrate how the single node results can be used to assess network-wide performance. We use the capability of assessing end-to-end PLRs to develop network-wide routing algorithms designed to minimize the maximal PLR occurring in the network. In case studies on pan-European networks, we first compare two algorithm variants and thereafter we compare the PLR-based routing algorithm with both load balancing and shortest path routing. While load balancing achieves PLRs that are multiple orders of magnitude lower than shortest path routing, the PLR-based algorithm can reach PLRs up to two orders of magnitude better. The improvement in PLR comes at the price of only a small increase in used bandwidth (a few percent). Subsequently we show that the discussed PLR-based routing algorithm can be easily extended to multiple priorities. By introducing multiple priorities we can keep the loss rates for high priority traffic very low. However, it may lead to an increase of the obtained minimal max-PLR value for low priority traffic. But as we prove this increase to be limited, the cost of introducing multiple priorities is small.     

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。     

异步光分组交换的光电混合队列及调度

研究了以光纤延迟线作为主要的常规缓存,以电存储器作为辅助缓存的光电混合缓存的光电混合缓存结构,并用改进的FF-VF算法调度冲突的分组,达到改善长度可变光分组交换的分组丢失率目的.分析和仿真结果都表明,光电混合缓存和改进的FF-VF算法能改善可变长光分组交换在负载较高时的分组丢失率性能,并减少光纤延迟线的数目.     

自适应弹性环光缓存结构设计及其网络性能分析

最大缓存时间限制、时延粒度限制、光分组长度限制3大限制因素,对传统光缓存器的前馈型和反馈型两种结构进行了分析。分析表明,影响光缓存器性能的3大限制因素在两种结构中的相互制约关系限制了光缓存器性能的进一步提高。在此基础上提出的一种自适应弹性环光缓存器(E-FLOB)结合了两种传统结构的优势,并分离了3大限制因素间的相互制约关系。结构分析显示,E-FLOB在缓存级数为16时可减少反馈型光缓存器噪声积累约3个数量级。网络性能仿真表明,弹性环结构比前馈型结构使用更少的缓存级数,获得比两种传统结构更低的分组丢失率。     

基于光传输的精密标准延时模块设计

该文在分析了基于光传输的延时系统原理的基础上,介绍了精密标准延时模块的组成。对模块的发射、传输、接收和放大等组成部分进行了理论分析和实际设计,重点讲述了光纤链路及逻辑控制的设计和实现。介绍了该模块时延特性测试系统的组成和搭建,并通过矢量网络分析仪对设计完成的光延时模块实物进行标准延时测试,分析对比测试结果,得出测量误差,并分析误差原因。该模块的实现为某系统的自校准提供了标准延时参考,同时可作为便捷有效的溯源手段。     

多抽头宽带光纤延迟线的设计与分析

提出一种具有实用价值的步进延迟可调的多抽头宽带光纤延迟线。首先简要介绍了光纤延迟线的优点、工作原理和基本结构,分析了光纤延迟线的增益、带宽、动态范围和失真指标,着重分析了多抽头宽带光纤延迟线的光纤分配网络的设计和实现。最后对设计的多抽头宽带光纤延迟线进行了测试,给出了测试方法和测试结果,并将它同国际、国内其他同类产品做了对比,描述了它的应用前景和应用领域。