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.     

应用于无线信道的混合型冲突分解算法

冲突分解算法是一种能够有效改善无线信道多址接入协议性能的方式.传统的冲突分解算法包括树形分解算法和先到先服务的冲突分解算法,但是这两种分解算法都存在着一定的不足.本文提出了一种新型的混合型冲突分解算法(Hybrid Splitting Algorithm-HSA),HSA算法继承了树形分解算法和先到先服务冲突分解算法的优点,不仅考虑了碰撞分组的产生时间,使先产生的分组先得到服务,同时当系统中存在产生间隔比较接近的分组时,采用树形分解算法,使整个分解过程不再仅仅局限于分组的产生时间,从而有效地减少了分解所需的总时隙数,提高了冲突分解算法的性能.理论分析和仿真结果显示HSA算法是一种正确可行的算法.     

基于同波长光纤延迟线集光突发交换结构及其性能分析

由于光突发交换机制本身就避免了光缓存的使用，但是现实中，光突发包之间竞争以及提供优先级服务又依靠光纤延迟线来解决。为此，我们设计了应用光纤延迟线的光突发交换网络核心节点结构。为了避免光纤延迟线色散引起的突发包输入排队缓存偏移，在该结构中设计了同波长光纤延迟线集。采用了空分交换矩阵，避免了波长转换的需要。为了有效运行该交换结构，我们提出了输入排队与自适应光缓存调度算法，而该算法不仅仅适用于光突发交换，也适合于光纤延迟线得到普遍应用的光分组交换。该调度算法能够提供优先级服务，避免队头阻塞，对该调度算法建立了严格的理论分析模型，并进行了仿真。仿真结果表明，与传统的延迟线竞争解决方案相比，这一调度算法能够改善交换性能1到2个数量级，是利用光纤延迟线解决光突发交换中竞争问题的一个较佳方案。     

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.     

一种用于光组播冲突解决的节点结构及其调度策略

光分组在核心节点处的冲突解决问题是实现全光 组播分组交换的关键。本文提出了一种新型的解决光组播冲突的节 点结构,用于冲突解决的部分包括输出共享的网络编码模块和光纤延迟线(FDL)环 形反馈共享缓存(FDL-LSFB)模块。网络编码 模块将异或网络编码作为冲突解决方式,利用全光异或门将冲突组播进行网络编码并且改变 编码后分组波长,从而避免波长 冲突。而FDL-LSFB模块由子交换矩阵和FDL缓存组连接成环状,且冲突组 播可从任意子交换矩阵进出缓存模块, 使用少数的FDL可以提供大容量的光缓存、提高FDL利用率。针对FDL-LSFB模块冲突组播调 度问题,为减小缓存时延,设计了最小缓存长度级联控制算法(MLCBST),进而提出冲突光 组播的总调度策略。仿真结果表明,本文提出的组播节点结构和调度策略在降低丢包率(PLP)和减小缓存时延方面具有明显的效果。     

一种全包交换实验网络——光弹性分组环

选择了一种使用光缓存器比较少的网络--光弹性分组环进行了全光分组交换实验.该网络的净负荷不进行光/电/光转换,只对帧头进行转换、地址识别和调度,从而克服了光电转换的电子瓶颈.在光节点上,只需使用一个全光缓存器作为转发缓存器,而使用了两个电缓存器分别作为下路接收缓存器和上路发送缓存器.报告了该实验网络的拓扑、节点结构、数据通道、MAC层的数据通道控制子层以及所使用的光缓存技术.     

混合缓存型异步光分组交换的一种改进FF-VF算法

光纤延迟线（FDL）是异步光分组交换（OPS）采用的时域冲突解决方案,通过计算其分组丢失率（PLR）发现,在业务负载高,特别是业务负载大于0．7时,PLR性能较差。研究以FDL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结构,并用改进的首选即中的填空（IFF-VF）算法调度冲突的分组,达到改善可变长OPS的PLR目的。分析和仿真结果表明,光电混合缓存和IFF-VF算法能改善可变长OPS在负载较高时的PLR性能,并减少FDL的数目。     

战术局域网TDMA动态优先级轮询调度算法研究

主要针对战术局域网动态时隙分配的优先级轮询调度算法进行了研究。传统的战术局域网集中式轮询算法不能很好地满足节点报文传输的动态时隙需求。为此,文章提出了一种动态时隙分配的优先级轮询调度算法。     

一种具有低时延的分组公平循环调度

本文提出了一种新的分组循环调度算法LFRR(Large weight First Round Robin)。为了具有良好的时延特性和较低的实现复杂度,LFRR采取了以下方法:(1)在调度表中为流分配时隙时,LFRR以时隙完全均匀分布为参照,确保分配给一个流的时隙不会过早或过晚地出现在调度表中。(2)LFRR算法中采用了等权值流合并的技术,把权值大于1且权值相等的流合并成一个虚流,以虚流为处理对象,使算法需要处理的对象数目大为减小。(3)当一个时隙适合分配给多个虚流时,LFRR采用了简单的权值大的虚流优先占用时隙的原则。本文对LFRR进行了理论分析和计算机仿真,结果表明LFRR算法的时延性能比WRR(Weighted Round Robin)有了很大提高,同时LFRR算法的公平性也有保证。     

光码标签交换网络边缘节点FEC的研究

构建了光码标签交换网边缘节点的结构,结合光码分复用技术提出了转发等价类(FEC)分组结构的设计方案。分组结构适合变长数据分组的传输,在核心节点能够实现对标签信息的可并行处理,提高了处理效率。在此基础上,针对开销比对网络传输性能的影响,对FEC结构中的各参量与开销比的关系进行了仿真研究;采用了固定时隙算法对数据分组进行封装,对到达率和封装时延与分组丢失率的关系进行仿真分析。     

Performance of two-stage shared fiber delay line optical packet switch under bursty traffic

Packet contention is a major issue in an optical packet switching network. It is not a trivial task to resolve contention due to lack of optical RAM technology. This article proposes a two-stage shared fiber delay line (FDL) optical packet switch for contention resolution. In this article, shared FDLs are used to buffer optical packets, in which a pool of buffer memory is shared among all switch output ports. Most of the existing optical buffering schemes are output-based which require a huge number of FDLs as well as a larger switch size that incur extra implementation cost. However, a shared buffering approach is considered in this article in order to reduce implementation cost. In this article, FDLs are implemented in two stages using an extremely simple auxiliary switch. The proposed switch architecture leads to more efficient use of buffer space. The superiority of the proposed switch architecture has been established by means of extensive simulations. The performance of the proposed switch is investigated under bursty traffic. Simulation result shows that the proposed switch can achieve satisfactory performance at the price of a reasonable amount of FDLs. Moreover, the significance of the proposed switch is confirmed by simulation.     

A Quantized Delay Buffer Model for Single-Wavelength Fiber Delay Line Buffer

The fiber delay line (FDL) buffer is widely used in optical packet switching networks for contention solution. In this paper, a quantized delay buffer model is proposed to analyze the performance of the single-wavelength FDL buffer. Considering the delay quantization in the FDLs, the delay time and the waiting time of the packet are discussed. Without specific assumptions of the packet arrival process and length distribution, the model presents a generic approach to study the delay time distribution and modify the integral equation for the waiting time distribution. Analytic and exact results of the two aforementioned distributions can be obtained without any approximation. The accuracy of the model is validated through simulation.     

Blocking and Delay Analysis of Single Wavelength Optical Buffer With General Packet Size Distribution

Buffers are essential components of any packet switch for resolving contentions among arriving packets. Currently, optical buffers are composed of fiber delay lines (FDL), whose blocking and delay behavior differ drastically from that of conventional RAM at least two-fold: 1) only multiples of discrete time delays can be offered to arriving packets; 2) a packet must be dropped if the maximum delay provided by optical buffer is not sufficient to avoid contention, this property is called balking. As a result, optical buffers only have finite time resolution, which may lead to excess load and prolong the packet delay. In this paper, a novel queueing model of optical buffer is proposed, and the closed-form expressions of blocking probability and mean delay are derived to explore the tradeoff between buffer performance and system parameters, such as the length of the optical buffer, the time granularity of FDLs, and to evaluate the overall impact of packet length distribution on the buffer performance.     

Heuristic performance model of optical buffers for variable length packets

Optical switching (optical packet switching, optical burst switching, and others) provides alternatives to the current switching in backbone networks. To switch optically, also packet buffering is to be done optically, by means of fiber delay lines (FDLs). Characteristic of the resulting optical buffer is the quantization of possible delays: Only delays equal to the length of one of the FDLs can be realized. An important design challenge is the optimization of the delay line lengths for minimal packet loss. To this end, we propose a heuristic based on two existing queueing models: one with quantization and one with impatience. Combined, these models yield an accurate performance modeling heuristic. A key advantage of this heuristic is that it translates the optical buffer problem into two well-known queueing problems, with accurate performance expressions available in the literature. This paper presents the heuristic in detail, together with several figures, comparing the heuristic’s output to existing approaches, validating its high accuracy.     

Scheduling algorithms for shared fiber-delay-line optical packet Switches-part I: the single-stage case

In all-optical packet switching, packets may arrive at an optical switch in an uncoordinated fashion. When contention occurs, fiber delay lines (FDLs) are needed to delay (buffer) the packets that have lost the contention to some future time slots for the desired output ports. There have been several optical-buffered switch architectures and FDL assignment algorithms proposed in the literature. However, most of them either have high implementation complexity or fail to schedule in advance departure time for the delayed packets. This paper studies the packet scheduling algorithms for the single-stage shared-FDL optical packet switch. Three new FDL assignment algorithms are proposed, namely sequential FDL assignment (SEFA), multicell FDL assignment (MUFA), and parallel iterative FDL assignment (PIFA) algorithms for the switch. The proposed algorithms can make FDLs and output-port reservation so as to schedule departure time for packets. Owing to FDL and/or output-port conflicts, the packets that fail to be scheduled are discarded before entering the switch so that they do not occupy any FDL resources. It is shown by simulation that with these algorithms, the optical-buffered switch can achieve a loss rate of /spl sim/10/sup -7/ even at the load of 0.9. These algorithms are extended to the three-stage Clos-Network optical packet switches in the companion paper.     

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。     

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.     

Performance modeling of QoS differentiation in optical packet switching via FDL access limitation

We present an exact analytical model for single-wavelength quality of service (QoS) differentiation in a two-class optical packet switch. In this system, QoS differentiation is achieved by limiting the set of fiber delay lines (FDLs) to the low-priority class, whereas the high-priority class is allowed to access the entire FDL bank. The analytical model is based on multi-regime Markov fluid queues and is extensible to multi-class systems with more than two classes. Markovian arrival process packet arrivals and phase-type distributed packet sizes are considered for the purpose of generality. The proposed analytical model is validated through simulations. The numerical results provide insight into determining appropriate subsets of FDLs allowed for the access of the low-priority class. The results also show that it is possible to direct almost all the packet losses to the low-priority class under moderate loads.     

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.