时隙光分组交换网络中一种新的光缓存优化配置方案

研究了时隙光分组交换网中的光缓存配置方案,针对反馈共享式缓存结构,通过对传统的连续分布式光缓存结构中不同延迟粒度的光缓存丢包的分布情况仿真结果研究,发现在传统的连续分布式光缓存结构中,丢包主要发生在小粒度的光缓存上,为此,提出通过适当增加小粒度的光缓存的方法,达到有效地降低丢包率,仿真结果显示,这种光缓存方案可以明显降低节点的丢包率.     

一种反馈FDL结构竞争解决丢包率的研究

对反馈FDL结构的光分组交换竞争解决方案建立了数学模型并进行了理论分析，推导出了在反馈FDL输入分组比输入光纤输入分组具有更高输出优先级时的系统丢包率公式，对系统丢包率与负载、输入光纤端口数和FDL数目的关系进行了数值计算和讨论.结果表明：由于FDL缓存分组的概率与输入分组负载的非线性关系导致了反馈FDL结构在低负载时对丢包率的改善非常明显，对高负载的改善却十分有限.随着FDL数目的增加，对系统丢包率的改善不会趋于一个极限值，这是与使用波长转换器进行竞争解决的不同之处，因此使用反馈FDL结构可以降低波长转换器的丢包率极限.     

光突发交换的交换控制策略和光缓存配置

光突发交换是面向下一代互联网的光交换模式.讨论了异步光突发交换系统的交换控制策略以及相应光缓存的优化配置策略.除了传统预约模式的交换策略,还研究了非预约和改进型预约模式,它们的性能评估由计算机仿真给出.结果表明:在条件相当情况下,改进型预约模式具有最低的丢包率.同时光缓存的配置对上述几类交换控制策略的性能都有很大影响,仿真结果指出:光缓存的粒度对系统性能具有重要影响,所讨论的几类交换模式都存在最佳时延粒度,研究结果对光交换矩阵的设计有指导意义.     

自相似业务下光缓存设计

提出了在数据包长可变的自相似业务下研究光纤延时线所组成的光缓存问题的解析模型.利用Pareto到达过程来模拟自相似业务.研究表明,缓存深度越大,包丢失率越低,而且存在与业务强度对应的最佳光纤延时线单位,使得在给定的缓存深度下,数据包丢失率最小,在业务强度和缓存深度相同时,Pareto到达比Poisson到达有更大的包丢失率.     

光弹性分组环(ORPR)节点中光分组组装算法研究

介绍了光弹性分组环(ORPR)节点模型,分析了ORPR网络中流量成型时光分组组装算法,提出一种适合ORPR网络的基于控制发送时间的光分组组装算法,给出了该算法的算法结构,并和传统的光分组组装算法做了比较。该算法通过分组发送间隔的调整,使得分组单位时间内的流量的自相似性被平滑,具有很好地抑制突发性的效果,同时,分组组装的时间门限可以被ORPR调度算法动态调整,可以适应缺乏缓存的ORPR网络的调度机制。     

基于半导体光放大器的环路型全光缓存器中功率均衡的新方法

全光缓存器能够在光域内对数据包进行存储而不需经过光电光的变换,成为全光网的重要组成部分,其性能的优劣将直接影响到网络的丢包率等。但在半导体光放大器中交叉增益调制和交叉相位调制效应并存,导致基于半导体光放大器的环路型全光缓存器中缓存后输出的数据包与未缓存数据包的输出功率间存在不均衡,使得网络误码率增加。在详细分析全光缓存器工作原理的基础上,利用半导体光放大器中交叉增益调制和交叉相位调制并存的现象,巧妙地提出了将控制脉冲反相并配合电可调衰减器的新方法。该方法简单易行,有效解决了此类全光缓存器中数据包输出功率不均衡的难题,缓存器性能得到了极大改善。此方法适用于所有基于半导体光放大器的环路型全光缓存器。     

光突发交换网络试验平台

研究并实现了几种光突发交换网络的关键技术,包括高速的突发组装技术、突发调度技术及突发光发射及接收技术等,其中突发接收具有较高的灵敏度和小于80 ns的时钟数据恢复时间.在这些技术的基础上,建立了一个灵活且可扩展的光突发交换网络实验平台.在OBS网络平台上进行了TCP性能评估实验和多QoS业务传输实验。实验结果表明光突发网络中丢包率严重影响其上TCP的性能,但若丢包率小于0.1%,则TCP性能可得到一定程度的保证.光突发交换网络实验平台上的TCP传输实验还表明了OBS物理层带来的额外延时对上层TCP带宽有极大的影响.实验结果还验证了OBS网络中的QoS保证机制.     

光分组组装机制对自相似流的整形效应分析

通过系统仿真和数值分析，全面地分析了光分组交换网中分组组装机制对自相似流的整形效应，结果表明：光分组组装机制通过改善流量的关键特性，包括：自相似性、短程相关性和边缘分布，来实现自相似流量整形. 而且，业务强度越小、光分组组装门限越大、组装计时间隔越小，光分组组装机制对自相似流的整形效果越好.     

光弹性分组环节点光分组的组装及时延分析

分析了光弹性分组环(ORPR)网络中流量成型时光分组组装算法,提出一种适合ORPR网络的基于控制发送时间的光分组组装算法,并给出了该算法的算法结构.该算法在混合门限组装算法的基础上,通过增加一个控制分组发送间隔的参数,使得光分组单位时间内流量的突发性被平滑,并可以保证ORPR网络的服务质量(QoS)性能,适合于使用容量有限光缓存的ORPR网络.对ORPR节点光分组平均组装时延进行了详细的分析,新算法通过对分组发送间隔的调整,使在不同负载条件下,组装时延的概率分布基本相同.在ORPR中,平均组装时延的稳定对ORPR网络的QoS性能和公平性调度有重要意义,而发送时机的合理选择,可以保证ORPR网络的QoS性能以及公平性.仿真结果表明,新算法使得ORPR网络中的光分组平均组装时延相对稳定,在大多数情况下,可以保证ORPR网络的调度要求.     

半导体光放大器引起的光控器件中的信号损伤分析

在双环耦合全光缓存器的基础上分析了全光分组交换网络中以半导体光放大器（SOA）为相移器件的反馈型全光缓存器输出的信号损伤,包括SOA的非线性及载流子恢复时间限制引起的脉冲畸变与连续码流中的图样失真和SOA的自发辐射噪声累积引起的信噪比恶化及缓存器结构引起的“漏光”问题.理论分析及实验结果表明,在采用反相控制并注入高功率控制光的情况下,脉冲畸变与图样失真被抑制,由信噪比恶化及漏光决定的光分组的缓存圈数被限制在20—30圈.得到的结果对基于SOA的光缓存器及逻辑器件同样具有借鉴作用. 关键词： 全光分组交换 全光缓存器 信号损伤 半导体光放大器的噪声分析     

Analysis of Wavelength-Routed Optical Burst-Switched Network Performance

This paper studies a novel scalable network architecture combining optical burst switching (OBS) with dynamic wavelength allocation to guarantee quality of service (QoS), forming a wavelength-routed optical burst-switched network. All processing and buffering functions are concentrated at the network edge and bursts are assigned to fast tuneable lasers and routed over a bufferless optical transport core using dynamic wavelength assignment. Different burst aggregation mechanisms are evaluated for a range of traffic statistics in terms of delay and packet loss rate. New network performance parameters in an analytical model quantify the advantages of dynamic wavelength allocation. The results define the operational gain achievable with dynamic wavelength assignment compared to quasi-static wavelength routed optical networks.     

Analysis of Wavelength-Routed Optical Burst-Switched Network Performance

This paper studies a novel scalable network architecture combining optical burst switching (OBS) with dynamic wavelength allocation to guarantee quality of service (QoS), forming a wavelength-routed optical burst-switched network. All processing and buffering functions are concentrated at the network edge and bursts are assigned to fast tuneable lasers and routed over a bufferless optical transport core using dynamic wavelength assignment. Different burst aggregation mechanisms are evaluated for a range of traffic statistics in terms of delay and packet loss rate. New network performance parameters in an analytical model quantify the advantages of dynamic wavelength allocation. The results define the operational gain achievable with dynamic wavelength assignment compared to quasi-static wavelength routed optical networks.     

Hybrid buffering architecture for packet contention resolution of an optical packet switch

Packet contention is a major issue in optical packet switching network and it is not a trivial task to resolve due to lack of optical RAM technology. In order to resolve contention optical buffering approach is used using fiber delay lines (FDLs). Yet there is a heavy packet loss rate due to unavailability of output port and free FDLs. This paper proposes a hybrid buffering architecture using feed-forward and feedback shared FLDs to resolve packet contention resolution of an optical packet switch. Feed-forward FDLs are used as primary buffer and feedback FDLs are implemented as supplementary buffer. Simulation result shows that proposed hybrid buffering switch achieves packet loss rate between 10⁻¹ and 10⁻² at heavy traffic load (ρ = 0.9) for a 32 × 32 switch using different FDL length.     

Blocking and delay performance for differential output-ports choosing probability scheme applied optical burst switching network

Differential output-ports choosing probability (DOCP) scheme is a novel traffic outputting model for core router in optical burst switching (OBS) network. In this paper, we provide an analytical model for studying the performance of traffic blocking and delay in DOCP-applied OBS network. We first evaluate blocking probabilities using DOCP and confirm it by simulation. Then, in optical buffer-equipped OBS core router, we consider the average delay time for buffered traffic and the average total traffic queueing length in core router. The knowledge of delay performance is useful for the optical buffer architecture configuration in differential traffic scenario. Several results indicate that, under the same load condition, the blocking probabilities and the delay time will change along with the changeable ports choosing probability and the ratio between different length bursts in the OBS system.     

Modeling and design of WDM optical buffers in asynchronous and variable-length optical packet switches

This paper aims to analyze the influence of wavelength conversion on the design of optical fiber delay line (FDL) buffers in a wavelength-division multiplexing (WDM) packet switch. We focus on the network scenario that variable-length packets arrive at the optical switch asynchronously. Through a detailed analysis of the behaviors of packets in the WDM FDL buffer, an approximate analytical traffic model is established. And the theoretical model is proved to be reasonable by simulations. Based on the model, it is clear that, under the same traffic load per wavelength channel, the utilization of tunable wavelength converters (TWCs) to resolve the output contention significantly reduces the number of fiber delay lines (FDLs) in optical buffers, and to achieve a given packet loss probability under a certain number of FDLs, the required number of tunable wavelengths can be predicted. The model can also estimate the optimal value of the basic time unit of the FDLs, and examine the influence of WDM on the optimal value. Finally, the impact of wavelength conversion on the optical switch size is analyzed. To the best of our knowledge, it is the first time that modeling on this problem is presented.     

An optimal burst assembly approach employing traffic shaping (OBATS) for OBS

Optical burst switching (OBS) aims at combining the strengths of packet and circuit switching and is considered as a promising technology for implementing the next generation optical Internet, required to cope with the rapid growth of Internet traffic and the increased deployment of new services. In this paper, an optimal burst assembly approach employing traffic shaping (OBATS) for OBS networks has been proposed in order to improve network performance in terms of reduced blocking probability, congestion control and better utilization of bandwidth. Particularly, the proposed scheme aims at reducing the average delay experienced by the packets during the burstification process in optical burst switched (OBS) networks, for a given average size of the bursts produced. Reducing the packet burstification delay, for a given average burst size, is essential for real-time applications; correspondingly, increasing the average burst size for a given packet burstification delay is important for reducing the number of bursts injected into the network and the associated overhead imposed on the core nodes. Simulation results show that the proposed burst assembly approach gives better network performance in terms of burst drop, resource contention and delay as compared to conventional burst assembly approaches.     

用于WDM光突发交换网的改进JIT信令协议

提出了一种用WDM光突发交换网的良好时间通信协议(MJIT-SP)该协议结合了光线路交换和光分组交换的优点与用于光突发交换的其他信令协议相似,MJIT-SP的特点也是采用带外控制信号处理来排除核心节点处对光缓存器的需求然而,与其它协议如JIT-SP相比,它能最小化数据源端的建立时间和最大化交叉连接的带宽利用率而且,MJIT-SP还能支持光网络中无连接和面向连接的数据包传递并介绍了MJIT-SP的基本结构并从三个方面分析了它的基本性能,即建立时间、端到端延时和信道占用时间然后,对本协议与JIT-SP的性能进行了比较,结果显示:MJIT-SP不仅优于JIT-SP,而且还克服了JIT-SP的一个缺点,即过长的信道占用时间此外,还给出了MJIT-SP的信令信息,尤其是非常关键的信号与脉座电平差(SETUP)消息MJIT-SP中的SETUP与JIT-SP中的SETUP不同,它需要给出数据包路由和交换所需的信息,包括数据包长度、比特率、SETUP与数据包之间的偏置时间以及数据业务的质量控制系统(QoS)要求等最后讨论了MJIT-SP两种可能的变化并且分析了它们的优缺点.     

适用于光突发交换网的可编程光缓存器

提出了两种适用于光突发交换网的可编程光缓存器结构：交叉型和多端口开关型.两种结构都能满足突发包缓存的超长性和可变性的要求，且结构简单紧凑，成本低，可扩展.交叉型缓存器通过指定信号在每个子缓存模块的光纤环中的循环次数即能实现可变时间的延迟.多端口开关型缓存器通过指定信号在两个多端口开关相应端口与所接光纤延迟线组成的光纤环中的循环次数实现可变时间的延迟.仿真结果表明，两种可编程光缓存器都能对光突发包实现ns级指定时间延迟，可用于解决光突发交换网突发包的冲突问题.