面向大规模网络的聚集TCP流量模拟方法研究

为平衡大规模网络骨干网上TCP流量模拟的准确性和复杂度,提出模拟接入网出口处的TCP聚集流量,而不从单台主机或会话的层面进行流量模拟。从网络流量的自相似性出发,提出基于应用层和网络传输层自相似的TCP聚集流量模型:在应用层通过聚集多个服从Pareto分布的ON/OFF源模拟生成自相似流量,在网络传输层根据TCP机制实现对应用层流量的聚集传输控制。模拟结果显示,在流量负载比例、流量自相似性以及骨干节点丢包率等方面,模拟结果与采集自某互联网交换中心的实际数据吻合良好,表明了该模型的有效性。     

自相似模型下的交换式网络仿真

传统模式下的网络仿真,报文到达均服从的是一种具有短相关特性的泊松分布。而经过大量业务流量监测表明,网络流量实际呈现出的确是一种具有长相关特性的自相似分布,这种特性对网络流量建模、性能分析、接纳控制等产生了重要影响。在对自相似特性深入分析的基础上,利用分型布朗运动模型的RMD算法产生自相似序列来模拟网络业务,并对该业务流特性下的交换式以太网进行了仿真实验。结果表明业务量的自相似性对交换式网络的各项性能影响很大,这与传统流量模型形成鲜明对比。     

蓝牙无线个域网及其流量特性分析

对蓝牙无线个域网的各项流量特性进行了分析,探讨了蓝牙设备在4种工作模式间的切换对蓝牙网络性能的影响,分析了影响蓝牙网络有效带宽的各个因素。另外,通过仿真,发现蓝牙无线链路流量特性具有自相似的特性,即适合采用自相似类型的流量模型来进行分析、描述及预测。     

一种基于小波的网络流量发生器设计

网络流量发生器在网络性能分析和协议实现中具有重要的作用。文章基于多分形小波模型，设计了一种自相似网络流量发生器。其中对随机数的生成、序列的截断、自相似序列的生成以及自相似流量的生成等主要设计部分进行了论述。与常用的基于分形布朗运动的模型的流量发生器相比，该发生器生成的流量具有更准确的自相似流量特性。     

自相似网络业务流量的研究与实现

为了准确测试和评估网络交换设备及其调度算法的性能,一个能够真实反映实际网络业务流量特点的业务流量产生系统是十分必要的。近年来通过对大量网络业务流量的测量和分析,人们认识到网络业务流量呈现为长相关、自相似的特性,而非泊松过程。将这一特性和现有的业务流量描述模型相结合,利用具有重尾特性的概率分布函数:Pareto分布和截尾重尾分布,构造了在宏观上表现为自相似特性的业务流量模型。针对路由交换机构调度算法的性能测试的实际需要,建立了一个可用于软件测试的网络业务流量产生系统。     

以太网流量的自相似性

以太网ＬＡＮ流量在统计上是自相似的，通常使用的流量模型都不能俘获这一分形（ｆｒａｃｔａｌ）特性，这类特性对于基于信元的高速网络的设计、控制和分析都具有重要的意义。     

无线Mesh网络流量自相似性研究

近年来,无线Mesh网络已成为一个倍受关注的研究领域.对无线Mesh网络流量特性的研究将有助于网络协议的研究、评估,以及网络结构的规划和建设.本文通过对无线Mesh测试网上采集的数据包进行统计分析,揭示了网络流量具有自相似的特性.同时,解释了无线Mesh网络流量自相似性是由网络中具有重尾分布特性的多个流叠加形成的,并通过仿真进一步分析了节点移动性对流量自相似性的影响.     

自相似业务:基于多分辨率采样和小波分析的Hurst系数估计方法

新近对局域网和广域网上大量突发业务流量的监测结果表明，采用自相似建模表征业务到达过程的长时间相关特性具有较高精度，其中Ｈｕｒｓｔ系数是表征业务突发特性的重要参数，因此在一定的观察时间内对突发业务的Ｈｕｒｓｔ系数进行快速、准确的估计是高速宽带网络（如ＡＴＭ）实施流量控制和缓冲资源分配的前提。本文提出一种基于多分辨率采样和小波分析的Ｈｕｒｓｔ系数快速估计方法，对严格二阶自相似模型下Ｈｕｒｓｔ系数的估计     

TELNET的客户端流量模型

本文针对英特网上的一个常用协议－远程登录（ＴＥＬＮＥＴ）协议分析了它的客户端数据包产生的时间间隔分布,发现泊松模型的指数分布不能很好地刻画它的特性。本文依据Ｔｃｐｌｉｂ提供的经验分布曲线,认为Ｐａｒｅｔｏ分布在很大时间范围内能较好地描述ＴＥＬＮＥＴ的客户端流量特性,并对其突发序列的特性进行了分析。本文最后指出在描述网络流量时自相似模型要比泊松模型有效和精确得多,并给出了Ｐａｒｅｔｏ分布在建立自相似     

分析重尾ON/OFF源功率谱密度的TAM近似法

经过十年的研究，发现电信网络业务流量显示自相似和长相关性。传统模型不能很好的仿真网络特性，而重尾分布的ON／OFF模型能够很好地解释计算机网络业务流量的自相似性的形成机理，它的功率谱密度(PSD)成为判断其突发性的有效手段。本文在Laevens K的基础上，结合Harris CM提出的TAM方法，提出一种计算重尾ON／OFF源的PSD的TAM近似法，并通过MATLAB仿真得到PSD曲线，符合其长相关特性，证明了该方法的有效性。     

局域网流量自相似及相关性新特征分析研究

自相似业务量对计算机网络的管理和控制有着非常重要的影响。通过对一个中等规模局域网流量组成特征的分析,得出了流量组成、大小分布等特征;并通过计算流量主成分自相似参数,得出在当前网络流量组成环境下网络自相似行为新特征,确定影响自相似程度的诸多因素;通过计算诸协议间的相关性特征,得出网络流量趋势并分离出性能问题,为网络优化提供直接依据。     

Self-similarity in World Wide Web traffic: evidence and possiblecauses

The notion of self-similarity has been shown to apply to wide-area and local-area network traffic. We show evidence that the subset of network traffic that is due to World Wide Web (WWW) transfers can show characteristics that are consistent with self-similarity, and we present a hypothesized explanation for that self-similarity. Using a set of traces of actual user executions of NCSA Mosaic, we examine the dependence structure of WWW traffic. First, we show evidence that WWW traffic exhibits behavior that is consistent with self-similar traffic models. Then we show that the self-similarity in such traffic can be explained based on the underlying distributions of WWW document sizes, the effects of caching and user preference in file transfer, the effect of user “think time”, and the superimposition of many such transfers in a local-area network. To do this, we rely on empirically measured distributions both from client traces and from data independently collected at WWW servers     

A nonstationary traffic train model for fine scale inference from coarse scale counts

The self-similarity of network traffic has been convincingly established based on detailed packet traces. This fundamental result promises the possibility of solving on-line and off-line traffic engineering problems using easily collectible coarse time-scale data, such as simple network management protocol measurements. This paper proposes a statistical model that supports predicting fine time-scale behavior of network traffic from coarse time-scale aggregate measurements. The model generalizes the commonly used fractional Gaussian noise process in two important ways: (1) it accommodates the recurring daily load patterns commonly observed on backbone links and (2) features of long range dependence and self-similarity are modeled only at fine time scales and are progressively damped as the time period increases. Using the data we collected on the Chinese Education and Research Network, we demonstrate that the proposed model fits 5-min data and generates 10-s aggregates that are similar to actual 10-s data.     

业务自相似性对光突发交换调度算法影响分析

使用泊松业务流模型对光突发交换网络进行性能分析不能准确地反映网络状态。该文从理论上对突发包长度进行了推导,对基于时间门限汇聚机制下突发包数据流自相似程度进行了计算机仿真测量,并利用自相似业务流模型对光突发交换网络中比较常用的LAUC和LAUC-VF调度算法进行了性能仿真。仿真结果表明:基于时间门限的汇聚机制能够有效地降低数据流自相似程度,数据流的自相似特性对LAUC算法的影响并不非常明显,但对LAUC-VF算法的性能则产生了比较严重的影响,其突发包丢失率较泊松流平均增加了近3个百分点。     

On optical burst switching and self-similar traffic

In this letter we consider burst switching for very high speed routing in the next generation Internet backbone. In this scenario, Internet protocol (IP) packets to a given destination are collected in bursts at the network edges. We propose a burst assembly mechanism that can reduce the traffic autocorrelation or degree of self-similarity, and at the same time keep the delay due to burst formation limited at the network edges     

TCP批量业务的自相似特性

通过对简单网络拓扑结构下不同参数TCP批量传输实测流量数据的统计分析,研究了TCP批量稳定流量的自相似特性.分析结果表明,在10BaseT环境下,TCP批量传输的流量比较稳定,没有明显的突发性与自相似特性.而在100BaseTx环境下,TCP批量传输的流量表现出明显的突发性与自相似性,其自相似性强弱程度与通信方式、网卡缓存大小密切相关.同样条件,全双工TCP流自相似强度大于半双工流;而网卡缓存越少,TCP流突发性与自相似性越强.     

移动因特网不同流量下切换损失率研究

根据移动因特网中基本的硬切换和改进的半软切换算法时间流程仿真研究了 2种切换在泊松和自相似流量下的切换损失率。仿真数据表明 ,在网络负载均值相同的情况下 ,对于硬切换和半软切换 ,自相似流量的切换损失率要明显低于传统泊松流量 ,并通过分析泊松和自相似流量的概率密度函数尝试给出产生这一区别的原因。     

Interleaved Polling with Adaptive Cycle Time (IPACT): A Dynamic Bandwidth Distribution Scheme in an Optical Access Network

While in recent years backbone bandwidth has experienced substantial growth, little has changed in the access network. Last mile still remains the bottleneck between a high capacity LAN or home network and the backbone. Passive optical network (PON) is a technology viewed by many as an attractive solution to this problem.In this study, we discuss and evaluate design issues for PON access networks. Specifically, to drive the cost of an access network down, it is very important to have an efficient, scalable solution. We believe that a PON based on polling, with data encapsulated in Ethernet frames, possesses the best qualities, such as dynamic bandwidth distribution, use of a single downstream and a single upstream wavelength, ability to provision a fractional wavelength capacity to each user, and ease of adding a new user.To support dynamic bandwidth distribution, we propose an interleaved polling algorithm. We then suggest a scheme for in-band signaling that allows using a single wavelength for both downstream data and control message transmission.To obtain realistic simulation results, we generated synthetic traffic that exhibits the properties of self-similarity and long-range dependence. We then analyzed the network performance and its effect on various types of traffic, e.g., best-effort data traffic, VBR video traffic and CBR streams.     

A simulation study of adaptive burst assembly algorithms in optical burst switched networks with self-similar traffic sources

It has been extensively demonstrated that the traffic pattern in today’s Internet is Self-Similar. Burst assembly algorithms utilized in optical burst switched (obs) edge routers can be used to reduce the degree of self-similarity. This work investigates the impact of time and size-based burst assembly algorithms utilized in obs edge routers, on the self-similarity level of the output traffic. Both static and adaptive algorithms are examined. Our study is based on the opnet simulation tool focusing on the characteristics of the output traffic in the presence of self-similar input traffic. To estimate the Hurst parameter of the aggregated input and output traffic streams, we have applied various Hurst parameter estimators. The performance impact of the burst assembly algorithms in terms of burst assembly delay and its jitter is also assessed. Our study has shown that the burst assembly mechanism at the obs edge router reduces the self-similarity level of the output traffic and that this reduction depends on the parameters of the algorithm. Our results reveal that the proposed adaptive burst assembly algorithm performs better comparing to its non-adaptive counterpart.     

自相似业务流复用特性分析

现有研究将复用的自相似业务流Hurst参数值确定为各个业务流中最大的H参数值，与业务流的其他性质无关，这一结论用于网络设备的设计不利于网络资源的有效利用。本文采用简单近似估算，并用分形布朗运动模型生成自相似业务流，彩用小波分析方法估计Hurst参数值。实验结果表明，由于复用合成业务流的渐近自相似的本质，在可以观测的时间尺度范围内业务流的Hurst参数比这理论预测值小；在一定的序列长度下，复用流的Hurst参数的不仅和最大Hurst参数业务流有关，还受到其它业务流，特别是业务流的方差系数所表现出的短时突发性影响，因此对合成业务流的自相似参数具有重要的影响。