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。     

MANET中路由算法对通信流自相似特性的影响

着重分析无线多跳移动网络中,不同路由算法对多媒体通信流自相似特性的影响.通过NS2仿真产生基于不同路由算法的通信流数据,运用V-T法和R/S图法分别分析其突发性参数.结果表明,基于表驱动的DSDV自相似参数最大,而分簇路由算法CBRP自相似参数最小,更有利于实时流媒体的传输.研究对提高无线网络路由协议的性能和多媒体服务的质量具有重要意义.     

自相似业务环境下IP网络的排队性能分析

网络流量分析表明很多信息源的聚合会产生具有自相似特性的信息流，在自相似环境下分析IP网络的排队性能成为当前热点。文中采用具有Pareto分布的ON／OFF叠加模型作为输入业务，分析IP交换机缓冲区队列溢出概率，得到与实际网络相似的结论：溢出概率并不随缓存长度的增加而呈指数规律下降，其下降速度相对要慢得多。在自相似业务环境下，增加缓存长度并不能有效地降低丢失率。     

基于仿真的并发流媒体汇聚特性分析

通过仿真的方式,分析不同汇聚程度下的流媒体业务时延特性和汇聚流量自相似特征变化情况.实验结果显示:流媒体流量科学汇聚能够明显改善节点处理时延,同时随着汇聚规模的增大汇聚流量的自相似性能够显著弱化.这些结果对于当前正在开展的下一代广电网(NGB)等网络的建设有重要的参考意义.     

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。     

重尾ON/OFF源模型生成自相似业务流研究

因为传统模型没有考虑网络业务流量各种时间尺度都具有突发性,因此是不完善的,一系列的测量结果表明,网络业务流量显示自相似性,重尾分布ON／OFF模型能比较好地解释自相似业务流的产生原因,可以把LAN上的业务分解为多个活动（active)主机对之间的业务流,本文通过系统的仿真实验研究了重尾ON／OFF源模型生成自相似流的机理,并与理论结果进行了对比,而且补充了理论结果。     

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.     

虹桥机场软交换网络流量Hurst参数的算法研究

自相似网络模型具有长相关性特点,研究网络流量的自相似特性对于分析传输过程中的丢包率、信道利用率以及检测网络异常流量都具有重要意义。文章将一种改良的R/S算法用于计算虹桥机场软交换网络的Hurst参数,计算结果表明虹桥机场软交换网络具有较强的自相似性。     

自相似业务量的流量控制研究

由于自相似性是宽带网络中业务量的一个普遍特性,因此在进行宽带网络管理和流量控制时必须考虑它所带来的影响。目前,有关基于自相似业务量的流控机制的研究已经引起了人们广泛地注意。一些研究表明自相似业务量表现出了与传统模型不同的排队特征。本文围绕业务质量保证和流量控制机制,具体研究和分析了业务量的自相似性质对业务量成形、用法参数控制和呼叫接纳控制等流量控制机制的影响,并得到了一些重要结论。     

一种改进的CSFQ算法的设计与仿真

针对CSFQ算法存在的对TCP流的抑制及缓存策略等问题,提出采用ARED作为缓存管理的CSFQ改进算法A-CSFQ,并在多瓶颈链路下对其性能进行仿真。仿真结果表明,改进算法在保持CSFQ其他优点的基础上,显著减弱了对TCP流的抑制作用,提高了其对TCP流的公平性。     

基于网络业务流的RMD算法模型设计

现代实际网络业务相比传统业务更为复杂，在各个时间尺度下表现出自相似的突发特性（相关函数上表现为长相关特性）。我们可以在线测量网络中的高速业务流，再根据实测时间序列数据，用RMD方法建立并分析高速业务流的自相似模型。RMD算法速度快，同时能很好的匹配业务流的自相似特性。     

Queue Analysis and Multiplexing of Heavy-tailed Traffic in Wireless Packet Data Networks

Recent research based on traffic measurements shows that Internet traffic flows have a fractal nature (i.e., self-similarity property), which causes an underestimation of network engineering parameters when using the conventional Poisson model. Preliminary field measurements demonstrate that packet data traffic in wireless communications also exhibits self-similarity. In this paper, we investigate the queuing behavior of self-similar traffic flows for data applications in a packet-switching single-server wireless network. The traffic is generated by an on–off source with heavy-tailed on periods and exponentially distributed off periods. We extend previous analysis of a relation among the asymptotic distribution of loss probability, traffic specifications, and transmission rate for a wireline system to a wireless system, taking into account wireless propagation channel characteristics. We also investigate the multiplexing of heavy-tailed traffic flows with a finite buffer for the downlink transmission of a wireless network. Computer simulation results demonstrate that assumptions made in the theoretical analysis are reasonable and the derived relationships are accurate.     

有限尺度汇聚流带宽规划研究

互联网分组传输具有尽力而为的服务特性,基于目前复杂的接入网结构难以满足中国下一代广播电视网中具有长相关特性实时互动流媒体流量传输的要求。该文根据统计复用框架下服务质量保障策略,分析了有限时间尺度集汇聚流媒体流量带宽规划的有效性;并根据泊松帕雷多突发过程流量模型,给出了基于链路瓶颈造成流量突发程度粗糙度的带宽规划方法。进一步分析表明汇聚流量自相似程度由具有较强粗糙度的子流决定,采用大规模接入汇聚的方式可以有效地避免由于链路瓶颈造成的突发,基于流量粗糙度的有限尺度汇聚流带宽规划方法可为下一代广播电视网的部署实施提供技术支撑。     

Low-rate TCP-targeted denial of service attacks and counter strategies

Denial of Service attacks are presenting an increasing threat to the global inter-networking infrastructure. While TCP's congestion control algorithm is highly robust to diverse network conditions, its implicit assumption of end-system cooperation results in a well-known vulnerability to attack by high-rate non-responsive flows. In this paper, we investigate a class of low-rate denial of service attacks which, unlike high-rate attacks, are difficult for routers and counter-DoS mechanisms to detect. Using a combination of analytical modeling, simulations, and Internet experiments, we show that maliciously chosen low-rate DoS traffic patterns that exploit TCP's retransmission timeout mechanism can throttle TCP flows to a small fraction of their ideal rate while eluding detection. Moreover, as such attacks exploit protocol homogeneity, we study fundamental limits of the ability of a class of randomized timeout mechanisms to thwart such low-rate DoS attacks.     

Performance of in-call buffer/window allocation schemes for short intermittent file transfers over broadband packet networks

While static open loop rate controls may be adequate for handling continuous bit rate (CBR) traffic, relatively smooth data traffic, and relatively low speed bursty data traffic over broadband integrated networks, high speed bursty data sources need more dynamic controls. Burst level resource allocation is one such dynamic control. Potential benefits and other issues for burst level resource parameter negotiations for bursty data traffic over high speed wide area packet networks have been discussed earlier.^1–6 A detailed analysis of an adaptive buffer/window negotiation scheme for long file transfers using these concepts is presented in Reference 1. In this paper we discuss two burst level buffer/window negotiation schemes for short intermittent file transfers, focusing on the specific needs of such traffic streams. We develop closed network of queues models to reflect the behaviour of the proposed schemes. These models, while being simple, capture essential details of the control schemes. Under fairly general assumptions, the resulting network of queues is of product form and can be analysed using the mean value analysis. We use such an analysis to compare the proposed schemes and to determine appropriate sizes of trunk buffers to achieve the desired balance between bandwidth utilization and file transfer delay. The effects of other parameters on the performance of these schemes as well as on the buffer sizing rules are also discussed. Burst level (in-call) parameter negotiation may be carried out by the end system with the network elements or by an interface system (access controller) with the broadband network elements. We discuss implications of this location as well as the needed protocol features. Finally, the service discrimination capabilities desired at the trunk controllers in switching nodes are briefly discussed.     

Self-similar traffic and network dynamics

One of the most significant findings of traffic measurement studies over the last decade has been the observed self-similarity in packet network traffic. Subsequent research has focused on the origins of this self-similarity, and the network engineering significance of this phenomenon. This paper reviews what is currently known about network traffic self-similarity and its significance. We then consider a matter of current research, namely, the manner in which network dynamics (specifically, the dynamics of transmission control protocol (TCP), the predominant transport protocol used in today's Internet) can affect the observed self-similarity. To this end, we first discuss some of the pitfalls associated with applying traditional performance evaluation techniques to highly-interacting, large-scale networks such as the Internet. We then present one promising approach based on chaotic maps to capture and model the dynamics of TCP-type feedback control in such networks. Not only can appropriately chosen chaotic map models capture a range of realistic source characteristics, but by coupling these to network state equations, one can study the effects of network dynamics on the observed scaling behavior We consider several aspects of TCP feedback, and illustrate by examples that while TCP-type feedback can modify the self-similar scaling behavior of network traffic, it neither generates it nor eliminates it     

On traffic scaling transformation at ingress optical burst switches

Ingress nodes in optical burst switching (OBS) networks are responsible for assembling burst from incoming packets and forwarding these bursts into the OBS network core. Changes in the statistical characteristics of a traffic stream at an ingress switch can affect the capacity of the network to provide quality of service. Therefore, the statistical characteristics of the output flow of an ingress node must be known for appropriate network dimensioning. This paper evaluates the impact of burst assembly mechanisms on the scaling properties of multifractal traffic flows. Results show that the factor most relevant in determining the nature of the output traffic flow is the relationship between the cut-off time scale of the input traffic and the time scale of assembly threshold. Moreover, a procedure for the detection of the cut-off scale of incoming traffic is introduced.     

通信网络的QTES建模

现有的业务流模型难以描述通信网络业务流的突发性。我们根据实测的通信网络时间序列数据,用QTES方法建立自相似模型。模型能较好的匹配流量的自相关函数。     

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。