一种自适应的高精度可用带宽测量算法

针对现有可用带宽测量技术在突发背景流及多跳链路下测量精度较低的问题,提出了一种自适应的高精度可用带宽测量算法FPU-ABM(Five-Packet-Unit for Available Bandwidth Measurement);该算法采用五包结构构成探测单元,结合TTL值设置,分别测量瓶颈链路前后的探测包间隔,提高了在多跳链路下带宽测量精度;算法根据反馈包的间隔自适应地调整探测速率,加快了测量速度且减小了探测流对网络的入侵度,增强了算法的适应性;仿真表明,在多跳链路下TFP-ABM算法的测量精度可达到10%以内,相比现有算法,TFP-ABM响应速度快、测量精度高、适应性好。     

网络主动带宽测量算法设计

本文基于Cruz流量模型.通过主动检测单向时延连续上升的概率.推断探测速率与端到端可用带宽之间的关系,提出一种网络可用带宽主动测量算法PathPCQ.NS2仿真显示,PathPCQ算法测量精度和效率都优于现有的带宽测量工具Pathload.     

基于非液体流模型的可用带宽测量精度

现有的可用带宽测量技术大多基于单跳链路和液体流模型,在突发背景流及多跳链路下测量精度较低。因此,分析了更符合网络实际的非液体流模型,提出了一种参数设置方法,减小了探测包长、探测速率、背景流速率及背景流包长等因素对测量精度的影响。在此基础上,改进了探测包对结构,该结构结合生存时间(TTL)值设置减小了探测包对间隔的测量误差,增强了带宽测量算法在多跳链路环境下的健壮性。仿真表明,基于非液体流模型的参数设置方法及改进的包对结构提高了可用带宽测量精度。     

一种速率自调节可用带宽测量算法

可用带宽是网络路由、网络服务质量、流量工程等方面的一个关键参数。目前很多研究方法都基于PGM模型和PRM模型,但这两种方法大都假设背景流量速率为固定比特流,不适用于低带宽的测试。提出一种端值自调节可用带宽测量算法,该算法充分考虑了低链路带宽的情况。通过对排队延时的处理、探测分组列速率端值自适应调节,实现了端到端可用带宽快速准确的测量。实验结果表明,该算法具有良好的测量效果,尤其在低带宽条件下较其它同类算法提高了测量准确性,加快了测量速度并减小了对网络的影响。     

网络可用带宽测量算法的改进

重点研究了网络端到端可用带宽的测量方法,对现有的基于自拥塞理论的可用带宽的测量方法Pathload进行了简要分析.针对该方法的缺点提出了改进的可用带宽测量算法,改进的可用带宽测量算法采用周期流组到达目的端的速率代替周期流的发送速率,能快速测量网络的可用带宽,测量准确性更高,降低了测量开销.NS-2上的模拟实验结果表明,该方法是可行的和有效的.     

多路径数据传输中的可用带宽测量算法研究

在分布式中转服务器网络辅助的多路径数据传输系统中,为获得最快的数据传输速率,需要使用可用带宽测量技术以获得数据发送端至各中转服务器的可用带宽值列表.然而,传统的可用带宽测量算法难以同时兼顾测量精度与收敛速度,故无法达到实际数据传输系统中准确快速完成维护可用带宽值列表的目的.为解决上述问题,提出了一种可用带宽测量算法.通过收集初始探测流的包对在发送端及接收端的时间间隔关系数据获得可用带宽估测值,再以此值为后续探测流的发送速率初始值,通过自适应方法调整探测流发送速率以逐渐逼近可用带宽真实值.实验结果表明,改进算法能快速获得高精度的测量结果,有效提升可用带宽的测量效率,满足数据传输系统的需求.     

WPathload:一种改进的可用带宽测量方法

可用带宽是网络的重要资源,对其准确的估计与测量是流量工程和网络监测等必须解决的问题,但对它的实际测量存在许多困难.针对Pathload可用带宽测量方法存在收敛慢、开销大的问题,提出了一种Pathload可用带宽测量的改进方法(WPathload).该方法基于时延变化的统计规律,改进发送速率调整算法,并采用周期流组到达目的端的速率代替周期流的发送速率,更新可用带宽上界,从而加快收敛速度,降低测量开销.实验结果表明,改进后的方法能快速反映可用带宽的变化,增强了跟踪带宽变化的能力.     

一种测量任意链路可用带宽的方法

可用带宽测量对于网络行为分析、网络服务质量(quality of service,简称QoS)的验证等有很重要的作用.现有可用带宽测量工作主要集中在端到端路径可用带宽测量,仅提供路径上承压链路(tight link)的信息,而不能提供其他关键链路的信息.为此,提出一种新颖的链路可用带宽测量算法LinkPPQ(trains of pairs of packet-quartets used to measure available bandwidth of arbitrary links),它采用由四探测分组结构对构成的探测序列,能够测量网络中任意链路的可用带宽,并跟踪该链路上背景流的变化.在仿真环境和实际网络环境下研究了LinkPPQ 的性能.仿真结果表明,在几种不同背景流场景下,对于具有单狭窄链路的路径和具有多狭窄链路的路径,LinkPPQ 都能够对各个链路的可用带宽进行有效的测量.绝大多数情况下测量误差小于30%,且具有较好的测量平稳性.实验网的实验结果也表明,LinkPPQ 可以准确测量以下几种情况下的链路的可用带宽:a) 从容量为10Mbps 的链路准确地测量一条100Mbps 链路的可用带宽;b) 准确测量容量10 倍于紧邻其后狭窄链路的容量的链路的可用带宽;c) 准确测量具有多狭窄链路的路径上各狭窄链路的可用带宽.     

基于自拥塞理论的可用带宽测量算法

在分析网络可用带宽测量算法性能及存在问题的基础上,提出一种轻负载、高精度、自适应的端到端可用带宽测量算法iChirp。基于自拥塞理论采用近似指数分布的动态探测队列结构,以可用带宽预测值为中心设置关键域,在其中加快采样频率,增加报文密度,并能根据反馈自适应的对探测范围和关键域进行调整。仿真实验结果表明,该算法对网络干扰性较小,能够快速准确地测量出端对端可用带宽。     

一种改进离群区间计算的PRM带宽测量算法

主动式网络路径可用带宽测量是目前网络路径带宽测量使用的主要方法,与被动式网络路径可用带宽测量相比,具有更高的灵活性且部署方便。为解决主动式网络路径可用带宽测量定义不明确、通用性不强、协议不规范和结果不准确等问题,规范定义了探测通信协议和报文结构,建立了较为完整、统一和规范的主动式网络路径可用带宽测量框架,提出了序列时延增加度和基于序列时延增加度的离群区间计算方法,改进了网络背景流量分析方法,降低了背景流量对网络路径可用带宽测量的干扰,最后使用NS2仿真对比验证了该算法的有效性。     

Available bandwidth estimation for the network paths with multiple tight links and bursty traffic

Available bandwidth (ABW) estimation is useful for various applications such as network management, traffic engineering, and rate-based multimedia streaming. Most of the ABW estimation methods are based on the fluid cross-traffic model. Inevitably, their estimation accuracy is limited in the network environments with bursty cross-traffic. In this paper, we apply packet trains (a series of probing packets) and a modified Ping to probe the ABW of a network path. Our proposed probing method can identify several tight links along a path and can infer their individual ABWs. The ABW estimation algorithm developed in this study, GNAPP, is also based on the fluid traffic model, but it can effectively filter out probing noise incurred in networks that carry bursty traffic. The algorithm employs not only the gaps of any two consecutive probing packets but also those of nonadjacent probing packets for ABW estimation. Thus, the number of samples for ABW estimation increases significantly without resorting to sending more probing packets and the estimation efficiency and accuracy are improved. In addition, two-stage filtering and moving averages are used in GNAPP for reducing estimation errors. Numerical results demonstrate that the estimation scheme based on GNAPP can achieve good accuracy even when the traffic is bursty and there are multiple tight links on the path being observed. Thus, it outperforms other well-known ABW estimation tools.     

网络并行计算环境中网络通信开销的分析与测试

网络通信开销是影响网络并行计算的重要原因，但精确定量分析网络通信销中各个组成部分的报道不多。本文利用精度可达０．１微秒的计时工具，定量地分析了以太网中广泛使用的ＮｅｔＷａｒｅ网络操作系统的网络层／传输层通信协议ＩＰＸ／ＳＰＸ与ＮｅｔＢＩＯＳ仿真会话层通信协议的性能，研究了网络通信销的主要因素，从而找出提高网络通信性能的途径。     

On the Accuracy of Packet Delay Estimation in Distributed Service Networks

Packet delay (either one-way time or round-trip time) is a very important metric for measuring the performance of networks in a highly dynamic environment such as the Internet. Many network applications are also sensitive to packet delay or delay variation for ensuring an acceptable level of quality in providing network-based services such as VoIP, multimedia streaming, etc. A very important property of packet delay is that it is very dynamic and therefore should be measured frequently with measurement results being updated on a timely basis. Measurement of packet delay has thus generated a great deal of interest in the past years and a lot of research has been performed in the development of measurement architecture as well as specific measurement techniques. However, how to reduce network overhead resulting from measurement while achieving a reasonable level of accuracy still remains a challenge. In this paper, we propose to use delay estimation as an alternative to delay measurement for reducing measurement overhead and, in particular, examine the level of accuracy that delay estimation can achieve. With delay estimation, measurement nodes can be dynamically selected and activated and other nodes can share measurement results by performing delay estimation, thus reducing measurement overhead while supporting the dynamic requirement for delay measurement. Consequently, while measurement overhead can be reduced by activating only a subset of network nodes to perform actual measurement, desired accuracy can be achieved by exploring the correlation between delays as well as by sharing measurement results to do delay estimation based on such a correlation. We illustrate how packet delays of network nodes can correlate to each other based on topological properties and show how delays can be estimated based on such a correlation to meet accuracy requirements, which would make delay measurement in the Internet highly dynamic and adaptable to the accuracy requirements and measurement results highly reliable. We also show how delay estimation can be applied by presenting three application scenarios as well as an example to demonstrate the usefulness and effectiveness of delay estimation in the measurement of packet delays.     

无线传感器网络中干扰模型的低开销测量方法

无线传感器网络中的干扰会严重影响传输性能.最近的研究表明干扰模型能够很好的反映出干扰存在下传输的真实性能.目前建立干扰模型的方法会导致巨大的开销.本文提出一种无线传感器网络中干扰模型的低开销测量方法.该方法利用信号强度表,基于回归分析的模型以及一种新的时钟校准方法来降低开销.实验结果表明,跟传统的测量方法相比较,该方法能够在降低开销的同时达到很高的准确度.     

SDN中基于蚁群优化的网络测量节点选择算法

在软件定义网络（SDN）中,当流传输路径信息获取受限时,现有的测量节点选择算法只能基于网络拓扑的中心性指标进行测量节点选择,存在测量精度较低、测量负载不均衡、运行时间长等问题。将SDN网络中测量节点选择问题抽象为最小顶点覆盖模型,提出一种基于蚁群优化的测量节点选择算法ACO-NS。利用复杂网络的度分布理论缩减状态转移过程中的候选集规模,同时设计一种信息素局部增强-全局挥发机制,增大可行解的信息素浓度,提高算法的准确度和收敛度,并且缩短搜索时间。通过OpenFlow消息在线计算测量节点的负载,采用邻域搜索策略对过载节点进行筛选和替换,以降低过载处理的时间。实验结果表明,与ACO算法相比,该算法的准确度和收敛度分别提高56.7和28.2个百分点,且单位时间内的过载处理开销降低79.8个百分点,具有较高的测量精度。     

基于Pathneck网络测量的采样算法研究

针对Pathneck测量网络瓶颈的周期性采样算法无法有效的适应网络的动态变化的问题,结合Patheck测量延迟值的特点,提出一种基于延迟值分布函数的自控式采样的算法.     

Reconfigurable bandpass filter with constant absolute bandwidth based on neural network

In this paper, a novel design method for reconfigurable bandpass filter (BPF) with constant absolute bandwidth (ABW) based on neural network is proposed. A lumped-element circuit is used to design the reconfigurable BPF, which consists five series LC tanks. Three series tanks can provide three transmission poles, while two parallel tanks can introduce two same transmission zeros (TZs). This method allows designing BPFs with tunable center frequency and constant ABW. A set of inductance and capacitance values for the center frequency and ABW requirements are optimized by using neural network. Then, optimize the capacitance values to adjust the center frequency with fixed inductance values by the three series tanks and the TZ by the parallel tanks. In order to verify this design method, three varactor diodes are employed to achieve the reconfigurable BPFs with the constant ABW under different work states. Experiments show that this method can optimize multiple LC circuit parameters of BPFs, which meet design requirements, with the same ABW and different center frequencies effectively and accurately     

基于词素特征的轻量级域名检测算法

对网络中DNS交互报文进行检测以发现恶意服务,是网络安全监测的一个重要手段,这种检测往往要求系统能够实时或准实时地发现监测域名中的可疑对象.面对庞大的域名集合,若对所有域名使用同样强度的监测通常开销过大.通过挖掘域名字面蕴含的词素（词根、词缀、拼音及缩写）特征,提出一种轻量级检测算法,能够快速锁定可疑域名,以便后续有针对性地进行DPI检测.实验结果表明：基于词素特征的检测算法比统计n元组频率分布的方法虽然略微增加了58.3%的内存开销,但却具备抗逃避能力以及更高的准确率（相对提高35.2%）;与基于单词特征的方法相比,极大地降低了计算复杂度（相对降低64.8%）,并减少了2.6%的内存开销,而准确率仅下降2.5%.     

Hybrid Signal-and-Link-Parametric Speech Quality Measurement for VoIP Communications

A hybrid signal-and-link-parametric approach to speech quality measurement for voice-over-Internet protocol (VoIP) communications is described. Connection parameters are used to determine a base quality representative of the transmission link. Degradation factors, computed from perceptual features extracted from the decoded speech signal, are used to quantify distortions not captured by the connection parameters. The algorithm is tested on speech degraded by acoustic noise, temporal clippings, and noise suppression artifacts, thus simulating degradations present in wireless-VoIP tandem connections. Hybrid measurement is shown to overcome the limitations of pure link parametric and pure signal-based measurement methods, resulting in better measurement accuracy for modern VoIP communications. In addition, the proposed algorithm incurs modest computational overhead relative to pure link parametric measurement and attains up to 88% reduction in processing time relative to the ITU-T standard P.563 signal-based algorithm.      

FC-AMAT: factor-based C-AMAT analysis in memory system measurement

The “memory wall” problem has necessitated the introduction of more accurate memory metrics. C-AMAT, an extension of AMAT that considers memory access concurrency, can evaluate the performance of modern memory systems more accurately and comprehensively. However, compared to AMAT, calculating C-AMAT means additional complexity and more hardware resources, which incurs high overhead for this metric. In this paper, we propose FC-AMAT, an analysis model based on C-AMAT. We first explore the numerical relations between factors’ C-AMAT and overall C-AMAT, then try to use factor’s-first (changed factor or leading factor) C-AMAT to evaluate effects of changes applied to a memory system, which can not only reduce measurement overhead, but also guarantee acceptable evaluation accuracy through a rigorous check. Furthermore, we provide the method to determine the leading factor of a memory system. Simulations with varied configurations are conducted to study the numerical relations between factors’ C-AMAT and overall C-AMAT, as well as to evaluate the effects of FC-AMAT. Experimental results show that (1) parameters of factors’ C-AMAT have different influence degrees on overall C-AMAT, (2) the leading factor of a memory system remains unchanged across various configurations and (3) using factor’s C-AMAT as the evaluation metric reduces the hardware overhead for measurement, including detecting logic and storage cost, which demonstrates the effectiveness of FC-AMAT.