大规模互联网端到端行为评价指标研究

目前,Internet端到端行为的研究仅仅局限在包延迟、包丢失等测量指标的研究上,但如何根据测量指标对链路的性能进行评价却没有做深入研究。文章针对链路特性提出了两个评价指标:稳定系数和总体评价系数,对链路的稳定性和总体性能进行了评价。其中,稳定系数是评价网络链路稳定性的一个系数,总体评价系数是体现链路稳定性和链路速率的综合特性的一个系数,它反映了目前链路给用户的总体使用效果。接着文章介绍了在实际测量中用到的笔者自己编写的测量工具Posip。该工具采用指数间隔进行测量采样,并解决了一般ping工具中的“应答包丢失”问题。最后,文章使用工具posip对我国Internet教育网和科技网中的43条链路进行了测量和分析,并使用两种评价指标对所测链路进行了评价,取得了较好的效果。     

基于信息熵的IP网端到端行为分析与建模

具有开放、分布式、不协作、异构、无中心控制等特点的Internet复杂巨系统的管理、容量规划、新一代网络体系结构设计与分析和性能预测都离不开对网络行为的充分理解。而端到端行为作为网络行为的一个重要组成部分,具有一定的研究价值。该文利用信息熵原理建立用于分析端到端整体宏观行为的信息熵模型,该模型能很好地反映端到端整体宏观行为与链路上各节点的状态概率之间关系,根据该模型可以分析端到端链路上各节点之间的相互作用关系以及它们是如何引起端到端整体宏观行为的。最后,给出了该模型的有效性和稳定性定量分析的判别式。     

一种基于pathchar算法的改进的网络端到端带宽测量方法

在网络端到端带宽的测量中,Pathchar测量算法是目前网络链路带宽测量算法中最成功的算法之一,但是也存在不能对反方向路径上各段链路带宽进行测量、背景流量和逐跳误差累积影响等问题.本文提出一种改进的基于pathchar的测量方法较好的解决了上述问题,提高了测量的精度和抗干扰性.     

基于路由数目的通信链路重要性分析

为了分析通信网络中通信链路对端到端通信的重要程度,提出一种基于路由数目的链路重要性计算方法。该方法采用一种快速算法,寻找出端到端的所有通信路由,再通过比较不同通信链路的损坏使端到端之间传输路由减少的数目,判断不同通信链路对端到端通信的重要性,如果某通信链路损坏导致路由减少越多,则该链路越重要。计算实例表明,该方法计算简单,易于编程实现,具有一定的实用性和有效性。     

网络链路性能参数估计的层析成像方法综述

网络层析成像能够在网络内部节点不提供测量协作的情况下,根据端到端的测量结果,间接地估计网络内部链路性能参数,是一种重要的网络测量手段,能直接指导网络管理和网络优化,目前受到国内外学术界和工业界广泛的关注.在广泛收集国内外资料的基础上,首先总结了目前网络层析成像使用的主要端到端测量方法和技术;再根据不同参数对链路性能刻画程度的不同,将链路性能参数的网络层析成像方法分为两类:定量参数推断方法和定性参数推断方法;然后,针对不同类型参数的估计问题,概括分析了现有算法的特点;最后指出该类方法未来的研究方向与潜在的应用前景.     

面向端到端溯源攻击对手的Tor安全性模型

Tor匿名通信系统在全球范围内被广泛部署与使用,但其抵御溯源攻击的能力有待进一步建模分析。为精确衡量Tor用户在端到端溯源攻击下的安全性,综合Tor节点选择算法、用户使用模式、溯源攻击对手能力等要素,建立针对端到端溯源攻击对手的Tor安全性模型。经实验验证与分析结果表明,该模型可在统计意义下较精确计算对手捕获通信链路的概率及次数,以此衡量不同端到端溯源攻击对手对用户安全性的破坏程度。     

IP网端到端性能指标测试方法研究

IP网端到端传输性能与业务应用的关系最为直接和密切,在网络开通验收测试以及日常维护中都需要进行端到端性能指标测试。首先论述了端到端的基本性能指标,包括吞吐量、包时延、包时延抖动等。然后给出了针对每项性能指标的详细、规范的测试方法,以及待测链路的抽样方法。最后说明了各种测试方法的适用性。     

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。     

基于最大伪似然准则估计的故障链路诊断*

识别网络内部的故障链路对提升网络性能具有重要参考价值。研究了树型拓扑下基于端到端测量的故障链路诊断问题,提出一种最大伪似然估计方法估计链路先验故障概率,把树型拓扑划分为一系列具有两个叶节点的子树,并使用期望最大化(EM)算法最大化每个子树的似然函数,求出链路先验概率。仿真实验表明,该方法与现有的联立方程组求解方法估计精度相当,但是大大降低了算法时间复杂度,证明了该方法的有效性。     

移动Ad Hoc网络中基于链路质量预测的多路径源路由算法的研究

在移动Ad Hoc网络中,数据传输的端到端延时是衡量网络性能的重要指标[1],为了减少因节点移动而导致的链路中断,本文提出了一种基于底层信号质量进行路由状态预测的多路路由算法,它改进DSR路由的单一路径传输方式,减少路由发起的次数,仿真实验证明该算法改善了数据传输的端到端延时,并减少了路由控制开销。     

An optical burst reordering model for time-based and random selection assembly strategies

Contention resolution schemes in optical burst switched networks (OBS) as well as contention avoidance schemes delay burst delivery and change the burst arrival sequence. The burst arrival sequence usually changes the packet arrival sequence and degrades the upper layer protocols performance, e.g., the throughput of the transmission control protocol (TCP).In this paper, we present and analyze a detailed burst reordering model for two widely applied burst assembly strategies: time-based and random selection. We apply the IETF reordering metrics and calculate explicitly three reordering metrics: the reordering ratio, the reordering extent metric and the TCP relevant metric. These metrics allow estimating the degree of reordering in a certain network scenario. They estimate the buffer space at the destination to resolve reordering and quantify the number of duplicate acknowledgements relevant for investigations on the transmission control protocol.We show that our model reflects the burst/packet reordering pattern of simulated OBS networks very well. Applying our model in a network emulation scenario, enables investigations on real protocol implementations in network emulation environments. It therefore serves as a substitute for extensive TCP over OBS network simulations with a focus on burst reordering.     

Metrics for MT evaluation: evaluating reordering

Translating between dissimilar languages requires an account of the use of divergent word orders when expressing the same semantic content. Reordering poses a serious problem for statistical machine translation systems and has generated a considerable body of research aimed at meeting its challenges. Direct evaluation of reordering requires automatic metrics that explicitly measure the quality of word order choices in translations. Current metrics, such as BLEU, only evaluate reordering indirectly. We analyse the ability of current metrics to capture reordering performance. We then introduce permutation distance metrics as a direct method for measuring word order similarity between translations and reference sentences. By correlating all metrics with a novel method for eliciting human judgements of reordering quality, we show that current metrics are largely influenced by lexical choice, and that they are not able to distinguish between different reordering scenarios. Also, we show that permutation distance metrics correlate very well with human judgements, and are impervious to lexical differences.     

Packet reordering in high-speed networks and its impact on high-speed TCP variants

Several recent Internet measurement studies show that the higher the packet sending rate, the higher the packet-reordering probability. This implies that recently proposed high-speed TCP variants are more likely to experience packet reordering than regular TCP in high-speed networks, since they are designed to achieve much higher throughput than regular TCP in these networks. In this paper, we first study the characteristics of packet reordering in high speed networks. Second, we verify the impact of packet reordering on high speed TCP variants and evaluate the effectiveness of the existing reordering-tolerant TCP enhancements using simulations. Our simulation results demonstrate that high-speed TCP variants perform poorly in the presence of packet reordering, and existing reordering-tolerant algorithms can significantly improve the performance of high-speed TCP variants.     

基于NewReno拥塞控制机制的TCP分组乱序影响分析

报文乱序是互联网中普遍存在的现象,深入理解互联网报文乱序的行为属性和影响,对于设计高性能网络协议和新型网络设备体系结构、优化网络整体效能具有重要的意义。本文建立了NewReno拥塞控制算法的工作模型,通过实验验证了模型的有效性。基于该模型,分析报文乱序对TCP连接的影响,发现乱序报文对TCP连接吞吐率的影响显著,而且乱序报文的影响与报文丢失率紧密相关:当报文丢失率较低时,报文乱序会导致TCP连接的吞吐率急剧下降;当丢失率较高时,报文乱序的影响比较小。这些结论可为报文乱序友好的网络协议和新型网络设备体系结构的设计提供指导。     

一种采用流切割实现报文保序的负载均衡算法

网络链路过载或链路失效时,使用负载均衡技术可以避免网络发生拥塞。负载的分派粒度决定了负载均衡系统的均衡性能。分派粒度越细,均衡效果越理想。基于包水平粒度的负载分派可以实现理想的均衡性能,但是会造成同一TCP业务流中报文乱序;基于流水平的分派可以保证报文不乱序,但均衡效果不理想。提出了按照报文段粒度分派负载的FSLB算法。仿真实验表明,该算法可避免报文乱序并能达到较理想的均衡效果。     

Modelling and robust stability of networked control systems with packet reordering and long delay

In this article, modelling and robust stability of networked control systems (NCS) are discussed. Considering the existence of packet reordering and network-induced delay, a new mathematical model of NCS whose network-induced delay is longer than one sampling period is obtained, which can fully describe packet reordering and effectively eliminate the impact of packet reordering on the performance of NCS such that the newest control input can be executed by the actuator. Based on this model, the time-varying NCS is converted into an uncertain discrete linear system with multi-step delay in terms of matrix theory. Furthermore, a sufficient condition for robust stability of NCS is presented. Linear matrix inequality approach has been employed to solve the controller design problems. Numerical examples are compared with previous schemes to demonstrate the effectiveness of the proposed method.     

一种MPLS的故障恢复方案*

在备份路径预建立的前提下,提出了一种MPLS的故障恢复方案--EB,该方案在现有的Bridge模型基础上引入了Backpressure信令以解决分组失序问题.理论性能评估及仿真实验均表明,EB较好地继承了Bridge方案原有的优势,并且解决了分组失序问题.经综合评估,EB有着良好的恢复性能.     

Sorting Reordered Packets with Interrupt Coalescing

TCP performs poorly in networks with serious packet reordering. Processing reordered packets in the TCP-layer is costly and inefficient, involving interaction of the sender and receiver. Motivated by the interrupt coalescing mechanism that delivers packets upward for protocol processing in blocks, we propose a new strategy, Sorting Reordered Packets with Interrupt Coalescing (SRPIC), to reduce packet reordering in the receiver. SRPIC works in the network device driver; it makes use of the interrupt coalescing mechanism to sort the reordered packets belonging to the same TCP stream in a block of packets before delivering them upward; each sorted block is internally ordered. Experiments have proven the effectiveness of SRPIC against forward path reordering.     

Minimum information rate for observability of linear systems with stochastic time delay

This paper investigates the state estimation problem for linear time-invariant systems where sensors and controllers are geographically separated and connected via stationary memoryless uncertain digital communication channels with the information rate limitation. Such channels introduce data packet dropout, stochastic time delay, and data packet reordering. In the TCP/IP model, the transport layer provides a reliable service on top of an unreliable communication channel. However, the performance of such systems is still affected by packet reordering and stochastic time delay. In particular, we present an optimal encoding and decoding scheme to guarantee observability by employing the minimum information rate, and derive a necessary and sufficient condition on the delay distribution and information rate for observability. Illustrative examples are given to demonstrate the effectiveness of the proposed scheme.