基于GPS的Internet端到端时延测量的实现

网络行为测量是网络行为分析的基础,而端到端的时延又是网络行为测量中一个重要的参数.但是由于传统的端到端测量存在时钟不同步问题,因此测量的误差较大.文中采用基于GPS接收机的同步方法设计出网络时延测量仪来测量端到端时延,解决了收发时钟不同步的问题,提高了测量的精度.     

基于GPS的端到端时延测量方法设计方案

端到端时延是评估Internet的网络性能的重要参数之一,也是近年来的研究热点。由于端到端时延的测量存在收发时钟不同步问题,所以常用的网络时延测量方法大多是通过测往返时延来间接求得端到端时延,测量结果的误差较大。文中基于GPS接收机的同步方法设计出网络时延测量仪来测量端到端时延,解决了收发时钟不同步的问题,提高了测量的精度。     

基于线性规划的Internet端到端时延的估计

测量Internet端到端时延特征是研究Internet端到端分组行为的重要内容之一,它能够应用于QoS(Quality of Service),SLA(Service Level Agreement)的管理、拥塞控制算法研究等许多方面.常用的端到端时延测量方法大多依赖于GPS接收机或采用NTP协议来实现收发端时钟的同步,但由于GPS接收机价格较高不可能每台主机都能配备, NTP协议的精度不能满足要求。该文基于线性规划的方法估计收发时钟的频差、相对时钟偏差等参数,以获得端到端时延的估计。作者在几条不同的链路上进行了测试,结果表明该方法能有效消除收发时钟不同步的影响。     

用移动探针构造端到端故障诊断系统

将具有网络测量智能的探针移动到用户端系统中,再通过Web浏览器控制其测试参数并显示测试结果,这种端到端故障诊断系统能够方便、迅速地诊断出网络故障,结合使用网络测量策略系统更容易改变测试条件和增加测试功能.提出了基于智能代理的端到端故障诊断系统的体系结构,讨论了其实现技术并介绍了相关的应用。     

基于端到端测量的路由变化分析

对路由变化的分析和预测，是网络测量的一个重要方面。通过对端到端路由测量结果的分析，来验证Internet路由的若干特性。路由的变化与路由选择策略是密不可分的，同时，路由的变化也会造成网络性能的变化，从而影响其他网络测量的度量。通过对RTT和返回分组TTL值的变化规律的分析，可以帮助定位网络瓶颈，预测路由变化，因此可以作为研究网络路由的一个重要手段。     

一种新的故障链路识别算法RPI

针对目前大多数故障链路识别算法不能兼顾良好稳定性和低计算复杂性的问题,该文提出一种基于参考路径的故障链路识别算法RPI(Reference Path based lossy link Identification algorithm)。该算法根据路径间的性能差异,从经过同一链路的所有路径中选取一部分作为该链路的参考路径,然后采用启发式方法根据参考路径间的性能相关性识别该链路的状态。相较已有算法,RPI更充分地利用了测量数据的可用信息,具有更好的稳定性,同时启发式估计策略保证了算法的低计算复杂性。仿真结果表明RPI能够在多种网络场景下较同类算法更精确地识别出故障链路。     

非时钟同步的单向排队时延测量估计方法

提出了一种测量和估计网络端到端单向排队时延的新方法。与消除时钟偏差和时钟频差的现有方法相比,新方法完全不需要测量端之间的时钟同步。探测分组之间的发送和到达时间间隔在两端分别测量,然后利用傅立叶域-时间域的迭代重构算法估计端到端单向排队时延的分布特性。仿真和分析结果表明新方法具有很好的实时性、准确性和顽健性。     

基于主动测量的HTTP端到端体验质量测量技术研究

随着互联网的普及和发展,网络应用业务用户使用感受的测量愈发重要。HTTP作为互联网典型应用万维网服务的传输协议,对它的体验质量进行测量不仅有助于了解各个网站的用户体验,同时也将为互联网的其他应用业务的测量提供参考。通过使用基于主动测量的测量工具SimBrowser对若干网站进行测量,以及对比用户的实际体验,验证了测量方法的可行性,并初步了解了一些HTTP端到端体验质量与服务质量的关系。     

三端稳压器测试仪简介

1.综述 GH2911M3三端稳压器测试仪,用于测量各种封装的三端固定、三端可调稳压器的性能参数。主要包括三端稳压器的输出电压V_0,电压调整率Sv,电流调整率Si,静态电流Id,纹波抑制比Sr,静态电流变化量ΔId。测试仪由计算机作为控制机,配备GH2911M3集成稳压器测试单元构成测试系统。测试仪在Window环境下,采用Visual BASIC语言编程,界面友好。测试仪具有多种测量模式供用户选择,方便、快捷、容易掌握。在“常规测试”模式下,用户只需输入被测件型号,仪器将按照国家标准所规定的测量方法对三端稳压器的七个参数逐一测量。测量结果用CRT显示,打印机打印,并按照产品规范判定器件好坏,统计测量数据和合格率。在“自定     

基于随机网络演算的LTE网络端到端时延分析

本文主要分析了基于随机网络演算的LTE网络端到端时延问题,本文首先介绍了研究背景,其次分析了随机网络演算的相关理论,最后就LTE网络端到端时延的几点问题进行了分析。     

Segment cooperation communication in multi-hop wireless networks

Cooperative communication could enhance the performance of wireless communications by allowing nodes to cooperate with each other to provide spatial diversity gain. In cooperative communications, rational helper selection is an important issue to obtain good cooperative gain at destinations. There are many works on this topic; however, most of them are based on hop-by-hop model and few works investigate how to select helpers for the nodes in a multi-hop path to optimize the end-to-end performance. The helper selection for one node could affect the helper selection for other nodes on the same route and in turn affect end-to-end performance. In other words, the traditional hop-by-hop helper selection methods could not lead to optimal performance in multi-hop environments. To solve this, this paper firstly defines a novel cooperation mode, named segment cooperation, and deduces the capacity and outage probability of cooperation segment. Then new performance metrics, end-to-end capacity and end-to-end outage probability, are defined to measure the end-to-end performance of multi-hop route. Finally, a segment cooperation method is proposed to maximize these metrics.     

Unicast probing techniques for estimation of shared loss rate

The paper introduces two new unicast active end‐to‐end measurement techniques, called the single–double unicast probing (SDUP) and the delay‐based unicast probing (DUP), to estimate the rate of losses which occurs on the shared network path of two flows. A comprehensive performance evaluation and a comparison between these two techniques and an existing one having the same objective, the striped unicast probing (SUP) (Proceedings of the INFOCOM 2001—The IEEE Conference on Computer Communications, No. 2, Anchorage, Alaska, U.S.A., 2001; 915–923), were carried out. We demonstrate that our proposed SDUP technique provides even better estimation accuracy compared to that of the SUP while it requires only one piece of measurement equipment at only one receiver instead of deploying units to both receivers. Furthermore, with only one sender and receiver pair we can measure not only one shared path, but any partial path that begins at the sender and is located on the sender–receiver path. We also show that while the DUP have the same accuracy as the SUP in the case of Drop‐Tail buffer management, the DUP is capable of measuring loss rates of RED buffers, which the other techniques do not work with. The SDUP and the DUP are less intrusive and cause less bursty traffic compared to the SUP. Finally, the adaptation of these techniques into passive measurements is also considered. Copyright © 2006 John Wiley & Sons, Ltd.     

基于测量的网络性能评价方法研究

网络性能评价方法的研究对于指导网络设计和改进网络运行性能状况有着重要的意义。为了综合地评价网络的运行状况，在测量的基础上，提出了基于多个测量指标的多指标综合评价方法，并应用到路径性能评价和网络性能评价上，该值反映了路径和网络的综合性能状况，并可以按照不同的策略分析路径和网络之间的性能变化情况。实验结果表明，该方法可以有效的评价目标路径和网络的运行状况。     

Performance assessment approach based on change-point detection for network moving target defense

A performance assessment approach based on change-point detection for network moving target defence was proposed.Directed to the problem of network resource graph not being able to present the effect of network resource vulnerabilities to network nodes,a conversion relationship between resource vulnerability changes and node security states was established by defining the concept of a hierarchical network resource graph and the efficiency of resource graph construction and updating were improved.Furthermore,directed to the problem of static detection algorithm not being able to precisely measure the dynamic change of network moving target defense,a change-point detection algorithm and standard degree measurement algorithm was designed.The security cost and benefit of network moving target defense in real-time and dynamically on the basis of unified metrics were defected and measured,which improved the evaluation accuracy.The analysis result of typical examples has proved the feasibility and the effectiveness of the proposed approach.     

Quality-Aware Routing Metrics for Time-Varying Wireless Mesh Networks

This paper considers the problem of selecting good paths in a wireless mesh network. It is well-known that picking the path with the smallest number of hops between two nodes often leads to poor performance, because such paths tend to use links that could have marginal quality. As a result, quality-aware routing metrics are desired for networks that are built solely from wireless radios. Previous work has developed metrics (such as ETX) that work well when wireless channel conditions are relatively static (DeCouto , 2003), but typical wireless channels experience variations at many time-scales. For example, channels may have low average packet loss ratios, but with high variability, implying that metrics that use the mean loss ratio will perform poorly. In this paper, we describe two new metrics, called modified expected number of transmissions (mETX) and effective number of transmissions (ENT) that work well under a wide variety of channel conditions. In addition to analyzing and evaluating the performance of these metrics, we provide a unified geometric interpretation for wireless quality-aware routing metrics. Empirical observations of a real-world wireless mesh network suggest that mETX and ENT could achieve a 50% reduction in the average packet loss rate compared with ETX     

基于多项服务质量的域间路由方案

针对广域网中节点数量多,范围广的特点,提出了一种将节点划分成域,并以带宽、时延作为服务质量（ＱｏＳ）指标在域间寻找可行路径的路由方案。该方案由两个算法组成,它们在把真实网络映射成为具有分级结构图的同时给出了满足服务质量要求的可行路径。     

IP网络性能指标体系的研究

网络性能指标是网络测评的基础。本文从网络测评的不同角度对IP网络的性能指标进行了综合分析，指出了一种能系统反映IP网络性能的指标体系，并给出了IP网络性能指标体系的形式描述。在此基础上引入了泛化指标和确定性指标的概念，探讨了确定性指标的内容有及描述框架。该研究突破了目前IP网络性能指标体系研究的简单性、局限性，对IP网络测试和性能评价具有指导意义。     

Reinforcement learning based routing in wireless mesh networks

This paper addresses the problem of efficient routing in backbone wireless mesh networks (WMNs) where each mesh router is equipped with multiple radio interfaces and a subset of nodes serve as gateways to the Internet. Most routing schemes have been designed to reduce routing costs by optimizing one metric, e.g., hop count and interference ratio. However, when considering these metrics together, the complexity of the routing problem increases drastically. Thus, an efficient and adaptive routing scheme that takes into account several metrics simultaneously and considers traffic congestion around the gateways is needed. In this paper, we propose an adaptive scheme for routing traffic in WMNs, called Reinforcement Learning-based Distributed Routing (RLBDR), that (1) considers the critical areas around the gateways where mesh routers are much more likely to become congested and (2) adaptively learns an optimal routing policy taking into account multiple metrics, such as loss ratio, interference ratio, load at the gateways and end-to end delay. Simulation results show that RLBDR can significantly improve the overall network performance compared to schemes using either Metric of Interference and Channel switching, Best Path to Best Gateway, Expected Transmission count, nearest gateway (i.e., shortest path to gateway) or load at gateways as a metric for path selection.     

一种基于跨层设计和蚁群优化的自组网负载均衡路由协议

针对大部分现有替代路径共同存在的替代路径老化和构建效率问题,本文提出了一种基于跨层设计和蚁群优化的负载均衡路由协议(CALRA),利用蚁群优化算法特有的信息素挥发方法实现对替代路径的老化问题,将蚁群优化和跨层优化方法结合起来解决自组网中的负载均衡问题,通过双向逐跳更新的方式较好的解决了替代路径构建效率问题,并将蚂蚁在所经过的各中间节点为路由表带来的信息素增量映射为蚂蚁离开源节点的距离、移动过程中所遇到的节点拥塞程度、节点当前信息素浓度和节点移动速度等各协议层的统计信息的函数,通过对各种信息所对应的参数赋予不同加权值的方法对概率路由表进行控制,改善了自组网中现有基于蚁群优化的路由协议中普遍存在的拥塞问题、捷径问题、收敛速度问题和引入的路由开销问题.仿真表明,CALRA在分组成功递交率、路由开销、端到端平均时延等方面具有优良性能,能很好地实现网络中的业务负载均衡.