数据包大小对TCP流性能的影响

在互联网时代,如何提高网络通信质量一直是研究热点,当前网络通信大部分数据流都采用TCP流。对于TCP流性能的影响因素如丢包、时延已有大量研究,但是数据包大小对其的影响却罕有涉及。另一方面,网络通信的质量很大程度上取决于路由器的性能,而路由器的性能又很大程度上取决于路由器的缓存设置。因此本文从数据包大小这一新的切入点入手,研究在不同的路由器缓存下,其对TCP流性能的影响。论文介绍了TCP协议、路由器缓存、数据包等相关概念,提出了实验方案的网络拓扑模型,选择了NS2平台进行网络仿真。在实验中,我们通过改变数据包大小和路由器缓存容量,得到了对应的实验数据并进行了分析整理,总结出了TCP流吞吐量和丢包率在数据包大小改变时的变化规律,即丢包率随数据包大小的增加呈线性增长,路由器缓存越小丢包率越大;TCP流的吞吐量随数据包大小的增加缓慢变大,路由器缓存达到一定值后不再成为瓶颈因素。     

一种基于Markov及反馈机制的网络拥塞控制方法

在研究现有网络数据传递拥塞控制问题的基础上,提出了一种基于路由器缓冲区队列长度的网络拥塞预测机制,并以该预测机制为基础提出了一种计费策略(PPBC,Per-Packet Billing Control)来控制网络拥塞.在拥塞控制模式中,将路由器缓冲区队列长度作为拥塞指标,通过马尔可夫链建模预测网络拥塞度.在服务器终端和数据发送方之间建立反馈机制,利用网络拥塞度,通过数据包计费方式控制网络拥塞.最后采用NS2仿真软件对PPBC性能进行仿真测评,仿真结果表明:PPBC不仅能够有效缓解网络拥塞,还能够使网络保持较低的丢包率.     

光突发交换网络的突发包组装和调度

光突发交换(OBS)由于结合了光线路交换和光分组交换的优点并且改进了两者的不足之处,成为实现IP over WDM的重要手段。主要研究实现光突发包在边缘路由器的组装生成和调度机制。通过模拟的方法研究边缘路由器的输出性能,包括输出流量的形状和时延特性。结果显示,不同服务等级的时延要求可以通过组装控制输出流的最大时延得以保证。同时边缘路由器组装和分配信道缓冲区设置和优先分配机制可以影响到输出光突发包的长度和突发度。     

输入排队Crossbar架构下的流量模型

 本文基于IP包在路由器各端口到达流量的统计特性,建立了输入排队Crossbar架构下的流量模型,对IP包流量的平均到达速率、突发性和均衡性等流量特征进行了分类定义,给出了各自的充要条件.文中所讨论的突发度B和不均衡度U为到达流量提供了精细的计算粒度,从而为基于IQ-VOQ的调度算法性能评估提供了理论依据.与LAN的自相似模型、WAN的Poisson模型以及数据业务的ON/OFF模型相比,本文讨论的流量模型更适用于基于IQ-VOQ调度算法性能的精确评估,为路由器交换架构的工程设计提供了理论依据.     

对路由器性能评测指标的研究

定义了不同的数据流转发模型,并利用网络仿真工具OPNET在所定义模型下分别对路由器的一些关键性能指标进行了测试,测试结果表明当转发模型为均匀流量时路由器的性能要远远好于非均匀流量转发模型下的性能。故得出IETF有关性能评测的方法与度纲不完备,未能对网络一般和极端环境下设备的性能进行评测,必须扩展IETF现有的性能评测度纲,从而为路由器的性能评价提供更全面的评价指标体系。     

路由器分布式控制研究综述

 光传输技术飞速发展和互联网流量快速增长对路由器性能提出了更高的需求.路由器经常因控制平面过载导致网络振荡,甚至路由器失效.为了克服路由器集中控制存在的问题,研究人员提出了路由器分布式控制方案.本文深入分析了路由器集中控制面临的问题,围绕路由器实现分布式控制需要解决分布式控制平面、分布式控制平面内部通信和分布式路由协议和算法这三个关键问题,综述和比较了现有的路由器分布式控制方案.最后对下一步工作进行了展望.     

一种顽健的自校正主动队列管理机制

现有基于控制理论的主动队列管理机制（AQM）大多数是根据简化的线性被控对象模型设计的,或者根据特定的网络条件设置算法的参数,当网络条件大范围变化时算法的性能难以保证.为了解决这些问题,提出了一种自校正的主动队列管理机制STR,通过在线估计TCP/AQM闭环系统被控对象模型的参数,并相应地调节报文丢弃概率,使路由器的缓冲区队列长度与期望值之间的方差最小.通过仿真实验验证了当网络条件大范围变化时算法的队列长度、链路利用率、报文丢弃率等性能,实验结果表明该算法具有良好的顽健性.     

虫洞路由交换及其缓冲区设计

文章在分析虫洞路由交换机制及其路器缓冲区组织方法的基础上，设计并实现了基于缓冲式虫洞路由交换机制，采用伸缩缓冲区实现流量控制方法的DawingUX8路由器芯片，应用结果表明该设计方案中以很好地解决刹车问题并有效地减少阻塞发生，所实现的路由芯片速度快，延迟时间短，可以有效提高网络性能。     

云时代的智能弹性新平台——迈普推出全球首款众核高端路由器

日前,迈普推出了其具有自主知识产权的全球首款,基于众核处理器技术的高端分布式核心路由器MP8800,MP8800基于智能众核处理技术以及高级电信计算架构eATCA构建. 路由器的发展经历了单核、双核到4核,再到多核,至目前的众核(8颗CPU以上)的过程. 路由器作为互联网的主要节点设备,是网络中进行网间连接的关键设备,可以说是互联网络的枢纽.而对于路由器的发展,性能和业务这两个因素起着非常关键的作用.一方面,带宽和网络规模的增长推动着路由器在性能、容量方面不断提升;另一方面,业务的发展驱动着路由器更加智能化和具备更强的业务提供能力.     

基于SRAM的核心路由器交换矩阵输入端口设计

交换矩阵是核心路由器的重要组成部分,为了避免来自不同输入端口的信元同时发往同一个输出端口,需要在输入端口设置缓冲区,即输入排队交换结构。基于静态随机存储器完成了交换矩阵输入端口虚拟输出队列（VOQ）的设计,该设计可以降低核心路由器交换芯片的面积,提高输入端口缓冲区信元的响应速率,并通过DE-115开发板完成对设计的验证。     

基于NS2的局域网路由器队列调度算法仿真分析

通过对一中等规模局域网流量分析,得出其流量组成、大小分布等特征;使用实际采集数据,用NS2模拟器模拟分析路由器在实施区分服务前后不同队列调度算法下的性能表现,发现了一些新的特征,由这些新特征可知在实际设备配置过程中,要充分考虑网络实际流量和应用需求,并非所用配置越复杂越好。     

利用Cisco路由器的ACL技术实现对中小型网络的安全管理

随着计算机网络的迅速发展,中小型网络作为互联网的基本组成部分,其安全问题不容忽视。本文通过具体的网络配置实例,说明了如何利用Cisco路由器的ACL技术实现对中小型网络进行控制和管理,限制特定网络流量,提高网络性能和安全。     

基于ATCA的交换单元设计

随着互联网规模以及通信容量迅速增加,作为网络核心节点的路由交换设备逐渐成为网络发展的瓶颈,而交换结构是限制其容量和性能的主要因素。简要介绍了几种交换结构的原理,分析了相关结构的优点和缺点,进而设计了基于ATCA规范的多平面Clos交换结构的交换单元。通过测试数据表明,这种交换结构能够达到线速80Gbps的交换能力,并具备一定的可扩展性。     

NetScope: traffic engineering for IP networks

Managing large IP networks requires an understanding of the current traffic flows, routing policies, and network configuration. However, the state of the art for managing IP networks involves manual configuration of each IP router, and traffic engineering based on limited measurements. The networking industry is sorely lacking in software systems that a large Internet service provider can use to support traffic measurement and network modeling, the underpinnings of effective traffic engineering. This article describes the AT&T Labs NetScope, a unified set of software tools for managing the performance of IP backbone networks. The key idea behind NetScope is to generate global views of the network on the basis of configuration and usage data associated with the individual network elements. Having created an appropriate global view, we are able to infer and visualize the networkwide implications of local changes in traffic, configuration, and control. Using NetScope, a network provider can experiment with changes in network configuration in a simulated environment rather than the operational network. In addition, the tool provides a sound framework for additional modules for network optimization and performance debugging. We demonstrate the capabilities of the tool through an example traffic engineering exercise of locating a heavily loaded link, identifying which traffic demands flow on the link, and changing the configuration of intradomain routing to reduce the congestion     

IP network configuration for intradomain traffic engineering

The smooth operation of the Internet depends on the careful configuration of routers in thousands of autonomous systems throughout the world. Configuring routers is extremely complicated because of the diversity of network equipment, the large number of configuration options, and the interaction of configuration parameters across multiple routers. Network operators have limited tools to aid in configuring large backbone networks. Manual configuration of individual routers can introduce errors and inconsistencies with unforeseen consequences for the operational network. In this article we describe how to identify configuration mistakes by parsing and analyzing configuration data extracted from the various routers. We first present an overview of IP networking from the viewpoint of an Internet service provider and describe the kinds of errors that can appear within and across router configuration files. To narrow the scope of the problem, we then focus our attention on the configuration commands that relate to traffic engineering-tuning the intradomain routing protocol to control the flow of traffic through the ISP network. We present a case study of a prototype tool, developed in collaboration with AT&T IP Services, for checking the configuration of the AT&T IP Backbone and providing input to other systems visualization and traffic engineering     

IP网络传输控制的性能评价标准研究

性能评价标准是进行网络传输控制机制和算法研究的一个非常重要的问题.由于传输控制本身的多目标性,导致了性能评价标准也需要同时考虑多项内容,即需要研究综合性能评价标准.本文通过讨论包括服务质量、服务数量和公平性在内的性能评价指标、性能评价的时间尺度和评价粒度等几个基本问题,针对不同的粒度,分别从有效性和公平性两个方面提出了相应的性能评价标准.在有效性方面,定义了规格化性能函数这一概念,把时延、丢包率等服务质量和服务数量统一在一起进行评价;在公平性方面,利用随机过程均值和方差的关系,以及Raj Jain公平指数的改进公式进行评价.     

Preconfiguring IP-over-Optical Networks to Handle Router Failures and Unpredictable Traffic

We consider the realization of traffic-oblivious routing in IP-over-optical networks where routers are interconnected over a switched optical backbone. The traffic-oblivious routing we consider is a scheme where incoming traffic is first distributed in a preset manner to a set of intermediate nodes. The traffic is then routed from the intermediate nodes to the final destination. This splitting of the routing into two phases simplifies network configuration significantly. In implementing this scheme, the first and second phase paths are realized at the optical layer with router packet grooming at a single intermediate node only. Given this unreliability of routers, we consider how two-phase routing in IP-over-optical networks can be made resilient against router node failures. We propose two different schemes for provisioning the optical layer to handle router node failures-one that is failure node independent and static, and the other that is failure node dependent and dynamic We develop linear programming formulations for both schemes and a fast combinatorial algorithm for the second scheme so as to maximize network throughput. In each case, we determine (i) the optimal distribution of traffic to various intermediate routers for both normal (no-failure) and failure conditions, and (ii) provisioning of optical layer circuits to provide the needed inter-router links. We evaluate the performance of the two router failure protection schemes and compare it with that of unprotected routing     

Netpiler: detection of ineffective router configurations

Configuring a network is a tedious and error-prone task. In particular, configuring routing policies for a network is complex as it involves subtle dependencies in multiple routers across the network. Misconfigurations are common and certain misconfigurations can bring the Internet down. In 2005, a misconfigured router in AS 9121 blackholed traffic for tens of thousands of networks in the Internet. This paper describes NetPiler, a system that detects router misconfigurations. NetPiler consists of a routing policy configuration model and a misconfiguration detection algorithm. The model is applicable to routing policies configured on a single router as well as to network-wide configuration. Using the model, NetPiler detects configuration commands that do not influence the behavior of the network - we call these configurations ineffective commands. Although the ineffective commands could be benign, sometimes when the commands are mistakenly configured to be ineffective, they cause the network to misbehave deviating from the intended behavior. We have implemented NetPiler in approximately 128,000 lines of C++ code, and evaluated it on the configurations of four production networks. NetPiler discovers nearly a hundred ineffective commands. Some of these misconfigurations can result in loss of connectivity, access to protected networks, and financial implications by providing free transit services. We believe NetPiler can help networks to significantly reduce misconfigurations.     

IEEE 802.11 goodput analysis for mixed real-time and data traffic for home networks

Increasingly, wireless networks are being used to provide connection services for devices running applications with very different quality of service requirements. Although this issue has been addressed by the IEEE 802.11e standard, the fact is that most networks deployed in home/office environments nowadays use IEEE 802.11a/b/g standard devices. Unfortunately, administrators often do not set configuration parameters of network devices to maximize resources performance, thus providing poor quality of service. In this paper, two IEEE 802.11a/b/g analytical performance evaluation models for mixed traffic Ad Hoc and infrastructure WLANs are presented, assuming that some network devices are executing single applications, like VoIP, videoIP or network browsing. In our analysis, network devices are grouped according to the expected traffic pattern of the applications they are running. Then, global and individual group goodput are calculated assuming a congested network. Based upon the outcome of this analysis for different settings of the device configuration parameters, it is shown that the performance of a standard home/office IEEE 802.11 wireless network can be significantly improved by choosing appropriate values of these parameters.     

ByPass流量旁路技术组网实现探析

文章根据现网中的核心路由器"过境"流量负担重的问题,提出了流量旁路技术(ByPass)的IP层与光层联合组网策略。文章指出通过引入光层和IP层协同的机制,网络可以得到优化,并且光层OTN设备能够代替核心路由器来转发部分业务流量,这也是解决IP承载网所面临的扩展性问题的一个重要途径。