采用轮询机制提高Linux系统的网络性能

目前,Linux操作系统被广泛应用在网络数据包收发系统中。这是因为,Linux采用中断机制来响应外部事件,保证了系统能够合理高效地利用CPU资源。但是,在高负荷网络环境下,大量的CPU资源将会被频繁到达的网卡中断占用,导致系统遭遇性能瓶颈,出现接收活锁1。为了避免在高负荷网络环境下系统性能下降,该文采用轮询机制处理网络数据的收发,而在低负荷网络环境中,仍然采用原有的中断机制。     

网络数据采集技术研究

随着网络带宽的不断增长,网络安全系统(如网络入侵检测系统--NIDS)对网络数据包捕获能力要求越来越高,为了提高网络数据包的捕获能力以适应当今高速网络环境,本文在分析传统网络数据采集系统的基础上,采用地址映射、零拷贝捕包和零拷贝存储等技术,提出一种新的捕包系统,该系统的性能较传统的方法有了大幅的提高,在千兆网络环境下,能够满足网络安全对网络数据包捕获能力的需求.     

优化Linux网络处理性能的软中断处理机制

软中断在Linux内核中,作为一种对时间要求最为严格的中断下半部处理机制,在处理网络数据包的过程中发挥着无可替代的作用,而软中断处理函数采用固定的循环检测次数,以至于系统可能在网络负载高的情况下对数据包不能进行及时有效处理。提出了一种最大循环检测次数可动态变化的方法来优化软中断处理机制,实验表明,相比现有的软中断机制而言,在同样的环境下可以处理更多的软中断例程,表现为捕获更多的网络数据包,提升了系统处理软中断的能力,进而在系统级上优化了Linux网络处理性能。     

网络控制系统的一种变采样周期动态调度策略

提出一种基于网络运行状态的网络控制系统动态调度器的设计方法．首先利用监测器在线获取当前的网络利用率、网络诱导误差和数据包执行时间，基于获取的网络状态，预测下一监测周期内的网络利用率和数据包执行时间．然后按照网络运行性能和控制性能的需求，基于网络利用率和数据包执行时间的预估值分配网络资源，计算控制系统新的采样周期．当数据包传输发生冲突时，采用MEF（Maximum Error First）作为辅助调度策略，确定数据包的发送优先级．最后通过一组仿真结果验证了所设计的动态调度器的有效性．     

网络数据包捕获工具的开发与实现

捕获网络数据包可以用来检测并分析网络面临的安全性威胁,网络数据包的捕获广泛应用于IP网络性能测量、流量分析、用户计费、网络入侵检测、网络协议分析及口令拦截等多种场合.介绍了以太网数据包的捕获机制,并在此基础上采用Linux的Lipcap和Socket两种方法,讨论了网络数据包捕获工具的开发过程,同时给出TCP/IP首部的提取方法,以便对捕获的数据作进一步的分析与处理.     

一种基于.NET的网络数据包捕获引擎实现

介绍了一种可供.NET环境使用的网络数据包捕获引擎Npcap的开发过程。首先简单介绍了广泛使用的数据包捕获引擎Winpcap的功能及其用法,接下来详细介绍了如何在.NET环境下对Winpcap进行封装和改进形成Npcap,最后给出了Npcap的应用领域。     

网络数据包的协议分析算法设计与实现

为有效地监听网络状况和数据传输，截获网络传输的数据包，分析网络性能，排除网络故障，文中在以太网的基础上，通过对网络数据包的协议分析，殴计并实现了一个网络数据包的协议分析算法（PLA算法）。PLA算法可以有效地对网络中传输的数据包进行协议分析，解决了如何判别在网络上传输的数据包是什么类型的数据包，每一个数据包都用到了哪些协议。通过PLA算法对数据包的分析，可以使得流量统计和流量收费更加精确。     

网络优化建议

如何最大限度地提升网络的速度与性能,一直是企业网络管理者们所关注的问题。本文将围绕如何进一步提升网络的速度与性能这一问题,给出业内资深人士和网络专家的七条建议。使用巨型数据包使用巨型数据包技术可使网络获得性能上的提升,支持巨型数据包的交换机和网络接口卡可以处理最大长度超过IEEE标准(1.5kbits)的数据包,一些设备支持长度超过9k bits的数据包,但在巨型数据包长度方面还没有统一的标准。业内人士指出,对于吉比特网和10G网这样的高速以太网来说,使用巨型数据包技术更为有效,包括3C om、C isco、Extrem eN etw orks等等的…     

基于Linux的网络数据包捕获机制研究

文章基于Lmux平台,分析传统Libpcap技术如何捕获以太网环境下网络数据包,来描述传统捕包技术的简易性。但在高速、大流量网络环境下,传统捕包技术丢包现象比较严重,引入零拷贝技术能够减少数据拷贝次数,解放CPU,有效地提高捕包系统的整体性能。     

基于通信干扰观测器的网络控制系统研究

网络控制系统有着极其广泛的应用背景。为克服网络控制系统中含有延迟、数据包顺序混乱等问题造成的系统性能降低甚至不稳定,提出了采用通信干扰观测器策略进行解决的方案。以某网络控制调速系统为例,介绍了系统的设计和参数调节方法。在Simulink环境下进行了全面的仿真验证,结果显示改进方法能有效处理网络系统中的延迟问题,且对延迟变化具有很强的适应能力,保证了系统的稳定性和性能。     

An artificial neural network approach for routing in distributed computer networks

This paper presents a new approach based on the Hopfield model of artificial neural networks to solve the routing problem in a context of computer network design. The computer networks considered are packet switching networks, modeled as non-oriented graphs where nodes represent servers, hosts or switches, while bi-directional and symmetric arcs represent full duplex communication links. The proposed method is based on a network representation enabling to match each network configuration with a Hopfield neural network in order to find the best path between any node pair by minimizing an energy function. The results show that the time delay derived from flow assignment carried out by this approach is, in most cases, better than those determined using conventional routing heuristics. Therefore, this neural-network approach is suitable to be integrated into an overall topological design process of moderate-speed and high-speed networks subject to quality of service constraints as well as to changes in configuration and link costs.     

RCSP and stop-and-go: a comparison of two non-work-conserving disciplines for supporting multimedia communication

To support emerging real-time applications, high-speed integrated services networks must provide end-to-end performance guarantees on a per-connection basis in a networking environment. Resource management algorithms must accommodate traffic that may get burstier as it traverses the network due to complex interactions among packet streams at each switch. To address this problem, several non-work-conserving packet-service disciplines have been proposed. Non-work-conserving servers may be idle and hold packets under certain conditions, to reconstruct, fully or partially, the traffic pattern of the original source inside the network and prevent the traffic from becoming burstier. We compare two non-work-conserving service disciplines. Stop-and-go uses a multilevel framing strategy to allocate resources in a single switch and to ensure traffic smoothness throughout the network. Rate controlled static priority (RCSP) decouples the server functions with two components: (1) a regulator to control traffic distortion introduced by multiplexing effects and load fluctuations in previous servers, and 2) a static priority scheduler to multiplex the regulated traffic. We compare the two service disciplines in terms of traffic specification, scheduling mechanism, buffer space requirement, end-to-end delay characteristics, connection admission-control algorithms, and achievable network utilization. The comparison is first done analytically, and then empirically by using two 10-min traces of MPEG compressed video.     

Video placement and configuration of distributed video servers on cable TV networks

A large-scale, distributed video-on-demand (VOD) system allows geographically dispersed residential and business users to access video services, such as movies and other multimedia programs or documents on demand from video servers on a high-speed network. In this paper, we first demonstrate through analysis and simulation the need for a hierarchical architecture for the VOD distribution network.We then assume a hierarchical architecture, which fits the existing tree topology used in today's cable TV (CATV) hybrid fiber/coaxial (HFC) distribution networks. We develop a model for the video program placement, configuration, and performance evaluation of such systems. Our approach takes into account the user behavior, the fact that the user requests are transmitted over a shared channel before reaching the video server containing the requested program, the fact that the input/output (I/O) capacity of the video servers is the costlier resource, and finally the communication cost. In addition, our model employs batching of user requests at the video servers. We study the effect of batching on the performance of the video servers and on the quality of service (QoS) delivered to the user, and we contribute dynamic batching policies which improve server utilization, user QoS, and lower the servers' cost. The evaluation is based on an extensive analytical and simulation study.     

Traffic Control in ATM Networks

Editor's Note: Zbynek Bazanowski is a doctoralcandidate specializing in managing high-speed networks.I met him in St. Petersburg where he gave an excellenttalk on managing ATM networks and he has done important work in understanding the dynamicbehavior of ATM networks under load. I worry that thecontrol mechanisms for high-speed networks mustanticipate bottlenecks, and relying on feedback control will lead to servo lags that will make thesenetworks inherently unstable when they regularly exceed40% utilization. This is real and not a theoreticalproblem demonstrated by the September, 1995 INTERNETtraffic jams. Here is Zbynek's prognosis on managingthese high-speed networks.     

Using proxies to enhance TCP performance over hybrid fiber coaxial networks

Using cable modems that operate at several hundred times the speed of conventional telephone modems, many cable operators are beginning to offer World Wide Web access and other data services to residential subscribers. Initial experiences indicate that real-world hybrid fiber coaxial (HFC) networks are susceptible to a variety of radio-frequency impairments that significantly reduce the benefits of using high-speed cable modems. The effects of packet losses in the access network are particularly accentuated during subscriber accesses to remote servers on the Internet. The longer round-trip times in such accesses together with the high packet loss rate result in dramatic degradations in performance perceived by subscribers. This paper shows that by using proxy servers to handle all remote accesses from an HFC access network, the performance of remote accesses can be significantly enhanced even in cases when the proxy servers do not function as data caches. By handling packet losses that occur in the HFC network locally, at low latencies and without the remote server even being aware of the loss, a proxy server enables faster recovery from packet losses. Most importantly, since it controls data transmissions over the local HFC network, the proxy server's transmission control protocol (TCP) implementation can be optimized for the loss of characteristics of the HFC access network, enabling a significant increase in performance when the access network is lossy.     

基于HTTP协议的高速代理服务器

本文在简要介绍HTTP协议及代理服务器原理的基础上,给出了如何用VC++实现HTTP协议解析及高速代理服务器。     

Queueing networks with mobile servers: The mean-field approach

We consider queueing networks which are made from servers exchanging their positions on a graph. When two servers exchange their positions, they take their customers with them. Each customer has a fixed destination. Customers use the network to reach their destinations, which is complicated by movements of the servers. We develop the general theory of such networks and establish the convergence of the symmetrized version of such a network to some nonlinear Markov process.     

State diagrams and steady-state balance equations for open queuing network models

In this paper, the state diagrams and steady-state balance equations for two kinds of open queuing network models are presented. The first model comprises a network of single queues with single servers, while the second model comprises multiple servers for single queues. State diagrams are drawn for (2, 3) queuing networks with (i) single servers and (ii) multiple servers. Steady-state balance equations are derived from the state diagrams. The paper provides a method to solve open queuing networks by analyzing the stochastic process involved in the transition of states in a continuous time Markov chain which represents the state diagram of a queuing system.     

Integrated office systems over LANs — a performance study

In this paper, an integrated office system environment is modelled and studied. Composed of multi-media workstations, printer servers, database servers, electronic mail servers etc., the office information system (OIS) is interconnected by a LAN. The performance of three selected networks namely Appletalk, Starlan and Ethernet, in handling the typical office system applications, is evaluated. The study applies discrete-event computer simulation, using the QNAP2 simulation software. Results comparing the performance and utilization of the three networks are presented and some useful conclusions obtained.     

基于随机流模型的校园网格存储服务分析

校园网格存储服务是汇聚校园高性能计算中心、各个院系或研究所的服务器以及单个PC机贡献的存储资源,建立三级存储架构,为用户提供数据存储的注册、分配、调度、释放服务。由于节点的动态性,导致所提供的存储空间总数动态变化,为研究存储服务性能,采用随机流模型进行分析。它是一种宏观上对高速网络进行有效分析的模型,是基于排队论模型分析的一种替代方法。通过该模型分析校园网格存储服务性能,得出节点请求分配概率随节点数目变化的关系。