提高无线网络TCP流量性能的方法

简述了目前无线网络中传输控制协议(TCP)的应用现状，探讨了三种改善TCP性能的基本解决方案：分离连接方法、端到端方法、链路层方法，并对每一轩方法的性能进行了比较分析，展望了基于无线链路的TCP将来的研究方向和发展趋势。     

无线网络中传输控制协议的研究

传统TCP(传输控制协议)拥塞控制协议本是为有线网络设计,它假设包丢失完全是由网络拥塞引起。在无线网络环境下除了拥塞丢包外,还存在较高的比特误码率、路由故障等因素引起的丢包现象。当出现非拥塞丢包时,传统TCP将错误地触发拥塞控制,从而引起TCP性能低下。文章在分析传统TCP在无线网络中存在问题的基础上,对目前无线TCP发展和技术进行归纳和比较,进一步给出无线传输协议的研究和发展方向。     

TCP—IP协议的最新发展

简述了ＴＣＰ／ＩＰ协议在Ｉｎｔｅｒｎｅｔ中的重要作用产通过对Ｉｎｔｅｒｎｅｔ协议第６版与第４版的比较，说明了两个版本的差异     

中件TCP／IP网络接口实现

中件是网络环境中一系列分布式服务软件的集合，提供比操作系统和网络系统服务本身更简单和有效的应用程序接口。论述了中件的概念，讨论了如何在Ｗｉｎ３２环境下，采用ＶＣ通过ＭＦＣ调用，ＶＢ通过ＡｃｔｉｖｅＸ控件，Ｄｅｌｐｈｉ通过ＶＣＬ可视元件等多种途径实现中件对ＴＣＰ／ＩＰ网络的接口。     

无线网络TCP研究探讨

随着网络技术的发展,无线网络和设备得到了一定的普及,对人们的生活产生了很大的影响,为人们提供了便捷的服务。随着人们需求的不断增加,无线通信不仅要实现语音通信,同时还要提高数据传输的可靠性。本文笔者分析了无线网络TCP的性能和影响其性能的因素,重点探讨改进无线网络TCP性能的方法,目的是为TCP的改进方向提供指导和借鉴。     

一种提高无线环境中TCP性能的改进方案

本文针对无线信道的特点提出了一种用于提高无线环境中TCP性能的改进方案－Wireless-TCP，通过尝试对TCP的拥塞控制中时间的算法进行调整并增加Probe模块以应对无线信道中的长时间中断，保证TCP连接的存在，通过爱立信通信实验室的仿真实验验证了该改进方案的有效性。     

超高频RFID系统与其他无线网络的电磁兼容性研究

无线射频识别（RFID）技术与互联网、移动通信网络等技术结合应用,可以实现全球范围内物品跟踪与信息共享。然而,RFID作为无线通信系统,其发射的射频信号可能对其它无线网络造成干扰,降低系统性能,影响系统正常工作。中国已经发布了840～845MHz和920～925MHz频段RFID的试用标准,其中920～925MHz的RFID应用和点对点立体声广播处在一个同一个频段,与无中心对讲机和GSM网络处在相邻频段,RFID系统与这些系统之间的电磁兼容性就成为系统能否稳定实现的最主要因素。     

无线网络中TCP拥塞控制算法的性能分析

根据无线网络中存在随机数据包丢失的特定情况,对TCP拥塞控制算法在无线网络中的性能进行了分析。理论分析和仿真结果表明,随着无线链路中随机数据包丢失概率的增加,TCP拥塞控制算法将导致无线网络性能的严重下降。     

改进无线网络TCP性能的研究

对采用TCP协议传输数据的实现过程及其在无线网络中可能遇到的问题进行了描述。对因无线信道误码率较高和频繁切换而导致网络性能下降的问题,提出了无线链路层快速重传技术改善网络性能的有效措施,并研究了在无线网络中链路层快速重传技术对无线TCP数据传输的影响。仿真表明链路层快速重传可以有效地改善无线TCP的性能,进一步提高了网络利用率和吞吐量。     

无线网络TCP协议性能分析

改进的TCP协议又称TCP-AP(Transport Control Protocol with AP),主要是针对无线网络下TCP性能下降做出的改动。TCP发送方的丢包问题能此办法解决,该协议区分丢包是由比特错误造成还是网路拥塞造成主要通过层与层之间的通信,此改动对于提高TCP在无线网络中的性能具有重大意义。本文通过仿真工具Network Simulator对各种场景进行模拟后试验,对于TCP-AP协议性能的提高进行验证。     

Compatibility Issues of IPSec and TCP in Wireless Networks

1　Introduction　TransmissionControlProtocol (TCP)isthedefactotransportprotocolfortheglobalInternet.TCPusesbasicIPservicestoprovideapplicationswithanend to endconnection oriented packettransportmechanism ,whichensuresthereliableandordereddeliveryofdata .ButconventionalTCPschemesmaysufferfromaseveredegradationinperformanceinwirelessenvironmentbecauseofcertaincharacteris ticsofwirelessnetworks ,suchasnon congestionlosses[1 ] ,longdelays[2 ] ,anddynamicchangingtopology[3] .　ManyTCPperform…     

TCP Westwood: End-to-End Congestion Control for Wired/Wireless Networks

TCP Westwood (TCPW) is a sender-side modification of the TCP congestion window algorithm that improves upon the performance of TCP Reno in wired as well as wireless networks. The improvement is most significant in wireless networks with lossy links. In fact, TCPW performance is not very sensitive to random errors, while TCP Reno is equally sensitive to random loss and congestion loss and cannot discriminate between them. Hence, the tendency of TCP Reno to overreact to errors. An important distinguishing feature of TCP Westwood with respect to previous wireless TCP extensions is that it does not require inspection and/or interception of TCP packets at intermediate (proxy) nodes. Rather, TCPW fully complies with the end-to-end TCP design principle. The key innovative idea is to continuously measure at the TCP sender side the bandwidth used by the connection via monitoring the rate of returning ACKs. The estimate is then used to compute congestion window and slow start threshold after a congestion episode, that is, after three duplicate acknowledgments or after a timeout. The rationale of this strategy is simple: in contrast with TCP Reno which blindly halves the congestion window after three duplicate ACKs, TCP Westwood attempts to select a slow start threshold and a congestion window which are consistent with the effective bandwidth used at the time congestion is experienced. We call this mechanism faster recovery. The proposed mechanism is particularly effective over wireless links where sporadic losses due to radio channel problems are often misinterpreted as a symptom of congestion by current TCP schemes and thus lead to an unnecessary window reduction. Experimental studies reveal improvements in throughput performance, as well as in fairness. In addition, friendliness with TCP Reno was observed in a set of experiments showing that TCP Reno connections are not starved by TCPW connections. Most importantly, TCPW is extremely effective in mixed wired and wireless networks where throughput improvements of up to 550% are observed. Finally, TCPW performs almost as well as localized link layer approaches such as the popular Snoop scheme, without incurring the overhead of a specialized link layer protocol.     

虚拟专用网技术与IPsec协议

分析了VPN的发展现状 ,从理论和技术实现层面介绍了虚拟专用网的结构、关键技术以及安全性分析 ,着重对IPsec作了阐述 ,探讨了如何应用VPN解决Internet的安全性的威胁 ,最后 ,给出了一个基于Ipsec的企业级VPN解决方案。     

TCP在无线衰落信道下的性能研究

本文在分析无线TCP原理的基础之上,讨论了各种提高无线链路TCP性能的方法,并对其优缺点进行了分析和总结.最后给出无线环境下TCP改进的基本原则,并初步探讨了进一步改进的方向.     

基于流的无线网络编码

针对无线链路的不可靠性和物理层的广播特性,将网络编码与无线网络相结合,提出一种基于流的无线网络编码算法——FNC。该算法在先验参考路径的基础上,充分利用每个节点处的路由表项,探测编码机会,在有编码机会的节点对满足编码条件的数据流进行网络编码,达到提高网络吞吐量的目的。仿真结果表明：FNC有效提高了整个网络的吞吐量,改善了网络性能。     

无线数据通信网建设的探讨

本文介绍了无线数据通信网的概念及其接入方式，并对江苏省无线数据通信网建设作了初步探讨，基于无线数据通信的优点和特性，其有关广泛的应用前景和巨大的市场潜力，对国民经济信息化和对外经济发展有着重要意义。     

Use of TCP Decoupling in Improving TCP Performance over Wireless Networks

We propose using the TCP decoupling approach to improve a TCP connection's goodput over wireless networks. The performance improvement can be analytically shown to be proportional to , where MTU is the maximum transmission unit of participating wireless links and HP_Sz is the size of a packet containing only a TCP/IP header. For example, on a WaveLAN [32] wireless network, where MTU is 1500 bytes and HP_Sz is 40 bytes, the achieved goodput improvement is about 350%. We present experimental results demonstrating that TCP decoupling outperforms TCP reno and TCP SACK. These results confirm the analysis of performance improvement.     

Ad Hoc网络路由技术

无线自组织网络(Adhoc)是一个复杂的系统,其中路由协议是该领域中的研究热点。通过采用合理的路由技术,可使无线自组网具有更为灵活的组网方式,从而达到提升网络性能、减少网络开销等目的。通过与认知无线电(CR)技术、协同通信(CC)技术以及多输入多输出(MIMO)天线技术等物理层新技术的有效结合,可以大大改善Adhoc路由协议的性能。     

Low Power Downlink MAC Protocols for Infrastructure Wireless Sensor Networks

This paper addresses low power medium access control (MAC) protocols for the downlink channel of infrastructure wireless sensor networks. Access points are assumed to be energy unconstrained. The trade-off between the power consumption of the sensor nodes and the transmission delay is analyzed, focusing on low traffic. We describe WiseMAC (Wireless Sensor MAC), a new protocol for the downlink of infrastructure wireless sensor networks. Another original contribution is the presentation and analysis of PTIP (Periodic Terminal Initiated Polling). Here, polling is used in the reversed direction as compared to common polling protocols. WiseMAC and PTIP are compared with PSM (Power Save Mode), the power save protocol used in both the IEEE 802.11 and IEEE 802.15.4 ZigBee standards. Analytical expressions are derived for the power consumption and the transmission delay for each protocol, as a function of the wake-up period. It is shown that WiseMAC provides, with low bit rate radio transceivers, a significantly lower power consumption than PSM. Although less energy efficient than WiseMAC and PSM, it is shown that PTIP can, thanks to its implementation simplicity, become attractive for applications tolerating large transmission delays.Amre El-Hoiydi received the electrical engineer degree from the Swiss Federal Institute of Technology in Zurich (ETHZ), Switzerland, in 1994. In 1995, he was a teaching assistant at the Swiss Federal Institute of Technology in Lausanne (EPFL), working on mobility management for low earth orbit mobile satellite communication systems. In 1996, he joined CSEM (Neuchâtel, Switzerland). Since then, he has been working on several research and development projects dealing with various aspects of wireless communications. In the ACTS RAINBOW and FRAMES projects, he was involved with the network and air interface aspects of 3rd generation cellular systems. In the ESPRIT INFOGATE and IST OPENROUTER projects, he worked on electronic design and embedded programming of Linux based wireless LAN gateways. His current research focus is low power communication protocols for wireless sensor networks.Jean-Dominique Decotignie is head of the real-time and networking group at the Swiss Center for Electronics and Microsystems (CSEM) in Neuchâtel. He is professor at the School of Computer and Communication Sciences of EPFL (Swiss Federal Institute of Technology in Lausanne) and teaches real-time systems as well as hardware and software design. From 1977 to 1982, he has worked at EPFL and the University of Tokyo in the area of optical communications. In 1983, he joined the Industrial Computer Engineering Lab. at EPFL where he became Assistant Professor in 1992. From 1989 to 1992, he has been the head of an interdisciplinary project on Computer Integrated Manufacturing at EPFL. Since January 1997, he is with CSEM. His current research interests include industrial and real-time local area networks, distributed control systems and software engineering for real-time systems as well as real-time wireless networks.