共查询到19条相似文献,搜索用时 265 毫秒
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在分析TCP Westwood (TCPW)算法优缺点的基础上,针对其应用于同步轨道(GEO)卫星链路时存在的不足,结合Vegas、Veno及LogWestwood+等改进算法的优势,基于预测的下一时刻的网络带宽,把窗口调整与带宽利用情况相结合,提出了一种新的适合于GEO卫星链路的基于丢包区分的TCP Westwood改进算法。改进算法将每个阶段的窗口调整与带宽估计、网络状态紧密联系起来,结合网络状态和带宽估计判断拥塞窗口的合理性,动态地调整拥塞窗口,使拥塞即将发生时,窗口能及时下降到适宜的水平,尽量避免由于拥塞而导致的分组丢失。仿真结果表明,改进算法提高了TCP westwood在GEO卫星链路中应用时的性能,具有较好的吞吐量、公平性、友好性和较低的丢包率。 相似文献
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针对无线网络链路干扰大、误码率高等特点,以及TCP Westwood算法(TCPW)存在估算带宽时过度依赖包的反馈,缺乏区分传输过程中丢包类型的缺点等问题,提出一种TCPW拥塞控制优化算法--TCPW-F。该算法利用发送速率等构建拥塞因子[F]作为判断丢包类型的依据,同时对判定发生噪声丢包时的拥塞窗口进一步调整,避免噪声丢包引起的窗口下降,提高该情况下窗口的发送效率。仿真结果表明,TCPW-F算法在时延性能方面表现更优,单位时间抖动趋于稳定的速度更快。在同一信道带宽下增大包生成速率,改进算法的实时吞吐量明显高于原算法,具备一定的噪声丢包感知能力,无线网络的TCP传输质量获得较大改善。 相似文献
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基于自相似流量预测的TCP拥塞控制算法 总被引:1,自引:1,他引:0
针对高带宽网络环境下传统TCP Reno的拥塞控制效率低的问题,提出了一种适用于随机丢失网络的TCP拥塞控制改进算法.介绍并分析了网络流量自相似特性和预测的时间尺度,并进行了TCP链路流量预测及可用带宽估计,当网络出现丢包时根据估计的带宽动态设置慢启动阈值.OPNET仿真结果表明,该算法在高随机丢包的情况下吞吐量得到了明显改善. 相似文献
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针对SCPS-TP(Space Communications Protocol Standards Transport Protocol)协议的Vegas算法在LEO (Low Earth Orbit)卫星网络中吞吐量下降的问题,提出了一种自适应Vegas-AD(Adaptive)拥塞控制算法。该算法在分析Vegas的基础上,细化往返时延RTT的计算方法,使其能够更加精确地调整拥塞窗口;优化拥塞窗口的增长策略,提高了拥塞避免阶段的带宽竞争力;同时,提出基于网络拥塞程度的自适应窗口调整因子。仿真结果表明,Vegas-AD算法的带宽竞争力明显高于Vegas,并且该算法能较大幅度地提高网络吞吐量。 相似文献
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刘俊 《计算机工程与设计》2012,33(5):1715-1719
针对TCP Reno在无线环境下的性能恶化问题,在研究分析TCP Reno拥塞控制算法问题的基础上,提出一种基于RTT自适应的改进算法.该算法实现了丢包区分的拥塞窗口与慢启动门限调整,减轻了传统TCP由于无法区分拥塞丢包与误码丢包、盲目将拥塞窗口减半带来的性能下降.分析了该算法的可行性,并通过NS仿真对其吞吐量、带宽利用率、公平性等指标进行评估.仿真结果表明,相对TCP Reno,改进算法实现了无线环境下的TCP性能改善,同时具有一定的友好性与公平性. 相似文献
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数据报拥塞控制协议(Datagram Congestion Control Protocol,DCCP)是提供拥塞控制和不可靠传输特点的实时多媒体基础协议,DCCP中的CCID2算法仍然采用AIMD的控制机制,这种传统的Loss-Base拥塞控制模型已经不适用于目前高BDP的网络环境,容易引起缓冲区膨胀现象,导致网络延迟增加和抖动等问题.与Loss-Base的算法相比,BBR算法可以有效地控制网络延时,最大限度避免网络排队的情况,在丢包率较高的情况下仍可以保持一定的带宽利用率和较低的链路延时,因此适合于DCCP实时流媒体的应用的协议.本文在DCCP中引入了BBR算法并做相应的改进,增加了丢包率检测模型,使用延时与带宽积模型的拥塞控制算法对上述问题进行改进.通过模拟实验证明,本方法在高负载情况下连接的平均延迟相比CCID2降低了20%,在丢包率较高的环境下也能保持良好的吞吐量. 相似文献
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传统的TCP协议,假设丢包都是由网络拥塞造成的,这不适用于错误丢包比拥塞丢包更容易发生的无线链路,而且现有的很多改进方案无法用于加密通讯中.在分析现有改进算法的基础上,提出一种适用于有线/无线混合网络IPSec兼容的端到端的优化机制.通过接收端数据包到达时间间隔的变化累积来判断无线链路的状况,用ACK标记ELN通知发送端,避免不必要的拥塞控制而导致性能下降.通过NS2仿真实验表明该机制能有效提高TCP传输性能还与现有的安全机制兼容. 相似文献
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Jansi Rani Sella Veluswami 《计算机系统科学与工程》2022,43(3):1231-1239
Most of the internet users connect through wireless networks. Major part of internet traffic is carried by Transmission Control Protocol (TCP). It has some design constraints while operated across wireless networks. TCP is the traditional predominant protocol designed for wired networks. To control congestion in the network, TCP used acknowledgment to delivery of packets by the end host. In wired network, packet loss signals congestion in the network. But rather in wireless networks, loss is mainly because of the wireless characteristics such as fading, signal strength etc. When a packet travels across wired and wireless networks, TCP congestion control theory faces problem during handshake between them. This paper focuses on finding this misinterpretation of the losses using cross layer approach. This paper focuses on increasing bandwidth usage by improving TCP throughput in wireless environments using cross layer approach and hence named the proposed system as CRLTCP. TCP misinterprets wireless loss as congestion loss and unnecessarily reduces congestion window size. Using the signal strength and frame error rate, the type of loss is identified and accordingly the response of TCP is modified. The results show that there is a significant improvement in the throughput of proposed TCP upon which bandwidth usage is increased. 相似文献
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针对无线网提出了一种基于带宽估计的拥塞控制机制。该机制利用TCP确认帧携带的数据包到达时间来估算包到达速率,从而得到带宽的估计值。在此基础上用带宽的估计值更新拥塞窗口,避免在发生链路错误时启动拥塞控制机制,由此提高了TCP在无线网上的性能。实验结果表明,算法能减少链路差错对TCP性能带来的影响,提高了TcP在无线网上的吞吐率。 相似文献
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For accessing plentiful resources in the Internet through wireless mobile hosts, diverse wireless network standards and technologies have been developed and progressed significantly. The most successful examples include IEEE 802.11 WiFi for wireless networks and 3G/HSDPA/HSUPA for cellular communications. All IP-based applications are the primary motivations to make these networks successful. In TCP/IP transmissions, the TCP congestion control operates well in the wired network, but it is difficult to determine an accurate congestion window in a heterogeneous wireless network that consists of the wired Internet and various types of wireless networks. The primary reason is that TCP connections are impacted by not only networks congestion but also error wireless links. This paper thus proposes a novel adaptive window congestion control (namely Logarithmic Increase Adaptive Decrease, LIAD) for TCP connections in heterogeneous wireless networks. The proposed RTT-based LIAD has the capability to increase throughput while achieving competitive fairness among connections with the same TCP congestion mechanism and supporting friendliness among connections with different TCP congestion control mechanisms. In the Congestion Avoidance (CA) phase, an optimal shrink factor is first proposed for Adaptive Decreasing cwnd rather than a static decreasing mechanism used by most approaches. Second, we adopt a Logarithmic Increase algorithm to increase cwnd while receiving each ACK after causing three duplicate ACKs. The analyses of congestion window and throughput under different packet loss rate are analyzed. Furthermore, the state transition diagram of LIAD is detailed. Numerical results demonstrate that the proposed LIAD outperforms other approaches in goodput, fairness, and friendliness under diverse heterogeneous wireless topologies. Especially, in the case of 10% packet loss rate in wireless links, the proposed approach increases goodput up to 156% and 1136% as compared with LogWestwood+ and NewReno, respectively. 相似文献
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The traditional windows-based TCP congestion control mechanism produces throughput bias against flows with longer packet roundtrip times; the flow with a short packet roundtrip time preoccupies the shared network bandwidth to a greater extent than others. Moreover, the blind window reduction that occurs whenever packets are lost decreases the network utilization severely, especially in networks with high packet losses. This paper proposes a sender-based TCP congestion control, called TCP-BT. The scheme estimates the network bandwidth depending on the transmission behavior of applications, and adjusts the congestion window by considering both the estimated network bandwidth and the packet roundtrip time to improve fairness as well as transmission performance. The scheme has been implemented in the Linux platform and compared with various TCP variants in real environments. The experimental results show that the proposed scheme improves transmission performance, especially in networks with congestion and/or high packet loss rates. Experiments in real commercial wireless networks have also been conducted to support the practical use of the proposed mechanism. 相似文献
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门户环境中基于语义数据协作应用集成方法 总被引:2,自引:0,他引:2
目前,门户的功能定位已经从传统的信息集成转向应用集成.门户环境中应用间的进一步集成实际上表现为Portlet互操作问题. 现有Portlet互操作方法在共享范围、标准兼容方面存在不足且难于集成已有应用系统.提出了一种基于语义数据协作的Portlet互操作方法,其基本思想是:将参与互操作的Portlet抽象为ShadowComponent组件,然后基于本体建立ShadowComponent之间的语义数据关联,并使用ECA(event-condition- action)规则实现Portlet互操作.实验证明,该方法无须对已有应用作任何修改即可完成门户中的应用集成. 相似文献
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当传统TCP协议用于卫星网络时面临各种问题,原因包括:卫星信道的高传输延迟、较大的误码率、带宽不对称、信号衰减等.为了提高卫星网络环境下TCP的性能,在不破坏TCP端到端特性的前提下,提出了一种新的主动代理方案.拥塞控制算法通过具有不同优先级的双报文对实施主动监测,能够根据网络带宽的变化自适应地调整TCP窗口.并且,对代理控制系统进行了稳定性分析.针对卫星网络下的TCP丢包恢复,提出了一种不依赖时钟同步的选择性否定应答算法.模拟实验表明,提出的TCP代理能够充分利用卫星网络的带宽,从而达到获得最佳有效吞吐率的目的. 相似文献
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提出一种新的拥塞控制算法(TCP MS).该算法更适用于流媒体应用,有更高的带宽利用率、公平性,传输速率也更平滑.不同于传统的利用丢包率和排队延迟来探测拥塞的TCP拥塞控制算法,该算法通过确认数据包的速率来探测拥塞,并在每一轮往返时间内及时调整窗口.该算法提供的拥塞窗口变化更准确,传输速率抖动更小.因此,提高了网络带宽的利用率以及传输速率的平滑性.最后,文章将TCP MS与典型的基于丢包率的TCP Reno算法和基于排队延迟的TCP Vegas算法在带宽利用率、速率抖动以及公平性等方面分别做了比较,仿真结果表明TCP MS是一种理想的流媒体拥塞控制算法. 相似文献
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分析目前TCP拥塞控制的慢启动策略及其存在的短连接带宽浪费、过度丢包等实际问题,提出一种基于RTT(Round Rrip Time,往返时延)反馈的TCP慢启动改进算法SS IM(Slow Start Improved)。改进算法在慢启动过程前期为快速利用当前有效网络带宽,拥塞窗口保持较高速度增长,后期为避免加重网络拥塞,根据当前网络状况动态地缓慢调整拥塞窗口增长因子,使cwnd(congestion window,拥塞窗口)平滑过渡到ssthresh(slow start threshold,慢启动阈值)。性能分析和NS2仿真实验结果表明,改进算法能有效地减少分组丢包数,提高网络吞吐量,降低路由排队时延,平缓数据突发量冲击,降低网络拥塞发生的可能性,利于网络性能的提高。 相似文献