一种基于链路带宽估计的TCP慢启动算法

在慢启动阶段，TCP以指数方式增加其拥塞窗口，这导致了慢启动阶段的多包丢失，并恶化了TCP的性能．该文对TCP连接的等效带宽进行了深入的理论分析．在此基础上，提出了一种改进的TCP慢启动算法——基于链路带宽估计的TCP慢启动算法，并通过仿真对其吞吐量、公平性和兼容性进行了评估．仿真的结果表明，该算法避免了慢启动阶段的多包丢失，并能有效改进TCP的性能，是简单、实用和有效的．     

带宽保证环境下TCP算法改进及其模型分析

基于差分服务模型的带宽保证服务已经得到较多的应用，这类通过分组标记和丢弃算法实现的非刚性带宽保证具有实现简单、扩展性强的特点。但是，由于端系统的TCP协议对合约带宽信息的不感知，使得应用难以获得网络提供的带宽保证。在分析了双窗口TCP拥塞控制算法的基础上，提出了基于合约窗口的拥塞控制算法，并对算法进行了测试和建模分析。该算法简单、易于实现。并且在网络突发拥塞时，收敛速度快，不影响网络的稳定性。     

一种基于带宽估计的无线网拥塞控制机制

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。     

基于带宽估计和ECN的无线TCP改进

针对无线环境下TCP调用拥塞控制算法致使性能下降的问题,提出一种基于带宽估计和显式拥塞通知的无线TCP改进方法。在数据发送端采用带宽估计算法优化拥塞窗口尺寸,与具有显式拥塞通知的路由器配合区分分组丢失性质,利用选择性确认选项,加快单窗口多包丢失时拥塞窗口恢复速度。仿真结果表明,改进后的TCP吞吐量超过TCP_SACK近30%,超过TCP_Reno近52%。     

一种基于窗口的拥塞控制：TCPImpv

在高带宽延迟积网络中,传统TCP导致很低的网络效率。我们研究了窗口增量函数对网络稳定性和效率的作用,并提出TCPImpv拥塞控制。仿真结果表明,在高带宽延迟积网络中,TCPImpv的网络效率和分组丢弃性能明显优于HSTCP;在一般网络条件下,TCPImpv保持了传统TCP的性能。     

基于RTT自适应的无线TCP改进算法

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.     

可用带宽测量的TCP友好性仿真分析

以发送包链为特征的可用带宽测量会产生较大探测流量而影响网络性能.设计了三种具有不同包链长度的测量模式模拟典型的包链发送策略,仿真分析了可用带宽测量的TCP友好性.发现可用带宽测量的TCP友好性并不理想,原因在于探测流会增大TCP流的时延及丢包而触发TCP的拥塞控制机制.仿真中最大降低TCP数据传输量近16%;且太长或过短的包链发送策略对TCP性能有更大影响.在Pathoad这一典型可用带宽测量工具中的分析结果进一步验证了该结论,且得出了Pathload的应用策略.     

一种基于RTT公平性的TCP慢启动算法

分析标准慢启动算法应用于包含GEO卫星链路的网络时存在的问题,提出一种基于RTT公平性的TCP慢启动改进算法。改进算法采用大初始窗口机制,慢启动初期窗口保持指数增长,慢启动后期引入窗口增长控制因子,使RTT较大的窗口增加较快,反之增加较慢。性能分析和仿真结果表明,改进算法可以在慢启动后期减缓拥塞窗口的增长速度,削弱RTT较小的TCP流竞争带宽的侵略性,在一定程度上保证不同RTT数据流共享带宽的公平性。     

EHSTCP:改进的高速TCP算法

TCP在高带宽时延积网络中不能获得良好的性能,主要表现为低的吞吐量和大的窗口震荡.HSTCP算法解决了传统TCP算法在高带宽时延积网络下的性能瓶颈,但HSTCP在拥塞点时会产生大量的数据包丢失,同时当队列管理为去尾算法时,存在着严重的RTT不公平性问题.针对HSTCP算法的性能缺陷,该文提出一种在拥塞避免阶段进行拥塞避免模式切换的改进算法,称为EHSTCP.基于拥塞窗口历史值的端到端可用带宽预测方法,利用拥塞窗口历史信息来判断拥塞避免切换点.同时引入RTT公平因子,消除了HSTCP的RTT不公平性问题.NS2仿真实验验证了算法的有效性.     

几种TCP带宽估计算法的分析比较

基于TCP拥塞控制的研究需要,文章介绍并分析比较了TCP Vegas算法、CSFQ算法、TCP Westwood算法、TIBET算法、DFBE算法等几种目前主要的TCP带宽估计算法,并通过OPNET仿真软件对TCP Westwood1算法、TIBET算法和DFBE算法的带宽估计性能进行了仿真比较。仿真结果表明,TIBET算法和DFBE算法估计出的带宽在拥塞控制中具有良好的性能。     

Modeling two-windows TCP behavior in differentiated services networks

Two important issues in assured services within differentiated services architecture are bandwidth guarantee and fair sharing of unsubscribed bandwidth among TCP flows with and without bandwidth reservations. Although the subscribed bandwidth can be guaranteed by increasing network capacity or deploying strict admission control mechanisms, the costs of such solutions are very high. The issue of fair sharing of excess bandwidth is also not well solved. To address those issues, a modified TCP, named two-windows TCP, has been proposed. The performance of the protocol is evaluated by simulations. But its effectiveness is not validated theoretically under general network conditions, which is important for understanding the benefits and costs of using the protocol. In this paper, an analytical model is developed for the purpose. The model characterizes throughput of individual two-windows TCP flow as a function of contract rate, round trip time, loss rates of In and Out packets. Extensive simulations validate the analytical model. It's shown two-windows TCP is effective not only on solving the issues of bandwidth guarantee and fair sharing of unsubscribed bandwidth, but also on increasing the utilization of bottleneck link bandwidth. Moreover, its performance is robust to network conditions, which is important for wide deployment over Internet.     

V2G网络中基于带宽自适应的拥塞控制协议优化

V2G网络下PLC链路带宽受限、高误码率等特点导致现有的TCP NewReno拥塞控制机制缺乏对丢包类型的有效判断,将链路上由噪声干扰的随机错误丢包与网络拥塞丢包统一当做拥塞事件处理,从而造成不必要的拥塞避免,导致了低吞吐量问题.根据此问题,提出了一种基于带宽自适应的拥塞控制算法.该算法通过分组预测拥塞等级感知网络状态,由此估计可用带宽来判断丢包类型,实现了拥塞窗口自适应调节.仿真结果表明该算法在拥塞窗口的增长、吞吐量、公平性、收敛性和友好性等方面都优于现有算法,V2 G网络的吞吐量得到明显提升.     

确保服务中一种基于动态阈值的数据包标记算法

确保转发过程中带宽享用的公平性问题一直是区分服务网络研究的热点，影响这种公平性的因素包括回路响应时间RTT、数据包大小、目标速率及聚流中包含的单流数量等．确保服务的实现依赖于在边界路由器执行的数据包标记策略和在核心路由器执行的队列管理策略，基于动态阈值的数据包标记策略DTBM的目的就是处理异质的TCP流之间带宽享用的公平性问题。DTBM通过测量局部吞吐量来调整标记算法中的阈值，以改变不同颜色的标记概率从而达到公平带宽享用的目的。DTBM的主要优点在于其实现简单、对参数不是很敏感并且对端结点主机是“透明”的，仿真实验表明，和其他几种标记算法相比，DTBM能有效地消除上述因素的影响，具有更好的公平性。     

一种边界到边界的拥塞感知的三色标记器*

通过对基本的流量标记,特别是在CATC、CASR3CM和ITSW3CM研究的基础上提出了拥塞感知的流量标记器CATSW3CM。理论分析和仿真实验表明,CATSW3CM与CATC相比,不仅提高了AS TCP流的平均吞吐量,而且增强了吞吐量的稳定性,提高了AS TCP流之间占用带宽的公平性,并且更为简单,具有很好的扩展性。     

异构网络中保障业务QoS的TCP协议研究

当TCP协议应用于异构网络时业务的QoS无法得到保障,具体而言,一方面TCP协议与无线网络适配性较差,导致网络丢包率升高、吞吐量下降;另一方面,TCP协议对于业务不区分优先级,不能满足高优先级业务的需求。因此,文章提出了异构网络中基于捕食模型的保障业务QoS的TCP协议(QoS - Internet Predator based on Prey Model,Q-IPPM)。Q-IPPM算法不仅会根据异构网络的带宽改进TCP协议的拥塞控制架构,还根据不同业务的负载状况和优先级控制不同业务流量占比。实验结果表明,Q-IPPM算法不仅可以提显著提高异构网络的吞吐量,降低网络丢包率,还能够根据业务优先级和负载状况将带宽“按需分配”给不同业务,从而保障了异构网络中业务的QoS。     

Improving Throughput of Transmission Control Protocol Using Cross Layer Approach

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.     

Enhancing TCP for networks with guaranteed bandwidth services

In this paper, we consider TCP based applications with bandwidth guarantees, but can also benefit from any additional best-effort service offered by the network. Through simulations we show that default TCP cannot offer such applications the ideal throughput – the aggregate throughput of the reserved bandwidth and the best effort bandwidth. To illustrate the reasons for its degraded performance, we study TCP’s congestion window adaptation and self-clocking mechanisms in detail. Based on the insights obtained from the study, we propose an adaptation of TCP called GTCP that employs changes to TCP’s congestion control mechanisms to provide applications the optimal aggregate throughput of best-effort and reserved bandwidth. Compared with TCP, GTCP does not involve any additional implementation overhead, and only the sender need to be changed (the receiver remains to be a default TCP implementation). Through simulations and experiments over the Internet we show that GTCP achieves significantly better performance than default TCP in the target environment.     

TCP/IP traffic over ATM networks with FMMRA ABR flow and congestion control

In this paper, we study and compare the performance of TCP/IP traffic running on different rate based ABR flow control algorithms such as EFCI, ERICA and FMMRA by extensive simulations. The FMMRA algorithm is shown to exhibit the favorable features of least buffer requirement, fair bandwidth allocation to TCP connections, fast and accurate ACR rate adjustment according to the changes of network traffic, and the highest effective TCP throughput.     

面向卫星网络的TCP代理

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.     

门户环境中基于语义数据协作应用集成方法

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.