TCPW BR: A Wireless Congestion Control Scheme Base on RTT

The wireless network is limited by the transmission medium,and the transmission process is subject to large interference and jitter.This jitter can cause sporadic loss and is mistaken for congestion by the congestion control mechanism.The TCP Westwood protocol(referred to as TCPW)is such that it cannot distinguish between congestion loss and wireless jitter loss,which makes the congestion mechanism too sensitive and reduces bandwidth utilization.Based on this,the TCPW protocol is modified based on the estimate of the Round-Trip Time(referred to as RTT)value-called TCPW BR.The algorithm uses the measured smooth RTT value and divides the congestion level according to the weighted average idea to determine congestion loss and wireless jitter loss.The simulation results show that the TCPW BR algorithm enhances the wireless network’s ability to judge congestion and random errors.

TCP Window Based Congestion Control -Slow-Start Approach

Transmission control protocol (TCP) has undergone several transformations. Several proposals have been put forward to change the mechanisms of TCP congestion control to improve its performance. A line of research tends to reduce speed in the face of congestion thereby penalizing itself. In this group are the window based congestion control algorithms that use the size of congestion window to determine transmission speed. The two main algorithm of window based congestion control are the congestion avoidance and the slow start. The aim of this study is to survey the various modifications of window based congestion control. Much work has been done on congestion avoidance hence specific attention is placed on the slow start in order to motivate a new direction of research in network utility maximization. Mathematical modeling of the internet is discussed and proposals to improve TCP startup were reviewed. There are three lines of research on the improvement of slow start. A group uses the estimation of certain parameters to determine initial speed. The second group uses bandwidth estimation while the last group uses explicit request for network assistance to determine initial startup speed. The problems of each proposal are analyzed and a multiple startup for TCP is proposed. Multiple startups for TCP specify that startup speed is selectable from an n-arry set of algorithms. We then introduced the e-speed start which uses the prevailing network condition to determine a suitable starting speed.

Congestion Control Algorithms for the Internet-A Secondary Publication

In the last five years,there has been a V-shaped recovery in the number of papers on congestion control algorithms on the Internet.In this paper,congestion problems on the Internet are discussed,such as congestion collapse and bufferbloat from the perspective of the necessity of congestion control algorithms.The typical congestion control algorithms are introduced,and the research areas and methods of congestion control algorithms are described.Recent research trends and future prospects of congestion control algorithms are also presented.

D-AIMD——一种改进的TCP拥塞控制机制

0引言 TCP是目前Internet中广泛采用的一种传输控制协议,为各主机之间提供可靠按序的传输服务[1].代P拥塞控制[1,2]机制是其成功应用于Internet的关键所在.TCP拥塞控制机制主要基于AIMD(α,b)(Additive-Increase MuItiplicative-Decrease)算法[3～7],即每一往返时间,拥塞窗口值增加a,而当网络发生拥塞时,拥塞窗口降为原先的(1-b)倍.

Improving Network Performance by Ameliorating TCP Congestion Control Mechanism

With the rapid growth of rate-based services and wirelessapplications, improving Transmission Control Protocol(TCP)congestioncontrol has been becoming more important in the network researchfield. This paper first Briefly introduces the Additive-IncreaseMultiplicative-Decrease(AIMD)(a,b)algorithm, and then presents an im-Proved TCP congestion control mechanism(D-AIMD)whose principles andsimulation results are discussed in detail. This mechanism can beeasily implemented with lower additional overheads and canefficiently improve network per- Formance.

A Dynamic Adaptive Layered Multicast Congestion Control Mechanism

To solve the problem that most of existing layered multicast protocols cannot adapt todynamic network conditions because their layers are coarsely granulated and static,a new congestioncontrol mechanism for dynamic adaptive layered multicast(DALM) is presented.In this mechanism,anovel feedback aggregating algorithm is put forward,which can dynamically determine the number oflayers and the rate of each layer,and can efficiently improve network bandwidth utilization ratio.Additionally,because all layers is transmitted in only one group,the intricate and time-consuminginternet group management protocol(IGMP) operations,caused by receiver joining a new layer orleaving the topmost subscribed layer,are thoroughly eliminated.And this mechanism also avoids otherproblems resulted from multiple groups.Simulation results show that DALM is adaptive and TCPfriendly.

Nonlinear dynamics in Internet congestion control model with TCP Westwood under RED

This article develops a discrete time dynamic feedback model of a congestion control system for a simple network with TCP Westwood （TCPW） connections and a single bottleneck link with random early detection （RED） gateway. By using this model, the nonlinear dynamics of the TCPW/RED network are analyzed and its parameter sensitivities are studied. It is shown that periodic doubling bifurcation occurs when the RED control parameters or other parameters are varied. By theoretical analysis, the fixed point, the critical value of parameters and the nature of the bifurcation are determined. Moreover, by using bifurcation diagrams and Lyapunov exponent, the result of theoretical analysis is validated and the bifurcation and chaotic phenomena are numerically studied of the congestion control system with TCPW connections and RED gateway.

On Approaches to Congestion Control over Wireless Networks

Congestion control in wireless networks has been extensively investigated over the years and several schemes and techniques have been developed, all with the aim of improving performance in wireless net-work. With the rapid expansion and implementation of wireless technology it is essential that the congestion control problem be solved. This paper presents a survey of five congestion control schemes which are dif-ferent in slow start threshold calculation, bandwidth estimation, and congestion window manipulation. A comprehensive comparison of these approaches is given in relation to assumptions, bandwidth estimation, congestion window size manipulation, performance evaluation, fairness and friendliness and improved throughput.

TCP-ATCA: Improved Transmission Control Algorithm in Satellite Network

An adaptive transmission control algorithm based on TCP （TCP-ATCA） is proposed to reduce the effects of long propagation delay and high link error rate of the satellite network on the performances. The flow control and the error recovery are differentiated by combined dynamic random early detection-explicit congestion notification （DRED-ECN） algorithm, and, moreover, the pertaining congestion control methods are used in TCP-ATCA to improve the throughput. By introducing the entire recovery algorithm, the unnecessary congestion window decrease is reduced, and the throughput and fairness are improved. Simulation results show that, compared with TCP-Reno, TCP-ATCA provides a better throughput performance when the link capacity is higher （ ≥600 packet/s）, and roughly the same when it is lower. At the same time, TCP-ATCA also increases fairness and reduces transmission delay.

Stability condition of FAST TCP in high speed network on the basis of control theory

Considering the instability of data transferred existing in high speed network, a new method is proposed for improving the stability using control theory. Under this method, the mathematical model of such a network is established. Stability condition is derived from the mathematical model. Several simulation experiments are performed. The results show that the method can increase the stability of data transferred in terms of the congestion window, queue size, and sending rate of the source.

BIFURCATIONS AND CHAOS CONTROL IN TCP-RED SYSTEM

Objective Analyzing the nonlinear dynamics of the TCP-RED congestion control system is of great importance. This study will help investigate the loss of stability in Internet and design a proper method for controlling bifurcation and chaos in such system. Methods Based on bifurcation diagram, the effect of parameter on system performance is discussed. By using the state feedback and parameter variation strategy, a simple real time control method is proposed to modify the existing RED scheme. Results With our control method, the parametric sensitivity of RED mechanism is attenuated. Moreover, a sufficient condition on the robust stability of the system is also derived to adjust the parameters in TCP-RED system. Conclusion The proposed method has the advantages of simple implementation and unnecessary knowledge of the exact system.

Controlling Middleware for Reducing the TCP ACK Packet Backlog at the WLAN Access Point

Although modem loss-based Transmission Control Protocols take aggressive congestion window （CWND） control strategies in order to gain better throughput, such strategies may cause a large number of packets to be backlogged and eventually dropped at the entry point to the wireless access network. This problem applies not only to the downstream TCP sessions but also to the upstream TCP sessions when the terminal is connected via a Wireless Local Area Network （WLAN）, which disregards the size of packets in its scheduling. This paper focuses on the ACK packet backlog problem with the upstream TCP sessions, and proposes a CUBIC based CWND control mechanism as part of the middleware for the Android terminals. It utilizes the Round Trip Time （RTT） as an indication for the TCP ACK backlog condition at the WLAN AP, and controls the upper and lower bounds of its CWND size to suppress excessive transmissions of own TCP DATA packets. Unlike the existing works, the proposed mechanism is based on WLAN CSMA/CA performance studies and then it does not require manual performance tuning. An experimental study with up to 10 Android terminals shows that the proposed mechanism can improve both aggregate throughput and faimess of the WLAN, and that it is highly effective particularly for cases where very long RTTs are observed.

An Adaptive Congestion Control Optimization Strategy in SDN-Based Data Centers

The traffic within data centers exhibits bursts and unpredictable patterns.This rapid growth in network traffic has two consequences:it surpasses the inherent capacity of the network’s link bandwidth and creates an imbalanced network load.Consequently,persistent overload situations eventually result in network congestion.The Software Defined Network(SDN)technology is employed in data centers as a network architecture to enhance performance.This paper introduces an adaptive congestion control strategy,named DA-DCTCP,for SDN-based Data Centers.It incorporates Explicit Congestion Notification(ECN)and Round-Trip Time(RTT)to establish congestion awareness and an ECN marking model.To mitigate incorrect congestion caused by abrupt flows,an appropriate ECN marking is selected based on the queue length and its growth slope,and the congestion window(CWND)is adjusted by calculating RTT.Simultaneously,the marking threshold for queue length is continuously adapted using the current queue length of the switch as a parameter to accommodate changes in data centers.The evaluation conducted through Mininet simulations demonstrates that DA-DCTCP yields advantages in terms of throughput,flow completion time(FCT),latency,and resistance against packet loss.These benefits contribute to reducing data center congestion,enhancing the stability of data transmission,and improving throughput.

针对车地传输TCP协议优化的TTI-RTT拥塞控制算法

为适应铁路5G专用移动通信系统动态易变的网络环境,解决现有算法中存在的吞吐量减少、传输时延增加、检测数据车地传输可靠性难以保证的问题,在分析传输控制协议(TCP)传输拥塞控制过程,以及对比TCP-Reno,TCP-Vegas和TCP-Westwood 3种基础拥塞控制算法存在问题的基础上,提出一种联合传输时间间隔(TTI)和往返时延(RTT)的拥塞控制算法——TTI-RTT算法,即将RTT的成对比较测试统计量和网络当前拥塞因子联合起来作为网络拥塞判断标准,根据反映网络拥塞程度的拥塞因子动态调节加性和乘性因子,并在传输控制协议拥塞控制的不同条件下灵活调整传输时间间隔。采用NS-3仿真软件,构建考虑高速铁路5G-R无线信道误码影响的点对点通信网络拓扑结构,对TTI-RTT拥塞控制算法进行仿真验证,并与3种基础算法进行性能比较。结果表明:不同丢包率下所提算法的平均吞吐量均保持在9 Mb·s^(-1)以上,较基础算法中吞吐量最高且最稳定的TCP-Reno算法增加了约5.9%,且实时吞吐量稳定性具有显著改善。

TCP协议在Ad Hoc网络中的性能及其改进策略

Ad Hoc网络的动态自组织特性使得传统的传输层协议不再适用。首先阐述了TCP协议在Ad Hoc网络中存在的问题，然后介绍了TCP协议在无线网络中的改进。接下来，详细分析了Ad Hoc网络中TCP协议的性能并讨论了其改进策略和方法。最后对全文进行了小结并给出了今后的工作方向。

无线网络TCP协议纯端到端解决方案研究

针对无线环境中误码率偏高的特点,着重讨论改善TCP协议性能的方案,并重点研究了纯端到端解决方案中的两种典型TCP协议:TCPW和TCPReal协议。纯端到端解决方案保持了TCP协议端到端的语义。通过不同误码率下传输性能的仿真,表明两种协议在无线环境下性能均明显优于其他TCP协议。

基于TCP Vegas的网络拥塞控制改进算法

由于TCP Vegas在与TCP Reno算法共存的网络环境中不能公平地竞争到带宽,TCP Vegas-A拥塞控制算法有效地改进了TCP Vegas算法在带宽竞争力弱方面的缺陷。对TCP Vegas-A算法进行了仿真研究并提出一种拥塞控制改进算法TCP NewVegas。基于NS2的仿真实验证明TCP New Vegas算法提高了与TCP Reno共存时在网络中的带宽竞争能力。

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.

CB-HSTCP:高速网络中的公平TCP算法

通过实验发现HSTCP存在严重的RTT(Round Trip Time)不公平性,另外发现拥塞时存在大量的包丢失.用模型对RTT不公平现象进行了分析,并分析了包丢失问题.提出了CB-HSTCP算法,包括CW机制和Block-pacing机制,用于改善公平性和降低包丢失率.为衡量算法性能,提出了一个相对公平性标准.通过分析并使用ns2进行模拟实验,证实该方案在保证HSTCP性能的基础上,解决了RTT不公平性问题、降低了包丢失率,同时具有良好的扩展性和TCP友好性.

无线多跳网络中Semi-TCP协议的实现

为解决传统TCP协议在无线多跳网络中经常误判网络拥塞状况且反应迟钝的问题,提出一种Semi-TCP协议的实现方法。添加虚拟TCP层控制包的过滤和重发,采用逻辑信道传递跨层信息,应用一跳式ACK速率控制策略调节发送速率。仿真实验结果表明,该实现方法能在不改变原TCP协议框架的基础上提高系统性能。