基于XCP协议的拥塞控制算法研究

本文首先对TCP协议存在的问题进行了阐述,随着每一流的带宽时延乘积的增长,在不考虑排队方案的条件下,TCP协议变得不稳定和效率低下。然后对XCP协议的结构和执行算法进行详细分析,分析结果表明在高带宽时延乘积网络中,XCP协议能更好的保持效率、公平性和稳定性。     

XCP协议的稳定性分析及其仿真

随着每一流的带宽时延乘积的增长,在不考虑排队方案的条件下,TCP协议变得不稳定和效率低下。XCP协议扩展了ECN显式拥塞指示机制,它通过在拥塞头携带控制信息极大地改善了因特网的拥塞控制。路由器能通知发送端瓶颈链路的拥塞程度而不是网络是否拥塞,发送端就可以根据网络的状态相应地增加和减少它的发送窗口。同时对XCP协议的稳定性进行分析,并对协议做了相应的仿真。仿真结果表明,在高带宽时延乘积网络中,XCP协议能更好地保持效率、公平性和稳定性。     

XCP协议的仿真分析

对XCP协议的结构和执行算法进行了详细分析,并对协议做了相应仿真.仿真结果表明,在高带宽时延乘积网络中,XCP协议能更好地保持效率、公平性和稳定性.     

高带宽时延乘积网络中的TCP性能仿真分析

在高带宽时延乘积网络中,现有TCP协议由于其使用的拥塞控制机制使得数据流长时间以低速率发送数据,不能有效利用网络带宽,造成带宽利用率随着带宽的增大而下降。对高带宽时延乘积网络中TCP的性能进行仿真,结果表明在该网络环境中使用TCP传输数据不能有效利用网络带宽。最后详细分析拥塞控制机制造成TCP使用带宽利用率低的原因。     

大带宽时延积网络中TCP,HighSpeed TCP及XCP性能比较

介绍了TCP协议在大带宽时延积网络（HighBDP）境中存在的问题，论述了High BDP网络环境中目前存在的两种解决拥塞控制的方法，一种是只修改端节点拥塞控制协议如HighSpccd TCP，另一种是需要路由器进行速率协同调整的机制，如XCP协议。然后对比三者在瓶颈链路利用串、公平性、TCP．Friendly、动态特性等指标上的性能，仿真结果表明XCP在这些性能指标上优于前两者，但同时在分组中增加了更多信息，增加了路由器的工作负荷以及布置困难。     

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.     

高速网络拥塞控制协议VCP的研究

互联网正在逐步进入一种高带宽延时积的高速网络时代.当网络的带宽或者时延增大时,TCP协议的性能严重下降,最显著的就是网络瓶颈处带宽利用率很低.在高速拥塞控制方面比较理想的XCP协议却存在部署方面的问题.变结构拥塞控制协议(VCP)可有效地解决上述问题.VCP协议联合使用ECN机制的两个二进制来编码拥塞信息.根据来自接收端的拥塞信息,VCP协议的发送端选择控制算法来响应拥塞信号.仿真实验表明VCP协议与TCP协议、XCP协议相比不仅具有较高的链路利用率,并且对现有的协议改动非常小,有利于逐步地实施.     

窗口限制系统中基于令牌的Fast-TCP的延时性能分析

给出了在高带宽时延乘积网络中无拥塞丢包的TCP缓冲区的占用量的微分方程,然后针对广域网中窗口大小小于网络带宽时延乘积和无线网络中,由于误码丢包而使窗口尺寸无法达到链路带宽时延乘积(如卫星网)的情况,分析了一种基于令牌的Fast-TCP机制,得出基于令牌的ACK延时机制,不仅能够大大减少缓冲区的占用量结论,而且可获得与TCP在无限缓冲区下的同样的吞吐量.还把这个结论推广到多连接的情况,在以前论文中没有涉及.     

高速网络TCP改进协议NS2仿真性能比较

传统TCP协议在现代高速网络中传输性能存在瓶颈。基于NS2,通过改变瓶颈带宽、往返时延及TCP并行流数等参数,仿真实验了各种TCP改进协议的传输性能,在吞吐率、时延和丢包率等性能指标上对各种协议进行比较。结果表明,多数改进协议在某些方面表现出比传统TCP协议更好的性能,其中采用显式拥塞反馈改进方案的XCP和VCP协议性能表现最好。     

以太网带宽管理机制下TCP性能的建模研究

随着以太网技术的迅速发展,基于以太网的链路层流量控制技术成为流量工程的一个重要组成部分,基于漏桶式流控的以太网带宽控制算法被应用于驻地同环境当中。考虑到互联同中长时TCP业务流量增长迅速这一背景,评估以太网流量控制算法对长时TCP性能的影响有其积极意义。论文通过建模分析的方法,对于NewReno TCP算法在漏桶式带宽控制机制下的性能进行了分析,并通过仿真对结论进行了说明。     

Improving the efficiency and fairness of eXplicit Control Protocol in multi-bottleneck networks

The Transmission Control Protocol (TCP) has been extensively credited for the stability of the Internet. However, as the product of bandwidth and latency increases, TCP becomes inefficient and prone to instability. The eXplicit Control Protocol (XCP) is a novel and promising congestion control protocol that outperforms TCP in terms of efficiency, fairness, convergence speed, persistent queue length and packet loss rate. However, the XCP equilibrium solves a constrained max–min fairness problem instead of a standard max–min fairness problem. The additional constraint under XCP leads to inefficiency and unfairness for the topologies that have multiple bottleneck links.In this paper, according to classical control theory, we propose an XCP bandwidth compensation algorithm on basis of the proportional integral controller (PI-XCP), which reconfigures the available bandwidth variable from the fixed hardware determined physical link capacity value to a configuration value that can be dynamically changed. Through a reasonable online compensation, PI-XCP gets efficient and fair bandwidth allocation in a multi-bottleneck network. Extensive simulations have shown that PI-XCP indeed achieves this goal. Simulations also have shown that PI-XCP preserves good properties of XCP, including fast convergence, negligible queue length and zero packet loss rate. Compared with iXCP, an enhancement to address the XCP equilibrium problem, PI-XCP decreases the computational complexity significantly, and achieves more effective control in highly dynamic situations, especially in the presence of short-lived flows.     

一种提高XCP协议在大RTT差异环境下的鲁棒性方法

现有TCP协议的拥塞控制机制存在很多不足,XCP(eXplicit Control Protocol)协议采用显式反馈的方式有效地克服了这些缺陷.XCP协议能容忍数据流之间一定的RTT差异,但当这种差异超出一定范围时,XCP协议性能恶化,变得不稳定.通过分析XCP协议路由控制周期与数据流RTT的关系,提出了一种控制周期根据RTT差异程度而自适应调整的方法,消除了系统振荡.仿真数据表明,该方法能有效地提高XCP协议在数据流RTT差异较大的环境下的鲁棒性,同时不给路由器带来过大的计算负担.     

Improving XCP to achieve max–min fair bandwidth allocation

TCP is prone to be inefficient and unstable in high-speed and long-latency networks [1]. The eXplicit Control Protocol (XCP) is a new and promising protocol that outperforms TCP in terms of efficiency, stability, queue size, and convergence speed. However, Low et al. recently discovered a weakness of XCP. In a multi-bottleneck environment, XCP may achieve as low as 80% utilization at a bottleneck link and consequently some flows may only receive a small fraction of their max–min fair rates.This paper proposes iXCP, an improved version of XCP. Extensive simulations show that iXCP overcomes the weakness of XCP, and achieves efficient and fair bandwidth utilization in both single- and multi-bottleneck environments. In addition, we prove that iXCP is max–min fair in steady state. This result implies that iXCP is able to fully utilize bottleneck bandwidth. Simulations show that iXCP preserves the good properties of XCP, including negligible queue lengths, near-zero packet loss rates, scalability, and fast convergence. Simulations also show that iXCP overcomes the under-utilization and instability problem of P-XCP [2], and outperforms JetMax [3] in terms of link utilization in the presence of highly dynamic traffic.     

Performance evaluation of bandwidth allocation methods in a geostationary satellite channel in the presence of internet traffic

Resource allocation represents an important issue for the next generation TCP/IP Quality of Service-based satellite networks. Many schemes, proposed in the recent literature, consider Internet traffic as the superposition of traffic sources without distinguishing between User Datagram Protocol (UDP) and Transmission Control Protocol (TCP) flows, even if UDP and TCP imply very different traffic characteristics. The basic idea of this work is that a resource allocation algorithm which is conscious of the difference may be more efficient because it can make use of the different behaviour of TCP and UDP in the presence of network congestion. Actually TCP reduces the source flow rate and, as a consequence, also the bandwidth occupancy when there is network congestion. The use of this feature within the bandwidth allocation scheme allows reducing the bandwidth waste due to over provisioning and using the residual bandwidth for other sources. The advantage is particularly clear over satellite channels where fading often affects the communication: having some residual bandwidth available for stations which have experienced fading can improve the satellite network performance.This paper presents a detailed performance evaluation of a bandwidth allocation scheme, called E-CAP-ABASC and studied for the satellite environment. The bandwidth is assigned to the earth stations that compose the network by a master station on the basis of a cost function whose main part is represented by a closed-form of the packet loss probabilities for the TCP and UDP traffic. The use of two different packet loss probability models for TCP and UDP allows exploiting the different features of the two traffic types, so improving the overall performance either in terms of packet loss or, on the other hand, in terms of the traffic admitted.The performance evaluation is carried out by varying the link degradation due to fading, the traffic load, and the flow balance between UDP and TCP. The results show a good performance of E-CAP-ABASC, compared with two other schemes. Advantages and drawbacks are discussed.     

Target bandwidth sharing using endhost measures

Recent congestion control protocols such as XCP and RCP achieve fair bandwidth sharing, high utilization, small queue sizes and nearly zero packet loss by implementing an explicit bandwidth share mechanism in the network routers. This paper develops new quantitative techniques for achieving the same results using only end-host measures. We develop new methods of computing bottleneck link characteristics, a new technique for sharing bandwidth fairly with Reno flows, and a new approach for rapidly converging to bandwidth share. A new transport protocol, TCP-Madison, that employs the new bandwidth sharing techniques is also defined in the paper. Experiments comparing TCP-Madison with FAST TCP, BIC-TCP and TCP-Reno over hundreds of PlanetLab and other live Internet paths show that the new protocol achieves the stated bandwidth sharing properties, is easily configured for near-optimal performance over all paths, and significantly outperforms the previous protocols.     

新一代的拥塞控制机制-XCP的研究

算法和分析表明,随着带宽延迟的增加,不管采用何种队列调度策略,TCP都变得不稳定和难于收敛.提出了一种新的拥塞控制机制-XCP(eXplicit Control Protocol),一个比TCP更加有效和公平的拥塞控制协议,并在模拟的环境中对XCP和TCP协议的性能进行了分析和比较.     

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.