一种改进的TCP拥塞控制算法的公平性研究

针对提高网络资源利用率,对TCP Reno拥塞控制算法进行改进,为实施拥塞优化控制,提出一种改进的拥塞控制算法。为判断该算法对所有数据流是否公平,在对其正确性和公平性进行理论分析后,构建NS2仿真模型并进行仿真,由于仿真结果数据量大,常规方法分析较为困难,故将仿真结果转换为数据库文件进行分析,该方法可操作性强,具有速度快,精度高,自主性强等优势;通过丢弃分组数的方差比较TCP Reno算法和改进算法在丢弃分组上的差异,通过延迟和延迟抖动标准差比较延迟和延迟抖动在不同数据流中的差异,上述参数更能从全局上反映多个比较项之间的整体差异。通过理论分析和仿真结果对比,该改进算法对于各数据流是公平的,且与TCP算法的公平性相当。     

GEO卫星网中基于拥塞状态区分的TCP Vegas改进算法

针对TCPVegas在GEO卫星网络中应用时难以准确估计BaseRTT而带来的不足,结合TCP Vegas-A和TCP New Veno算法的优势,提出了一种改进算法TCP Vegas-A＋。改进算法在TCP Vegas-A算法的基础上,引入基于相对队列时延的拥塞状态判断方法,对网络状态进一步细分,以准确判断网络拥塞状态,合理调整拥塞窗口。仿真结果表明,改进算法具有较好的吞吐量性能,并提高了与Reno竞争带宽的能力,能较好地适用于GEO卫星链路。     

基于ABR业务模型的TCP协议性能分析

ＡＢＲ精力是ＡＴＭ中新定义的一种业务类型，经主要面向数据传输服务，采用基于速率的端到端的拥塞控制机制。ＴＣＰ是Ｉｎｔｅｒｎｔ所主要数据输协议。采用基于窗口的拥塞控制机制。文中主要讨论了讨论了ＴＣＰ与ＡＢＲ业务所采用的两种不同的拥塞控制机制，分析了基于ＡＢＲ的ＴＣＰ协议所呈的一些特点以及ＡＴＭ交换机缓存的大小对ＴＣＰ性能的影响。     

对FASTTCP网络拥塞控制优缺点的分析

随着互联网规模与应用的扩大,网络环境变得复杂,传统的拥塞控制已经不能适应高速网络,FASTTCP因此应运而生。通过仿真实验与传统TCPReno进行对比,发现FASTTCP确实有很大的提高,但也存在问题需要改进。     

Improving fairness among TCP flows by stateless buffer control with early drop maximum

Transmission control protocol (TCP) has been recognized as the most important transport-layer protocol for the Internet. It is distinguished by its reliable transmission, flow control, and congestion control. However, the issue of fair bandwidth-sharing among competing flows was not properly addressed in TCP. As web-based applications and interactive applications grow more popular, the number of short-lived flows conveyed on the Internet continues to rise. With conventional TCP, short-lived flows will be unable to obtain a fair share of available bandwidth. As a result, short-lived flows will suffer from longer delays and a lower service rate. It is essential for the Internet to come up with an effective solution to this problem in order to accommodate the new traffic patterns.With a more equitable sharing of bottleneck bandwidth as its goal, a stateless queue management scheme featuring early drop maximum (EDM) is developed and presented in this article. The fundamental idea is to drop packets from those flows having more than an equal share of bandwidth. The congestion window size of a TCP sender is carried in the options field on each packet. The proposed scheme will be exercised on routers and make its decision on packet dropping according to the congestion windows. In case of link congestion, the queued packet with the largest congestion window will be dropped from the queue. This will lower the sending rate of its sender and release part of the occupied bandwidth for the use of other competing flows. By so doing, the entire system will approach an equilibrium point with a rapid and fair distribution of bandwidth. As a stateless approach, the proposed scheme inherits numerous advantages in implementation and scalability.Extensive simulations were conducted to verify the feasibility and the effectiveness of the proposed approach. As revealed in the simulation results, the proposed scheme outperforms existing stateless techniques, including Drop-Tail and Random Early Drop, in many respects, such as a fairer sharing of available bandwidth and a shorter response time for short-lived flows.     

Achieving high throughput and TCP Reno fairness in delay-based TCP over large networks

The transport control protocol （TCP） has been widely used in wired and wireless Intemet applications such as FTP, email and HTTP. Numerous congestion avoidance algorithms have been proposed to improve the performance of TCP in various scenarios, especially for high speed and wireless networks. Although different algorithms may achieve different performance improvements under different network conditions, designing a congestion algorithm that can perform well across a wide spectrum of network conditions remains a great challenge. Delay-based TCP has a potential to overcome above challenges. However, the unfairness problem of delay-based TCP with TCP Reno blocks widely the deployment of delay-based TCP over wide area networks. In this paper, we proposed a novel delay-based congestion control algorithm, named FAST-FIT, which could perform gracefully in both ultra high speed networks and wide area networks, as well as keep graceful faimess with widely deployed TCP Reno hosts. FAST-FIT uses queuing delay as a primary input for controlling TCP congestion window. Packet loss is used as a secondary signal to adaptively adjust parameters of primary control process. Theoretical analysis and experimental results show that the performance of the algorithm is significantly improved as compared to other state-of-the-art algorithms, while maintaining good faimess.     

Achieving high throughput and TCP Reno fairness in delay-based TCP over large networks

The transport control protocol (TCP) has been widely used in wired and wireless Internet applications such as FTP, email and http. Numerous congestion avoidance algorithms have been proposed to improve the performance of TCP in various scenarios, especially for high speed and wireless networks. Although different algorithms may achieve different performance improvements under different network conditions, designing a congestion algorithm that can perform well across a wide spectrum of network conditions remains a great challenge. Delay-based TCP has a potential to overcome above challenges. However, the unfairness problem of delay-based TCP with TCP Reno blocks widely the deployment of delay-based TCP over wide area networks. In this paper, we proposed a novel delay-based congestion control algorithm, named FAST-FIT, which could perform gracefully in both ultra high speed networks and wide area networks, as well as keep graceful fairness with widely deployed TCP Reno hosts. FAST-FIT uses queuing delay as a primary input for controlling TCP congestion window. Packet loss is used as a secondary signal to adaptively adjust parameters of primary control process. Theoretical analysis and experimental results show that the performance of the algorithm is significantly improved as compared to other state-of-the-art algorithms, while maintaining good fairness.     

主动网络与TCP融合的拥塞控制方法

最近有大量研究是针对网络拥塞控制的,但是问题仍然非常复杂。TCP的可伸缩性、灵敏性、稳定性和公平性是必需的特性。文章分析了主动网络体系结构的设计思想,在主动网络中,网络不仅具备基本的数据包寻址转发的功能,而且还具有动态编程的能力。在此基础上将主动网络设计思想引入到拥塞控制算法的研究中,针对其在传统网络中存在的一系列问题提出了基于主动网络的拥塞控制算法CCAAN,解决了它们在传统网络研究中存在的问题。实验结果显示AMCA收敛性很好,可以充分利用有效带宽,并且对于TCP公平的动态变化能够迅速做出反应。     

一种自适应改进无线TCP性能的算法

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，针对这些问题提出了一种算法对无线链路下一时刻的误码率进行了估计，根据这个估计对TCP进行了修改以自适应选取合适的TCP报文段尺寸来传输数据。在网络仿真器（NS2）中仿真一个误码率时变的无线信道，把修改后的TCP置于NS仿真环境中进行仿真，实验结果表明了该改进方法有效。     

TCP-Illinois: A loss- and delay-based congestion control algorithm for high-speed networks

We introduce a new congestion control algorithm for high-speed networks, called TCP-Illinois. TCP-Illinois uses packet loss information to determine whether the window size should be increased or decreased, and uses queueing delay information to determine the amount of increment or decrement. TCP-Illinois achieves high throughput, allocates the network resource fairly, and is incentive compatible with standard TCP. We also build a new stochastic matrix model, capturing standard TCP and TCP-Illinois as special cases, and use this model to analyze their fairness properties for both synchronized and unsynchronized backoff behaviors. We finally perform simulations to demonstrate the performance of TCP-Illinois.     

卫星网络的TCP慢启动策略改进

讨论了根据卫星网络链路所处的状态,通过增加初始窗口值、控制延迟响应以及共享信道信息等方法对慢启动进行改进,并通过实例说明这种改进对于改善卫星网络性能是有意义的。     

基于误码丢包率监测的无线TCP改进

针对无线环境下TCP错误调用拥塞控制算法致使性能下降的情况,提出一种基于误码丢包率监测的无线TCP改进方法。利用显式拥塞通知的路由器配合区分分组丢失性质,在数据发送端采用实时误码丢包率监测,并根据监测结果调整TCP段尺寸。仿真结果表明,改进后的TCP吞吐量在误码率为1E-4时超过TCP_SACK和TCP_Reno近1倍。     

无线异构网络环境中基于拥塞状态区分的TCP Vegas 改进算法

在无线网络环境中,TCP Vegas应用时会受到无线信道干扰和噪声的影响,对往返延时（RTT）难以进行准确的估计,导致其性能大幅度降低。结合TCP New Vegas和TCP Vegas A+等的优点提出一种改进算法TCP Vegas-P。该算法针对慢启动过早结束和拥塞避免阶段拥塞出现在反向链路上导致吞吐量下降的问题,以及在与NewReno共存时公平性恶化的问题进行了综合的改进。经仿真实验,改进的算法在无线网络中能够进行比较好的RTT估计,对解决上述Vegas存在的问题达到了良好的效果。     

改进显式拥塞通知提高无线应用中的TCP性能

介绍了TCP拥塞控制、积极队列管理以及显式拥塞通知的基本原理,提出了适用于无线环境中的各种ECN改进方案,并就各方案及其对TCP性能改善作了分析讨论,为TCP在无线环境中的应用研究提供了较好的参考。     

TCP flow control technique for an interworking interface: hardware implementation

Current TCP flow control depends on packet losses to find the workload that a network can support. A variety of situations, including lossy wireless networks, asymmetric networks and web traffic workload, violates many of the assumptions made by TCP, causing degraded end-to-end performances. To improve the performance of TCP over heterogeneous networks (Ethernet and ATM interconnection), we propose a new technique, which we call Vegas–Snoop+, based on Vegas and Snoop protocols. Two modified service elements take part on the Vegas–Snoop+ technique. First, Vegas service element manages the connection parameters to achieve better throughput. Second, Snoop service element isolates the Ethernet senders from the characteristics of the ATM link. The objective in this paper is to win from advantages of Vegas and Snoop protocols, as well as to search an interconnection interface for networks interoperability. Actually, the development of two new integrated circuits (the BCM5680 (switch) and the BCM5401 (PHY)) orientate researchers to implement, at higher layer of the OSI model, flow control mechanisms to ensure reliability. Vegas–Snoop+ is an implementation of TCP, which gives in this way a solution for traffic management and congestion control improving good throughput with more reliability.     

Fair rate control for wireless ad-hoc networks with time varying channel capacities

We consider the problem of fair rate control for wireless ad-hoc networks with time varying channel capacities. The interaction between links in wireless ad-hoc networks introduces additional constraints on the flow rate. A primal-dual algorithm that guarantees fair rate control is proved to be trajectory stable. Various fairness indexes are obtained by choosing the specified form of the utility functions, and the numerical results validate the effectiveness of the proposed algorithm.     

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.     

Fuzzy logic controlled RED: congestion control in TCP/IP differentiated services networks

The use of the Internet for time-sensitive services, such as voice and video applications, requires a predictable quality of service. The TCP/IP differentiated services (Diff-Serv) architecture was introduced to achieve such performance. Network congestion control, however, still remains a critical and high priority issue. A number of researchers are looking at alternative schemes such as random early detection (RED) and its variants to handle congestion. In this paper we present the results of a fuzzy logic control approach to the implementation of RED – Fuzzy-RED. We believe that with fuzzy logic we are able to use linguistic knowledge to implement better understood nonlinear probability discard functions, achieve better differentiation for packet discarding behaviors for aggregated flows, and so provide better quality of service to different kinds of traffic whilst maintaining high utilization.     

MANET中TCP改进研究综述

传统TCP(transmission control protocol)本是为有线网络设计,它假设包丢失全是由网络拥塞引起,这个假设不能适应于MANET (mobile ad hoc network),因为MANET中除了拥塞丢包以外,还存在由于较高比特误码率、路由故障等因素引起的丢包现象.当出现非拥塞因素丢包时,传统TCP将错误地触发拥塞控制,从而引起TCP性能低下.任何改进机制都可以分为发现问题和解决问题两个阶段.首先概括了MANET中影响TCP性能的若干问题;然后针对发现问题和解决问题两个阶段,详细地对每一阶段中存在的各种可行方法进行了分类、分析和比较;最后指出了MANET中TCP性能优化的研究方向.     

UDP数据流对TCP流影响的分析和模拟

通过计算机模拟，说明了无拥塞控制的UDP数据流同TCP流共享带宽时的不公平性，并通过分析TCP的端到端流量控制机制指出了产生不公平的原因。