【作者】 刘辉；

【导师】 陈建二；

【作者基本信息】 中南大学 ， 计算机科学与技术， 2011， 硕士

【摘要】 随着网络技术的飞速发展,特别是大量多媒体实时音／视频业务的广泛应用发展,对传统以TCP协议为主的传输提出了新的挑战。TCP拥塞控制使用的AIMD策略,会引起速率很大的抖动,不适用于多媒体传输。而当基于UDP协议的多媒体应用和TCP协议的应用共享网络带宽时,由于UDP不具有拥塞控制机制,当网络拥塞时,UDP流不公平地抢占大量带宽,影响TCP流的正常应用,同时自身丢包增加,加剧网络拥塞。因此,为了实时多媒体业务的健康发展,研究适用于多媒体传输,具有拥塞控制机制并能够与TCP协议公平共享带宽的传输协议是非常必要的。近年来,各种TCP-Friendly协议得到广泛的研究。其中最具代表性的TFRC (TCP-Friendly Rate Control),是本文研究的重点。本文首先研究分析TFRC的运行机理,使用网络仿真工具ns2对TFRC协议进行仿真,研究TFRC的性能。研究发现,TFRC在高速网络和无线网络下的性能都存在一定的问题。我们的研究工作将主要从高速和无线网络环境对TFRC的性能分别进行改进。在高速网络下的研究发现,TFRC的慢启动性能不太理想,因此,我们对TFRC慢启动阶段进行改进,采用三个阶段的策略来提高网络利用率的同时减少丢包率。仿真实验表明,改进后的TFRC协议——TFRC-Astart协议有效地改善了TFRC的慢启动性能,增加了网络吞吐量,提高利用率,减少了丢包率,特别在高带宽延时网络中的表现更为突出。然后我们针对无线网络环境下的TFRC协议延时抖动明显,吞吐量下降的性能表现,提出了基于延时自适应的速率调节机制,通过设置门限阈值判断网络拥塞状态,利用延时信息进行网络状态划分,根据网络状态调节RTT的计算,从而控制发送速率。仿真实验表明改进后的TFRC协议——TFRC-P提高了吞吐量,有效减少了延时抖动,提高发送速率,整体上增强了TFRC的性能。本文最后对所做的研究工作进行总结,阐述了在高速和无线网络环境下TFRC协议所存在的问题及进一步的研究思路。更多还原

【Abstract】 With the rapid development of network technology and a large increament of multimedia real-time audio/video services, the traditional congestion control (TCP) suffers new challenges. The AIMD mechanism of TCP is not appropriate for multimedia transmission. When UDP protocols and TCP protocols sharing the network bandwidth, because UDP protocols have no congestion control mechanism and access the most of the bandwidth. Therefore, many scholars provide a new congestion control mechanisms TCP-Friendly congestion control protocols. In recent years, a variety of TCP-Friendly protocol been widely studied. TFRC (TCP-Friendly Rate Control) is the most important one.Firstly, the thesis reviews the researches of TCP-Friendly protocols in recent years, mainly focuses on the performance of TFRC protocols. Based on this study, there are some performance problems of TFRC in high speed and wireless networks. We will study these problems independently from the high speed and wireless networks.Second, we discuss the performance of slow start phase in TFRC. Based on the performance of TFRC in high bandwidth-delay product Networks, we divided the slow start strategy into three stages to improve network utilization and reduce packet loss rate. Simulation results show that the improved TFRC protocol－TFRC-Astart has improved the slow start performance,especially in high bandwidth-delay product networks.Then we study the performance of TFRC in wireless networks. Based on the poor performance of TFRC, we provide the improvement from two sides:the method of caluating RTT and distinguishment of the network status, which is based on Spike algorithm. Simulation results show that the improved TFRC protocol－TFRC-P has improved sending rate and reduced the delay jitter in wirless networks.Finally, the thesis summarizes the current existing open issues, and provides some further interesting directions on TFRC and TCP-Friendly congestion control protocols over new networks.更多还原