文档介绍：摘要
在互联网不断发展的同时,多种无线通讯技术也逐步成熟,无线网络以其灵活、高效、便利的优势迅速融入全球互联网络,因而互联网络出现了无线和有线混合化的特性。然而,传统的针对有线网络设计的 TCP 协议在应用于有线/无线异构网络中时,不仅存在拥塞丢包,还会因无线链路的比特误码、信道衰落、噪声干扰等产生频繁的无线随机丢包,传统 TCP 协议会将所有数据包丢失均归因于网络拥塞,盲目降低拥塞窗口进行流量控制,势必导致 TCP 性能的恶化。因此, 在有线/无线异构网络中通过有效的丢包区分机制有针对性地对网络进行拥塞控制,是优化 TCP 性能的一个关键,具有重大研究意义。
本文针对现有 TCP 协议在高比特误码的有线/无线异构网络环境下 TCP 性能恶化的问题,分别围绕端到端丢包区分、显式拥塞反馈以及跨层联合优化等策略进行研究与算法改进,主要研究工作及创新如下:
(1)为了更准确地区分丢包,本文提出了一种基于动态往返时延抖动的丢包区分算法,采用与网络状态变化相适应的动态滤波权值来平滑实时采集的往返时延抖动样本,计算网络拥塞标识,从而详细划分拥塞等级,并根据预测的拥塞等级区分丢包、调整拥塞窗口。经 NS2 仿真验证,该算法的性能比现有 TCP 有较大提升。
(2)为克服依靠单一测度进行丢包区分的局限性与消减反向链路拥塞的影响,本文提出了一种基于时间戳的相对单向时延的丢包区分算法,同时联合相对单向时延差、瓶颈链路中排队的数据包个数、以及网络实时吞吐量等多个端到端测度,更全面地估测网络拥塞程度。实验证明,该算法的性能在高误码率以及反向链路拥塞的情况下均得到了有效提高。
(3)提出了一种基于 ECN 拥塞概率与端测度跨层联合的丢包区分方法,改进算法为了提高端系统对拥塞感知的准确性,首先依据在源端统计的最近一段时间返回的带有 ECN 反馈标记的 ACK 的概率,实时预测拥塞概率,降低非实时性对反馈的影响;其次通过基于 ECN 的拥塞概率与多个端测度的联合判断更加充分地识别丢包原因,实现了网络层与传输层的跨层优化。仿真结果表明,该算法已有方案相比,能达到更高的吞吐量、更好的稳定性,同时兼顾友好性与公平性。
关键词:丢包区分,TCP 拥塞控制,端到端,ECN,跨层优化
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ABSTRACT
With the development of , various munication technologies are ing matured. Since the work is integrated into the global with its advantages of high flexibility, efficiency and convenience, the appears to have a hybrid characteristic of wired and wireless. However, the traditional TCP protocol is originally designed for the works, when it is applied to the wired/wireless works, there are not only congestion losses, but also wireless losses due to bit error rate, channel fading and noise interferences of the wireless link. All the lost packets will be regarded as congestion losses and the congestion window will be decreased blindly for the flow control, leading to a deterioration of TCP performance. Therefore, an work congestion control mechanism based on loss differentiation between congestion losses and wireless packet losses which has an important research significance es the key to optimize the TCP performance.
Aiming at solving the problem of TCP performance deterioration in the existing TCP protocol when it is applied i