【作者】 王晓媛；

【导师】 梁丰；

【作者基本信息】 浙江工业大学 ， 通信与信息系统， 2006， 硕士

【摘要】 无线局域网(WLAN)以其移动性和灵活性的特点得到了广泛应用。随着网络速率的不断提高以及多媒体应用的发展,人们更希望无线网络能够提供服务质量(Ouality of Service,QoS)的保证,如何保证各用户公平地享有带宽是提供QoS保证的基础。公平性问题也因此成为解决OoS的关键问题之一。本文讨论基础结构模式的无线局域网中TCP上下行流之间的公平性问题。 本文基于TCP平均窗口理论,提出为满足TCP公平所需的AP缓存区大小的估计方法。但是通过改变缓存区大小实现TCP流的公平是不现实的。因此,本文在估计方法的基础上考虑网络传输延迟对吞吐量的影响,提出解决TCP不公平问题的方案TFBR。TFBR是在Drop Tail队列管理的基础上进行改进,通过设置经过AP队列中包的通告窗口字段,限制发送速率,从而解决TCP上下行流之间的公平。仿真实验结果表明该方法能在单个上行和多个下行流的情况下有效地解决公平性问题,而且具有较好的网络性能。但是,TFBR方法运用到实际中还存在一定的不足。针对TFBR应用上的不足,本文在TFBR的基础上,提出一种保证TCP公平的新型队列管理机制TF_PDAR。TF_PDAR算法在窗口值的计算上做了改进,不再通过准确计算得到窗口值,而是根据AP队列中的丢包事件动态地调整窗口大更多还原

【Abstract】 Wireless Local Area Network (WLAN) based on IEEE 802.11 has been applied widely due to its mobility and facility. With the increasing high speed in data transmission and the development of multimedia applications, supporting Quality of Service (QoS) in WLAN has been increasingly demanded. The basic issues of QoS are how to ensure the fair allocation of the bandwidth for all wireless users. Hence the fairness issue is one of the key issues to provide QoS in WLAN. In this paper, we will discuss the unfairness problem between TCP upstream flows and downstream flows over infrastructure-mode WLAN.This thesis presents an estimation algorithm of AP buffer size for TCP fairness over WLAN based on TCP average window. But it is unpractical to regulate the AP buffer size to achieve TCP fairness. Hence, with the estimation algorithm and considering the influence of the propagation delay on throughout, we suggest a solution TFBR for TCP unfairness problem between TCP upstream flows and downstream flows. The TFBR modifies the Drop Tail, and controls the sender rate bysetting the advertised receiver window of the packets in queue of the Access Point (AP) before executing drop tail program. Simulation results exhibit the efficiency and good performance of TFBR on the scenario of one upstream flow and several downstream flows. But application of TFBR has some problems. In order to avoid those application problems, a new queue management named TFPDAR is presented based on TFBR, which utilizes packet loss to auto-regulate the advertised receiver window size instead of calculating exact window size in TFBR. Simulation results indicate that TFPDAR offers fair allocation of bandwidth between TCP upstream and downstream flows and better performance on throughout, average delay and packet dropping rate compared with Drop tail, RED and EDCF schemes. Moreover, TF_PDAR scheme dose not need to modify the hardware of wireless equipments, so that the TCP fairness problem could be solved more simply and economically with TFPDAR.更多还原