發(fā)布時(shí)間：2019-06-04 21:03

【摘要】：近幾年來,無線網(wǎng)絡(luò)得到了快速的發(fā)展,尤其是基于IEEE 802.11協(xié)議族的基礎(chǔ)結(jié)構(gòu)型無線局域網(wǎng)。由于具有易于部署、成本低和支持移動(dòng)性等特點(diǎn),該類無線局域網(wǎng)被廣泛應(yīng)用于世界各地。此外,越來越多的移動(dòng)設(shè)備都支持與無線局域網(wǎng)的連接,進(jìn)一步推動(dòng)了無線局域網(wǎng)的發(fā)展。統(tǒng)計(jì)數(shù)據(jù)表明,基礎(chǔ)結(jié)構(gòu)型無線局域網(wǎng)中傳輸?shù)闹饕獦I(yè)務(wù)是基于TCP協(xié)議的。然而,傳統(tǒng)的基礎(chǔ)結(jié)構(gòu)型無線局域網(wǎng)并不能很好的為TCP業(yè)務(wù)提供服務(wù)。無線局域網(wǎng)中無線信道的特性和用戶的移動(dòng)性對(duì)TCP擁塞控制機(jī)制產(chǎn)生了負(fù)面的影響,使得無線局域網(wǎng)傳輸TCP業(yè)務(wù)時(shí)吞吐量較低。除此之外,無線局域網(wǎng)使用的DCF機(jī)制限制了AP接入無線信道的能力,導(dǎo)致無線局域網(wǎng)中的上、下行TCP數(shù)據(jù)流的吞吐量具有較大差距�；A(chǔ)結(jié)構(gòu)型無線局域網(wǎng)中的這種上、下行TCP數(shù)據(jù)流不公平的現(xiàn)象,在機(jī)場和大型會(huì)議等場所,表現(xiàn)得尤為明顯,嚴(yán)重影響了用戶的體驗(yàn)。在這種情況下,為了有效地提升無線局域網(wǎng)的服務(wù)質(zhì)量,我們有必要對(duì)無線局域網(wǎng)及TCP擁塞控制機(jī)制之間的問題進(jìn)行研究。在本文中,我們根據(jù)國內(nèi)外相關(guān)研究的現(xiàn)狀,采用理論分析與實(shí)驗(yàn)評(píng)估相結(jié)合的技術(shù)路線,研究了無線局域網(wǎng)中的TCP性能增強(qiáng)技術(shù)。本文中的主要工作概括如下:1.概述了無線局域網(wǎng)的網(wǎng)絡(luò)結(jié)構(gòu)、標(biāo)準(zhǔn)化進(jìn)程及其使用的接入?yún)f(xié)議的主要內(nèi)容。同時(shí),分析了TCP協(xié)議擁塞控制機(jī)制的基本原理及其應(yīng)用于無線局域網(wǎng)時(shí)遇到的一些問題。2.詳細(xì)地介紹了目前無線局域網(wǎng)中主要的TCP性能增強(qiáng)技術(shù),同時(shí)對(duì)其中典型技術(shù)的優(yōu)缺點(diǎn)進(jìn)行了分析。3.結(jié)合無線局域網(wǎng)及TCP協(xié)議擁塞控制機(jī)制的特點(diǎn),提出了一種自適應(yīng)流控代理的方法。該方法不需要修改無線局域網(wǎng)的底層協(xié)議,易于實(shí)施。自適應(yīng)流控代理實(shí)施于AP的IP層,可以提供TCP代理的功能,以減小無線局域網(wǎng)中無線信道及用戶移動(dòng)性對(duì)TCP業(yè)務(wù)的負(fù)面影響。此外,該方法能夠監(jiān)控經(jīng)過AP的流量信息,并根據(jù)統(tǒng)計(jì)的流量信息,周期性地計(jì)算出無線局域網(wǎng)的傳輸能力和其中每個(gè)TCP數(shù)據(jù)流對(duì)應(yīng)的往返傳輸時(shí)延。該方法利用計(jì)算出的結(jié)果,進(jìn)一步求出每個(gè)TCP數(shù)據(jù)流應(yīng)使用的滑動(dòng)窗口值,并利用計(jì)算出的值,修改對(duì)應(yīng)TCP ACK報(bào)文的窗口域,以控制每個(gè)TCP數(shù)據(jù)流的吞吐量。通過這種方式,自適應(yīng)流控代理可以在充分利用無線局域網(wǎng)傳輸能力的同時(shí),盡量減小無線局網(wǎng)中上、下行TCP數(shù)據(jù)流吞吐量的差距,以提升用戶的體驗(yàn)。4.利用NS-3對(duì)通信場景進(jìn)行仿真,驗(yàn)證了自適應(yīng)流控代理的有效性。利用仿真場景,我們做了三組仿真實(shí)驗(yàn)。我們在第一組仿真實(shí)驗(yàn)中不對(duì)無線局域網(wǎng)中的AP進(jìn)行任何修改;在第二組仿真實(shí)驗(yàn)中修改AP的MAC層,以實(shí)現(xiàn)自適應(yīng)優(yōu)先級(jí)控制功能;在第三組仿真實(shí)驗(yàn)中修改AP的IP層,以實(shí)現(xiàn)自適應(yīng)流控代理功能。在每一組實(shí)驗(yàn)對(duì)應(yīng)的子實(shí)驗(yàn)中,我們改變了WLAN中站點(diǎn)的數(shù)量以及WLAN傳輸?shù)臉I(yè)務(wù)類型,以研究每個(gè)方法在不同條件下性能的變化趨勢。為了得到較為準(zhǔn)確的統(tǒng)計(jì)結(jié)果,我們利用不同的隨機(jī)數(shù)種子,對(duì)每一組子實(shí)驗(yàn)進(jìn)行多次重復(fù)的試驗(yàn)。我們利用WLAN的總吞吐量、下行TCP數(shù)據(jù)流的平均吞吐量和不同TCP數(shù)據(jù)流之間的公平性來衡量WLAN的性能。通過仿真結(jié)果,容易看出自適應(yīng)流控代理可以有效地提升WLAN的性能。
[Abstract]:In recent years, the wireless network has been developed rapidly, especially based on the basic structure type wireless local area network based on the IEEE 802.11 protocol family. The wireless local area network is widely used in various parts of the world due to the characteristics of easy deployment, low cost, and support mobility. In addition, more and more mobile devices support the connection with the wireless local area network, and further promote the development of the wireless local area network. The statistics show that the main traffic in the base-structured wireless local area network is based on the TCP protocol. However, the traditional infrastructure type wireless local area network can not provide service to the TCP service well. The characteristics of the wireless channel and the mobility of the user in the wireless local area network have a negative influence on the TCP congestion control mechanism, so that the throughput is low when the wireless local area network transmits the TCP service. In addition, the DCF mechanism used by the wireless local area network limits the ability of the AP to access the wireless channel, resulting in a large gap in the throughput of the up and down TCP data streams in the wireless local area network. In the base-structured wireless local area network, the phenomenon of the unfairness of the downlink TCP data is especially obvious in the fields such as the airport and the large-scale conference, and the experience of the user is seriously affected. In this case, in order to effectively improve the service quality of the wireless local area network, it is necessary to study the problem between the wireless local area network and the TCP congestion control mechanism. In this paper, we study the technology of TCP performance enhancement in wireless local area network based on the current situation of domestic and foreign research and the combination of theoretical analysis and experimental evaluation. The main work in this paper is as follows:1. The network structure, the standardization process and the main content of the access protocol used in the wireless local area network are summarized. At the same time, the basic principle of the congestion control mechanism of the TCP protocol and some problems encountered in the application of the wireless local area network are analyzed. In this paper, the main TCP performance enhancement technology in the wireless local area network is introduced in detail, and the advantages and disadvantages of the typical technology are analyzed. Based on the characteristics of the congestion control mechanism of the wireless local area network and the TCP protocol, a self-adaptive flow control agent is proposed. The method does not need to modify the bottom layer protocol of the wireless local area network and is easy to implement. The adaptive flow control agent is implemented in the IP layer of the AP, and the function of the TCP proxy can be provided to reduce the negative influence of the wireless channel and the user mobility on the TCP service in the wireless local area network. In addition, the method can monitor the flow information through the AP and periodically calculate the transmission capacity of the wireless local area network and the round-trip transmission time delay corresponding to each TCP data stream according to the statistics flow information. The method further obtains the sliding window value to be used for each TCP data stream by using the calculated result, and modifies the window domain corresponding to the TCP ACK message by using the calculated value to control the throughput of each TCP data stream. In this way, the adaptive flow control agent can reduce the gap of the throughput of the upper and lower TCP data streams in the wireless local network to improve the user's experience while making full use of the wireless local area network transmission capability. The communication scene is simulated by NS-3, and the effectiveness of the adaptive flow control agent is verified. Using the simulation scene, we made three groups of simulation experiments. In the first group of simulation experiments, the AP in the wireless local area network is not modified; the MAC layer of the AP is modified in the second group of simulation experiments to realize the adaptive priority control function; and the IP layer of the AP is modified in the third group simulation experiment to realize the self-adaptive flow control agent function. In the sub-experiments corresponding to each set of experiments, we changed the number of sites in the WLAN and the traffic type of the WLAN transmission to study the trend of the performance of each method under different conditions. In order to get more accurate statistical results, we used different random number seeds to test every group of sub-experiments. We use the total throughput of the WLAN, the average throughput of the downlink TCP traffic, and the fairness between the different TCP data streams to measure the performance of the WLAN. Through simulation results, it is easy to see that the adaptive flow control agent can effectively improve the performance of WLAN.
【學(xué)位授予單位】：西安電子科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TN925.93;TN915.04

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