發(fā)布時(shí)間：2018-10-22 07:38

【摘要】：目前，計(jì)算機(jī)網(wǎng)絡(luò)技術(shù)得到了飛躍發(fā)展，網(wǎng)絡(luò)在日常生活中扮演的角色越來越重要。隨之而來的是網(wǎng)民數(shù)量飛速增加和網(wǎng)絡(luò)流量急劇增長。網(wǎng)絡(luò)一旦出現(xiàn)擁塞情況，網(wǎng)絡(luò)會(huì)出現(xiàn)大量丟包現(xiàn)象，吞吐量也會(huì)受到影響，甚至嚴(yán)重時(shí)會(huì)導(dǎo)致網(wǎng)絡(luò)崩潰；因此如何對(duì)網(wǎng)絡(luò)進(jìn)行擁塞控制對(duì)網(wǎng)絡(luò)繼續(xù)發(fā)展具有重要意義。 本文主要是對(duì)TCP/IP中的TCP擁塞控制協(xié)議進(jìn)行分析，并提出了Reno-J算法，避免了Reno算法在慢啟動(dòng)后期出現(xiàn)大量突發(fā)數(shù)據(jù)量的不足： 對(duì)TCP協(xié)議進(jìn)行了詳細(xì)分析，主要介紹了TCP報(bào)文段的首部格式，并且通過詳細(xì)分析三步握手機(jī)制和滑動(dòng)窗口機(jī)制說明TCP是如何實(shí)現(xiàn)可靠傳輸?shù)�，分別解釋了擁塞產(chǎn)生的原因和擁塞控制的概念，詳細(xì)分析了慢啟動(dòng)、擁塞避免、快速重傳/快速恢復(fù)、超時(shí)重傳四個(gè)階段的工作原理，，簡要闡述了擁塞控制協(xié)議經(jīng)歷的版本演進(jìn)。 根據(jù)現(xiàn)在的擁塞控制算法中閾值設(shè)置恒定帶來的問題，重點(diǎn)分析比較了Westwood算法及升級(jí)版本的優(yōu)缺點(diǎn)并對(duì)帶寬估計(jì)算法做出改進(jìn)，分別通過對(duì)確認(rèn)的包長度和確認(rèn)到達(dá)時(shí)間進(jìn)行采樣求得它們各自的平均值，然后兩者相除得到帶寬估計(jì)值，改進(jìn)的可用帶寬估計(jì)算法能更加準(zhǔn)確的對(duì)網(wǎng)絡(luò)帶寬的使用情況進(jìn)行估計(jì)； 在慢啟動(dòng)階段，TCP Reno以指數(shù)方式增加其擁塞窗口，這會(huì)導(dǎo)致慢啟動(dòng)后期出現(xiàn)大量突發(fā)數(shù)據(jù)，正因如此，通過數(shù)學(xué)分析提出一種關(guān)于中點(diǎn)對(duì)稱的分段數(shù)學(xué)函數(shù)模型，使得在慢啟動(dòng)前期，擁塞窗口增長速率加快，而到了后期，擁塞窗口增長速率減慢，從而平滑過渡到擁塞避免階段；最后通過NS2仿真對(duì)其擁塞窗口、吞吐量、丟包率、友好性進(jìn)行評(píng)估驗(yàn)證；實(shí)驗(yàn)結(jié)果顯示，新算法能夠有效的降低網(wǎng)絡(luò)傳輸分組丟棄，提高網(wǎng)絡(luò)吞吐量，減少網(wǎng)絡(luò)的抖動(dòng)的次數(shù)，維持網(wǎng)絡(luò)穩(wěn)定；除此之外，新算法與Reno算法一同應(yīng)用時(shí)，體現(xiàn)了友好性。
[Abstract]:At present, with the rapid development of computer network technology, network plays a more and more important role in daily life. What follows is the netizen quantity to increase rapidly and the network traffic to grow sharply. Once the network congestion occurs, the network will have a large number of packet loss phenomenon, throughput will also be affected, and even serious will lead to network collapse, so how to control the network congestion is of great significance for the continued development of the network. This paper mainly analyzes the TCP congestion control protocol in TCP/IP, and puts forward the Reno-J algorithm, which avoids the shortage of a large amount of burst data in the Reno algorithm in the later stage of slow start. The TCP protocol is analyzed in detail. This paper mainly introduces the first format of TCP message segment, and explains how TCP realizes reliable transmission by analyzing the three-step handshake mechanism and sliding window mechanism in detail, and explains the causes of congestion and the concept of congestion control, respectively. The principles of slow start, congestion avoidance, fast retransmission / fast recovery and timeout retransmission are analyzed in detail, and the evolution of congestion control protocol is briefly described. According to the problem of constant threshold setting in the current congestion control algorithm, the advantages and disadvantages of the Westwood algorithm and the upgraded version are analyzed and compared, and the bandwidth estimation algorithm is improved. Their average values are obtained by sampling the confirmed packet length and the confirmed time of arrival, and then dividing the two to obtain the bandwidth estimate. The improved available bandwidth estimation algorithm can estimate the bandwidth of the network more accurately. In the slow start phase, TCP Reno increases its congestion window exponentially, which leads to the emergence of a large number of burst data in the late stage of slow start. For this reason, a piecewise mathematical function model of midpoint symmetry is proposed through mathematical analysis, which makes the growth rate of congestion window increase faster in the early stage of slow start, but slow down in later stage. Finally, the congestion window, throughput, packet loss rate and friendliness are evaluated and verified by NS2 simulation. The experimental results show that the new algorithm can effectively reduce packet dropping in network transmission. In addition, the new algorithm and Reno algorithm show friendliness when it is used together with the Reno algorithm to improve the network throughput, reduce the number of times of network jitter, and maintain the stability of the network.
【學(xué)位授予單位】：沈陽理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TP393.04

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