传输控制协议中拥塞控制算法的改进
发布时间：2018-10-22 07:38
【摘要】：目前，计算机网络技术得到了飞跃发展，网络在日常生活中扮演的角色越来越重要。随之而来的是网民数量飞速增加和网络流量急剧增长。网络一旦出现拥塞情况，网络会出现大量丢包现象，吞吐量也会受到影响，甚至严重时会导致网络崩溃；因此如何对网络进行拥塞控制对网络继续发展具有重要意义。 本文主要是对TCP/IP中的TCP拥塞控制协议进行分析，并提出了Reno-J算法，避免了Reno算法在慢启动后期出现大量突发数据量的不足： 对TCP协议进行了详细分析，主要介绍了TCP报文段的首部格式，并且通过详细分析三步握手机制和滑动窗口机制说明TCP是如何实现可靠传输的，分别解释了拥塞产生的原因和拥塞控制的概念，详细分析了慢启动、拥塞避免、快速重传/快速恢复、超时重传四个阶段的工作原理，，简要阐述了拥塞控制协议经历的版本演进。 根据现在的拥塞控制算法中阈值设置恒定带来的问题，重点分析比较了Westwood算法及升级版本的优缺点并对带宽估计算法做出改进，分别通过对确认的包长度和确认到达时间进行采样求得它们各自的平均值，然后两者相除得到带宽估计值，改进的可用带宽估计算法能更加准确的对网络带宽的使用情况进行估计； 在慢启动阶段，TCP Reno以指数方式增加其拥塞窗口，这会导致慢启动后期出现大量突发数据，正因如此，通过数学分析提出一种关于中点对称的分段数学函数模型，使得在慢启动前期，拥塞窗口增长速率加快，而到了后期，拥塞窗口增长速率减慢，从而平滑过渡到拥塞避免阶段；最后通过NS2仿真对其拥塞窗口、吞吐量、丢包率、友好性进行评估验证；实验结果显示，新算法能够有效的降低网络传输分组丢弃，提高网络吞吐量，减少网络的抖动的次数，维持网络稳定；除此之外，新算法与Reno算法一同应用时，体现了友好性。
[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.
【学位授予单位】：沈阳理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TP393.04
本文编号：2286526
[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.
【学位授予单位】：沈阳理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TP393.04
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