【作者】 李亮；

【导师】 刘洺辛；

【作者基本信息】 燕山大学 ， 信息与通信工程， 2016， 硕士

【摘要】 目前网络通信快速发展,在通信过程中数据流量的增长越来越迅猛,网络拥塞已经成为一个被广泛关注的问题。当负载过大,而网络中的资源十分有限时,就会造成吞吐量下降、网络延时变大、数据包掉包率变大等问题,使得系统的性能以及鲁棒性严重下降,因而在此基础上提出了网络拥塞控制算法来缓解拥塞问题。为了提高网络服务质量,保证数据的正确传输,提出了各种网络拥塞控制算法,其中比较有代表性的就是主动式队列管理机制的随机早丢弃算法(Random Early Detection,RED)。相较于被动式队列管理机制的Drop Tail算法,RED队列管理机制解决了TCP全局同步问题。主动队列管理机制是在队列满之前就开始把数据包丢弃,限制将要拥塞的转发设备的发送端的流量速度,可以有效的避免队列溢出所导致的吞吐量下降、丢包率骤增、延时变长和低链路利用率等问题。但是RED算法还有稳定性、参数敏感性等方面的不足。因此,本文通过详细的学习和深入的研究RED算法,应用Linux系统下NS2仿真软件来对RED算法进行改进仿真—ERED、2SSRED和3SSRED。首先,新算法提出了新的非线性平滑,并且调整了算法中的掉包概率函数。新算法通过科学的数学计算推导得出了掉包概率与队列长度的关系,关系式表明掉包概率与队列长度并不是简单的线性关系也不是简单的曲线关系,而是一种类似S型函数的关系。其次,将缓冲区长度的整个区域分为不同的管理区域。可以简单的分为两个区域:积极区和消极区;也可以分为更为复杂的三个区域:积极区、稳定区和消极区。在不同的区域将要对掉包概率函数进行不同的调整,这样数据的分发和处理将会更加准确快速。最后,在Linux系统下应用NS2软件下对新的算法进行了仿真验证,仿真结果表明三种新的算法在吞吐量、丢包率等方面相比基础算法表现出了显而易见的优势。更多还原

【Abstract】 With the rapid development of computer network, The explosive growth in the network data flow take place, the data flow of network congestion problem has become a more and more valued. When the load is too large, but in the network resource i s very limited, it will cause throughput degradation and the network latency increasing and packet substitution rate increasing, which makes the system performance and robustness of serious decline, and network congestion control algorithms become an effec tive way to solve this problem.In order to improve the network quality of service and ensure the correct transmission of data, It proposed a variety of network congestion control algorithm, in which the most representative of active queue management mechanism is Random Early Detection Algorithm. Compared to the Drop Tail passive queue management algorithm, RED queue management mechanism solve the problem of global TCP synchronization, but before the queue of the active queue management mechanism is full, the mechanism start to drop the packet and limit the speed of the transmission side, so it could effectively avoid the queue overflow caused by throughput decreasing, packet loss rate surging, the delay increasing, and low link utilization. But the lacks of the RED algorithm are stability and parameter sensitivity and so on. Therefore, this article detailed study and research about the RED algorithm applied NS₂ to simulate and improve the RED algorithm on ERED, 2SSRED and 3SSRED in Linux system.First, the new algorithm proposes a new nonlinear smoother and the loss probability function of the RED has been adjusted. New algorithm calculated the relationship between probability of loss rate and average queue length by scientific mathematical method, which shows that the relationship probability of loss rate and average queue length is not a simple linear relationship yet a simple curve relationship, but the relationship of a function of similar S-type.Secondly, the entire length of the queue area divided into different regions. It can be simply divided into two areas: economic zone and the negative zone; It can also be more complex divided into three areas: active area, stable area and negative area. In different regions adjustment of the probability function of the loss rate will be different, distribution and processing of the data will be more accurate and rapid.Finally, applying NS₂ to simulate and verification the new algorithm in Linux system. Simulation results show that the three new algorithms in network throughput, packet loss rate compared showed a clear advantage in RED algorithm.更多还原