带宽抖动环境下的TCP流量控制研究

发布时间：2018-06-06 07:48

本文选题：移动通信 + TCP流量控制　；参考：《华东师范大学》2014年硕士论文

【摘要】：近年来,移动终端的广泛普及和移动应用的高速发展推动着移动通信技术的不断进步。人们对于移动通信的要求也越来越高,这促使移动通信的带宽越来越高,延迟越来越短,可以支持的应用越来越丰富。另一方面,TCP作为Internet协议中最为广泛应用的协议之一,在整个网络中不可或缺。但是TCP在设计之初是为有线网络提供可靠的、面向连接的传输服务,并没有将无线移动通信的因素考虑在内。相对于有线环境而言,移动通信环境有着自身的特点：带宽抖动,物理链路不可靠,差错率高,丢包率高,信号易受干扰,信道切换,移动节点自身硬件能力不足等,都会造成非拥塞丢包,但是TCP无法区分丢包是否是由于拥塞引起的,导致TCP性能的下降。为了解决上述问题,在2001年,由Mascolo等学者,提出了著名的TCP Westwood协议。TCP Westwood提出了一种带宽预测的方式,当TCP发生丢包或者超时时,通过预测带宽来调整TCP的状态,以改善TCP的性能。TCP Westwood的带宽预测比较准确,可以反映出网络带宽的变化情况。TCP Westwood在丢包率较高的环境下的性能表现优秀,可以判断出丢包是否是由于拥塞引起的,成为了很多无线TCP改良算法的基础。在移动通信中,由于节点的移动,或者是其他节点的加入或离开,带宽会随时发生变化,这种现象称之为带宽抖动。对于TCP协议而言,网络状况就像一个黑盒,TCP除了能够得到ACK反馈之外,无法获得其他的信息,所以对于带宽抖动而言,会导致TCP不能随时调整自己的状态来应对,造成性能的下降。TCP Westwood虽然提供了带宽预测机制,但是它仅在TCP发生了丢包或者超时时才会启用该机制,并没有利用它的带宽预测技术处理带宽抖动,所以没有对这一现象进行及时的处理。本文主要着眼于处理移动通信中带宽抖动的TCP协议的改进,主要基于TCPWestwood提出一种新的流量控制方案,称之为Improved Westwood。通过采用TCPWestwood既有的带宽预测技术,用于分析、判断带宽的变化情况,调整TCP的状态,尽可能快地将TCP适配于当前的网络带宽。为了验证Improved Westwood的性能,本文通过NS-2仿真实验平台进行实验仿真。本文通过实际手机在3G网络测速软件得到实验场景的参数来设计实验场景。通过NS-2仿真实验结合实际采集到的移动网络通信数据确定流量控制策略的参数。然后通过一些场景验证Improved Westwood与TCP Westwood在带宽抖动环境下表现上的区别。接着跟其他TCP协议进行性能上的对比,验证Improved Westwood改善了TCP在移动通信环境下的性能。
[Abstract]:In recent years, the widespread popularity of mobile terminals and the rapid development of mobile applications promote the continuous progress of mobile communication technology. The demand for mobile communication is becoming higher and higher, which makes the bandwidth of mobile communication become higher and higher, the delay is shorter and shorter, and the applications that can be supported are more and more abundant. On the other hand, as one of the most widely used protocols in Internet protocol, it is indispensable in the whole network. However, TCP was designed to provide reliable, connection-oriented transport services for wired networks, without taking wireless mobile communication into account. Compared with wired environment, mobile communication environment has its own characteristics: bandwidth jitter, unreliable physical link, high error rate, high packet loss rate, signal vulnerable to interference, channel switching, insufficient hardware capability of mobile node, etc. However, TCP can not distinguish whether the loss of packet is caused by congestion, which leads to the degradation of TCP performance. In order to solve the above problems, in 2001, Mascolo and other scholars proposed a famous TCP Westwood protocol .TCP Westwood proposed a bandwidth prediction method. When TCP lost packets or timed out, the state of TCP was adjusted by predicting the bandwidth. In order to improve the performance of TCP, the bandwidth prediction of TCP / Westwood is more accurate, which can reflect the variation of network bandwidth. The performance of TCP Westwood in the environment with high packet loss rate is excellent, and it can be determined whether the loss of packet is caused by congestion. It has become the basis of many improved wireless TCP algorithms. In mobile communication, the bandwidth will change at any time due to the movement of nodes or the addition or departure of other nodes. This phenomenon is called bandwidth jitter. For the TCP protocol, the network condition is like a black box TCP can get ACK feedback, but can not get any other information, so for bandwidth jitter, TCP can not adjust its state at any time to deal with it. Although it provides a bandwidth prediction mechanism, it only enables TCP when it loses packets or times out, and does not use its bandwidth prediction technology to handle bandwidth jitter. Therefore, this phenomenon has not been dealt with in a timely manner. This paper focuses on the improvement of TCP protocol which deals with bandwidth jitter in mobile communication, and proposes a new flow control scheme based on TCPWestwood, which is called Improved Westwood. The existing bandwidth prediction technology of TCPWestwood is used to analyze and judge the change of bandwidth, adjust the state of TCP, and adapt TCP to the current network bandwidth as quickly as possible. In order to verify the performance of Improved Westwood, this paper carries on the experiment simulation through the NS-2 simulation experiment platform. In this paper, the parameters of the experimental scene are obtained by using the mobile phone in 3G network speed measurement software to design the experimental scene. The parameters of the flow control strategy are determined by NS-2 simulation combined with the collected mobile network communication data. Then some scenarios are used to verify the difference between Improved Westwood and TCP Westwood in bandwidth jitter environment. Then compared with other TCP protocols, we verify that Improved Westwood improves the performance of TCP in mobile communication environment.
【学位授予单位】：华东师范大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TP393.06

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