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为了解决无线TCP传输拥塞时通信性能不稳定的状况,作者首先对传统TCP拥塞产生的原因及标准的TCP协议所采取的控制算法进行了深入的分析,并结合跨层协议设计的优势提出了保证Qo S的无线TCP拥塞控制机制。通过建立HSDPA跨层模型和TCP模型,设计了基于自适应可用带宽的TCP拥塞控制算法。此机制和核心思想是:若拥塞丢包严重时,则通过可以带宽估计算法估计出当前可用带宽,控制源节点发送窗口大小;若较短时间内误码丢包率极高时,本机制在信道条件变化的形势下,能够依据信道情况和用户的Qo S要求,得到最优的传输速率调节参数值,进而提升数据传输的稳定性。通过NS-2中的仿真验证,本文设计的拥塞控制机制较传统标准的TCP拥塞控制算法在丢包率和吞吐量方面性能有一定程度的提升。
In order to solve the problem of instability of communication performance in wireless TCP transmission congestion, the author first makes an in-depth analysis of the causes of traditional TCP congestion and the control algorithm adopted in the standard TCP protocol, and puts forward the guarantee in combination with the advantages of cross-layer protocol design Qo S’s wireless TCP congestion control mechanism. By establishing HSDPA cross-layer model and TCP model, a TCP congestion control algorithm based on adaptive available bandwidth is designed. The mechanism and the core idea are as follows: if the congested packet loss is serious, the available bandwidth can be estimated by the bandwidth estimation algorithm to control the size of the source node to send the window; if the error packet loss rate is very high in a short time, Under the condition that the channel conditions change, the optimal transmission rate adjustment parameter value can be obtained according to the channel condition and the Qo S requirement of the user, so as to improve the stability of the data transmission. Through the simulation in NS-2, the congestion control mechanism designed in this paper has a certain degree of improvement in terms of packet loss rate and throughput compared with the traditional TCP congestion control algorithm.