基于带宽估计的无线TCP拥塞控制

Wireless TCP Congestion Control Based on Bandwidth Estimation

针对在无线网络中,由于链路本身的特性,丢包存在拥塞丢包及无线误码丢包两种不同情况,但出现丢包时,传统TCP协议不会分析丢包原因,而盲目地进行拥塞窗口(cwnd)及慢启动门限值(ssthresh)的调整,引起数据发送速率波动较大,导致TCP吞吐量下降的问题。为了改善无线网络传输性能,提出了一种基于带宽估计的无线TCP拥塞控制算法。该算法通过在每往返时延(RTT)确认的发送数据量来实时估计带宽,为获得更准确的估计值,计算过程中对RTT及带宽估计值进行了滤波平滑处理。在此基础上,计算出带宽利用率来分析丢包原因及拥塞程度,并据此对拥塞控制参数进行自适应动态调整。运用NS-2完成实验,从拥塞窗口、抖动、平均吞吐量等方面等经典的TCP版本进行比较,仿真结果表明,算法对拥塞控制参数的调整更加平滑,提高了系统吞吐量,增强了无线网络的传输性能。

In the paper, an algorithm based on bandwidth estimation was proposed in order to improve the wireless network transmission performance. The algorithm calculated the amount of send data confirmed in each round trip delay （RTT） to estimate real-time bandwidth. In order to obtain a more accurate estimated value, the RTT and estimated bandwidth was smoothed in the process of calculation, and then the bandwidth utilization was calculated. The algorithm used the bandwidth utilization to analyze the reason of packet loss and congestion degree, and control parameters were adaptively and dynamicly adjusted according to analysis results. Experiment is completed using NS-2 platform, and comparison was made based on the aspects of congestion window, jitter, and average throughput with classic TCP version. Simulation results show that the algorithm makes the change of congestion control parameters smoother, improves the system throughput and enhances the wireless network transmission performance.