基于正向时延的卫星网络拥塞控制算法研究

在具有带宽不对称特点的卫星网络中，反向(地对空)链路带宽较小，更容易发生拥塞。当反向链路发生拥塞时，可以通过减小发送端的发送窗口来降低拥塞，但是这也降低了网络正向(空对地)链路的吞吐率。针对以上问题，提出了基于正向时延的TCP Vegas正向拥塞控制（Vegas_FD）算法。该算法通过测量数据分组的正向延迟时间，判定通信链路是否发生拥塞，并根据通信链路不同的拥塞类型采取不同的控制策略，使拥塞控制算法在反向链路发生拥塞时仍保持较高的吞吐率，适应了卫星网络带宽不对称特性。基于网络仿真软件Opnet进行了实验，结果表明，在卫星网络中Vegas_FD算法比Vegas算法、Westwood算法吞吐率性能明显提高，验证了该算法的有效性。

Research on Congestion Control Algorithm of Satellite Network Based on Forword Direction Delay

In satellite networks featuring asymmetric bandwidth,the bandwidth of reverse (earth-to-satellite) links is narrow,and congestion is more likely to occur in these links.Congestion occurring in a reverse link is alleviated by decreasing the send window at the sending end,during which,however,the throughput of forward (satellite-to-earth) links in the network is also lowered.Vegas_FD,a TCP Vegas forward congestion control algorithm based on forward direction delay,is proposed so as to tackle the foregoing problems.The proposed algorithm judges whether a communication link is congested or not by measuring the forward direction delay time of data packets,and adopts different control strategies as per different congestion types of the communication link,so as to ensure that the congestion control algorithm could keep a high throughput when the reverse link is congested.With these functions,the algorithm is adapted to the asymmetry of the satellite network's bandwidth.The simulated results based on Opnet software show that Vegas_FD algorithm is used to improve remarkably the throughput in satellite networks compared to Vegas and Westwood algorithms.