自适应虚拟队列算法AVQ的公平性研究

Study on fairness of adaptive virtual queue algorithm

从理论上对自适应虚拟队列(AVQ)算法的拥塞控制机制和TCP的吞吐量模型进行了分析,在不同网络配置条件下使用NS2网络仿真器对其进行了仿真,考察公平性和网络中长期TCP流的数量、路由器缓冲区大小、AVQ算法中的平滑因子α、期望链路利用率γ等之间的关系.结果表明,AVQ算法在长期TCP流数量较多和各种缓冲区容量条件下均表现出良好且稳定的公平性,α对公平性影响不大,但γ的取值对公平性有很大影响,当该参数取值较大时,算法的公平性明显下降.

A theoretic analysis is firstly presented concerning the congestion control mechanism of the adaptive virtual queue （AVQ） algorithm and the throughput model of TCP （ transmission control protocol）. Then the relationship between fairness and some fundamental parameters （the number of long-lived TCP flows, the link buffer size, the smoothing parameter, the desired link utilization parameter etc. ） is evaluated under different network conditions based on the NS2 simulation platform.It is demonstrated that AVQ enjoys fairly good and stable fairness when the number of heterogeneous TCP flows is large while being insensitive to the link buffer size, but the fairness performance is quite sensitive to the desired link utilization parameter in that fairness decreases heavily when this parameter grows high。