Research On Congestion Control Mechanism Over Heterogeneous Networks

With the rapid development of wireless networks (including cellular network, satellite network, mobile ad-hoc network and sensor network), heterogeneous networks become the new trend of computer networks. In heterogeneous networks, because of the property of high bit error rate, mobile handoff, unstable link state and high bandwidth delay product, the traditional congestion control mechanisms suffer great performance degradation such as link throughput decreasing, packet loss ratio increasing, end-to-end delay raising and even congestion collapse. Therefore congestion control mechanisms over heterogeneous networks are meaningful for the quality of network service.Considering the characteristics of heterogeneous networks, this paper improves the performance of congestion control over heterogeneous networks. The main studies and contributions are presented in the following aspects:1. In the research of router based active queue management, we proposed a new rate-based AQM scheme (NRAQM). NRAQM scheme uses a new marking/dropping module and a timer updating module for packets dropping/marking and dropping/marking probability updating, which are different from other existing AQM schemes. The objectives of our proposed scheme are to stabilize networks with low end-to-end delay and high link utilization regardless the dynamics of wired-cum-wireless networks. Simulation results show that our proposed scheme outperforms the existing AQM schemes over wired-cum-wireless networks.2. In the research of end-to-end TCP congestion control, we analyzed the drawbacks of TCP Vegas over heterogeneous networks such as the calculation of RTT and base RTT issue, the fairness issue. Then we proposed the improved algorithm TCP Vegas+. We modify the bandwidth prediction algorithm, adaptive parameter adjustment algorithm and the loss differentiation algorithm. The simulation results show the effectiveness of TCP Vegas+over heterogeneous networks.3. In the research of the effect of buffer sizing over heterogeneous networks, we carefully analyzed two famous buffer sizing rules, Bandwidth-delay-product discipline and Square-root discipline. Then we used the simulation experiments method to analyze their performance over heterogeneous networks and give suggestions for buffer sizing over heterogeneous networks.