Fast Convergence of Variable-Structure Congestion Control Protocol with Explicit Precise Feedback

Abstract

Traditional TCP has significant limitations such as unclear congestion implication, low utilization in high bandwidth delay product networks, unstable throughput and limited fairness. In order to overcome such limitations, research on design and development of more effective congestion control algorithms, especially in the high bandwidth delay product networks, is very active. Variable-structure congestion Control Protocol (VCP) uses two ECN bits to deliver the bottleneck link utilization region to end systems, and achieves high utilization, low persistent queue length, negligible packet loss rate and reasonable fairness. Owing to the utilization of large multiplicative decrease factor, VCP flows need very long time to finish fairness convergence. To address this problem, a new method called VCP-Fast Convergence (VCP-FC) is proposed in this paper. VCP-FC uses more bits to deliver precise network load factor back to end systems. The end system calculates the fairness bandwidth based on the variance rates of the load factor and throughput, and then quickly adjusts the congestion window to approach the fairness bandwidth. VCP-FC shortens the fairness convergence time effectively, and meanwhile improves the efficiency and fairness of VCP. At last, the performance of VCP-FC is evaluated using ns2 simulations.