P-Start:一种分阶段TCP慢启动机制

针对现有TCP算法慢启动机制窗口指数增长导致一个窗口中出现多个包丢失现象，提出了一种分阶段的TCP慢启动机制－P-Start．该方法利用零界点（ssthresh／2）将慢启动分为两个阶段．窗口小于零界点，呈指数增长；窗口大于零界点，则以负指数方式增长，逐步迭代逼近门限值；使拥塞窗口增加幅度在连接启动时和过渡到拥塞避免阶段比较小，而在零界点附近窗口增加幅度大．从而有效避免了多个包丢失现象的发生，实现连接的平滑接入和过渡到拥塞避免阶段．考虑到慢启动传输效率低，改进算法通过参数配置，加快窗口的增加速度．减少慢启动的持续时间，提高其性能．仿真实验结果表明P-tart有效地提高了TCP协议的稳定性和网络的性能．

P-Start: a Phase-Divided TCP Slow Start Mechanism

This paper investigates multiple packets losses of exponential growth of congestion window of standard slow-start and proposes a new phase-divided TCP slow-start mechanism. This mechanism divides TCP slow-start into two phases at the dividing point, provides exponential and negatively exponential growth of congestion window under and over dividing point respectively, greatly decreases probability of multiple packets losses in one congestion window, and ensures that connections smoothly join and transforms into congestion avoidance phase, considering low utility, the enhanced algorithm shortens its duration and improves network utility through agile parameter configuration. And the simulation results show that this new method significantly improves the stability of TCP protocol and network utility.