Abstract: The current slow start strategy of TCP congestion control and its existing practical problems like short connection bandwidth waste, excessive packet loss are analyzed, and a kind of Improved Slow Start algorithm SSIM(SlowStart Improved) is put forward, which is based on RTT(RoundRrip Time) feedback. In the early stage of the process of slow start, improved algorithm can quickly use the current effective network bandwidth so as to keep congestion window high speed growth, and in the later stage, to avoid aggravating network congestion, a dynamic incremental factor is introduced based on the current network status, so as to make the cwnd (congestion window) smooth transition to the ssthresh (slowstart threshold). Performance analysis and NS2 simulation results show that the improved algorithm can effectively reduce packet number of packet loss, improve the network throughput, reduce routing queuing delay, gentle data quantity of sudden impact, reduce the possibility of network congestion, conduce to the improvement of the network performance.

Key words: TCP, congestion control, slow start, RTT, congestion window(cwnd)