A new congestion control mechanism for mitigating TCP global synchronization

With Drop-Tail at gateways, TCP Reno may easily lead to global synchronization. To partially solve the problem while without the loss of compatibility with TCP Reno, a new congestion control mechanism named P-TCP was proposed. Upon receiving the third duplicate acknowledgement, P-TCP may halve the congestion window like TCP Reno, or decrease the congestion window very lightly in which case the intentional decreasing for the congestion window is introduced. For the instance in this paper, comparing with TCP Reno, the global synchronization is effectively mitigated; the network throughput may be improved about 16%, and the retransmit probability may be decreased around 67% relatively. In the scenario where P-TCP and TCP share the same bottleneck link, the fairness factor reaches around 99%, the bottleneck link utilization is improved, and the retransmit probability is decreased. In addition, P-TCP is obtained from a little modification for TCP Reno at the sender side, so the additional overheads are very low.