A Simple Refinement of Slow-start of TCP Congestion Control

Abstract — This paper presents a new variant of Slow-start, called Smooth-start, which provides a smooth transition between the exponential and linear growth phases of TCP congestion window. Slow-start is known to make an abrupt transition between the Slow-start and Congestion-Avoidance phases, and hence, often causes multiple packet losses from a window of data and retransmission timeouts, which, in turn, reduce effective throughput and result in global synchronization. Smooth-start solves this problem by approaching the Slow-start threshold more gradually. Our extensive simulation results show that Smooth-start can significantly reduce both packet losses and traffic burstiness, thus improving the performance of TCP congestion control at the start of a TCP connection or after a retransmission timeout. Furthermore, Smooth-start is very simple to implement and requires TCP modifications at the sender side only. I