A simple refinement of slow-start of TCP congestion control

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 the 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 the 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.