SSthreshless Start: A Sender-Side TCP Intelligence for Long Fat Network

Measurement shows that 85% of TCP flows in the internet are short-lived flows that stay most of their operation in the TCP startup phase. However, many previous studies indicate that the traditional TCP Slow Start algorithm does not perform well, especially in long fat networks. Two obvious problems are known to impact the Slow Start performance, which are the blind initial setting of the Slow Start threshold and the aggressive increase of the probing rate during the startup phase regardless of the buffer sizes along the path. Current efforts focusing on tuning the Slow Start threshold and/or probing rate during the startup phase have not been considered very effective, which has prompted an investigation with a different approach. In this paper, we present a novel TCP startup method, called threshold-less slow start or SSthreshless Start, which does not need the Slow Start threshold to operate. Instead, SSthreshless Start uses the backlog status at bottleneck buffer to adaptively adjust probing rate which allows better seizing of the available bandwidth. Comparing to the traditional and other major modified startup methods, our simulation results show that SSthreshless Start achieves significant performance improvement during the startup phase. Moreover, SSthreshless Start scales well with a wide range of buffer size, propagation delay and network bandwidth. Besides, it shows excellent friendliness when operating simultaneously with the currently popular TCP NewReno connections.Comment: 25 pages, 10 figures, 7 table

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