TCP with sender-based delay control

This paper describes a congestion control method for TCP that adjusts the transmission rate of a TCP connection by changing not only the congestion window size as in normal TCP, but also by delaying the transmission of packets at the sender. We refer to this method as TCP with sender-based delay control, or simply SDC. SDC can keep the window size of a TCP connection above a certain threshold even when its fair share of bandwidth is arbitrarily small. Since TCP fast retransmit and recovery is likely to work when the window size of the connection is sufficiently large, the new method can result in reduced frequency of TCP timeouts for the connection. In particular, SDC allows many TCP flows to share a link without experiencing many timeouts. In addition, SDC can reduce a well-known TCP bias against connections with large RTTs. This paper presents the principle behind SDC, and simulation results demonstrating its properties and advantages.