A dual-window model for flow and congestion control

This paper examines the window mechanism that has been widely used for flow and congestion control. The analysis shows that the mono-window model, which combines flow control and congestion control in a single window, can cause pipe breakdown after packet losses. A dual-window model is then presented, in which flow control and congestion control are decoupled. The dual-window model allows the traffic flow to be sustained while retransmission is being carried out. The dual-window model is particularly suitable for high-speed and long-delay networks where the pipelining of the packets is more crucial. The estimation of the window sizes, advance of the window edges, acknowledgement and retransmission are discussed in detail. Finally the performance of the dual-window model is examined with illustrated examples and by simulation.