Zhang and Shin: Second-order Rate-based Flow Control with Decoupled Error Control for High-throughput Transport Protocols

We propose an efficient flow and error control scheme for highthroughput transport protocols, which (i) decouples flow control from error control, and (ii) uses a second-order rate control, called -control, for flow control and a new sliding-window scheme for error control. The -control minimizes the need for packet retransmissions by adjusting the rate-gain parameter in response to the variations of cross-traffic flows and their roundtrip delays (RTDs). Using selective retransmission, the sliding-window scheme guarantees lossless transmission. Separation of flow and error control simplifies both components and enhances the throughput since the source rate control is independent of the dynamics of the error-control window. Applying the -control, the proposed scheme can drive the flow-controlled system to a retransmission-free equilibrium state. Using the fluid analysis, we model the packet-loss behavior and derive the closed-form expressions for packet losses, loss rate, and the link-transmission efficiency. We prove that the -control is feasible and optimal linear control in terms of efficiency and fairness. Also presented are the vector-space analysis and simulation results that verify the analytical results, and demonstrate the superiority of the proposed scheme to others in dealing with cross-traffic and RTDs variations, controlling packet losses/retransmissions, and achieving buffer-use fairness and a high throughput.