Using Precise Feedback for Controlling Congestion in the Internet

This paper explores the potential of improving Internet congestion control by providing precise congestion feedback to the sources instead of the implicit and binary feedback used by TCP. We propose a window-based protocol in which each sender maintains its congestion window and round trip time and communicates this information to the routers in a congestion header attached to every packet. The routers use the congestion header to tell each sender the exact amount by which to increase or decrease its congestion window. They apportion the feedback among the flows based on their congestion windows and round trip times provided in the header. The proposed protocol does not require any per-flow state at the routers; nevertheless, its fairness is significantly superior to TCP’s. Further, the queue size under the new protocol is smaller, the link utilization is near optimal and the drop rate is zero in most cases. Moreover, the high responsiveness of the protocol allows efficient operation in very high bandwidth environments and dynamic environments with many short flows. We use simulations in various settings to demonstrate these desirable properties and explore their limitations.