Short-circuiting the congestion signaling path for AQM algorithms using reverse flow matching

Recently, we introduced a new congestion signaling method called ACK spoofing, which offers significant benefits over existing methods, such as packet dropping and Explicit Congestion Notification (ECN). Since ACK spoofing requires the router to create a ‘short circuit’ signaling path, by matching marked data packets in a congested buffer with ACK packets belonging to the same flow that are traveling in the opposite direction, the focus of this paper is evaluating the feasibility of reverse flow matching. First, we study the behavior of individual flows from real bi-directional Internet traces to show that ACK spoofing has the potential to significantly reduce the signaling latency for Internet core routers. We then show that reverse flow matching can be implemented at reasonable cost, using essentially the same hardware as the packet filtering logic commonly employed in Layer 2 transparent bridges. Finally, we show that this architecture can be scaled to accommodate worst-case traffic patterns on multi-gigabit links that would render ordinary route caching algorithms completely ineffective.