BBR-ES: An Extended-State Optimization for BBR Congestion Control

In recent years, many optimization proposals for TCP BBR have been introduced, but most rely mainly on delay variations and do not fully resolve BBR’s limitations in RTT fairness, link utilization, and delay control in networks. This paper proposes BBR with Extended State (BBR-ES), which extends BBR’s state machine with a short stabilization state and a trend-based transition mechanism that react to per-flow bandwidth and RTT evolution instead of global delay alone. BBR-ES uses lightweight bandwidth and RTT trend tracking to adjust its sending rate while preserving BBR’s model-based design. Experiments on both emulated (Mininet) and real-world Internet paths (Amazon EC2) show that BBR-ES consistently improves RTT fairness and link utilization over BBRv1, BBRv3, and CUBIC while keeping queuing delay moderate and bounded; in most settings, it achieves Jain’s fairness index above 0.9 and link utilization above 98%. These results indicate that BBR-ES is a practical candidate for deployment in large-scale content delivery and a useful design reference for future model-based congestion control schemes.