DHERC: Dynamic Hybrid ECN-RTT Congestion Control for RDMA Networks

Modern data centre networks demand ultra-low latency and high throughput, making Remote Direct Memory Access (RDMA) increasingly important. However, RDMA’s performance degrades significantly under congestion due to limited built-in congestion control. Existing approaches, based on Explicit Congestion Notification (ECN) and Round-Trip Time (RTT) suffer from limitations including delayed feedback and noisy signals when used alone. We propose Dynamic Hybrid ECN-RTT Congestion Control (DHERC), a novel algorithm that integrates RTT-based early detection with ECN-based confirmation to achieve balanced congestion control. Through extensive simulations, we demonstrate that DHERC outperforms state-of-the-art schemes across key performance metrics. DHERC achieves better flow completion time performance, improved throughput fairness, and good goodput efficiency while maintaining competitive tail performance. The results establish multi-signal congestion control as a promising approach for RDMA networks requiring predictable performance, efficiency, and fairness.