PSN-PATH: When Multipath RDMA Meets Lossy Networks

Remote Direct Memory Access (RDMA) is widely adopted for high-performance datacenter workloads, but its strict ordering requirement conflicts with multipath transport in lossy networks. RDMA Network Interface Cards (RNICs) may interpret Out-of-Order (OOO) arrivals caused by diverse path latencies as packet loss. This triggers unnecessary retransmissions, severely degrading goodput collapse and inflating Flow Completion Time (FCT). We present PSN-PATH, a novel RDMA protocol to distinguish packet loss from OOO and avoid unnecessary retransmission, improving goodput and FCT of multi-path RDMA in lossy networks. PSN-PATH maps Packet Sequence Numbers (PSN) to network paths, enabling the receiver to verify packet continuity within each mapped path and distinguish real losses from OOO arrivals. PSN-PATH only retransmits lost packets and redirects traffic away from degraded paths. We implement PSN-PATH on Xilinx Alveo U50 FPGA using Vitis HLS and validate it via extensive simulation experiments. Experimental results demonstrate that PSN-PATH significantly outperforms existing solutions, reducing FCT by 95.81%, enhancing goodput by 5.11×, and reducing retransmissions by over 99% under high-load, lossy conditions.