What is it about?

Remote Direct Memory Access (RDMA) is widely used in data centers to move data quickly between machines. Using multiple network paths can improve network efficiency, but it also creates a problem: packets traveling along different paths may arrive in a different order. Existing RDMA systems can mistake these harmless out-of-order arrivals for packet loss, causing unnecessary retransmissions and slowing down communication. We introduce PSN-PATH, a new approach that helps RDMA tell the difference between packets that are simply arriving out of order and packets that are actually lost. It tracks packet ordering separately for each network path, retransmits only the packets that are truly missing, and moves traffic away from poorly performing paths when necessary. The design runs directly on the network interface card and does not require changes to network switches. In our experiments, PSN-PATH substantially improves the performance of multipath RDMA in lossy networks. Under high-load and lossy conditions, it reduces flow completion time by up to 95.81%, improves useful data throughput by up to 5.11×, and cuts unnecessary retransmissions by more than 99%. This makes multipath RDMA more practical and reliable for large-scale data center networks.

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Why is it important?

Modern data centers increasingly rely on RDMA for fast communication and use multiple network paths to make better use of available bandwidth. However, combining multipath transmission with lossy networks creates a fundamental problem: packets that arrive out of order can be mistaken for lost packets, leading to unnecessary retransmissions and significant performance degradation. PSN-PATH is unique because it addresses this problem directly at the network interface card. Instead of treating packet ordering as one global sequence, it checks packet continuity within each transmission path. This allows the system to distinguish harmless out-of-order arrivals from real packet losses and to react quickly when a path becomes unreliable. Importantly, PSN-PATH does not require changes to existing network switches, making it easier to integrate with current data center infrastructure. By reducing unnecessary retransmissions and improving both data transfer efficiency and completion time, PSN-PATH can help make high-performance multipath RDMA more practical, scalable, and reliable in real-world lossy networks.

Perspectives

What interested me most in this work is a simple but important observation: in multipath RDMA, an out-of-order packet does not necessarily mean that a packet has been lost. Existing reliability mechanisms often overlook this distinction, which can lead to many unnecessary retransmissions and offset the benefits of multipath transmission. From my perspective, the most meaningful part of PSN-PATH is that it changes how packet continuity is interpreted. Instead of enforcing one global packet order, we check continuity within each network path. This makes it possible to separate harmless reordering from real packet loss while keeping the design lightweight enough for RNIC implementation. I hope this work can encourage more research on making high-performance network protocols better suited to realistic, imperfect data center networks, rather than assuming that the network will always behave ideally.

Zhexiong Li
China University of Geosciences

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This page is a summary of: PSN-PATH: When Multipath RDMA Meets Lossy Networks, August 2026, ACM (Association for Computing Machinery),
DOI: 10.1145/3789240.3829128.
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