RoCE is the correct answer because it provides RDMA over Ethernet for low-latency, efficient data movement. NVIDIA networking documentation states: “Remote Direct Memory Access (RDMA) is the remote memory management capability that allows server-to-server data movement directly between application memory without any CPU involvement.” It then states: “RDMA over Converged Ethernet (RoCE) is a mechanism to provide this efficient data transfer with very low latencies on lossless Ethernet networks.” NVIDIA DOCA documentation similarly states that RoCE extends RDMA functionality to lossless Ethernet networks, delivering “high-throughput, ultra-low latency communication.”

This is especially important for large AI clusters because distributed training requires fast GPU-to-GPU and node-to-node communication. NVIDIA states that Spectrum-X builds on Ethernet with RoCE extensions to enhance performance for AI, bringing InfiniBand-style best practices such as adaptive routing and congestion control to Ethernet.

Why the other options are incorrect: DCTCP and ECN can support congestion control, but they are not the core GPU-to-GPU low-latency data-transfer protocol. PFC-only Ethernet without RDMA does not provide the direct memory-access benefit. iWARP is RDMA over TCP, but NVIDIA AI Ethernet designs emphasize RoCE for high-performance AI networking.