Implementations of this disclosure provide data transmission operations and network interface controllers. An example method performed by a first RDMA network interface controller includes obtaining m data packets from a host memory of a first host; sending the m data packets to a second RDMA network interface controller of a second host; backing up the m data packets to a network interface controller memory integrated into the first RDMA network interface controller; determining that the second RDMA network interface controller does not receive n data packets of the m data packets; and in response, obtaining the n data packets from the m data packets that have been backed up to the network interface controller memory integrated into the first RDMA network interface controller, and retransmitting the n data packets to the second RDMA network interface controller.