An error control mode that provides for retransmission of errored data packets. The error detection logic can be implemented not only in the receiving device but also in intermediate routers, switches, and other intelligent nodes.The device detecting an error issues a retransmission request to the device immediately upstream, or perhaps to the original transmitter, which holds some amount of data in a buffer until it has received an indication that the data either was received correctly or that the data was received in an errored state. If the upstream device receives no indication either way within a specified time interval, it assumes that the data was lost in transit and automatically initiates a retransmission through a protocol known as automatic repeat request (ARQ). As examples, recognition and retransmission is used in X.25 networks, and by applications running the Transmission Control Protocol (TCP) over Internet Protocol (IP) networks. Block parity is an example of recognition and retransmission. See also ARQ, block parity, buffer, checksum, error control, FEC, IP, recognition and flagging, TCP, upstream, and X.25.