Acknowledgement (data networks)

In data networking, an acknowledgement (or acknowledgment or ACK) is a signal passed between communicating processes or computers to signify acknowledgement, or receipt of response, as part of a communications protocol. For instance, ACK packets are used in the Transmission Control Protocol (TCP) to acknowledge the receipt of SYN packets when establishing a connection, data packets while a connection is being used, and FIN packets when terminating a connection.

The acknowledgement function is used in the automatic repeat-request (ARQ) function. Acknowledgement frames are numbered in coordination with the frames that have been received, and then sent to the transmitter. This allows the transmitter to remain within the window size of the receiver's buffers, and to become aware of any missed frames.

See also

• NAK (protocol message)