In data networking, telecommunications, and computer buses, an acknowledgement (ACK) is a signal passed between communicating processes, computers, or devices to signify acknowledgement, or receipt of message, as part of a communications protocol. The negative-acknowledgement (NAK or NACK) signal is sent to reject a previously received message, or to indicate some kind of error. Acknowledgements and negative acknowledgements inform a sender of the receiver's state so that it can adjust its own state accordingly. == Acknowledgement characters == When the ASCII code is used to communicate between...