Acknowledge character

In computing, an ACK (also known as an acknowledgment code) 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 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.

For teleprinters, the acknowledge character (ACK) is a transmission control character transmitted by the receiving station as an affirmative response to the sending station: this is defined in Federal Standard 1037C. In Unicode, the hexadecimal code number is 0x06.

The ACK function is heavily used in the automatic repeat-request (ARQ) function. The ACK 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. An acknowledge character may also be used as an accuracy control character.

It is also used as a slang abbreviation in internet forums and chats (mainly technology) for "Understood".[1]

See also

• NAK, the negative acknowledge code
• C0 and C1 control codes
• ARQ
• Acknowledgement of receipt

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