Negative-acknowledge character
"Nak" and "NAK" redirect here. For other uses, see Nak (disambiguation).
- In telecommunications, a negative-acknowledge character (NAK or NACK) is a transmission control character sent by a station as a negative response to the station with which the connection has been set up.
- In Binary Synchronous Communications protocol, the NAK is used to indicate that an error was detected in the previously received block and that the receiver is ready to accept retransmission of that block.
- In multipoint systems, the NAK is used as the not-ready reply to a poll.
In the ASCII code, the NAK character is 21 (decimal), or ^U (CTRL-U). EBCDIC uses 0x3D. Unicode also defines a visible representation at U+2415(␕).
See also
References
This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).