negative acknowledgement

1. character (NAK) The mnemonic for ASCII character 21.

Sometimes used as the response to receipt of a corrupted

packet of information.

Opposite of acknowledgement.

2. communications (NAK) Any message transmitted to indicate

that some data has been received incorrectly, for example it

may have a checksum or message length error. A NAK message

allows the sender to distinguish a message which has been

received in a corrupted state from one which is not received

at all.

An alternative is to use only ACK messages, in which case

the non-receipt of an ACK after a certain time is counted as a

NAK but gives no information about the integrity of the

communications channel.

See also ACK.

(1997-01-07)