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NAK (Negative Acknowledgment)

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An ACK (acknowledgment) is a confirmation of receipt. When data is transmitted between two systems, the recipient can acknowledge that it received the data. If a station receives packets that are corrupted, it can return a NAK (negative acknowledgment) to the sender. A checksum error may indicate a corrupted packet. A NAK is different than a normal acknowledgment in that it indicates that a packet was received in a corrupted state rather than not received at all.

An alternative to sending a NAK is for the receiving station to not acknowledge that it has received packets. By not receiving an ACK, the sender may assume that the receiver is overflowing or the network is congested and slow down its transmission. Keep in mind that TCP receivers use ACK to inform a sending host that packets have arrived. If the ACK is not sent, the sender assumes packets have been lost. NAK is used to indicate that a packet has been corrupted and to resend it, but there is no need to change the transmission rate.

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