NAK (negative acknowledgment or not acknowledged)

NAK is an abbreviation for negative acknowledgment or not acknowledged. It is a signal used in digital communications to ensure that data is received with a minimum of errors. Sometimes the NAK signal is called REJ (for rejection or rejected). An alternative signal is ARQ (automatic request for retransmission).

Download this free guide

Download: Overcome Virtual Network Management Challenges

The virtualized network poses challenges to network management systems -- and as more hardware components become virtualized, that challenge becomes even greater. This handbook discusses the steps IT must take to both build and corral their virtualized infrastructure.

Start Download

• Corporate E-mail Address:

  You forgot to provide an Email Address.

  This email address doesn’t appear to be valid.

  This email address is already registered. Please login.

  You have exceeded the maximum character limit.

  Please provide a Corporate E-mail Address.

• • I agree to TechTarget’s Terms of Use, Privacy Policy, and the transfer of my information to the United States for processing to provide me with relevant information as described in our Privacy Policy.

  Please check the box if you want to proceed.

• • I agree to my information being processed by TechTarget and its Partners to contact me via phone, email, or other means regarding information relevant to my professional interests. I may unsubscribe at any time.

  Please check the box if you want to proceed.

By submitting my Email address I confirm that I have read and accepted the Terms of Use and Declaration of Consent.

The NAK, REJ, or ARQ signal is typically sent by the recipient of a message (destination) back to the sender (source) after the receipt of an unrecognizable block of data of specific size. When the source receives a NAK or REJ signal from the destination, the source either repeats the block of data until the destination station recognizes the protocol and responds with an ACK (acknowledgment or acknowledged) signal, or else stops transmission entirely. When the source receives an ARQ signal from the destination, the source retransmits the block of data.

NAK, REJ, or ARQ signals are special ASCII characters reserved so they are not confused with data characters.

Compare ACK.