What is a negative acknowledgment (NAK) and when would it be used in the EPD Pilot?

• A. A NAK is a positive confirmation.
• B. A NAK requests faster throughput.
• C. A NAK informs the sender that a specific frame was received with errors or is invalid, prompting retransmission.
• D. A NAK indicates the connection should close.

Answer: (C)

A negative acknowledgment signals that a received frame was not correct or is invalid, and it prompts the sender to retransmit that specific frame. In the EPD Pilot, this happens when the receiver detects errors (such as a CRC/checksum mismatch) or an invalid frame; the receiver then sends a NAK to request retransmission of that frame. This mechanism preserves data integrity by ensuring errors are corrected without forcing the sender to resend everything and allows targeted retransmission, which is more efficient. It’s not a positive confirmation, nor a request to speed up throughput, nor a signal to close the connection.