What does the term "ARQ" mean in SITOR (NBDP) operations?

The term "ARQ" in SITOR (Selective Information Tray Over Radio) or NBDP (Narrow Band Direct Printing) operations stands for "Automatic Repeat Request." This is a key concept in digital communications, particularly in the context of error handling and data transmission reliability.

In ARQ systems, a receiver can request the sender to retransmit data that has not been correctly received. This mechanism ensures that the communication is efficient and accurate, as it allows for the identification and correction of errors that may occur during transmission.

The use of the word "automatic" in the correct answer signifies that this request for retransmission does not require human intervention, making the process streamlined and more effective. The integration of ARQ in SITOR protocols plays a significant role in enhancing communication reliability, which is crucial for maritime operations where SITOR is extensively used for distress communications and navigational data.

The other options, while they may be similar in wording, either misrepresent the functionalities or use incorrect terminology related to ARQ in this context, which is why they do not accurately describe the term as recognized in the field of GMDSS communications.