What is true regarding SITOR (NBDP) ARQ mode?

In SITOR (Simple In/Out Teleprinting Over Radio), also known as NBDP (Narrowband Direct Printing), ARQ (Automatic Repeat reQuest) mode is a crucial feature that ensures reliable communication over radio channels. The correct choice indicates that when a ship station transmits a group of three characters, the shore station actively checks the received data for proper parity. If the parity is correct, the shore station then indicates that it is ready to receive the next group of three characters. This method effectively allows for real-time acknowledgment from the shore station, minimizing delays while maintaining data integrity.

The importance of verifying parity at the shore station cannot be overstated. Parity checks are essential for detecting errors in the transmission, ensuring that the received information is accurate before the next transmission occurs. This process is a fundamental part of ARQ protocols, as it allows for immediate feedback and adjustments, enhancing the overall communication reliability.

Other options involve different procedures that do not align with the standard ARQ process used in SITOR. For instance, transmitting the same group of characters multiple times (as suggested in the other options) suggests a different approach to error correction that is not part of how ARQ functions in this context. The focus on immediate acknowledgment and