What statement is true regarding the exchange between two parties engaged in SITOR (NBDP) communications?

The correct answer pertains to how Automatic Repeat reQuest (ARQ) functions in the context of SITOR (Selective Information Transmission Over Radio), which is a method for sending digital messages, particularly in maritime communications.

ARQ is a communication protocol that ensures the reliable transmission of data by providing error correction. In the context of ARQ within NBDP (Narrow Band Direct Printing) systems, the Initial Station Sending (ISS) indeed transmits a block of three characters. This block is crucial because it allows for a compact and efficient method to send information while keeping track of any errors that may occur during transmission.

The receiving station, known as the Initial Receiving Station (IRS), plays an essential role in monitoring the integrity of the incoming data. As the IRS checks the received characters, it can determine if there are any errors. If the IRS detects an error in the received block of characters, it has the capability to request a retransmission, ensuring that data integrity is maintained throughout the communication process.

In this context, the other statements do not accurately describe the ARQ process as it applies to SITOR communications. For instance, transmitting each character twice or having the receiving station send back a one-character Repeat Request are not standard practices within ARQ,