Subelement B: MF-HF-DSC-SITOR (NBDP) Equip. & Operations— Topic :
Question 20B1
Element 9 (GMDSS Maintainer)Which of the following statements concerning SITOR (NBDP) communications is true?
Explanation
SITOR (SImplex Teletype Over Radio) in ARQ (Automatic Repeat reQuest) mode is designed for reliable, two-way communication.
In ARQ mode, the "information sending station" transmits data in blocks, typically three characters at a time. After sending a block, it pauses and waits for an acknowledgment from the "information receiving station." If the receiving station successfully decodes the block, it sends a positive acknowledgment (ACK). If it detects an error, it sends a negative acknowledgment (NACK), prompting the sending station to re-transmit that specific block. This block-based, acknowledge/retransmit mechanism ensures data integrity.
Options A and C describe characteristics more aligned with SITOR's FEC (Forward Error Correction) or broadcast mode (SITOR-B), where characters are often transmitted redundantly (twice) or interleaved to combat fading, without requiring an acknowledgment. Option D is incorrect because NAVTEX is a one-way broadcast system for maritime safety information, not an interactive system that allows user stations to request specific repeats via SITOR.
Related Questions
1A5 Using a frequency counter with an accuracy of 2 ppm — which of the following are within legal tolerance for the frequencies of 156.800 MHz and 156.525 MHz?1A6 Using a frequency counter with an accuracy of 5 ppm — which of the following are within legal tolerance for the frequencies of 156.875 MHz and 157.200?20B2 What statement is true regarding the exchange between two stations engaged in SITOR (NBDP) communications?20B3 Which of the following is true of SITOR (NBDP) ARQ mode:20B4 Which of the following keystrokes or characters follows most commands in ARQ communications when working an automated Coast Station?