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Subel. J
6 questions
Subelement J

MF-HF Equip. and Comms:

Section 92

MF-HF ARQ Operation-Technical Characteristics

Which of the following statements concerning SITOR (NBDP) communications is true?

  • In ARQ, each character is transmitted twice, about 250 milliseconds apart.
  • Correct Answer
    In ARQ, the "information sending station" will transmit a block of three characters that the receiving station will subsequently acknowledge or request be retransmitted.
  • In ARQ, the "information sending station" transmits a block of three characters twice, about 250 milliseconds apart.
  • SITOR (NBDP) communications can be used to contact a NAVTEX transmitting station when requesting a repeat transmission of a missed NAVTEX message.
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What statement is true regarding the exchange between two parties engaged in SITOR (NBDP) communications?

  • In ARQ, each character is transmitted twice, with the second displaced in time from the first.
  • In ARQ, the "sending" station transmits a block of three characters and the "receiving" station responds with a one character Repeat Request. Following this the "transmitting" station will send a new block.
  • Correct Answer
    In ARQ, the ISS transmits a block of 3 characters and the IRS checks for parity. If the received block is correct a one-character control signal is sent notifying the ISS to proceed with the next block. If the parity check fails the block must be resent.
  • Broadcasts of Maritime Safety Information, traffic lists, etc. can be copied by the receiving station in ARQ mode.
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Of the following, which is true of SITOR (NBDP) ARQ mode?

  • The acceptance code consists of three characters.
  • A continuous data stream is transmitted.
  • Forward error correction reduces the number of errors.
  • Correct Answer
    Each data block consists of three characters.
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Which of the following is true of SITOR (NBDP) ARQ mode?

  • Correct Answer
    This is an interactive mode.
  • Each character is repeated three times.
  • Each character is transmitted twice.
  • This mode is generally used to broadcast messages.
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In ARQ, when the information sending station (ISS) receives a signal that the parity check failed what happens?

  • The next block will be sent.
  • The data link will break.
  • The acknowledge light should illuminate.
  • Correct Answer
    The last block will be resent.
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Which of the following is true of SITOR (NBDP) ARQ mode:

  • Correct Answer
    The ship station sends a group of 3 characters, the shore station checks for proper parity. If parity is OK, the shore station indicates readiness for transmission of the next 3 characters.
  • The ship station sends a group of 3 characters twice and then waits for an "RQ" signal to indicate proper receipt before continuing transmission.
  • The Ship station sends each character twice, using a time diversity system to ensure proper parity.
  • The ship station sends a group of 3 characters, the shore station checks for proper parity and then requests the same group be resent to enable error correction.
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