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

Correct Answer: Option C — 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.

In ARQ mode, the ISS transmits a three-character block. The IRS performs a constant ratio parity check. If the block is valid, the IRS sends a control signal (CS) to the ISS to proceed. If invalid, the ISS must retransmit the block until successful reception occurs.