🔍 Key Concepts

• SITOR (Simplex Telex Over Radio) / NBDP (Narrow-Band Direct-Printing) basic procedures • Difference between ARQ mode and FEC mode in SITOR, and which one uses a "direct telex" style connection • Standard ITU/IMO control signal codes used to start, continue, and terminate a telex/NBDP call

💭 Think About

• Think about how a direct telex circuit is set up and then cleared: what special sequence or control signal is used to end the connection, rather than just stopping transmission? • Which of these options looks like a specific, recognized control sequence from telex/NBDP procedures, not just a plain-language word or random characters? • Consider what would be used to positively signal to the distant station and the equipment that the circuit should be released, so the system knows the call is officially over.

✅ Before You Answer

• Verify in your study material which character sequence is defined as the "disconnect" or "clearing" signal for a direct TELEX connection in SITOR/NBDP. • Check whether any of the choices match a known telex control character sequence, rather than a general abbreviation like "END" or "EOM". • Confirm that the correct sequence is specifically used to terminate the link, not just mark the end of a message page or end of a sentence.